Abstract
Anisotropic density-near-zero (ADNZ) acoustic metamaterials are investigated theoretically and numerically in this paper and are shown to exhibit extraordinary transmission enhancement when material loss is induced. The enhanced transmission is due to the enhanced propagating and evanescent wave modes inside the ADNZ medium thanks to the interplay of near-zero density, material loss, and high wave impedance matching in the propagation direction. The equi-frequency contour (EFC) is used to reveal whether the propagating wave mode is allowed in ADNZ metamaterials. Numerical simulations based on plate-type acoustic metamaterials with different material losses were performed to demonstrate collimation and subwavelength imaging enabled by the induced loss in ADNZ media. This work provides a different way for manipulating acoustic waves.
Highlights
Inspired by the study on ENZ metamaterials, this article will examine the effect of material loss in Anisotropic density-near-zero (ADNZ) metamaterials where only one component of the mass density tensor is close to zero
While the material losses in passive acoustic metamaterials are largely ignored in most studies, its effect on wave confinement and enhanced transmission are demonstrated in this article, which could lead to useful applications such as subwavelength imaging
The enhanced transmission phenomenon in loss-induced ADNZ acoustic metamaterials is studied based on effective medium and plate-type acoustic metamaterials
Summary
Density-near-zero Acoustic received: 21 September 2016 accepted: 02 November 2016 Published: 25 November 2016. Anisotropic density-near-zero (ADNZ) acoustic metamaterials are investigated theoretically and numerically in this paper and are shown to exhibit extraordinary transmission enhancement when material loss is induced. The enhanced transmission is due to the enhanced propagating and evanescent wave modes inside the ADNZ medium thanks to the interplay of near-zero density, material loss, and high wave impedance matching in the propagation direction. Numerical simulations based on plate-type acoustic metamaterials with different material losses were performed to demonstrate collimation and subwavelength imaging enabled by the induced loss in ADNZ media. The enhanced transmission and collimation effect of ADNZ acoustic metamaterial induced by material loss will be demonstrated. The underlying mechanism is discussed, which reveals that high impedance matching condition can be realized by material loss These effects are verified by the EFC analysis and full wave numerical simulations based on real structures exhibiting anisotropic density-near-zero property
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