From Structural Health Monitoring with Piezoelectric Wafer Active Sensors

11.2 PHASED-ARRAYS IN CONVENTIONAL ULTRASONIC NDE

The phased array principle was introduced into ultrasonic testing because of its multiple advantages (Krautkramer, 1990; Rose, 1999; Ahmad et al., 2005). Some of the advantages of phased arrays over conventional ultrasonic transducers are high inspection speed, flexible data processing capability, improved resolution, and the capability of scanning without requiring mechanical movement, i.e., dynamic beam steering and focusing (Wooh and Shi, 1998). The backscattered ultrasonic signals can be analyzed and then mapped into an image. By using an ultrasonic phased array, the ultrasonic wave front can be focused in a certain point or steered in a specific direction; the inspection of a wide area can be achieved by electronically sweeping and/or refocusing without physically manipulating the transducers. Damage, which can be characterized as a local change in impedance, is diagnosed by using the echoes received from the propagating ultrasonic waves. However, in comparison to sonar and medical phased arrays, ultrasonic NDE phased arrays encounter several aspects that are of special concerns (i) the wave speed in solids is much higher than in water and tissues; (ii) the wave propagation is much more complicated, since dispersive and multi-mode waves may be present. For these reasons, the electronics required for ultrasonic phased array implementation may be rather complicated and sophisticated.

Current ultrasonic phased array technology mostly employs pressure waves generated through normal impingement on the material surface. Such phased arrays have shown clear advantages in the inspection of very thick specimens and in the sidewise inspection...

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Topics of Interest

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