New design and analysis for point-focusing of surface waves in contact testing

A method was presented for the intensive focusing of surface ultrasonic waves in contact testing, and an ultrasonic contact transducer was fabricated and characterized. The acoustic contact lens of the transducer was in a shape which was obtained by rotating a right-angled triangle having a critical angle for the generation of surface waves. PVDF film was employed as an ultrasonic transmitter and receiver. The fabricated transducer showed the focusing feature of a narrow lateral half width and high sound intensity at a focal point. Also, a simple model was presented to estimate theoretically the stress pattern on a symmetry axis of the transducer. The stress pattern predicted using the model showed good agreement with the experimental result. This concept can also be used in acoustic microscopy.