ACOUSTIC-RESONANCE IN HIGHLY POROUS, FLEXIBLE, LAYERED FINE FIBER MATERIALS

A standing wave tube apparatus employing multiple microphones described by Zuroski et al. [J. Acoust. Soc. Am. 88, 1929-1938 (1990)] has been utilized in the study of resonance in fibrous materials. Such materials have long, flexible, thin fibers that can vibrate and possibly resonate when assembled in bulk form. This work reports a comparison between theoretical and experimental studies of various aspects of this resonance phenomena. All of the common propagation parameters including attenuation, phase speed, intrinsic admittance, and complex density, exhibit significant departures from characteristics developed on the basis of a rigid frame. The analysis required the development of a new theoretical model for the propagation of sound in such flexible fiber, highly porous materials. The agreement between theory and experiment is very satisfactory at and near resonance if the theory permits only a fraction g of the fibers to resonate. The value of g ranged between 0.6 and 0.8 for the samples of Kevlar that were studied.