Optimized acoustic properties of cellular solids

The optimized cell size and shape, cell size variations, sample thickness, and air cavity depth behind the sample for best sound absorption performanc e of air-filled porous materials having simple cell morphologies are studie d in this paper. The focus is on cellular foams that are rigidly framed, e. g., aluminum alloy foams and honeycombs. The governing equations of wave pr opagation are solved by using the point-matching method, and the prediction s are compared with known analytical solutions. The effects of cell size va riations are studied for Voronoi polygons. A domain-matching method is intr oduced to obtain the optimal combination of cell size and shape, sample thi ckness, and cavity depth for selected ranges of frequency. At given porosit y, the effect of cell shape on sound absorption is small. The optimized cel l size for best sound absorbers is on the order of similar to 0.1 mm for pr actical combinations of sample thickness, cavity depth, and porosity. A ran dom distribution of cell sizes tends to tighten the region where combinatio ns of sample thickness and cavity depth achieve high sound absorption coeff icient. (C) 1999 Acoustical Society of America. [S0001-4966(99)06408-5].