Dissertations / Theses on the topic 'Flexible Sensors'

Flexible scintillating radiation detectors have gained increasing attention in the scientific community in the last decade. They represent a fast and easy way for monitoring the impinging radiation in real time and acquire the dose released in medical treatments, like cancer radio- or proton-therapy sessions. Flexible linear-chain polysiloxane detectors offer the possibility to overcome geometrical limitations, they possess superior optical transparency and flexibility, and can be obtained with contained production costs and times, making them highly competitive with respect to traditional single-crystals and plastics. Unlike phenyl-containing siloxanes, linear polysiloxanes does not show direct interaction with the impinging radiation, therefore they can be used just as matrices for hosting luminescent materials, such as nanocrystals or nanopowders. Quantum dots (QDs) are nanocrystals showing quantum confinement effects, with an incredible light yield, a tunable emission wavelength and a fast decay lifetime. For these reasons, they are worth being incorporated in siloxane-based scintillators as primary dyes, without the need of complex ternary systems. Part of this thesis analyzes the effects of ionizing radiation on the luminescence and temporal response of QD-loaded polysiloxanes for radiation detection and monitoring, with special focus on real-time measurements under proton beam. Another possibility is to embed luminescent nanopowders, such as zinc oxide (ZnO) and reduced zinc oxide (ZnO:Zn). The Zn-rich form shows a remarked green luminescence, with increasing light yield as a function of the reduction degree, i.e. zinc content. In view of the above, this thesis reports the advances on polysiloxanes loaded with ZnO and ZnO:Zn phosphors. The core of the thesis is devoted to the progresses in ZnO production and treatment for the realization of multi-layered flexible scintillators. A special focus is putted on a novel production route based on atmospheric pressure plasma (APPJ), that allows for the co-deposition of ZnO-loaded plasma polymers and for the doping via liquid precursor solution.

Flexible scintillating radiation detectors have gained increasing attention in the scientific community in the last decade. They represent a fast and easy way for monitoring the impinging radiation in real time and acquire the dose released in medical treatments, like cancer radio- or proton-therapy sessions. Flexible linear-chain polysiloxane detectors offer the possibility to overcome geometrical limitations, they possess superior optical transparency and flexibility, and can be obtained with contained production costs and times, making them highly competitive with respect to traditional single-crystals and plastics. Unlike phenyl-containing siloxanes, linear polysiloxanes does not show direct interaction with the impinging radiation, therefore they can be used just as matrices for hosting luminescent materials, such as nanocrystals or nanopowders. Quantum dots (QDs) are nanocrystals showing quantum confinement effects, with an incredible light yield, a tunable emission wavelength and a fast decay lifetime. For these reasons, they are worth being incorporated in siloxane-based scintillators as primary dyes, without the need of complex ternary systems. Part of this thesis analyzes the effects of ionizing radiation on the luminescence and temporal response of QD-loaded polysiloxanes for radiation detection and monitoring, with special focus on real-time measurements under proton beam. Another possibility is to embed luminescent nanopowders, such as zinc oxide (ZnO) and reduced zinc oxide (ZnO:Zn). The Zn-rich form shows a remarked green luminescence, with increasing light yield as a function of the reduction degree, i.e. zinc content. In view of the above, this thesis reports the advances on polysiloxanes loaded with ZnO and ZnO:Zn phosphors. The core of the thesis is devoted to the progresses in ZnO production and treatment for the realization of multi-layered flexible scintillators. A special focus is putted on a novel production route based on atmospheric pressure plasma (APPJ), that allows for the co-deposition of ZnO-loaded plasma polymers and for the doping via liquid precursor solution.

This work describes a model of the piezoresistive behavior in nanocomposite sensors. These sensors are also called flexible sensors because the polymer matrix allows for large deformations without failure. The sensors have conductive nanoparticles dispersed through an insulative polymer matrix. The insulative polymer gaps between nanoparticles are assumed to be possible locations for electron tunneling. When the distance between two nanoparticles is small enough, electrons can tunnel from one nanoparticle to the next and ultimately through the entire sensor. The evolution of this gap distance with strain is important to understand the overall conductivity of the strain sensor. The gap evolution was modeled in two ways: (1) applying Poisson's contraction to the sensor as a homogenous material, referred to as Simple Poisson's Contraction (SPC) and (2) modeling the nanoparticle-polymer system with Finite Element Analysis (FEA). These two gap evolution models were tested in a random resistor network model where each polymer gap was treated as a single resistor in the network. The overall resistance was calculated by solving the resistor network system. The SPC approach, although much simpler, was sufficient for cases where various orientations of nanoparticles were used in the same sensor. The SPC model differed significantly from the FEA, however, in cases where nanoparticles had specific alignment, e.g. all nanoparticles parallel to the tensile axis. It was also found that the distribution used to determine initial gap sizes for the polymer gaps as well as the mean of that distribution significantly impacted the overall resistivity of the sensor.Another key part of this work was to determine if the piezoresistivity in the sensors follows a percolation type behavior under strain. The conductance versus strain curve showed the characteristic s-curve behavior of a percolative system. The conductance-strain curve was also compared to the effective medium and generalized effective medium equations and the latter (which includes percolation theory) fit the random resistor network much more closely. Percolation theory is, therefore, an accurate way to describe this polymer-nanoparticle piezoresistive system.Finally, the FEA and SPC models were compared against experimental data to verify their accuracy. There are also two design problems addressed: one to find the sensor with the largest gauge factor and another to determine how to remove the characteristic initial spike in resistivity seen in nanocomposite sensors.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
O interesse no monitoramento da integridade estrutural de risers flexíveis tem crescido significativamente nos últimos anos. Para dutos que já estão atingindo sua vida de projeto, sistemas de monitoramento podem fornecer alertas antecipados de possíveis falhas e também auxiliar o operador na programação de paradas para manutenção. Diferentes técnicas estão sendo testadas pelos operadores de dutos flexíveis tais como inspeção visual automatizada, monitoramento de vibrações e emissão acústica, além de técnicas baseadas em métodos eletromagnéticos. Algumas destas técnicas já estão sendo implementadas em unidades de exploração e produção marítimas no Brasil e em outros países. A presente contribuição aborda o monitoramento contínuo e em tempo real utilizando sensores a fibra óptica (Redes de Bragg) para detectar a ruptura dos arames nas armaduras de tração de risers flexíveis. Duas linhas são seguidas, monitoramento direto e monitoramento indireto. O monitoramento indireto consiste na instrumentação da capa polimérica do riser, de forma não intrusiva, e avalia possíveis alterações na mesma, causadas pelo rompimento dos arames. Para isso foi desenvolvido um transdutor, denominado Colar 3D, capaz de detectar variações no diâmetro externo, elongação e torção no duto. A técnica de monitoramento direto é denominada MODA (Monitoramento Óptico Direto nos Arames). Nesta técnica os arames são instrumentados individualmente com os sensores ópticos, que monitoram as tensões/deformações dos mesmos, assim, rompimentos de arames e comportamentos inesperados podem ser facilmente detectados. Resultados de ensaios em escala real mostraram que a probabilidade de detecção do monitoramento indireto aumenta significativamente quando o sistema é empregado em conjunto com outros tipos de monitoramento indireto. Os resultados de laboratório para o monitoramento direto apontaram alta sensibilidade e confiabilidade do sistema, que já foi instalado em três plataformas operadas pela Petrobra na Bacia de Campos.
The interest in structural health monitoring of flexible risers has grown significantly in recent years. For ducts that are already reaching their design life, monitoring systems can provide early warnings of potential failures and also assist the operator in scheduling downtime. Different techniques are being tested by operators of flexible pipes such as automated visual inspection, vibration monitoring and acoustic emission, in addition to techniques based on electromagnetic methods. Some of these techniques are already being implemented in units of maritime exploration and production in Brazil and other countries. This contribution discusses the continuous monitoring and real-time using optical fiber sensors (FBGs) to detect the breaking of wires in the tensile armor of flexible risers. Two lines are followed, direct monitoring and indirect monitoring. The proposed indirect monitoring technique consists in the nonintrusive instrumentation of the riser’s polymeric outer sheath, which will provide strain signals that change due to the breaking of wires in the armor layer. For that, a transducer capable of detecting variations in the outer diameter, as well as stretching and twisting in the duct was developed. In the direct monitoring technique, all the wires in the external armor layer are individually instrumented with optical sensors that continuously monitor their strains, so that any disruptions of wires and unexpected behavior can be easily detected. Results of full scale laboratory tests showed that the probability of detection of indirect monitoring increases significantly when the system is used in conjunction with other types of indirect monitoring. The laboratory results for the direct monitoring showed high sensitivity and reliability of the system, which has already been installed in three oil rigs operated by Petrobras in the Campos Basin.

Els sensors de gasos s’utilitzen per a monitoritzar ambients interiors i exteriors. Algunes aplicacions comuns són per a mesurar el nivell de contaminants als carrers, els gasos alliberats per les fuites industrials i d’automòbils, els gasos a la mineria, el contingut d’alcohol en sang a través de l’alè exhalat, etc. A mesura que creix el camp d’aplicació dels sensors de gasos, es fa necessari adaptar els sensors de gasos als nostres dispositius i pertinences diàries. Es requereixen materials mecànicament flexibles i resistents per a fabricar sensors de gasos flexibles. A banda de proves de detecció de gas, la resistència a la flexió dels sensors ha de provar-se per anomenar “flexible” a un sensor. L’objectiu principal d’aquesta tesi és fabricar sensors de gasos flexibles mitjançant processos additius emprant òxids metàl·lics com a materials sensibles. Els sensors de gasos flexibles es varen fabricar utilitzant un substrat polimèric flexible (Kapton). Els diferents processos emprats varen ser compatibles amb la temperatura de funcionament del substrat. Entre les tècniques emprades estan la plantilla, la serigrafia, la injecció de tinta, AA-CVD. A més a més, es varen realitzar processos superficials per a millorar l’adhesió dels òxids metàl·lics al substrat polimèric. La flexibilitat dels sensors es va provar realitzant una prova de flexió cíclica.
Los sensores de gas se utilizan para monitorear ambientes interiores y exteriores. Algunas aplicaciones comunes son para medir: el nivel de contaminantes en las calles, los gases liberados por los escapes industriales y de automóviles, los gases en la minería, el contenido de alcohol en la sangre a través del aliento exhalado, etc. A medida que crece el campo de aplicación de los sensores de gas, se hace necesario adaptar los sensores de gas a nuestros dispositivos y pertenencias diarias. Se requieren materiales mecánicamente flexibles y resistentes para fabricar los sensores de gas flexibles. Además de las pruebas de detección de gas, la resistencia a la flexión de los sensores debe probarse para llamar “flexible” a un sensor. El objetivo principal de esta tesis es fabricar sensores de gas flexibles a través de procesos aditivos utilizando óxidos metálicos como materiales sensibles. Los sensores de gas flexibles se fabricaron utilizando un sustrato polimérico flexible (Kapton). Los diferentes procesos empleados fueron compatibles con la temperatura de la temperatura de funcionamiento del sustrato. Entre las técnicas empleadas están la plantilla, la serigrafía, la inyección de tinta, AA-CVD. Además, se realizaron procesos superficiales para mejorar la adhesión de los óxidos metálicos al sustrato polimérico. La flexibilidad de los sensores se probó realizando una prueba de flexión cíclica.
Gas sensors are used to monitor indoor and outdoor environments. Some common applications are to measure: the level of pollutants in the streets, the gases liberated by industrial and car exhausts, gases in mining, blood alcohol content through the exhaled breath, etc. As the field of application for gas sensors is growing, it becomes necessary to adapt the gas sensors to our daily devices and belongings. This requires mechanically flexible and resistant materials to fabricate the flexible gas sensors. In addition to gas sensing tests, the resistance to bending of the sensors should be tested to call a sensor flexible. The main objective of this thesis is to fabricate flexible gas sensors through additive processes using metal oxides as sensitive materials. The flexible gas sensors were fabricated using a flexible polymeric substrate (Kapton). The different processes employed were compatible with the temperature of the operating temperature of the substrate. Among the techniques employed are stencil, screen-printing, inkjet-printing, AA-CVD. Also, surface processes were performed to improve the adhesion of the metal oxides to the polymeric substrate. The flexibility of the sensors was tested by performing a cyclical bending test.

L'émergence des nouvelles applications dans le domaine de la micro et nanotechnologie requière de faibles coûts de fabrication et la caractérisation de dispositifs électroniques ayant des propriétés telles que la flexibilité, la portabilité, la légèreté, et des matériaux de faibles coûts. Les méthodes traditionnelles de fabrication impliquent de longues étapes de production, et des procédés de fabrication impliquant des étapes avec des produits chimiques. Le but de cette thèse est d'étudier la conception et la caractérisation de capteurs d'ammoniac et d'ozone sur support souple fabriqués par des processus de photolithographie et de gravure laser. Le support flexible est composé de Kapton avec des électrodes interdigitées de Ti/Pt pour la détection de gaz et un microchauffage. Les motifs du circuit ont été réalisés par photolithographie et gravure laser. L'utilisation de gravure laser sur support souple permet de réduire les coûts liés au temps de fabrication, aussi représente une excellente alternative aux processus chimiques. Des nanoparticles de ZnO déposées par gouttes ont été utilisées comme matériaux sensibles en raison de leurs excellentes propriétés dans la détection de gaz. Les conditions de détection de gaz ont été étudiées pour différentes concentrations d'ozone et d'ammoniac. Afin de tester une méthode de dépôt utilisée dans la production industrielle à grande échelle, un dépôt par spray ultrasonique a été effectué. Les capteurs réalisés montrent une large gamme de détection de 5 ppb à 500 ppb à 200 °C pour l'ozone et de 5 ppm à 100 ppm à 300 °C pour l'ammoniac avec une bonne reproductibilité, stabilité et de rapides temps de réponse et de retourn
Nowadays the emerging of new applications in the micro and nanotechnology field required to reduce fabrication costand to improve electronic devices with properties such as flexibility, portability, lightweight, and low cost. Traditional methods involve expensive and long production steps, and chemical vapor deposition. The purpose of this work is to present the conception and characterization of flexible ammonia and ozone sensors fabricated by photolithography and laser ablation processes. The flexible platform is composed of Kapton substrate with interdigitated Ti/Pt electrodes for gas detection and a micro-heater device. The circuit patterns were realized by photolithography and laser ablation. Photolithography is a well-known and reliable patterning process used on rigid substrate. The application of laser ablation process not only reduces fabrication time, but also represents an excellent viable alternative instead of chemical processes. ZnO thin films deposited by drop coating have been used as sensitive materials due to their excellent properties in the gas detection. The gas sensing condition and the performances of the devices are investigated for ozone and ammonia at different gas concentrations and different thin film thicknesses. In order to test a deposit methodology used in large scale industrial production, an ultrasonic spray deposition was done. The sensor provides a wide range of detection from 5 ppb to 500 ppb for ozone and from 5 ppm to 100 ppm for ammonia. Their best sensibilities were obtained at 200°C for ozone and 300 °C for ammoniac with good repeatability, stability and fast response/recovery time

Il miglioramento delle condizioni di vita ottenuto negli ultimi anni ha generato un aumento e un invecchiamento della popolazione, creando il bisogno di un nuovo paradigma di sanità intelligente dove sia possibile monitorare da remoto la variazione dello stato fisiologico dei pazienti. In questo contesto, gli e-skin, definibili come dispositivi flessibili che incorporano array di sensori, rappresentano una tecnologia all'avanguardia che permette il monitoraggio di differenti parametri fisiologici direttamente dal corpo umano in modo non invasivo grazie alle loro ridotte dimensioni. Per via di queste loro caratteristiche, gli e-skin sono promettenti in varie applicazioni come quello industriale, la prostetica e al già citato campo clinico. Questa loro grande applicabilità è resa possibile dai molteplici sensori che permettono di acquisire dati in modo preciso e distribuito. In questo contesto infatti, i sensori hanno assunto un ruolo centrale dal momento che hanno come compito principale la trasduzione dei differenti segnali d'interesse come ad esempio temperature, pressioni, deformazioni, biopotenziali e marcatori biochimici (e.g. ioni, metaboliti, metalli pesanti, amminoacidi, ormoni, farmaci, stupefacenti, ...). Quest'ultimo gruppo di marcatori sta recentemente suscitando un enorme interesse da parte della comunità scientifica dal momento che permettono il veloce riconoscimento di molteplici stati fisiologici e patologici. Ad oggi, per la misura di questi marcatori biochimici, la ricerca si sta concentrando sui biosensori dal momento che sono un'alternativa valida, più economica e di uso più facile rispetto ad altre tecniche di analisi di laboratorio (e.g. protocolli ELISA, cromatografia, ...) ad oggi usate come gold standard. Fra i possibili principi di trasduzione adottati correntemente per i biosensori in letteratura, l'elettrochimica presenta molteplici vantaggi fra cui un basso costo, un' alta sensibilità e l'uso di strumentazioni relativamente semplici. In questa tesi, verranno descritti differenti approcci per lo sviluppo e il miglioramento di sensori elettrochimici stampati applicati agli e-skin. La discussione partirà da una breve descrizione del principio di trasduzione di questi sensori e si focalizzerà in seguito prima su differenti approcci per il miglioramento delle caratteristiche metrologiche e poi sulla valutazione, monitoraggio e mitigazione delle componenti d'incertezza che possono influire sui dispositivi proposti. In questo contesto, la tesi si aprirà con una revisione della letteratura per introdurre i concetti generali riguardanti gli e-skin e i biosensori, in modo tale da poter comprendere meglio sia il loro principio di trasduzione e le loro limitazioni attuali. In seguito, sarà presentato un primo prototipo di un e-skin multisensing per la misura non invasiva e personalizzata dell'affaticamento muscolare che comprende sia un sensore elettromiografico (EMG) a 8 canali sia un sensore elettrochimico. I risultati ottenuti sono promettenti, ma per quanto riguarda il sensore elettrochimico le prestazioni non sono completamente soddisfacenti per l'applicazione e devono pertanto essere migliorate. Partendo da queste considerazioni, i successivi due progetti si concentrano sulle modalità di miglioramento della sensibilità e del limite di identificazione (limit of detection, LOD) sfruttando micro- e nano- strutturazione della superficie. In seguito, il lavoro si è concentrato su tutti gli elementi che possono introdurre incertezza sul segnale misurato in modo tale da comprendere meglio la qualità e l'affidabilità dei sensori elettrochimici stampati con AJP proposti. Fra queste fonti d’’incertezza si è riscontrato che la temperatura agisce da variabile d’influenza e pertanto se ne è approfondito lo studio per provare poi a compensare per mezzo di sensori stampati innovativi.
In the modern era where the overall living conditions improve, the population increases and ages, the need for a new paradigm of smart healthcare is arising where the need to monitor and track the changes in the physiological status of patients or sports professionals represents the main objective of the scientific community. In this frame, e-skin devices, defined as flexible devices that embed arrays of sensors, are cutting-edge technology that is promising to monitor different physiological parameters from the human body in a non-invasive way thanks to their reduced size and bulkiness. Thanks to these characteristics, e-skins are promising in a plethora of applications and fields other than the clinical one such as the industrial environment and prosthesis. Their wide applicability is enabled by the vast amount of sensors that allow precise and distributed data collection. In this frame, sensors become central to transduce from the body the signals of interest such as temperatures, pressures, deformations, biopotentials and biochemical markers (e.g. ions, metabolites, heavy metals, amino acids, hormones, drugs...). This last class of markers is lately attracting huge interest from the scientific community since they allow the quick detection of a plethora of physiological conditions. Currently, biosensors are researched to detect those signals as they are valid, cheaper and easier to use than standard in-lab analysis methods (e.g ELISA protocols, chromatography, ...). Moreover, among the possible transduction principles currently employed for biosensors, the electrochemical one presents, according to the literature, many advantages such as low cost, high sensitivity and simple instrumentation. In this thesis, different approaches for the development and improvement of printed electrochemical sensors for e-skin application will be investigated. Exploiting the opportunities offered by novel printing technologies, such as Aerosol Jet Printing, the main focus was to improve the metrological characteristics as well as to evaluate, monitor and mitigate the uncertainty sources that could affect the devices. Before going into the experimental detail, the first part of the thesis will be dedicated to provide a description of the transducing principle behind the electorchemical measurements investigated. Further, literature will be deepened in order to the general concepts about e-skins and biosensors, including opportunities and limitations. Then, a prototype of a multi-sensing e-skin patch for unobtrusive and personalized fatigue assessment, that uses both an 8-channel electromyographic (EMG) sensor and an electrochemical sensor, will be presented. The achieved results are promising, but underline the need to increase the sensitivity of the printed electrochemical sensors. Starting from these cues, the next two projects that will be presented are focused on the scientific evidence to try to improve the sensitivity and the limit of detection of printed electrochemical sensors using both micro- and nano- structures. The final part of the thesis will focus on all those elements that can introduce uncertainty on the overall measured signals in order to better understand the quality and the reliability of the proposed aerosol jet printed electrochemical sensors. In this, a wide set of uncertainty components and influence variables can be identified. Among the latter, the temperature is one of the most relevant components of noise (and thus uncertainty) on those kinds of sensors, that have to be compensated using novel, fully-printed sensors.

Atrial fibrillation is a cardiac condition in which the heart rate is abnormally fast and/or irregular. While not yet proven to be fatal on its own, it severely increases the probability of developing further medical conditions including a five times higher risk of getting stroke. The prevalence has, over the past decades, increased significantly across the world and was in 2014 approximated at roughly 2% in the European population. Though, this number is expected to further increase in the coming years and decades. Therefore, in order to reduce suffering and save lives, it is vital that there is an efficient way of treating this condition. Current treatment methods include medicine, cardioversion, and tissue ablation. This thesis focuses on tissue ablation, more particularly cryoballoon ablation, which is a minimally invasive procedure in which a cryoballoon catheter is guided through a blood vessel (generally accessed through an incision made in the groin area) to the heart. When inside the atrial chambers the balloon can be inflated, put into contact with the faulty tissue and then be injected with liquid nitrous oxide which vaporizes and freezes said tissue isolating the currents causing the irregular heartbeat. This thesis aims to attach flexible electronics to the outside of the cryoballoon, which should then be able to inform the operator that adequate contact has been achieved before freezing, thereby increasing the probability of successful ablation. Three prototypes were created using polyurethane balloons, flexible circuit boards and a biocompatible, flexible cyanoacrylate adhesive. The flexible circuit boards were arranged in different patterns for each prototype to see which configuration would best suit the application. It was found that narrow strips (single trace) aligned axially and spaced evenly along the circumference best accomplished the goal. The traces did, however, not adhere as well to the balloon as was hoped which likely was due to user error during the gluing procedure but a further investigation may be desired to ensure that the materials and adhesive are compatible.
Förmaksflimmer är ett hjärtfel som gör att hjärtslagen blir ovanligt snabba och/eller oregelbundna. Trots att det inte bevisats vara direkt dödligt än, ökar det kraftigt risken för att utveckla ytterligare medicinska besvär, bland annat fem gånger större risk att drabbas av stroke. Utbredningen av förmaksflimmer har under de senaste decennierna ökat avsevärt över hela världen och under 2014 uppskattades det att ungefär 2 % av den europeiska befolkning var drabbade. Den här siffran förväntas dock fortsätta öka under de kommande åren och decennierna. Därför, för att i största mån lindra smärta samt förhindra dödsfall, är det mycket viktigt att det finns ett effektivt sätt att behandla tillståndet. I nuläget innefattas behandling av medicin, elektrokonvertering eller vävnadsablation. Det här examensarbetet fokuserar på ablation, närmare bestämt kryoballongsablation, vilket är ett minimalinvasivt ingrepp som innebär att en kryoballongskateter förs in genom en blodådra (ofta via ett snitt i ljumsken) in i hjärtat. Väl inne i förmakskammarna kan ballongen blåsas upp, läggas emot den felaktiga vävnaden och sedan fyllas med flytande kväveoxid som förångas och fryser vävnaden vilket isolerar strömmarna som ger upphov till den felaktiga hjärtrytmen. Målet med det här examensarbetet är att fästa flexibla kretskort på utsidan av dessa kryoballonger, vilka då ska kunna känna av fysisk kontakt med vävnaden och informera operatören om detta innan frysningen sker. Därmed bör sannolikheten för lyckad ablation öka. Tre prototyper tillverkades med polyuretanballonger, flexibla kretskort och ett biokompatibelt, flexibelt cyanoakrylatlim. Kretskorten arrangerades i olika mönster för respektive prototyper för att undersöka vilken konfiguration som skulle passa ändamålet bäst. Det visade sig att smala kretskort placerade längs med ballongen axiellt och jämnt utspridda längs med omkretsen gav bäst resultat. Däremot höll inte limmet så bra som förväntat vilket troligtvis handlar om användarfel vid limningen men en vidare utredning kan vara att önska för att säkerställa att limmet är kompatibelt med övriga material.

The active vibration reduction of plane and stiffened plates was investigated using a genetic algorithm based on finite element modelling to optimise the location of sensors and actuators. The main aspects of this work were:  Development of a finite element model for a plate stiffened by beams with discrete sensors and actuators bonded to its surface.  Development of a finite element program for steel plates with various symmetrical and asymmetrical stiffening and edge conditions.  Development of a genetic algorithm program based on the finite element modelling for the optimisation of the location and number of sensor/actuator pairs and feedback gain.  Determination of optimum locations and feedback gain for collocated piezoelectric sensors and actuators on steel plates with various symmetrical and asymmetrical stiffening and edge conditions.  Development of fitness and objective functions to locate sensors and actuators.  Development of fitness and objective functions to determine the optimal number of sensors and actuators.  Development of a reduced search space technique for symmetrical problems.  Optimisation of vibration reduction control scheme parameters using the genetic algorithm.  Optimisation of the number and location of sensor/actuator pairs and feedback gain to reduce material costs and structural weight and to achieve effective vibration reduction. The modelling was validated by comparison with conventional finite element analysis using ANSYS, and by experiment. The modelling was developed using a quadrilateral isoparametric finite element, based on first order shear deformation theory and Hamilton’s principle, which may be arbitrarily stiffened by beams on its edges. The model can be applied to flat plates with or without stiffening, with discrete piezoelectric sensors and actuators bonded to its surfaces. The finite element modelling was tested for flat and stiffened plates with different boundary conditions and geometries, and the results of the first six natural frequencies were validated with the ANSYS package and experimentally. A genetic algorithm placement strategy is proposed to find the global optimal distribution of two, four, six and ten sensor/actuator pairs and feedback gain based on the minimisation of optimal linear quadratic index as an objective function, and applied to a cantilever plate to attenuate the first six modes of vibration. The configuration of this global optimum was found to be symmetrically distributed about the dynamic axes of symmetry and gave higher vibration attenuation than previously published results with an asymmetrical distribution which was claimed to be optimal. Another genetic algorithm placement strategy is proposed to optimise sensor/actuator locations using new fitness and objective functions based on . This is applied to the same cantilever plate, and was also found to give a symmetrical optimal sensor/actuator configuration. As before, it was found that the optimal transducer locations are distributed with the same axes of symmetry and in agreement with the ANSYS results. A program to simulate the active vibration reduction of stiffened plates with piezoelectric sensors and actuators was written in the ANSYS Parametric Design Language (APDL). This makes use of the finite element capability of ANSYS and incorporates an estimator based on optimal linear quadratic and proportional differential control schemes to investigate the open and closed loop time responses. The complexity of the genetic algorithm problem is represented by the number of finite elements, sensor/actuator pairs and modes required to be suppressed giving a very large search space. In this study, this problem was reduced by the development of a new half and quarter chromosomes technique exploiting the symmetries of the structure. This greatly reduces the number of generations, and hence the computing time, required for the genetic algorithm to converge on the global optimal solution. This could be significant when the technique is applied to large and complex structures. Finally, new fitness and objective functions were proposed to optimise the number of sensor/actuator pairs required for effective active vibration reduction in order to reduce the added cost and weight. The number, location and feedback gain were optimised for the same cantilever plate and it was found that two sensor/actuator pairs in optimal locations could be made to give almost as much vibration reduction as ten pairs.

Thesis (M.S.)--State University of New York at Binghamton, Thomas J. Watson School of Engineering and Applied Science, Department of Systems Science and Industrial Engineering, 2008.
Includes bibliographical references.

Integrated (IUTs) and flexible ultrasonic transducers (FUTs) have been found to be of great interest for structural health monitoring (SHM) of graphite/epoxy (Gr/Ep) composite parts and structures. Because certain Gr/Ep composites do not have sufficient electrical conductivity, bottom electrodes are required for the IUT fabrication. Also FUTs using insulating polyimide (PI) membrane which offers high flexibility, bottom electrode is required as well. One main objective is to develop the electroless plating technique to deposit nickel (Ni) or silver (Ag) onto Gr/Ep composites and PI for IUT or FUT fabrication. The pre-treatments (cleaning, etching, sensibilization, activation and reduction) and reaction conditions (bath chemistry, temperature, time, agitation, etc.) have been investigated. Recipes of electroless nickel (EN) plating at room temperature (RT) and 90°C and RT electroless Ag plating have been developed. The interfacial adhesion of the Ni or Ag/substrate was also tested. The conductivity of the fabricated bottom electrodes was tested by ohmmeter. A 50~60µm piezoelectric film was fabricated by sol-gel spray technique. IUTs and FUTs consisting of these EN bottom electrodes, piezoelectric film and Ag paste top electrode perform well for SHM purposes.
Les capteurs ultrasonores flexible (CUF) et intégré (CUI) sont très intéressants pour le suivi de la santé structurelle (SSS) des pièces de structures et de composites, composées à partir de carbone/époxyde (C/Ep). Parce que le C/Ep n'a pas suffisamment de conductivité électrique, une électrode de base est nécessaire pour la fabrication de CUIs. De plus, pour le CUF utilisant du polyimide (PI) comme membrane isolante nécessite aussi l'utilisation d'une électrode de base. Un des principaux objectifs de ce mémoire est de remédier à ce problème par le développement d'une technique de placage au tampon. Cette dernière déposera du nickel (Ni) ou de l'argent (Ag) sur le C/Ep et le PI pour obtenir des CUIs ou des CUFs. Les prétraitements (nettoyage, attaque chimique, sensibilisation, activation et réduction) et les conditions de réaction (bain chimique, température, temps, agitation, etc.) ont été étudiés. Les procédures pour le placage au tampon du nickel (PTN) à la température de la pièce (TP) et à 90C ainsi que pour l'Ag à TP furent développées. Les adhésions de surface du Ni ou de l'Ag avec le substrat furent testées. Les conductivités électriques des électrodes de base furent testées avec un ohmmètre. Un film piézo-électrique de 50~60 μm fut fabriqué par une technique sol-gel. Les CUI et CUF fabriqués avec l'électrode de base faite à partir du PTN, du film piézo-électrique et une pâte d'Ag comme électrode de surface, excelle bien pour les besoins en SSS.

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This thesis details the experimental analysis of an active damping control technique applied to the Naval Postgraduate School's Flexible Spacecraft Simulator using piezoceramic sensors and actuators. The mass property of the flexible arm is varied to study the frequency effects on the Positive Position Feedback (PPF) algorithm. Multi-modal dynamics response is analytically studied using a finite-element model of a cantilevered beam while under the influence of three different control laws: a basic law derived rom the Lyapunov Stability Theorem, PPF and Strain Rate Feedback (SRF). The advantages and disadvantages of using PPF and SRF for active damping control are discussed.

pH sensors are broadly used in chemical and biological applications. Example, Metal oxide-based pH sensors have many appealing features that include chemical resistance, insolubility, stability, outstanding mechanical strength, electrocatalyst and manufacturing technology. This thesis focuses on recent pH measurement techniques which incorporate miniaturization and optimization of the sensor and fabrication with super Nerstian pH sensitive materials. Such sensors have high sensitivity, fast response, excellent corrosion resistance, wide detection range, low hysteresis, long-term stability and good reversibility/reproducibility. The research validates the feasibility of developing a low-cost, rugged, miniaturized ruthenium oxide (RuO2) thin-film pH sensor comprising a RuO2 on platinum sensing electrode deposited using R.F. magnetron sputtered in conjunction with an integrated thick Ag/AgCl reference electrode. Ion diffusion condition (O2:Ar ratio), electrode film thickness (50-425 nm), sensing media temperature (1.5-50 °C) and working electrode area to reference electrode area ratio, are investigated for alumina and flexible substrates. Sensitivity values ranging from of 58.50 mV/pH to 84.50 mV/pH are attained with the developed sensors, for water quality, urease, biomedical application and standard buffer solutions of pH values 4.0 and 10.0. These results are in excellent agreement with the theoretical Nernstian response. The performance and characterization of the pH sensors with regards to sensitivity, response time, pH resolution, stability and reversibility are also investigated. A feasibility study for developing a ruthenium oxide (RuO2)-based pH sensor on a flexible substrate was also investigated. Moreover, the suitability of sensors demonstrate the concept of electrodes for monitoring engine oil acidity by adding nitric acid. Experimental results show a linear potential-versus-acid-concentration response for nitric acid concentration between 0 (fresh oil) to 400 ppm, thus demonstrating the accuracy of the RuO2 sensor in real-time operation, making it attractive for use in cars and industrial engines.

Thesis (M.S. in Systems Technology (Space Systems Operations)) Naval Postgraduate School, September 1993.
Thesis advisor(s): Brij N. Agrawal. "September 1993." Includes bibliographical references. Also available online.

Zinc oxide and graphene nanostructures are important technological materials because of their unique properties and potential applications in future generation of electronic and sensing devices. This dissertation investigates a brief account of the strategies to grow zinc oxide nanostructures (thin film and nanowire) and graphene, and their applications as enhanced field effect transistors, chemical sensors and transparent flexible electrodes. Nanostructured zinc oxide (ZnO) and low-gallium doped zinc oxide (GZO) thin films were synthesized by a magnetron sputtering process. Zinc oxide nanowires (ZNWs) were grown by a chemical vapor deposition method. Field effect transistors (FETs) of ZnO and GZO thin films and ZNWs were fabricated by standard photo and electron beam lithography processes. Electrical characteristics of these devices were investigated by nondestructive surface cleaning, ultraviolet irradiation treatment at high temperature and under vacuum. GZO thin film transistors showed a mobility of ~5.7 cm 2/ V•s at low operation voltage of ~0.5 V with a sub threshold swing of ~85 mV/decade. Bottom gated FET fabricated from ZNWs exhibit a very high on-to-off ratio (~10 6) and mobility (∼28 cm 2 /V•s). A bottom gated FET showed large hysteresis of ~5.0 to 8.0 V which was significantly reduced to ~1.0 V by the surface treatment process. The results demonstrate charge transport in ZnO nanostructures strongly depends on its surface environmental conditions and can be explained by formation of depletion layer at the surface by various surface states. A nitric oxide (NO) gas sensor using single ZNW, functionalized with Cr nanoparticles was developed. The sensor exhibited average sensitivity of ~46% and a minimum detection limit of ~1.5 ppm for NO gas. The sensor also is selective towards NO gas as demonstrated by a cross sensitivity test with N2, CO and CO2 gases. Graphene film on copper foil was synthesized by chemical vapor deposition method. A hot press lamination process was developed for transferring graphene film to flexible polymer substrate. The graphene/polymer film exhibited a high quality, flexible transparent conductive structure with unique electrical-mechanical properties; ~88.80 % light transmittance and ~1.1742 kΩ/sq sheet resistance. The application of a graphene/polymer film as a flexible and transparent electrode for field emission displays was demonstrated.

Recently, adding more lanes becomes less and less feasible, which is no longer an applicable solution for the traffic congestion problem due to the increment of vehicles. Using the existing infrastructure more efficiently with better traffic control and management is the realistic solution. An effective traffic management requires the use of monitoring technologies to extract traffic parameters that describe the characteristics of vehicles and their movement on the road. A three-dimension glass fiber-reinforced polymer packaged fiber Bragg grating sensor (3D GFRP-FBG) is introduced for the traffic monitoring system. The proposed sensor network was installed for validation at the Cold Weather Road Research Facility in Minnesota (MnROAD) facility of Minnesota Department of Transportation (MnDOT) in MN. A vehicle classification system based on the proposed sensor network has been validated. The vehicle classification system uses support vector machine (SVM), Neural Network (NN), and K-Nearest Neighbour (KNN) learning algorithms to classify vehicles into categories ranging from small vehicles to combination trucks. The field-testing results from real traffic show that the developed system can accurately estimate the vehicle classifications with 98.5 % of accuracy. Also, the proposed sensor network has been validated for low-speed and high-speed WIM measurements in flexible pavement. Field testing validated that the longitudinal component of the sensor has a measurement accuracy of 86.3% and 89.5% at 5 mph and 45 mph vehicle speed, respectively. A performed parametric study on the stability of the WIM system shows that the loading position is the most significant parameter affecting the WIM measurements accuracy compared to the vehicle speed and pavement temperature. Also the system shows the capability to estimate the location of the loading position to enhance the system accuracy.

L’analyse du mouvement humain intervient dans de nombreux domaines, permettant par exemple de comprendre les subtilités de la performance physique ou de la biomécanique. Les données et les informations issues de cette analyse des mouvements peuvent permettre d’améliorer les performances, de prévenir les blessures ou d’optimiser la rééducation. De nombreux systèmes existent comme la vidéo, mais sa mise en place et le traitement des données constituent des limites. Une solution consiste à développer des systèmes portables intégrés offrant un suivi discret et continu des activités. Les enjeux se situent dans le domaine des matériaux et de l’instrumentation pour répondre aux exigences des systèmes portables et autonomes. Ces travaux de thèse portent sur la conception de transducteurs piézorésistifs jusqu’au développement de systèmes autonomes en énergie comme une semelle permettant d’estimer la force plantaire et un vêtement pour la détermination des angles articulaires. Un modèle viscoélastique du transducteur piézorésistif a été établi permettant ainsi en l’inversant d’estimer la force plantaire. Des expérimentations de comparaison avec des systèmes commerciaux comme une plateforme de force ont été menées
Human motion analysis plays a vital role in numerous fields, enabling, for instance, the understanding of the nuances of physical performance or biomechanics. The data and information derived from this motion analysis can enhance performance, prevent injuries, or optimize rehabilitation. Various systems exist, such as video, but their implementation and data processing pose limitations. One solution is to develop integrated wearable systems offering discreet and continuous activity tracking. One challenge lies in the materials and instrumentation domain, where the objective is to develop wearable and autonomous systems that meet the requisite specifications. This thesis work focuses on the design of piezoresistive transducers for the development of energy-autonomous systems, such as an insole for estimating plantar force and a garment for determining joint angles. A viscoelastic model of the piezoresistive transducer has been established, which enables the estimation of plantar force by inversion. Comparative experiments have been conducted with commercial systems, including a force platform

In real operating environments, flexible structures exhibiting dynamic oscillations such as aircraft and spacecraft can experience large changes in temperature during their normal operating cycle, typically in the range -70 to 80 degrees Celsius. The use of piezoelectric actuators and sensors to control these dynamic oscillations have been widely explored at constant temperature, although only limited studies have been conducted on the effect that varying temperature has on the active control of flexible structures. The objective of this research is to study the influence of PZT sensors and actuators for vibration control of flexible structures where nonlinearities in piezoelectric and structural material properties change as the system temperatures vary significantly with time. This involved the development of a set of data based parameters that enabled the accurate modelling of a nonlinear flexible system in which its dynamics are actively controlled via the use of piezoelectric sensors and actuators. These parameters determined the design of a control scheme to actively control the system over a large range of operating temperatures, and give an optimised control performance throughout its operating regime. The work reported in this thesis describes selected methods for rapidly examining a number of the more common nonlinear properties of PZT associated with vibration control. An extensive numerical and experimental investigation is performed which shows that when used in active vibration control applications, the variations in PZT properties with temperature can ultimately affect the ability of the piezoelectric actuator and sensors to suppress vibration in flexible structures. Accurate simulation models of the lightweight piezo-actuated cantilevered structures were developed to evaluate the performance of a number of common vibration control schemes subject to significant temperature variations. This research was then extended to an innovative scaled wing-type structure subjected to temperature variations. A suitable adaptive self-tuning control scheme was developed and investigated numerically and experimentally, illustrating the benefit of adaptive control in this instance. The adaptive control technique was shown numerically and experimentally to provide improved settling times and damping ratios over equivalent fixed gain controllers for the class of structures investigated where limited control authority exists. The experimental investigation of PZT sensors and actuators has provided further understanding of the nonlinear behaviour of various light, flexible structures where temperature effects on the system dynamics and control are significant. This research has unveiled previously unreported nonlinearities and has expanded on traditional nonlinearities. These results can assist with the detailed design of applications involving PZT sensors and actuators in for example the aerospace and automotive industries.

This thesis reports the discovery of a wide negative di↵erential resistance (NDR) region in a graphite-silicone composite that was utilized to create a strain-tuned flexible oscillator. Encoding the strain into frequency mimics the behavior of mechanoreceptor neurons in the skin and demonstrates a flexible and electronically active material suitable for state of the art bio-electronic applications. The NDR was investigated over a range of composite filling fractions and temperatures; alongside theoretical modelling to calculate the tunneling current through a graphite-silicone barrier. This led to the understanding that the NDR is the result of a semi-metal to insulator transition of embedded graphene bilayers within the graphite nanoparticles. The transition, brought about by a transverse bias across specifically orientated particles, opens a partial band-gap at the Fermi level of the bilayer. NDR in a flexible material has not been observed before and has potential for creating a flexible active device. The electromechanical properties of the composite were considered through a bend induced bilayer strain. The piezoresistance was found to be dominated by transient resistance spiking from the breaking of conduction lines, which then reform according to the viscoelasticity of the polymer matrix. The resistance spiking was embraced as a novel method for sensitive di↵erential pressure detection, used in the development of two applications. Firstly, it was employed for the detection of ultrasound waves and found to have an acoustic pressure detection threshold as low as 48 Pa. A commensurability was observed between the composite width and ultrasound wavelength which was shown to be consistent with the formation of standing waves, described by Bragg’s law. Secondly, a differential pressure array of 64 composite pixels was fabricated and demonstrated to image pressures under 3.8 kPa at a resolution of 10 dpi. The NDR active region was incorporated into an LC circuit where it was demonstrated to sustain oscillations of up to 12.5 kHz. The composite was then strained and an intrinsic frequency was observed which had a linear dependence on the strain with a frequency shift of 84 Hz / % strain. Lastly the composite was used in a strain-tuned amplifier circuit and shown to provide a gain of up to 4.5. This thesis provided the groundwork for a completely flexible electronically active device for futuristic bio-electronic skins with resolutions and sensitivities rivalling those of human tactile sensing.

In this work the problem of actuator and sensor mapping and controller design for the flexible structure control is approached as minimization of the residual deformations index (Hinfinity norm of the closed-loop disturbance - deformation path) over the set of non-destabilizing feedback controllers and over the set of possible actuator and sensor mappings. Computational load associated with this approach is reduced by restricting the search to the mapping areas where an inexpensive lower estimate of residual deformations index (derived as a part of this study) is less than the desired value of this index. Further improvement is achieved by including statistical description of the difference between the actual and the estimated performance index over the set of mappings, in order to adjust the level of the mapping acceptance/rejection in such a way that the number of rejected mappings is increased. Serial and parallel optimization procedures based on exhaustive search and genetic algorithms are discussed. These concepts and algorithms are applied to test cases of simply supported beam, the UCLA Large Space Structure, and a telescope mirror model: a hinged round plate.

Graphene is a novel carbon material with great promise for a range of applications due to its electronic and mechanical properties. Its two-dimensional nature translates to a high sensitivity to surface chemical interactions thereby making it an ideal platform for sensors. Graphene's electronic properties are not degraded due to mechanical flexing or strain (Kim, K. S., et al. nature 07719, 2009) offering another advantage for flexible sensors integrated into numerous systems including fabrics, etc.

We have demonstrated a graphene NO2 sensor on a solid substrate (100nm SiO2/heavily doped silicon). Three different methods were used to synthesize graphene and the sensor fabrication process was optimized accordingly. Water is used as a controllable p-type dopant in graphene to study the relationship between doping and graphene's response to NO2. Experimental results show that interface water between graphene and the supporting SiO2 substrate induces higher p-doping in graphene, leading to a higher sensitivity to NO2, consistent with theoretical predications (Zhang, Y. et al., Nanotechnology 20(2009) 185504).

We have also demonstrated a flexible and stretchable graphene-based sensor. Few layer graphene, grown on a Ni substrate, is etched and transferred to a highly stretchable polymer substrate (VHB from 3M) with preloaded stress, followed by metal contact formation to construct a flexible, stretchable sensor. With up to 500% deformation caused by compressive stress, graphene still shows stable electrical response to NO2. Our results suggest that higher compressive stress results in smaller sheet resistance and higher sensitivity to NO2.

A possible molecular detection sensor utilizing Surface Enhanced Raman Spectrum (SERS) based on a graphene/gallium nanoparticles platform is also studied. By correlating the enhancement of the graphene Raman modes with metal coverage, we propose that the Ga transfers electrons to the graphene creating local regions of enhanced electron concentration modifying the Raman scattering in graphene.

Dissertation

This thesis is concerned with the advanced topics of thin film magnetoimpedance (MI) sensors. The author proposes and develops novel MI sensors that target on the challenges arising from emerging applications such as flexible electronics, passive wireless sensing, etc. In the study of flexible MI sensor, the investigated sensors of NiFe/Cu/NiFe tri-layersare fabricated on three flexible substrates having different surface roughness: Kapton, standard and premiumphotopaper. Sensitivity versus substrate roughness analysis is carried out for the selection of optimal substrate material. The high magnetic sensing performance is achieved by using Kapton substrate. Stress simulation, incorporated with the theory of magnetostriction effect, reveals the material composition of Ni/Fe being as a key factor of the stress dependent MI effect for the flexible MI sensors. In the development of MI-SAW device for passive wireless magnetic field sensing, NiFe/Cu/NiFe tri-layersand interdigital transducers(IDT) are designed and fabricated on a single piece of LiNbO3substrate, providing a high degree of integration and the advantage of standard microfabrication. The double-electrodeIDT has been utilized and proven to have an optimal sensing performance in comparison to the bi-directional IDT design. The optimized high frequency performance of the thin film MI sensor results in a MI-SAW passive wireless magnetic sensor with high magnetic sensitivity comparing to the MI microwire approach. Benefiting from the high degree of integration of the MI thin film element, in the following study, two additional sensing elements are integrated to the SAW device to have a multifunctional passive wireless sensor with extended temperature and humidity sensing capabilities. Analytical models havebeen developed to eliminate the crossovers of different sensing signals through additional reference IDTs, resulting in a multifunctional passive wireless sensor with the capability of detecting all three measurands individually and simultaneously.

In recent decades, there has been increasing interest in the development of new materials in order to achieve the "Internet of Things (IoT)" which provided for the connection of 20 to 30 billion devices to the Internet by 2020. The implementation of the "Internet of Things "requires the development of base technology, which includes transducers, actuators and sensors. Sensors are often used in biomedical applications that require flexibility, biocompatibility and sustainability. In this context, the motivation of this work was the preparation of a bionanocomposite for biocompatible piezoelectric sensors for biomedical applications. Thus, a polysaccharide that have the ability to form films (films), and particles of barium titanate which is ferroelectric and piezoelectric material at room temperature, having no lead in its composition. The BaTiO3 particles were synthesized by hydrothermal method at moderate temperature (200 °C) and in the absence of organic solvents. Several reaction times were studied in order to select the ideal conditions for the particles preparation with the required properties to be incorporated in the chitosan-based films. The structural characterization by X-ray diffraction (XRD) and Raman spectroscopy allowed us to verify that the particles synthesized at 200 °C showed a well-defined tetragonal crystallographic structure after 24 hours of synthesis. The particles showed uniformed cubic morphology and average size of about 306 nm. In general, particle and crystallite sizes increase with reaction time. The films were obtained by the solvent evaporation method, after dispersing the particles in different proportions, in a solution of chitosan. Structural properties (XRD) and morphological (SEM); physical-chemical (mechanical, degree of humidity, solubility in water and contact angle, and Raman); and electrical (dielectric behavior, hysteresis curves and nanoscale piezoelectric response) of the films were characterized. The addition of particles improved the mechanical properties of the chitosan films, making them more resistant, elastic and ductile. These films have also been shown to be more resistant to water, which reveals that there is an interaction between the particles and the chitosan matrix. In relation to the electric behavior of the films, the increase of particles improves the permittivity of the samples five times in relation to the biopolymer material. It was verified a great difficulty of deposition of electrodes in the flexible films that can be justified on the basis of the characteristics of the samples and / or the inadequacy of the experimental conditions of deposition of the electrodes in the sample. It was not possible to measure the piezoelectric response at the macroscopic scale nor to polarize an area of the bionanocomposite sample. Thus, the piezoelectric response at the nanometric scale was studied by atomic microscopy of piezoelectric response. It was found that nanocomposite films with the highest concentration of nanoparticles clearly showed piezoelectric domains, but it is not possible to obtain an acceptable hysteresis curve and to polarize a small area of the nanocomposite. These observations, together with the analysis by surface potential microscopy of the control film (chitosan only) that indicates the presence of charges in the pure polymer, lead to the conclusion of an electret type behavior, being necessary a strategy to eliminate (or reduce) the matrix's contribution. Despite the difficulties encountered due to degree of innovation of the work, the bionanocomposites developed based on chitosan and barium titanate are promising to be used in biomedical devices (drug release pads, etc.) since they have high mechanical resistance, elasticity, and ductility, as well as have higher resistance to conditions with high degree of humidity. In addition, they are biocompatible and partially biodegradable, being an excellent alternative to synthetic polymers
Nas últimas décadas, tem havido um interesse crescente no desenvolvimento de novos materiais com o intuito de alcançar a "Internet of Things (IoT)" que prevê a ligação de 20 a 30 bilhões de dispositivos à internet até 2020. A implementação da “Internet of Things” exige o desenvolvimento de tecnologia base, onde se incluem os dispositivos de captação de energia, atuadores e sensores. Os sensores são muitas vezes utilizados em aplicações biomédicas que exigem flexibilidade, biocompatibilidade e sustentabilidade. Neste contexto, a motivação deste trabalho foi a preparação de um bionanocompósito para sensores piezoelétricos biocompatíveis para aplicações biomédicas. Assim, escolheu-se como matriz um polissacarídeo que tem a capacidade de formar películas (filmes) facilmente, e partículas de titanado de bário que é um material ferroeléctrico e piezoeléctrico à temperatura ambiente, não possuindo chumbo na sua composição. As partículas de BaTiO3 foram sintetizadas por método hidrotermal a temperatura moderada (200 °C) e na ausência de solventes orgânicos. Foram estudadas vários tempos de reação de forma a selecionar as condições ideais para a preparação das partículas com as propriedades adequadas para a incorporação nos filmes à base de quitosana. A caracterização estrutural por difração de raios-X (DRX) e espectroscopia de Raman permitiu verificar que as partículas sintetizadas a 200 °C apresentavam, ao fim de 24 horas de síntese, a estrutura cristalográfica tetragonal bem definida. As partículas mostraram morfologia cúbica uniforme e tamanho médio de cerca de 306 nm. Em geral, os tamanhos das partículas e de cristalites aumentam com o tempo de reação. Os filmes foram obtidos pelo método de evaporação de solvente, após a dispersão das partículas, em diferentes proporções, numa solução de quitosana. As propriedades estruturais (DRX) e morfológicas (SEM); físico-químicas (mecânicas, grau de humidade, solubilidade em água e ângulo de contacto e Raman); e elétricas (comportamento dieléctrico, curvas de histerese e resposta piezoelétrica à escala nanométrica) dos filmes foram caracterizadas. A adição de partículas melhorou as características mecânicas dos filmes de quitosana, tornando-os mais resistentes, elásticos e dúcteis. Estes filmes revelaram também serem mais resistentes à água, o que revela que existe uma interação entre as partículas e a matriz de quitosana. Em relação ao comportamento elétrico dos filmes, o aumento de partículas melhora a permitividade das amostras cinco vezes em relação ao material biopolimérico. Foi verificada uma grande dificuldade de deposição de elétrodos nos filmes flexíveis que se pode justificar com base nas características das amostras e/ou na inadequação das condições experimentais de deposição dos elétrodos na amostra. Como não foi possível medir a resposta piezoeléctrica à escala macroscópica, nem polarizar uma área da amostra de bionanocompósito, fez-se o estudo da resposta piezoelétrica à escala nanométrica por microscopia atómica de resposta piezoelétrica. Os filmes com a concentração mais elevada de nanopartículas mostraram claramente domínios piezoelétricos, não sendo, contudo, possível traçar uma curva de histerese aceitável nem polarizar uma pequena área do nanocompósito. Esta observação, juntamente com a análise por microscopia de potencial de superfície do filme controlo (só de quitosana) que indica a presença de cargas no polímero puro, leva à conclusão da existência de um comportamento do tipo electret pelo que será necessário encontrar uma estratégia para eliminar (ou reduzir) a contribuição da matriz. Apesar das dificuldades encontradas, os bionanocompóstos desenvolvidos, à base de quitosana e titanato de bário são promissores para serem usados em dispositivos biomédicos (por exemplo em compressas para libertação de fármacos, etc.) devido à sua elevada resistência mecânica, elasticidade e ductilidade, sendo adaptados a condições de elevado grau de humidade. Estes bionanocompósitos são ainda biocompatíveis e parcialmente biodegradáveis, tendo potencial para serem usados como alternativa aos polímeros sintéticos
Mestrado em Materiais e Dispositivos Biomédicos

碩士
清雲科技大學
電子工程所
99
In this paper, a water-based, low-cost flexible sensor which uses carbon nanotubes (CNTs) as the channel material is fabricated on the plastic substrate. To verify the sensing properties, we use NaCl ion solution as the testing sample. By using the device the different channel length and sensing region, the simple, low-cost, low-toxic (no organic solvent) sensor show a good sensitivity and we also demonstrate this sensor has a highly reusable.

The interest and need in portable, comfortable and durable health care sensors have increased along the years, due to their practicability and potential in helping people monitoring their vital signs. However, an all biodegradable low-cost sensor still poses a challenge to fabricate. So, cellulose is being used in the nanoscale form, due to filling all the necessary requirements with their excellent properties. The same can be said for metals like gold, silver and copper, which in the form of nanowires makes them great alternatives as sensing materials for pressure sensors. This work aims to develop a facile craft, low-cost, completely biodegradable, paper-based flexible and wearable pressure sensor for health care. The AgNWs are produced by the microwave-assisted polyol synthesis and purified with 3 decantation phases. The sensor substrate is made by pressing the bacterial nanocellulose (BNC) of nata de coco. The interdigitated electrodes (IDEs) are then screen-printed on its surface. The tissue paper is dip coated with the AgNWs, placed in the middle of the IDEs and encapsulated with the BNC, concluding the sensor construction. The sensor displayed a fast response time of 1.8 ms, a recovery time of 0.8 ms and it also showed high stability during 15000 cycles. The best sensitivity values achieved were 12.05 kPa-1 (0.031-1.4 kPa), 4.29 kPa-1 (1.4-2.8 kPa), 1.59 kPa-1 (2.8-5.6 kPa) and 0.38 kPa-1 (5.6-14 kPa), with the 6 dip coating cycles paper Tork on the sensor. The lowest detectable pressure was 31 Pa and the minimum and maximum energy consumption values recorded were 3.75×10-5 W and 1.32×10-2 W with a 2V working voltage.
O interesse e a necessidade em sensores de saúde portáteis, confortáveis e duráveis têm aumentado ao longo dos anos, devido à sua praticabilidade e potencial em ajudar as pessoas a monitorizarem os seus sinais vitais. No entanto, a produção de um sensor completamente biodegradável de baixo custo ainda representa um desafio. Por isso, vários tipos de celulose estão a ser usados à nanoescala por preencherem os requisitos necessários com as suas excelentes propriedades, assim como metais como o ouro, prata e cobre, que na forma de nanofios os torna ótimas alternativas como materiais de deteção em sensores de pressão. Este projeto tem como objetivo desenvolver um sensor de pressão fácil de fabricar, de baixo custo, completamente biodegradável, à base de papel, flexível e de fácil uso em cuidados de saúde. Os nanofios de prata são produzidos pela síntese poliol assistida por micro-ondas e purificados em 3 fases de decantação. O substrato do sensor é criado pressionando a nanocelulose bacteriana da nata de coco. Os elétrodos interdigitais são produzidos na sua superfície por impressão em tela. O papel é revestido com nanofios de prata por imersão, colocado no meio dos elétrodos interdigitais e encapsulado com a nanocellulose bacteriana, concluindo assim a construção do sensor. O sensor apresentou um rápido tempo de resposta de 1.8 ms, um tempo de recuperação de 0.8 ms e uma elevada estabilidade durante 15000 ciclos. Os melhores valores de sensibilidade obtidos foram 12.05 kPa-1 (0.031-1.4 kPa), 4.29 kPa-1 (1.4-2.8 kPa), 1.59 kPa-1 (2.8-5.6 kPa) e 0.38 kPa-1 (5.6-14 kPa) com o sensor a utilizar 6 ciclos de revestimento por imersão no papel Tork. O sensor também conseguiu detetar uma baixa pressão de 31 Pa e apresentou um consumo mínimo e máximo de energia de 3.75×10-5 W e 1.32×10-2 W, com uma tensão de trabalho de 2V.

碩士
國立臺灣科技大學
機械工程系
98
In this work, we present the development of a reliable piezoresistive strain sensing array fabricated by a solution based thin film method. The strain sensing array were made on a polyimide (PI) substrate by patterned hydrophilic treatment and tilted-drop process. The technique of patterned surface modification was performed by atmospheric plasma for enhancing surface energy in specific area. The measured water contact angles were 118.8° and 0.9° before and after hydrophilic treatment respectively. The materials used in the tilted-drop process were conductive polymer composites solutions with different ingredients and proportions. Fabricated strain sensor samples with different conductive fillers, including carbon nano-fiber, multi-wall carbon nano-tube and carbon black, and different surfactants, including sodium dodecyl sulfate (SDS) and polystyrene sulfonate (PSS), have been investigated by measuring resistivity in different strain. Finally, the fabricated strain sensing array has been tested by using a LabView program to capture the multi-meter values of resistivity. A scanning circuite were also developed to capture the signal from the flexible sensing array. The developed system has been applied to human posture correction and artificial muscle research.

Programa Doutoral em Líderes para as Indústrias Tecnológicas.
Polymer nanocomposites (PNCs) are defined as polymers bonded with nanoparticles to create materiais with improved properties. The development of this type of material is rapidly emerging as a multidisciplinary research activity, since their final properties can benefit many different fields of application, namely in the development of electrical devices as studied herein. A fabrication technique to produce conductive PNCs was developed in this work and used to fabricate flexible capacitive pressure sensors. The process is based on vertically aligned-carbon nanotubes (A-CNTs) embedded in a flexible and biocompatible matrix of polydimethylsiloxane (PDMS). Thin A-CNTs/PDMS nanocomposite films ( ~ 400 Jlm) were produced using wetting of as-grown A-CNTs with uncured PDMS and the resulting nanocomposites were used to fabricate flexible pressure sensors. The sensing capability of this A-CNTs/PDMS nanocomposite is attributed to the distinctive combination of mechanical flexibility and electrical properties. The fabricated nanocomposites were characterized and mechanical and electrical properties evaluated. The PDMS is significantly modified by the reinforcing A-CNT fibers, demonstrating non-isotropic (as opposed to the isotropic neat PDMS) elastic properties ali different than the PDMS (Young's modulus of 0.8 MPa), including an anisotropy ratio of 4.8 and increases in the modulus of A-CNTs/PDMS nanocomposites over PDMS by more than 900 % and I 00 %, in the CNTs longitudinal and transverse directions, respectively. Regarding the electrical measurements, A-CNTs/PDMS nanocomposites presented an electrical conductivity of 0.35 Sim. The rather low conductivity does not compromise the developed capacitive sensor, but since passive telemetry is required to measure and power the sensor, solutions to overcome this problem were also studied. The configuration of the developed flexible sensor is similar to typical silicon-based capacitive pressure sensors. It is composed of three thin films, where two of them are A-CNTs/PDMS nanocomposites (defining the diaphragm type electrodes) separated by a film made of neat PDMS (defining the dielectric) and its operating principie is based on the change of the deflection of the nanocomposite layers due to the change of an externa! pressure. The developed flexible pressure sensors tested for pressures between O kPa and I 00 kPa (operation required to measure the blood pressure in the aneurysm sac) showed good linearity, mainly in the region near to the atmospheric pressure (pressure inside of dielectric ). ln the sarne range, the dynamic response of the pressure sensors presented two distinct comportments, which are related with the viscoelastic behaviour of the PDMS-based nanocomposites used to build the pressure sensor. ln addition, from the experimental measurements of the prototype pressure sensors used, the sensitivities are in the range of2.5- 20 fF/kPa. To demonstrate feasibility for practical applications, the flexible sensor technology was used in a biomedical application, more specifically in the context of abdominal aortic aneurysms. The proposed implantable flexible pressure sensing system (capacitive sensor plus inductor) consists of a mixed technology that uses A-CNTs/nanocomposites to build the capacitar electrodes and flexible printed circuit board (PCB) technology to build an inductor. The complete system was assessed by applying pressures varying from O kPa to 1 00 kPa. The results showed that the flexible sensors responded to pressure variations with a well-defined characteristic curve and oscillation frequencies centered around 5.3 MHz (the sensor receives energy and reflects back its oscillation frequency by means of inductive coupling). ln addition to these experiments, the performance of both pressure sensors and reader system was assessed using a hydraulic model that mimics the abdominal aorta. The proof-of-concept experiments validated the proposed telemetry system functionality and showed feasibility in integrating the flexible, biocompatible and passive sensor into a stent-graft, in arder to the detect blood pressure in the aneurysm sac. Finally, the developed technology to fabricate flexible pressure sensors based on A-CNTs/PDMS nanocomposites proved successful in sensing applications and due to its biocompatibility and versatility, can be used in other fields of application such as portable medical devices and e-textiles (to monitor the vital signs of an individual, such as heart rate and temperature, by using textile substrates with integrated electronics).
Os nanocompósitos de polímeros (PNCs) são definidos como polímeros ligados com nanopartículas, originando materiais com propriedades melhoradas. O desenvolvimento deste tipo de material está a surgir rapidamente como uma atividade de investigação multidisciplinar, uma vez que as suas propriedades finais podem beneficiar diferentes áreas de aplicação, nomeadamente no desenvolvimento de dispositivos elétricos como estudado aqui. Neste trabalho foi desenvolvida uma técnica de fabricação de PNCs condutores e utilizada para produzir sensores de pressão capacitivos. O processo é baseado em CNTs verticalmente alinhados (A-CNTs) embutidos numa matriz flexível e biocompatível de polidimetilsiloxano (PDMS). Membranas de nanocompósitos de A-CNTs/PDMS ( ~ 400 Jlm de espessura) foram produzidas através do molhamento dos A-CNTs, utilizados conforme crescidos, pelo PDMS e os nanocompósitos resultantes foram utilizados para fabricar sensores de pressão flexíveis. A capacidade de deteção destes nanocompósitos é conferida pela combinação distintiva da flexibilidade mecânica e propriedades elétricas. Os nanocompósitos fabricados foram caracterizados e as suas propriedades mecânicas e elétricas foram avaliadas. O PDMS é significativamente alterado pelo reforço das fibras de A-CNT, demonstrando propriedades elásticas anisotrópicas (ao contrário do PDMS puro que é isotrópico ), incluindo uma razão de anisotropia de 4.8 e aumento do módulo dos nanocompósitos de A-CNTs/PDMS relativamente ao PDMS acima dos 900 % e 100 %, na direção longitudinal e transversa dos CNTs, respetivamente. Relativamente aos testes elétricos, os nanocompósitos apresentaram uma condutividade elétrica de 0.35 S/m. O valor bastante baixo da condutividade não compromete o sensor capacitivo desenvolvido, mas uma vez que é necessária telemetria passiva para medir e energizar o sensor, foram também estudadas outras soluções para superar este problema. A configuração do sensor flexível desenvolvido é semelhante aos típicos sensores de pressão capacitivos de silício. Este é composto por três filmes finos, onde dois deles são nanocompósitos de A-CNTs/PDMS (definem o diafragma) separados por um filme de PDMS (define o dielétrico), e o seu princípio de funcionamento é baseado na deformação das membranas de nanocompósitos devido a variações de uma pressão externa. Os sensores de pressão flexíveis testados para pressões entre O kPa e 100 kPa (necessário para medir a pressão sanguínea no saco do aneurisma) apresentaram boa linearidade, principalmente na região próxima da pressão atmosférica (pressão no interior do dielétrico ). Para a mesma gama de pressões, a resposta dinâmica dos sensores apresentou dois comportamentos distintos, que estão relacionados com o comportamento viscoelástico dos nanocompósitos utilizados para fabricar o sensor. Além disso, testes experimentais realizados com sensores de pressão protótipos mostraram sensibilidades na gama de 2.5-20 fF/kPa. De forma a demonstrar a viabilidade para aplicações práticas, foi apresentada a utilização da tecnologia do sensor de pressão numa aplicação biomédica, mais concretamente no contexto de aneurismas na aorta abdominal. O sistema flexível de monitorização da pressão proposto (sensor capacitivo mais indutor) consiste numa tecnologia mista que utiliza nanocompósitos de A-CNTs/PDMS para construir os elétrodos do condensador e uma placa flexível de circuito impresso para construir o indutor. O sistema completo foi avaliado para variações de pressão entre O kPa e I 00 kPa. Os sensores flexíveis responderam às variações de pressão com uma curva característica bem definida e frequências de oscilação centradas nos 5.3 MHz. O desempenho dos sensores de pressão e do sistema de leitura foram também avaliados utilizando um modelo hidráulico que imita a aorta abdominal. Os testes experimentais validaram a funcionalidade do sistema telemétrico proposto e mostraram viabilidade em integrar o sensor flexível, biocompatível e passivo num stent-graft, de forma a detetar variações da pressão sanguínea no saco do aneunsma. A tecnologia desenvolvida para fabricar sensores de pressão flexíveis, que se baseia em nanocompósitos de A-CNTs/PDMS, provou ser bem-sucedida em aplicações de deteção de pressão e devido à sua biocompatibilidade e versatilidade, esta tecnologia pode ser utilizada em outras áreas de aplicação, tais como dispositivos médicos portáteis e têxteis eletrónicos (para controlar os sinais vitais de um indivíduo, como a frequência cardíaca e temperatura, utilizando substratos têxteis com eletrónica integrada).
Fundação para a Ciência e a Tecnologia (FCT) SFRH/BD/42922/2008. ERDF (European Regional Development Fund) through COMPETE (Operational Competitiveness Program) and national funds through FCT in the framework of the projects MIT-Pt/EDAM-EMD/007/2008/ and PTDC/EEI-ELC/1838/2012.

Tese de Doutoramento Ciência e Engenharia de Polímeros e Compósitos.
Conductive ink has extraordinary properties. The printing of patterns with conductive inks on polymer surfaces gives them new properties and functionalities, making them ideal for several diverse application areas. These printed polymeric materials can be embedded in a system to perform a given function, e.g., to change their electrical resistivity as a response to an applied deformation. The use of printed electronics on the fabrication of flexible pressure sensors is of particular interest. Flexible Pressure Sensor (FPS) technology provides more accurate reading and contact area thanks to its ability to fold/roll, when compared to other traditionally used materials. However, they remain unsatisfactory and inaccessible to the general population. Developing a more intelligent and efficient sensor, capable of being integrated in complex environments, with improved properties, lighter and more robust, elastically deformable with quick back response, which does not sacrifice the freedom of motion, and equally important, economically attractive and suitable for mass production, is essential. Inkjet Printing Technology (IPT) has evolved in a way that ceased to be known only as a manufacturing tool in the paper and newspapers industry and it became one of the most important technologies in organic, flexible electronics and printing polymeric substrates, as well as a topic in scientific research. This technology as attracted the attention of the industrial community over the past due to a number of features, which makes a compelling argument for an interesting alternative to the conventional Printed Electronics (PE) technologies. But, there are many challenges in the use of direct printing. Most polymers are hydrophobic showing a low surface energy. Therefore, they are difficult to adhere to other materials. A new developed method for the surface treatment of polymeric substrates in order to increase their surface energies is presented. This novel surface treatment of thermoplastic polymers was applied to the inkjet printing of Thermoplastic Polyurethane (TPU) substrates with conductive inks, and significant improvements on the printability were obtained. Still, to reach the spatial geometry of the printed pattern, electrical conductivity, resolution and durability, several studies were performed and depending on the material involved, a specific know-how is required. A compromise between several criteria must be performed in order to select the proper substrate and conductive ink to get the desired sensor performance (achieve the desired sensor characteristics like resolution and bandwidth). The focus of this thesis is the development of a new generation of good performance and lower cost thin flexible pressure sensors. The applied research was focused from a materials science point of view (selectively applying commercially available and compatible materials or defining viable material alternatives), with resource to a Drop-on-Demand inkjet printer with a piezoelectric printhead to process the materials, and exploring it’s potential to be integrated into electronic applications. Three different inks with different characteristics were studied. After inkjet printing parameters definition and depending on the ink and substrate, the characterization of the printed system was conducted for pattern resolution, adhesion of the ink to the substrate, and electromechanical properties evaluation. The design, fabrication and experimental results of a FPS system and its readout electronics interface are also presented here. The developed sensing platform for postural imbalance monitoring consists of an array of flexible capacitive pressure sensors, in the millimeter range and uses a simple manufacturing process (enabling a reasonable density of sensors in the active zone). Thus, it is possible to achieve good performance results (comparable to existing solutions in the industry), with the particularity of offering an economically viable alternative, allowing its use in rehabilitation activities. The results obtained are very promising and encouraging. The developed pressure platform could be successfully inkjet printed and was fully functional.
As tintas condutoras têm propriedades extraordinárias. A impressão de padrões com tintas condutoras na superfície de polímeros atribui-lhes novas propriedades e funcionalidades, tornando-os ideais para diversas áreas de aplicação. Estas tintas impressas em substratos poliméricos podem ser incorporados num sistema para realizar uma dada função, i.e., a sua resistividade elétrica muda em resposta à deformação exercida. O uso da eletrônica impressa na fabricação de sensores de pressão flexíveis tem particular interesse. A tecnologia de sensores de pressão flexíveis permite maior precisão de leitura e maiores áreas de contato graças à sua capacidade para dobrar/enrolar, quando comparados aos materiais tradicionalmente utilizados. No entanto, estes sensores continuam a ser incipientes e inacessíveis a população em geral. Desenvolver um sensor inteligente e eficiente, capaz de integrar ambientes complexos, com propriedades, de tamanho ainda mais reduzido, leves e robustos, deformáveis e com elasticidade, com rápida resposta, e que não sacrifique a liberdade de movimentos, economicamente atrativos e adequados para produção à escala industrial é essencial. A tecnologia de impressão a Jato de Tinta evoluiu de tal forma que deixou de ser conhecida apenas como uma ferramenta de produção na indústria do papel e de jornais e, tornou-se uma das tecnologias mais importantes na eletrônica flexível e na impressão de substratos poliméricos, bem como um tópico pesquisa científico. Nos últimos anos, esta tecnologia atraiu a atenção da comunidade industrial principalmente devido a uma série de características que a torna num argumento convincente como uma alternativa interessante as tecnologias convencionais para a eletrônica impressa. No entanto, são muitos os desafios do uso de impressão direta. A maioria dos polímeros são hidrofóbicos, apresentando uma baixa energia de superficial. Por esta razão são difíceis de aderir a outros materiais. Um novo tratamento da superfície foi desenvolvido para os substratos poliméricos, a fim de aumentar as suas energias de superfície. Na superfície do substrato de termoplástico poliuretano (TPU) com o novo tratamento de superfície, tintas condutoras foram impressas e melhorias significativas na capacidade de impressão foram observados. Ainda assim, a obtenção a geometria especial da estrutura impressa, condutividade elétrica, resolução de impressão e durabilidade, exigiu estudo, e dependendo dos materiais envolvidos, um know-how específico é necessário. Será um compromisso entre vários critérios de forma a selecionar o substrato e a tinta condutora ideal para obter a performance desejada do sensor (atingir as caraterísticas desejadas do sensor como a resolução e largura de banda). O foco deste trabalho reside no desenvolvimento de uma nova geração de sensores de pressão flexíveis com bom desempenho e baixo custo. O estudo focou-se no ponto de vista da ciência dos materiais (aplicação seletiva de materiais comercialmente disponíveis e compatíveis, ou definir alternativas viáveis), utilizando uma impressora jato de tinta com sistema Drop-on-Demand com uma cabeça de impressão piezoelétrica para processar os materiais, e explorar o seu potencial para ser integrado em aplicações eletrônicas. Foram estudadas três tintas com características diferentes. Após a definição dos parâmetros de impressão a jacto de tinta de acordo com a tinta e o substrato, o sistema impresso foi caracterizado para uma avaliação da resolução de impressão, adesão da tinta ao substrato, e das propriedades eletromecânicas. O design, fabricação e resultados experimentais de um sensor de pressão flexível e sua interface eletrônica de leitura também foram aqui apresentados. O sensor de pressão flexível desenvolvido para monitorização do desequilíbrio postural consiste numa matriz de sensores capacitivos de pressão flexíveis, no intervalo milímetro, e, usa um processo de fabrico simples (permitindo uma densidade razoável de sensores na zona ativa). Assim, é possível conseguir bons resultados de desempenho (comparáveis às soluções existentes na indústria), com a particularidade de oferecer uma alternativa economicamente viável, permitindo o seu uso em atividades de reabilitação. Os primeiros resultados obtidos são muito promissores e encorajadores. A plataforma de pressão desenvolvida pode ser produzida com sucesso por impressão a jato de tinta e demonstrou ser totalmente funcional.
TICE-Healthy - Sistemas de Saúde e Qualidade de Vida projeto nº 13842, co-financiado por FEDER.

碩士
大葉大學
機械工程研究所碩士班
95
The purpose of this paper is to apply Surface Micromachining of MEMS techniques to manufacture a micro flexible sensor. Micro sensors not only have a smaller physical size than their traditional counterparts, but also provide a greater measurement accuracy and a higher sensitivity. MEMS components integrate with measured circuit or devices and miniature dimension is easier to get well to be conveniently portable. In this study, a platinum layer is deposited to form resistors and a Au layer is deposited on the resistors to serve as an electrode and to provide electrical leads, which are sandwiched between two polyimide layers as flexible substrates. Then we manufacture a bottom plate of PDMS which be broached five different diameters of holes. When we apply a weight on the pressure sensor placed on the PDMS, bottom plate we can measure the resistance variation to determine the pressure. The experimental data indicate that sensitivity increases as the diameters of holes of PDMS plates. Not only the measured resistance value increases as the temperature increases, the sensitivity of the temperature increases as the bending curvature decreases. Therefore it is easy to measure pressure and temperature by the simplified structure.

Soft actuators and sensors are currently used in many industrial applications due to their capability to produce an accurate response. Researchers have studied dielectric electroactive polymers (DEAPs) because these types of structures can be utilized as actuators and as sensors being able to convert electrical energy into mechanical and vice versa. However, production of this kind of structures is complex and in general involve several steps that are time consuming. Customization of these types of structures will be ideal to enhance the performance of the devices based on the specific application. 3D printing technologies have emerged as innovative manufacturing processes that could improve fabrication speed, accuracy, and consistency with low cost. This additive manufacturing technique allows for the possibility of increased device complexity with high versatility.

This research studied the potential of 3D printing technologies to produce DEAPs, soft actuators, and flexible sensors. The study presents novel designs of these composite flexible structures, utilizing the most flexible conductive and nonconductive materials available for fused deposition modeling, achieving versatility and high performance in the produced devices. Produced DEAP actuators showed an actuation and electric resistivity higher than other electroactive structures like shape memory alloys and ferroelectric polymers. In addition, this research describes the electromechanical characterization of a flexible thermoplastic polyurethane, (TPU), produced by additive manufacturing, including measurement of the dielectric constant, percentage radial elongation, tensile proprieties, pre-strain effects on actuation, surface topography, and measured actuation under high voltage. DEAP actuators were produced with two different printing paths, concentric circles and lines, showed an area expansion of 4.73% and 5.71% respectively. These structures showed high resistance to electric fields having a voltage breakdown of 4.67 kV and 5.73 kV respectively. Those results are similar to the resistant of the most used dielectric material “VHB 4910”.

The produced soft pneumatic actuators were successfully 3D printed in one continuous process without support material. The structures were totally sealed without the use of any sealing material or post process. Computational simulations were made to predict the response of the designed structures under different conditions. These results were compared with experimental results finding that the theoretical model is able to predict the response of the printed actuators with an error of less than 7%. This error is satisfactorily small for modeling 3D printed structures and can be further minimized by characterization of the elastomeric material. Besides that, two different grippers were designed based on the opening and closing movements of single bellows actuators. The functionality of both designs was simulated and tested, finding that both designs are capable lifting a heavier rigid structure.

Finally, this study presents a computational simulation of a 3D printed flexible sensor, capable of producing an output signal based on the deformation caused by external forces. Two different sensors were designed and tested, working based on a capacitance and resistance change produced by structural deformation. Computational analysis indicate the capacitance sensor should undergo change of capacitance from 3 to 8.5 pF when is exposed to 30 kPa; and the resistance sensor should experience an increase from 101.8 to 103 kΩ when is exposed to 30 kPa.

博士
國立成功大學
工程科學系碩博士班
97
Flexible electronics have developed rapidly in recent years for sensors and actuators due to their large area applications and low cost manufacturing. These flexible devices can be bent, expanded, and manipulated during use. In addition, flexible electronics made with organic materials, carbon-based materials, or transistors could be patterned onto thin films or bendable surfaces using printing technologies. However, there are few practical applications of flexible electronics in passive sensors; most studies have focused on small scale devices or imbedded bulk devices on flexible substrates. Furthermore, the material characteristics of flexible materials have yet to be completely investigated for applications in fabrication processes. Therefore, this study proposes analysis methods for flexible materials, investigates the material characteristics of flexible substrates, and designs and fabricates the flexible sensors. The material characteristics of flexible substrates, PVDF and PI films, include phase transformation, surface morphologies, optical spectra, thermomechanical, behavior, nanoindentation phenomena, and mechanical properties. Experimental results show that thermomechanical characteristics of PVDF film are greatly influenced at stretching ratios of over 4 in the stretching direction. The hardness is almost uniform and Young’s modulus is about 0.25 ± 0.01 and 3.44 ± 0.14 GPa, respectively. Unstretched PVDF films have a higher absorbance in the UV light range than stretched films do. PVDF with a stretching ratio of over 3 has above 90% transmittance at near infrared light. For PI film, UV light is not transmitted into the films and the transmittance of IR light is about 86%. Nanoindentation experiments show an almost uniform hardness and a reduced Young’s modulus of about 0.181 ± 0.03 and 3.21 ± 0.06 GPa, respectively. Thermomechanical characteristics are greatly influenced for specimens with thicknesses of 8.3 and 25 μm due to the higher relaxation of thin PI films. Thus, the material characteristics analysis provides useful information for the design and fabrication of flexible substrates. A flexible tactile sensor and a flexible physiological sensor are investigated in this study. Flexible tactile sensors were designed and fabricated using printing technologies for applications in multi-touching and large area sensing. The sensors are based on polyimide substrates, with thixotropy materials used to print novel organic resistance and a bump on the top polyimide. The gap between the bottom electrode layer and the resistance layer provides a buffer distance to reduce erroneous contact during extreme bending. Experimental results show that the top membrane with a bump protrusion and the resistance layer have a large deflection and a quick sensitive response. The bump and resistance layer provide a concentrated force of von Mises stress and inertial force on the top membrane center. Linear algorithm matrixes with Gaussian elimination are used for multi-touching detection. The flexible physiological sensor is based on a PI substrate for a printed circuit and uses on a non-woven material to package the module with a hot-press. The module is sufficiently thin and light to be pasted on human wrists for monitoring body temperature and heart beat. The thickness of the flexible physiological sensor is about 2 mm and the minimum radius of curvature is about 2.5 cm. The sensor can detect a temperature and heart rate of 25 - 45℃ and 50 - 200 bpm, respectively. The feasibility studies show that printing technology is appropriate for large area applications and that it can be used for the low-cost fabrication of flexible electronics.

碩士
國立雲林科技大學
機械工程系
107
In this study,liquid rubber were used to manufacture a flexible pressure strain sensors. Liquid silicone as flexible substrate for sensor. Bonding two slices of test pieces after the compression molding of liquid silicone. Buried wire and injected liquid metal. The sensors was used to test by tensile testing and pressure testing and records strain rate,pressure,resistance changes. The strain sonsor has been tested by using tensile testing equipment.The gauge factor of strain sensor is about 0.02 is smaller than commercial strain strain sensor,strain sensor can reach 200% strain. In the experiment, it can be known that the slower speed tensile sensor can obtain better resistance response effect, and the reliability experiment shows that the cycle change is stable, and the sensor is applied to the wearable device and the robot. In the pressure sensor test, the liquid silicone film is deformed by the air pressure, and the resistance of the liquid metal changes when the silicone film is deformed. The pressure sensor can be applied to a range of 36 psi with a linear change in pressure from 0 to 26 psi.

碩士
國立交通大學
應用化學系分子科學碩博士班
100
In this study, we fabricated Au nanowires (NWs), nanoslices (NSs), and nanocorals (NCs) on flexible polyethylene terephthalate (PET) substrates via direct current electrochemical depositions. Without any modification, the Au nanostructures were used as the electrodes for dopamine (DA) sensing. Among them, the Au NW electrode performed exceptionally well. The determined linear range for DA detection was 0.2 – 600 uM (N = 3) while the detection limit was 26 nM (S/N = 3).

碩士
國立交通大學
照明與能源光電研究所
103
This study was designed to fabricate graphene strain sensors, prepared from the material transfer of chemical vapor deposition - grown graphene onto a flexible PDMS substrate. Raman Spectroscopy determines the number of layers of graphene, and finally using a tensile testing instrument to measure the gauge factor of graphene strain sensors. In addition, we also test the sensitivity of the graphene strain sensor in bending and also under normal pressure, which makes graphene strain sensors widely used in future to have more possibilities. In order to make the sensor on flexible substrates, polydimethylsiloxane (PDMS) is used, which is a high molecular organic silicon compound with the properties, like non-toxic, hydrophobic, transparent and having elasticity. In future, graphene strain sensors could be used into biomedical application, such as blood pressure monitors.

碩士
元智大學
機械工程學系
98
Based on micro-electro-mechanical systems (MEMS), this study focuses on the fabrication design and production of flexible micro sensors. Flexible micro sensors are then embedded into the flat micro methanol reformer to determine the variations inside the micro channel plate. This study has the following objectives: design different micro channel plates based on MEMS technology, discuss the design and the fabrication of flexible micro sensors by using theoretical calculations and an experimental database, integrating the production of the micro methanol reformer components and the chemical catalyst preparation, analyzing the characteristics of flexible micro sensors, and incorporating the flat methanol reformer to measure the variations inside the micro channel plate. Interior reaction of the micro methanol reformer is diagnosed by embedding the flexible array micro sensors in adjusting the injecting rate allows us to raise or maintain the ratio of the water and catalyst, the temperature control and the conversion efficiency of methanol and the rate of producing hydrogen, ultimately achieving real time monitoring of the micro methanol reformer. Keyword: Real time monitoring, micro methanol reformer, flexible micro sensors.

碩士
國立中興大學
奈米科學研究所
106
A high-sensitive, low-cost and portable strain sensing technology based on gold nanoparticles (AuNps) is developed. For this goal, AuNPs were self-assembled on flexible substrates, forming closely packed multilayer films by centrifugal method, followed by appropriate chip packaging technique. AuNPs were modified with 3-mercaptopropionic acid(MPA), which has a length of about 0.9nm. As such the typical resistance of our sensors are in the range of 1-20 MΩ. When strains are applied to the substrate, the distance between adjacent AuNPs is changed, inducing the variations on the device resistance and capacitance. The sensors made on polydimethylsiloxane (PDMS) substrate may have the gauge factor up to 430. It can sense the pressure change with a sensitivity of 0.396kPa^(-1). The nominal power consumption is very low, about 15~24 nW. The capacitance change with a sensitivity of -36.4 and 22.5. For studying the response time, sensors were tested under mechanical vibrations of different frequency. The resistance change can be clearly identified up to a vibration frequency of 1 kHz. With the different frequency response, the sensors can find theirs applications in human pulse sensing, motion detection, and voiceprint recognition.

博士
國立清華大學
動力機械工程學系
107
Due to their low cost, bendable and stretchable characteristics, flexible tactile sensors are widely used in touch panel, prostheses, robots, and artificial electronic skin (e-skin) to mimic the sensing capabilities of human skin. In this thesis, two kinds of novel flexible tactile sensors with different sensing mechanisms, piezoresistivity and capacitance, are developed. In the first part, the proposed piezoresistive tactile sensor is investigated. It utilizes the interlocked structures with high-aspect-ratio ZnO nanorod arrays to increase the available conducting paths and thus to increase the contact areas for electrical conduction between two electrodes. As a result, the sensitivity is significantly improved. To become a multifunctional tactile sensor, except for measuring the static and dynamic forces, the developed tactile sensor can be employed to detect the environmental temperature using the characteristics of the thermal resistance of ZnO nanorods. Furthermore, with 3 × 3 sensor units, the piezoresistive tactile sensor can provide high resolution and identify the difference in the strengths of multiple-touch forces applied. In the second part, a novel capacitive tactile sensor has been proposed. The perceptive unit of tactile sensor consists of five sensing electrodes to detect three-axial force. Each capacitive sensing unit comprises a pair of the same shape but different size electrodes (top electrode and bottom electrode). By the unique design of electrode shapes, the developed tactile sensor is able to detect the applied normal force and the shear force, to have the capability of decoupling the applied normal and shear force and the torsion sensing. In the future, the proposed tactile sensor with the ability of sensing torque can be utilized in the wearable devices, flexible interface in the touch panel, and bionic robotic skins.

博士
國立臺灣科技大學
電子工程系
102
Optical waveguide has been widely used in various applications because it is immunity to electromagnetic interference. The most common optical waveguide for long-distance transmission is optical fiber. Due to optical fibers offer the advantages of low propagation loss, light weight, and low costs, it has been widely applied to fiber-optics sensor as well. But optical fiber is difficult to achieve in-device integration. However, optical polymer waveguides and silicon waveguides can resolve this problem because of their ability to satisfy the high-density integration. In this thesis, we introduce these optical waveguides and their applications. We propose using a two-stage optical low-coherence Mach-Zehnder (MZ) interferometer containing a super-luminescent emitting diode (SLED) for fiber sensing sensitivity enhancement. This fiber-optic structure was used to several types of sensors such as strain, force, and birefringence sensors. An single mode fiber with a 3-m-long sensing arm exhibited strain and force sensitivities as high as 6.8 μm/με and 8.5 μm/mN, respectively. In addition, the beat-length value of a polarization-maintaining fiber (PMF) was measured using an optical MZ interferometer. The experimental results indicate that the birefringence values of 1-m and 3-m PM fibers were 3.85 × 10-4 and 3.92 × 10-4, respectively. Using an optical ruler derived from a 1310-nm wavelength distributed feedback (DFB) laser assisted by a stable stepper motor improved strain resolution. Theoretically, a 3-m-long fiber sensing arm in a MZ interferometer can be used to obtain a 2.7-nε high-strain resolution. The sensitivity values of 1-m and 30-m fiber strain sensing were 2.3 and 66.7 μm/με, respectively. The experimental results indicated that a long optical fiber provides high sensitivity. In addition, we propose using a flexible multimode waveguide for high-speed transmission. We demonstrated that a highly flexible multimode waveguide implemented on an electronic printed circuit board (PCB) can be used in folded-type applications. An optical interconnection using polymer waveguides on an optical and electronic printed circuit board (OEPCB) was designed and fabricated to achieve low optical propagation loss and a high-speed data rate. The optical flexible waveguides were fabricated using the roll-to-roll lamination method. To achieve a simple fabrication process and high position accuracy, the polymer waveguides were forming 45° reflective mirrors using dicing approach and followed by the e-beam deposition for 90° beam turning. To simplify the fabrication process, laser-to-waveguide and waveguide-to-detector coupling were implemented using the total internal reflection (TIR) method. A transmission rate of up to 12.5 Gb/s and an optical propagation loss of 0.1 dB/cm were produced using the board-embedded flexible polymer waveguide. The additional optical loss of 0.3 dB was experimentally shown on the 2-mm bending radius and 180° curvature angle. Because of the advantageous effects of silicon material on transparency in telecommunication wavelengths, complementary metal–oxide–semiconductor (CMOS)-compatible processing, and the high index contrast for a small footprint, the silicon-on-insulator (SOI) platform has attracted increasing attention for processing photonic integrated circuits in a massive electronics fabrication infrastructure. We developed the use of SOI photonic wire microring resonators, which use a multimode interference (MMI) coupler between the ring and waveguides. The MMI coupler exhibited a wide operating wavelength and high fabrication tolerance for maintaining insensitivity MMI-coupled ring resonator. The MMI-coupled ring resonator was designed and fabricated with a circumference of 110 μm and a stable quality factor of 1199 across a wide range of wavelengths. The use of a tunable microwave phase shifter (a tunable phase shift range of 350°) based on a wavelength-tuning SOI microring resonator, which can be tuned using a tunable laser source (TLS). Based on the rapid development of silicon and polymer waveguide transmissions, a concept of unidirectional interconnection between silicon and polymer waveguides is proposed in this study. The concept of combining flexible polymeric waveguide links with CMOS-compatible silicon waveguides is also proposed for next-generation applications.

碩士
國立暨南國際大學
電機工程學系
97
This study aimed to develop a flexible and portable potentiometric pH sensor arrays composed of silver reference electrode and tin oxide (SnO2) working electrode. The fabrication procedures were screen-printing the silver reference electrode and carbon working electrode on top of a PET substrate. Then, SnO2 was sputtered on top of the carbon working electrode to form the SnO2 working electrode. 　　This potentiometric pH sensor arrays was tested using standard pH buffer solution (pH2~pH12). It was found that the sensitivity of this sensor arrays was 50~55mV/pH. Also, this pH sensor arrays on measuring pH was compared to a commercial glass reference electrode and both findings agreed with each other. Therefore, this showed that the screen-printing silver reference electrode could substitute the traditional glass reference electrode. 　　 　　In conclusion, a flexible and portable potentiometric pH sensor arrays was developed and this pH sensor arrays gave a fundamental structure for the development of a potentiometric biosensor. The advantages of this pH sensor arrays were that it was possible to allow multi-analytes to be analyzed. Finally, since screen-printing technique was employed on the fabrication, this could facilitate massive production with lower cost.

Flexible self-powered sensors have great potential in the medical field, offering a means of continuous monitoring of patients, helping to prevent and diagnose diseases. The present work explores biodegradable and low-cost alternatives to produce flexible sensors, from polylactic acid, for biomedical applications. Flexible sensors are composed of 3 main parts: transducers, electrodes, and substrate. In this work, the flexible sensors object of study are constituted by an incapsulating substrate of transparent adhesive tape, electrodes produced by 3D printing of a conductive composite of polylactic acid doped with carbon black and by 2 types of transducers; poly-L-lactic (PLLA) and commercial polylactic acid (PLA) To produce the poly-L-lactic acid (PLLA) and polylactic acid (PLA) transducers, two production methods were used: solvent cast and electrospinning, corona pooling methodology was used to change its electrical state. The response of sensors to mechanical and electrical stimuli was investigated and compared. The results show that both PLA and PLLA work based on the principle of piezoelectricity and triboelectricity and respond to mechanical deformation, the best results were obtained by transducers produced by solvent casting treated by corona pooling.
Sensores flexíveis autoalimentados têm grande potencial no campo da medicina, podendo oferecer meios de monotorização continua de pacientes ajudando na prevenção e diagnóstico de doenças. O presente trabalho explora alternativas biodegradáveis e de baixo custo para produção de sensores flexíveis, a partir de ácido poliláctico, destinados a aplicações biomédicas. De uma forma geral os sensores flexíveis são compostos por 3 partes principais: transdutores, elétrodos e substrato, Neste trabalho os sensores flexíveis objeto de estudo são constituídos por um substrato incapsulante de fita cola transparente, elétrodos produzidos por impressão 3D de um compósito condutor de ácido poliláctico dopado com negro de fumo e por 2 tipos de transdutores; poli-L-láctico (PLLA) e ácido poliláctico (PLA). Para produzir os transdutores de ácido poli-L-láctico (PLLA) e ácido poliláctico (PLA) foram usados dois métodos de produção: solvent cast e electrospinnig e recorreu-se à metodologia de corona pooling para alteração do seu estado elétrico. A resposta dos sensores a estímulos mecânicos e elétricos foi investigada e comparada. Os resultados mostram que tanto o PLA quanto o PLLA funcionam com base no princípio da piezoeletricidade e triboeletricidade e respondem a deformação mecânica, os melhores resultados foram obtidos pelos transdutores produzidos por solvent casting tratados por corona pooling.
Mestrado em Materiais e Dispositivos Biomédicos