Ultrasound transmission through monodisperse 2D microfoams.

While the acoustic properties of solid foams have been abundantly characterized, sound propagation in liquid foams remains poorly understood. Recent studies have investigated the transmission of ultrasound through three-dimensional polydisperse liquid foams (Pierre et al., 2013, 2014, 2017).

Multiple scattering of an ultrasonic shock wave in bubbly media.

This experimental study deals with the propagation of an ultrasonic shock wave in a random heterogeneous medium, constituted of identical 75μm radius bubbles, trapped in a yield-stress fluid. The fundamental frequency of the incident wave (in the MHz range) was much larger than the resonance frequency of bubbles (38kHz). A well-expanded coda, resulting from the multiple scattering of the incident shock wave through the heterogeneous medium, was experimentally measured in transmission.

Investigating the origin of acoustic attenuation in liquid foams.

Liquid foams are known to be highly efficient to absorb acoustic waves but the origin of the sound dissipation remains unknown. In this paper, we present low frequency (0.5-4kHz) experimental results measured with an impedance tube and we confront the recorded attenuations with a simple model that considers the foam as a concentrate bubbly liquid.

Investigating the Existence of Bulk Nanobubbles with Ultrasound.

Nanobubbles are expected to dissolve in milliseconds. Experimental evidence of nanobubbles that were stable for days had thus been first received with circumspection. If the large number of experimental confirmations has now made clear that surface nanobubbles could exist, bulk nanobubbles are still subject to debate.

Combined effects of marinating and γ-irradiation in ensuring safety, protection of nutritional value and increase in shelf-life of ready-to-cook meat for immunocompromised patients.

The aim of this study was to evaluate the effect of combining marinating and γ-irradiation at doses of 1, 1.5 and 3kGy on Escherichia coli O157:H7, Salmonella typhimurium and Clostridium sporogenes in raw meat packed under vacuum and stored at 4°C and to estimate its safety and shelf-life. Further, the effect of combined treatments on sensorial, nutritional values (lipid oxidation, concentration of thiamin and riboflavin) and color was evaluated.

Resonant acoustic propagation and negative density in liquid foams.

We measured the dispersion relation for acoustic longitudinal waves in liquid foams, over a broad frequency range (60-600 kHz). Strong dispersion was found, with two nondispersive behaviors, separated by a negative density regime. A new model, based on the coupled displacements of films, liquid channels, and gas in the foam, rationalizes all the experimental findings.

Acoustic characterisation of liquid foams with an impedance tube.

Acoustic measurements provide convenient non-invasive means for the characterisation of materials. We show here for the first time how a commercial impedance tube can be used to provide accurate measurements of the velocity and attenuation of acoustic waves in liquid foams, as well as their effective "acoustic" density, over the 0.5-6kHz frequency range.

Influence of positional correlations on the propagation of waves in a complex medium with polydisperse resonant scatterers.

We present experimental results on a model system for studying wave propagation in a complex medium exhibiting low-frequency resonances. These experiments enable us to investigate a fundamental question that is relevant for many materials, such as metamaterials, where low-frequency scattering resonances strongly influence the effective medium properties. This question concerns the effect of correlations in the positions of the scatterers on the coupling between their resonances, and hence on wave transport through the medium.

Temperature-dependent diffusing acoustic wave spectroscopy with resonant scatterers.

The influence of a slight temperature change on the correlation of multiply scattered acoustic waves is studied, and experimental results are discussed. The technique presented here, similar to diffusing-acoustic-wave spectroscopy, is based on the sensitivity of a multiply scattering medium to a slight change. Ultrasonic waves around 3 MHz are transmitted through a sample made of steel rods in water and recorded by an array of transducers at different temperatures.

Sound velocity and attenuation in bubbly gels measured by transmission experiments.

Measurements of the phase velocity and attenuation of sound in concentrated samples of bubbly gels are presented. Hair gel was used as a matrix material to obtain well characterized distributions of bubbles. Ultrasonic measurements were conducted over a large range of frequencies, including the resonance frequencies of the bubbles.

Characterizing a model food gel containing bubbles and solid inclusions using ultrasound.

Ultrasonic spectroscopy is used to characterize a model aerated food system consisting of agar gel in which both bubbles and polystyrene beads are embedded. By exploiting the distinct frequency dependence of each inclusion's acoustic resonances, it is demonstrated that the sizes of the bubbles and beads can be measured by ultrasound even when the size distributions are so similar that these inclusions are difficult to distinguish in optical images. While these results demonstrate the potential for applying ultrasonic spectroscopy to evaluate any soft heterogeneous material in which both bubbles and solid inclusions are present, the technique is especially relevant for functional foods, in which solid functional ingredients must be incorporated without degrading the aerated structure of the food and causing unacceptable quality impairment.

Phase conjugation with a single bubble.

It is recalled how the nonlinear interaction between a gas bubble and an external extra pressure can yield phase conjugation. Using the Glauber representation, we show that the effect of the latter is formally analogous to that of a pi pulse in nuclear magnetic resonance, so that the acoustic equivalent of spin echoes may be expected in a bubble cloud. An experimental attempt to observe phase conjugation is reported in the single-bubble case.