Characterization of high-frequency transducers with small aperture hydrophones

The characterization of very-high-frequency transducers (>30 MHz) is a challenging task. Typical hydrophones have -3 dB bandwidths of 15 to 20 MHz and effective spot sizes of approximately 500 μm. They often suffer severely from spatial averaging and cannot fulfill the task of characterizing high-frequency transducers. A new generation of membrane hydrophone from Hewlett-Packard makes a possibility of characterizing very-high-frequency transducers. The hydrophone has a measured effective spot diameter of less than 100 μm and a -3 dB bandwidth of 150 MHz. A 50 MHz Panametrics transducer with an aperture size of 6.35 mm and a geometrical focal length of 12.7 mm was measured. The measured -3 dB beam width of 73.7 μm showed a good agreement with the theoretical value of 60.9 μm. For comparison, the beam width was also measured with a state-of-the-art Precision Acoustics PVDF needle hydrophone and found to be 112.1 μm. Experimental beam profiles show that the HP membrane hydrophone is a promising method of characterizing high-frequency transducers