The direct problem of acoustic diffraction of an audible probe radiation by an air-saturated porous cylinder

Abstract

International audienceGas-saturated, solid skeleton, porous media like geomaterials, polymeric and metallic foams or biomaterials are fundamental in a diverse range of applications, from structural materials to energy technologies. Most polymeric foams are used for noise control applications and knowledge of the manner in which the energy of sound waves is dissipated with respect to the intrinsic acoustic properties is important for the design of sound packages. Foams are often employed in the audible, low frequency range where modeling and measurement techniques for the recovery of physical parameters responsible for energy loss, are still few. Accurate acoustic methods for the characterization of porous media are based on the measurement of the transmitted and/or reflected acoustic waves by platelike specimens at ultrasonic frequencies. In this study we have developed a method based on the theory and experiment of diffraction of acoustic waves by a rigid-frame, air-saturated polymeric foam in cylindrical form in the audible frequency regime. A dispersion relation for sound wave propagation in the porous medium is derived from the propagation equations and a model solution is sought based on plane-wave decomposition using orthogonal cylindrical functions. The explicit analytical solution equation of the scattered field show that it is also dependent on the intrinsic microstructural parameters of the porous cylinder namely, porosity, tortuosity, and the flow resistivity (related to permeability)

Carbon Nanotubes/Polyurethane Foam for Noise Passivation at 4000 Hz

“…Such reinforcement changes the cellular porosity, density, and overall cellular structure of formed FPU. , While another important factor for sound absorption is tortuosity, which plays an important role in the high-frequency range . Recovery of tortuosity along with porosity helps attenuate sound adequately . Consequently, the morphological dual-3D structure formation through a novel route could allow increasing tortuosity and other gain factors for the broadband absorption of sound frequency .…”

“…13 Recovery of tortuosity along with porosity helps attenuate sound adequately. 14 Consequently, the morphological dual-3D structure formation through a novel route could allow increasing tortuosity and other gain factors for the broadband absorption of sound frequency. 15 Therefore, reinforcement of nanomaterials in FPU via a route different than that in situ needs to be optimized.…”