Optimized Broadband Acoustic Insulator With a Modular Side-Branch Structure Based on the Rainbow-Trapping Effect

Abstract Acoustic rainbow trapping has demonstrated significant potential in applications such as noise control, acoustic sensing, and stealth or isolation technologies. Its unique advantage lies in its ability to isolate specific sound frequencies and trap them at precisely defined spatial locations. By exploiting this property, broadband acoustic trapping can be achieved through gradient frequency designs, while the precise regulation of specific frequency bands can be realized by adjusting acoustic parameters, such as material gradients and geometric configurations. In this work, we propose a modular and tunable acoustic side-branch tube structure (MTAS), which integrates modular design and tunable parameters to achieve broadband acoustic trapping. The dispersion relations, trapping positions, and spatial field distributions are systematically derived. Building on the broadband trapping characteristics, we employ a genetic algorithm (GA) combined with finite element methods (FEM) to realize effective sound insulation over an extensive frequency range of 120–10,000 Hz. Furthermore, leveraging the multiband response, frequency separation, and spatial control inherent to rainbow trapping, we design a band-pass filter-like structure. This structure enables precise frequency selection and efficient sound energy concentration, offering a novel approach for tailored acoustic control. Experimental validation showed transmission below 0.1 across most frequencies from 100 to 2000 Hz, further supporting the reliability of the simulations.