Electromechanical Coupling Analysis And Structural Design On Novel Piezoelectric Devices

Owing to the natural electromechanical coupling property, piezoelectric materials have been used in many fields, such as industry, transport, healthcare, aviation, aerospace and so on. Recently, energy generator, wireless energy transmission and nondestructive evaluation are hot issues which have attracted the attention of many researchers. In this thesis, based on electromechanical coupling analysis, we present some novel methods and models on energy harvester, wireless energy transmission and nondestructive evaluation using piezoelectric devices. A wide-band piezoelectric energy harvester was established. Three more realistic models for transmitting a certain amount of power to the electronic devices inside the sealed armor using piezoelectric transducers to generate acoustic waves propagating through a sealed armor were presented. Theoretical analyses of the excitation and detection of acoustic waves in an elastic plate and a circular cylindrical shell to detect the creation and evolution of structural defects using piezoelectric actuators were performed. In the end, optimal electrode size and shape were determined for a few common cuts of crystal resonators. The valuable results obtained are instructional significance to enhance the integral performance of these models in application. Specific contents are as follows.(1) A wide-band piezoelectric energy harvester was established. We propose to use connected or coupled bimorph beams whose resonant frequencies are very close to each other and are adjustable. The harvester can scavenge ambient vibration energy by converting mechanical energy into electric energy, which will then be used for powering small electronic wireless devices in both civilian and military applications of a very low power requirement. It will be shown through a theoretical analysis that with proper design such a structure is wide-band in the sense that it can pick up vibration energy over a wider frequency range than a single-beam harvester structure.(2) Three more realistic models for transmitting a certain amount of power to the electronic devices inside the sealed armor using piezoelectric transducers to generate acoustic waves propagating through a sealed armor were presented. This technique can be used for the devices operating in a sealed armor or other hazardous environments, such as nuclear storage facilities, into which the physical access is prohibited. Transmitted voltage, current, power, efficiency, stress distribution were obtained. Energy trapping which describes the confinement and localization of the vibration energy in energy transmission by finite piezoelectric transducers was examined. We also studied the nonlinear behavior of transmission of electric energy through a closed elastic wall by piezoelectric transducers near resonance based on the theory of piezoelectricity and elasticity. The results are useful in understanding the behavior of a piezoelectric transformer near strong resonance and to predict the range of the driving voltage for a linear response.(3) Theoretical analyses of the excitation and detection of acoustic waves in an elastic plate and a circular cylindrical shell to detect the creation and evolution of structural defects using piezoelectric actuators were performed. Basic electric and acoustic properties including impedance, resonant frequencies and mode shapes were calculated. Energy trapping, an important phenomenon in which the waves are confined to be under and close to the transducers, was observed and examined. The results obtained are useful to nondestructive evaluation (NDE).(4) Optimal electrode size and shape were determined for a few common cuts of crystal resonators. Results show that the usual rectangular or circular electrodes differ from the optimal electrodes in shape and size significantly. In certain cases the optimal electrodes are nearly elliptical. Optimal electrode size and shape are significant for resonator miniaturization.