Theoretical and experimental evidence of level repulsion states and evanescent modes in sonic crystal stubbed waveguides

The complex band structures calculated using the Extended Plane Wave Expansion (EPWE) reveal the presence of evanescent modes in periodic systems, never predicted by the classical \omega(\vec{k}) methods, providing novel interpretations of several phenomena as well as a complete picture of the system. In this work we theoretically and experimentally observe that in the ranges of frequencies where a deaf band is traditionally predicted, an evanescent mode with the excitable symmetry appears changing drastically the interpretation of the transmission properties. On the other hand, the simplicity of the sonic crystals in which only the longitudinal polarization can be excited, is used to interpret, without loss of generality, the level repulsion between symmetric and antisymmetric bands in sonic crystals as the presence of an evanescent mode connecting both repelled bands. These evanescent modes, obtained using EPWE, explain both the attenuation produced in this range of frequencies and the transfer of symmetry from one band to the other in good agreement with both experimental results and multiple scattering predictions. Thus, the evanescent properties of the periodic system have been revealed necessary for the design of new acoustic and electromagnetic applications based on periodicity

Fast bubble dynamics and sizing

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Experimental Method for Microbubbles Dynamics Monitoring and Radius Sizing

International audienceRationale and aim: Within the context of divers' decompression illness prevention, ultrasonic detection and sizing of circulating microbubbles in blood is of great interest. In order to be representative of the divers gas tension level (supersaturation) and thus, to optimize decompression stages, the measurements (made in the right ventricle region) should be performed during a short period of time (ventricle filling <20 ms), efficient to detect a broad range of bubbles' radii population (radius from 20 to 200 _m) and harmless (Mechanical Index MI<0.3). Materials and methods: Based on a bi-frequency ultrasound excitation, the purpose of our method is to measure the relative and the absolute microbubble size variations. Because of our research interests, the experimental investigations were conducted on natural microbubbles, with radius ranging between 20 and 200 μm, excited around their resonance frequencies by a low frequency transducer. Different types of excitation were tested (sweep, burst, pulse). A pair of high frequency transducers were arranged to focus at a common point. One of the transducers was used to transmit a 2ms duration high-frequency (1 MHz) pulse while the other was used to passively receive backscattered signals. The scattered signal was acquired and visualized on a digital oscilloscope and transferred for offline calculations. Signal treatment were conducted in order to recover the amplitude and frequency modulations. Results: Using the same experimental setup, simple signal processing applied on both the amplitude and the frequency modulations leads to a double characterization of the microbubble dynamics. Moreover, under the assumption of small radial oscillations, the equilibrium radius of the microbubble can be accurately estimate

Evolution of localized surface plasmon resonance made of gold nanowire chain embedded in WS2multilayers

International audienceRecently, the transition metal dichalcogenides (TMDs) have emerged as a new class of building blocks for engineering enhanced plasmonic sensors. This class of materials can be made with a low production cost and can be easily hybridized with metallic nanoparticles whereby desired molecules are thoroughly detected. In this work, we evidence coupling between metallic gold nanowires and a WS2multi-layer. The novelty lies in the resilient stability of the effect of the thickness layer variation on both, the sensitivity performances and the electric field distribution in the visible and near-infrared spectra. Such configuration can consequently be regarded as an unwavering avenue towards conception of promising and reliable new generation of sensors. © 2021 Elsevier Ltd. All rights reserved

Unveiling extreme anisotropy in elastic structured media

Periodic structures can be engineered to exhibit unique properties observed at symmetry points, such as zero group velocity, Dirac cones, and saddle points; identifying these and the nature of the associated modes from a direct reading of the dispersion surfaces is not straightforward, especially in three dimensions or at high frequencies when several dispersion surfaces fold back in the Brillouin zone. A recently proposed asymptotic high-frequency homogenization theory is applied to a challenging time-domain experiment with elastic waves in a pinned metallic plate. The prediction of a narrow high-frequency spectral region where the effective medium tensor dramatically switches from positive definite to indefinite is confirmed experimentally; a small frequency shift of the pulse carrier results in two distinct types of highly anisotropic modes. The underlying effective equation mirrors this behavior with a change in form from elliptic to hyperbolic exemplifying the high degree of wave control available and the importance of a simple and effective predictive model

Clamped seismic metamaterials: Ultra-low broad frequency stop-bands

The regularity of earthquakes, their destructive power, and the nuisance of ground vibration in urban environments, all motivate designs of defence structures to lessen the impact of seismic and ground vibration waves on buildings. Low frequency waves, in the range 1–10 Hz for earthquakes and up to a few tens of Hz for vibrations generated by human activities, cause a large amount of damage, or inconvenience; depending on the geological conditions they can travel considerable distances and may match the resonant fundamental frequency of buildings. The ultimate aim of any seismic metamaterial, or any other seismic shield, is to protect over this entire range of frequencies; the long wavelengths involved, and low frequency, have meant this has been unachievable to date. Notably this is scalable and the effects also hold for smaller devices in ultrasonics. There are three approaches to obtaining shielding effects: bragg scattering, locally resonant sub-wavelength inclusions and zerofrequency stop-band media. The former two have been explored, but the latter has not and is examined here. Elastic flexural waves, applicable in the mechanical vibrations of thin elastic plates, can be designed to have a broad zero-frequency stop-band using a periodic array of very small clamped circles. Inspired by this experimental and theoretical observation, all be it in a situation far removed from seismic waves, we demonstrate that it is possible to achieve elastic surface (Rayleigh)wave reflectors at very large wavelengths in structured soils modelled as a fully elastic layer periodically clamped to bedrock. We identify zero frequency stop-bands that only exist in the limit of columns of concrete clamped at their base to the bedrock. In a realistic configuration of a sedimentary basin 15 m deep we observe a zero frequency stop-band covering a broad frequency range of 0–30 Hz

Elastic wave control beyond band-gaps: shaping the flow of waves in plates and half-spaces with subwavelength resonant rods.

In metamaterial science, local resonance and hybridization are key phenomena strongly influencing the dispersion properties; the metasurface discussed in this article created by a cluster of resonators, subwavelength rods, atop an elastic surface being an exemplar with these features. On this metasurface, band-gaps, slow or fast waves, negative refraction, and dynamic anisotropy can all be observed by exploring frequencies and wavenumbers from the Floquet–Bloch problem and by using the Brillouin zone. These extreme characteristics, when appropriately engineered, can be used to design and control the propagation of elastic waves along the metasurface. For the exemplar we consider, two parameters are easily tuned: rod height and cluster periodicity. The height is directly related to the band-gap frequency and, hence, to the slow and fast waves, while the periodicity is related to the appearance of dynamic anisotropy. Playing with these two parameters generates a gallery of metasurface designs to control the propagation of both flexural waves in plates and surface Rayleigh waves for half-spaces. Scalability with respect to the frequency and wavelength of the governing physical laws allows the application of these concepts in very different fields and over a wide range of lengthscales

The influence of building interactions on seismic and elastic body waves

We outline some recent research advances on the control of elastic waves in thin and thick plates, that have occurred since the large scale experiment [S. Brûlé, Phys. Rev. Lett. 112, 133901 (2014)] that demonstrated significant interaction of surface seismic waves with holes structuring sedimentary soils at the meter scale. We further investigate the seismic wave trajectories of compressional body waves in soils structured with buildings. A significant substitution of soils by inclusions, acting as foundations, raises the question of the effective dynamic properties of these structured soils. Buildings, in the case of perfect elastic conditions for both soil and buildings, are shown to interact and strongly influence elastic body waves; such site-city seismic interactions were pointed out in [Guéguen et al., Bull. Seismol. Soc. Am. 92, 794–811 (2002)], and we investigate a variety of scenarios to illustrate the variety of behaviours possible

Dispersion relation of coupled-resonator acoustic waveguides formed by defect cavities in a phononic crystal

[EN] We investigate the dispersion of phononic crystal waveguides formed by evanescent coupling of a chain of defect cavities and supporting slow-wave propagation. These coupled-resonator acoustic waveguides (CRAWs) are analogous to the coupled-resonator optical waveguides formed in photonic crystals. CRAW dispersion can be controlled by increasing the distance between cavities, with the result of decreasing their coupling, and hence flattening the dispersion relation. Based on the tight-binding model, the dispersion relation is found in the form of a Fourier series expansion with explicitly given coefficients. This model is tested against the exact dispersion relation of a two-dimensional solid-solid phononic crystal of tungsten inclusions in a silicon matrix and only partial agreement is found. An alternative model of a linear chain of coupled resonators, resting only on the hypotheses of linearity and periodicity, is then proposed. While the Fourier coefficients in this model are a priori unspecified, they can be fitted against the exact dispersion relation, resulting in an excellent agreement with only a few terms in the Fourier series expansion. The Fourier coefficients are shown to be a direct measure of the coupling of neighbouring resonators.Financial support from the European Community's Seventh Framework program (FP7/2007-2013) under grant agreement number 233883 (TAILPHOX) is gratefully acknowledged. VL acknowledges the support of the Labex ACTION program (contract ANR-11-LABX-01-01).Escalante Fernández, JM.; Martínez Abietar, AJ.; Laude, V. (2013). Dispersion relation of coupled-resonator acoustic waveguides formed by defect cavities in a phononic crystal. Journal of Physics D Applied Physics. 46(47):475301-475307. https://doi.org/10.1088/0022-3727/46/47/475301S475301475307464