Acoustic and Mechanical Metamaterials for Various Applications

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(A) Schematic diagram of the gradient parallel numerical model. (B–D) Sound absorption curve before and after parallel connection. (E–G) Relative acoustic impedance after parallel connection.
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16 citations
2,522 views
8 citations
Original Research
07 February 2022
Broadband Sound Absorption of Subwavelength Porous Meta-Liner
Heye Xiao
5 more and 
Jintao Gu
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This work proposes a subwavelength porous meta-liner with broadband sound absorption from 900 to 1,200 Hz. The meta-liner consists of four subunits, which are made up of porous material and hollow coiling slit embedded in it. Each subunit is designed by adjusting the length of its coiling slit to achieve resonance in the target frequency and examined by the finite element method (FEM). These subunits are arranged in an axial direction uniformly and radial direction periodically to propose a meta-liner duct. Then, the noise reduction of the propeller system with the meta-liner duct is measured by the microphone array. The result shows that the propeller with the meta-liner duct can reduce the noise level of the ducted propeller between 3.6 and 5.5 dB in the design frequency range, which also effectively reduces the noise level in the broadband frequency range. Therefore, the meta-liner shows a good application prospect in the noise reduction of the propeller.

3,106 views
6 citations
2,775 views
10 citations
Original Research
05 November 2021

We show efficient elastic energy transfer and wave confinement through a graded array of resonators attached to an elastic beam. Experiments demonstrate that flexural resonators of increasing lengths allow to reduce wave scattering and to achieve the rainbow effect with local wavefield amplifications. We show that the definition of a monotonically decreasing distribution of the natural frequencies of the resonators along the wave propagation direction, is the preferable choice to increase the energy efficiency of the system. The proposed configuration is suitable for micro-fabrication, envisaging practical applications for micro-scale vibration energy harvesting.

3,551 views
22 citations
Original Research
30 September 2021
Ultra-Thin Metasurface-Based Absorber of Low-Frequency Sound With Bandwidth Optimization
Yi-jun Guan
4 more and 
Xiao-jun Liu
Simulated sound absorption spectra as a function of parameters (A)b and (B)d, and the corresponding measured sound absorption spectra for the parameters (C)b and (D)d, in which the other parameters remain unchanged.

We report, both theoretically and experimentally, a type of ultra-thin metasurface-based low-frequency sound absorber with bandwidth optimization. Such a metasurface unit consists of an ultrathin resonator (thickness∼1/90 wavelength) with a circular hole on the upper panel and four narrow slits inside a multiple-cavity structure. Eigenmode simulations of the unit show rich artificial Mie resonances, in which a type of monopolar Mie resonance mode can be obtained at 238.4 Hz. Based on the excitation of the monopolar mode, we can realize the near-perfect low-frequency sound absorption with the maximum absorption coefficient and fractional bandwidth of 0.97 and 12.9%, respectively, which mainly arises from the high thermal-viscous loss around the circular hole and four narrow slits of the unit. More interestingly, by combining 4 units with different diameters of the circular hole, we further enhance the fractional bandwidth of the compound unit to 18.7%. Our work provides a route to design ultra-thin broadband sound absorbers by artificial Mie resonances, showing great potential in practical applications of low-frequency noise control and architectural acoustics.

3,316 views
6 citations
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Frontiers in Nanotechnology

Nanomaterials for Affordable Biomedical Devices, Environmental and Energy Applications
Edited by Sandeep Kumar, Gaurav Bhanjana
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