Tunable underwater acoustic metamaterials via quasi-Helmholtz resonance: From low-frequency to ultra-broadband

Abstract

We report a lightweight tunable acoustic metamaterial with deep subwavelength thickness (e.g., λ/300) and strong load-bearing capability for underwater low-frequency and ultra-broadband acoustic perfect absorption. The metamaterial is constructed by introducing a rubber coating and an embedded metallic neck into a metallic hexagonal honeycomb Helmholtz resonator. Physically, the quasi-Helmholtz resonance triggered by the rubber coating together with the anti-phase cancellation caused by the embedded neck leads to superior sound absorption. Theoretical predictions of the metamaterial performance agree well with finite element simulation results. With fixed external morphology (e.g., honeycomb-cored sandwich panel) and fixed overall thickness (e.g., 50 mm), key internal geometrical parameters of the proposed metamaterial can be tailored to achieve tunable perfect absorption from, e.g., 100 Hz to 300 Hz. Further, combining such tunable quasi-Helmholtz resonance leads to ultra-broadband quasi-perfect absorption from, e.g., 306 Hz to 921 Hz. This work contributes to designing underwater acoustic metamaterials and controlling underwater acoustic waves.

Tunable, reconfigurable, and programmable acoustic metasurfaces: A review

“…This mechanism can be applied macroscopically to the entire metasurface such that the overall configuration is changed, or microscopically at the unit cell level to modify the constitutive structures. For example, Helmholtz resonators (Li et al, 2017;Xia et al, 2018;Gong et al, 2019;Tian et al, 2019;Gong et al, 2021), fan-shaped (Wang et al, 2020), space-coiling (Yuan et al, 2015), gap-tunable (Liu and Jiang, 2018;Tao et al, 2022), and tunable broadband (Fang et al, 2016;Zhang et al, 2020;Chen et al, 2021;Duan et al, 2021;Mostaan and Saghaei, 2021;Xu et al, 2021) are all working methods for tuning acoustic waves. Tian et al (2019) obtained versatile wave manipulation functions with the help of Helmholtz resonators as illustrated in Figure 2A.…”

“…For example, Helmholtz resonance exhibits excellent sound absorption with a small footprint. Adding rubber coating and a tunable embedded neck provided sufficient elasticity and damping to achieve tunable low-frequency and perfect ultra-broadband absorption, while maintaining the external morphology and fixing the thickness at the deep subwavelength scale (Duan et al, 2021).…”

Multifunctional sound-absorbing and mechanical metamaterials via a decoupled mechanism design approach

“…Numerous engineering solutions to high-frequency (> 1.0 kHz) noise control exist. [1][2][3][4][5] However, it is really noises in the low-frequency regime that are the most difficult to be eliminated. Governed by the general rules of linear response, 6 commercial sound-absorbing materials, such as foams, fabrics, and panels, are inherently weak in attenuating lowfrequency (< 1.0 kHz) acoustic waves owing to their long wavelengths and strong penetrating capacities.…”

Underwater metamaterial absorber with impedance-matched composite

“…One reason for this state of affairs is the difficulty of experimental measurements, owing to the large wavelength involved and the required large impedance mismatch of the solid material for a water impedance tube (11,12). As a result, considerable studies on underwater absorption are only limited to theoretical analyses and numerical calculations (13)(14)(15)(16)(17)(18)(19)(20)(21)(22), whose idealized assumptions may not hold in practical scenarios, while almost all the existing experimental works (23)(24)(25)(26)(27)(28)(29)(30), measured in the water impedance tube, are based on small samples, which may not reflect the true performance in complex environments (31). There is simply a lack of research works based on large-scale samples, measured in water pools.…”