Perfect absorption of low-frequency sound waves by critically coupled subwavelength resonant system

Abstract

The perfect absorption (PA) for low-frequency audible sound waves has been achieved by critically coupling the inherent loss factor to the inherent leakage factor of a system, which is constructed by attaching a deep-subwavelength lossy resonant plate (LRP) to a backed rigid wall closely. We have certified it by using the graphical method in the complex frequency plane. By coupling the LRP to an air cavity in front of the rigid wall, the high efficient (>80%) low-frequency broadband absorption is obtained from 99.1 Hz to 294.8 Hz. Here, the thickness of LRP is only 1/13.5 of the relevant wavelength at 294.8 Hz. The impedance analyses further demonstrate that the impedances are perfectly matched between the system and the surrounding background medium at PA.

Subwavelength broadband sound absorber based on a composite metasurface

“…Simultaneously, the sponge coating makes the original perfect absorptive peaks over-damped as displayed by the log 10 R distribution in complex frequency plane (by introducing an imaginary frequency f I into propagation constant), as shown in Fig. 5e and f. Without sponge coating, the zeros of reflectance lie in real frequency axis which confirms that the system is critically coupled at the specific resonant frequencies 30,31 . However, the zeros of reflectance moves above the real frequency axis in case with sponge coating, indicating the system being over-damped; namely, the sponge coating introduces extraordinary loss and breaks the original critical coupling conditions.…”

Reconfigurable sound anomalous absorptions in transparent waveguide with modularized multi-order Helmholtz resonator

“…We also note that the design and fabrication of advanced sound absorbers, which exhibits superior characteristics than conventional sound absorber such as acoustic porous materials 24 , has attracted considerable interest recently. To efficiently absorb the low-frequency sound energy with (deep−) subwavelength structure, a significant number of resonators have been employed to build up sound absorbers spanning from acoustic membrane 17 , 25 , 26 , acoustic metasurface 27 , 28 , acoustic split-ring resonator 29 , 30 , Mie resonator 31 , to labyrinthine Fabry-Perot resonator 32 , 33 , et al . However, most absorbers are based on single-port systems which need a rigid-backed wall to block the sound energy.…”

Low Frequency Sound Absorption by Optimal Combination Structure of Porous Metal and Microperforated Panel

“…Many sound absorbers have been developed for low frequency noise reduction [8][9][10][11][12]. Zhao et al [8] modified a microperforated panel by using a mechanical impedance plate, and the low frequency absorption was effectively enhanced without the need to increase the total thickness of the absorber.…”

“…Cai et al [9] proposed ultrathin low frequency sound absorbing panels based on coplanar spiral tubes or coplanar Helmholtz resonators, and the efficacy of sound absorption by these panels was validated by the strong agreement between the theoretical analysis and experimental measurement. Perfect absorption of low frequency sound by the critically coupled subwavelength resonant system was proposed and developed by Long et al [10], and a highly efficient (> 80%) low frequency broadband absorption was achieved in the frequency range of 99. 1-294.8 Hz.…”