Acoustic labyrinthine porous metamaterials for subwavelength low-frequency sound absorption

An acoustic labyrinthine porous metamaterial (ALPM) or the so-called acoustic labyrinthine metaporous surface is designed for the subwavelength sound absorption by perforating folded slits in a porous material matrix. A theoretical model is developed to study the sound absorption of the ALPM by combining the acoustic properties of two components: the porous material matrix and the folded slit configuration. The theoretical model is favorably validated by finite element (FE) simulations and experimental measurements. The proposed ALPM shows an excellent subwavelength low-frequency sound absorption performance: the material thickness is only 1/22 of the sound wavelength in air at the sound absorption peak frequency. The electronic-acoustic analogy method proves that this metamaterial can achieve a perfect impedance match with air at low frequencies. The FE simulations for energy transmission and dissipation reveal its sound absorption mechanisms, showing a frequency-dependent sound transmission path characteristic. Moreover, the influence of the slit folding number on the sound absorption is analyzed and it shows that a longer slit corresponds to a lower-frequency peak. This work is valuable to guide the novel design of acoustic metamaterials for the subwavelength low-frequency sound absorption.