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Keywords = acoustic coherent perfect absorption (CPA)

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11 pages, 2375 KiB  
Article
Bidirectional Acoustic Negative Refraction Based on a Pair of Identical Purely Imaginary Metamaterials Slabs
by Ling-Ling Zhang, Yang Ji, Peng Chen, Qian Dai and Xiao-Jun Liu
Appl. Sci. 2022, 12(19), 9914; https://doi.org/10.3390/app12199914 - 1 Oct 2022
Viewed by 1736
Abstract
Acoustic purely imaginary metamaterials (PIMs) slabs can support the coexistence of coherent perfect absorption and laser modes and are used to achieve negative refraction. Previous works have focused on a pair of different PIM slabs, one operating in CPA mode and the other [...] Read more.
Acoustic purely imaginary metamaterials (PIMs) slabs can support the coexistence of coherent perfect absorption and laser modes and are used to achieve negative refraction. Previous works have focused on a pair of different PIM slabs, one operating in CPA mode and the other in laser mode. However, this structure has restrictions on the incident wave direction, specifically the wave can only be incident from the CPA side. In this paper, we derive the analytical expressions for the parameters required for the coexistence of CPA and laser modes in acoustic PIM slabs. Numerical simulation results show that such PIM slab can freely switch states between the coherent complete absorber and the laser depending on the incidence direction. On this basis, by using a pair of identical PIM slabs, bidirectional negative refraction and planar focusing can be achieved. In addition, the parameters in the appropriate range can be found by adjusting the mode order, which facilitates the experimental verification. So far, the required acoustic purely imaginary metamaterials (PIMs) have not been experimentally demonstrated, and the results presented in the manuscript are theoretical speculations on their existence, so practical applications may require more sophisticated design and engineering. Full article
(This article belongs to the Special Issue Recent Advance in Acoustic Metamaterials)
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10 pages, 3635 KiB  
Article
Acoustic Negative Refraction and Planar Focusing Based on Purely Imaginary Metamaterials
by Ling-Ling Zhang and Xiao-Jun Liu
Appl. Sci. 2022, 12(12), 5962; https://doi.org/10.3390/app12125962 - 11 Jun 2022
Cited by 3 | Viewed by 1787
Abstract
Acoustic purely imaginary metamaterials (PIMs) contain loss and gain uniformly distributed in space, but in different parameters. Therefore, the PIMs contain the elements of gain and loss simultaneously. As a result, some extraordinary wave modes may appear depending on whether gain or loss [...] Read more.
Acoustic purely imaginary metamaterials (PIMs) contain loss and gain uniformly distributed in space, but in different parameters. Therefore, the PIMs contain the elements of gain and loss simultaneously. As a result, some extraordinary wave modes may appear depending on whether gain or loss elements dominate. In this work, we theoretically and numerically investigate the general excitation conditions for acoustic lasing, coherent perfect absorption (CPA) and for their co-existence in the framework of acoustic PIMs. All-angle negative refraction and planar focusing are achieved by pairing two PIM slabs with conjugating parameters. The proposed structure provides an alternative basis for possible applications of acoustic perfect imaging. Full article
(This article belongs to the Special Issue Recent Advance in Acoustic Metamaterials)
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14 pages, 3627 KiB  
Article
Acoustic Equivalent Lasing and Coherent Perfect Absorption Based on a Conjugate Metamaterial Sphere
by Xing-Xing Ma, Qi Wei, Xing-Feng Zhu, Jie Yao and Da-Jian Wu
Appl. Sci. 2022, 12(4), 1777; https://doi.org/10.3390/app12041777 - 9 Feb 2022
Cited by 3 | Viewed by 2176
Abstract
Acoustic conjugate metamaterials (ACMs), in which the imaginary parts of the effective complex mass density and bulk compressibility are cancelled out in the refractive index, possess the elements of loss and gain simultaneously. Previous works have focused on panel ACMs for plane wave [...] Read more.
Acoustic conjugate metamaterials (ACMs), in which the imaginary parts of the effective complex mass density and bulk compressibility are cancelled out in the refractive index, possess the elements of loss and gain simultaneously. Previous works have focused on panel ACMs for plane wave incidence. In this paper, we explore the extraordinary scattering properties, including the acoustic equivalent lasing (AEL) and coherent perfect absorption (CPA) modes, of a three-dimensional ACM sphere, where incident spherical waves with specific topological orders could be extremely scattered and totally absorbed, respectively. Theoretical analysis and numerical simulations show that the AEL or CPA mode with a single order can be realized with a small monolayer ACM sphere with appropriate parameters. A huge (relative to incident wavelength) ACM sphere with pure imaginary parameters could support the even- (or odd-) order AEL and odd- (or even-) order CPA modes simultaneously. In addition, the AEL and/or CPA with multiple orders could be realized based on a small multilayered ACM sphere. The proposed ACM sphere may provide an alternative method to design acoustic functional devices, such as amplifiers and absorbers. Full article
(This article belongs to the Special Issue Recent Advance in Acoustic Metamaterials)
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