Labyrinthine Acoustic Metamaterials with a Subwavelength Bandgap Inspired by Topology‐Optimized Structural Design

Herein, a structural design for labyrinthine acoustic metamaterial is proposed using a topology optimization method to realize a subwavelength bandgap preventing the transmission of low‐frequency sounds. The optimized design is composed of air‐filled channels of different widths, which exhibit the subwavelength bandgap based on the monopole resonance induced in the meta‐atom. In addition to the optimized meta‐atom design, a simplified meta‐atom design with a small coiling coefficient is proposed by extracting structural features of the optimized design. The bandwidth and central frequency of the subwavelength bandgap can be controlled by adjusting the size parameters of the simplified meta‐atom. Numerical analysis for acoustic waves based on the finite‐element method is conducted to demonstrate the low transmission coefficients of the obtained designs for a wide‐ and low‐frequency range. Furthermore, using a 3D printer, experimental specimens of optimized and simplified meta‐atoms are constructed, and impedance tube experiments are performed to show their functionality.