Validation of a polyimide foam model for use in transmission loss applications.

In this paper, the use of polyimide foam as a lining in double panel applications is considered. Polyimide foam has a number of attractive functional attributes, not the least of which is its high fire resistance, thus making its use desirable in some sound transmission applications. The configuration studied here consisted of two 0.04×94 thick, flat aluminum panels separated by 5 in., with a 3 in. thick layer of foam centered in that space. Random incidence transmission loss measurements were conducted on this buildup, and conventional poro‐elastic models were used to predict the performance of the lining material. The Biot parameters of the foam were determined by a combination of direct measurement (for density, flow resistivity and Young’s modulus) and inverse characterization procedures (for porosity, tortuosity, viscous and thermal characteristic length, Poisson’s ratio, and loss factor). The inverse characterization procedure involved matching normal incidence standing wave tube measurements of absorption coefficient and transmission loss of the isolated foam with finite element predictions. When the foam parameters determined in this way were used to predict the performance of the complete double panel system, reasonable agreement between the measured transmission loss and predictions made using commercial statistical energy analysis codes was obtained.