Applications of through-air ultrasound for rapid NDE scanning in the aerospace industry

This work describes two separate applications of air-coupled ultrasonic nondestructive evaluation (NDE) for rapid inspection of aerospace components. First, air-coupled transducer arrays are used for through transmission scanning of relatively large preproduction test samples. In this case a focused array system was designed to facilitate faster inspection rates and at the same time match the resolution and performance of available water jet apparatus. The second approach is geared toward in situ inspection and involves single-sided scanning using a dual transducer configuration for generation of surface, shear, and Lamb waves within the test specimen. In both cases, the difficulties of practical air-coupled inspection are discussed and the design solutions presented for each application. Piezocomposite transducer technology, in conjunction with narrow-band low-noise electronics, constitutes the basis for achieving the required signal to noise ratio (SNR) to ensure robust operation within the industrial environment. A number of scan images, performed on realistic samples, are shown and the results compared with those obtained using alternative methods. Excellent image quality is demonstrated from real time scanning and without recourse to any off-line data processing.