Subwavelength sound screening by coupling space-coiled Fabry-Perot resonators

We explore broadband and omnidirectional low frequency sound screening based on locally resonant acoustic metamaterials. We show that the coupling of different resonant modes supported by Fabry-Perot cavities can efficiently generate asymmetric lineshapes in the transmission spectrum, leading to a broadband sound opacity. The Fabry-Perot cavities are space-coiled in order to shift the resonant modes under the diffraction edge, which guaranty the opacity band for all incident angles. Indeed, the deep subwavelength feature of the cavities leads to avoid diffraction that have been proved to be the main limitation of omnidirectional capabilities of locally resonant perforated plates. We experimentally reach an attenuation of few tens of dB at low frequency, with a metamaterial thickness fifteen times smaller than the wavelength (lambda / 15). The proposed design can be considered as a new building block for acoustic metasurfaces having a high level of manipulation of acoustic waves.Comment: 7 pages, 8 figure

Density-near-zero using the acoustically induced transparency of a Fano acoustic resonator

We report experimental results of near-zero mass density involving an acoustic metamaterial supporting Fano resonance. For this, we designed and fabricated an acoustic resonator with two closely coupled modes and measured its transmission properties. Our study reveals that the phenomenon of acoustically induced transparency is accompanied by an effect of near-zero density. Indeed, the dynamic effective parameters obtained from experimental data show the presence of a frequency band where the effective mass density is close to zero, with high transmission levels reaching 0.7. Furthermore, we demonstrate that such effective parameters lead to wave guiding in a 90-degrees–bent channel. This kind of acoustic metamaterial can, therefore, give rise to acoustic functions like controlling the wavefront, which may lead to very promising applications in acoustic cloacking or imaging

Density-near-zero using the acoustically induced transparency of a Fano acoustic resonator

International audienceWe report experimental results of near-zero mass density involving an acoustic metamaterialsupporting Fano resonance. For this, we designed and fabricated an acoustic resonatorwith two closely coupled modes and measured its transmission properties. Our study reveals thatthe phenomenon of acoustically induced transparency is accompanied by an effect of near-zerodensity. Indeed, the dynamic effective parameters obtained from experimental data show thepresence of a frequency band where the effective mass density is close to zero, with high transmissionlevels reaching 0.7. Furthermore, we demonstrate that such effective parameters lead towave guiding in a 90-degrees–bent channel. This kind of acoustic metamaterial can, therefore,give rise to acoustic functions like controlling the wavefront, which may lead to very promisingapplications in acoustic cloacking or imaging

Subwavelength waveguiding of surface phonons in pillars-based phononic crystal

In this study, we theoretically analyze the guiding of surface phonons through locally resonant defects in pillars-based phononic crystal. Using finite element method, we simulate the propagation of surface phonons through a periodic array of cylindrical pillars deposited on a semi-infinite substrate. This structure displays several band gaps, some of which are due to local resonances of the pillar. By introducing pillar defects inside the phononic structure, we show the possibility to perform a waveguiding of surface phonons based on two mechanisms that spatially confine the elastic energy in very small waveguide apertures. A careful choice of the height of the defect pillars, allows to shift the frequency position of the defect modes inside or outside the locally resonant band gaps and create two subwavelenght waveguiding mechanisms. The first is a classical mechanism that corresponds to the presence of the defect modes inside the locally resonant band gap. The seconde is due to the hybridation between the phonon resonances of defect modes and the surface phonons of the semi-infinite homogenous medium. We discuss the nature and the difference between both waveguiding phenomena

Acoustically induced transparency using Fano resonant periodic arrays

International audienceA three-dimensional acoustic device, which supports Fano resonance and induced transparency in its response to an incident sound wave, is designed and fabricated. These effects are generated from the destructive interference of closely coupled one broad- and one narrow-band acousticmodes. The proposed design ensures excitation and interference of two spectrally close modes by locating a small pipe inside a wider and longer one. Indeed, numerical simulations and experiments demonstrate that this simple-to-fabricate structure can be used to generate Fano resonance aswell as acoustically induced transparency with promising applications in sensing, cloaking, and imagin

Guiding and confinement of interface acoustic waves in solid-fluid pillar-based phononic crystals

Pillar-based phononic crystals exhibit some unique wave phenomena due to the interaction between surface acoustic modes of the substrate and local resonances supported by pillars. In this paper, we extend the investigations by taking into account the presence of a liquid medium. We particularly demonstrate that local resonances dramatically decrease the phase velocity of Scholte-Stoneley wave, which leads to a slow wave at the solid/fluid interface. Moreover, we show that increasing the height of pillars introduces a new set of branches of interface modes and drastically affects the acoustic energy localization. Indeed, while some modes display a highly confined pressure between pillars, others exponentially decay in the fluid or only propagate in the solid without disturbing the fluid pressure. These theoretical results, performed by finite element method, highlight a new acoustic wave confinement suitable in various applications such as acoustophoresis, lab on chip and microfluidics