Abstract
Soft porous silicone rubbers are demonstrated to exhibit extremely low sound speeds of tens of m/s for these dense materials, even for low porosities of the order of a few percent. Our ultrasonic experiments show a sudden drop of the longitudinal sound speed with the porosity, while the transverse sound speed remains constant. For such porous elastomeric materials, we propose simple analytical expressions for these two sound speeds, derived in the framework of Kuster and Toksöz, revealing an excellent agreement between the theoretical predictions and the experimental results for both longitudinal and shear waves. Acoustic attenuation measurements also complete the characterization of these soft porous materials.
Highlights
Since the pioneering works of Liu et al about locally resonant sonic materials[1], so-called acoustic metamaterials[2], the soft silicone rubber materials have brought renewed attention due to their supposed ‘ultra-low’ longitudinal sound speed[3,4,5,6,7]
In the case where the incident wavelength λ0 of the propagating elastic wave is much longer than the pore size a, various more-or-less simple models have been reported to describe the effective properties of porous materials in the quasi-static limit[16]
We propose to use the model of Kuster and Toksöz[17], in order to analyze the measured ultrasonic properties of soft porous silicone rubber materials with controlled porosities φ ranging from 0% to 35% (Fig. 1)
Summary
Since the pioneering works of Liu et al about locally resonant sonic materials[1], so-called acoustic metamaterials[2], the soft silicone rubber materials have brought renewed attention due to their supposed ‘ultra-low’ longitudinal sound speed[3,4,5,6,7]. In the case where the incident wavelength λ0 of the propagating elastic wave is much longer than the pore size a, various more-or-less simple models have been reported to describe the effective properties of porous materials in the quasi-static limit[16].
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