Fabrication and Evaluation of a VHF Focusing Ultrasonic Transducer Made of PVDF Piezoelectric Film

Abstract

In order to obtain high resolution images, a focusing ultrasonic transducer operated in very high frequency (VHF) range was fabricated and its characteristics were evaluated. A 9- thick PVDF film with only one metalized surface for electric ground was adhered to a CCP (Copper-clad polyimide) film by using epoxy. It was pressed by a metal ball to form a concave surface and its rear side was filled with the epoxy. The radius of curvature and the -number of the fabricated transducer are 7.5  and 1.7, respectively. The pulse-echo measurement results from a target located at the focal point showed that the frequency bandwidth was 35.0  and the insertion loss near the peak frequency of approximately 40  was about 60 . Those values agreed well with the simulation results by the KLM equivalent circuit analysis including the effect of the epoxy bonding layer. When the image of thin copper lines by the 35  transducer of the UBM (Ultrasonic Backscattering Microscope) system was compared with the image by the transducer fabricated in this study, the fabricated transducer was observed that the axial resolution was improved although the lateral resolution was degraded.