Lattice Defect‐Inspired Metastructures Enabling Ultralight and Mechanically Robust Broadband Microwave Absorbers

Additively manufactured lightweight lattice metastructures offer a promising route for electromagnetic interference (EMI) mitigation in aerospace systems, owing to their highly tailorable electromagnetic (EM) response and mechanical performance. However, progress is hindered by poorly understood structure–property relationships and the rapid loss of mechanical integrity due to ultrafine structures at low densities. Herein, we establish a quantitative structure–effective permittivity–absorption performance mapping and EM optimization framework based on effective medium approximation and transmission line theory. Inspired by crystal defect engineering, defect‐engineered octet‐truss (DOT) metastructures are introduced via this framework to overcome the trade‐off between mechanical strength and microwave absorption while pushing the density limit toward foam‐like regimes. DOTs achieve an exceptional effective absorption bandwidth (EAB) of 37.5 GHz (2.5–40 GHz, 15 mm thickness) and up to 3.8× higher compressive strength compared with conventional gradient octet‐truss (OT) counterparts. Furthermore, a strut–sheet hybrid DOT reaches an ultralow density of 0.09 g cm − 3 with great printability while maintaining a broad EAB of 35.6 GHz (4.4–40 GHz). The proposed optimization framework and design methodology could be applicable to additive manufacturing technologies with diverse material systems for developing high‐performance multifunctional lattice metastructure absorbers for EM compatibility in next‐generation aerial platforms.