Boundary-Layer Effects on Acoustic Transmission Through Narrow Slit Cavities

Ward, Gareth P.; Lovelock, Ruth Kathleen; Murray, Alasdair; Hibbins, Alastair P.; Sambles, J. R.; Smith, John David

doi:10.1103/physrevlett.115.044302

Cited by 83 publications

(95 citation statements)

References 20 publications

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“…The space-coiling design has not yet been demonstrated in water, where common solids such as steel that might be used to confine the coils cannot be assumed to be perfectly rigid due to their significantly smaller density contrast with water-thus introducing the challenge of elastic coupling [37] that must be incorporated into any design strategy. Although the kinematic viscosity of water is less than that of air [23], recent measurements of air-borne space-coiled metamaterials [36] demonstrate significant attenuation, and we caution that viscous effects should not be neglected in aqueous designs.…”

Section: Discussionmentioning

confidence: 99%

“…For our measurement temperature of 293 K and the lowest operational frequency of 5 kHz, the viscous and thermal boundary layers in water are calculated to be 8 and 3 μm, respectively. These boundary layers are less than 0.3% of the smallest cylinder separation in our lattice, a value that is much lower than the approximately 5% threshold that was recently demonstrated to impact acoustic performance in small channels [23]. The impact of viscosity and heating is also derived for sonic crystal lattices composed of rigid [24] and elastic [25] scatterers, and the application of this theory to our lattice geometry under a rigid approximation results in a negligible dissipation factor of one part in a thousand.…”

Section: Methodsmentioning

confidence: 99%

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Transparent Gradient-Index Lens for Underwater Sound Based on Phase Advance

et al. 2015

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Spatial gradients in a refractive index are used extensively in acoustic metamaterial applications to control wave propagation through phase delay. This study reports the design and experimental realization of an acoustic gradient-index lens using a sonic crystal lattice that is impedance matched to water over a broad bandwidth. In contrast to previous designs, the underlying lattice features refractive indices that are lower than the water background, which facilitates propagation control based on a phase advance as opposed to a delay. The index gradient is achieved by varying the filling fraction of hollow, air-filled aluminum tubes that individually exhibit a higher sound speed than water and matched impedance. Acoustic focusing is observed over a broad bandwidth of frequencies in the homogenization limit of the lattice, with intensity magnifications in excess of 7 dB. An anisotropic lattice design facilitates a flatfaceted geometry with low backscattering at 18 dB below the incident sound-pressure level. A threedimensional Rayleigh-Sommerfeld integration that accounts for the anisotropic refraction is used to accurately predict the experimentally measured focal patterns.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Transparent Gradient-Index Lens for Underwater Sound Based on Phase Advance

et al. 2015

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“…These values are less than 2% of the minimum separation, d, between building units in the metamaterial lattice; d ¼ 2R ext − a. This value is lower than the approximately 5% threshold that was recently demonstrated to impact acoustic performance in small channels [36]. Regarding the separation between walls inside a building unit, the minimum distance is given by 2πR a =16.…”

Section: Scaling Of the Metamaterialsmentioning

confidence: 99%

Viscothermal Losses in Double-Negative Acoustic Metamaterials

2017

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The influence of losses in double-negative metamaterial slabs recently introduced by Graciá-Salgado et al. [Phys. Rev. B 88, 224305 (2013)] is comprehensively studied. Viscous and thermal losses are considered in the linearized Navier-Stokes equations with no flow. Despite the extremely low thicknesses of boundary layers associated with each type of losses, the double-negative behavior is totally suppressed for the rigid structures under analysis. In other words, almost 100% of the energy transmitted into the slab is dissipated by viscothermal effects, in agreement with experimental data. Simulations undertaken for larger structures, using scale factors of up to 20 times, show that double-negative behavior is never recovered. The huge dissipation obtained by these structures leads us to propose them as interesting alternatives to conventional absorbers for specific situations, e.g., when treating low frequencies or when the excitation is narrow banded.

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“…When dealing with such subwavelength structures, it was notably showed that dissipation due to boundary layer effects cannot be neglected [37]. In our numerical calculation of transmission spectrum, represented in Figure 6, we have included thermoacoustic equations in order to take into account dissipations.…”

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confidence: 99%

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

Elayouch

Addouche

Farhat

et al. 2017

EPL

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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...

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Boundary-Layer Effects on Acoustic Transmission Through Narrow Slit Cavities

Cited by 83 publications

References 20 publications

Transparent Gradient-Index Lens for Underwater Sound Based on Phase Advance

Transparent Gradient-Index Lens for Underwater Sound Based on Phase Advance

Viscothermal Losses in Double-Negative Acoustic Metamaterials

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

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