1981 年 37 巻 10 号 p. 477-483
A new method for measuring acoustic velocities of thin materials is proposed in a VHF range. The principle is to measure the phase changes, as interference fringe-shifts, caused by inserting a specimen in a liquid whose acoustic velocity is known. In this method, a specimen immersed in a liquid cell is illuminated obliquely by plane waves which are launched from a plane ultrasonic transducer. Ultrasonic waves transmitted obliquely through the specimen are detected and changed into an electrical signal by a focussing ultrasonic transducer, which is scanned mechanically in a raster pattern to produce interference fringe patterns on the CRT display by combining an electrical reference signal with the received electrical signal. Acoustic velocities of some polymer films and a biological tissue, for example, are measured in a frequency range between 160 and 190 MHz. Measurement errors are discussed for this experimental system.