Dissertations / Theses on the topic 'Dielectric imaging'

Doctor of Philosophy
Department of Food Science
Randall K. Phebus
Intervention techniques to control foodborne pathogens, and rapid identification of pathogens in food are of vital importance to ensure food safety. Therefore, the first objective of this research was to study the efficacy of radio frequency dielectric heating (RFDH) against C. sakazakii and Salmonella spp. in nonfat dry milk (NDM) at 75, 80, 85, or 90°C. Using thermal-death-time (TDT) disks, D-values of C. sakazakii in high heat (HH)- and low heat (LH)-NDM were 24.86 and 23.0 min at 75°C, 13.75 and 7.52 min at 80°C, 8.0 and 6.03 min at 85°C, and 5.57 and 5.37 min at 90°C, respectively. D-values of Salmonella spp. in HH- and LH-NDM were 23.02 and 24.94 min at 75°C, 10.45 and 12.54 min at 80°C, 8.63 and 8.68 min at 85°C, and 5.82 and 4.55 min at 90°C, respectively. The predicted (TDT) and observed (RFDH) destruction of C. sakazakii and Salmonella spp. were in agreement, indicating that the organisms' behavior was similar regardless of the heating system (conventional vs. RFDH). However, RFDH can be used as a faster and more uniform heating method for NDM to achieve the target temperatures. The second objective of this research was to study if hyperspectral imaging can be used for the rapid identification and differentiation of various foodborne pathogens. Four strains of C. sakazakii, 5 strains of Salmonella spp., 8 strains of E. coli, and 1 strain each of L. monocytogenes and S. aureus were used in the study. Principal component analysis and kNN (k-nearest neighbor) were used to develop classification models, which were then validated using a cross-validation technique. Classification accuracy of various strains within genera including C. sakazakii, Salmonella spp. and E. coli, respectively was 100%; except within C. sakazakii, strain BAA-894, and within E. coli, strains O26, O45 and O121 had 66.67% accuracy. When all strains were studied together (irrespective of their genera) for the classification, only C. sakazakii P1, E. coli O104, O111 and O145, S. Montevideo, and L. monocytogenes had 100% classification accuracy; whereas, E. coli O45 and S. Tennessee were not classified (classification accuracy of 0%).

In the year 2000 John Pendry described a new kind of lens that could focus both the propagating and evanescent components of light. This ‘super’ lens, which took the form of a thin slab of silver with a negative effective index of refraction under certain conditions, had the ability to reproduce images much smaller than the wavelength of light, seemingly in violation of the diffraction limit that governed the performance of conventional optics. Despite significant controversy regarding the purported operation of such superlenses, the first experimental samples were fabricated in 2005, with features as small as 63 nm successfully imaged with 365 nm light. These results put to rest disbelief in the feasibility of superlenses and ushered in an era of intense interest in near-field phenomena and negative index materials (NIMs). Despite sustained effort, progress on the practical implementation of superlenses was slow, with a further five years passing before improved experimental results were published. In the meantime, a proliferation of analytical and modelling studies appeared on the behaviour and properties of superlenses, as well as numerous suggestions for improved physical designs, very few of which had accompanying experimental evidence. The primary aim of this thesis arose from these many proposals, namely, to reconcile predictions made about the behaviour of superlenses with observed experimental results. The measurement of the theoretical and practical behaviour of superlenses is addressed in this thesis by the development of a set of characterisation metrics that can be used to describe the imaging performance of a number of near-field imaging systems. These metrics are initially calculated via transfer matrix modelling (TMM), which is a one-dimensional analytical technique traditionally used to find the transmission and reflection coefficients of planar structures. Two families of metrics are derived; one that describes imaging systems in terms of their abilities in generic situations and the other that gives the suitability of an imaging system for application to a given class of object. Transfer functions, bandwidth and peak wavenumber measurements form this first group of characterisation functions, while contrast, pseudo-contrast and correlation coefficients are used to assess the quality of imaging systems when exposed to well-defined input profiles. Both sets of metrics show that the performance of superlenses is highly application-specific, with the fidelity or otherwise of a generated image dependent more on the construction of the superlens than on the maximum spatial frequencies present in the object. The results from the characterisation metrics are also used to guide the design of hypothetical superlens structures; these suggest that sub-diffraction limited resolution may still be available with almost a full wavelength separation between object and image. The quantitative accuracy of the TMM method is assessed by comparison to full-field vector simulations performed via finite element modelling (FEM), these reveal systematic inadequacies in the application of the TMM technique to superlensing applications. These inadequacies stem from near-field mask-lens interactions that are present in superlens experiments but are not accounted for in TMM calculations. A new technique, based on a modified transfer matrix model (M-TMM), is proposed that accounts for the effects between masks and superlenses by approximating masks as solid slabs of known thickness. Results generated via M-TMM are shown to be in better agreement with FEM models than similar TMM data, even when the duty cycle of the actual mask becomes significant and the approximation in M-TMM is at its most coarse. Finally, experiments are designed and executed that directly measure the transfer functions of superlenses and other near-field imaging techniques. The problem of intimate contact between optics components, which normally hinders any such attempts to perform lithography in the near-field, is mitigated by including a flexible layer of poly (dimethylsiloxane) (PDMS) between various components in the mask:lens:resist stack. Furthermore, high spatial frequency data corresponding to low nanometre-scale features are retrieved from masks with periodic, micron-scale patterns, greatly easing the requirements on mask construction for these experiments. The end results show good agreement with FEM and M-TMM data and satisfy the aim of this thesis, which was to bridge the divide between the performance expected and experienced from silver superlenses.

Recent advances in medical imaging have greatly improved the success of cardiovascular and intracardiac interventions. This research aims to improve capacitive micromachined ultrasonic transducers (CMUT) based imaging catheters for intravascular ultrasound (IVUS) and intra-cardiac echocardiography (ICE) for 3-D volumetric imaging through integration of high-k thin film material into the CMUT fabrication and array design. CMUT-on-CMOS integration has been recently achieved and initial imaging of ex-vivo samples with adequate dynamic range for IVUS at 20MHz has been demonstrated; however, for imaging in the heart, higher sensitivities are needed for imaging up to 4-5 cm depth at 20MHz and deeper at 10MHz. Consequently, one research goal is to design 10-20MHz CMUT arrays using integrated circuit (IC) compatible micro fabrication techniques and optimizing transducer performance through high-k dielectrics such as hafnium oxide (HfO2). This thin film material is electrically characterized for its dielectric properties and thermal mechanical stress is measured. Experiments on test CMUTs show a +6dB improvement in receive (Rx) sensitivity, and +6dB improvement in transmit sensitivity in (Pa/V) as compared to a CMUT using silicon nitride isolation (SixNy) layer. CMUT-on-CMOS with HfO2 insulation is successfully integrated and images of a pig-artery was successfully obtained with a 40dB dynamic range for 1x1cm2 planes. Experimental demonstration of side looking capability of single chip CMUT on CMOS system based FL dual ring arrays supported by large signal and FEA simulations was presented. The experimental results which are in agreement with simulations show promising results for the viability of using FL-IVUS CMUT-on-CMOS device with dual mode side-forward looking imaging. Three dimensional images were obtained by the CMUT-on-CMOS array for both a front facing wire and 4 wires that are placed perpendicular to the array surface and ~4 mm away laterally. For a novel array design, a dual gap, dual frequency 2D array was designed, fabricated and verified against the large signal model for CMUTs. Three different CMUT element geometries (2 receive, 1 transmit) were designed to achieve ~20MHz and ~40MHz bands respectively in pulse-echo mode. A system level framework for designing CMUT arrays was described that include effects from imaging design requirements, acoustical cross-talk, bandwidths, signal-to-noise (SNR) optimization and considerations from IC limitations for pulse voltage. Electrical impedance measurements and hydrophone measurements comparisons between design and experiment show differences due to inaccuracies in using SixNy homogenous material in simulation compared to fabricated thin-film stacks (HfO2-AlSi-SixNy). It is concluded that for “thin” membranes the effect of stiffness and mass of HfO2 and AlSi (top electrode) cannot be ignored in the simulation. Also, it is understood that aspect ratio (width to height) <10 will have up to 15% error for center frequency predicted in air when the thin-plate approximation is used for modelling the bending stiffness of the CMUT membrane.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 115-[121]).
In this thesis work, design and fabrication of micro- and nano-photonic structures both in the diffraction regime and sub-wavelength regime have been investigated. In the diffraction regime, two types of optical systems and optical elements were investigated for application in LCD manufacturing. With the increasing demand for larger LCD screens at lower cost, technology for low-cost high-throughput manufacturing systems, as well as efficient repair systems within the manufacturing line for any manufacturing defects, are crucial for manufacturers. The first system investigated in this work is a novel optical lithography system for LCD manufacture using a computer generated hologram (CGH). The fabrication challenges for a highly complex pattern inherent in CGHs are addressed. The second system is a defect repair system utilizing a blazed grating matrix (BGM). The BGM generates multiple high intensity spots from a high-power pico-second pulsed laser, controlled by a spatial light modulator, which can ablate the surface of the substrate to eliminate residues and excess material. In both systems, high efficiency and pattern fidelity are required for the optical element, and micro- and nano-fabrication techniques were used in order to achieve the required specifications. In the sub-wavelength regime, locally periodic dielectric photonic structures with adiabatic variation were designed and verified, with application in lensing in optical frequencies. Structures such as rod lenses and Luneburg lenses are investigated. Especially the latter type of lenses have been conventionally difficult to implement in optical frequencies due to its specific refractive index profile. With the high flexibility of gradient effective index design with the " aperiodic" dielectric nanostructures, along with the design method using Hamiltonian Optics investigated in this research, the Luneburg lens was designed, fabricated, and verified at the wavelength of A[gamma] = 1.55[mu]m.
by Satoshi Takahashi.
Ph.D.

Although 1.5 and 3 Tesla (T) magnetic resonance (MR) systems remain the clinical standard, the number of 7 T MR systems has increased over the past decade because of the promise of higher signal-to-noise ratio (SNR), which can translate to images with higher resolution, improved image quality and faster acquisition times. However, there are a number of technical challenges that have prevented exploiting the full potential of ultra-high field (≥ 7 T) MR imaging (MRI), such as the inhomogeneous distribution of the radiofrequency (RF) electromagnetic field and specific energy absorption rate (SAR), which can compromise image quality and patient safety.

To better understand the origin of these issues, we first investigated the dependence of the spatial distribution of the magnetic field associated with a surface RF coil on the operating frequency and electrical properties of the sample. Our results demonstrated that the asymmetries between the transmit (B₁⁺) and receive (B ₁^–) circularly polarized components of the magnetic field, which are in part responsible for RF inhomogeneity, depend on the electric conductivity of the sample. On the other hand, when sample conductivity is low, a high relative permittivity can result in an inhomogeneous RF field distribution, due to significant constructive and destructive interference patterns between forward and reflected propagating magnetic field within the sample.

We then investigated the use of high permittivity materials (HPMs) as a method to alter the field distribution and improve transmit and receive coil performance in MRI. We showed that HPM placed at a distance from an RF loop coil can passively shape the field within the sample. Our results showed improvement in transmit and receive sensitivity overlap, extension of coil field-of-view, and enhancement in transmit/receive efficiency. We demonstrated the utility of this concept by employing HPM to improve performance of an existing commercial head coil for the inferior regions of the brain, where the specific coil’s imaging efficiency was inherently poor. Results showed a gain in SNR, while the maximum local and head SAR values remained below the prescribed limits. We showed that increasing coil performance with HPM could improve detection of functional MR activation during a motor-based task for whole brain fMRI.

Finally, to gain an intuitive understanding of how HPM improves coil performance, we investigated how HPM separately affects signal and noise sensitivity to improve SNR. For this purpose, we employed a theoretical model based on dyadic Green’s functions to compare the characteristics of current patterns, i.e. the optimal spatial distribution of coil conductors, that would either maximize SNR (ideal current patterns), maximize signal reception (signal-only optimal current patterns), or minimize sample noise (dark mode current patterns). Our results demonstrated that the presence of a lossless HPM changed the relative balance of signal-only optimal and dark mode current patterns. For a given relative permittivity, increasing the thickness of the HPM altered the magnitude of the currents required to optimize signal sensitivity at the voxel of interest as well as decreased the net electric field in the sample, which is associated, via reciprocity, to the noise received from the sample. Our results also suggested that signal-only current patterns could be used to identify HPM configurations that lead to high SNR gain for RF coil arrays. We anticipate that physical insights from this work could be utilized to build the next generation of high performing RF coils integrated with HPM.

After nearly 100 years of particle acceleration, particle accelerator experiments continue providing results within the field of high energy physics. Particle acceleration is used worldwide in practical applications such as radiation therapy and materials science research. Unfortunately, these accelerators are large and expensive. Dielectric Laser Acceleration (DLA) is a promising technique for accelerating particles with high acceleration gradients, without requiring large-scale accelerators. DLA utilizes the electric field of a high energy laser to accelerate electrons in the proximity of a nanostructured dielectric surface.The aim of this project was limited to laser beam routing and imaging techniques for a DLA experiment. The goal was to design the laser beam pathway between the laser and the dielectric sample, and testing a proposed imaging system for aiming the laser. This goal was achieved in a test setup using a low-energy laser. In the main setup including a femtosecond laser, the result indicated lack of focus. For a full experimental setup, a correction of this focus is essential and the beam path would need to be combined with a Scanning Electron Microscope (SEM) as an electron source.

La microscopie champ proche micro-onde, qui fait partie de la famille des microscopies à sonde locale, est envisagée aujourd’hui dans de nombreux domaines d’applications de la physique, de la biologie et des micro et nanotechnologies. Dans ce manuscrit, le microscope micro-onde à champ proche qui est exploité est un instrument développé au laboratoire IEMN bénéficiant d’une grande sensibilité dans une large bande de fréquences de travail [2-18 GHz]. Le potentiel d’applications du microscope est démontré au travers de la caractérisation de liquides avec différentes modalités de caractérisation (sonde en contact, sans contact et en immersion). En particulier, cet outil est mis en œuvre pour la spectroscopie diélectrique de solutions aqueuses de glucose.Cet instrument qui offre une capacité d'imagerie sub-longueur d'onde est également testé pour différentes situations (imagerie de surface et de sub-surface). La résolution d'imagerie ainsi que la précision de mesure sont évaluées puis des méthodes de traitement d'images simples sont proposées pour améliorer la qualité de l'imagerie. Enfin, une piste pour une intégration plus grande de l’instrument, qui consisterait à remplacer l’analyseur de réseau par un dispositif plus compact (type réflectomètre six-ports) est explorée
Near-field microwave microscopes, which belong to the local scanning probe microscopes family, are considered today as advanced characterization tools in many applications areas including physics, biology and micro and nanotechnologies. The near-field microwave microscope that is used in the work and described in this manuscript is an instrument developed at IEMN owning a great sensitivity in a wide operating frequency band [2-18 GHz]. The potential of the microscope in terms of applications is demonstrated through the characterization of liquids with different modalities of characterization (probe in contact, non-contact and immersed in a liquid). In particular, this instrument is investigated for dielectric spectroscopy of aqueous glucose solutions.This characterization tool that offers sub-wavelength imaging capability is also tested in different situations (surface and subsurface imaging). Imaging resolution and measurement accuracy are evaluated and easily implementable processing methods are proposed to improve the quality of imaging. Finally, a solution towards a larger compactness of the instrument is investigated through the replacement of the network analyzer by a more compact device (six-port reflectometer type)

The sensitive and specific detection of biomolecular interactions is at the heart of many routine analyses in fundamental research, medical diagnosis and environmental monitoring. In contrast to laborious and costly multiwell plate assays, recent years have witnessed a significant progress in miniaturized and integrated biosensors, such as surface plasmon resonance (SPR), tailored to these applications. While the design of various SPR biosensors has been described in literature, a robust, multichannel, low-cost and highly sensitive solution has not yet been presented. Specifically, an integrated system that can allow surface functionalization in array format, low-volume multichannel fluidic interfacing, and increased sensitivity is sought. This thesis describes a novel electro-wetting-on-dielectric (EWOD) digital microfluidic device with integrated nanostructured biosensor interface that addresses the aforementioned issues for enhanced surface plasmon resonance imaging (SPRi) detection. We have taken the opportunity of the most recent advances in microfabrication, nanotechnology and SPR technique to develop this integrated platform.
EWOD device is employed for the dynamic immobilization of bioreceptors on SPRi biosensor surface in an array fashion from sub-µL volume solutions. Programmable EWOD electric interface allows the application of an electric field at the biosensor surface for active control of the immobilized probe density and orientation, enhancing SPRi detection. Two-dimensional SPRi detection is achieved by coupling the EWOD device to SPRi instrumentation. Parallel manipulation of individual droplets allows more efficient exploitation of the biosensor surface by separating different samples for simultaneous and selective SPRi detection. Periodic gold structures (nanoposts, nanogratings and nanogrooves) residing on a surface of glass and plastic substrates are investigated to improve the SPRi sensitivity. The corresponding electromagnetic field enhancements lead to up to a five-fold increase in SPRi response and provide an order of magnitude improvement in the limit of detection. This optimized nanostructure design is integrated with the EWOD platform to increase the capability and enhance SPRi detection. The integrated platform is successfully employed for parallel detection of multiple DNA hybridization reactions in 90 nL droplets. More than a two-fold SPRi signal amplification is achieved within 15 min, while the detection time could be further reduced to 2 min for a simple "yes" or "no" answers for the presence of the target DNA in a sample. The proposed system holds a great potential for ultra-low volume, sensitive and rapid detection of biomolecules, such as DNA and proteins, for clinical diagnosis and other bioanalysis applications.
La détection sensible et spécifique des interactions biomoléculaires est au coeur de plusieurs analyses au niveau de la recherche fondamentale, du diagnostic médical et du contrôle de l'environnement. Les analyses conduites sur des plaques de multipuits sont généralement laborieuses et coûteuses. Pour remedier a ceci, ces dernières années ont été témoin d'un progrès significatif dans la production de biocapteurs miniaturisés et intégrés, tel que la résonance plasmonique de surface (SPR), conçus pour ces applications. Tandis que la conception du biocapteur de SPR a été bien décrite dans la littérature scientifique, une solution comprenant un multicanal peu coûteux et hautement sensible n'a pas été encore présentée. Spécifiquement, le système intégré recherché doit permettre la functionalization des surfaces dans le format de réseau, l'interface fluidique multicanale en petit volume et une augmentation de la sensibilité. Cette thèse décrit une nouvelle plateforme microfluidique numérique de l'Électro-mouillage-sur-diélectrique (EWOD) avec un biocapteur à interface nanostructureé intégrée qui aborde les critères mentionnés ci-dessus pour une meilleure détection de l'imagerie SPR (SPRi). Nous avons profité des récents progrès dans la microfabrication, la nanotechnologie et en la technique du SPR pour développer ce dispositif intégré.
La plateforme EWOD est utilisée pour l'immobilisation dynamique des biorécepteurs sur la surface du biocapteur de SPRi sous forme de réseau de solutions dont le volume est sous les µL. L'interface électrique programmable d'EWOD permet l'application d'un champ électrique sur la surface du biocapteur pour contrôler activement la densité et l'orientation des sondes immobilisées, augmentant ainsi la détection du SPRi. La détection bidimensionnelle de SPRi est réalisée en couplant le dispositif microfluidique d'EWOD à l'instrument SPRi. La mise en action d'EWOD manoeuvre en parallèle différentes gouttelettes pour une exploitation plus efficace de la surface du biocapteur, permettant la séparation de différents échantillons pour la detection simultanés et spécifique par SPRi. Des structures d'or périodiques (nanoposts, nanogratings et nanogrooves) qui se trouvent sur des surfaces en verre et des substrats en plastique sont étudiées pour améliorer la sensibilité de la détection de SPRi. Le perfectionnement du champ électromagnétique correspondant mène jusqu'à une augmentation quintuple de la réponse du SPRi et augmente d'un seul ordre de grandeur le perfectionnement de sensibilité. Finalement, la conception optimisée de nanostructure est intégrée avec la plate-forme d'EWOD pour augmenter les possibilités et améliorer l'interface de biocapteurs de SPRi. La plateforme intégrée est utilisée avec succès pour la détection parallèle de multiples réactions d'hybridation d'ADN dans des gouttelettes de 90 nL. Plus d'une amplification double du signal sont réalisées en seulement 15 minutes. La période de détection peut être encore réduite à minute 2 pour des réponses simples « oui » ou « non » pour la présence d'ADN dans un échantillon. Le système proposé a un grand potentiel pour la détection de petit volume, sensible et rapide, des biomolécules tels que l'ADN et les protéines pour le diagnostic clinique et d'autres

Dans le domaine de l'imagerie infrarouge, on distingue deux types de technologies : les détecteurs refroidis, coûteux et très performants, et les détecteurs thermiques, bas coût et moins encombrants. Dans les deux cas le système optique associé au détecteur représente une part importante du coût total du fait de la production unitaire de lentilles et du besoin en une résolution de plus en plus importante pour suivre la diminution du pas pixel et l'augmentation du format des détecteurs. Dès lors il est intéressant d'explorer des solutions pour diminuer le coût et l'encombrement du système optique tout en maintenant ou en améliorant les performances optiques. Dans ce contexte, ce travail de thèse s'intéresse à l'utilisation d'optiques sub-lambda ou métasurfaces optiques en matériau diélectrique au sein de systèmes d'imagerie infrarouge. De telles optiques sont peu encombrantes et fabriquées par des moyens issus de l'industrie de la microélectronique ce qui permet d'envisager une fabrication collective donc une diminution des coûts. Ces objets sont obtenus en structurant un substrat plan avec des motifs de taille inférieure à la longueur d'onde. La géométrie de ces motifs, dans des matériaux à forts indices de réfraction et transparents dans l'infrarouge comme le silicium, permettent de modifier les propriétés d'une onde optique : sa polarisation, sa phase, sa dispersion et la transmission. Cependant il est complexe de contrôler tout ces paramètres tout en prenant compte des limites technologiques des outils de fabrication. Ce travail s'est donc orienté vers la conception de systèmes optiques mêlant lentilles réfractives et lames sub-lambda de correction de front d'onde. Pour ce faire nous avons (i) développé un outil de simulation mêlant calculs électromagnétiques par la méthode RCWA, pour rendre compte du comportement d'une optique sub-lambda, et conception optique pour la partie réfractive. Nos optiques sub-lambda ont dès lors des dimensions millimétriques à centimétriques pour être couplées à des lentilles réfractives au sein de systèmes d'imagerie, et notre méthode permet de simuler efficacement de tels systèmes optiques. Dans un second temps nous avons (ii) développé des procédés de fabrication de prototypes d'optiques sub-lambda, notamment pour la correction d'aberration sphérique dans le LWIR (bande 8-14µm de longueur d'onde). (iii) Enfin la caractérisation de nos systèmes optiques a permis de valider notre modèle et de démontrer une forte amélioration de la FTM d'un système optique aberrant associé à une lame sub-lambda de correction de front d'onde (FTM multipliée par 3 à 25 cycles par millimètre). Nos derniers résultats montrent une amélioration sur une bande 8-12µm de nos systèmes optiques et ouvrent la voie vers la conception d'optiques sub-lambda large bande au sein de systèmes d'imagerie infrarouge
In the field of infrared imaging, there are two main types of detectors : cooled detectors, with great sensitivity but expensive, and uncooled detectors, exhibiting precise temperature measurement at moderate cost. In both technologies, the optical systems associated with the detectors represent an important part of the overall cost because of the unitary fabrication process of infrared lenses and the need of more resolved imaging system to follow the shrinkage of the pixel and the increasing array format. Thus, it is important to search for cost effective and low footprint optical solutions exhibiting a high level of performance for infrared imaging systems. In this thesis work we study how dielectric subwavelength structures, or metasurfaces, can adress these issues in infrared systems. Such devices can be made using microelectronics based collective fabrication process, which are cost effective compared to molded infrared optics. Subwavelength optics can be made with silicon, which is transparent in long wave infrared (LWIR) imaging and exhibiting a high refractive index. By designing the geometry of resonators with subwavelength dimensions, one can control light properties like its polarization, phase, transmission and dispersion. However as it is challenging to control all those parameters, even more with fabrication process limitations, we first propose to mix refractive lenses with subwavelength phase blades which correct wavefront errors. (i) We first developed a time effective simulation method mixing electromagnetic calculations with RCWA, for the subwavelength part of the optical system, and classical optical design for the refractive optics. It is worth noting that our subwavelength optics have millimetric to centimetric dimensions to be coupled with refractive lenses, and our method allows us to simulate the overall system. (ii) Then we developed the fabrication process for prototyping subwavelength optics, mainly for spherical aberration correction in LWIR imaging systems. (iii) Finally, we conducted optical characterisations of our systems to validate our model. Our subwavelength optics show an important improvement of the MTF (more than 3 times better at 25 cycles per millimeter) of an optical infrared system by correcting its spherical aberration. Our last results show a improvement of the image quality on a large bandwith (8-12µm) paving the way to large bandwidth subwavelength optics in infrared imaging systems

Recently there has been a surge in the field of mass spectrometry centered around the concept of rapid analysis of target analytes with minimal or no sample preparation. The target analyte undergoes desorption from its surface of origin and is subsequently ionized under ambient conditions. The technique is termed ambient desorption/ionization mass spectrometry (ADI-MS). Since the introduction of ADI-MS in 2004, there has been an explosion of research based around the development of novel ambient desorption/ionization (ADI) sources with the capability of desorbing and ionizing a variety of target analytes from various sampling surfaces. One type of ADI source uses the properties of an electrical discharge, typically a helium gas plasma, for desorption and ionization. For electrical-discharge-based sources, ionization is the result of an atmospheric pressure chemical ionization (APCI) process. The initiation of the APCI process it generally attributed to the Penning ionization of atmospheric nitrogen (N2) by highly energetic helium metastable species (Hem). In this work, I describe the direct imaging of the densities of helium metastable atoms in atmospheric pressure plasma jet (APPJ) of a helium-based dielectric-barrier discharge (DBD) using collisionally-assisted laser-induced fluorescence. Axial Hem distributions are compared to the emission of excited helium (He*) and nitrogen ion (N2+*) species in the plasma. A correlation is found between Hem densities and the performance of the ionization source in ADI-MS. Fluorescence images also show that Hem densities increase substantially when a glass slide is placed 10 mm from the discharge capillary in a geometry typical for desorption/ionization experiments. Advantage is taken of the time-varying nature of the plasma to produce axial profiles of temporally and spectrally resolved fluorescence images of Hem atoms and ground state nitrogen ions in the plasma jet. The axial distribution and similarities in the temporal behavior of the helium metastable and ground state nitrogen ion species give strong evidence that nitrogen ion species are created via Penning ionization by helium metastable atoms. Although axial distributions of He*,N2+*, and N2* emission support the fluorescence data, temporally-resolved emission measurements show that emission from key plasma species is almost entirely the result of excitation by a temporal energy wave. The effect that hydrogen (H2) has on the helium metastable atom densities is also presented. The addition of hydrogen to the discharge gas severely quenches the metastable state, leaving it virtually undetectable. The addition of 0.9% H2 to the helium in the source provides an order of magnitude increase in ADI-MS signal for target analytes despite the quenching of the Hem population.

Millimeter-wave systems introduce a set of particular severe requirements from the antenna point of view in order to achieve specific performances. In this sense, high directive antennas are required to overcome the huge extra path loss. Moreover, each particular application introduces additional requirements. For example, in very high throughput (VHT) wireless personal area networks (WPANs) communication systems at 60 GHz band beam-steering antennas are needed to deal with high user random mobility and human-body shadowing characteristic of indoor environments. Similarly, beam-steering capabilities are also needed in automotive radar applications at 79 GHz, since the determination of the exact position of an object is essential for most of the functions realized by the radar sensor. In the same way, beam-scanning, which is still commonly mechanically performed nowadays, is also needed in passive imaging systems at 94 GHz. Finally, from the integration perspective, the antennas must be small, low-profile, light weight and low-cost, in order to be successfully integrated in a commercial millimeter-wave wireless system. For these reasons, many types of antenna structures have been considered to achieve high directivity and beam-steering capabilities for the aforementioned millimeter-wave communication, radar and imaging applications at 60, 79 and 94 GHz. The most part of the currently adopted solutions are based on the expensive, complex and bulky phased-array antena concept. Actually, phased-array antenna systems can scan the beam at a fast rate. However, they require a complex integration of many expensive, lossy and bulky circuits, such as solid-state phase shifters and beam-forming networks. This doctoral thesis has contributed to the study, development, and assessment of the performance of innovative antena solutions in order to improve the existing architectures at millimeter-wave frequencies, conveniently solving the problems related specifically to short-range high data rate communication systems at 60 GHz WPAN band (including future 5G millimeter-wave systems), automotive radar sensors at 79 GHz band, and communications, radar, and imaging systems at 94 GHz. The specific goals pursued in this work, focused on defining an alternative antenna architecture able to achieve a full reconfigurable 2-D beam-scanning of high gain radiation beams at millimeter-wave frequencies, has been fulfilled. In this sense, this thesis has been mainly devoted to study in depth and practically develop the fundamental part of an innovative switched-beam antenna array concept: novel inhomogeneous gradient-index dielectric flat lenses, which, despite their planar antenna profile configurations, allow full 2-D beam-scanning of high gain radiation beams. A transversal study, going from theoretical investigations, passing by numerical analysis, new fabrication strategies, performance evaluation, and to full experimental assessment of the new antenna architectures in real application environment has been successfully carried out.
Los sistemas a frecuencias de ondas milimétricas introducen una serie de requisitos muy estrictos desde el punto de vista de la antena con el objetivo de conseguir unos rendimientos específicos. En este sentido, se requieren antenas con una muy alta directividad con tal de conseguir superar las enormes pérdidas adicionales por propagación. Además, cada aplicación en concreto introduce unos requisitos adicionales. Por ejemplo, en redes de área personal de alta velocidad para sistemas de comunicación a la banda de 60 GHz, antenas con la capacidad de reconfiguración del haz de radiación son necesarias para poder tratar la problemática de la alta movilidad de los usuarios en entornos cerrados. De la misma forma, capacidades de reconfiguración de la orientación del haz de radiación son necesarias en aplicaciones relacionadas con radar de automoción a 79 GHz, dado que la determinación de la posición exacta de un objeto es esencial para muchas de las funciones del sensor de radar. De forma muy similar, la capacidad de apuntamiento del haz, que muchas veces todavía se realiza mediante sistemas mecánicos, es también imprescindible en sistemas de escaneo para aplicaciones biomédicas y de seguridad a 94 GHz. Finalmente, desde la perspectiva de la integración, las antenas deben ser eléctricamente pequeñas, ligeras, y económicas para poder ser incorporadas a un sistema inalámbrico comercial a frecuencias de onda milimétricas. Por todos estos motivos, diferentes tipos de estructuras de antenas han sido propuestos para conseguir alta directividad, junto con capacidades de reconfiguración y apuntamiento del haz de radiación para las aplicaciones anteriormente mencionadas y descritas en la banda de 60, 79, y 94 GHz. La solución tradicionalmente adoptada en este tipo de casos està estrictamente basada en el siempre caro, complejo y aparatoso concepto del phased-array. De hecho, los phased-arrays permiten el rápido escaneo de haces de radiación de alta directividad. Sin embargo, el hecho que requieran una compleja integración de muchos y caros componentes a alta frecuencia, tales como desfasadores de estado sólido o redes de conformación, los cuales introducen ciertos niveles de pérdidas, siendo además aparatosos, hacen que esta solución resulte inviable. La presente tesis doctoral contribuye al estudio, desarrollo, y ensayo experimental del rendimiento de soluciones de antenas innovadoras para la mejora de las existentes arquitecturas de antena en la banda frecuencial de las ondas milimétricas, convenientemente solucionando los problemas asociados específicamente a los sistemas de comunicación de corto alcance y alta velocidad a 60 GHz (incluyendo los futuros sistemas 5G a milimétricas), a los sistemas de radar de automoción a 79 GHz, y a los sistemas de comunicación, radar, y escaneo para aplicaciones a 94 GHz. Los objetivos específicos perseguidos en este trabajo académico, focalizados en definir una arquitectura alternativa de antena, capaz de conseguir una completa reconfiguración y escaneo de los haces de radiación en dos dimensiones del espacio a frecuencias de onda milimétricas, se han conseguido plenamente. En este sentido, esta tesis doctoral ha sido dedicada esencialmente al estudio en profundidad y desarrollo práctico de la parte fundamental del innovador concepto del switchedbeam array: nuevas lentes dieléctricas inhomogéneas de gradiente de índice con estructura plana, las cuales, a pesar de su configuración física totalmente llana, permiten una reconfiguración total, en dos dimensiones del espacio, de haces de radiación de alta directividad. Un estudio eminentemente transversal, que abarca desde la investigación teórica, pasando por el análisis numérico, nuevas metodologías y técnicas de fabricación, evaluación de rendimientos, hasta una completa caracterización y ensayo del rendimiento en entornos reales de aplicación de las nuevas arquitecturas de antena, se ha llevado a cabo con total éxito.
Els sistemes a freqüències d'ones mil·limètriques introdueixen una sèrie de requisits molt estrictes des del punt de vista de l'antena per tal d’aconseguir uns rendiments específics. En aquest sentit, es requereixen antenes amb una alta directivitat per aconseguir superar les enormes pèrdues addicionals per propagació. A més a més, cada aplicació en concret introdueix uns requeriments addicionals . Per exemple, en xarxes d'àrea personal d'alta velocitat per a sistemes de comunicació a la banda de 60 GHz, antenes amb la capacitat de reconfiguració del feix de radiació són necessàries per tal de poder tractar la problemàtica de l'alta mobilitat dels usuaris en entorns tancats . De la mateixa manera, capacitats de reconfiguració de l'orientació del feix de radiació són necessàries en aplicacions associades a radar d'automoció a 79 GHz, donat que la determinació de la posició exacta d'un objecte és essencial per moltes de les funcions portades a terme pels ens or del radar. De forma molt similar, la capacitat d'apuntament del feix, que moltes vegades encara es realitza per mitjà de sistemes mecànics, és també imprescindible en sistemes d'escaneig per aplicacions mèdiques i de seguretat a 94 GHz. Finalment, des de la perspectiva de la integració, les antenes han de ser petites en termes elèctrics, lleugeres, i econòmiques per tal de poder ser incorporades en un sistema sense fils comercial a freqüència d'ones mil·limètriques. Per aquestes raons , diversos tipus d'estructures d'antenes han sigut proposats per aconseguir alta directivitat, conjuntament amb la capacitat d'apuntament del feix de radiació per les aplicacions anteriorment descrites a les bandes de 60, 79, i 94 GHz. La solució tradicionalment adoptada en aquests casos és estrictament basada en el sempre car, complexe, i aparatós concepte del phased-array. De fet, els phased-arrays tenen la capacitat de reconfigurar a gran velocitat feixos de radiació d'alta directivitat. Tot i això, el fet que requereixin la complexa integració de molts components cars a alta freqüència, amb certs nivells de pèrdues i aparatosos, com són els desfasadors d'estat sòlid, i les xarxes de conformació, fan d'aquesta solució inviable. La present tesis doctoral contribueix a l'estudi, des envolupament, i assaig experimental del rendiment de solucions d'antenes innovadores per tal de millorar les existents arquitectures d'antena a la banda freqüencial de les ones mil·limètriques, convenientment solucionant els problemes associats específicament als sistemes de comunicació de rang proper d'alta velocitat a 60 GHz (incloent els futurs sistemes 5G a mil·limètriques ), als sistemes de radar d'automoció a la banda dels 79 GHz, i als sistemes de comunicació, radar, i escaneig per aplicacions a 94 GHz. Els objectius específics perseguits en aquest treball acadèmic, focalitzats en definir una arquitectura d'antena alternativa, capaç d'aconseguir una completa reconfiguració i escaneig dels feixos de radiació en dues dimensions de l'espaia freqüències d'ona mil·limètriques , s'han plenament aconseguit. En aquest sentit, aquesta tesis doctoral s'ha dedicat essencialment a l'estudi en profunditat i desenvolupament pràctic de la part fonamental de l'innovador concepte del switched-beam array: noves lents dielèctriques inhomogenees de gradient d'índex amb estructura planar, les quals, tot i preservar una configuració física totalment plana, permeten una reconfiguració total en dues dimensions de l'espai de feixos de radiació d'alta directivitat. Un estudi transversal, que comprèn des de la investigació teòrica, passant per l'anàlisi numèric, noves metodologies i tècniques de fabricació, avaluació de rendiments, fins a una completa caracterització i assaig del rendiment en entorns reals d'aplicació de les noves arquitectures d'antena s'ha dut a terme amb total èxit.

La production de foie gras représente une part non négligeable de l’économie française et fait d’elle le leader mondial dans ce domaine. Face aux enjeux économiques, les producteurs se doivent de répondre aux attentes des consommateurs que ce soit pour la qualité du foie gras mais aussi en ce qui concerne la méthode d’élevage et le bien-être animal. Actuellement, les canards sont gavés deux fois par jour pendant 12 jours avec la même quantité alimentaire tout au long du processus. Il n’y a pas d’adaptation de la dose alimentaire en fonction de l’animal au cours du gavage. C’est pourquoi, certains animaux subissent un sur-gavage au cours de ce processus. C’est ce phénomène, qui reste la source principale de mortalité chez le canard en élevage. C’est dans ce contexte, que cette thèse trouve tout son intérêt. Différentes techniques sont connues pour l’imagerie et l’analyse de tissus biologiques. Cependant la majorité des techniques sont encombrantes, invasives pour la préparation des échantillons ou trop coûteuses pour la mise en place à l’échelle de la production de foie gras. La spectroscopie diélectrique radiofréquence est une technique d’imagerie rapide, non invasive et portable pouvant tout à fait convenir à la détection du poids de foie chez le canard vivant au cours du gavage afin de moduler la dose alimentaire à fournir à chaque animal. Ces travaux visent donc à contribuer au développement d’une instrumentation radiofréquence (RF) dédiée à une telle application. Dans la première partie de cette thèse, le contexte actuel du gavage des canards pour la production de foie gras et les différentes techniques d’imagerie pour l’étude de tissus biologiques sont décrits. Dans ce cadre, la spectroscopie radiofréquence est introduite comme possible solution de détection pour une application en élevage. La seconde partie traite du capteur radiofréquence développé par l’équipe MH2F du LAAS, de sa caractérisation et de son optimisation pour répondre à la problématique de cette thèse. Différentes conceptions de capteurs sont étudiées pour déterminer la version la plus optimale. Le capteur hyperfréquence doit permettre de sonder le foie, au milieu des autres organes, dans l’animal vivant. Les ondes électromagnétiques doivent donc permettre de différencier les divers organes à une profondeur de pénétration spécifique. Ainsi la caractérisation RF et l’évaluation avec des modèles fantômes des différentes configurations de capteurs a permis de sélectionner deux capteurs pour la suite de l’étude. Des mesures ex vivo présentées dans un troisième chapitre sont ensuite faites sur des échantillons d’organes prélevés sur canards à différents stades de gavage afin de déterminer la réponse diélectrique de chaque tissu, et la bonne répétabilité des résultats. Ces mesures montrent que la profondeur de pénétration des ondes rayonnées par le capteur sélectionné est suffisante pour sonder le foie au travers de la peau et des plumes et que la réponse diélectrique est différente selon le tissu étudié. La variation de composition du foie au cours du gavage a aussi été démontré par cette étude diélectrique. Enfin, dans l’optique de développer une instrumentation RF pour le suivi non-invasif du poids de foie, l’anatomie du canard gras et l’approche suivie sont introduites. Le capteur est ensuite utilisé et adapté sur carcasse puis sur canard vivant. Sensibilité et répétitivité des mesures RF sont évaluées sur plusieurs animaux. L’un des capteurs radiofréquence sélectionné est évalué pour sonder la zone où se situe le foie afin de déterminer sa taille et ensuite son poids. Pour chaque position du capteur un spectre en fréquence de 10 MHz à 6 GHz est obtenu. Enfin, la dernière partie de cette thèse décrit le traitement des données associé pour remonter à l’information d’intérêt. Ce travail pose donc les premières bases d’une instrumentation RF dédiée à l’imagerie non invasive du foie de canard en élevage afin d’adapter la technique de gavage à chaque animal
The production of duck fat liver represents a significant part of the French economy and makes it the world leader in this field. Faced with economic challenges, producers must meet consumer expectations, not only for the quality of fat liver but also with regard to the breeding method and animal welfare. Currently, ducks are force-fed twice a day for 12 days with the same amount of food throughout the process. There is no adjustment of the food dose according to the animal during force-feeding. Therefore, some animals undergo over-feeding during this process. It is this phenomenon, which remains the main source of mortality in farmed ducks. It is in this context that this thesis finds all its interest. Different techniques are known for imaging and analyzing biological tissue. However, the majority of techniques are bulky, invasive for sample preparation or too costly to scale up to produce fat liver. Radio-frequency dielectric spectroscopy is a rapid, non-invasive and portable imaging technique that may be suitable for detecting liver weight in live ducks during gavage in order to modulate the dietary dose to be provided to each animal. This work therefore aims to contribute to the development of radiofrequency (RF) instrumentation dedicated to such an application. In the first part of this thesis, the current context of force-feeding ducks for the production of fatty liver and the different imaging techniques for studying biological tissues are described. In this context, radiofrequency spectroscopy is introduced as a possible detection solution for an application in breeding. The second part deals with the radiofrequency sensor developed by the MH2F team of LAAS, its characterization and its optimization to answer the problem of this thesis. Different sensor designs are studied to determine the most optimal version. The microwave sensor should make it possible to probe the liver, among other organs, in the living animal. The electromagnetic waves must therefore make it possible to differentiate the various organs at a specific depth of penetration. Thus, the RF characterization and evaluation with phantom models of the different sensor configurations made it possible to select two sensors for the rest of the study. Ex vivo measurements presented in a third chapter are then made on organ samples taken from ducks at different stages of gavage in order to determine the dielectric response of each tissue, and the good repeatability of the results. These measurements show that the depth of penetration of the waves radiated by the selected sensor is sufficient to probe the liver through the skin and feathers and that the dielectric response is different depending on the tissue studied. The change in liver composition during gavage was also demonstrated by this dielectric study. Finally, with a view to developing RF instrumentation for the non-invasive monitoring of liver weight, the anatomy of the fatty duck and the approach followed are introduced. The sensor is then used and adapted on a carcass and then on a live duck. Sensitivity and repeatability of RF measurements are evaluated on several animals. One of the selected radio frequency sensors is evaluated to probe the area where the liver is located to determine its size and then its weight. For each position of the sensor a frequency spectrum of 10 MHz to 6 GHz is obtained. Finally, the last part of this thesis describes the associated data processing to go back to the information of interest. This work therefore lays the groundwork for RF instrumentation dedicated to non-invasive imaging of farmed duck liver in order to adapt the force-feeding technique to each animal

Les liquides ioniques (LIs) sont des sels à faible température de fusion (plus petit 100 °C). Ils disposent généralement de bonnes stabilités thermique et chimique ainsi qu’une haute conductivité ionique. Ces propriétés les rendent par exemple intéressants en tant que lubrifiant, électrolyte ou additif en sciences des polymères. Dans le cadre de cette thèse, les liquides ioniques sont proposés comme alternative aux problématiques d’accumulation de charges au sein d’un isolant composite à base époxy pour postes sous enveloppe métallique (PSEM) sous haute tension en courant continu (HVDC). Une augmentation des phénomènes de conduction électrique est recherchée afin d’évacuer les charges accumulées en surface de l’isolant au cours de son utilisation. L’influence de l’addition de LI sur les mécanismes de polymérisation et sur les propriétés finales du réseau époxy et a été évaluée avec et sans durcisseur anhydride et en présence d’un liquide ionique à cation phosphonium et anion phosphinate, connu comme réactif et amorceur de la polymérisation des polyépoxydes. Les mécanismes de polymérisation ont été déterminés par résonance magnétique nucléaire (RMN) et analyse calorimétrique différentielle (DSC), les réseaux et leur microstructure par analyse mécanique dynamique (DMA), et leur morphologie par microscopie électronique (SEM ou TEM). Enfin, les propriétés diélectriques et mécanismes de conduction ont été étudiés par spectroscopie diélectrique et mesures de conductivité DC et discutés en fonction des architectures des différents réseaux
Ionic liquids (Ils) are salts exhibiting a low melting temperature (minus 100 °C). They display interesting properties such as good thermal and chemical stabilities and a high ionic conductivity. For example, these properties make them attractive as lubricant, electrolyte or additive in polymer science. In this thesis, ionic liquids are proposed as a solution for charge accumulation occurring in epoxy based insulators of gas insulated substations (GIS), under high voltage direct current (HVDC). An increase of conduction phenomenon is researched in order to reduce charge accumulation on the surface of insulators during their service. The influence of the addition of IL on the polymerisation of the epoxy network and its properties has been evaluated with and without a conventional anhydride hardener, using a phosphonium based IL, known as reactive and initiator of the epoxy polymerisation. Polymerisation mechanisms were identified by nuclear magnetic resonance (NMR) in liquid phase and differential scanning calorimetry (DSC), the networks and their microstructure by dynamic mechanical analysis (DMA), and their morphology by electronic microscopy (SEM or TEM). Finally, dielectric properties were studied by broadband dielectric spectroscopy and DC conductivity measurements and were discussed in function of the architecture of the different networks

L’imagerie multispectrale permet d’améliorer la détection et la reconnaissance de cibles dans les applications de surveillance. Elle consiste à analyser des images de la même scène acquises simultanément dans plusieurs bandes spectrales grâce à un filtrage. Cette thèse étudie la possibilité de réaliser une matrice de 4 filtres Fabry Pérot (FP) intégrés 3D et ajustables par actionnement électrostatique dans le domaine visible-proche infrarouge. Les miroirs fixes des filtres FP sont des multicouches ZnS/YF₃ déposés sur un wafer de borosilicate, et les miroirs mobiles sont des membranes multicouches PECVD SiNH/SiOH encastrées sur une structure mobile très compacte micro-usinée dans un wafer en silicium. Les performances optiques des filtres FP ont été optimisées en prenant en compte la dissymétrie et le déphasage à la réflexion des miroirs. La structure mobile a été modélisée par éléments finis pour minimiser ses déformations lors de l’actionnement. Les étapes critiques des procédés de fabrication des miroirs mobiles en technologie Si ou SOI ont été mises au point : i) la fabrication et la libération par gravures profondes DRIE et XeF₂ des membranes multicouches avec une contrainte résiduelle ajustée par recuit et une réflectance voisine de 50% dans une large gamme spectrale, ii) le contrôle des vitesse de la gravure DRIE avec des motifs temporaires permettant la gravure simultanée de motifs de largeur et de profondeur variables, et iii) la délimitation de motifs sur surfaces fortement structurées à l’aide de pochoirs alignés mécaniquement ou de films secs photosensibles. Ces travaux ouvrent la voie vers une réalisation complète d’une matrice de filtres FP intégrés 3D
Multispectral imaging is used to improve target detection and identification in monitoring applications. It consists in analyzing images of the same scene simultaneously recorded in several spectral bands owing to a filtering. This thesis investigates the possibility to realize, an array of four 3D integrated Fabry-Perot (FP) filters that are tunable in the visible-near infrared range by electrostatic actuation. The fixed mirrors of the FP filters are ZnS/YF₃ multilayers deposited on a borosilicate wafer, and the movable mirrors are PECVD SiNH/SiOH multilayer membranes clamped in a very compact movable structure micromachined in a Si wafer. A 3rd glass wafer is used for filters packaging. Optical performances of the FP filters have been optimized by taking into account the asymmetry and the reflection phase shift of the mirrors and the mobile structure has been modeled by finite elements analysis notably to minimize its deformation during actuation. The critical steps of the movable mirrors fabrication process in Si or SOI technology have been developed : i) the fabrication and the release by DRIE and XeF₂ etching of 8 or 12 layers membranes with a residual stress tunable by annealing and a reflectance close to 50% in broad wavelength range (570-900nm), ii) the control with temporary patterns of the simultaneous deep etching of patterns with different widths and depths, and iv) various patterning techniques on highly structured surfaces based on shadow masks (with mechanical alignment) or laminated photosensitive dry films. These results open the way towards the full realization of an array of 3D integrated FP filters

A ocorrência de arborescências em água (water tree) ou elétrica (electrical tree) é apontada como o principal fenômeno de degradação em isolações sólidas de cabos de distribuição de energia elétrica. A evolução destas arborescências pode levar a camada de isolação à ruptura dielétrica e, como conseqüência, à falha destes equipamentos, com a interrupção do fornecimento de energia elétrica. O entendimento deste fenômeno é necessário para desenvolver métodos de análise e prevenção da ruptura de materiais isolantes. Este trabalho mostra a aplicação da técnica contraste de fase por raios X como metodologia para o estudo das arborescências formadas em materiais isolantes de borracha de propileno etileno (EPR) e polietileno reticulado (XLPE).
The water tree or electrical tree occurrence is identified as the main phenomena in the degradation in solid isolations of the electric energy distribution cables. The water tree evolution can lead to dielectric breakdown of the isolation layer and, consequently, to the failure this equipment and the interruption of the electric energy supply. The understanding this phenomenon is necessary for the development analysis methods and to prevent collapse in the polymeric insulation. This work demonstrates the application of X-ray phase contrast technique as a methodology for the study of the water tree and electrical tree in Ethylene propylene rubber (EPR) and crosslinked polyethylene (XLPE).

碩士
國立臺灣大學
物理研究所
101
It has been a long time since scientists put their efforts on obtaining super-resolution images for biological or medical applications. In the past few decades, scientists tried to magnify and transmit evanescent waves to far field by fabricating novel nanostructures or utilizing special scanning techniques to recombine images to achieve the super-resolution condition. Although significant advancements have been demonstrated, the sophisticated structures, difficulty in manufacturing, and time consuming process in obtaining images have hindered the widespread applications. Recently, the discovery of super-resolution under white-light illumination via microsphere lenses have helped us to achieve super-resolution images by direct observation via visible light without complex fabrication processes, making a great breakthrough in the field of optical imaging. In the thesis I try to improve the stability of the image quality by non-volatile polymer semi-immersion mechanism. Furthermore, I succeed in transferring microsphere superlenses to various kinds of samples of interests. Besides I also employ computer simulations to investigate the imaging characteristics of microspheres and try to have better understanding of the mechanism on microsphere-based super-resolution.

Optical dielectric metasurfaces have shown great advances in the last two decades and become promising candidates for next-generation free-space optical elements. In addition to their compatibility with scalable semiconductor fabrication technology, metasurfaces have provided new and efficient ways to manipulate diverse characteristics of light. In this thesis, we demonstrate the potential of dielectric metastructures in the realization of compact imaging devices, reconfigurable optical elements, and multi-layer inverse-designed metasurfaces. With the metasurfaces’ extreme capability to simultaneously control phase and polarization, we first showcase their potential toward optical field imaging applications. In this regard, we demonstrate a system of dielectric metasurfaces and designed random metasurfaces for single-shot phase gradient microscopes and computational complex field imaging system, respectively. Then, we propose nano-electromechanically tunable resonant dielectric metasurfaces as a general platform for active metasurfaces. For example, we demonstrate two different types of the phase and amplitude modulators. While one utilizes resonant eigenmodes in the lattice such as leaky guided mode resonances and bound-states in the continuum modes, the other is based on the high-Q Mie resonances in the dielectric nanostructures where symmetry is broken. In addition to the modulation of the phase and amplitude, we also show tuning of strong chiroptical responses in dielectric chiral metasurfaces. Next, we experimentally demonstrate inverse-designed multi-layer metasurfaces. Not only do they provide increased degree of freedom in the design space, but also overcome limits of conventional design methods of the metasurfaces. Finally, we summarize the presented works and conclude this thesis with a brief outlook on what aspects of the metasurfaces can be important for their real-world applications in the future and what challenges and opportunities remain.

碩士
淡江大學
電機工程學系碩士班
106
This thesis presents the reconstruction of a periodic homogeneous dielectric object buried in rough surfaces. First, a TM (Transverse Magnetic) polarized wave is transmitted through the surface to a buried object. Integral equations are derived by using the Maxwell equation, the two-dimensional periodic Green function, and the boundary condition. The integral equations are numerical solved by the method of moment (MOM) to obtain the scattering field. For inverse problem, the Fourier series expansion is used to describe the shape of the object, then the problem of inverse scattering is transformed into an optimization problem. Next, the self-adaptive dynamic differential evolution method is used for numerical calculation and object reconstruction. Numerical results show that the SADDE converges to the overall extreme value (global extreme) regardless of the initial guess. Even if the initial guess is far away from the actual value, SADDE can get the correct shape, periodic length and the relative permittivity of the periodic homogeneous dielectric object. We have found that the convergence speed of the periodic length is always better than the shape function and dielectric constant. Moreover, we can still obtain good reconstruction results even if the noise is added in the scattered field.

碩士
國立海洋大學
電機工程學系
89
Abstract Iterative method are suitable for solving large-sized problems in the electromagnetic wave scattering. The conjugate gradient method combined with the fast Fourier transform (CGFFT) is an efficient solver in the forward scattering problems. In microwave imaging, material permittivity is the parameter to retrieve. Traditionally, the standard method used is to minimize the cost function with Tikhonov regularization. This method can retrieve smooth object functions successfully, but there is serious Gibbs phenomenon appearing near the neighborhood of discontinuous boundaries in the reconstructed images. The total variation (TV) regulated method for retrieving the discontinuous object functions as well as denoising has been proposed recently and been proven very successful for both retrieving the profile at sharp boundaries and denoising. In this thesis, we investigate five subjects:(1)By incorporating the conjugate gradient method in the distorted Born iterative method (DBIM), we can find the minimun of cost function with total variation regularization and retrieve the permittivity in solving inverse scattering problems. (2)By DBIM, the permittivity of background medium needs to be updated at each iteration. Therefore the Green’s function of the inhomogeneous background medium does not have the analytic form.We implement the Green’s function numerically by casting its form into forward scattering problem under homogeneous background. In this way, the transmitter locations are not necessarily the same with receiver ones, which is more flexible in applications. (3)We also use the multiple frequency scheme to reconstruct the image of a large-sized object which is a biological model of human arm. We applied the TV enhanced method form the lowest frequency to the highest frequency reconstruction and have obtained a good result. (4)Selections for parameters and have a great influence on retrieved images of the objcet function. We obsevere that in some case, when and are different, it yields better reconstructed images than when and are the same. (5)We parallelize the subroutines in calculating the gradient and Hessian matrix of the cost function. After parallelizing the subroutines, the whole program will have better parallel efficiency.

Several novel optical devices, which were designed to manipulate terahertz waves for broadband near-field imaging, wave-guiding (invisible space), and sensing (resonator), are presented in this thesis. We developed the original working concepts of each device, and demonstrated the prototype experimentally in our lab. The working concepts of physics were investigated in experiment, in simulation and in theoretical analysis. We exploited a tapered parallel-plate waveguide (PPWG) as a novel probe for broadband near-field imaging. This imaging probe consists of two metal plates with the plate spacing gradually tapered from one end to the other. We proved that the space tapering enables this probe to propagate the broadband THz waves efficiently (with low-loss, no cut-off and nearly no dispersion) from the input end of large spacing into the narrow end of sub-wavelength spacing. Working in a reflection mode, this imaging probe is proved to be able to differentiate the dielectric features as well as topographic information on the sample. Combined with the methodology of filtered back projection, we reconstructed a two-dimensional image of a gold pattern on a GaAs chip by using this tapered PPWG probe. The smallest feature of ~100 µm is resolved by using the waves with average wavelength of 1.5 mm. We studied the phenomenon of surface plasmon-polariton in THz range on the platform of a parallel-plate waveguide (PPWG). In this thesis, we show the characterization of the waveguide mode of a finite-width parallel plate waveguide by using an improved scattering-probe technique. An abrupt waveguide mode transition was observed at a very narrow frequency range. We demonstrated that this transition frequency is determined by the material properties of the waveguide, the frequencies of the electromagnetic waves as well as the geometry of the waveguide. This result provides a good guidance for the waveguide design for THz transmission. We also exploited the capability of using the spoof surface plasmon to enhance the reflectivity of an interface between free space and a PPWG. We demonstrated that the reflection coefficient of this interface can be enhanced up to ~100 % at a designed frequency, by cutting a designed pattern of periodic rectangular groove on the output facet of the PPWG. A lateral shift and a phase shift of the reflected beam is observed in the experiment, which is a strong reminiscent of Goos-Hanchen shift. We carried out the experimental, simulation and theoretical characterizations of the lateral and phase shift. As an application, we designed and demonstrated a prototype of a band-pass THz resonator. We introduced the concept of a waveguide-based two-dimensional inhomogeneous artificial dielectric into THz range. This artificial dielectric is the space between the two metal plates of a PPWG working in TE1 mode. We designed a THz mirage device (or an invisible space device) by using ray-tracing and full-wave simulations, which contributed to the first experimental demonstration of such a device. A metal coin of size several times larger than the working wavelength can be hidden in the device without casting any shadow. This work is in collaboration with Dr. Rajind Mendis and the author of this thesis contributed to the design and characterization of the device in simulations.

碩士
淡江大學
電機工程學系
86
In this thesis, the application of the genetic algorithm(GA)in microwave imaging is investigated. The concept of the microwave imaging (electromagnetic scattering) is that an unknown permittivity object is illuminated by a TM and/or TE wave . Using the scattered field data that are measured outside, we can find the permittivity distribution of this object. The TM wave that is incident upon the object is considered.. The object is single or multi-layered. Considering the forward scattering problem, we use the concept of equivalent current to analyze it. Using the appropriate boundary condition and moment method(MoM),we can obtain the forward scattering formula. From this, we can obtain the data that are about the scattered field. For the inverse scattering problem, the genetic algorithm(GA) is introduced. By GA, if we choose the parameter types adequately and use the scattering formula, we can find the scattered field data. Then we can derive the reconstructed result of the dielectric distribution and shape of the cylinder. In order to reconstruct the permittivity distribution and shape, we consider different parameter types . First, we use the variety of the boundary of the cylinder to obtain the shape and dielectric distribution of the cylinder. Second, the cross-section of the cylinder is considered. We use the different rectangular shape to consist of it. Combining the above methods, we can derive the reconstructed result of the dielectric distribution. Finally, we use the arbitrary shape to consist of the cross-section of the cylinder. The boundary equations of the arbitrary shape are presented by cubic spline. In numerical simulation, we present the arbitrary shape, single and multi-layered cylinders. From the numerical result, we obtain the good reconstructed effect. Finally, the effect of the noise is investigated.

碩士
淡江大學
電機工程學系碩士班
95
The inverse scattering of buried inhomogeneous biaxial dielectric cylinders is investigated. Dielectric cylinders of unknown permittivities are buried in a slab scatters a group of unrelated incident waves from outside. The scattered field is recorded outside the slab. By proper arrangement of the various unrelated incident fields, the difficulties of ill-posedness and nonlinearity are circumvented, and the permittivity distribution can be reconstructed through simple matrix operations. The algorithm is based on the moment method and the unrelated illumination method. Numerical results show that satisfactory reconstruction has been obtained. Good reconstruction is obtained even in the presence of additive Gaussian random noise in measured data. In addition, the effect of noise on the reconstruction result is also investigated.

碩士
國立成功大學
光電科學與工程學系
104
In this thesis, a few ways used to fabricate liquid crystal lens arrays without disclination line issues are investigated. Simultaneously, free disclination line liquid crystal lens arrays are demonstrated their optical performance in integral imaging system. Comparing experimental results for preventing disclination line occurrence among the executed ways, a fabrication way with an extra dielectric layer in asymmetric homogeneous cells is an optimal choice to successfully fabricate free disclination line LC lens arrays. The completed LC lens array shows its minimum focal length of 0.7 cm when operating voltages in the range of 4~15 Vrms. The optimal LC lens array is also used in integral image system to demonstrate autostereoscopic performance. As a result, it achieves capability of viewing angle about 4.5˚ for autostereoscopic images and obvious motion parallax performance. In conclusion, free disclination line LC lens arrays in this study show better optical performance than that in previous work.

This dissertation presents the contributions and the research conducted in developing and implementing Microwave Tomography (MWT) systems. MWT is an imaging modality which aims to interrogate an object of interest by microwave energy, and quantitatively “find” the interior spatial distribution of its dielectric properties using field measurements taken outside the object. Due to the inherent non-linearity of the MWT problem, a substantial amount of electromagnetic scattering data is required to ensure a robust inversion and quantitatively accurate imaging results. This research benefits a variety of applications including biomedical imaging, industrial non-destructive testing, and security applications. Developing a MWT system, requires many critical components including the bandwidth and polarization purity of the collected fields as well as calibration of the fields scattered by the object of interest. Two generations of MWT systems were designed, implemented, calibrated and tested at the University of Manitoba (UM). These systems aim different approaches for near-field measurements which are referred to as the direct and indirect methods. With regard to the antenna design, a novel methodology applicable to broadband planar antennas is introduced. This technique is based on a combination of field modelling, herein, the finite element method and transmission line modelling. In the first generation of the UM MWT systems, a suitable antenna system was utilized. The system under study was a prototype, where twenty-four co-resident antennas encircle the object of interest to directly measure the fields. In the second generation of the UM MWT systems, the feasibility of using a novel technique to indirectly measure the fields by a secondary array of near-field scatterer probes was studied. The technique is based on the Modulated Scatterer Technique (MST). In this system, antennas are called ``collectors", since the role of antennas are changed to collecting probes' scattered fields. A number of PIN diodes were utilized to activate the probes. Finally, the capability of the probe system was investigated and its performance with the previously constructed tomography systems was compared. Various dielectric phantoms were utilized to test the accuracy of the systems.

This thesis is devoted to numerical simulations of integrated optical isolators and circulators. The results contain: Polarization independent isolators Different magneto-optical configurations are required to produce large nonreciprocal phase shifters for orthogonally polarized modes. The polarization independent isolator can be realized by placing two different nonreciprocal phase shifters into the interferometer arms. The light interferes constructively or destructively at the end of the interferometer depending on the propagation direction. Another possibility is to find a magnetic configuration that yields equal nonreciprocal phase shift for transverse electric (TE) and transversemagnetic (TM) modes. Compared to the concept of polarization independent isolators with two different phase shifters in the interferometer arms, the concept with a polarization independent phase shifter has an advantage: the entire length of the device can be almost halved placing an additional nonreciprocal phase shifter into the second arm. Another advantage is that the power loss inside the nonreciprocal phaseshifter may differ from that in the rest of the structure. For the non-symmetrical setup it can lead to a reduction of the device performance. Utilization of multimode waveguides in magneto-optical devices The principle distinction of a Mach-Zehnder type isolator and an isolator based on multimode imaging is that in the latter case the input power is distributed between modes propagating in the same waveguide, whereas in the first case two separate waveguides are used. Nonreciprocal phaseshifters with different effects on guided modes are needed to produce a magneto-optic multi-mode imaging (MMI) isolator or circulator. Multimode imaging splitters with non zero phase difference between the output modes can be used in integrated optical isolators. If the essential phase difference is utilized by the splitter, the rest of the interferometer should be symmetrical.

We are reporting on a study of the near-field sensitivity and resolution of a metal-dielectric probe (MDP). The propagation of the electromagnetic field across the probe was studied experimentally by means of time-domain terahertz spectroscopy and numerically simulated by CST MicroWave Studio 2008. Several localised areas at the probe end facet were distinguished and showed to be sensitive to the local dielectric properties and local anisotropy of the sample. Contrast and sensitivity measurements were conducted in several configurations of a MDP; the results were confirmed by simulations. The acquired data were analysed by using singular value decomposition that enabled separating independent physical phenomena in the measured datasets and filtering external disturbances out of the signal. Independent components corresponding to the changes in the output terahertz pulse upon varying the probe-sample distance and reflecting the local anisotropy in a ferroelectric barium titanate (BaTiO3) crystal were extracted and identified. The domain structure with characteristic dimensions of about 5 um was resolved during imaging experiments on the ferroelectric BaTiO3 sample, i.e. the resolved structures were ten times smaller than the characteristic dimensions of the end facet of the probe and forty times smaller than...