By investigating a square-shaped metamaterial structure we discover that wave diffraction at diagonal corners of such a structure excites transverse magnetic harmonics of 210 mode (TM₂₁₀ harmonics). Multi-layer overlapping and deliberately regulating period length between adjacent unit cells can significantly enhance TM₂₁₀ harmonics, leading to a strong absorption waveband. On such a basis, a design strategy is proposed to achieve broadband, thin-thickness multi-layered metamaterial absorbers (MMAs). In this strategy big pyramidal arrays placed in the “white blanks” of a chessboard exhibit two isolated absorption bands due to their fundamental and TM₂₁₀ harmonics, which are further connected by another absorption band from small pyramidal arrays in the “black blanks” of the chessboard. The as-designed MMA at a total thickness (h) of 4.36 mm shows an absorption of above 0.9 in the whole frequency range of 7–18 GHz, which is 38% broader with respect to previous design methods at the same h. This strategy provides an effective route to extend the absorption bandwidth of MMAs without increasing h.

Achieving broadband microwave absorption with non-magnetic thin coatings is quite challenging due to the lack of dielectric dispersion in most materials. In this work, significant microwave dielectric dispersion (SMDD) in a broad bandwidth was realized using silver-coated glass microspheres (GM@AgCPs) as fillers at a near percolating volume fraction in composites. First, the dense silver shells of GM@AgCPs are critical to enhancing the dielectric properties of the composites at low frequency owing to their strong interface polarization, oscillation resonance and coupling interaction. Second, GM@AgCPs exhibit long effective paths for electron oscillation, which result in long relaxation times. Therefore, the strong dielectric responses are not extended to the high frequency because the excited electrons on GM@AgCPs cannot respond rapidly to changes in the external electromagnetic field, leading to significant microwave dielectric relaxation. Subsequently, high-performance microwave absorbing materials (MAMs) were for the first time demonstrated by SMDD coupled with the quarter-wavelength resonance in a broad bandwidth. Consequently, the as-obtained MAMs with a matching thickness of 2.2 mm at a volume fraction (V) of 45% exhibited an absorption bandwidth of at least 11.8 GHz for reflection loss ≤−8.0 dB, which greatly surpasses the performance of their literature dielectric counterparts. Our work has potential important applications in electromagnetic compatibility and stealth.

A quaternionic metasurface consisting of two pairs of units with destructive phase difference is proposed to extend the bandwidth of radar cross section (RCS) reduction. The two pairs of units are designed to have complementary phase-different bandwidth, which extends the bandwidth of RCS reduction. The overlaps of their bandwidth enhance the RCS reduction, resulting in a metasurface having broadband and strong RCS reduction. This design and the wideband RCS reduction of the quaternionic metasurface were verified by analytical calculation with superposition principle of electric field, numerical simulation with commercial software package CST Microwave Studio and experiment in microwave anechoic chamber. The scattering mechanism and the angular performance of the quaternionic metasurface were also investigated.

Nanocrystalline soft magnetic alloy powders are promising microwave absorbents since they can work at diverse frequencies and are stable in harsh environments. However, when the alloy powders are in austenite phase, they are out of the screen for microwave absorbents due to their paramagnetic nature. In this work, we reported a strategy to enable strong microwave absorption in nanocrystalline austenite FeCoCr powders by deformation-thermal co-induced ferromagnetism via attritor ball milling and subsequent heat treatment. Results showed that significant austenite-to-martensite transformation in the FeCoCr powders was achieved during ball milling, along with the increase in shape anisotropy from spherical to flaky. The saturation magnetization followed parabolic kinetics during ball milling and rose from 1.43 to 109.92 emu/g after milling for 4 h, while it exhibited a rapid increase to 181.58 emu/g after subsequent heat treatment at 500 °C. A considerable increase in complex permeability and hence magnetic loss capability was obtained. With appropriate modulation of complex permittivity, the resultant absorbents showed a reflection loss of below −6 dB over 8~18 GHz at thickness of 1 mm and superior stability at 300 °C. Our strategy can broaden the material selection for microwave absorbents by involving Fe-based austenite alloys and simply recover the ferromagnetism of industrial products made without proper control of the crystalline phase.