The performance of flexible interdigital PVDF lamb wave transducers

The time domain wave forms and spatial amplitude distributions produced by interdigital PVDF transducers on a steel plate have been investigated both experimentally and theoretically using a simple finite element model in which it is assumed that the motion of the plate does not affect the behaviour of the transducer, and. that the transducer simply applies out-of-plane forces to the plate. Excellent agreement between the measured time domain waveforms at different frequency-thickness products and predictions obtained with a two dimensional finite element analysis have been obtained. The spatial distribution of wave amplitude over the surface of the plate generated by different transducer designs predicted using a three dimensional finite element analysis also agreed very well with experiments both for a rectangular transducer and a "pie slice" transducer in which the length of the fingers increased along the transducer. It has therefore been shown that the simple, un-coupled model provides a good representation of the behaviour of PVDF based interdigital transducers on metal plates. The spatial and temporal wave fields generated by the rectangular and 'pie slice' transducers were very similar, indicating that it would be possible to produce a polygonal transducer split into sectors, each interrograting well-defined region of a structure.