Micromachined microphones with diffraction-based optical displacement detection are presented. A compliant membrane is made part of a phase sensitive diffraction grating, and the deflection resulting from external acoustic pressure alters the intensities of the diffracted orders which are monitored with integrated photodiodes. The scheme provides the displacement sensitivity of a Michelson interferometer and can be integrated without beam splitters or critical alignment problems into volumes on the order of 1mm³. The method is implemented and characterized using microphone membranes with integrated diffraction grating back electrodes fabricated on silicon using Sandia National Laboratories' dedicated processing platform. Detailed response characterization in both air and vacuum environments is performed to extract the diaphragm properties and high frequency cutoff frequencies of the microphone. Results from a finite element model of the microphone structure are in good agreement with measured data. The sensor's internal noise is characterized with measurements performed in the anechoic acoustic test facility at Georgia Tech. While utilizing 2.4mW of laser power, an (A) weighted displacement resolution of 6×10⁻⁴Å/√Hz is measured which is limited by thermal acoustic noise caused by the microphone's back-plate flow resistance.

Thesis (Ph. D.)--Auburn University. / Abstract. Vita. Includes bibliographical references (p. 118-124).

Thesis Presented for the Degree of Magister Technologiae in the Department of Electrical Engineering Cape Peninsula University of Technology 2006 / Because of the nature of piezoelectric ceramics and the physical construction pf high power piezoelectric transducers, such devices are inherently non-linear and become unpredictable when driven at high power. To drive an ultrasonic transducer or an array thereof efficiently, specific resonant points are used. These poin~s are characterised by the devices' mechanical modes of oscillation. At high electrical power levels, the resonance points of PZT transducers vary. The movement of the resonances points in the frequency domain, coupled with the transducers high Q, is severe enough to seriously hamper the devices' efficiency. The problem is specifically apparent when multiple transducer arrays are driven at power. The electrical fluctuations and interactions of the characteristics of separate transducers cause arrays to be driven efficiently at a single resonance point. To efficiently drive an array of PZT transducers it is necessary to employ a .suitable technique. Although several methods exist in the literature, each is designed for a specific configuration of transducers and dedicated matching circuitry. The fundamental flaw in most methods is that they are conceived with the assumption all PZT transducers are identical and can be driven as such. Inherent nonlinearities caused by poling and construction methods, result in each transducer to be slightly different causing a superposition of resonance frequencies for each transducer array. Existing methods cannot be used to efficiently drive generic transducer arrays and a novel approach has been adopted to accommodate transducer nonlinearities. This novel approach can be described as a culmination of two driving techniques and has been named, Swept Frequency Dwelling (SFD). This thesis examines five different driving techniques and quantifies their effectiveness by means of experimental evaluation proficiencies. The driving techniques are grouped into two categories - straight driving techniques and frequency sweeping techniques - which are compared and evaluated. In conclusion, a novel method for driving ultrasonic transducer arrays was established with the aim of eliminating some detrimental effects of other driving techniques, while exploiting some of their positive attributes and was found to be effective.

Fundamental to the design of intelligent material systems and structures are the realization of attributes of the constitutive transducer materials—the sensors and actuators—and the ability to model the characteristics of these transducers. In this thesis, electromechanical behaviors of the electrostrictive relaxor ferroelectric lead magnesium niobate-lead titinate (PMN-PT) are experimentally characterized and phenomenologically modeled. The dependencies of PMN-PT electromechanical transduction on temperature and frequency, characteristics of relaxor ferroelectrics, and on applied direct-current electric field, an attribute of electrostrictors which enables tunable transduction sensitivities, are investigated and modeled with respect to electrical, sensing, and actuation properties. A general procedure for using the developed constitutive models to quantitatively describe the behavior of PMN-PT is introduced for sensing and for the three types of actuation—servo, on/off, and alternating current. / Master of Science

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Du, Xiaona. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 65-74). / Abstracts in English and Chinese. / ABSTRACT --- p.i / 摘要 --- p.iii / ACKNOWLEDGEMENTS --- p.iii / TABLE OF CONTENTS --- p.iv / LIST OF FIGURES --- p.xi / LIST OF TABLES --- p.ix / Chapter CHAPTER ONE --- INTRODUCTION --- p.1 / Chapter 1.1 --- Background --- p.2 / Chapter 1.1.1 --- Development of portable devices --- p.2 / Chapter 1.1.2 --- Energy harvesting --- p.2 / Chapter 1.1.3 --- Piezoelectric energy harvesting --- p.5 / Chapter 1.1.4 --- Impact based piezoelectric energy harvester --- p.10 / Chapter 1.1.5 --- Operation of piezoelectric materials --- p.14 / Chapter 1.2 --- Research Objective --- p.16 / Chapter 1.3 --- Thesis Organization --- p.19 / Chapter CHAPTER TWO --- DESIGN AND MODELING OF AN EXTENDED ROTARY ENERGY HARVESTER --- p.20 / Chapter 2.1 --- Design Considerations of an Extended Rotary Energy Harvester --- p.20 / Chapter 2.2 --- Models of Rotary Energy Harvesters --- p.24 / Chapter 2.3 --- Simulation Results --- p.33 / Chapter 2.4 --- Chapter Summary --- p.37 / Chapter CHAPTER THREE --- "PROTOTYPE, TESTING AND OUTPUT POWER OF EXTENDED ROTARY ENERGY HARVESTER" --- p.38 / Chapter 3.1 --- Prototype and Experiment --- p.38 / Chapter 3.2 --- Output Power --- p.44 / Chapter 3.2.1 --- Maximum tip displacement on output power --- p.44 / Chapter 3.2.2 --- Rotational frequency on output power --- p.47 / Chapter 3.3 --- Chapter Summary --- p.50 / Chapter CHAPTER FOUR --- COMPARISON BETWEEN E-REH AND REH --- p.51 / Chapter 4.1 --- Force on Output Power --- p.52 / Chapter 4.2 --- Rotational Frequency on Output Power --- p.54 / Chapter 4.3 --- Comparison on Design Space --- p.59 / Chapter 4.4 --- Chapter Summary --- p.62 / Chapter CHAPTER FIVE --- CONCLUSION AND FUTURE WORK --- p.63 / Chapter 5.1 --- Conclusion --- p.63 / Chapter 5.2 --- Future Work --- p.64 / BIBLIOGRAPHY --- p.65

Nonlinear acoustic media for implementations of parametric generation of low frequencies has so far been restricted to small values of the parameter B/A, typically between 3 and 13. Parametric amplification, defined as the generation of a low difference frequency signal resulting from the nonlinear interactions of two higher frequency fundamentals is enhanced by medium with a large coefficient of nonlinearity and low sound speed. The acoustic properties of a highly nonlinear medium were estimated and introduced in a numerical model, to evaluate the parametric amplification induced by a thin layer of such material in contact with a spherical transducer. The numerical model predicted a significant enhancement of the sound pressure level for the difference frequency component relative to that obtained when the transducer is driven linearly at the difference frequency. A source was then constructed to compare the theoretical predictions with experimental values and an enhancement of 17dB compared to the linear operation of the transducer was measured. The difference between the parametric amplification achieved with the nonlinear medium and the parametric amplification that would be obtained in water is 73dB.

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