Abstract: Although existing carbon-based absorbers show good microwave absorption performance, they still face challenges in achieving broadband efficiency, low density, and large-scale production simultaneously. This study proposes a green and sustainable strategy that constructs nitrogen-doped three-dimensional porous carbon (N-3DPC) through a room-temperature antisolvent-induced precipitation method. A bio-inspired geometric metamaterial structure is also designed to match the N-3DPC, enabling the development of a broadband and low-cost absorber. Soluble salts (NaCl, Na₂CO₃, Na₂SO₄ and KCl) serve as templates for preparing N-3DPC. Among them, the NaCl-templated sample exhibits the largest specific surface area, well-distributed and interconnected pores, which enhance dielectric loss and impedance matching. It achieves an RL_min (Minimum Reflection Loss) of -29.96 dB at 2.9 mm, with an EAB (Effective Absorption Bandwidth) of 7.43 GHz. By introducing a genetic algorithm to globally optimize the structural parameters, a periodic metamaterial absorber composed of hybrid bionic units is constructed. Under optimized conditions, the absorber achieves broadband absorption ranging from 5.52 to 18 GHz (EAB = 12.48 GHz) with an RL_min of -28.1 dB. The simulation and experimental results show strong consistency, while CST and COMSOL simulations reveal the cooperative loss mechanism that occurs between the absorbing and matching layers. This design strategy achieves ideal broadband electromagnetic wave absorption through cross-scale synergy between the microscopic carbon architecture and the macroscopic geometric configuration, providing a promising pathway toward lightweight and efficient microwave absorbers.

Key words: Porous carbon-metamaterials, Microwave absorber, Periodic structure, Geometric structure