Extraordinary absorption of sound in porous lamella-crystals

Abstract

We present the design of a structured material supporting complete absorption of sound with a broadband response and functional for any direction of incident radiation. The structure which is fabricated out of porous lamellas is arranged into a low-density crystal and backed by a reflecting support. Experimental measurements show that strong all-angle sound absorption with almost zero reflectance takes place for a frequency range exceeding two octaves. We demonstrate that lowering the crystal filling fraction increases the wave interaction time and is responsible for the enhancement of intrinsic material dissipation, making the system more absorptive with less material.

Superabsorption of acoustic waves with bubble metascreens

“…These materials are made of "meta-molecules", i.e., local resonators that can couple to the incoming wave despite being small compared to the wavelength. By designing judiciously the structure of a metamaterial, one can obtain exotic properties such as negative refraction [1][2][3][4], invisibility cloaks [5][6][7][8], sub-wavelength focusing [9,10], or super absorption [11][12][13][14][15][16]. Many types of resonators have been identified and investigated, from split rings for electromagnetic waves [11] to loaded membranes for acoustic waves [14,15].…”

Anomalous sound absorption in lattices of cylindrical perforated shells

“…However, in the last years, 2D SCs consisting of cylinders fabricated with lossy materials are deserving attention due to their potential application as acoustic barrier for broadband noise. [5][6][7][8][9][10] The attention is paid here to 2D lattices of cylindrical perforated shells at normal incidence. These scattering units are obtained by rolling up perforated plates whose parameters (thickness, radius of the perforations, and perforation ratio) will determine the absorptive properties of the SC structure based on them.…”

Additional Sound Absorption Within a Poroelastic Lamella Network Under Oblique Incidence

“…An important limitation of the impedance tube method is that the dimensions of the sample are generally small, and even if the minimum size of samples in the impedance tube have been shown to be slightly expanded [30], out-of-tube methods are generally preferred since they generally allow simpler setups and testing large samples. Temporal separation and acoustic field approaches can mainly be distinguished (see a review paper in [31]), the latter mostly having been applied following the transfer function method using two microphones, a sound source and different field assumptions (plane or spherical waves, with fixed [32] or rotating samples [22] in anechoic rooms). The first alternative approach of which mention can be made is the increasingly common use of spherical microphone arrays [33].…”

“…To illustrate the different effects of the skeleton, a simple configuration made of a periodic arrangement of porolelastic lamellas and supported by a rigid backing as in Ref. [22] was chosen. When coupled with an acoustic excitation at oblique incidence, additional absorption peaks were observed linked to the bending resonance or shear resonance of the frame [23].…”