Non-Hermitian scattering systems respecting parity-time symmetry exhibit unidirectional invisibility or reflectionlessness at an exceptional point of the scattering matrix. In this study, we investigate the scattering properties of a one-dimensional acoustic parity-time-symmetric multilayered medium. Parity-time symmetry is defined by a spatial small-amplitude square-wave modulation of the medium parameters in the complex plane. Such a multilayered medium has been demonstrated to reach an exceptional point and support unidirectional invisibility for balanced real and imaginary part modulations of the refractive index. Through the analysis of interference within the medium, we show that the complex modulation of acoustic impedance instead of the refractive index governs the exceptional point of the scattering matrix and determines the occurrence of the unidirectional invisibility. This unidirectional invisibility is further investigated for more general cases of complex parameter distribution including unequal modulation amplitudes and rectangular wave modulation. Our study provides an intuitive physical picture of the occurrence of unidirectional invisibility induced by an exceptional point in acoustic wave systems. Moreover, this study could facilitate the design and practical realization of acoustic parity-time-symmetric structures.
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7 May 2021
Research Article|
May 04 2021
Unidirectional invisibility of an acoustic multilayered medium with parity-time-symmetric impedance modulation
Special Collection:
Acoustic Metamaterials 2021
Shuowei An;
Shuowei An
1
Department of Mechanical Engineering, The Hong Kong Polytechnic University
, Hung Hom, Kowloon, Hong Kong SAR, China
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Tuo Liu
;
Tuo Liu
a)
1
Department of Mechanical Engineering, The Hong Kong Polytechnic University
, Hung Hom, Kowloon, Hong Kong SAR, China2
The Hong Kong Polytechnic University Shenzhen Research Institute
, Shenzhen 518057, People's Republic of China
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Shanjun Liang;
Shanjun Liang
3
Division of Science, Engineering and Health Studies, College of Professional and Continuing Education, Hong Kong Polytechnic University
, Hung Hom, Kowloon, Hong Kong SAR, China
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He Gao;
He Gao
1
Department of Mechanical Engineering, The Hong Kong Polytechnic University
, Hung Hom, Kowloon, Hong Kong SAR, China2
The Hong Kong Polytechnic University Shenzhen Research Institute
, Shenzhen 518057, People's Republic of China
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Zhongming Gu
;
Zhongming Gu
1
Department of Mechanical Engineering, The Hong Kong Polytechnic University
, Hung Hom, Kowloon, Hong Kong SAR, China2
The Hong Kong Polytechnic University Shenzhen Research Institute
, Shenzhen 518057, People's Republic of China
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Note: This paper is part of the Special Topic on Acoustic Metamaterials 2021.
J. Appl. Phys. 129, 175106 (2021)
Article history
Received:
December 03 2020
Accepted:
April 16 2021
Citation
Shuowei An, Tuo Liu, Shanjun Liang, He Gao, Zhongming Gu, Jie Zhu; Unidirectional invisibility of an acoustic multilayered medium with parity-time-symmetric impedance modulation. J. Appl. Phys. 7 May 2021; 129 (17): 175106. https://doi.org/10.1063/5.0039432
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