Geometric optimisation of a multiple coiled-up resonator for broadband and octave band acoustic absorption

This study presents a comprehensive approach to designing sound absorption metamaterials, aiming to achieve broadband absorption capabilities while maintaining a compact thickness, starting from an exceptionally low frequency of 100 Hz. By employing a parallel arrangement of resonators with varying lengths, the proposed approach exploits the envelopes of absorption frequencies to realize broad-spectrum sound absorption. An analytical model is utilized in the geometric optimization phase, accounting for inlet losses and thermo-viscous losses near the walls. The absorption for multiple ducts coupled in parallel is derived using the series and parallel impedance method. A geometric parameterization procedure is implemented to maximize normal incidence acoustic absorption, leading to design optimization for both broadband and octave-band absorbers. Design maps are established to assess acoustic performance and physical space requirements, facilitating informed decision-making in metamaterial design. Prototype fabrication and experimental validation involve 3D printing of optimized geometries using polylactic acid, followed by testing within impedance tubes according to ISO 10534–2 standards. The results demonstrate the effectiveness of the proposed method in achieving broadband sound absorption across specified frequency ranges.