A Biomimetic Double Water Meta-Atom Lattice for Ultra-Broadband Multi-Gradient Microwave Absorption

Water-based metamaterial absorbers have demonstrated promising broadband absorption capabilities. However, their performance at lower frequencies, particularly in the S and C bands, remains limited due to impedance mismatch and low loss factors. Herein, inspired by the anti-reflective microstructure of moth eyes, we propose a dual-phase optimization strategy to develop a multilayered gradient absorber. This approach employs a double meta-atom lattice of conical water units with their geometry refined by a genetic algorithm to enhance impedance matching and energy dissipation. The resulting water-based absorber achieves an ultra-broadband of 3.1-25.1 GHz, fully covering the C, X, and Ku bands, along with partial coverage of the S and K bands, superior to the advanced water-based absorber at such low frequencies. Systematic analysis of impedance matching, reflection losses of different structures and power loss distribution reveals that the broadband absorption arises from synergistic inter-layer and inter-meta-atom resonances as well as multiple reflections between structures. This study provides a low-cost and scalable strategy for preparing high-performance ultra-wideband absorbers, with significant potential applications in electromagnetic stealth and protection.