Comparison of Different Piezoelectric Transducer Materials for Optically Scanned Acoustic Imaging
Recent work has shown that optically-scanned piezoelectric transducers may be employed for transmission imaging of objects with a high spatial frequency content, in the 1–10 MHz frequency rangel. The optically scanned transducer shown in Fig. 1, consists of a monolithic piezoelectric receiving transducer with its front face electrode removed and replaced by a semiconductor layer which has a semi-transparent metal film evaporated on it. A scanning light beam samples the local amplitude and phase of an incident acoustic wavefront sequentially, by photoconductively switching the semiconductor. In practical devices, however, an unwanted background reference signal from the dark regions of the transducer is present, largely because of the semiconductor capacitance. Brightness modulation of the scanning light beam overcomes this problem by producing sidebands originating only from the switched (or illuminated) part of the transducer. Typically a modulation frequency of 50kHz is used with an acoustic wave frequency of 3MHz. An acoustic image obtained with this device is shown in Fig. 2.
KeywordsPiezoelectric Transducer Angular Spectrum Polar Response Spatial Response Acoustic Frequency
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