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

Abstract

PACS 43-Acoustics PACS 68.60.Bs -Mechanical and acoustical properties PACS 81.05.Xj -Metamaterials for chiral, bianisotropic and other complex media Abstract -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 (λ/15). The proposed design can be considered as a new building block for acoustic metasurfaces having a high level of manipulation of acoustic waves.The advent of phononic crystals in the landscape of elastic/acoustic waves has opened up new prospects in understanding and controlling wave propagation [1][2][3]. Indeed, phononic crystals use fundamental properties of waves, such as diffusion or Bragg interference phenomena, in order to generate the so-called band gaps, which are basically frequency bands where there is no wave propagation [4]. Sound control, in the audible range, is the most evident application of band gaps. For the human ear, the frequency range under consideration is approximately from 20 Hz to 20 kHz, which corresponds to wavelength up to several meters in air. Therefore, dealing with a sonic crystal with a period in this size range would be certainly cumbersome. The sculptureÓrgano of Eusebio Sempere is an excellent example of this [5].Recently, various studies involving resonators have shown how to overcome these limitations and reach promising applications [6,7]. This is the case of the Locally Resonant Sonic Crystal (LRSC) introduced in 2000 by Liu et al. consisting of metal spheres coated with an elastic material, and for which a negative dynamic mass density is generated leading to band gaps at frequencies lower than that of a classical Bragg-based sonic crystal of equal dimensions [8]. More recently, a panel version of the LRSC was proposed in the form of an elastic membrane fixed by a grid, in the middle of which was attached a small mass [9]. In this metamaterial, a near-total reflection occurs around the resonance. Besides these, recent studies have highlighted some properties arising from using spacecoiling in acoustic metamaterials, introduced by Liang and Li [10]. Among them, the possibility of generating extreme effective parameters, which offer promising applications such as negative refraction. Therefore, subsequent studies have brought to light both non-resonant [11][12][13][14], and resonant [15] ac...

Low-frequency Gibbs-type oscillation in finite solid–fluid sonic crystals and its application in sub-wavelength wave isolation for waterborne sound

“…Due to their remarkable effective characteristics, e.g. negative mass density and/or bulk modulus, zero or negative effective refractive index, etc, low-frequency wave isolation can be realized with compact structures [14][15][16][17][18][19][20][21]. For example, locally resonant metamaterials with negative mass density exhibit a sound-blocking effect in the low-frequency region, in which the lattice constants can be two orders of magnitude smaller than the relevant sound wavelength [14].…”

“…For example, locally resonant metamaterials with negative mass density exhibit a sound-blocking effect in the low-frequency region, in which the lattice constants can be two orders of magnitude smaller than the relevant sound wavelength [14]. Besides this, labyrinthine or space-coiling metamaterials based on the creation of a network of sub-wavelength internal channels are capable of reflecting sound waves at much lower frequencies, whose corresponding wavelengths are several times the length of the structures [18][19][20]. In addition, Cheng and coworkers have proposed an ultra-sparse metamaterial based on artificial 'space-coiling' Mie resonances for the high reflection of low-frequency sound [21].…”