Hybrid porous Helmholtz resonator for low-frequency broadband absorption

The effective control of low-frequency noise remains a formidable challenge due to the inherently long wavelengths involved, which typically require large-scale physical barriers to achieve meaningful attenuation. Against this backdrop, metamaterials present a viable alternative, exploiting deep subwavelength structures that capitalize on thermal losses associated with local resonances to dampen sound. Here, we introduce a hybrid porous Helmholtz resonator (HPHR) that markedly improves acoustic absorption by amalgamating the Helmholtz resonator with specially designed porous necks to optimize acoustic impedance matching. It is promising as the basic unit of the metamaterial for low-frequency broadband acoustic absorption. Based on parallel HPHRs, we expand the effective absorption (>0.8) bandwidth using a one-dimensional convolutional neural network to engineer composite structures. The thickness of the sample is approximately 1/13th of the wavelength at the lowest target frequency. Our designs integrate resonant structures and porous materials, providing promising potential for creating broadband acoustic absorption systems and low-frequency noise control.