Transient acoustic near field in air generated by impacted plates

Abstract

The transient acoustic near field in air from impacted cantilever plates of two different geometrical shapes and materials is studied using two-reference-beam double-pulsed holographic interferometry. The acoustic waves, observed in two directions simultaneously, are generated by traveling flexural waves in the plates and by the impact process itself. A subsequent phase-stepping procedure is used for quantitative evaluation of the registered two-dimensional projections of the acoustic fields. An interesting observation is the acoustic radiation at the free end of the plate, where sound waves propagate into the air in oblique directions from the plate. At the region right above the free end no acoustic waves are observed. Supersonic flexural waves in the plates generate trace-matched acoustic waves in the surrounding air. Calculations of the corresponding two-dimensional transient acoustic fields are performed. Those are based on an analytical solution of the Kirchhoff plate equation. Calculated results reproduce the character of the observed transient acoustic waves quite well.