Point Contact Transducer of Waveguiding Structure for High-frequency Operation

Time-of-flight measurements with point-like contact transducers have successfully been applied for the detection of anisotropy, and for in situ measurements of film thickness and temperature. The operation frequency range of the pin transducers made so far was, however, restricted at several hundreds of kHz. This paper presents a new type of Hertzian-contact transducer of waveguiding structure operating in the MHz range. The transducer is composed of a fused quartz tube and a radially-polarized annular piezoelectric element bonded to one of its ends. The edge-bonded shear-wave transducer effectively excites a surface wave on the interior surface of the tube. A small bullet pin made of quartz is inserted and fixed on the other end of the tube to make a point contact and transmit the wave energy to a specimen to be inspected. Using a pair of these transducers, we have succeeded in the excitation and detection of surface acoustic waves as well as Lamb waves in the 3MHz frequency range.