Numerical investigation into acoustic wave propagation in felt-type material with band gap and negative group velocity

In this paper acoustic wave propagation through nonlinear porous felt-like material is studied numerically. A 1D model equation based on the experimentally obtained constitutive relation is used. A dispersion and dissipation analysis are performed. The possible effects of band gap (BG) and negative group velocity (NGV) on the wave propagation are investigated. For this reason, the propagation of pulses with characteristic widths corresponding to wavenumbers that are located in and near the BG and the region with NGV are studied. It is claimed that if the material loading and unloading timescale is much too great in comparison to the felt relaxation time, then any possible contribution of BG and NGV on the wave shape evolution is negligibly small. Paper concludes that felts are not metamaterials with noteworthy properties. Possible reasons for these conclusions are given. It is obvious that the proper understanding of NGV phenomenon will lead to significant breakthroughs in unwoven fibrous felt-type material engineering and applications. These applications may include vibration and noise control and even wave manipulation.