Acoustic microscopy of curved surfaces

To date, imaging and metrology in the acoustic microscope have been performed exclusively on planar specimens. While imaging is accomplished by raster scanning in the plane transverse to the axis of the acoustic beam, metrology is practiced by variation of the specimen‐lens separation along the beam axis. This operation yields an acoutic material signature at a single location on the specimen plane. The two modes of operation are in effect simultaneously employed when a nonplanar surface of known curvature is scanned. The resulting images reveal concentric rings with radial periodic brightness variation if the surface is spherical in shape. The technique is demonstrated with stainless‐steel bearing balls of the type used in precision gyros. The application of this technique to the diagnostic inspection and analysis of both bearing balls and raceways are discussed. It is suggested that the obtained images represent a two‐dimensional map of elastic properties of the bearing surface regions.