Study on the acoustic performance of bending metasurface with ultra-thin broadband quasi-perfect sound absorption

In order to achieve low-frequency broadband noise control under subwavelength thickness, this paper established a theoretical model for calculating the sound absorption coefficient of curled acoustic metasurface (CAM) composed of embedded hole, equal width curled channel, and gradient width curled channel, which is based on the thermal viscosity equivalent model and impedance equivalent model. Considering the over resistance effect caused by multi-unit composite structure, a multi-parameter control strategy was used to design bending acoustic metasurface (BAM) units for perfect sound absorption at four discrete frequencies of 546 Hz, 563 Hz, 585 Hz, and 601 Hz, which is based on the complex frequency plane method. and the thicknesses of these unites are only (1.2 cm). The broadband and efficient sound absorption effect of the four parallel composite BAM units was theoretically studied. The simulation and experiment verified that the composite BAM not only achieved perfect sound absorption at 573 Hz with a subwavelength thickness of 12 mm, but also had an efficient sound absorption(alpha > 0.8) frequency band of 512Hz-621Hz, with a bandwidth up to 109 Hz. The research in this paper provides a certain theoretical basis for the design of low-frequency broadband compact acoustic structures, and has certain reference value for low-frequency broadband noise control.