Inverse modeling and design of additively manufactured hybrid acoustic metamaterials for low-frequency absorption

Introduction Environmental noise is a growing problem with a negative impact on individuals, particularly at low frequencies. 3D printed acoustic metamaterials have emerged as possible load-bearing solutions for noise management. Several designs have been investigated in the literature to construct 3D lattices for optimized sound absorption including gyroid and honeycomb. Nevertheless, there exists a need for a framework to propose the best metamaterial design for application-focused target frequencies, in particular at low frequencies. Methods In this work, an inverse design framework is presented to propose an optimal hybrid metamaterial for sound absorption at low frequencies. To enhance broadband low-frequency absorption, the design space was extended to include a gyroid porous layer stacked in series with a honeycomb layer and an elastic wall. The inverse optimization then adjusts the porosities and effective thicknesses of gyroid and honeycomb layers to match a prescribed target absorption spectrum, while respecting additive manufacturing constraints. Results The results of the proposed optimal hybrid design show that it achieves near unity sound absorption across the 250 – 2000Hz frequency range, with absorption coefficients exceeding 0.93 at all target frequencies. The resulting Noise Reduction Coefficient (NRC) reaches 0.95, demonstrating excellent broadband acoustic performance within practical thickness and manufacturing constraints. Discussion The proposed framework integrates inverse design with manufacturing-aware optimization to enable the development of high-performance, tunable acoustic metamaterials.