Dissertations / Theses on the topic 'MEMS Piezoelectric Acoustic Transducers'

Microelectromechanical resonators have found widespread applications in timing, sensing and spectral processing. One of the important performance metrics of MEMS resonators is the temperature sensitivity of their frequency. The main objective of this dissertation is the compensation and control of the temperature sensitivity of silicon resonators through engineering of device geometry and structural composition. This has been accomplished through formation of composite platforms or novel geometries based on dispersion characteristics of guided acoustic waves in single crystalline silicon (SCS) microstructures. Furthermore, another objective of this dissertation is to develop efficient longitudinal piezoelectric transduction for in-plane resonance modes of SCS resonators that have lithographically-defined frequencies, to reduce their motional resistance (Rm). A uniformly distributed matrix of silicon dioxide pillars is embedded inside the silicon substrate to form a homogenous composite silicon-oxide platform (SilOx) with nearly perfect temperature-compensated stiffness moduli. Temperature-stable micro-resonators implemented in SilOx platform operating in any desired in- and out-of-plane resonance modes show full compensation of linear temperature coefficient of frequency (TCF). Overall frequency drifts as small as 80 ppm has been achieved over the industrial temperature range (-40°C to 80°C) showing a 40x improvement compared to uncompensated native silicon resonators. A 27 MHz temperature-compensated MEMS oscillator implemented using SilOx resonator demonstrated sub-ppm instability over the industrial temperature range. Besides this, a new formulation of different resonance modes of SCS resonators based on their constituent acoustic waves is presented in this dissertation. This enables engineering of the acoustic resonator to provide several resonance modes with mechanical energy trapped in central part of the resonator, thus obviating narrow tethers traditionally used for anchoring the cavity to the substrate. This facilitates simultaneous piezoelectric-transduction of multiple modes with different TCFs through independent electrical ports, which can realize highly accurate self-temperature sensing of the device using a beat frequency (fb) generated from linear combination of different modes. Piezoelectrically-transduced multi-port silicon resonators implemented using this technique provide highly temperature-sensitive fb with a large TCF of ~8500 ppm/°C showing 100x improvement compared to other Quartz/MEMS counterparts, suggesting these devices as highly sensitive temperature sensors for environmental sensing and temperature-compensated/oven-controlled crystal oscillator (TCXO/OCXO) applications. Another part of this dissertation introduces a novel longitudinal piezoelectric transduction technique developed for implementation of low Rm silicon resonators operating in lithographically defined in-plane modes. Aluminum nitride films deposited on the sidewalls of thick silicon microstructures provides efficient electromechanical transduction required to achieve low Rm. 100 MHz SCS bulk acoustic resonators implemented using this transduction technique demonstrates Rm of 33Ω showing a 100x improvement compared to electrostatically transduced counterparts. Low-loss narrow-band filters with tunable bandwidth and frequency have been implemented by electrical coupling of these devices, showing their potential for realization of truly reconfigurable and programmable filter arrays required for software-defined radios.

Structural health monitoring (SHM) is an active research area devoted to the assessment of the structural integrity of critical components of aerospace, civil and mechanical systems. Guided wave methods have been proposed for SHM of plate-like structures using permanently attached piezoelectric transducers, which generate and sense waves to evaluate the presence of damage. Effective interrogation of structural health is often facilitated by sensors and actuators with the ability to perform directional scanning. In this research, the novel class of Frequency Steerable Acoustic Transducers (FSATs) is proposed for directional generation/sensing of guided waves. The FSATs are characterized by a spatial arrangement of the piezoelectric material which leads to frequency-dependent directionality. The resulting FSATs can be employed both for directional sensing and generation of guided waves, without relying on phasing and control of a large number of channels. Because there is no need for individual control of transducer elements, hardware and power requirements are drastically reduced so that cost and hardware limitations of traditional phased arrays can be partially overcome. The FSATs can be also good candidates for remote sensing and actuation applications, due to their hardware simplicity and robustness. Validation of the proposed concepts first employs numerical methods. Next, the prototyping of the FSATs allows an experimental investigation confirming the analytical and numerical predictions. Imaging algorithm based on frequency warping is also proposed to enhance results representation.

Piezoelectric transducers are widely used in electro-acoustic, hydroacoustic, ultrasonic, medical and measuring techniques, security and control systems. One of the main characteristics of the piezoelectric transducers is operation frequency band. Despite the fact that it is used to be expanded, narrowband piezoelectric transducers also can be used. In particular, the fields of application of piezoelectric transducers are narrowband alarm systems, for example, glass breakage detectors [1].

Thesis (M.S. in Engineering Acoustics)--Naval Postgraduate School, March 2004.
Thesis advisor(s): Thomas R. Howarth, Dehua Huang. Includes bibliographical references (p. 67-69). Also available online.

Thesis (Ph. D.)--West Virginia University, 2009.
Title from document title page. Document formatted into pages; contains vi, 84 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 79-84).

This study presents a basis for the analytical and experimental procedures as well as design techniques required in achieving adaptive structures for active structural acoustic control (ASAC). Test structures studied in this work included a baffled simply supported beam and a baffled simply supported plate which were subjected to a harmonic input disturbance created physically with a shaker and modelled by a point force input. Structural acoustic control was achieved with piezoelectric actuators bonded to the surface of the test structure. The primary focus of this work was devoted to studying alternative sensing techniques in feed forward control applications. Specifically, shaped distributed structural sensors constructed from polyvinylidene fluoride (PVDF), distributed acoustic near-field sensors constructed from PVDF, and accelerometers were explored as alternatives to microphones which are typically implemented as error sensors in the cost function of the control approach. The chosen control algorithm in this study was the feed forward filtered-x version of the adaptive LMS algorithm. A much lower level of system modelling is required with this method of control in comparison to state feedback control methods. As a result, much of the structural acoustic coupling (i.e. system modelling) must be incorporated into the sensor design.
Ph. D.

Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Brand, Oliver; Committee Member: Adibi, Ali; Committee Member: Allen, Mark G.; Committee Member: Bottomley, Lawrence A.; Committee Member: Degertekin, F. Levent.

Orientador: Vera Lúcia da Silveira Nantes Button
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
Made available in DSpace on 2018-08-22T22:55:05Z (GMT). No. of bitstreams: 1 Nascimento_ValeriaMonteirodo_D.pdf: 6068450 bytes, checksum: 537e820daa45af6d8d50ccee4ad135e5 (MD5) Previous issue date: 2013
Resumo: Para observar o efeito no campo acústico dos diversos parâmetros de configuração do projeto de um transdutor ultrassônico, foram simuladas várias configurações de transdutor de alta frequência (5 a 50 MHz), tipo array anular, com kerf e kerfless, de cerâmica PZT-5H e de filme de PVDF. Transdutores com configurações de três, quatro, cinco e seis anéis, em que os anéis possuíam a mesma largura foram simulados com elemento ativo de cerâmica. E transdutores com cinco, seis, sete, oito e dez anéis de mesma área, com separação física entre os elementos (kerf) e sem separação física entre os elementos (kerfless) foram simulados com elementos piezoelétricos de cerâmica PZT-5H e filme de PVDF. Também foram testados materiais de diferentes impedâncias acústicas nas camadas de retaguarda (epóxi, epóxi e Araldite, ferro, tungstênio, alumina e madeira), foram usadas diversas funções de excitação dos elementos piezoelétricos (Blackman, Wavelet, Gauss, Seno, Step) em frequências variadas, além de se acionar os diversos elementos anelares isoladamente, em grupos e com atraso temporal. O objetivo das simulações realizadas foi determinar a melhor configuração de um transdutor array anular, quanto ao número de anéis, espaçamento entre eles e necessidade ou não de separação física entre os elementos, levando-se em conta a complexidade de construção e as características do campo acústico gerado. Para isso, os parâmetros observados no campo acústico foram à amplitude do pico, a amplitude média de pressão, a profundidade do campo, a colimação do feixe principal e a presença de lóbulos laterais. Outros parâmetros observados foram à tensão e a carga nos elementos. Os resultados obtidos nas simulações dos transdutores arrays circulares, feitas com o programa PZFlex®, foram processados no Matlab® para visualização do campo acústico e extração de parâmetros. As funções de transferência do sinal de excitação e da resposta à estimulação foram calculadas com os dados obtidos. O transdutor kerfless foi simulado no PZFlex® e seus resultados processados no Matlab®, para comparar com os resultados do transdutor com kerf de mesma configuração. Os resultados das simulações mostraram que o campo acústico neste tipo de transdutor, array anular, tem a região de campo distante começando bem próximo à face do transdutor. A camada de retaguarda de epóxi e Araldite® apresentaram valores mais elevados de amplitude do campo acústico. A função de excitação foi Wavelet na frequência de 30 MHz devido às restrições da relação diâmetro / espessura da cerâmica PZT-5H. O transdutor kerfless apresentou um campo acústico com as mesmas características do transdutor com kerf, com a vantagem de sua construção ser mais simples
Abstract: In order to observe the effect of ultrasound transducers parameters configurations in an acoustic field, simulations were made in some different configuration of an annular array ultrasound transducer in high frequency (5 to 50 MHz), kerf and kerfless, with active element of PZT - 5H ceramic or PVDF. The transducers configurations simulated were three, four, five and six annulus, with the same width, and the active element was PZT-5H. And transducers with five, six, seven, eight and ten annulus, with the same area, with and without physical separation between the elements had been simulated with active element of PZT-5H ceramics or PVDF. The materials of backing layer (epoxy, epoxy and Araldite, iron, tungsten, alumina and wood dust) with different impedance were also be tested, and a variety of excited functions (Blackman, Wavelet, Gauss, Sine, Step), in different frequencies, and also with time delay in active elements. The objective of this simulation was to find out the better configuration of an annular array ultrasound transducer in high frequency, the number of annulus, spacing between them, the area, the transducer is kerf or kerfless, considering the build complexity and the characteristics of acoustic field. To do this, the peak amplitude, the depth and the average amplitude of the acoustic field was measured. The charge and the voltage in the elements were also observed. The results obtained in simulations in PZFlex® software were run in Matlab® to visualize the acoustic field and to extract parameter. The ultrasound kerfless transducer was simulated in PZFlex® and the data obtained runs in Matlab®, the results were compared with the results of a transducer with kerf in the same configuration. The simulation results showed that the acoustic field of this kind of transducer has Fraunhofer zone began near the transducer's face. The backing layer with epoxy and Araldite® showed high amplitude of acoustic field. The frequency 30 MHz was choice due to diameter/thickness relations. The excitation function was wavelet, as this present high values response in acoustic field. Kerfless transducer showed acoustic field characteristics the same as the kerf transducers, with the advantage of a simple construction
Doutorado
Engenharia Biomedica
Doutora em Engenharia Elétrica

Ce travail novateur étudie l'intérêt d'intégrer des transducteurs piézoélectriques (à base céramique et/ou polymère) au sein de matériaux composites à matrice organique (CMO) pour effectuer une surveillance en temps réel et in-situ de leur processus de fabrication (Process Monitoring PM) ainsi que de leur vie en service (Structural Health Monitoring SHM). Pour ce faire, les transducteurs piézoélectriques ont été intégrés au cœur des empilements fibreux suivant une méthodologie innovante développée au sein de l’équipe de recherche « Matériaux et Surfaces » du laboratoire Roberval. Le système de fabrication par infusion de résine liquide (LRI) utilisé (campagne en PM) ainsi que les échantillons résultants testés mécaniquement (campagne en SHM) ont été multi-instrumentés à l'aide de plusieurs dispositifs de Contrôle Non Destructif (CND : Emission Acoustique (EA), Thermographie Infrarouge (TIR), Corrélation d’Images Numériques (CIN), etc.) afin d’établir des couplages multi-physiques entre les signaux des techniques CND externes et la signature interne (capacité électrique) provenant des transducteurs intégrés au cœur de la matière. En PM, la sensibilité des transducteurs piézocéramiques (PZT) aux diverses étapes clés du processus LRI (passage du front, imprégnation, arrêt de l’injection, transitions physico-chimiques de réticulation et taux de consolidation) réalisé à divers taux de durcisseur ainsi que leur aptitude à la détection de défauts de fabrication ont montré un fort potentiel digne d’une future utilisation à l’échelle industrielle. En SHM, après une vérification de la non-intrusivité des transducteurs à base céramique et polymère intégrés au cœur des échantillons de tests mécaniques, les transducteurs polymères ont permis une évaluation en temps réel de l’état triaxial de déformation et de la perte de rigidité subis par le CMO hôte durant son chargement mécanique. En revanche, malgré un seuil de non fonctionnement (NWT) lié à la fragilité de leur matériau constitutif, les transducteurs piézocéramiques ont montré une forte sensibilité à la détection et au suivi de l’endommagement en temps réel dès lors qu’ils sont positionnésintelligemment vis-à-vis de la sollicitation mécanique. Ces travaux de thèse se sont achevés sur une première tentative visant à transposer les connaissances acquises en PM et SHM des transducteurs piézoélectriques in-situ d'une échelle 2D « laboratoire » à une échelle structurelle 3D plus proche des réalités industrielles. La fabrication multi-instrumentée d’une structure CMO de type raidisseur « Omega » intégrant 14 transducteurs piézoélectriques (PZT ou copolymère P(VDF-TrFE)) et renforcée en épaisseur par un fil en carbone a permis de confirmer les aptitudes PM du PZT précédemment mises en évidence, et a montré une différence entre la manière dont les signaux de capacité électrique du PZT et des copolymères réagissent à l'ensemble du processus de fabrication
This innovative work studies the interest of integrating piezoelectric transducers (ceramic and/or polymer-based) within Polymer- Matrix Composite materials (PMC) to perform real-time and in-situ monitoring of their manufacturing process (Process Monitoring PM) as well as their lifespan (Structural Health Monitoring SHM). To do this, the piezoelectric transducers were integrated into the heart of the fibrous stacks using an innovative methodology developed within the "Materials and Surfaces" research team at the Roberval laboratory. The Liquid Resin Infusion (LRI) manufacturing system used (PM campaign), as well as the resulting samples tested mechanically (SHM campaign), were multi-instrumented using several Non-Destructive Testing devices (NDT: Acoustic Emission (AE), Infrared Thermography (IRT), Digital Image Correlation (DIC), etc.) in order to establish multi-physical couplings between the signals of external NDT techniques and the internal signature (electrical capacitance) coming from the transducers integrated into the heart of the material. In PM, the piezoceramic (PZT) transducers were found to be sensitive to the various key steps of the LRI process (flow front passing, impregnation, end of injection, chemo-physical transitions during curing and associated consolidation rates) achieved at different hardener rates, and able to detect manufacturing defects. These results showed great potential, worthy of future use on an industrial scale. In SHM, after verification of the non-intrusiveness of the ceramic and polymer-based transducers integrated into the heart of the mechanical test specimens, the polymer transducers allowed a real-time evaluation of the triaxial strain state and the rigidity loss experienced by the host PMC during its mechanical loading. However, despite a Non-Working Threshold (NWT) linked to the brittleness of their constitutive material, the piezoceramic transducers have shown a high sensitivity to the detection and monitoring of damage in real-time when they are positioned intelligently with respect to the mechanical stress. These thesis works ended with a first attempt aimed at transposing the knowledge acquired on PM and SHM of in-situ piezoelectric transducers from a 2D “laboratory” scale to a 3D structural one closer to industrial realities. The multi-instrumented manufacturing of an “Omega” stiffener PMC structure integrating 14 piezoelectric transducers (PZT and P(VDF-TrFE) copolymer) and reinforced through-the-thickness by a carbon tuft thread allowed confirming the previously evidenced PM abilities of the PZT, and showed a difference between how the electrical capacitance signals of PZT and copolymers react to the whole manufacturing process

Structural Health Monitoring (SHM) is an emerging area of research associated to improvement of maintainability and the safety of aerospace, civil and mechanical infrastructures by means of monitoring and damage detection. Guided wave structural testing method is an approach for health monitoring of plate-like structures using smart material piezoelectric transducers. Among many kinds of transducers, the ones that have beam steering feature can perform more accurate surface interrogation. A frequency steerable acoustic transducer (FSATs) is capable of beam steering by varying the input frequency and consequently can detect and localize damage in structures. Guided wave inspection is typically performed through phased arrays which feature a large number of piezoelectric transducers, complexity and limitations. To overcome the weight penalty, the complex circuity and maintenance concern associated with wiring a large number of transducers, new FSATs are proposed that present inherent directional capabilities when generating and sensing elastic waves. The first generation of Spiral FSAT has two main limitations. First, waves are excited or sensed in one direction and in the opposite one (180 ̊ ambiguity) and second, just a relatively rude approximation of the desired directivity has been attained. Second generation of Spiral FSAT is proposed to overcome the first generation limitations. The importance of simulation tools becomes higher when a new idea is proposed and starts to be developed. The shaped transducer concept, especially the second generation of spiral FSAT is a novel idea in guided waves based of Structural Health Monitoring systems, hence finding a simulation tool is a necessity to develop various design aspects of this innovative transducer. In this work, the numerical simulation of the 1st and 2nd generations of Spiral FSAT has been conducted to prove the directional capability of excited guided waves through a plate-like structure.

Contactless ultrasonic power transfer (UPT), using piezoelectric transducers, is based on transferring energy using acoustic waves, in which the waves are generated by an acoustic source or transmitter and then transferred through an acoustic medium such as water or human tissue to a sensor or receiver. The receiver then converts the mechanical strain induced by the incident acoustic waves to electricity and delivers to an electrical load, in which the electrical power output of the system can be determined. The execution and efficiency of this technology can be significantly enhanced through patterning, focusing, and localization of the transmitted acoustic energy in space to simultaneously power pre-determined distributed sensors or devices. A passive 3D-printed acoustic hologram plate alongside a single transducer can generate arbitrary and pre-designed ultrasound fields in a particular distance from the hologram mounted on the transmitter, i.e., a target plane. This dissertation presents the use of these simple, cost-effective, and high-fidelity acoustic holograms in UPT systems to selectively enhance and pattern the electrical power output from the receivers. Different holograms are numerically designed to create single and multi-focal pressure patterns in a target plane where an array of receivers are placed. The incident sound wave from a transmitter, after passing through the hologram, is manipulated, hence, the output field is the desired pressure field, which excites the receivers located at the pre-determined focal points more significantly. Furthermore, multi-functional holograms are designed to generate multiple images at different target planes and driving frequencies, called, respectively, multi-image-plane and multi-frequency patterning holograms. The multiple desired pressure distributions are encoded on the single hologram plate and each is reconstructed by changing the axial distance and by switching the frequency. Several proof-of-concept experiments are performed to verify the functionality of the computationally designed holograms, which are fabricated using modern 3D-printers, i.e., the desired wavefronts are encoded in the hologram plates' thickness profile, being input to the 3D-printer. The experiments include measurement of output pressure fields in water using needle hydrophones and acquisition of receivers' voltage output in UPT systems. Another technique investigated in this dissertation is the implementation of acoustic impedance matching layers deposited on the front leading surface of the transmitter and receiver transducers. Current UPT systems suffer from significant acoustic losses through the transmission line from a piezoelectric transmitter to an acoustic medium and then to a piezoelectric receiver. This is due to the unfavorable acoustic impedance mismatch between the transducers and the medium, which causes a narrow transducer bandwidth and a considerable reflection of the acoustic pressure waves at the boundary layers. Using matching layers enhance the acoustic power transmission into the medium and then reinforce the input as an excitation into the receiver. Experiments are performed to identify the input acoustic pressure from a cylindrical transmitter to a receiver disk operating in the 33-mode of piezoelectricity. Significant enhancements are obtained in terms of the receiver's electrical power output when implementing a two-layer matching structure. A design platform is also developed that can facilitate the construction of high-fidelity acoustically matched transducers, that is, the material layers' selection and determination of their thicknesses. Furthermore, this dissertation presents a numerical analysis for the dynamical motions of a high-intensity focused ultrasound (HIFU)-excited microbubble or stable acoustic cavitation, which includes the effects of acoustic nonlinearity, diffraction, and absorption of the medium, and entails the problem of several biomedical ultrasound applications. Finally, the design and use of acoustic holograms in microfluidic channels are addressed which opens the door of acoustic patterning in particle and cell sorting for medical ultrasound systems.
Doctor of Philosophy
This dissertation presents several techniques to enhance the wireless transfer of ultrasonic energy in which the sound wave is generated by an acoustic source or transmitter, transferred through an acoustic medium such as water or human tissue to a sensor or receiver. The receiver transducer then converts the vibrational energy into electricity and delivers to an electrical load in which the electrical power output from the system can be determined. The first enhancement technique presented in this dissertation is using a pre-designed and simple structured plate called an acoustic hologram in conjunction with a transmitter transducer to arbitrarily pattern and shape ultrasound fields at a particular distance from the hologram mounted on the transmitter. The desired wavefront such as single or multi-focal pressure fields or an arbitrary image such as a VT image pattern can simply be encoded in the thickness profile of this hologram plate by removing some of the hologram material based on the desired shape. When the sound wave from the transmitter passes this structured plate, it is locally delayed in proportion to the hologram thickness due to the different speed of sound in the hologram material compared to water. In this dissertation, various hologram types are designed numerically to implement in the ultrasonic power transfer (UPT) systems for powering receivers located at the predetermined focal points more significantly and finally, their functionality and performances are verified in several experiments. Current UPT systems suffer from significant acoustic losses through the transmission from a transmitter to an acoustic medium and then to a receiver due to the different acoustic impedance (defined as the product of density and sound speed) between the medium and transducers material, which reflects most of the incident pressure wave at the boundary layers. The second enhancement technology addressed in this dissertation is using intermediate materials, called acoustic impedance matching layers, bonded to the front side of the transmitter and receiver face to alleviate the acoustic impedance mismatch. Experiments are performed to identify the input acoustic pressure from a transmitter to a receiver. Using a two-layer matching structure, significant enhancements are observed in terms of the receiver's electrical power output. A design platform is also developed that can facilitate the construction of high-fidelity acoustically matched transducers, that is, the material layers' selection and determination of their thicknesses. Furthermore, this dissertation presents a numerical analysis for the dynamical motions of a microbubble exposed to a high-intensity focused ultrasound (HIFU) field, which entails the problem of several biomedical ultrasound applications such as microbubble-mediated ultrasound therapy or targeted drug delivery. Finally, an enhancement technique involving the design and use of acoustic holograms in microfluidic channels is addressed which opens the door of acoustic patterning in particle and cell sorting for medical ultrasound systems.

Apresentam-se as bases teóricas do Método de Elementos Finitos (MEF) piezoelétrico, e a sua aplicação na modelagem de transdutores de ultra-som piezoelétricos, que consiste na determinação das características vibracionais (frequências de ressonância e anti-ressonância, modos de vibrar e coeficiente de acoplamento eletromecânico), obtenção da curva de admitancia, análise transiente da estrutura piezoelétrica sujeita a uma excitação pulsada e análise da influência da variação das constantes piezoelétricas do transdutor com o raio. Utilizando-se o MEF aplicado a acústica obteve-se o campo acústico gerado pelo transdutor operando em onda contínua, bem como iniciou-se o estudo da propagação de ondas num líquido, analisando-se as ondas geradas pela excitação pulsada de um pistão plano em contato com o fluido. Os modos de vibrar e os valores de frequências de ressonância obtidos para um transdutor, foram comparados com os resultados experimentais.
The theoretical basis of piezoelectric finite element method (FEM), and its application in piezoelectric ultrasonic transducer modelling is presented. Among these applications we have the calculation of resonance and antiresonance frequencies, vibration modes, piezoelectric coupling coefficient, admittance curve and transient analysis of piezoelectric structure excited by a short pulse. By means of piezoelectric FEM the influence of variation of piezoelectric constant with radius is analysed. It is discussed three kind of functions (linear, cosinoidal and Gaussian). This technique is called apodization. The acoustic filed generated by the transducer operating in continuous wave (CW) was calculated by using FEM applied to acoustic, considering the fluid-structure coupling. The study of wave propagation in liquids is started by using FEM, analyzing the waves generated by a plane piston in contact with the fluid, excited by a short pulse. For each case discussed above, all boundary conditions and hypothesis assumed in the construction of finite element models are discussed. Although the models considered are circular transducers, the concepts acquired can be expanded to other geometries. The vibrational modes were visualized by means of a laser interferometry technique (ESPI), and the admittance curves were measured by using an impedometer. These results were compared with the FEM results, and the models precision was discussed.

This dissertation investigates dissipation in microelectromechanical (MEMS) resonators via detailed analysis and modeling of the energy loss mechanisms and provides a framework toward creating resonant devices with ultra-low dissipation. Fundamental mechanisms underlying acoustic energy loss are explored, the results of which are applied to understanding the losses in resonant MEMS devices. Losses in the materials, which set the ultimate limits of the achievable quality factor of the devices, are examined. Other sources of loss, which are determined by the design of the resonator, are investigated and applied to example resonant MEMS structures. The most critical of these designable loss mechanisms are thermoelastic dissipation (TED) and support (or anchor) loss of acoustic energy through the attachment of the MEMS device to its external environment. The dissipation estimation framework enables prediction of the quality factor of a MEMS resonator, which were accurate within a factor of close to 2 for high-frequency bulk acoustic wave MEMS resonators, and represents a signficant step forward by closing one of the largest outstanding problems in MEMS devices: how to predict the quality factor for a given device. Dissipation mitigation approaches developed herein address the most critical dominant loss mechanisms identified using the framework outlined above. These approaches include design of 1D phononic crystals (PCs) and novel 3D MEMS structures to trap and isolate vibration energy away from the resonator anchors, optimization of resonator geometry to suppress thermoelastic dissipation, and analysis of required levels of surface polish to reduce surface dissipation. Phononic crystals can be used to manipulate the properties of materials. In the case of the 1D PC linear acoustic bandgap (LAB) structures developed here, this manipulation arises from the formation of frequency stop bands, or bandgapwhich convert silicon from a material capable of supporting acoustic waves to a material which rejects acoustic propagation at frequencies in the bandgap. The careful design of these LAB structures is demonstrated to be able to enhance the quality factor and insertion loss of MEMS resonators without significant detrimental effects on the overall device performance.

Dans cette thèse nous proposons de développer un système d’imagerie ultrasonore innovante de micro- défauts basé sur l’utilisation conjointe de techniques d’acoustique non linéaire et du concept de "transducteur à cavité chaotique". Ce transducteur correspond à la combinaison d’une céramique piézoélectrique collée sur une cavité de forme chaotique et du principe de retournement temporel. La faisabilité et les performances de ce nouveau système sont explorées par des simulations numériques. Des paramètres optimaux d’utilisation pour une implémentation expérimentale sont proposés. Une grande partie des travaux menés dans le cadre de cette thèse se concentre sur le développement d’outils numériques permettant l’amélioration de telles techniques d’imagerie. Un schéma d’éléments finis de type Galerkin Discontinu (GD) est étendu à l’élastodynamique non linéaire. Un type de zone absorbante parfaitement adaptée, appelée "Nearly Perfectly Matched Layer" (NPML) a aussi été développé. Dans le cas de matériaux orthotropes, comme des problèmes de stabilité apparaissent, un mélange de NPML et de zone atténuante, dont on contrôle la proportion respective, est introduit afin de stabiliser les NPML. Une validation expérimentale du concept de "transducteur à cavité chaotique" pour la focalisation dans un milieu solide, réverbérant ou non, en utilisant une seule source est réalisée. Les méthodes de retournement temporel et de filtre inverse sont présentées et comparées. La démonstration expérimentale qu’un "transducteur à cavité chaotique" peut être utilisé conjointement avec les méthodes d’inversion d’impulsion afin de réaliser une image de non linéarités localisées est présentée
In this thesis we propose the development of an innovative micro-damage imaging system based on a combination of Nonlinear Elastic Wave Spectroscopy techniques and “chaotic cavity transducer” concept. It consists of a combination of a PZT ceramic glued to a cavity of chaotic shape with the time reversal principle. The feasibility and capabilities of these new ideas is explored by numerical simulations, and optimal operational parameters for experimental implementation are suggested based on the modelling support. A large part of the research work conducted in this thesis is concentrated on the development of numerical simulation tools to help the improvement of such nonlinear imaging methods. A nodal Discontinuous Galerkin Finite Element Method (DG-FEM) scheme is extended to nonlinear elasto-dynamic including source terms. A Perfectly Matched Layer absorbing boundary condition well adapted to the DG-FEM scheme, called Nearly Perfectly Matched Layer (NPML), is also developed. In the case of orthotropic material as stability problems appear, a mixture of NPML and sponge layer, with a controllable ratio of these two kinds of absorbing layers, is introduced. The experimental validation of “chaotic cavity transducer” to focalize in reverberant and non-reverberant solid media with only one source is made. Classical time reversal, inverse filter and 1 Bit time reversal process are discussed and compared. The experimental demonstration of the use of a “chaotic cavity transducer”, in combination with the pulse inversion and 1-bit methods, to obtain an image of localized nonlinearity is made. This opens the possibility for high resolution imaging of nonlinear defects

Ultra low power wireless sensors and sensor systems are of increasing interest in a variety of applications ranging from structural health monitoring to industrial process control. Electrochemical batteries have thus far remained the primary energy sources for such systems despite the finite associated lifetimes imposed due to limitations associated with energy density. However, certain applications (such as implantable biomedical electronic devices and tire pressure sensors) require the operation of sensors and sensor systems over significant periods of time, where battery usage may be impractical and add cost due to the requirement for periodic re-charging and/or replacement. In order to address this challenge and extend the operational lifetime of wireless sensors, there has been an emerging research interest on harvesting ambient vibration energy. Vibration energy harvesting is a technology that generates electrical energy from ambient kinetic energy. Despite numerous research publications in this field over the past decade, low power density and variable ambient conditions remain as the key limitations of vibration energy harvesting. In terms of the piezoelectric transducers, the open-circuit voltage is usually low, which limits its power while extracted by a full-bridge rectifier. In terms of the interface circuits, most reported circuits are limited by the power efficiency, suitability to real-world vibration conditions and system volume due to large off-chip components required. The research reported in this thesis is focused on increasing power output of piezoelectric transducers and power extraction efficiency of interface circuits. There are five main chapters describing two new design topologies of piezoelectric transducers and three novel active interface circuits implemented with CMOS technology. In order to improve the power output of a piezoelectric transducer, a series connection configuration scheme is proposed, which splits the electrode of a harvester into multiple equal regions connected in series to inherently increase the open-circuit voltage generated by the harvester. This topology passively increases the rectified power while using a full-bridge rectifier. While most of piezoelectric transducers are designed with piezoelectric layers fully covered by electrodes, this thesis proposes a new electrode design topology, which maximizes the raw AC output power of a piezoelectric harvester by finding an optimal electrode coverage. In order to extract power from a piezoelectric harvester, three active interface circuits are proposed in this thesis. The first one improves the conventional SSHI (synchronized switch harvesting on inductor) by employing a startup circuitry to enable the system to start operating under much lower vibration excitation levels. The second one dynamically configures the connection of the two regions of a piezoelectric transducer to increase the operational range and output power under a variety of excitation levels. The third one is a novel SSH architecture which employs capacitors instead of inductors to perform synchronous voltage flip. This new architecture is named as SSHC (synchronized switch harvesting on capacitors) to distinguish from SSHI rectifiers and indicate its inductorless architecture.

Piezoelectric micromachined ultrasound transducer (pMUT) two-dimensional (2D) arrays have been proposed as an alternative to conventional bulk-PZT thickness-mode transducers for high frequency, forward-looking, catheter-based ultrasound imaging of the cardiovascular system. The appeal of pMUTs is based on several key advantages over conventional transducer technologies, including high operational frequencies, small element size, and low cost due to their microelectromechanical system (MEMS) silicon-based fabrication. While previous studies have demonstrated acoustic performance characteristics suitable for ultrasound image formation, pulse-echo B-mode imaging of tissue and tissue-like phantoms using 2D pMUT arrays small enough for forward-looking catheter-based applications have been demonstrated only at Duke University by Dausch et al.

Having demonstrated the suitability of 2D pMUT arrays for tissue imaging, an important step is to demonstrate effective design control. The frequency of operation is a fundamental component of transducer design. Previous modeling efforts for pMUT vibration have used classical/Kirchoff thin plate theory (CPT) or Mindlin thick plate theory, however pMUTs with geometric dimensions similar to those explored here, have not been modeled with experimental comparison to physical devices.

It is hypothesized that the frequency of vibration of pMUTs can be predictively modeled based on experimental data from various pMUT configurations. Experimental frequency results were acquired and used to develop an empirical model based on a modified Mindlin thick plate theory. This dissertation presents the development of the frequency design theory culminating in a set of predictive design equations for the frequency of vibration of 2D pMUT arrays aimed at improving their use in high-frequency, forward-looking, catheter-based ultrasound imaging applications.

Dissertation

abstract: ABSTRACT This work seeks to develop a practical solution for short range ultrasonic communications and produce an integrated array of acoustic transmitters on a flexible substrate. This is done using flexible thin film transistor (TFT) and micro electromechanical systems (MEMS). The goal is to develop a flexible system capable of communicating in the ultrasonic frequency range at a distance of 10 - 100 meters. This requires a great deal of innovation on the part of the FDC team developing the TFT driving circuitry and the MEMS team adapting the technology for fabrication on a flexible substrate. The technologies required for this research are independently developed. The TFT development is driven primarily by research into flexible displays. The MEMS development is driving by research in biosensors and micro actuators. This project involves the integration of TFT flexible circuit capabilities with MEMS micro actuators in the novel area of flexible acoustic transmitter arrays. This thesis focuses on the design, testing and analysis of the circuit components required for this project.
Dissertation/Thesis
M.S. Electrical Engineering 2012

Ultrasonic sensors are well known for various applications such as NDT, ultrasound imaging, and proximity sensing. Conventional ultrasound transducers are bulky, work at notoriously high voltages, and consume significant power. Microfabrication techniques are leading to a paradigm shift in the field of ultrasonics by enabling development of low power - small footprint ultrasound transducers. This work focuses on the development of piezoelectric type flexural mode micromachined ultrasound transducer also known as PMUTs. We start by establishing a system level analytical model of a PMUT and use it to offer insights into scaling of the performance of the transducer with respect to various design parameters. In this analysis we give special attention to residual stresses thus establishing a contrast between membrane type and plate type PMUTs. After going through various steps of material development and microfabrication, we obtain arrays of PMUTs with different designs. PZT thin films deposited by sol-gel method are used as the piezoelectric layer in the multilayer stack. Further, we present a thorough characterization of fabricated PMUTs which includes measurement of the piezoelectric properties of the embedded PZT thin film, electrical impedance of the electromechanical transducer, its vibrational charac-teristics and acoustic radiation from a single PMUT cell. We also develop a pre-amplifier circuit for a PMUT receiver and present its working as a simple proximity sensor. After establishing the repeatability and predictability of our PMUT sensors we delve into application development beyond ultrasound imaging. Experiments and analysis of PMUTs submerged in water show strong structural-acoustic coupling between the PMUT membrane and the surrounding fluid. We hypothesize the applicability of this feature to sense changes in the acoustic environment of a PMUT. To this end, we integrate an array of PMUTs with a micro-fluidic chip and study the changes in the vibrational behaviour of the PMUT in response to change in the air-water ratio in a closed cell around a PMUT membrane. We also present our preliminary results on presence of micro-bubbles in the closed cell around the PMUT.

碩士
國立交通大學
機械工程系
88
This thesis presents an investigation of the acoustic field induced by linear array piezoelectric transducers using transient finite element analysis. Ultrasonic inspection of defects near roots of turbine blades was numerically studied by assuming that the ultrasound were transmitted simultaneously and received individually by the phase array transducers. The influences of various inspection parameters are also discussed and used as a reference for design of an array transducer and planning of an inspection. Conventional B-scan can only provide time-of-flight information of the reflected/diffracted signals from internal discontinuities in specimens. The spatial relations among those discontinuities can not be directly interpreted from B-scan images. The interpretation results in a need of well-experienced inspectors. However, the echoes reflected from complex dovetails of the blades usually have greater amplitudes than those diffracted signals from the crack tips. The inspectors were often confused with signals of geometric reflection. This research applied an angular-spectrum-based synthetic aperture imaging technique to reconstruct images of the defects and geometric boundaries of the dovetails. The present study provides a promising method to improve the capability of ultrasonic inspection for the defects and their orientations in turbine blade dovetails.

碩士
國立臺灣大學
材料科學與工程學研究所
95
A novel active matching layer made of lead zirconate titanate (PZT) plate has been developed as an “impedance matching layer” for high-intensity focused ultrasound (HIFU) applications. The PZT matching layer redistributes the frequency spectrum of an original broadband ultrasonic probe, and acts as a frequency filter without reducing the wave amplitude. These behaviors are contributed to electromechanical and mechanical properties at the PZT matching layer, and are investigated in this study by a series of experiments on PZT matching plates with different electromechanical properties and polarization and surface charge conditions. Traditional passive matching layers, such as ceramic-polymer composites, are also studied. Three different ceramic-epoxy composite are developed and their impedance properties studied. Among the three, the zirconium oxide-epoxy composite exhibits a tolerable attenuation level and an optimum impedance value. It is then integrated on to a home-made HIFU transducer to test its effectiveness. The beam profile of the matched HIFU transducer is characterized by a hydrophone, and an in-vivo experiment is carried out to gauge its performance. In this study, structure materials such as porous ceramics and porous ceramic-epoxy composites are also proposed as candidate materials for impedance matching for water and human tissues due to their low attenuations and impedances.

A prototype acoustic streaming pump for microfluidic applications was developed. A novel integration scheme was devised based on the acoustic reflector concept. Numerical simulations were conducted to predict the flow patterns around the transducer. Ultrasound transducers using P(VDF-TrFE) as the piezoelectric element were fabricated using lithography-based microfabrication technology. Silicon channels were fabricated using anisotropic etching. A heat-press bonding technique was adopted to bond the transducers with the silicon chips using CYTOP fluoropolymer as the adhesive. The piezoelectric transducers were characterized to have a resonance frequency of 82 MHz. Micro-PIV experiments were performed in the near and far-fields of the ultrasonic transducer/pump. The near field experiments showed complex flow patterns that could enhance mixing. Estimates of the pumping pressure were obtained using transient flow velocities in the far-field. Conservative estimates indicate the total back pressure the micropump can pump against is 39 Pa. Future research directions were suggested.

The work detailed here is the development of simulations and fabrication techniques used for the construction of thin-film acoustic transducers for use in the parametric pumping of spin waves. The Mason Model, a 1-D equivalent circuit simulating the responses of multilayer acoustic transducers, is implemented using ABCD-parameters in MATLAB to determine the expected response from fabricated devices. The simulation is tested by varying device parameters and comparing the changes in device resonance response to those of prior published results. Three-layer thin-film acoustic transducers were also fabricated. These transducers use zinc oxide (ZnO) as a piezoelectric layer with aluminum (Al) electrodes. Construction is accomplished using the common thin-film fabrication techniques of sputtering, thermal evaporation, etching, and lift-off patterning processes. The response of the fabricated transducers is compared to that of the simulated response by observing the transducer's resonance frequency and characteristics. These results are used to validate the simulation and the transducer fabrication process. Finally, their usefulness for the design and fabrication of an acoustic spin wave amplification system is considered.
Graduation date: 2013

碩士
國立清華大學
動力機械工程學系
105
In recent years, people pay more attention to food safety. Traditional detection technology is expensive, complicated and time-consuming, so that it is impossible to do the real-time and on-site detection for the irregular additives in food samples. This study further investigate and improve the droplet-based piezoelectric polymer deposition. In addition, the deposited piezoelectric polymer deivces are integrated on a biochip for rapid detection of drug residue in foods. First, we changed the wire width of electrode to design and choose different area ratio of P(VDF-TrFE). In the electrodeposition process, we discussed the optimization parameter, including electrodeposition time, volume of droplet, supplying voltage, and the pre-treatment of relative humidity. In the examination of acoustic property, the maximum output power was 86.31 μW (10 kHz). Compare of past study, the signal strengthen was enhanced by 62 % (10 kHz), the output power was enhanced by 37 %, the efficiency was enhanced by 220 %. In the property of acoustic transceiver, the signal coefficient of variation was reduced to 0.38 % from 17.79 % by the pre-tunable treatment. The developed acoustic transceiver was applied to the detection of animal drugs residue in meat samples after the optimization process and pre-tunable treatment. The detection frequency was 10 kHz, and the target drugs were ractopamine、benzylpenicillin、doxycycline. The response, including fluid disturbance and steady tim) was 80 sec, and the SNR of steady signal was up to 29.03 dB. Linear range was 0 ~ 100 ppb, and sensitivity was up to 2.4 mV/ppb and the detection limit was 2.06 ppb (3 dB). Finally, the acoustic transceiver was integrated with MIP films on microfluidic chip, and 20 ppb pork sample was applied to our chip for drugs residue detection. The detection result was up to 23.7±1.15 ppb. The detection time was 4 min, including fluid operation and dynamic signal measurement. In this study, the developed high-sensitivity piezoelectric acoustic transceiver presented the advantages of low cost, simple steps and high integration. Besides the drugs residue detection, it also was applied as others biosensor in the future.

MEMS microphones have been a research topic for the last two and half decades. The state-of-the-art comprises surface mount MEMS microphones in laptops, mobile phones and tablets, etc. The popularity and the commercial success of MEMS microphones is largely due to the steep cost reduction in manufacturing afforded by the mass scale production with microfabrication technology. The current MEMS microphones are de-signed along the lines of traditional microphones that use capacitive transduction with or without permanent charge (electret type microphones use permanent charge of their sensor element). These microphones offer high sensitivity, stability and reasonably at frequency response while reducing the overall size and energy consumption by exploiting MEMS technology. Conceptually, microphones are simple transducers that use a membrane or diaphragm as a mechanical structure which deflects elastically in response to the incident acoustic pressure. This dynamic deflection is converted into an electrical signal using an appropriate transduction technique. The most popular transduction technique used for this application is capacitive, where an elastic diaphragm forms one of the two parallel plates of a capacitor, the fixed substrate or the base plate being the other one. Thus, there are basically two main elements in a microphone { the elastic membrane as a mechanical element, and the transduction technique as the electrical element. In this thesis, we propose and study novel design for both these elements. In the mechanical element, we propose a simple topological change by introducing slits in the membrane along its periphery to enhance the mechanical sensitivity. This simple change, however, has significant impact on the microphone design, performance and its eventual cost. Introduction of slits in the membrane makes the geometry of the structural element non-trivial for response analysis. We devote considerable effort in devising appropriate modeling techniques for deriving lumped parameters that are then used for simulating the system response. For transduction, we propose and study an FET (Field Effect Transistor) coupled micro-phone design where the elastic diaphragm is used as the moving (suspended) gate of an FET and the gate deflection modulated drain current is used in the subthreshold regime of operation as the output signal of the microphone. This design is explored in detail with respect to various design parameters in order to enhance the electrical sensitivity. Both proposed changes in the microphone design are motivated by the possibilities that the microfabrication technology offers. In fact, the design proposed here requires further developments in MEMS technology for reliably creating gaps of 50-100 nm between the substrate and a large 2D structure of the order of a few hundred microns in diameter. In the First part of the thesis, we present detailed simulations of acoustic and squeeze lm domain to understand the effect slits could bring upon the behaviour of the device as a microphone. Since the geometry is nontrivial, we resort to Finite element simulations using commercial packages such as COMSOL Multiphysics and ANSYS in the structural, acoustic and Fluid-structure domains to analyze the behaviour of a microphone which has top plate with nontrivial geometry. On the simulated Finite element data, we conduct low and high frequency limit analysis to extract expressions for the lumped parameters. This technique is well known in acoustics. We borrow this technique of curve Fitting from the acoustics domain and apply it in modified form into the squeeze lm domain. The dynamic behaviour of the entire device is then simulated using the extracted parameters. This helps to simulate the microphone behaviour either as a receiver or as a transmitter. The designed device is fabricated using MEMSCAP PolyMUMPS process (a foundry Polysilicon surface micromachining process). We conduct vibrometer (electrostatic ex-citation) and acoustic characterization. We also study the feasibility of a microphone with slits and the issues involved. The effect of the two dissipation modes (acoustic and squeeze lm ) are quantified with the experimentally determined quality factor. The experimentally measured values are: Resonance is 488 kHz (experimentally determined), low frequency roll-off is 796 Hz (theoretical value) and is 780 Hz as obtained by electrical characterization. The first part of this thesis focusses on developing a comprehensive understanding of the effect of slits on the performance of a MEMS microphone. The presence of slits near the circumference of the clamped plate cause reduction in its rigidity. This leads to an increase in the sensitivity of the device. Slits also cause pressure equalization between the top and bottom of the diaphragm if the incoming sound is at relatively low frequencies. At this frequency, also known as the lower cutoff frequency, the microphone's response starts dropping. The presence of slits also changes the radiation impedance of the plate as well as the squeeze lm damping below the plate. The useful bandwidth of the microphone changes as a consequence. The cavity formed between the top plate and the bottom fixed substrate increases the stiffness of the device significantly due to compression of the trapped air. This effect is more pronounced here because unlike the existing capacitive MEMS microphones, there is no backchamber in the device fabricated here. In the second part of the thesis, we present a novel subthreshold biased FET based MEMS microphone. This biasing of the transistor in the subthreshold region (also called as the OFF-region) offers higher sensitivity as compared to the above threshold region (also called as the ON-region) biasing. This is due to the exponentially varying current with change in the bias voltage in the OFF-region as compared to the quadratic variation in the ON-region. Detailed simulations are done to predict the behaviour of the device. A lumped parameter model of the mechanical domain is coupled with the drain current equations to predict the device behaviour in response to the deflection of the moving gate. From the simulations, we predict that the proposed biasing offers a device sensitive to even sub-nanometer deflection of the flexible gate. As a proof of concept, we fabricate fixed-fixed beams which utilize CMOS-MEMS fabrication. The process involves six lithography steps which involve two CMOS and the remaining MEMS fabrication. The fabricated beams are mechanically characterized for resonance. Further, we carry out electrical characterization for I-V (current-voltage) characteristics. The second part of the thesis focusses on a novel biasing method which circumvents the need of signal conditioning circuitry needed in a capacitive based transduction due to inbuilt amplification. Extensive simulations with equivalent circuit has been carried out to determine the increased sensitivity and the role of various design variables.

Στο πλαίσιο της εργασίας αυτής πραγματοποιείται ανάλυση και εφαρμογή του διαχωρισμού ακουστικών σημάτων, τα οποία έχουν ληφθεί από το ανθρώπινο σώμα, όταν αυτό βρίσκεται σε κατάσταση ύπνου. Τα σήματα αυτά έχουν ληφθεί με τη βοήθεια μιας συσκευής πιεζοκρυστάλλων και ο διαχωρισμός τους επιτυγχάνεται με τη μέθοδο Ανάλυσης Ανεξάρτητων Συνιστωσών (ICA). Κύριος σκοπός όλων των παραπάνω είναι να χρησιμοποιηθεί η εν λόγω μεθοδολογία στη διάγνωση της αποφρακτικής άπνοιας (OSA). Στο πρώτο κεφάλαιο, παρουσιάζεται αναλυτικά η μέθοδος ICA και το μαθηματικό μοντέλο που την περιγράφει, όπως επίσης και όλα τα βήματα προεπεξεργασίας της. Στη συνέχεια αναλύεται διεξοδικά η λειτουργία του αλγορίθμου FastICA και οι ιδιότητες του, με τον οποίο υλοποιείται το πειραματικό μέρος της εργασίας αυτής. Στο δεύτερο κεφάλαιο, μελετάται η ασθένεια της αποφρακτικής άπνοιας (OSA), οι παράγοντες και η παθολογία της καθώς και το κύριο διαγνωστικό σύμπτωμα της: το ροχαλητό. Ύστερα, πραγματεύεται την διάγνωση και τους γνωστότερους τρόπους θεραπείας αυτής της νόσου και τελικά τη μέθοδο του Snoring Detection. Στο τρίτο κεφάλαιο γίνεται μια εισαγωγή στον πιεζοηλεκτρισμό, και μία μελέτη του πιεζοηλεκτρικού φαινομένου και του μαθηματικού του μοντέλου. Ακολουθεί αναφορά των ειδών πιεζοηλεκτρικών αισθητήρων με τους οποίους λαμβάνονται τα σήματα που εξετάζονται σε αυτή την εργασία. Στο επόμενο κεφάλαιο γίνεται μία σύνδεση των δεδομένων θεωρίας που αναφέρονται στα προηγούμενα κεφάλαια και μία εισαγωγή στην πειραματική μέθοδο. Στο κεφάλαιο πέντε παρατίθενται κάποια παραδείγματα εφαρμογής του αλγορίθμου FastICA με τυχαία σήματα, τα οποία έχουν σκοπό να δοκιμάσουν την απόδοση του. Στο κεφάλαιο έξι, 5 γίνεται η πειραματική διαδικασία όπου τώρα τα σήματα που διαχωρίζονται με τον αλγόριθμο FastICA προέρχονται από το ανθρώπινο σώμα. Η υλοποίηση της γίνεται σε Matlab. Έτσι, γίνεται εξαγωγή του ζητούμενου σήματος ροχαλητού και αναγράφονται κάποια συμπεράσματα για την απόδοση του αλγορίθμου. Στο τέλος της εργασίας παρατίθενται σε ένα παράρτημα όλοι οι κώδικες της MATLAB που χρησιμοποιήθηκαν για την ολοκλήρωση του πειραματικού της μέρους στα κεφάλαια πέντε και έξι.
In this particular thesis, analysis and application of separation of acoustic signals is carried out. These signals have been taken from the human body in a sleeping state. They are obtained by means of a piezocrystallic device and their separation is achieved by the method of Independent Component Analysis (ICA). The main purpose of all this is to use this methodology in order to diagnose the Obstructive Sleep Apnea (OSA). The first chapter presents the method of ICA and the mathematical model that describes it as well as all the pre-processing steps. Then it analyses, in detail, the algorithm FastICA, which is used in the experimental part of this thesis and its properties. The second chapter studies the disease of obstructive sleep apnea (OSA), its factors and its pathology and the major diagnostic symptom: snoring. Then, it discusses the diagnosis and the best known ways of treating this disease and eventually the method of Snoring Detection. The third chapter is an introduction to piezoelectricity and a study of the piezoelectric effect and its mathematical description. This is followed by a reference to the types of piezoelectric sensors which are used to obtain the signals used in this paper. In chapter five we have listed some examplesapplications of the FastICA algorithm with random signals, which are designed to test the performance. Section six is where the experimental procedure takes place. The signals derived from the human body are separated by the algorithm FastICA and the implementation is done in Matlab. In addition, some conclusions regarding the performance of the algorithm. At the end of this paper, all the MATLAB codes used for the completion of the experimental part of the chapters five and six are listed in an Annex.

Dissertação de mestrado em Engenharia Eletrónica Industrial e Computadores
O objetivo deste trabalho é desenvolver um sensor acústico capaz de medir correntes marítimas. Este projeto surge da necessidade de recolher alguns dados de interesse marítimo com o objetivo de criar modelos de funcionamento dos ecossistemas. Neste projeto pretende-se colocar vários sensores georreferenciados, a diferentes profundidades, a fazer medições e a armazenar os dados respetivos. Este sensor será responsável por medir a velocidade da água que flui num determinado nó do sistema. Este deverá ser capaz de medir a intensidade da corrente e a direção independentemente da sua posição no espaço, necessitando por isso de um magnetómetro (bússola digital) para utilizar o norte geográfico como referência. O sensor de corrente marítima que é apresentado utiliza transdutores piezoelétricos ultrassónicos pretendendo com isso tornar o sistema mais fiável e com maior robustez devido à ausência de partes móveis. A propriedade dos ultrassons explorada neste trabalho para obtenção da velocidade da corrente é o tempo de voo. O tempo de voo é o tempo que um determinado sinal demora a propagar-se num determinado meio entre dois pontos. No desenvolvimento do sensor será estudado o formato da estrutura, a posição e a orientação dos transdutores, de forma a melhorar a qualidade das medições em diferentes condições. Tal deverá ter em conta a robustez, dimensões razoáveis e evitar fenómenos de turbulência no volume de água a ser medido. O processamento dos sinais enviados e recebidos pelos transdutores será executado por um circuito integrado capaz de executar rotinas de medição de tempo de voo e de temperatura. Esse circuito integrado irá comunicar com um microcontrolador que irá interpretar os tempos de voo e converter na velocidade do fluido. Para além da comunicação com este circuito integrado, o microcontrolador, terá que comunicar com um relógio de tempo real, para obtenção de uma referência temporal, com um cartão de memória, para armazenamento de dados num ficheiro e com um magnetómetro, para obter uma referência de orientação ao norte geográfico já que o sensor não estará fixo. Com vários sensores destes é possível entender fenómenos de transporte à escala costeira, graças aos dados que é possível obter com um instrumento de medição desta escala.
The objective of this work is to develop an acoustic sensor capable of measuring sea currents. This project arises from the need to collect some data of maritime interest with the aim of creating models for the functioning of ecosystems. In this project, we intend to place several georeferenced sensors at different depths to make measurements and store the respective data. This sensor will be responsible for measuring the velocity of the water flowing in a particular node of the system. It should be able to measure the intensity of the current and direction independently of its position in space, thus necessitating a magnetometer (digital compass) to establish geographic north as a reference. The marine current sensor which is shown utilizes ultrasonic piezoelectric transducers in order to make the system more reliable and more robust due to the absence of moving parts. The property of the ultrasound explored in this work to obtain the velocity of the current is the flight time. Flight time is the time that a given signal takes to propagate in a certain medium between two points. In the development of the sensor will be studied the structure format, the position and the orientation of the transducers, in order to improve the quality of the measurements under different conditions. This should take into account the robustness, reasonable dimensions and avoid phenomena of turbulence in the volume of water to be measured. The processing of the signals sent and received by the transducers will be performed by an integrated circuit capable of performing flight time and temperature measurement routines. This integrated circuit will communicate with a microcontroller that will interpret flight times and convert to fluid velocity. In addition to communicating with this integrated circuit, the microcontroller must communicate with a real-time clock, to obtain a time reference, with a memory card, to store data in a file and with a magnetometer, to obtain a reference geographic north since the sensor will not be static. With several sensors of these it is possible to understand transport phenomena to the scale of the coast, thanks to the data that can be obtained with a measurement instrument of this scale.