The effect of flexibility on the acoustical performance of microperforated materials

Abstract

In conventional models of microperforated materials, the solid layer in which the holes are formed is usually considered to be rigid. However, microperforated materials are often thin, say less than 0.5 mm in thickness, and are sometimes made of lightweight polymeric materials. Experimental measurements suggest that when the mass per unit area of a microperforated material is less than approximately 0.5 kg per square meter, the motion of the solid layer becomes important. The solid layer is driven into motion both by the incident pressure acting on its surface and by viscous forces generated within the perforations. The ability of a microperforate to dissipate acoustical energy depends on there being relative motion between the air in the perforations and the solid layer: motion of the solid may either help or hurt this effect, particularly when the solid layer is supported on a grid-like structure, since the individual segments of the microperforate then exhibit modal behavior. In this presentation, models of this behavior will be described, and examples will be given in which essentially membrane-like behavior is modified by the presence of the perforations, and conversely, in which essentially rigid microperforated layer behavior is modified by vibration of the solid layer.