Sound absorption metasurface with symmetrical coiled spaces and micro slit of variable depth

An acoustic metasurface (AMS) is proposed comprising a panel containing a micro slit of variable depth coupled to a thin cavity of symmetrical coiled spaces. Theoretical and numerical analyses are used to demonstrate that this metasurface has an effective low frequency sound absorption capability (i.e., between 100 Hz and 600 Hz) with a deep-subwavelength thickness. The mechanism underlying the sound absorption is explored by the different ways in which energy is dissipated in the absorber. It was observed that the dissipation of viscous energy takes place in the narrow region of the micro slit and represents 99.7% of the total energy dissipated while the thermal dissipation is 0.3% and occurs in the inner coiled spaces. Furthermore sound absorption of the AMS was investigated experimentally in an impedance tube for normal incidence. The results of the experimental work show that, by varying the depth of micro slit simultaneously with increasing the number of symmetrical coiled spaces, the peak frequency of the absorption can be shifted to a lower frequency without changing the total absorber thickness. A control of 93% of the sound energy, with a relative bandwidth of 50.4% in the frequency range of interest, was acquired with the proposed absorber presenting a thickness of lambda/48. Furthermore, a coupled system was also evaluated experimentally which revealed the broadband absorption to be consistent with the theoretical model. (C) 2021 Elsevier Ltd. All rights reserved.