Performance Evaluation of a Bio-Inspired Hexafractal Resonator for Low-Frequency Noise Control

Acoustic metamaterials are artificially created geometries to obtain unusual acoustic results. These materials have the potential to be applied in a variety of sectors that require treatment at narrow-band frequencies. This work used a specific type called coilling-up spaces and sought to evaluate the efficiency of a bio-inspired acoustic resonator geometry in the shape of honeycombs, through a hexagonal fractal cell, called the "Hexafractal Resonator", in controlling noise at low frequencies. The proposed geometry consists of three concentric hexagons with small gaps between them. In terms of Transmission Loss (TL), the results were compared with those of resonators with two different cavity configurations: a cavity without spatial coilling-up, therefore a common Helmholtz resonator, filled only with air, and a cavity filled with half air and half porous material, characterized by the Johnson-Champux-Allar (JCA) theoretical method. The results of the cells tested using Finite Element Method (FEM) software showed, respectively, TL = 36.5 dB at 450 Hz and TL = 10.74 dB at 403 Hz. The Hexafractal Resonator model showed a TL = 25.4 dB at 205 Hz, which indicates its potential to reduce noise at low frequencies.