Using ultrasonics to measure vibrational amplitudes of auditory organs in fish

Abstract

A new underwater, nonintrusive technique using ultrasonics has been devised to measure the amplitude response of the fish swim bladder and otolithic organs to a low-frequency sound wave. The body of the fish is scanned with a 10-MHz source while being subjected to a single frequency sound field. The resulting echo due to the impedance mismatch at the swim bladder and otoliths is received by another 10-MHz transducer, and then fed into a spectrum analyzer. The relative magnitude between the 10-MHz peak and the side bands created by the low-frequency excitation provides the desired amplitude information. Preliminary measurements have been obtained to demonstrate the method. Further refinements will allow measurements of 25 Å over 0.1 mm. This technique is superior to previous methods using accelerometers, microphones, Laser light scattering, and holographic interferometry because all of these require that the organs be either directly exposed to the measuring device or removed from the body. [Work supported by ONR.]