TRANSIENT ACOUSTIC NEAR-FIELD IN AIR GENERATED BY IMPACTED PLATES

The transient acoustic near field in air from impacted cantilever plat es of two different geometrical shapes and materials is studied using two-reference-beam double-pulsed holographic interferometry. The acous tic waves, observed in two directions simultaneously, are generated by traveling flexural waves in the plates and by the impact process itse lf. A subsequent phase-stepping procedure is used for quantitative eva luation of the registered two-dimensional projections of the acoustic fields. An interesting observation is the acoustic radiation at the fr ee end of the plate, where sound waves propagate into the air in obliq ue directions from the plate. At the region right above the free end n o acoustic waves are observed. Supersonic flexural waves in the plates generate trace-matched acoustic waves in the surrounding air. Calcula tions of the corresponding two-dimensional transient acoustic fields a re performed. Those are based on an analytical solution of the Kirchho ff plate equation. Calculated results reproduce the character of the o bserved transient acoustic waves quite well. (C) 1996 Acoustical Socie ty of America.