Ultrasonic surface fault detection - monitoring sound pressure changes whilst interference pattern is varied

摘要

Workpieces are tested by irradiating them with h.f. ultrasonic radiation, varying the interference pattern of the coherent background radiation by changes in the position of measurement and/or angle of incident radiation and/or frequency of incident radiation and averaging measurements of sound pressure amplitude. In a practical arrangement, the ultrasonic transmit-receive transducer is coupled to a probe head and an impedance matching unit. The received analogue signal is converted to digital form at a max. frequency of 100 MHz in an A/D converter. The digital signal is averaged in an adding circuit and the resultant data may be stored on punched cards, transmitted by teleprinter or further processed in a calculator circuit. For positional averaging, the transducer has a moving probe head, and for frequency averaging a sweep-frequency generator is employed.