The master’s thesis deals with the proposal of microactuator based on SMART material. The thesis opens with the comparison of SMART materials which are suitable for actuator construction from the point of view of a reaction on stimulation in form of deformation. Subsequent part of the thesis is the report theory of piezoelectric effect, it also describes direct and indirect effects and it concerns about the description of piezoelectric materials. The thesis focuses on several principles of piezoactuators and motors. The last part of the thesis includes modeling and simulation of piezoelectric material in program ANSYS 13.0 and dimensioning geometric of actuator with evaluation of impact of parameters on final motion.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Chemistry / Master / Master of Philosophy

A frequency self-tuning energy harvesting methodology is proposed to achieve efficient energy harvesting. To simulate the self-tuning process, a theoretical model of the harvester made of an aluminum beam bonded with piezoelectric patches is developed for numerical simulation. The energy harvesting is realized by converting ambient vibration to electric charge through piezoelectric patches on the host beam. To accomplish the frequency self-tuning process, a control voltage is applied on a piezoelectric stack actuator to tune the natural frequency of the beam harvester matching the major excitation frequency of the ambient vibration with large power generation. Two tuning methods with different electric circuits are developed to find the efficient and feasible self-tuning process, which is then further verified by the finite element method. Research findings show that the optimal frequency self-tuning method significantly increases the power output from the harvester by more than 26 times compared with the one without tuning. / October 2016

Following the studies of natural frequency based damage detection methods, an advanced technique for damage detection and localization in beam-type structures using a vibration characteristic tuning procedure is developed by an optimal design of piezoelectric materials. Piezoelectric sensors and actuators are mounted on the surface of the host beam to generate excitations for the tuning via a feedback process. The excitations induced by the piezoelectric effect are used to magnify the effect of the damage on the change of the natural frequencies of the damaged structure to realize the high detection sensitivity. Based on the vibration characteristic tuning procedure, a scan-tuning methodology for damage detection and localization is proposed. From analytical simulations, both crack and delamination damage in the beams are detected and located with over 20% change in the natural frequencies. Finite element method (FEM) simulations are conducted to verify the effectiveness of the proposed methodology. / October 2016

Piezoelectric energy harvester has become a new powering choice for small electronic device. Due to its piezoelectric effect, electric energy can be obtained from ambient vibrations. This thesis is intending to build a frequency-adjustable piezoelectric energy harvester system. The system is structured with two piezoelectric bimorph beams, which are connected to each other by a spring. The feasibility of the frequency-adjustable piezoelectric energy harvester has been proved by investigating effects of the spring, loading mass and impedance on the operation frequencies.

Superhydrophobicity refers to surfaces with extremely large water droplet contact angles (usually greater than 150°). This phenomenon requires a hydrophobic material with micro or nano-scale roughness. Superhydrophobic surfaces exist in nature (e.g. the lotus leaf) and can be produced synthetically. This project focuses on the development and characterization of superhydrophobic materials with tunable wettability (i.e. smart superhydrophobic materials). In this study, surfaces were prepared by electrospinning thin, aligned polystyrene fibers onto a piezoelectric unimorph substrate. Results showed electric field induced changes in substrate curvature, which produced corresponding changes in surface wettability. From experiments, an average change in water contact angle of 7.2° ± 1.2° with 90% confidence was observed in ~2μm diameter fiber coatings electrospun for 5 minutes with applied electric field. In addition, fiber coatings electrospun with equivalent deposition showed average electric field induced changes in WCA of 2.5° ± 0.92° for lower diameter fibers (~1μm) and 3.5° ± 1.37° for higher diameter fibers (~2μm) with 90% confidence.

Piezoelectric composites have been investigated for use in a variety of areas, including flow control, structural control, energy harvesting, and fuel ignition systems. While many of the investigations conducted in these areas have utilized traditional piezo actuation systems, such as unimorphs or stack actuators, a growing number of research groups are examining the increased performance derived from the mechanical advantage, and enhanced domain rotation, found in prestressed unimorph designs. Prestressed devices, like Thunder® and LIPCA, have been shown well suited for a number of applications; however, the price associated with these devices can often prevent them from being implemented. In an effort to produce a low cost unimorph device that possesses a performance-enhancing curved form, the present investigation presents a novel technique for manufacturing prestressed piezoelectric actuators that are capable of meeting the same high displacement and load bearing capabilities exhibited by conventional prestressed devices. The newly proposed mechanically prestressed composite device, or MPC, is similar in form and function to well-documented thermally prestressed devices like Thunder®. However, rather than deriving its characteristic curved form from a thermally induced stress, the present class of devices relies on the resorting force incited in the piezoelectric ceramic upon adhesion to a mechanically deformed substrate to provide both the performance-enhancing prestress and final form of the device. To aid in refinement of the newly proposed design, beam theory was used to model the stress developed within the device. The model allowed designers to investigate the limitations imposed on the performance-enhancing curved form of the device by the stresses developed in the ceramic as a result of the curvature. Findings derived from the model were experimentally verified before a finalized design was specified for the composite, and a number of devices were manufactured. An initial characterization of the device was carried out based on the composite's response to mechanical and electrical loading. By determining the slope of the electrically and mechanically induced displacement response of the device, the investigation was able to define the center displacement constant and effective spring constant of the unimorph. These parameters not only allow designers to predict the displacement that will occur in response to a given electric field or tensile load, but also to allow for comparison with various devices. In the present investigation, the performance characteristics of mechanically prestressed composites were assessed as a function of substrate thicknesses and adhesive properties. With composites constructed using substrates approximately 9.2cm in length, devices were found to have typical center displacement constants on the order of 1.59 to 7.78kV/mm2 while retaining an effective stiffness between 4.5 to 7.5N/mm. These values were found to be similar to the .71 to 3.85kV/mm2 center displacement constants demonstrated by similarly sized and shaped Thunder® devices, which posses an effective stiffness in the range of 10 to 16.3N/mm. A comprehensive presentation of the test methods and procedures used to determine these values, along with other performance characteristics, are provided.

The goal of this thesis is to design, build and test a new measurement system for comprehensive studies of the magnetoelectric and the converse magnetoelectric effect. The research on multiferroic composites is an emerging field of research and there is no commercially available equipment. The method proposed here for testing magnetoelectric properties of the multiferroics is relatively inexpensive and versatile. The advantage of the new method described below is that the same set of instruments in different configurations enables multiple measurements of various parameters characterizing multiferroic composites. The system was tested using two samples Fe78Si10B12/AIN and Fe78Si10B12/PZT consisting of ferromagnetic and magnetostrictive ribbon of metallic glass glued to piezoelectric AlN or PZT. The final result was a working system that enables selective measurements of different responses of the multiferroic composites to the static and dynamic electric and magnetic fields. This demonstrates the versatility of the system. Magnetoelectrical effect, Piezoelectric, Piezomagnetic, magneticmechanical, electromechanical, magnetoelectrical measurement

by Fei Yang. / Title also in Chinese characters. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves 92-96). / ACKNOWLEDGEMENTS --- p.i / ABSTRACT --- p.ii / TABLE OF CONTENT --- p.iii / Chapter CHAPTER I. --- INTRODUCTION --- p.1 / Chapter §1.1 --- The Background of Pulsed Laser Ablation --- p.1 / Chapter §1.2 --- Properties of PZT --- p.3 / Chapter §1.3 --- Objectives of This Thesis --- p.7 / Chapter CHAPTER II. --- INTERACTION OF PULSED LASER RADIATION WITH A SOLID TARGET --- p.8 / Chapter §2.1 --- Introduction --- p.8 / Chapter §2.2 --- Absorption of Laser Radiation by the Target --- p.9 / Chapter §2.3 --- Absorption of Laser Radiation by the Plume --- p.11 / Chapter §2.4 --- Ablation Depth and Ablation Rate --- p.12 / Chapter §2.5 --- Formation and Evolution of the Plume --- p.14 / Chapter (a) --- Small-time Solution (c´Øt ζ) --- p.15 / Chapter (b) --- Large-time Solution (c´Øt ζ) --- p.15 / Chapter §2.6 --- Piezoelectric Signal --- p.17 / Chapter §2.7 --- Angular Distributions --- p.21 / Chapter §2.8 --- Target Surface Temperature --- p.26 / Chapter CHAPTER III. --- EXPERIMENTAL TECHNIQUES --- p.27 / Chapter §3.1 --- Pulsed Laser System --- p.27 / Chapter §3.2 --- Setup for Piezoelectric Detection of Laser Pulse --- p.28 / Chapter §3.3 --- Setup for Optical Measurement of Laser Plasma --- p.30 / Chapter §3.4 --- Setup for Ion Detection --- p.32 / Chapter §3.5 --- Sample Preparation --- p.35 / Chapter CHAPTER IV. --- PIEZOELECTRIC DETECTION OF LASER ABLATION --- p.38 / Chapter §4.1 --- Laser Ablation of a Piezoelectric Target --- p.38 / Chapter §4.1.1 --- Pyroelectric Effect --- p.38 / Chapter §4.1.2 --- Laser-induced Piezoelectric Signal (LIPS) --- p.39 / Chapter §4.2 --- Propagation of LIPS --- p.41 / Chapter §4.3 --- Laser Ablation Threshold --- p.45 / Chapter §4.4 --- Ablation Rate Measurement by LIPS --- p.47 / Chapter §4.5 --- Temperature Dependence of LIPS --- p.53 / Chapter §4.5.1 --- The Polarization Measurement --- p.53 / Chapter §4.5.2 --- The Piezoelectric Coefficient --- p.56 / Chapter CHAPTER V. --- STUDIES OF LASER PLASMA BY FARADAY PROBE METHOD --- p.59 / Chapter §5.1 --- Angular Distribution of The Plume Density --- p.59 / Chapter §5.2 --- The Plume Ionization Fraction --- p.64 / Chapter §5.3 --- The Plume Velocity Distribution and The Plume Temperature --- p.72 / Chapter §5.4 --- The Target Surface Temperature --- p.82 / Chapter §5.5 --- Plume Orientation Determination --- p.85 / Chapter CHAPTER VI. --- OVERALL CONCLUSION --- p.90 / REFERENCES --- p.92