Ultrasonic waves: their interferometric measurement and display

Abstract

A system for the measurement and visualization of small displacements has been developed that features high sensitivity and acoustic-wavelength-limited resolution over apertures as large as 15 cm at frequencies up to 10 MH(z). Acoustic-wave displacement amplitudes as small as 0.07 A are measured by interferometrically detecting the motion of a thin, acoustically transparent, metallized pellicle as the ultrasonic wave passes through it. The system can also be adapted to measure and display any small vibratory motion. The basic arrangement is that of the Michelson interferometer with the addition of an open-loop method to stabilize the response and a deflection system in one leg of the interferometer to scan the pellicle. Presently, the system is used in the study of the interactions of ultrasonic waves with biologic tissue and the observation and measurement of radiation patterns of acoustic transducers.