Bioinspired Spiral Carbon‐Fiber Ultrathin Metastructure for Broadband Electromagnetic Wave Absorption

Conventional metastructure absorbers are often constrained by considerable thickness due to design trade‐offs, limiting their applicability in aerospace systems that demand lightweight and low‐profile materials. Here, we report an ultrathin bioinspired conch metastructure (BCM) fabricated from a monolithic carbon fiber‐reinforced polymer composite via 3D printing. With a thickness of only 6.4 mm and a lower areal density (∼1.517 kg/m 2 ), the BCM exhibits an effective absorption bandwidth (EAB, RL ≤ −10 dB) of 11.32 GHz (6.68–18 GHz). This performance stems from its multi‐scale cavities, which promote multi‐mode resonance and enhance scattering, achieving broad bandwidth while maintaining compact volume. Guided by a multi‐objective Bayesian optimization framework, the BCM geometry was optimized for minimal thickness and maximum bandwidth before 3D printing. The absorber demonstrates angular stability (up to 60° incidence) and polarization insensitivity, and retains over 8 GHz bandwidth under bending, showing its suitability for conformal applications. Full‐wave simulations further indicate a substantial reduction in radar cross‐section (RCS), reaching values as low as −27 dB·m 2 at normal incidence. Mechanically, the structure exhibits an average compressive strength of 118 MPa. This work presents a high‐performance ultrathin absorber with a simple material system and data‐driven design, offering a promising solution for electromagnetic wave absorption.