Amplitude and phase acoustic microscopy for ceramic bearing ball inspections

The problem of inspecting different types of defects in ceramic bearing balls is addressed. An amplitude and phase acoustic microscope that operates in the frequency range of 1-200 MHz is used. In one configuration, an x-y scanner is used. With image processing, the circular interference fringes which are due to the spherical shape of the bearings are removed. Another system configuration uses a rotational scanning stage to rotate the bearing ball and applies differential phase measurement techniques to improve the phase measurement accuracy to 0.4°. The third configuration was developed for the measurement of subsurface defects. It also uses a rotation stage, but with a broadband transducer in order to separate the surface wave echo from the specular reflected signal. A theoretical model is to deal with wave propagation on the spherical surface, and it is predicted that the surface wave is focused to a diffraction-limited spot 0.36 Rayleigh wavelengths at the 3-dB points