Topological Flexible 3D Microwave Perfect Absorber

In this work, an approach to achieve perfect absorption and microwave absorption enhancement is proposed by combining traditional wave-absorbing materials with metamaterials. Specifically, an absorbing basement membrane (BM) is integrated with 3D woodpile (WP) photonic crystals, both of which are composed of flexible silicon materials as matrix and carbonyl iron powder (CIP) as absorbent. Direct ink writing (DIW) is used to fabricate the 3D photonic crystals with either single or coupled concentrations of absorbent. Experiments show that the 10-dB bandwidth of the integrated absorber can reach 10 GHz with a wide elevation angle of incidence. The absorber composed of BM and WP with coupled concentrations of absorbent leads to perfect absorption with a maximum absorption of over 100 dB at an elevation angle of 30 degrees. By changing the concentration of absorbent in BM, the frequency of perfect absorption can be engineered in the range of 6-16 GHz. Such absorption singularity reveals an experimentally observable topological charge that confirms the robustness of the singularity of perfect absorption. The topologically protected flexible 3D microwave absorber offers exceptional performance for versatile scenarios and enriches the studies on topology arising from scattering singularity. A flexible microwave-perfect absorber combining a basement membrane with coupled woodpile photonic crystal is proposed using direct ink writing. Experimental results demonstrate over 100 dB maximum absorption and a 15-GHz bandwidth, even at large incident angles. The perfect absorption is manifested as a phase singularity with a nontrivial topological charge, confirming its robustness and stability. image