Polarization insensitive hierarchical metamaterial for broadband microwave absorption with multi-scale optimization and integrated design

The structural destructive resonance caused by the single resonant thickness of flat microwave absorbers results in narrow absorption, hindering the progress of stealth materials. Multi-scale optimization and metastructure design are effective in the improvement of multiple resonance thickness as well as wavefront transmission, allowing for greater freedom in the realization of broadband. Herein, hierarchical metamaterials constructed from pyramid metastructure composites and Huygens' metasurface on the basis of Fibonacci spiral element are reported here, with effective absorption bandwidth (reflection loss ≤ −10 dB) ranging from 4.8 to 18 GHz in terms of subwavelength thickness. The hybrid absorber also exhibits robustness with incident angle across 0°–50° for transverse magnetic polarization. The gradient impedance model based on pyramid composites comprising spherical carbonyl iron particles and graphene sheets will serve as a driver for the enhancement of the electromagnetic wave transmission and the booster of impedance matching. Huygens’ resonance of HMS induces the magnetic field convergence effect due to the simultaneous balance of effective surface current and magnetic current, which facilitates the absorption of lossy composites for further broadening absorption bandwidth. This integrated design could be widely applied to other absorbent materials of choice. • In the case of the electrical and magnetic response are properly balanced, the field excited by the meta-atom composed of centrosymmetric Fibonacci spirals shows similar dispersion of electric and magnetic polarizabilities, resulting in a negligible reflection of the proposed Huygens' metasurface in the frequency range of 2–18 GHz. • A comprehensive design of hierarchical metamaterials from four perspectives: microscale, mesoscale, macroscale and metamaterials, which provides a rigorous and scientific route for the broadband directional design of microwave absorbing materials. • The effective absorption bandwidth of proposed hierarchical metamaterial ranges from 4.8 to 18 GHz across C, X and Ku-band in terms of subwavelength thickness (0.096 λ 0 ) which merely 7% over theoretical minimum thickness dictated by the causality limit, and exhibits robustness with incident angle across 0°–50° for transverse magnetic polarization.