An Optimization Model for Fibrous Metal Foam Sound Absorbers

It is well-established that wool and glass fibers are good absorbers for noise-control in air. However, inadequate levels of stiffness and strength have limited the range of the use of such fibers. The emergence of fibrous metal foams has meant rethinking of these limitations. Fibrous metal foams can be filled, not just with air, but also with other types of fluids. This means that altering both fluid-types as well as absorber-structures can optimize the quality of absorption and extend the range of application for metal foams. This paper builds on an earlier domain-match method. By extending the number of variables, this paper shows how it is possible for the domain-match method to have greater scope and generality of application. Dimensional analysis is employed to maintain basic physical features but reduce the number of parameters involved. In the first, and simplest, case, the absorber consists of straight though-holes perpendicular to a sandwiched perforated plate surface. This basic model is then generalized to other cases involving fibrous metal foams. Key non-dimensional parameters will be identified as well as the optimal ranges for these parameters. Castor oil will be used as an example liquid in a case involving absorption of sound around a frequency of 500 Hz. We will then show how silicone oil is better-suited for absorption of the sound. Specifically, we will demonstrate how the thickness of the absorber can be reduced more than three quarters when the absorber is immersed in silicone rather than simply in castor oil.