| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 92 === Valuable information such as defect position, impedance analysis, and vibration mode shapes, etc. can be revealed by observing the wave propagation behaviors in an object. However, accurate full-field wave propagation behaviors can neither be obtained by numerical simulation nor by experimental implementations. To truly verify the full-field wave propagation behavior, experimental implementation is even more important when considering the many factors that may affect the intricate wave propagation details. With an attempt to measure high-speed wave propagation phenomenon, a novel optical instrument was developed during the course of this dissertation. This newly developed system possesses characteristics such as non-contact, high-resolution, and short measuring time, etc.
This newly developed full-field three-dimensional transient strain metrology system was based on Electronic Speckle Pattern Interferometer (ESPI) technique, which adopted a Nd:YAG pulsed laser with 10 ns pulse duration, 100 ns ~ 6000 μs pulse to pulse separation capabilities as the light source to achieve MHz measurement bandwidth. The (5,1) phase-shifting algorithm, median filter technology, and weighted iterative DFT phase unwrap algorithm were all integrated to convert the 3-D speckle intensity maps acquired from three CCD cameras into 3-D deformation data of each instance.
As piezoelectric transformer is a technology currently being studied by many leading research groups due to its close tie to the power-supplier technology of future LCD displays, it was taken as the specimen to demonstrate the performance of the newly developed metrology system. Furthermore, since the nonlinear effect of piezoelectric transformers working at high frequency and high power conditions is the key point to improve performance of today’s piezoelectric transformers, experimental data obtained can provide some insight into the improvement of this type of innovative power supplies. Using the time sequences of deformation data obtained, the strain behavior of piezoelectric transformers operating at high power and frequency can be reconstructed step by step.
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