A non-contacting ultrasonic phase-sensitive displacement measurement system

A simple ultrasonic displacement measurement system is described, based on a phase-sensitive detection principle. A low-frequency ultrasonic transducer, operating in continuous-wave mode, is used to transmit a 44.2 kHz acoustic wave to the target body. The reflected signal is detected by a matched transducer and the phase difference between the transmitted and received signal is found in real time. Tests show that the system is capable of detecting displacement with an accuracy of +or-5.3 mu m, with targets situated over 2 m from the transducers.