Imaging flaws in thin multilayered metal sheets using an array of guided mode transducers

In a multilayered elastic structure, acoustic energy can be focused into a particular layer by identifying a suitable guided wave mode. Once this guided mode is identified, low profile surface mounted interdigital transducers can be designed to excite preferentially this mode in the multilayered elastic structure. This has led to the development of a novel eight-channel linear array based on guided mode interdigital transducers. The array has been used to generate data for a time domain reconstruction algorithm. Resulting images reveal 1–2-mm length cracks in the center layer of a 300-μm-thick composite steel plate.