A Compact Tunable Broadband Acoustic Metastructure with Continuous Gradient Spiral Channels

Abstract

Sound‐absorbing structures, an effective measure to reduce vibration and noise, have always been the desirable research hotspot in scientific and engineering communities. However, the mutual restriction between ultrathin thickness and broadband sound absorption is the key issue that hinders its development. Herein, a compact tunable broadband acoustic metastructure with continuous gradient spiral channels is presented, which has the ultrathin thickness and can efficiently realize low‐frequency broadband sound absorption. Coiled‐up individual absorbers are introduced to constitute the acoustic metastructure. The continuous gradient spiral channels are formed by successively decreasing the effective spiral length of labyrinthine cavity to achieve efficient broadband sound absorption. It is showed in the results that the sound‐absorption metastructure coupled with eight individual absorbers maintains the excellent broadband sound‐absorption effect over 0.8 in the frequency range of 487–930 Hz and a deep subwavelength thickness of 37 mm. In addition, the highly efficient low‐frequency broadband sound absorption can be implemented in the target range of 480–990 Hz through optimizing the adjustable parameters such as the effective spiral length, cross‐section height, orifice radius, and the coupling number of single absorbers. Herein, inspirations and threads are provided for the compact tunable broadband sound‐absorption design of acoustic metastructures.

Simulated and Experimental Research on Highly Efficient Sound Absorption of Low‐Frequency Broadband Acoustic Metamaterial Based on Coiled‐Up Space

“…The thickness of top panel l , hole radius a , and thickness of backing panel t b are 1.5 mm, and the external side length a s and wall thickness t of the labyrinthine cavity are 10 and 0.5 mm. The cross‐section width w and height h are 1.67 and 34 mm (minimum thickness to ensure sound absorption coefficient over 0.8 within the target frequency range [ 26 ] ). Table 1 lists the effective spiral length L c for each single absorber (considering it as an equivalent straight tube) in the eight‐coupled sound‐absorbing structure.…”

“…Obviously, the absorption coefficient of the broadband acoustic metamaterial is negatively correlated with the cavity wall thickness. Since the reduction of hole radius makes the sound absorption peak of the broadband acoustic metamaterial move to low frequency, [ 26 ] the absorption coefficient of the sound‐absorbing structure gradually decreases and the effective sound absorption band gradually narrates under the condition that the wall thickness increases and the hole radius decreases.…”

“…In addition, the novel compact tunable broadband sound absorption metastructure with continuous gradient spiral channels was also reported. [ 26 ] The wall thickness of 0.2 mm cannot be processed under current manufacturing conditions, so experiments cannot be carried out. Moreover, the effect of arrangement on the sound absorption performance of acoustic metastructure was only emphasized, without optimizing the performance of other arrangement methods.…”