AIR-COUPLED LAMB WAVE TOMOGRAPHY

An entirely air-coupled inspection system using a pair of micromachine d silicon capacitance transducers has been used to image defects in th in plates of different materials (0.7 mm to 2.22 mm thick) using air-c oupled Lamb wave tomography. A Altered back projection algorithm was u sed in a form of difference tomography to reconstruct images of defect s up to 10 mm diameter machined in aluminium and perspex (Plexiglas) p lates, as well as in samples of carbon fiber reinforced polymer (CFRP) . The technique was able to resolve non-central defects as well as mul tiple flaws within the scan area. This flexible tomographic system was able to produce images of the change in a variety of different acoust ic variables from only one set of experimental data, with success depe ndent on the size, shape, and location of the defect in the scan area.