以TiOPc/蜂鳴片控制壓電揚聲器之聲學研究

Abstract

本論文提出以光電導材料(photoconductive material)嘗試加入應用光調變的控制機制於蜂鳴片壓電平面揚聲器中，並製造出一結合光、機、電之複合式元件。而使用之複合材料是透過結合光電導材料TiOPc (Titanyl Phthalocyanine)與高分子聚合物(copolymer)結合之薄膜以及壓電材料PZT (Lead Zirconate Titanate) 來製作。利用材料光致電性變化特性調變電極之阻抗表現來達到可即時控制該複合揚聲器之頻率響應、聲束指向性及聲場等相關聲學特性。 在溶液與薄膜的製程部分，我們以精密阻抗分析儀(Agilent 4294A)進行量測，並且整理分析TiOPc/copolymer薄膜的電學特性與薄膜製程參數間的關聯，再以電學阻抗匹配的方式來決定最後的薄膜製程參數。 在量測的部分，由於此種壓電型揚聲器因受限於材料的選用和結構設計之影響，使得頻率響應在低頻的表現不甚理想。我們藉由光電導材料TiOPc之阻抗變化在中低頻段(約40~8000Hz)下較為顯著之特點下，與壓電揚聲器做結合，並且在光場調變的控制下得到較大的振幅來發出低頻的聲音，進而大大地提升揚聲器之低頻響應。由實驗結果證實，本研究中所製備的複合式壓電蜂鳴片可以照光的方式來調制聲壓的變化。為了達成聲束指向性圖形控制的應用，我們試著設計不同的照光圖形來使壓電片表面分壓不均造成不均勻之振動，影響其指向性圖形大小，並且分析照光圖形所對應之聲場變化，進而藉由所光照之圖形分析後加以控制。 為了與聲學測量的數據作相互驗證及比較，後段我們分別以雷射位移計和ESPI電子斑干涉儀兩種方式來量化及圖形化致動器的表面形變狀態，並且找出其與聲學量測數據之關係，也證實此複合式光調控壓電揚聲器之可行性。

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.