| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 88 === English Abstract
An innovative perspective and theoretical modeling that incorporates both electric and mechanical aspects of piezoelectric transformers were proposed in this dissertation. With the mechanical properties of piezoelectric transformer being incorporated into the newly developed theoretical model for the first time, many innovative features that can significantly enhance the performance of piezoelectric transformers including varying the effective surface electrode patterns, specifying the working modal frequency, examining the load characteristics, etc. were all detailed. Furthermore, methodologies that can be used to optimize the operating conditions, raise the output-input voltage gain, etc. were all examined. It was identified that surface electrode pattern, actuator length ratio (ratio of actuator and full transformer length) a, etc. were some of the most important design parameters in determining the performance of the piezoelectric transformers. None of these design parameters have been proposed or studied before. A series of innovative piezoelectric transformers were thus invented during the course of this research.
With the introduction of the innovative piezoelectric transformer modeling, three dimesionless parameters: modal actuating factor ri, modal sensing factor si, and modal gain factor gi, were defined in this dissertation to evaluate effects on the voltage gain of the piezoelectric transformer when different electrode shape functions and actuator length ratio a were implemented. It was identified that the modal actuating factor ri is equivalent to modal coordinate and modal gain factor gi is equivalent to gain of transformer in the theoretical model developed.
Since the approach taken in this dissertation considers both the mechanical and the electric state equations, many new design parameters were identified and were found to be particularly useful for developing innovative piezoelectric transformers that possess properties were not known to be possible before. For example, electrode shape functions for the actuator part of the piezoelectric transformer was identified to be a very powerful design parameters. With the introduction of this new design parameter, concepts such as quasi-modal actuator and wave modes can be applied to arrive at the optimum design configurations for piezoelectric transformers. Both theoretical and experimental results were shown to demonstrate that quasi-modal actuator is an important configuration that could be used to improve both the efficiency and the output signal waveform of piezoelectric transformers simultaneously. It was also identified that the classical uniform electrode piezoelectric transformer can achieve the highest voltage gain. By integrating these two concepts together, a new piezoelectric transformer configuration that incorporates two sets of surface electrodes on a piezoelectric transformer, connect to one set of surface electrode creates quasi-modal piezoelectric transformer and connect to both sets of surface electrodes creates classical uniform surface electrode, were invented. This newly invented piezoelectric transformer were shown to be easy to implement and can have the benefit of different design configurations. For example, this newly developed piezoelectric transformer can use the uniform surface electrode configuration to achieve the highest voltage gain in order to facilitate the lighting of plasma based light sources and then operate the lighted plasma based light sources by using the quasi-modal configuration in order to achieve maximum efficiency during the operation of the piezoelectric transformers.
Effect of the external load on the voltage gain, the frequency response, the resonance quality factors, the resonant frequency, etc. was all examined by using the newly developed theoretical model. It was discovered that gain of the piezoelectric transformer could be increased when connecting the output of the piezoelectric transformer to a series of capacitors. The added capacitance was found to work like parts of the output impedance of the piezoelectric transformer in this configuration. Higher-valued capacitance resulted in lower output impedance that acts like a reservoir to charge and discharge the resistive load, which was identified to get higher voltage output.
In summary, a newly developed theoretical modeling was developed to invent a whole series of piezoelectric transformers in this dissertation. Experimental results were found to agree well with the theoretical predictions.
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