Underwater sound transmission through arrays of disk cavities in a soft elastic medium

Abstract

Scattering from a cavity in a soft elastic medium, such as silicone rubber, resembles scattering from an underwater bubble in that low-frequency monopole resonance is obtainable in both cases. Arrays of cavities can therefore be used to reduce underwater sound transmission using thin layers and low void fractions. This article examines the role of cavity shape by microfabricating arrays of disk-shaped air cavities into single and multiple layers of polydimethylsiloxane. Comparison is made with the case of equivalent volume cylinders which approximate spheres. Measurements of ultrasonic underwater sound transmission are compared with finite element modeling predictions. The disks provide a deeper transmission minimum at a lower frequency owing to the drum-type breathing resonance. The resonance of a single disk cavity in an unbounded medium is also calculated and compared with a derived estimate of the natural frequency of the drum mode. Variation of transmission is determined as a function of disk tilt angle, lattice constant, and layer thickness. A modeled transmission loss of 18 dB can be obtained at a wavelength about 20 times the three-layer thickness, and thinner results (wavelength/thickness $ 240) are possible for the same loss with a single layer depending on allowable hydrostatic pressure.

Phenomenological law for the acoustic reflection by an array of cylindrical cavities in a soft elastic medium

“…The wavelength being of the order of 2 cm, this wave can be identified as a shear wave. Note that this phenomenon was already observed by Calvo et al 14 , and that this new source of damping was taken into account for 2D disks by Sharma et al In Fig. 6 we can notice that there is still an influence of G: for AR> 10, ω 3 increases with G. We find that it follows a scaling law close to ω 3 ∼ G 1/4 .…”

“…To investigate the effect of the aspect ratio, we performed numerical simulations with a single cylinder in a soft elastic medium. We used the same configuration as Calvo et al 14 , with a geometry depicted in Fig. 3.…”

“…[11][12][13] Elongated cavities are of particular interest because, for a given volume, they can be thinner and thus be embedded in thinner structures. Recently, Calvo et al 14 showed experimentally that flat cylindrical cavities were a promising option for reaching low frequency absorption with a thin layer of elastomer. Sharma et al 15 derived a model that is suitable for these experiments, considering the flat cylinders as two-dimensional disks.…”

Scattering of acoustic waves by a nonlinear resonant bubbly screen

“…Next, accounting for different shape of the bubbles would affect the microscopic solution, namely the response of a single bubble e.g. a disk with monopolar resonance (Calvo et al 2015). Following Ammari et al (2017aAmmari et al ( , 2018Ammari et al ( , 2019, it should be possible to extend our present work to any geometry.…”

Acoustics of bubbles trapped in microgrooves: From isolated subwavelength resonators to superhydrophobic metasurfaces

“…There are, however, challenges in using bubbles for metamaterial applications: beyond their tendency to dissolve, bubble screens and clusters are naturally disordered, mobile and polydisperse. Such difficulties could be overcome, at the cost of reducing the contrast between the phases, by embedding bubbles in a soft elastic matrix [23][24][25][26] or by encapsulating bubbles in elastic shells [27][28][29].…”