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Research Papers

Anomalous Manipulation of Acoustic Wavefront With an Ultrathin Planar Metasurface

[+] Author and Article Information
Shilong Zhai, Changlin Ding, Huaijun Chen, Fangliang Shen, Chunrong Luo

Smart Materials Laboratory,
Department of Applied Physics,
Northwestern Polytechnical University,
Xi'an 710129, China

Xiaopeng Zhao

Smart Materials Laboratory,
Department of Applied Physics,
Northwestern Polytechnical University,
Xi'an 710129, China
e-mail: xpzhao@nwpu.edu.cn

1Corresponding author.

Contributed by the Noise Control and Acoustics Division of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received September 25, 2015; final manuscript received March 7, 2016; published online May 25, 2016. Assoc. Editor: Michael Leamy.

J. Vib. Acoust 138(4), 041019 (May 25, 2016) (6 pages) Paper No: VIB-15-1408; doi: 10.1115/1.4033258 History: Received September 25, 2015; Revised March 07, 2016

The investigations of metasurfaces have introduced a new direction in researching metamaterials. We propose an ultrathin acoustic metasurface consisting of a series of structurally simple microunits. The microunit is constructed with a cavity filled with air and a membrane to seal the air. The designed metasurfaces can arbitrarily manipulate the reflected sound waves at 3.7 kHz. We also realize the planar focusing effects by elaborately arranging the microunits on the metasurfaces, including an axicon and a lens. The designed metamaterials may promote the development of many acoustic devices, such as cloaking, absorber, and spectrum splitter.

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Figures

Grahic Jump Location
Fig. 1

Schematic map of the microunit. (a) The rectangle box with dashed lines indicates a microunit. The side walls are rigid for sound waves. The thickness t of the membrane is fixed to be 0.07 mm, and the membrane widths w of eight microunits are optimized to be 6.485, 7.549, 7.801, 7.947, 8.072, 8.224, 8.504, and 10 mm, respectively. The upward and downward arrows refer to the incident and reflected waves, separately. The straight line and the curve right on the opening of the cavity indicate the membrane in the cases of quiescent state and forced oscillation, respectively. (b) The reflected phase and ratio of microunit as a function of w. The dots and diamonds denote the discrete phase shifts and reflected ratios of eight microunits, respectively.

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Fig. 2

Abnormal reflection of the metasurfaces for the /dx = 33.87 rad/m case. (a)–(d) The transient sound pressure fields of the reflected beams for different incident angles (10 deg, 0 deg, −10 deg, and −40 deg). The upward and downward arrows represent the directions of incident beams and reflected beams, individually. The dashed lines refer to the normal of the interface. The radius of the semicircular curve is 1800 mm. (e) The intensity distribution of scattered field as a function of θr (polar plots) for different incident angles. (f) The reflected angle as a function of θi. The straight line and the curve denote the theoretical results for a natural material and the metasurface, separately. The diamonds indicate the simulated results. The inset in the lower right corner exhibits the schematic of regulation for the signs of θi and θr.

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Fig. 3

Broadband property of this metasurface. Simulated results of the normalized scattered field intensity as functions of the reflected angle and the working frequency. (a)–(c) The incident angles are 0 deg, 10 deg, and 20 deg, respectively.

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Fig. 4

Numerical illustration of the axicon. The simulated region is from 0 to 3000 mm along the y direction, and from −500 mm to 500 mm along the x direction. The length of the metasurface is 1000 mm. The metasurface is composed of 107 microunits. The incident beam propagates along the –y direction. ((a) and (b)) The spatial distributions of squared absolute pressure |p|2 and transient sound pressure p of the reflected wave for the ideal axicon, respectively. ((c) and (d)) The results for the planar axicon metasurface. ((e) and (f)) The transverse (y = 1320 mm) and longitudinal (x = 0 mm) distributions of the normalized acoustic intensity at the focal point, respectively. The solid, dotted, and dashed lines indicate the results of metasurface, ideal axicon, and ideal plane, respectively, for comparison.

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Fig. 5

Numerical illustration of the lens. The simulated region is from 0 to 1000 mm along the y direction, and from −310 mm to 310 mm along the x direction. The length of the metasurface is 620 mm. The metasurface is composed of 61 microunits. The incident beam propagates along the –y direction. ((a) and (b)) The spatial distributions of squared absolute pressure |p|2 and transient sound pressure p for the ideal concave spherical mirror, respectively. ((d) and (e)) The results for the planar lens metasurface. ((c) and (f)) The longitudinal distributions of the normalized acoustic intensity at the focal point (x = 0 mm) for the ideal concave spherical mirror and the planar lens, respectively, with the frequency ranging from 3.3 kHz to 4.0 kHz.

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