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The meta-structural design of flat absorbers demonstrates significant potential for improving microwave attenuation performance. However, the single mechanism of amplitude attenuation through resonance-enhanced effect necessitates considerable material thickness, restricting its application in electromagnetic (EM) defense. Utilizing the synergistic effect of multiple mechanisms is expected to break through the performance limits of microwave stealth metamaterials at the sub-wavelength scale. Herein, absorption-diffusion integration stacked metamaterials (ADISM) were designed using a multi-compound strategy, which comprises bionic porous spherical carbonyl iron powder (SCIP) coatings and stacked vortex metasurfaces (VMs). Such a metamaterial integrates EM scattering modulation with microwave absorption, enabling the creation of a broadband, high-efficiency, low-reflection design, providing an effective absorption bandwidth (EAB) reaching 10.42 GHz (7.58–18 GHz) at a thickness of 2.48 mm. Manipulating the orbital angular momentum (OAM) to effect wavefront transformation, the dissipation of EM wave energy is achieved. The absorption peak frequency modulation and absorption bandwidth broadening are achieved by the intrinsic loss capability of the porous coating, and corresponding mechanisms are demonstrated by simulation models. In short, the synergistic effects of microwave absorption and scattering modulation significantly enhance the return loss capability and facilitate broadband microwave attenuation. This research offers new insights into the multifunctional integration of EM stealth metamaterials. [Display omitted] [ABSTRACT FROM AUTHOR]

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. [Display omitted] • 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. [ABSTRACT FROM AUTHOR]

Perfect stealth has attracted humanity for decades owing to the advent of metamaterials, however, despite long-standing efforts in design and fabrication, it has been challenging to achieve ultra-broadband absorption under deep-subwavelength thickness, the fundamental hurdle is Plank-Rozanov limit, which hindering the development of stealth materials. Herein, inspired by the absorption model of Pachliopta aristolochiae, present works demonstrate an approach with composition concept to ideal stealth, through the synergy of microwave melanin and bionic metastructure, the fabricated biomimetic metamaterials exhibit effective absorption over 2–18 GHz range under 0.04 λ max thickness for radar stealth, which breakthrough the Plank-Rozanov limit by utilizing the enhanced resonance of bionic metastructure in absorption, corresponding mechanisms are demonstrated by simulation models. The metamaterials also robustness for arrangement and polarizations, compatible infrared emissivity is reduced to 0.43, as well as flexibility and impact resistance during minus temperature. The principle behind here is universal and can be extended to many metamaterials and a broad range of absorption. Image 1 [ABSTRACT FROM AUTHOR]

In this paper, polyaniline/graphene oxide composites were prepared by a one-step intercalation polymerization of aniline in the presence of GO layers under different mechanical agitation duration period, and the formation mechanism and microwave absorbing mechanism were investigated for an entire hierarchical sandwich-like structured polyaniline/graphene oxide composites. The morphology and structure were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) nitrogen sorption-desorption measurement and vector network analysis (VNA). The results revealed that mechanical agitation duration promoted the heterogeneous nucleation of aniline on graphene oxide layers and induced the formation of PANI-GO-PANI sandwich-like microstructure. The minimum reflection loss of entire sandwich-like structure reaches −28.12 dB at 5.675 GHz and an ultra-wide effective absorbing bandwidth (RL < −10 dB) over 13.175 GHz from 4.825 GHz to 18 GHz with the thickness varies from 2 mm to 5.5 mm, performing much better than pristine PANI and mixtures of PANI nanorods and sandwich-like structure. This paper reveals that constructing a hierarchical microstructure can be a promising method for developing novel microwave absorbing materials. [ABSTRACT FROM AUTHOR]