A thin-walled mesoscopic hybrid slit-resonator metamaterial absorber

We propose a thin-walled mesoscopic hybrid slit-resonator metamaterial with excellent broadband sound absorption performance through developing an integrated material-structure- process-functional design method. The slit-resonator structure comprehensively utilizes the advantages of the porous material, the slit-type absorber and the Fabry-Pérot resonance unit, and exhibits unprecedented excellent large-broadband absorption capability. The ultra-thin walls ensure the high-porosity of the entire structure, and the narrow channel is equivalent to a designable porous medium, which can ensure excellent broadband absorption performance in the middle- and high-frequency ranges. As the challenging in fabricating of ultra-thin large-size walls, a ceramic-containing high-temperature resistant material is employed, and a 3D printing process with a special preheating-preservation-cooling cyclic heat treatment is accordingly developed. Through the joint development of materials and processes, the high-precision preparation of large-size and ultra-thin shell structures is realized. In addition, by embedding a few Helmholtz resonant units into the designed absorber to generate discrete low-frequency absorption peaks, the lowest absorption frequency is further reduced to 1/5 of the original one. The average absorption of absorber reach 0.8 above 50 Hz and 0.85 above 200 Hz, the thickness is reduced to 1/39 of the lowest absorption wavelength, which is only about 1/10 of the absorber used in traditional anechoic chambers.