Investigation on low-frequency broadband perfect sound absorption metastructure based on area coupling effect

Addressing the issue of broadband ideal sound absorption failure caused by area coupling effects in acoustic metamaterial field, which involves transitions from narrowband to broadband, this paper proposed a structure called the bending channel-Helmholtz coupled sound absorber (BCSA), which considering the area coupling effect. First, theoretical models for the bending channels and Helmholtz resonator (HR) structures are established using the thermal viscoelastic equivalent theory. Finite element analysis confirms the accuracy of the theoretical model. Based on above-mentioned theoretical models, the regulation of HR and bending channel geometrical parameters of acoustic absorption performance is investigated.Considering the adjustment of geometric variable on acoustic absorption capability and the area coupling effect between units, a theoretical model of the BCSA composed of multiple bending channels and HR units is constructed. An optimized design of a BCSA metastructure measuring only 35mm in thickness and an absorptive coefficient reaches above 0.8, within the frequency range of 288Hz to 365Hz. Subsequently, the mechanism for high-performance sound absorption in low frequencies broadband of the BCSA metastructure is analyzed using finite element software, and the theoretical model’s accuracy is validated. Finally, a BCSA sample with a thickness of 35mm is fabricated by 3D printing technology. Impedance tube experiment results illustrate that the optimized BCSA attains high-performance acoustic absorption above 0.8 in the frequency range of 294Hz to 364Hz.Compared with exiting bent channels or HR metamaterials, this study first turns BCSA’s area coupling side effects into design freedom. Traditional solutions broaden the frequency band by increasing unit number or thickness, easily causing impedance mismatch; BCSA uses impedance increment from parallel non-ideal units to reverse-compensate for each unit’s insufficient loss. The study clarifies how area coupling affects sound absorption, offering theoretical reference for solving over-loss damage in multi-unit coupling and significant implications for low-frequency broadband perfect sound absorption metamaterial design.