Propagation of the initial transient noise from an impacted plate

The near field initial transient noise of an impacted plate is studied, and the means of propagation of this noise is examined. Impacts are performed by a rigid spherical object at the center of a thin rectangular plate. Two different impact energy levels are produced. Acoustic pressure time-histories are obtained analytically and experimentally at four different locations near the impact point. An analytical model is produced, based on the classical theory of thin plate, Rayleighʹs surface integral, and modified Hertzian force. The results are in good agreement with the experiments. They show that on the impact axis (normal to the plate), the initial transient noise is similar to the acceleration noise of a piston subjected to the same force signal, and that the waveform shape varies with the impact energy level. Off-axis initial transient waveforms are examined through the analytical solution, and two different partial solutions. Results show that the initial transient noise of an impacted plate is partially structure-borne. Continuity with the initial bending wave causes the initial transient noise to be dispersive. The effects of dispersion are negligible in the vicinity of the impact axis, but become considerable at large observation angles.