Capacitance Microphones for Measurement of Ultrasonic Properties of Solids

Two capacitive transducer designs have been used in this laboratory for amplitude measurements of longitudinal ultrasonic waves in solids. The designs are simple, can be fabricated easily, are rugged, and should prove to be a useful ultrasonic laboratory item. Each of the microphones can be conveniently altered to be used with a variety of specimen sizes, and displacement amplitudes as small as 10−14 m have been measured for 30 MHz frequency longitudinal waves. As an example application of the transducer, measurement of phase shift upon reflection from an X‐cut quartz transducer bonded to an SrTiO3 crystal is given.