Dissertations / Theses on the topic 'Optical accelerometer'

MEMS Accelerometers are broadly used in the area of vibration sensor. Their applications range from seismic disturbances, to automotive industry such as airbag systems, active suspension, and smart braking. Traditionally, the acceleration is detected electrically by measuring either capacitive variations or piezoelectric signals. Those approaches suffer from a number of drawbacks, such as low sensitivity due to low signal-to-noise ratio (SNR), small dynamic range, high temperature sensitivity, etc. In this thesis, a MEMS-based optical accelerometer is designed and analyzed. The device can be fabricated on a silicon-on-insulator (SOI) wafer, on which a double-leg single-mode optical rib waveguide is used to propagate 1.55μm laser beam. The device integrates the waveguide with a mechanical oscillator, and is able to detect in-plane vibrations of the oscillator by taking advantages of optical interference. According to the analysis, the maximum working range of the oscillator can be as large as 50μm and the acceleration sensitivity can be below 1μg/Hz¹/². Device fabrication and characterization are also carried out and described in the thesis. All necessary fabrication steps and details as well as characterization setups are given. Due to several fabrication challenges in UBC (e.g. malfunctioned equipment), a complete device has not been fabricated. More fabrication and characterizations are to be continued as future work.

Linhas de transmissão de energia são estruturas importantes em um sistema de energia elétrica. Devido à elevada energia transportada por essas redes, falhas em linhas de transmissão podem ter reflexos severos no fornecimento aos consumidores, não raro levando a apagões em áreas geograficamente extensas. Entre as possíveis origens de falhas está o rompimento dos cabos elétricos pela fadiga provocada pela vibração eólica. As grandes extensões territoriais percorridas pelas linhas de transmissão e a variedade de climas, relevos, vegetação e condições meteorológicas aos quais estão submetidas dificultam qualquer trabalho de previsão da ação do vento. A medição da vibração permite detectar de antemão a aproximação da falha, porém os instrumentos convencionais dependem de transdutores elétricos os quais, além de exigirem uma fonte de energia (normalmente não disponível junto a linhas de transmissão) para seu funcionamento, sofrem influência dos intensos campos elétricos e magnéticos existentes em torno dos cabos de energia. A imunidade das fibras ópticas a campos elétricos e magnéticos e a possibilidade de uso de sinal de entrada de baixa potência oferecem uma alternativa para a criação de instrumentos de medição usando a técnica das redes de Bragg. A presente dissertação contribui com o desenvolvimento de um acelerômetro biaxial a redes de Bragg para medição de vibração em cabos de linhas de transmissão de energia. Além dos aspectos teóricos e práticos envolvidos, são discutidos os resultados de ensaios de calibração de elevada exatidão e outros ensaios especiais que fundamentaram a avaliação metrológica e o estabelecemento da eficácia do referido instrumento.
Overhead transmission lines play an important role on electric systems. Due to the high energy carried through those networks, failures on overhead lines can bring severe constraints on consumers supply, occasionally taking the form of blackouts in large geographic regions. Among the reasons of such failures is the breaking of electric cables caused by the fatigue originated from cyclic bending due to aeolian vibration. The large areas covered by overhead lines and the variety of climate, relief, vegetation and meteorological conditions under which they have to operate make it difficult to foresee the impact of wind Vibration measurements would allow anticipating the failure but conventional instruments depend upon electric transducers which, besides demanding a local source of energy (usually unavailable near overhead lines), suffer the influence of the high electric and magnetic fields around the energized cables. Optical fibers immunity against environments subjected to electrical and magnetic fields and the possibility of using low energy input signals offer the alternative of creating measuring instruments using Bragg gratings technique. This Master dissertation contributes with the development of a fiber Bragg grating biaxial accelerometer for measuring the vibration of overhead transmission line cables. Besides the theoretical and practical aspects related to the subject, the results of high precision calibration tests are discussed, together with other special tests which set the basis of the metrological evaluation and the establishment of the efficacy of the instrument.

L'utilisation des C. F. O. Couvre de plus en plus d'importants domaines de mesures. Cette thèse reprend dans la première partie l'état de l'art des C. F. O. Nous avons, dans la partie expérimentale effectué des mesures sur un capteur de vibration à fibre optique par effet de speckle, et avons montré au cours des expériences de l'amélioration du rapport signal signal sur bruit, dans le cas d'un filtrage spatial entre deux fibres multimodes différentes. La modélisation et la mise au point d'un capteur de vibrations, de type accéléromètre à fibre optique, par modulation d'intensité, fondé sur le micro-usinage de silicium ont été réalisées, ainsi qu'un prototype. Nous avons montré la faisabilité technologique d'un tel capteur. Celui-ci peut-être intégré dans un réseau à multiplexage chromatique. Le travail a consité également en la mise au point des interfaces optoélectroniques. Enfin un capteur de pression par couplage entre deux fibres a fait l'objet d'une étude théorique, et des mesures expérimentales. Grâce à la fusion des deux fibres optiques, on a amélioré la reproductibilité et la robustesse du capteur. Ceci ouvre ainsi la voie sur un grand nombre d'applications dans le domaine des composants optiques, tels que les coupleurs variables.

Ce mémoire décrit la conception d’un dispositif, communicant sans fil, estimant la dépense énergétique liée à une activité physique (DEAP) de patients présentant de faibles niveaux d’activité physique (post-AVC) dans un milieu sensible comme les hôpitaux en associant fiabilité et sécurité. La nécessité d’une nouvelle conception s’appuie sur les résultats d’études préalables et de tests des dispositifs commercialisés dans ce domaine basés sur des accéléromètres. Pour limiter l’impact des radiofréquences, nous utilisons une technologie optique sans fil avec un émetteur porté par le patient en mouvement (plateforme existante associée à un accéléromètre et un système d’émission par diode infrarouge) et des récepteurs fixés au plafond reliés via Ethernet à un ordinateur distant permettant l’analyse des données. La probabilité de coupure d’un lien mobile en optique sans fil par transmission diffuse a été établie théoriquement en considérant un débit faible et une haute qualité de service classique dans le domaine médical. La mesure du nombre de pertes de trame durant la communication a permis de valider les performances théoriques de la technologie optique sans fil et d’établir la fiabilité de ce type de transmission infrarouge en fonction du nombre de récepteurs. Le calcul de la DEAP a été effectué à partir d’un pré-étalonnage sur deux personnes en comparant les résultats obtenus avec ceux donnés par calorimétrie et ceux donnés par un dispositif commercial. Nous avons optimisé l’étalonnage en réalisant un protocole d’essais avec un échantillon de personnes plus vaste puis avec un échantillon de onze personnes post-AVC pour valider le prototype
This thesis describes the design of a wireless device, communicating and estimating the energy expenditure (EE) related to physical activity of patients with low levels of physical activity (post stroke) in a sensitive environment such as hospitals by combining reliability and safety. The necessity of a new device is based on the results of preliminary studies and tests of commercially available devices (for the same use) based on accelerometers. To limit the impact of radio frequencies, we use optical technology with a wireless transmitter worn by a mobile patient (existing platform combined with an accelerometer and a system of transmission with infrared diode) and receiver fixed on the ceiling and connected via Ethernet to a remote computer for data analysis. The outage probability of a mobile wireless diffuse optical transmission was theoretically established by considering a low speed and a high quality of service in the conventional medical area. Measuring the number of frame losses during communication validates the theoretical performance of the optical wireless technology and proves the reliability of this type of mobile infrared transmission according to the number of receivers. The calculation of the EE has been performed on a pre-calibration from two people by comparing the results with those given by calorimetry and those given by a commercial device. We optimized the calibration by performing a test protocol with a larger sample of people and with a sample of eleven stroke people to validate the prototype

A novel accelerometer based on light modulation has been designed and a prototype device manufactured. The device utilises the change in refractive index brought about by stress induced by the applied vibration. A detailed mathematical analysis of several feasible sensing designs has been performed to aid the design process. A mathematical model has been developed to assess the performance characteristics of the light modulated accelerometer the results of which were also used as a design tool. The prototype accelerometer was tested, from 1 g to 50 g between frequencies of 25 Hz to 2000 Hz, on a vibration system under three modulation schemes. The acceleration response of the device was seen to be linear over the testing range whilst the frequency response dropped off initially and levelled off at approximately 1 kHz. An experimental accelerometer was also assembled on the vibration table so that various materials could easily be tested without having to undergo precise machining. The acceleration and frequency responses showed similar behaviour to those obtained with the prototype accelerometer. However, the actual response levels varied with each material. To aid in the development of the accelerometer the stress-optic and thermo-optic coefficients have been determined for a range of polymeric materials. The stress optic coefficient was determined for polycarbonate, polymethyl methacrylate, polvinyl chloride and araldite epoxy resin using a circular polariscope and two interferometer configurations up to the yield stress of the materials tested. Each material showed a constant coefficient over the testing range. The results obtained using each technique were in good agreement with each other and the limited literature data available. The thermal variation of refractive index was also determined for the same materials. The Abbe refractometer was used for the determination between 5 and 140°C using five wavelength sources and two interferometer configurations using a HeNe laser from -50°C to approximately 30° above the glass transition temperatures. The change in index was found to be linear over the temperature range tested. However, at the glass transition temperature a change in gradient was observed with each material. Two simple mathematical relationships were used to predict the thermo-optic coefficient. These gave values reasonably close to those obtained in experiment.

A novel technique of coupling near-field evanescent waves by means of variable period subwavelength gratings (1.2 ìm and 1.0 ìm), using a 1.55 ìm infrared semiconductor laser is presented for the use of an optical MEMS accelerometer. The subwavelength gratings were fabricated on both glass and silicon substrates respectively. Optical simulation of the subwavelength gratings was carried out to obtain the maximum coupling efficiency of the two subwavelength gratings; the grating thickness, grating width, and the grating separation were optimized. This was performed for both silicon and glass substrates. The simulations were used to determine the total system noise, including the noise generated from the germanium photodiode, sensitivity, and displacement detection resolution of the coupled subwavelength grating MEMS accelerometer. The coupled gratings were utilized as optical readout accelerometers. The spring/proof mass silicon accelerometer was fabricated using a four mask process, in which the structure was completed using two deep reactive ion etching (DRIE) processes. The designed serpentine spring styles determine the sensitivity of the accelerometer; when the springs are made longer or shorter, thicker or thinner, this directly attributes to the sensitivity of the device. To test function of the example of the devices, the accelerometer is placed on a platform, which permits displacement normal to the plane of the grating. The 1.550 ìm infrared laser is incident on the coupled subwavelength grating accelerometer device and the output intensity is measured using a geranium photodiode. As the platform is displaced, the grating separation between the two gratings changes and causes the output intensity to change. Using the coupled subwavelength grating simulations as a reference to the output intensity change with respect to gap, the mechanical and coupling sensitivity properties of as it relates to acceleration is presented.

The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument, under development for the Subaru Telescope, has currently the fastest on-sky wavefront control loop, with a pyramid wavefront sensor running at 3.5 kHz. But even at that speed, we are still limited by low-frequency vibrations. The current main limitation was found to be vibrations attributed mainly to the rotation of the telescope. Using the fast wavefront sensors, cameras and accelerometers, we managed to identify the origin of most of the vibrations degrading our performance. Low-frequency vibrations are coming from the telescope drive in azimuth and elevation, as well as the elevation encoders when the target is at transit. Other vibrations were found at higher frequency coming from the image rotator inside Subaru's adaptive optics facility AO188. Different approaches are being implemented to take care of these issues. The PID control of the image rotator has been tuned to reduce their high-frequency contribution. We are working with the telescope team to tune the motor drives and reduce the impact of the elevation encoder. A Linear Quadratic Gaussian controller (LQG, or Kalman filter) is also being implemented inside SCExAO to control these vibrations. These solutions will not only improve significantly SCExAOs performance, but will also help all the other instruments on the Subaru Telescope, especially the ones behind A0188. Ultimately, this study will also help the development of the TMT, as these two telescopes share very similar drives.

Predictive maintenance based on condition monitoring uses sensor and system data to prevent damage, in advance to a failure occurring, allowing for a service to be performed at an optimal position in time. Condition based predictive maintenance estimates time of system failure based on a priori information, which has shown to be much more cost effective than traditional maintenance methods. Typically, there are applications where either of the maintenance methods, reactive, preventative or predictive maintenance, prove most sufficient. The expensive downtime in industrial processes and systems has come to focus development of predictive maintenance which often is found to be the optimal solution in these settings. In order for a predictive maintenance algorithm to be developed, there has to be in depth knowledge about the system and big data to base the algorithm on. This project is aimed at analysis and condition monitoring of the AkzoNobel - intelliCURE separate spreader used in the lamella and beam industry. Specifically targeted at the detection of cavitation in the transportation pumps, which is a common destructive phenomenon occurring in pumps. Cavitation which is the formation and implosion of cavities in the liquid, produces excessive shock waves resulting in vibrations. Depending on severity, cavitation can, in time, lead to internal damage and cause leakage. The type and amount of cavitation in a system is dependent on the rotational operating speed, which results in lower amount of vibrations for slow speeds. Where low amount of vibrations presents challenges of measurability. In order to detect the low amount of vibrations before severe cavitation development the optimal solution of measurability must be applied. Therefore, the research investigates the optimal solution for cavitation detection in terms of accelerometer configuration based on sensor position and sensor type in relation to reliability. The results of the study found that the fault mode vibrations caused by cavitation were detectable at lower rotational speeds than what industry recommended as the limit for an implementation. Additionally, the position and sensor type results in different performance to detect cavitation at slow pump speeds. An optimal configuration was found for the specific use case of the rotary bi-winged positive displacement pump.
Prediktivt underhåll baserat på tillståndsövervakning använder sensorer och systemdata för att förhindra skador, innan fel uppstår, vilket möjliggör att schemalägga en service vid en optimal tidpunkt. Tillståndsbaserat prediktivt underhåll estimerar tidpunkten för när fel uppstår i system baserat på a-priori information, som har visats vara mycket mer kostnadseffektiv än traditionella underhållningsmetoder. Typiskt finns tillämpningar där vardera av underhållsmetoderna, reaktivt-, förebyggande- eller prediktivt underhåll kan vara bäst lämpade. De dyra driftstoppen inom industri har lett till fokus på utveckling av prediktiva underhållsmetoder som ofta är ansett som den optimala lösningen i dessa förhållanden. För att en prediktiv algoritm ska kunna utvecklas krävs djup kunskap om systemet och stor mängd data att basera en algoritm på. Projektet fokuserar på vibrationsanalys och tillståndsövervakning av maskinen AkzoNobel - intelliCURE strängspridare som används i lamell- och balkindustrin. Forskningen är specifikt inriktad mot att upptäcka kavitation i transportpumparna som används i applikationen, där kavitation är ett relativt vanligt förekommande destruktivt fenomen som uppstår i pumpar. Kavitation, som är formandet och implosion av håligheter i vätska, leder till chockvågor som resulterar i vibrationer. Beroende på intensitet av förekommande kavitation, så kan det i tid leda till interna skador och resultera i läckage. Typen och intensiteten av förekommande kavitation i systemet är beroende av rotationshastigheten, som leder till lägre vibrationsgrad för lägre hastigheter. Där låg vibrationsintensitet presenterar utmaningar i mätbarhet. För att detektera den låga graden av vibrationer innan allvarlig kavitation utvecklas måste en optimal lösning för mätbarhet användas. Därav undersöker denna forskning en optimal lösning för att upptäcka kavitation med hjälp av accelerometerkonfiguration baserat på sensorplacering och sensortyp samt hur det relaterar till pålitlighet. Resultatet från studien visar att mätbarheten av vibrationerna som uppstår vid lägre hastigheter är bättre än vad som rekommenderas som gräns för användandet av vibrationsanalys på industriella applikationer. Samt att positionen och typen av sensor resulterar i olika möjligheter att detektera kavitation vid låga pumphastigheter. En optimal lösning hittades för det specifika användningsområdet av en dubbelvingad vingrotorpump som studien applicerades på.

Solar radiation pressure (SRP) is one of the major non-gravitational forces acting on spacecraft. Acceleration by radiation pressure depends on the radiation flux; on spacecraft shape, attitude, and mass; and on the optical properties of the spacecraft surfaces. Precise modeling of SRP is needed for dynamic satellite orbit determination, space mission design and control, and processing of data from space-based science instruments. During Earth penumbra transitions, sunlight is passing through Earth's lower atmosphere and, in the process, its path, intensity, spectral composition, and shape are significantly affected. This dissertation presents a new method for highly physical SRP modeling in Earth's penumbra called Solar radiation pressure with Oblateness and Lower Atmospheric Absorption, Refraction, and Scattering (SOLAARS). The fundamental geometry and approach mirrors past work, where the solar radiation field is modeled using a number of light rays, rather than treating the Sun as a single point source. This dissertation aims to clarify this approach, simplify its implementation, and model previously overlooked factors. The complex geometries involved in modeling penumbra solar radiation fields are described in a more intuitive and complete way to simplify implementation. Atmospheric effects due to solar radiation passing through the troposphere and stratosphere are modeled, and the results are tabulated to significantly reduce computational cost. SOLAARS includes new, more efficient and accurate approaches to modeling atmospheric effects which allow us to consider the spatial and temporal variability in lower atmospheric conditions. A new approach to modeling the influence of Earth's polar flattening draws on past work to provide a relatively simple but accurate method for this important effect. Previous penumbra SRP models tend to lie at two extremes of complexity and computational cost, and so the significant improvement in accuracy provided by the complex models has often been lost in the interest of convenience and efficiency. This dissertation presents a simple model which provides an accurate alternative to the full, high precision SOLAARS model with reduced complexity and computational cost. This simpler method is based on curve fitting to results of the full SOLAARS model and is called SOLAARS Curve Fit (SOLAARS-CF). Both the high precision SOLAARS model and the simpler SOLAARS-CF model are applied to the Gravity Recovery and Climate Experiment (GRACE) satellites. Modeling results are compared to the sub-nm/s^2 precision GRACE accelerometer data and the results of a traditional penumbra SRP model. These comparisons illustrate the improved accuracy of the SOLAARS and SOLAARS-CF models. A sensitivity analyses for the GRACE orbit illustrates the significance of various input parameters and features of the SOLAARS model on results. The SOLAARS-CF model is applied to a study of penumbra SRP and the Earth flyby anomaly. Beyond the value of its results to the scientific community, this study provides an application example where the computational efficiency of the simplified SOLAARS-CF model is necessary. The Earth flyby anomaly is an open question in orbit determination which has gone unsolved for over 20 years. This study quantifies the influence of penumbra SRP modeling errors on the observed anomalies from the Galileo, Cassini, and Rosetta Earth flybys. The results of this study prove that penumbra SRP is not an explanation for or significant contributor to the Earth flyby anomaly.
Ph. D.

碩士
南台科技大學
機械工程系
93
Abstract Accelerometer is a vibration measurement instrument used for measuring the acceleration. The principle is using displacement sensor to record the seismic mass inside the accelerometer and the relative movement within the base. Presently, the displacement sensors use capacitive sensor, LVDT, piezoelectric sensor, and strain gage in the design. The accelerometers based on such displacement sensors are expensive and mostly imported. To reduce the design cost of the accelerometer and improve the outcome of precision vibration measurement for higher application value, this study used optical displacement measuring probe, which is refined from the pickup head of the conventional DVD-ROM for the design of the displacement sensor. It also used the linear area of the S-curve measured by the pickup head to determine the seismic mass inside the accelerometer and the relative distance from the pickup head, in order to complete a single axial optical accelerometer of low cost and high sensitivity. This study removed the focus lens of the original optical path design, and used four-quadrant photo detector to detect the offsets of the optical path, thus, to deduce the angle change of the surface and complete two degree-of-freedom probes. As for the structural design of the accelerometer, pendulum style design was adopted, thus, to develop internal seismic mass with dual axial movement, along with two degree-of-freedom probes to complete a dual axial optical accelerometer of low cost and high sensitivity.

A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial ful lment of the requirements for the degree of Master of Science in Engineering. Johannesburg, 2015
Control of systems are important in most industrial sectors, they nd applications in electronics, machine design and navigation. These control systems often use sensors to work e ectively. One such sensor is an accelerometer, which is used to measure acceleration with one or more degrees of freedom. This research report investigates the modelling, system identi cation and controller design for an accelerometer, a Fibre Optic Accelerometer (FOA). Such a device may be applied in many applications such as anti-skid control, structural failure in buildings and bridges, as well as strategic missile guidance. This report presents a model of a FOA demonstrator which crudely models an industrially developed accelerometer, the demonstrator is made of a jig consisting of a guitar string and electromagnets. Such a model needs to account for a distributed parameter beam combined with a permanent magnet and four electromagnets. The guitar string is modelled using three beam models, namely a spring/damper model, an Assumed Modes Model (ASM) and a Transfer Function Model (TFM). The parameters for these beam models are identi ed using the Nelder-Mead simplex algorithm and the least squares method. The electromagnets within the jig, are modelled using a mathematical model obtained through curve tting of experimental data. The overall FOA sensor is optimised using a lead-lag controller. Five cost functions where investigated, these cost functions are H1, Integral Square Error (ISE), Integral Absolute Error (IAE), Integral Time Square Error (ITSE) and Integral Absolute Time Error (IATE). It was found that the guitar string may be modelled using a single degree of freedom beam model. This is based on a number of reasons, such as the aperture size - through which the tip Light Emitting Diode (LED) projects, the tip mass (permanent magnet) - acting as a natural damper and the fact that Position Sensing Device (PSD) only measures the tip position. It was found that a single degree of freedom model in two orthogonal axes, with a single link beam spring/damper model was the most suitable representation of the guitar string. And the IAE lead-lag controller was found to be the most e ective in controlling a guitar string, this e ectiveness was due to least settling time.
MT2017

碩士
南台科技大學
機械工程系
96
The objective of this study is to develop a set of low cost, high sensitivity, three-dimensional optical accelerometer. In the accelerometer structure, seismic mass is formed by a cross-form structure and four rectangular structures, the seismic mass is suspended from a symmetrical arrangement of thin steel strips. The dynamic response of the seismic mass was evaluated by performing a series of ANSYS finite element (FE) simulations. In constructing the model of the seismic mass and support mechanism, an assumption was made that the cross-form framework and rectangular masses were fabricated of 6061-T6 aluminum alloy, while the four strips supporting the seismic mass were fabricated of tool steel. The ANSYS FE simulations results revealed that the resonance frequencies of the seismic mass / suspension mechanism in the X, Y, and Z-axis directions were 132.99 Hz, 133.40 Hz and 132.49 Hz, respectively. Moreover, the simulations showed that the suspension mechanism limited the seismic mass to just three degrees of motional freedom, namely one translational motion in the vertical (Z-axis direction) and two rotational motions (about the X-axis and the Y-axis), respectively. Accordingly, cross-talk error between the different axes of the structure is reduced. The seismic mass has only three degrees of motional freedom, one translation motion and two rotational motions. These translational and rotational displacements are measured using just two sensors, both based on a commercial DVD optical pick-up head. The first sensor measures the translational motion of the seismic mass. During the calibration procedure, the positions of the two pick-up heads are adjusted such that the laser beams reflected from the two mirrors on the cross-form structure of the seismic mass are incident at the centers of the four-quadrant photodectors in the two devices. Any subsequent translational or rotational displacement of the seismic mass causes these reflected light spots to deviate from their initial positions, and therefore produces a measurable change in the focus error signals produced by the two pick-up heads. The error signals are then processed in order to determine the acceleration acting on the base. The experimental results indicate that the resonance frequencies of the accelerometer in the X, Y and Z-axis directions are 130.63 Hz, 130.90 Hz and 130.51 Hz, respectively. These experimental results are lower than the corresponding ANSYS by 0.149%, 0.177% and 0.12%, respectively. Meanwhile, the sensitivities of the accelerometer in the X, Y and Z-axis directions are 21.28 V/g, 22.94 V/g and 22.75 V/g, respectively. Furthermore, the useful frequency range of the accelerometer is found to be approximately 20% of its resonant frequency. It can be seen that the acceleration results obtained using the optical accelerometer are in good agreement with those obtained from the reference accelerometer at operating frequencies lower than 23 Hz. Furthermore, it is observed that a coupling of approximately 2.8%, 2.94% and 1.94% exists between the acceleration in the driven axis direction and that induced in the non-driven axial directions, respectively. In other words, no more than a minor cross-talk error exists between the different axes of the 3-D accelerometer.

碩士
國立高雄科技大學
機械工程系
107
In recent years, an accelerometer has been commonly used as a measurement tool in the fields of engineering and science. The biggest advantages of an accelerometer are small size and low cost, and it is used widely in vibration measurement. The main purpose of this study was to investigate the design of an accelerometer with fiber grating. Moreover, the influence of inertial mass on the sensitivity of the accelerometer was examined to reveal how different masses lengthen fiber grating. Also, the frequency of sine wave vibration on the sensing measurement by the accelerometer was experimentally demonstrated. In this study, the fiber grating was used as the main sensing components, encapsulated in two plastic hallo cylinder made by a 3D printer. A thin film was placed between the cylinders. a metal plate was glued to the film. The fiber grating went through two cylinders and the film. As the sensor detected a vibration frequency, the metal plates moved in response to the acceleration. The motion pulled on one end of the grating while compressing the other end, causing the central wavelength to drift to a long or short wavelength. When the wavelength of the fiber grating in the sensor was the same as the wavelength reflected from the matched grating, voltage was produced via the photodetector. The change of the wavelength displayed a periodic change in the oscilloscope. Thus, the effect of stress difference on the center wavelength shift could identify the magnitude of motion and direction of acceleration or reduction speed. The sensor could have practical application of the vibration measurement

Background: Physical inactivity has been consistently associated with numerous negative health outcomes that track from childhood into adulthood, making physical activity a special concern in the pediatric population. Dose-response studies are particularly useful when trying to understand the minimal and optimal amounts of physical activity needed to reduce the risk of negative health outcomes. Unfortunately, previous work within youth has relied on self-reported measures of physical activity, and this research does not provide a clear picture of the true relation between physical activity and health. Objectives: Manuscript 1. Describe the dose-response relation between dyslipidemia and moderate-to-vigorous physical activity (MVPA) in youth. Manuscript 2. Quantify the difference between self-reported and objectively measured MVPA in youth. Taken together, the overall objective of this thesis was to examine the dose-response relation between objectively measured MVPA and dyslipidemia in youth and determine how this may affect current Canadian physical activity guidelines. Methods: Both manuscripts used data from the U.S. National Health and Nutrition Examination Survey. Fractional polynomial regression modeling was used to fit the dose-response curves between MVPA and lipid/lipoprotein measurements. Regression analysis as well as a Bland-Altman plot was used to explain the discrepancy between self-reported and objective measures of MVPA. All analyses were completed using SAS statistical software. Results: Manuscript 1. Risks for high-risk HDL-cholesterol and triglyceride values decreased in a curvilinear manner with increasing minutes of MVPA. The greatest reduction in risk occurred within the first 30 min/d of MVPA. The relation between level of MVPA and LDL-cholesterol was unclear. Manuscript 2. The average youth over-reported their MVPA by ~30 min/d. The over-reporting was not mediated by basic demographic factors; however, the difference in reporting was systematic in nature such that inactive youth over-reported to the greatest extent. Conclusions: Manuscript 1. Youth need to accumulate 30 min/d of MVPA to greatly reduce their risk for dyslipidemia. Manuscript 2. Youth tend to over-report their daily MVPA by approximately 30 min/d. Combined, the results from this thesis suggest that physical activity recommendations for cardiovascular health in youth should suggest a minimum of 30 min/d of MVPA and preferred level of 60 min/d.
Thesis (Master, Kinesiology & Health Studies) -- Queen's University, 2009-09-07 08:48:03.896