Recent advances in acoustic microscopy for nondestructive evaluation

Driven by new demands from industry, the field of acoustic imaging is rapidly evolving new approaches to meet the demands. The current trend toward micro and nanotechnology has been pushing the operating frequency of scanning acoustic microscopes (SAM), from MHz to GHz. To become a useful tool for nondestructive evaluation (NDE), the SAM must give high resolution and also maintain reasonable depth of field below the sample surface, while overcoming the effects of surface roughness. A recent trend of needs for the SAM is to enhance resolution for detecting defects (e.g., microcracks, inclusions, debondings, delaminations), and develop a capability and an accuracy for obtaining quantitative data (e.g., velocities of waves, attenuation) for measuring residual stress, anisotropy, thickness of thin films, or the like. Furthermore, the SAM is to be modified to use in various environments. In this paper, a principle and some applications for both a practical shear wave lens and a noncontact lens will be summarized.