Dorsiventrally Bicolored Leaf-Inspired Metamaterial Absorbers for Tailorable Electromagnetic Absorption

Realizing tailorable broadband electromagnetic absorption within structurally concise architectures remains a key challenge for advanced absorber design. Inspired by dorsiventrally bicolored leaves that integrate broad-spectrum light management with directional regulation, we propose a bioinspired hybrid metastructure in which an impedance-graded hexagonal-frustum absorber serves as the broadband absorption backbone, and an underlying resonant feedback layer selectively reinforces weak-absorption frequencies in the baseline absorption spectrum. Mechanistically, the broadband absorption arises from continuous impedance transition, enhanced wave coupling, and multistage attenuation, while the reinforcement of selected frequencies is governed by the interplay of resonant feedback, material loss, and phase-assisted reflection suppression. Experimentally, the metastructure exhibits an intrinsic X-band absorption peak and a broadband high-absorption platform with absorptance exceeding 80% from 18 to 40 GHz. In addition, feedback-layer engineering enables targeted reinforcement at prescribed weak-absorption frequencies, forming tailorable absorption windows in selected X─K-band regions. In parallel, a genetic-algorithm-optimized ExtraTrees surrogate model enables rapid inverse identification of feedback-layer geometries, and the selected candidates show good agreement with full-wave simulations and experiments. This work establishes a bioinspired framework that integrates broadband response, targeted reinforcement, and inverse design, offering a promising route toward high-performance, tailorable electromagnetic absorbers.