Ultrasonic displacement system

An acoustic instrument system is described as a feasible tool for remote measurement of structural velocities. The system involves measurement of the Doppler shift of ultrasonic sound as it is reflected from an oscillating plate. Measurements were performed in air with an ultrasonic frequency source of 42.5 kilohertz. The surface under investigation was a plexiglass plate oscillating sinusoidally at 10, 13, and 15 Hz. Data are presented to show that, in such a system, the measurement of the Doppler shift is dependent upon the acoustic pathlength between the sensing device and the oscillating surface, with the distance between maximum shifts being half the wavelength of the ultrasonic source.