The Use of Huygens’ Principle to Model the Acoustic Field from Interdigital Lamb Wave Transducers

From a non-destructive evaluation point of view, Lamb waves are a highly attractive means of inspecting a large area of a structure from a single location. Interdigital transducers (IDTs) which make use of the piezoelectric properties of the polymer PVDF have been used previously in signal processing applications [1] to generate acoustic waves in piezoelectric substrates. Over the last two years, work has been carried out at Imperial College [2,3] to design PVDF IDTs that are capable of transmitting and receiving ultrasonic Lamb waves in non-piezoelectric plates for non-destructive testing purposes. Such transducers can be permanently bonded to a structure and hence have potential uses in smart structure applications. A schematic diagram of a simple PVDF IDT is shown in Figure 1. The wavelength and frequency of a single Lamb wave mode in the structure are selected by the spacing of the fingers in the IDT and the frequency at which the IDT is excited. Further details of their construction can be found in [2].