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The impedance matching characteristic parameters (IMCPs) of microwave absorbing materials for specular reflection under oblique incidence and surface wave attenuation are first proposed and defined. A microwave absorbing sheet was fabricated and its electromagnetic parameters were measured. The specular reflection suppression characterized by reflection loss and non-specular scattering suppression described by surface wave attenuation constants were studied with the change in thickness, polarization, and incident angle. The present results demonstrate that the definition of IMCPs for both specular reflection and non-specular scattering is effective. Meanwhile, the curves of IMCPs share the same shape and have the same peak frequency in specular reflection and non-specular scattering cases. In addition, Brewster angle properties are also consistent with the IMCPs under oblique incidence. Thus, this work develops a pathway for the design of microwave absorbing sheets suppressing both the specular reflection and non-specular scattering by adjusting the IMCPs. [ABSTRACT FROM AUTHOR]

Aimed at broadband microwave absorption, we present the linear polarization conversion metasurface (MS) by a novel design of a two-bit matrix-type coding method. The coding patterns are applied to a dielectric substrate and a magnetic substrate. The radar cross section (RCS) reduction curves of different matrices can fully verify the independence and correctness of the matrix-type coding method. As shown in simulation, the RCS reduction of 8 dB by a metal pattern with a dielectric layer has been achieved in the frequency range of 6–15 GHz. When the matrix-type coding pattern is placed in the middle of double-layered magnetic absorbing materials (MMs), a 10 dB RCS reduction can be achieved in the range of 8–16 GHz. Besides, the metal patterns can improve the high frequency reflection loss performance and broaden the absorption bandwidth of MMs almost without changing the thickness. The experimental results can nicely reproduce the simulated results. The correlative RCS reduction mechanism is further explored. This model provides a new idea in the design of coding MS, which implicates a potential application in stealth technology. [ABSTRACT FROM AUTHOR]

In this work, we presented an oblique incidence-insensitive metamaterial absorber (MA) based on the strong magnetic coupling resonance using the printed circuit board process, and the spacer is produced by a typical magnetic absorber material (MAM). As for reflection loss (RL) at oblique angles, it can achieve high-efficiency absorption for both transverse-electric (TE) and transverse-magnetic (TM) polarizations with a wide angular range from 0° to 60° in the low frequency of 2.33 GHz to 3.44 GHz. In addition, the magnetic coupling mechanism of the metamaterial absorber was deeply analyzed. Comparing the results of the simulation and experiment, it displays excellent absorption performance of the proposed absorber in TE and TM modes under large oblique incidence angles. [ABSTRACT FROM AUTHOR]

Metal-organic framework (MOF) crystals have promising applications in a number of different fields, but the growth of MOF crystals with controllable morphology and high uniformity remains a major challenge. By taking the advantage of the synergistic effects of water molecules in the mixed solvent and polyvinylpyrrolidone (PVP) surfactants, this work demonstrates an approach for the preparation of NH2-MIL-88B(Fe) MOF crystals with both highly customizable size and aspect ratios and high uniformity. The effects of the concentration of water in the mixed solvent and the amount of PVP surfactants on the morphology and size of the MOF crystals were investigated. The morphology and crystalline properties were characterized by scanning electron microscopy and X-ray diffraction techniques. The data showed that through controlling the concentration of water in the solvent and the amount of the PVP surfactant, the size of the MOF crystals can be tuned rather widely, over 344–5.14 μm, while the aspect ratio of the crystals can be varied widely over 1.0–7.1. Possible mechanisms for such high tunability were discussed. As an example of potential applications, the complex permeability and permittivity of MOF-derived composites (25 wt%) were measured over a wide frequency range of 2–18 GHz. The parameters were then used to evaluate the potential for electromagnetic wave absorption. The results indicate that the composite with a thickness of only 1.2 mm exhibits a "− 10 dB" absorption bandwidth of 4.1 GHz and a minimum reflection of − 20 dB. Such bandwidth and reflection properties provide inspiration for future design of lightweight, broadband electromagnetic wave absorbers from the perspective of fine morphology control. [ABSTRACT FROM AUTHOR]