A PDMS-based broadband acoustic impedance matched material for underwater applications.

Having a material that is matched in acoustic impedance with the surrounding medium is a considerable asset for many underwater acoustic applications. In this work, impedance matching is achieved by dispersing small, deeply subwavelength sized particles in a soft matrix, and the appropriate concentration is determined with the help of Coherent Potential Approximation and Waterman & Truell models. We show experimentally the validity of the models using mixtures of Polydimethylsiloxane (PDMS) and TiO particles.

Relation between ultrasonic properties, rheology and baking quality for bread doughs of widely differing formulation.

Background: The objective was to evaluate whether an ultrasonic reflectance technique has predictive capacity for breadmaking performance of doughs made under a wide range of formulation conditions. Two flours of contrasting dough strength augmented with different levels of ingredients (inulin, oil, emulsifier or salt) were used to produce different bread doughs with a wide range of properties. Breadmaking performance was evaluated by conventional large-strain rheological tests on the dough and by assessment of loaf quality.

Observation of infinite-range intensity correlations above, at, and below the mobility edges of the 3D Anderson localization transition.

We investigate long-range intensity correlations on both sides of the Anderson transition of classical waves in a three-dimensional disordered material. Our ultrasonic experiments are designed to unambiguously detect a recently predicted infinite-range C0 contribution, due to local density of states fluctuations near the source. We find that these C0 correlations, in addition to C2 and C3 contributions, are significantly enhanced near mobility edges.

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.

Observation of multifractality in Anderson localization of ultrasound.

We report the experimental observation of strong multifractality in wave functions below the Anderson localization transition in open three-dimensional elastic networks. Our results confirm the recently predicted symmetry of the multifractal exponents. We have discovered that the result of multifractal analysis of real data depends on the excitation scheme used in the experiment.

Transmission of ultrasound through a single layer of bubbles.

We investigate, both experimentally and theoretically, the effect of coupling between resonant scatterers on the transmission coefficient of a model system of isotropic scatterers. The model system consists of a monodisperse layer of bubbles, which exhibit a strong monopole scattering resonance at low ultrasonic frequencies. The layer was a true 2D structure obtained by injecting very monodisperse bubbles (with radius a approximately 100 microm) into a yield-stress polymer gel.

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.