86 research outputs found

    Numerical Transducer Modeling

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    Viscothermal effects in a two-dimensional acoustic black hole: A boundary element approach

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    [EN] The acoustic analog of the quantum black hole for airborne sound in two dimensions was denominated as an omnidirectional acoustic absorber by Climente et al. [see Appl. Phys. Lett., 100, 144103 (2012)], who characterized its absorbing properties without providing any theoretical support. The viscothermal losses of the underlying structure, which consists of an absorbing core and a surrounding gradient-index (GRIN) lens both made of periodic distributions of cylindrical rods, are here comprehensively studied by using the boundary element method (BEM) in two dimensions. It is shown that the numerical simulations in two dimensions reproduce fairly well the increase in absorption of the core when the GRIN lens is added and reveal that the discrepancy between measured and calculated values of absorbance is an artifact of the experimental setup. The possibility of independent calculation of viscous and thermal losses contributions in the two-dimensional (2D) BEM algorithm is employed for the comparison with a homogenization theory in which the cluster of cylinders is represented by a single fluidlike viscous cylinder with effective parameters. We conclude that viscous losses represent about 90% of the total energy dissipated in the core. The homogenization approach results are only 2% below the results calculated with 2D BEM, indicating that the effective parameters obtained by the homogenization are very accurate.Cutanda-Henríquez, V.; Sánchez-Dehesa Moreno-Cid, J. (2021). Viscothermal effects in a two-dimensional acoustic black hole: A boundary element approach. Physical Review Applied. 15(6):1-14. https://doi.org/10.1103/PhysRevApplied.15.064057S11415

    Numerical modeling of double-negative acoustic metamaterials: Should losses be included?

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    [EN] Viscous and thermal losses of acoustic waves are usually neglected or accounted for as boundary impedance. It is known, however, that acoustic losses become relevant in devices with some dimension in the millimeter range or below. On the other hand, the new class of structures called acoustic metamaterials can be affected by acoustic losses, but in this case the extension of these effects is less known. Acoustic metamaterials are intricate periodic structures where, at frequencies low enough ( corresponding to wavelengths much l arger than the structure period), elementary units interact producing interesting unusual effects. In this paper advanced modeling tools based on the Boundary Element Method (BEM) and the Finite Element Method (FEM) are used to study the effect of losses in an acoustic metamaterial scaled to different sizes. The conclusions are expected to give insight on the practical limitations when using acoustic metamaterialsJ. Sanchez-Dehesa acknowledges the support by the Spanish Ministerio de Economía y Competitividad, and the European Union Fondo Europeo de Desarrollo Regional (FEDER) through Project No. TEC2014-53088-C3-1-RCutanda Henriquez, V.; Andersen, PR.; Sánchez-Dehesa Moreno-Cid, J. (2016). Numerical modeling of double-negative acoustic metamaterials: Should losses be included?. Universidade do Porto. 1-8. http://hdl.handle.net/10251/181075S1
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