Two miniature ceramic ultrasonic probes

The design, construction and performance of two types of miniature ceramic hydrophones are described, which are intended for acoustic pressure measurements in liquids at low megahertz frequencies. One of the devices has a 1.6 mm diameter cylindrical element with good directional characteristics and a sensitivity of approximately -224 dB re 1 V mu Pa -1 up to 0.7 MHz. The other probe uses a 0.5 mm disc showing a sensitivity of -245 dB re 1 V mu Pa -1 from 0.5 to 6 MHz and diminishing uniformity of directional response with increasing frequency. The stability of the probes is also discussed.