铁电驻极体空气耦合声换能器的研制
Development of EMFi-based air-coupled ultrasonic transducer

基于多孔聚丙烯铁电驻极体薄膜系统研制了平面型和球型聚焦空气耦合超声波换能器。平面型换能器孔径为20mm，两个球型聚焦换能器的孔径和焦距分别为20mm和35mm、30mm和40mm。使用激光干涉仪测得了三个换能器作为发射器工作时的带宽和谐振频率，并且将在脉冲回波模式下测得的换能器作为接收机工作时的响应与激光干涉仪测试结果进行比较。最后选择孔径为20mm的球型聚焦换能器，在脉冲回波模式下对不同直径孔的聚乙烯阶梯楔进行扫描成像。
The planar and spherically focused air-coupled ultrasonic transducers are developed based on electrical mechanical film (EMFi) system, which contains two-sided Al electrodes and cellular polypropylene (cPP) ferroelectret films. Three transducers are fabricated and tested. The planar one has a diameter of 20 mm. One of the spherically focused transducers has an aperture of 20 mm and a focal length of 35 mm; another has an aperture of 30 mm and a focal length of 40 mm. The bandwidth and resonance frequency of the transducer as a transmitter are obtained by using laser interferometer. As a receiver, the pulse-echo response of the transducer is compared with the results of laser interferometer test. Finally, the spherically focused transducer of 20 mm aperture is selected to scan the polyethylene (PE) ladder wedge with different diameter holes in pulse-echo mode.