In the article on metal foams by John Banhart and Denis Weaire (Physics Today, July 2002, page 37), I saw no discussion of possible acoustical absorption applications. Controlled interconnection of pores is, of course, necessary for broadband sound absorption. Possibly that property, combined with certain of its structural abilities, would make metal foam a unique high-performance structural material.
When doing architectural acoustics consulting in New York and Chicago, Tony Paolello of the New York City Transit Authority and George Krambles of the Chicago Transit Authority both expressed the hope that an economical, easily cleaned, sound-absorbing, and extremely durable material would be found for lining subway tunnels. Could metal foams be such a material? Combined with damped sheet steel backup for sound isolation, these materials would seem ideal for the subway system’s sound-absorbing surfaces. Since metal foams can be rigid enough to bear the weight of workmen, transit systems might also be able to use them to make noise barriers that can pivot from the vertical to the horizontal to become maintenance walkways.
