Experimental Realization of Acoustic Bianisotropic Gratings

Letter

Experimental Realization of Acoustic Bianisotropic Gratings

Steven R. Craig, Xiaoshi Su, Andrew Norris, and Chengzhi Shi

Phys. Rev. Applied 11, 061002 – Published 6 June 2019

Abstract

Acoustic bianisotropic materials couple pressure and local particle velocity fields to simultaneously excite monopole and dipole scattering, which results in asymmetric wave transmission and reflection of airborne sound. We systematically realize an arbitrarily given bianisotropic coupling between the pressure and velocity fields for asymmetric wave propagation by an acoustic grating with inversion symmetry breaking. This acoustic bianisotropic grating is designed by optimizing the unit cells with a finite element method to achieve the desired scattering wavevectors determined by the bianisotropic induced asymmetric wave propagation. The symmetry and Bloch wavevectors in the reciprocal space resulting from the grating are analyzed, which match with the desired scattering wavevectors. The designed structures are fabricated for the experimental demonstration of the bianisotropic properties. The measured results match with the desired asymmetric wave scattering fields.

Received 30 December 2018
Revised 3 May 2019

DOI:https://doi.org/10.1103/PhysRevApplied.11.061002

Physics Subject Headings (PhySH)

Acoustic measurements Acoustic metamaterials Acoustic modeling Acoustic wave phenomena Refraction Ultrasonics

Symmetries

Sound wave techniques

General Physics

Authors & Affiliations

Steven R. Craig¹, Xiaoshi Su², Andrew Norris², and Chengzhi Shi^1,3,*

¹Meta Acoustics Lab, GWW School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
²Department of Mechanical and Aerospace Engineering, Rutgers University, Piscataway, New Jersey 08854, USA
³Parker H. Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, Georgia 30332, USA

^*chengzhi.shi@me.gatech.edu

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Vol. 11, Iss. 6 — June 2019

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Images

Figure 1
(a) The elements of the polarizability tensor of a bianisotropic particle that allows both forward and backward scattering as functions of frequency. (b) Asymmetric wave scattering for different incidences from the bianisotropic particle in (a). (c) The elements of the polarizability tensor of a bianisotropic particle with only backward scattering. (d) Asymmetric wave scattering for different incidences from the bianisotropic particle in (c). For both (b) and (d), the blue arrows represent incident and red arrows represent scattered waves, respectively.
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Figure 2
(a) Wave-grating interaction for the transmission case for −45-degree incidence in the reciprocal space. (b) Wave-grating interaction for +45-degree incidence as well as the time reversed case represented by the dashed lines. For both (a) and (b), the incident, scattered, and Bloch wavevectors are represented by ${\vec{k}}_{i}$ , ${\vec{k}}_{s}$ , and $Δ k$ , respectively. (c) Bianisotropic grating structure with asymmetric wave scattering in (a) and (b) determined by optimizing the unit cells using a finite element method. (d) 2D spatial Fourier transform of the grating geometry with the expected scattering wavevectors having the highest intensity. (e) Experimental set up for the bianisotropic transmission grating. The enlarged view shows the detailed structure of the grating. The outlined rectangles with red dashed lines represent the scanned areas. (f) Measured pressure field of acoustic waves propagating with positive $k_{x}$ component for −45-degree incidence. (g) Measured pressure field with negative $k_{x}$ component for −45-degree incidence. (h) Measured pressure field of acoustic waves propagating with positive $k_{x}$ component for +45-degree incidence. (i) Measured pressure field with negative $k_{x}$ component for +45-degree incidence. All the pressure fields in (f), (g), (h), and (i) are normalized by their corresponding maximum amplitude in each measurement.
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Figure 3
(a) Wave-grating interaction for the reflection case for 45-degree incidence in the reciprocal space. (b) Wave-grating interaction for normal incidence as well as the time reversed case represented by the dashed lines. For both (a) and (b), the incident, scattered, and Bloch wavevectors are represented by ${\vec{k}}_{i}$ , ${\vec{k}}_{s}$ and $Δ k$ , respectively. (c) Bianisotropic grating structure with asymmetric wave scattering in (a) and (b) determined by optimizing the unit cells using a finite element method. (d) 2D spatial Fourier transform of the grating geometry with the expected scattering wavevectors having the highest intensity to the left of the inversion symmetry about the y axis (e) Experimental set up for the bianisotropic reflection grating. The zoomed in image shows the detailed structure of the grating. The outlined rectangle with red dashed lines represents the scanned areas. (f) Measured pressure field of acoustic waves propagating with a positive $k_{x}$ component for normal incidence. (g) Measured pressure field with negative $k_{x}$ component for normal incidence. (h) Measured pressure field of acoustic waves propagating with positive $k_{x}$ component for +45-degree incidence. (i) Measured pressure field with negative $k_{x}$ component for +45-degree incidence. (j) Measured pressure field of acoustic waves propagating with positive $k_{x}$ component for −45-degree incidence. (k) Measured pressure field with negative $k_{x}$ component for −45-degree incidence. All the pressure fields in (f), (g), (h), (i), (j), and (k) are normalized by their corresponding maximum amplitude in each measurement.
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