Design of interdigital transducers for crack detection in plates.

Interdigital transducers (IDT) for non-destructive evaluation (NDE) of cracks in plates are designed based on an analytical model established previously. Key considerations include mode selectivity, excitation strength, collimation of wave and cost. The advantage of mode selectivity of IDT over PZT patch is presented both analytically and experimentally. Effects of parameters, namely finger spacing, width, length, number of fingers, and the size of IDT, on the excitation strength and mode selectivity are considered. This led to the design of a mobile double-sided IDT as an efficient device where excitation strength is strong and focused. The device was fabricated in-house using commercially available piezoelectric ceramics and used to develop a procedure for accurate identification of the direction and extent of cracks in plates. Three aluminum plates, one with a linear deep crack, another with a piecewise linear shallower crack and the third with a curved crack, were used to illustrate the accuracy and efficiency of both the proposed device and procedure for effective NDE.