Experimental evidence of isotropic transparency and complete band gap formation for ultrasounds propagating in stealth hyperuniform media

Following on recent experimental characterization of the transport properties of stealth hyperuniform media for electromagnetic and acoustic waves, we report here measurements at ultrasonic frequencies of the multiple scattering of waves by 2D hyperuniform distributions of steel rods immersed in water. The transparency, for which the effective attenuation of the medium is cancelled, is first evidenced by measuring the transmission of a plane wave propagating in a highly correlated and relatively dense medium. It is shown that a band gap occurs in the vicinity of the first Bragg frequency. The isotropy of both transparency and bang gap are also evidenced for the case of waves generated by a point source in differently ordered and circular shaped distributions. In other words, we thus obtain a representation of the Green's function. Our results demonstrate the huge potential of hyperuniform as well as highly correlated media for the design of functional materials

Influence of the microstructure of 2D-random heterogeneous media on the propagation of acoustic coherent waves

International audienceMultiple scattering of waves arises in all fields of physics either in periodic or random media. For random media the organization of the microstructure (uniform or non-uniform statistical distribution of scatterers) has effects on the propagation of coherent waves. Using a recent exact resolution method and different homogenization theories, the effects of the microstructure on the effective wavenumber are investigated over a large frequency range (ka between 0.1 and 13.4) and high concentrations. For uniform random media, increasing the configurational constraint makes the media more transparent for low frequencies and less for high frequencies. As a side but important result, we show that two of the homogenization models considered here appear to be very efficient at high frequency up to a concentration of 60%, in the case of uniform media. For non-uniform media, for which clustered and periodic aggregates appear, the main effect is to reduce the magnitude of resonances and to make network effects appear. In this case, homogenization theories are not relevant to make a detailed analysis

Propagation guidée d'ondes de cisaillement horizontales dans des plaques solides rugueuses

La propagation des ondes de cisaillement à polarisation horizontale (ondes SH) dans des guides d'ondes isotropes à surfaces rugueuses fait apparaître des mécanismes de couplage de modes guidés. La modélisation de ces mécanismes est basée sur la formulation intégrale, et les solutions reposent sur des développements modaux en guide à géométrie compatible, extérieur au guide réel. Les résultats obtenus pour des rugosités périodiques sont en accord avec des résultats numériques de la littérature

Beam distortion detection and deflectometry measurements of gigahertz surface acoustic waves

Gigahertz acoustic waves propagating on the surface of a metal halfspace are detected using different all-optical detection schemes, namely, deflectometry and beam distortion detection techniques. Both techniques are implemented by slightly modifying a conventional reflectometric setup. They are then based on the measurement of the reflectivity change but unlike reflectometric measurements, they give access to the sample surface displacement. A semi-analytical model, taking into account optical, thermal, and mechanical processes responsible for acoustic waves generation, allows analyzing the physical content of the detected waveforms

Codes for a pair of papers entitled "Multi-mode multiple wave scattering in suspensions of solid particles in viscous liquids"

Here we provide the model codes for the calculations presented in the papers by Valerie Pinfield and Tony Valier Brasier in Proceedings of the Royal Society A, 2024.Multimode multiple wave scattering in suspensions of solid particles in viscous liquids: Part 1 asymptotic resultsMultimode multiple wave scattering in suspensions of solid particles in viscous liquids: Part 2 numerical validationThe papers present asymptotic results for a mathematical model of multiple elastic wave scattering in systems of spherical particles in a viscous liquid, exploring the effects of the dipolar resonance, wave conversion contributions to multiple scattering and positional correlations between particles.© The Authors. This code is shared under GNU General Public License version 3.</p

Multimode multiple wave scattering in suspensions of solid particles in viscous liquids: Part 2: numerical validation

In the first paper in this series, we presented asymptotic results for the effective wavenumber of the coherent longitudinal waves propagating through a system of pseudorandomly-distributed spherical elastic scatterers in a viscous medium. The analysis was based on multi-modal multiple scattering theory to account for both longitudinal and shear waves in the viscous embedding medium, arising from wave conversions at the scatterers surface, and identified asymptotic results in the long wavelength limit of the longitudinal waves. In this second paper, we present numerical validation of the various asymptotic approximations presented previously, including truncation of the number of partial wave orders and the use of the low concentration expansion of the dispersion relation. We explore the important contributions of wave conversion and of correlations in particle positions to the effective attenuation and to the frequency of the dipolar resonance of the scatterers. A comparison of the experimental results obtained with water containing sub-micrometric silica beads shows the very good validity of the model, particularly in the vicinity of the dipolar resonance.</p

Data and code for a pair of papers by Pinfield and Valier-Brasier entitled "Multimode multiple wave scattering in suspensions of solid particles in viscous liquids"

Here we provide the dataset (model calculations and experimental data) and the code for the models presented in the papers by Valerie Pinfield and Tony Valier Brasier in Proceedings of the Royal Society A, 2024.Multimode multiple wave scattering in suspensions of solid particles in viscous liquids: Part 1 asymptotic resultsMultimode multiple wave scattering in suspensions of solid particles in viscous liquids: Part 2 numerical validationThe papers present asymptotic results for a mathematical model of multiple elastic wave scattering in systems of spherical particles in a viscous liquid, exploring the effects of the dipolar resonance, wave conversion contributions to multiple scattering and positional correlations between particles. </p

Coherent elastic waves in a multiple scattering solid media

The propagation of elastic waves in materials containing randomly distributed particles is a fundamental topic that has been treated by many authors for several decades. In particular, the advent of metamaterials has highlighted the need to determine the effective properties of samples and in particular the effective density. In this context, we are interested in the propagation of elastic waves in an epoxy resin containing a monodisperse distribution of spherical dense particles. This kind of scatterer has two sub-wavelength resonances: the dipolar resonances in translation and in rotation. The influence of the dipolar resonance in translation on coherent longitudinal waves has already been studied previously in the team [1]. In the continuity of this work, we present here coherent transverse wave measurements and we highlight the influence of the two dipolar resonances on these coherent waves. For this, we use a new and original technique of characterization of the samples, called the technique "Sandwich" [2]. This technique, which has already shown its potential to characterize very attenuating homogeneous samples, is based on the study of Fabry-Perot interferences in the sample. The use of this technique allows us to determine not only the effective transverse wavenumber, but also the effective density and the effective shear modulus. [1] :Duranteau et al., Random acoustic metamaterial with a subwavelength dipolar resonance, Journal of Acoustical Society of America, 139, 2016 [2] :Simon et al., Viscoelatic shear modulus measurement of thin materials by interferometry at ultrasonic frequencies. Journal of Acoustical Society of America, 146, 201

Multimode multiple wave scattering in suspensions of solid particles in viscous liquids: Part 1 asymptotic results

The propagation of coherent longitudinal waves in a viscous liquid containing a random distribution of spherical elastic particles is analysed using a model based on multiple scattering theory. This model, initially developed to describe the propagation of coupled longitudinal and transverse elastic waves in isotropic solid materials, takes into account wave conversions at the particle surface as well as positional correlations between particles via the pair correlation function. By modelling a Newtonian viscous liquid through complex frequency-dependent elastic moduli (i.e. using an imaginary shear modulus), the model is adapted to the case of viscous fluids and we show that conversions of longitudinal waves into transverse waves are important to take into account. We present asymptotic results from the model for case of long wavelength for the longitudinal waves, without assumptions on the shear wavelength. For high concentrations, these wave conversions are reinforced by the contribution of position correlations between the particles. In a subsequent paper, we present numerical validation of the asymptotic approximations and compare them with experimental results for solid particles in water.</p

Full characterization of Polyurethane by ultrasonic measurements and temperature control

Polyurethane (PU) is a polymer often used in underwater acoustics due to its water-like acoustic properties and good resistance to low temperatures, sea water ageing and salinity. The full characterization of PU is challenging and especially that of its shear modulus. In this context, we propose two ultrasonic measurement methods with a precise temperature control in order to identify the dynamic behavior of PU. On the one hand, we have adapted the � anvil � technique used to characterize fluid rheology, to determine the shear modulus of PU. This technique is based on the measurment of the reflection coefficents of shear horizontal waves at oblique incidence. On the other hand, measurements in transmission in immersion are peformed in order to determine the bulk modulus of the PU. With the help of the temperature control, the time-temperature superposition principle is studied. That allows to determine the rheology of the PU over a wide frequency band and fractionnar derivative models are then used to describe this rheology