Application of phase-sensitivity detector in air-coupled ultrasonic testing

The signal to noise ratio(SNR) of air-coupled ultrasonic testing is very poor and there is long time pulse residue, so it needs to adopt appropriate signal processing method to enhance the SNR of received signals. Factors which affected the received signals in ultrasonic testing process were analyzed. Phase sensitivity detection technology was presented to process the received signals, and ultrasonic testing information could be acquired by the calculation of phase signals. The principles of super-heterodyne receiver and phase sensitivity detector were introduced, some problems which should be payed attention in ultrasonic testing process were explained. Based on the research results, air-coupled ultrasonic testing system with phase sensitivity detector is constituted. Experimenal results of image testing on carbon fiber reinforced plastic plate indicate that, phase sensitivity detection technology can improved SNR of system and testing effects in evidence.