Tessellation-Enabled Hexagonal Hollow-Shell Cavity Arrays for Broadband Microwave Absorption via Acoustic-to-Electromagnetic Cavity Mapping.

Broadband microwave absorption in lightweight polymer composites is commonly constrained by the coupled requirements of attenuation capability, impedance accessibility, and propagation-path engineering. Here, we propose a dense-stacked polygonal hollow-shell cavity absorber and establish an acoustic-to-electromagnetic cavity mapping framework to guide its design. Rather than directly transplanting acoustic resonators into electromagnetics, the proposed framework is built on the transferable wave-governing ingredients shared by the two systems, namely impedance discontinuity, phase accumulation, effective propagation length, and cavity-assisted confinement. Based on this framework, tessellation is reinterpreted not merely as a packing condition but as an electromagnetic coupling mechanism that suppresses lateral leakage and strengthens inter-unit confinement. Carbon-black-filled PLA/TPU composites are first screened as cavity-compatible lossy media, and CB5 is identified as the optimal formulation because it provides the best balance between attenuation and impedance matching. Structural comparison among triangular, quadrilateral, and hexagonal tessellable cavities further shows that the hexagonal topology offers the most favorable combination of coupling aperture, path diversity, and dense-packing-induced confinement. The optimized hexagonal hollow-shell array achieves superior broadband absorption, maintains effective performance under oblique incidence, and exhibits reduced radar scattering. This work advances structural absorber design from empirical geometry optimization toward a physically interpretable topology-driven route.