Acoustic Research and Control of Piezoelectric Speakers Using A Spatially Modulated TiOPc/Piezo Buzzer Actuator

• Main Authors: Te-Chieh Chang, 章德傑
• Other Authors: Chih-Kung Lee
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/14629518599138743216

碩士 === 國立臺灣大學 === 應用力學研究所 === 102 === In this thesis, we added photoconductive material to enable optical illumination control mechanism onto the operations of flat piezoelectric loudspeakers. We also developed a new smart composite device based on interactions of optical, mechanical and electrical fields. This smart composite material was composed of photoconductive material TiOPc (Titanyl Phthalocyanine) and piezoelectric material PZT (Lead Zirconate Titanate) in order to perform newly developed Opto-Piezo modulation mechanism. More specifically, the instant variation of TiOPc impedance when illuminated with light beam patterns was introduced to provide spatial electric field distribution across PZT so as to provide spatial control of piezoelectric speakers. This real-time in-situ spatial impedance varying capabilities provided us with a platform to instantly control the acoustic characteristics such as frequency responses, sound beam directivity patterns, and sound field created, etc. of piezoelectric speakers. To characterize the solution and thin-film manufacturing process developed, the electrical impedance of TiOPc thin film was measured by Agilent 4294A Precision Impedance Analyzer. From the measured electrical impedance, the relationship between the thin-film processing parameters and the equivalent R-C value was retrieved by using the equivalent circuit model. The most appropriate parameters for the manufacturing processes developed were identified using the equivalent R-C values obtained. The low-frequency performance of the flat piezoelectric loudspeakers was measured and found to be poor due to the material selection and the corresponding structure design. Taking advantages of the characteristic of the photoelectric conductive material TiOPc, which demonstrated noticeable impedance change at low-mid range frequency (about 40~8000Hz), the low-frequency performance of the flat piezoelectric speakers was enhanced. A variety of illuminated pattern was tried and examined to control the acoustic beam patterns created. The experimental results confirmed the directivity controlling capability of acoustic pressure generated through external illuminated light patterns. Laser Displacement Meter and Electronic Speckle Pattern Interferometer (ESPI) was implemented to perform the measurement in order to compare and verify the numerical and graphical analysis of the light beam illumination pattern induced flat piezoelectric speakers outside shape/form changes. The correlation between the analysis results and the measurement data confirms the feasibility of our optically modulated flat piezoelectric speakers.