Piezoelectric materials have been widely used in applications such as transducers, acoustic components, as well as motion and pressure sensors. Because of the material’s biocompatibility and flexibility, its applications in biomedical and biological systems have been of great scientific and engineering interest. In order to develop piezoelectric sensors that are small and functional, understanding of the material behavior is crucial. The major objective of this research is to develop a test system to evaluate the performance of a sensor made from polyvinylidene fluoride and its uses for studying insect locomotion and behaviors. A linear stage laboratory setup was designed and built to study the piezoelectric properties of a sensor during buckling deformation. The resulting signal was compared with the data obtained from sensors attached a cockroach, Blaberus discoidalis. Comparisons show that the buckling generated in laboratory settings can be used to mimic sensor deformations when attached to an insect. An analytical model was also developed to further analyze the test results. Initial analysis shows its potential usefulness in predicting the sensor charge output. Additional material surface characterization studies revealed relationships between microstructure properties and the piezoelectric response. This project shows feasibility of studying insects with the use of polyvinylidene fluoride sensors. The application of engineering materials to insect studies opens the door to innovative approaches to integrating biological, mechanical and electrical systems.

This research investigates a novel class of active materials for energy and sensing applications. Magnetocaloric alloys, Gd5Si2Ge2, were developed into a composite with poly(vinylidine flouride) (PVDF), piezoelectric polymer. The giant megnetocaloric property combined with the piezoelectricity creates extraordinary properties for composite materials. The research approach was primarily experimental. Activities include synthesis, characterization, and device design and evaluation. Using the arc melting method, the magenetocaloric samples were created. Multi-length scales characterized using atomic force microscopy (AFM), optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-Ray diffraction (XRD), and X-Ray Photoelectron spectroscopy (XPS). The prototype devices were evaluated for their power generation and efficiency. Through those techniques, the fundamental understanding in the new materials was obtained. The relationships between process-microstructures, microstructure-properties, and structure-power generation were established. Results showed that the phase transformation of the magnetocaloric material at its Curie temperature induced a significant increase in power generation in the peizeoelectric polymer. Such transition was also beneficial for a laminated device for energy harvesting. In addition, it was found that the oxidation that occurred during high temperature melting stabilized the orthorhombic phase at room temperature. The multifunctional composites as well as the laminated structure use the thermal expansion of the magnetocaloric material for energy harvesting, cyclic monitoring, and/or thermal switching. This thesis consists of six chapters. Chapter I provides a history and explanation of the materials used. Chapter II provides an explanation of the motivation for this work. Chapter III addresses the experimental procedures. The results of which are presented in Chapter IV and discussed in Chapter V. The research is summarized and future recommendations are given in Chapter VI.

Piezoelectric energy harvesting is the process of taking an external mechanical input and converting it directly into electrical energy via the piezoelectric effect. To determine the power created by a piezoelectric energy harvester, a specific application with defined input and design constraints must first be chosen. The following thesis established a concept design of a hydrokinetic energy harvesting system, the piezoelectric artificial kelp (PAK), which uses piezoelectric materials to harvest coastal ocean waves while having a beneficial impact on the surrounding environment. The harvester design mimics the configuration of sea-kelp, a naturally occurring plant that anchors to the ocean floor and extends into the water column. Underwater currents caused by wave-action result in periodic oscillations in the kelp. In order to determine the average power generated by this design concept, predictive tools were devised that allowed for the determination of the optimized average power produced by the piezoelectric energy harvester. For a stiff energy harvester, the linear differential equations were analytically solved to find an equation for the average power generated as a function of design parameters. These equations were used to compare the effect on power output of the design configuration and piezoelectric material choice between a piezopolymer (PVDF) and a piezoceramic (PZT). The homogeneous bimorph was found to have the optimal design configuration and it was shown that a harvester constructed using PVDF would produce approximately 1.6 times as much power as one using PZT. For a flexible energy harvester, an iterative nonlinear solution technique using an assumed polynomial solution for the local curvature of the energy harvester was used to verify and extend the analytic solutions to large deflections. An energy harvester was built using off-the-shelf piezoelectric elements and tested in a wave tank facility to validate experimentally the voltage and average power predicted by the analytical solution. The iterative code showed the PAK harvester to produce volumetric power on the order of other energy harvesting concepts (17.8 micro [mu]W/cm³). Also, a full-scale PAK harvester approximately ten meters long in typical wave conditions was found to produce approximately one watt of power.

Abstract This paper reports about a precision positioning XY stage utilizing flexure hinges and piezoelectric actuators. XY stage was designed with the aim of reducing the stress-concentration of flexure hinges and the low interference between two actuating axes. Utilized the expression of matrix to figure out the properties of the bellow-type flexure hinges, and proved these by mathematical software. Experiments demonstrated that the stage actuated by a stairstep driving signal with maximum displacement 1.3£gm and interference 50nm along X axis; along Y axis with maximum displacement 0.8£gm and interference 11nm. The stage actuated by a ramp signal with maximum displacement 1.2£gm and interference 45nm along X axis; along Y axis with maximum displacement 0.9£gm and interference 35nm. The finite element method (FEM) was used to analyse the stress-concentration of the stage. and the simulated results were compared with the experiments. Referred to the testing results, the target object could be moved in the aimed position accurately.

In order to understand the dynamic characteristics of an ultrasonic motor stator, we proposed a modified two- dimensional axisymmetric finite element model to analyze the three-dimensional vibrational problem of piezoelectric annular and circular plates. In this work, displacement fields are properly assumed and the electric effect is included. Following the finite element method, analyses of axisymmetric and nonaxisymmetric vibration of circular and annular plate, and also the stator of ultrasonic motors can be conducted in a convenient way. Natural frequency, location of contact point and elliptic locus of the stator are then calculated. Effects by different geometry design and selected circumferential wave number are discussed. Comparisons of some typical examples are made between the present work and those available in the literature.

This thesis research focuses on the characterization of thinfilms made of poly(vinylidene fluoride) (PVDF) using an atomic force microscope. Thinfilms of PVDF were fabricated by a spin coating method with different conditions and characterized using the Atomic Force Microscopy (AFM) for morphological changes. Phase and conformational changes of PVDF were investigated using both wide angle X-ray diffraction (WAXD) and Fourier Transform Infrared Spectroscopy (FTIR). From this analysis, in-situ corona poling with annealing of spin-cast PVDF enabled a phase change from α to the mixture of β and γ phases. This process can decrease the complexity of the conventional method which requires mechanical stretching before poling PVDF in addition to thermal annealing for β phase transformation. This thesis describes some materials and surface properties of solution-cast PVDF thinfilms with various conditions such as topography and phase image, adhesion force, friction force, and roughness. Through the AFM topography and phase images, polymeric behavior and spherulites are discussed in the later part of the thesis.

In this study, T-ladder type thin film bulk acoustic wave filters had been fabricated based on thin film bulk acoustic wave resonators. The titanium (Ti) seeding layer and platinum (Pt) for bottom electrode were deposited on silicon substrates by a dual-gun DC sputtering system. Field-emission scanning electron microscopy, atomic force microscopy and the four-point probe method showed that the Pt bottom electrode deposited on the Ti seeding layer exhibited favorable characteristics, such as a surface roughness of 0.69 nm and a sheet resistance of 2.27 £[/¡¼. The ZnO piezoelectric film was deposited using the two-step deposition method by RF magnetron sputtering. Field-emission scanning electron microscopy, atom force microscopy and X-ray diffraction revealed that ZnO piezoelectric film exhibited excellent characteristics, such as a the high preferred c-axis orientation and a rigidly precise surface structure with surface roughness of 7.37 nm. The wet etching process is adopted to fabricate cavity of device. The concentration of 30 wt% KOH and etching temperature of 100 ¢J had been indicated appropriate for etching processes. Finally, the top electrodes of the devices are varied to approach the performances of device applications. The results showed the highest coupling coefficient (kt2) of FBAR device can be obtained using platinum top electrode. The high coupling coefficient of FBAR device is appropriate for wide passband filter. The annealing processes had been used in order to improve the characteristics of piezoelectric films. The stress of ZnO film has been improved from -1.656 Gpa to 0.611 Gpa through the annealing process. At the annealing temperature of 400¢J, the ZnO piezoelectric film exhibited excellent characteristics, such as a large grain size with smooth surface. The quality factor of FBAR device using ZnO film with 400¢J annealing was better than that without annealing. The optimal conditions of fabrication processes are adopted to fabricate top electrode, bottom electrode and piezoelectric film. The T-ladder type FBAR band pass filter was constructed by FBAR resonators. The frequency response is measured using an HP8720 network analyzer and a CASCADE probe station. The 3-dB bandwidth, insertion loss and band rejection of the T-ladder type thin film bulk acoustic wave filter are 79MHz, -3.5 dB and 8.4dB at 2,379MHz, respectively.

The present study developes a mixed finite element formulation for the analysis of piezoelectric circular and annular plates. This formulation combines the conventional displacement-electric potential type variational principle and the piezoelectric Reissner`s principle with a weighting factor which represents ratio of weights imposed on the above two variational principles, and which can be adjusted by comparing with experiment results. With this formulation, stresses and electric displacements, like displacements and electric potential, are primary variables and are continuous across elements and element interfaces. Also, all displacement, stress, electric displacement, and electric potential boundary conditions can be easily and exactly imposed. Static deformations and vibration frequencies of some typical piezoelectric circular and annular plates are then obtained with the present approach and are compared with those by other methods. Based on experiment results in the literature, it is found that better results could be obtained in general by the present mixed finite element formulation than the others when 1 is chosen as the weighting factor.

In this thesis, the study focuses on the antenna design for integrated passive devices. By using the substrate of piezoelectric material with high permittivity and introducing the fractal structures, the size reduction is obtained. Part of the research analyzes the influences of the surrounding environment on the antenna performances, including the effects of external formations, internal components, and interconnections. The results can provide the design rules for developing IPD antennas. The other part of the research emphasizes the design of IPD antenna itself, involving the investigations on the characteristics of substrate and fractals. The trade-off between compactness and radiation efficiency is pointed out, and then a design of modified ground plane is presented. When the modified design is placed on the system ground plane that exists in real system, the radiation efficiency can be improved significantly. Therefore, the concept of the compact IPD antenna is achieved.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keyword: turbulence. Includes bibliographical references (p. 75-78).