Lamb Waves Inspection by Using Chirp Signal and Mode Purification

Ultrasonic Lamb wave inspection is one of nondestructive testing approaches, and it has many advantages including large-area, omnidirectional, fast inspection. In common, narrow-band frequency sinusoidal tone burst signal modulated by window function is used to excite guided waves in waveguides for mode control and tuning. For obtaining the signals at different frequencies, guided wave inspection will need to be repeated many times. As an alternative of narrow-band guided waves excitation, a broadband chirp signal is used for excitation signal and the received signal is post-processed to obtain any one single frequency tone burst signal which frequency range is located in the frequency bandwidth. This approach greatly increases guided waves inspection efficiency and ensures the consistencies. As the receivers, two PZT elements are supposed to be attached on both sides of a PMMA plate in the same location. The received signals from two PZT elements are summed to obtain single S₀ mode, and are subtracted to obtain single A₀ mode achieving mode purification of Lamb waves. Ultrasonic Lamb wave technology is applied to inspect the plate-like structures using chirp signal and mode purification. This method is more efficient and accurate to obtain data and much easier to identify, interpret and extract the information of the defects.