Built-in transducer design for Lamb wave generation in composite structures

Abstract

Conventional ultrasonic inspection of large composite structures is very time consuming due to the necessity of surface scanning. Because they can propagate over long distances, Lamb waves are an attractive solution to this problem. Two methods are available for the generation of Lamb waves in composite plates. The first method, and the most useful one, consists of using bonded transducers. The second solution is to use a built-in transducer. In both cases, the transducers must be designed to generate efficiently the signal and choose the mode of propagation. In the following, a method to design a built-in transducer will be discussed. First, the case of a unidirectional composite plate is considered. An analytical method is developed, then the results are compared with those obtained using finite element analysis. In the case of a square element transducer embedded in the composite plate, the computed results are compared with experimental data. Then, the method is extended to the case of a multilayered plate. An analysis is performed to determine the optimal design of a built-in multi-element transducer.