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The propagation of coherent longitudinal and transverse waves in random distributions of spherical scatterers embedded in an elastic matrix is studied. The investigated frequency range is the vicinity of the resonance frequencies of the translational and rotational motion of the spheres forced by the waves, where strong dispersion and attenuation are predicted. A technique for making samples made of layers of carbide tungsten beads embedded in epoxy resin is presented, which allows control of the scatterers distribution, induce short-range positional correlations, and minimize the anisotropy of samples. Comparison between phase velocity and attenuation measurements and a model based on multiple scattering theory (MST) shows that bulk effective properties accurately described by MST are obtained from three beads layers. Besides, short-range correlations amplify the effect of mechanical resonances on the propagation of longitudinal and transverse coherent waves. As a practical consequence, the use of short-range positional correlations may be used to enhance the attenuation of elastic waves by disordered, locally resonant, elastic metamaterials, and MST globally correctly predicts the effect of short-range positional order on their effective properties., (© 2024 Acoustical Society of America.)

We present a thorough procedure for measuring the rheological properties of soft, highly attenuating, visco-elastic materials at ultrasonic frequencies. The material chosen for this illustration is a crosslinked Polyurethane (PU) elastomer (Sika UR3440 type), which is widely used in the field of underwater acoustics. We determine its complex longitudinal modulus M and shear modulus G as function of frequency in the range 1-5 MHz and of temperature in the range 5-40 °C. M is determined from the measurement of the transmission of longitudinal, plane waves by a slab of PU immersed in water. G is determined by contact measurements from the transmission and reflection of transverse, plane waves by a slab of PU. This determination of G for such a soft and viscous material as PU is made possible by the use of thin slabs and the implementation of an original signal analysis. M, G and bulk modulus K are found to obey the time-temperature superposition principle and to be accurately described by a fractional derivative rheological model. This allows us to propose analytic formulas for the frequency and temperature dependence of M, G and K valid above PU glass transition temperature., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Baudis reports financial support was provided by French Government Defense Innovation Agency., (Copyright © 2023 Elsevier B.V. All rights reserved.)

We report on numerical simulation of fluid interface deformations induced by either acoustic or optical radiation pressure. This is done by solving simultaneously the scalar wave propagation equation and the two-phase flow equations using the boundary element method. Using dimensional analysis, we show that interface deformation morphogenesis is universal, i.e., depends on the same dimensionless parameters in acoustics and electromagnetics. We numerically investigate a few selected phenomena-in particular the shape of large deformations and the slenderness transition and its hysteresis-and compare with existing and novel experimental observations. Qualitative agreement between the numerical simulations and experiments is found when the mutual interaction between wave propagation and wave-induced deformations is taken into account. Our results demonstrate the leading role of the radiation pressure in morphogenesis of fluid interface deformations and the importance of the propagation-deformation interplay.