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Frost, Harold M.

Physics

1969

MS

Relative displacements of the order of 10 um between the surface of a soft solid and an ultrasonically vibrating object are studied experimentally by means of a time-resolved displacement transducer technique. Ultrasound frequency is about 20 kHz. The vibrating object (fashioned from aluminum) penetrates into both agar-gel and paraffin-wax test samples. Repulsion between vibrating object and wax samples is also observed. Penetrations may be caused by weakening of the structure of test samples by the vibrating object, such that the viscosity of the test sample material is lowered. Repulsion is explained in terms of rapid periodic separations between the vibrating object and test sample, i.e., intermittent as opposed to continuous contact conditions.