電容式空氣耦合超音波換能器之開發與應用

Abstract

本研究開發電容式超音波換能器，實現適合高解析定位應用之寬頻及空間性廣的空氣耦合超音波探頭，此類可依應用需求設計的感測器中心頻率為數百kHz或數MHz。電容式換能器由單側表面鍍有金屬電極的背板與高分子薄膜組成，矽基背板以半導體製程乾蝕刻出許多個圓形孔穴。施予高直流電壓使薄膜吸附背板，並以低振幅交流電壓激發薄膜振動，拍打空氣產生寬頻聲輻射。本研究使用有限元素套裝軟體分析換能器單一致振元素的頻率響應，孔穴間距對輻射聲場影響的數值研究可避免相鄰致振元素相互干擾。本研究製作100kHz電容式超音波換能器，實驗量測顯示探頭具有寬頻響應，運用掃頻調制訊號，實現空耦超音波定位應用。

The aim of this thesis is to develop the capacitive micro-machined ultrasonic transducers (CMUTs). The broadband and wide view air-coupled CMUTs are designed for high-resolution source location applications. The transducers can be tailor-made with center frequency from hundreds of kHz to MHz. A number of circular cavities of the same diameter were dry etched on a Si substrate to function as a back plate by the semiconductor process. The sputtered metal electrode overlays the top surface of the wafer. An actuating element consists of a cavity and a one-side metallized polymer film. A high DC voltage is required to make the film attach to the back plate, and an additional low amplitude AC voltage stimulates vibration of the diaphragm. It induces the broadband ultrasound radiation into the air. The frequency response of a single actuating element is determined through numerical simulation using a commercial finite-element analysis code. Cavity interval has an influence on the radiation field. Numerical investigation can avoid the mutual interference between adjacent vibrating elements. Measurement results reveal that the assembled 100 kHz transducers feature broadband frequency responses. The application of source location has been accomplished by use of swept frequency modulated signals with the air-coupled CMUTs.