The presented work aims to optimize the performance of piezoresistive cantilevers in cases where the output signal originates either from a static deflection of the cantilever or from the dynamic (resonance) characteristic of the beam. Based on a new stress concentration technique, which utilizes silicon beams and wires embedded in the cantilever, the force sensitivity of the cantilever is increased up to 8 fold with only about a 15% decrease in the cantilever stiffness. Moreover, the developed stress-concentrating cantilevers show almost the same resonance characteristic as conventional cantilevers. The focus of the second part of the present work is to provide guidelines for designing rectangular silicon cantilever beams to achieve maximum quality factors for the fundamental and higher flexural resonance at atmospheric pressure. The applied methodology is based on experimental data acquisition of resonance characteristics of silicon cantilevers, combined with modification of analytical damping models to match the measurement data. To this end, rectangular silicon cantilever beams with thicknesses of 5, 7, 8, 11 and 17 um and lengths and widths ranging from 70 to 1050 um and 80 to 230 um, respectively, have been fabricated and tested. To better describe the experimental data, modified models for air damping have been developed. Moreover, to better understand the damping mechanisms in a resonant cantilever system, analytical models have been developed to describe the cantilever effective mass in any flexural resonance mode. To be able to extract reliable Q-factor data for low signal-to-noise ratios, a new iterative curve fitting technique is developed and implemented. To address the challenge of frequency drift in (mass-sensitive) resonant sensors, and especially cantilever-based devices, the last part of the research deals with a novel compensation technique to cancel the unwanted environmental effects (e.g., temperature and humidity). This technique is based on exploring the resonance frequency difference of two flexural modes. Experimental data show improvements in temperature and humidity coefficients of frequency from -19.5 to 0.2 ppm/˚C and from 0.7 to -0.03 ppm/%RH, respectively. The last part of the work also aims on techniques to enhance or suppress the flexural vibration amplitude in desired overtones.

The recent development of the commercially viable thin film electro-acoustic technology has triggered a growing interest in the research of plate guided wave or Lamb wave components owing to their unique characteristics. In the present thesis i) an experimental study of the thin film plate resonators (FPAR) performance operating on the lowest symmetrical Lamb wave (S0) propagating in highly textured AlN membranes versus a variety of design parameters has been performed. The S0 mode is excited through an Interdigital Transducer and confined within the structure by means of reflection from metal strip gratings. Devices operating in the vicinity of the stop-band center exhibiting a Q-value of up to 3000 at a frequency around 900MHz have been demonstrated. Temperature compensation of this type of devices has been studied theoretically and successfully realized experimentally for the first time. Further, integrated circuit-compatible S0 Lamb based two-port FPAR stabilized oscillators exhibiting phase noise of -92 dBc/Hz at 1 kHz frequency offset with feasible thermal noise floor below -180 dBc/Hz have been tested under high power for a couple of weeks. More specifically, the FPARs under test have been running without any performance degradation at up to 27 dBm loop power. Further, the S0 mode was experimentally demonstrated to be highly mass and pressure sensitive as well as suitable for in-liquid operation, which together with low phase noise and high Q makes it very suitable for sensor applications; ii) research in view of FPARs operating on other types of Lamb waves as well as novel operation principles has been initiated. In this work, first results on the design, fabrication and characterization of two novel type resonators: The Zero Group Velocity Resonators (ZGVR) and The Intermode-Coupled Thin Film Plate Acoustic Resonators (IC-FPAR), exploiting new principles of operation have been successfully demonstrated. The former exploits the intrinsic zero group velocity feature of the S1 Lamb mode for certain combination of design parameters while the latter takes advantage of the intermode interaction (involving scattering) between S0 and A1 Lamb modes through specially designed metal strip gratings (couplers). Thus both type of resonators operate on principles of confining energy under IDT other than reflection.

[Truncated abstract] This thesis studies current sensing techniques that are designed to meet the requirements for the next generation of power converters. Power converters are often standardised, so that they can be replaced with a model from another manufacturer without an expensive system redesign. For this reason, the power converter market is highly competitive and relies on cutting-edge technology, which increases power conversion efficiency and power density. High power density and conversion efficiency reduce the system cost, and thus make the power converter more attractive to the customer. Current sensing is a vital task in power converters, where the current information is required for monitoring and control purposes. In order to achieve the above-mentioned goals, existing current sensing techniques have to be improved in terms of cost, power loss and size. Simultaneously, current information needs to be increasingly available in digital form to enable digital control, and to allow the digital transmission of the current information to a centralised monitoring and control unit. All this requires the output signal of a particular current sensing technique to be acquired by an analogue-to-digital converter, and thus the output voltage of the current sensor has to be sufficiently large. This thesis thoroughly reviews contemporary current sensing techniques and identifies suitable techniques that have the potential to meet the performance requirements of the next-generation of power converters. After the review chapter, three novel current sensing techniques are proposed and investigated: 1) The usefulness of the resistive voltage drop across a copper trace, which carries the current to be measured, to detect electrical current is evaluated. Simulations and experiments confirm that this inherently lossless technique can measure high currents at reasonable measurement bandwidth, good accuracy and low cost if the sense wires are connected properly. 2) Based on the mutual inductance theory found during the investigation of the copper trace current sense method, a modification of the well-known lossless inductor current sense method is proposed and analysed. This modification involves the use of a coupled sense winding that significantly improves the frequency response. Hence, it becomes possible to accurately monitor the output current of a power converter with the benefits of being lossless, exhibiting good sensitivity and having small size. 3) A transformer based DC current sense method is developed especially for digitally controlled power converters. This method provides high accuracy, large bandwidth, electrical isolation and very low thermal drift. Overall, it achieves better performance than many contemporary available Hall Effect sensors. At the same time, the cost of this current sensor is significantly lower than that of Hall Effect current sensors. A patent application has been submitted. .... The current sensing techniques have been studied by theory, hardware experiments and simulations. In addition, the suitability of the detection techniques for mass production has been considered in order to access the ability to provide systems at low-cost.

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-08-28T20:29:05Z No. of bitstreams: 1 TONY CARLOS MOURA CAVALCANTI – TESE (PPGEEI) 2016.pdf: 4469755 bytes, checksum: 884382b3c566b4aca499dc522be900ab (MD5) / Made available in DSpace on 2018-08-28T20:29:05Z (GMT). No. of bitstreams: 1 TONY CARLOS MOURA CAVALCANTI – TESE (PPGEEI) 2016.pdf: 4469755 bytes, checksum: 884382b3c566b4aca499dc522be900ab (MD5) Previous issue date: 2016-12-12 / CNPq / O objetivo neste trabalho é propor um sistema para a hidrometria na faixa de submedição utilizando a anemometria térmica. O objetivo de medir vazão está presente em muitos campos da ciência, sendo necessário sabermos quais os valores de um material foram consumidos com o menor erro possível. Na primeira parte da pesquisa foram realizadas simulações em ambiente multifísico para identificar as condições de trabalho e possíveis pontos de localização do sensor. Para poder usar o sensor, é necessário conhecer valores limítrofes de trabalho do mesmo, ou seja, a faixa de operação, indicando assim a vazão mínima e máxima de operação do sensor anemométrico. Portanto, na segunda etapa do trabalho, foi proposta uma plataforma com um sistema de bombeamento para testar o sistema de medição proposto. A plataforma foi construída de modo a permitir que um fluído flua através de uma tubulação e, assim, determinar qual é a velocidade do fluído e, portanto, a vazão. / The objective of this work is to propose a system for the hydrometry in the sub-measurement range using thermal anemometry. The objective of measuring flow is present in many fields of science, it is necessary to know what values of a material were performed using COMSOL software to identify working conditions and maximum flow rate of the anemometric sensor. Therefore, in the second stage of the work, a platform with a pumping system was proposed in order to test the proposed measurement system. The platform was constructed so as to allow a fluid to flow through a pipeline, and thereby determine what the velocity of the fluid, and hence the flow, is.

Esta tese teve por objetivo desenvolver um algoritmo preciso e robusto capaz de compensar os erros térmicos volumétricos de um centro de usinagem 5 eixos em diferentes condições operacionais. O comportamento térmico da máquina foi modelado usando técnicas do método dos elementos finitos (MEF) com base na teoria do calor de atrito e calor de convecção, e validadas através dos vários campos de temperatura obtidos experimentalmente usando termopares e imagens térmicas. Os principais subsistemas da máquina foram inicialmente modelados, como o conjunto de fusos de esferas, guias lineares e motofuso, o que permitiu posteriormente a validação do comportamento termoelástico da máquina completa para onze ciclos de trabalho em vazio, seis ciclos de usinagem, nove ciclos de posicionamento e dois ciclos com temperatura ambiente variando, obtendo erros máximos inferiores a 9%, ao comparar os resultados numéricos com os resultados experimentais. A validação do modelo em elementos finitos permitiu usar os resultados obtidos para treinar e validar uma rede neural artificial (RNA) para prever os erros térmicos do centro de usinagem. Os desvios entre os erros térmicos previstos pela RNA e os calculados pelo MEF foram inferiores a 5%. Baseado nos resultados obtidos pelas medições das peças de trabalho usinadas foi possível formular e implementar um modelo de compensação dos erros térmicos no CNC do centro de usinagem, que obteve uma redução dos erros entre 62% e 100% nas peças usinadas com compensação. Foi também proposto um algoritmo de previsão e compensação dos erros térmicos para o centro de usinagem, baseado em todos os ciclos e simulações realizadas, e que se comparando com os resultados experimentais mostrou-se capaz de reduzir os erros térmicos entre 50% e 95%. Após sua validação, foi possível concluir que o algoritmo desenvolvido é uma ferramenta precisa e robusta para compensar os erros térmicos da máquina para várias condições de trabalho, podendo compensá-los mesmo com esta movendo-se a diferentes velocidades, em usinagem ou mesmo operando em temperatura ambiente variável. / This thesis aims to develop an accurate and robust algorithm capable of compensating the volumetric thermal errors of a 5-axis machining center under different operating conditions. The thermal behavior of the machine was first modeled using finite element method (FEM) techniques based on theory of friction heat and convection heat, and validated with the various experimentally raised temperature fields using thermocouples and thermal imaging. The main machine subsystems were initially modeled, such as the ball screw system, linear guides and spindle, which allowed for validating of the thermoelastic behavior of the entire machine for eleven no load duty cycles, six cycles of machining, nine cycles of positioning and two cycles with varying ambient temperature, obtaining errors lower than 9%, when comparing the numerical results with the experimental results. The validation of the finite element model allowed for the use of the results obtained to train and validate an artificial neural network (ANN) for predicting the thermal errors of the machining center. The deviations between the thermal errors predicted by ANN and the FEM simulation results were less than 5%. Based on the results obtained by the measurements of the machined workpieces, it was possible to formulate and implement a model of compensation of the thermal errors in the CNC of the machining center, which obtained a reduction of errors of 62% and 100% of the machined parts with compensation. It was also proposed a thermal error prediction and compensation algorithm for the machining center, based on all cycles and simulations performed, and that, comparing with the experimental results, it was able to reduce the thermal errors between 50% and 95%. After its validation, it was possible to conclude that the developed algorithm is an accurate and robust tool to compensate the thermal errors of the machine for various duty conditions, being able to compensate the errors even when it is moving at different speeds, in machining process or even operating in variable ambient temperature.

A piezoelectric impedance-based structural health monitoring technique was developed at the Center for Intelligent Material Systems and Structures. It has been successfully implemented on several complex structures to detect incipient-type damage such as small cracks or loose connections. However, there are still some problems to be solved before full scale development and commercialization can take place. These include: i) the damage assessment is influenced by ambient temperature change; ii) the sensing area is small; and iii) the ability to identify the damage location is poor. The objective of this research is to solve these problems in order to apply the impedance-based structural health monitoring technique to real structures. First, an empirical compensation technique to minimize the temperature effect on the damage assessment has been developed. The compensation technique utilizes the fact that the temperature change causes vertical and horizontal shifts of the signature pattern in the impedance versus frequency plot, while damage causes somewhat irregular changes. Second, a new impedance-based technique that uses multiple piezoelectric sensor-actuators has been developed which extends the sensing area. The new technique relies on the measurement of electrical transfer admittance, which gives us mutual information between multiple piezoelectric sensor-actuators. We found that this technique increases the sensing region by at least an order of magnitude. Third, a time domain technique to identify the damage location has been proposed. This technique also uses multiple piezoelectric sensors and actuators. The basic idea utilizes the pulse-echo method often used in ultrasonic testing, together with wavelet decomposition to extract traveling pulses from a noisy signal. The results for a one-dimensional structure show that we can determine the damage location to within a spatial resolution determined by the temporal resolution of the data acquisition. The validity of all these techniques has been verified by proof-of-concept experiments. These techniques help bring conventional impedance-based structural health monitoring closer to full scale development and commercialization. / Master of Science

In this study, we propose a multi-walled carbon nanotube epoxy composite sensor for force and pressure sensing in the range of 50 N–2 kN. A manufacturing procedure, including material preparation and deposition techniques, is proposed. The electrode dimensions and the layer thickness were optimized by the finite element method. Temperature compensation is realized by four nanocomposites elements, where only two elements are exposed to the measurand. In order to investigate the influence of the filler contents, samples with different compositions were prepared and investigated. Additionally, the specimens are characterized by cyclical and stepped force/pressure loads or at defined temperatures. The results show that the choice of the filler content should meet a compromise between sensitivity, temperature influence and noise behavior. At constant temperature, a force of at least 50N can be resolved. The measurement error due to the temperature influence is 150N in a temperature range of –20°C–50°C.

Le suivi de la déformation de la croûte terrestre durant la phase intersismique pour la recherche des transitoires nécessite des instruments précis capables d'opérer pour de très longues durées. Le projet ANR-LINES a visé le développement de trois nouveaux instruments : un sismomètre mono-axial, un inclinomètre hydrostatique à longue base et un inclinomètre de forage pendulaire. Ces trois instruments profitent d'un capteur interférométrique de déplacement à longues fibres optiques du type Fabry-Pérot Extrinsèque (EFFPI). Leurs architectures mécaniques et l'utilisation de longues fibres permettent à ces instruments géophysiques nouvellement fabriqués d'atteindre les objectifs fixés.Le premier objectif de cette étude est de proposer des méthodes adaptées à l'estimation de la phase du chemin optique dans les cavités Fabry-Pérot. Une modulation du courant de la diode laser, suivie par une démodulation homodyne du signal d'interférence et un filtre de Kalman permettent de déterminer la phase en temps réel. Les résultats sont convaincants pour des mesures de courtes durées mais exigent des solutions complémentaires pour se prémunir des effets de la variation des phénomènes environnementaux.Le capteur EFFPI intégré dans l'inclinomètre de forage LINES lui offre l'opportunité d'établir une mesure différentielle de l'oscillation de la masselotte pendulée grâce à trois cavités Fabry-Pérot. Le sismomètre LINES utilise lui aussi le capteur de déplacement EFFPI pour la mesure du déplacement de sa bobine. Une description de l'architecture mécanique de ces instruments et une analyse des phénomènes détectés (mouvements lents, marées, séismes, microséismes . . . ) font partie de cette thèse. / Monitoring crustal deformation during the interseismic phase when searching for earth transients requires precise instruments able to operate for very long periods. The ANR-LINES project aimed to develop three new instruments: a single-axis seismometer, a hydrostatic long base tiltmeter and a borehole pendulum tiltmeter. These three instruments benefit of an extrinsic Fabry-Pérot interferometer (EFFPI) with long optic fibers for displacement detections. Their mechanical architectures and their disposal of long fibers help these newly manufactured geophysical instruments complete their goals.The first objective of this study is to propose appropriate methods for estimating the phase of the optical path in the Fabry-Pérot cavities. A modulation of the laser diode current, followed by a homodyne demodulation of the interference signal and a Kalman filter, allow determining the phase in real time. The results are convincing while taking short periods measurements but require additional solutions for protection against environmental phenomena variations. The EFFPI sensor integrated in the LINES borehole tiltmeter gives it the opportunity to establish a differential measurement of the bob's oscillation thanks to three Fabry-Perot cavities. The LINES seismometer also uses the EFFPI displacement sensor to measure its coil's displacement. A description of the two instruments' mechanical structures and an analysis of the detected phenomena (slow movements, tides, earthquakes, microseisms . . . ) are part of this thesis.Keywords: Laser interferometry, wavelength modulation, synchronous homodyne demodulation, ellipse fitting, Kalman filter, temperature compensation, borehole tiltmeter, simple pendulum, differential measurements, slow drift, seismicobservations, seismometer.

Ce travail avait pour objet d’étudier les propriétés d’horloge et de synchronisation de la peau, un modèle potentiel d’horloge périphérique. L’activité rythmique a été analysée par bioluminescence en temps réel, sur des explants de peau abdominale et des fibroblastes dermiques primaires, isolés à partir de rats transgéniques Per1-luciférase. Nous avons montré que des explants de peau présentent une activité rythmique soutenue en culture, indiquant une importante synchronisation interne dans le tissu. Cette synchronisation se manifeste au cours du développement post-natal à partir de 1 mois et augmente jusqu’à 6 mois, avant de décroître, laissant place à des rythmes altérés à l’âge de 2 ans. Nous avons aussi établi que les fibroblastes dermiques présentent la propriété de compensation thermique commune à toutes les horloges circadiennes, et qu’ils sont potentiellement synchronisables par la mélatonine puisque celle-ci augmente leur amplitude en culture. Nous avons aussi préparé un vecteur lentiviral exprimant le gène rapporteur luciférase sous le contrôle du promoteur du gène horloge Bmal1, un nouvel outil pour compléter l’étude des rythmes dans les cellules de la peau. / This work aimed to investigate the skin as a potential model of peripheral clock by characterizing its rhythmic and synchronization properties. Circadian activity was examined in abdominal skin explants and fibroblasts derived from Per1-Luciferase transgenic rats by real-time recording of bioluminescence. First, the skin clock was characterized from early postnatal to old age. Low amplitude oscillations appeared at 1 month only and their robustness increased until 6 months. In 1-2 year-old rats, skin circadian rhythms showed decreasing amplitude and abnormal cycles. Primary fibroblasts derived from the skin at the same ages demonstrated similar pattern of clock activity. Temperature compensation, an intrinsic clock feature, was shown the first time in skin and primary fibroblasts. Secondly, we demonstrated a phase-dependent effect of melatonin to increase the amplitude of oscillations in skin primary fibroblasts, indicating it displays a synchronising role in the circadiansystem. Finally, to facilitate our studies on the multioscillatory skin tissue, we constructed a lentivirus carrying a Bmal1-luciferase reporter, to measure clock genes activities in human skin cells.

This dissertation reports very novel solutions for the trimming and compensation of various parameters of silicon micromechanical resonators and resonator-arrays. Post-fabrication trimming of resonance frequency to a target value is facilitated by diffusing in a deposited thin metal layer into a Joule-heated silicon resonator. Up to ~400 kHz of trimming-up and trimming-down in a 100 MHz Silicon Bulk Acoustic Resonators (SiBARs) are demonstrated via gold and aluminum diffusion respectively. The dependence of the trimming range on the duration of Joule heating and value of current passed are presented and the possibility of extending the trimming range up to ~4 MHz is demonstrated. Passive temperature compensation techniques are developed to drastically reduce the temperature coefficient of frequency (TCF) of silicon resonators. The dependence of TCF on the charge carriers in silicon are extensively studied and exploited for the very first time to achieve temperature compensation. A charge surplus via degenerate doping using boron and aluminum is shown to reduce a starting TCF of -30 ppm/°C to -1.5 ppm/°C while a charge depletion effected by creating multiple pn-junctions reduces the TCF to -3 ppm/°C. Further, shear acoustic waves in silicon microresonators have also been identified to effect a TCF reduction and have been excited in a concave SiBAR (or CBAR) to exhibit a TCF that is 15 ppm/°C lesser than that of a conventional rectangular SiBAR. The study on quality factor (Q) sensitivity to the various crystallographic axis of transduction in silicon resonators show that the non-repeatability of Q across various fabrication batches are due to the minor angular misalignment of ≤ 0.5° during the photolithography processes. Preferred axes of transduction for minimal misalignment sensitivity are identified and novel low-loss resonator-array type performances are also reported from a single resonator while transduced along certain specific crystallographic axes. Details are presented on an unprecedented new technique to create and fill charge traps on the silicon resonator which allows the operation of the capacitive SiBARs without the application of any polarization voltages (Vp) for the first time, making them very attractive candidates for ultra-low-power oscillator and sensor applications. Finally, a fabrication process that integrates both the capacitive and piezoelectric actuation/sensing schemes in microresonators is developed and is shown to compensate for the parasitics in capacitive silicon resonators while maintaining their high-Q.