Single point contact measurements of mechanical resonances

A technique for measuring the material properties of spherical objects is presented. The technique is also capable of detecting the presence of surface defects in these objects. Resonances of spheres are excited at both low and high frequencies. Resonances are generated by forming a one-point Hertzian contact between the sphere and a spherical depression in a buffer rod with a transducer. The resonance spectrum is detected from the opposite pole of excitation using a heterodyne interferometer. At low frequencies, bulk resonances of the sphere are excited and material properties are determined. At high frequencies, surface wave resonances of the sphere are excited and the dispersion relation of the waves is measured. The measured dispersion relation of the sphere is correlated to the surface wave velocity on the sphere and to the presence of surface defects