Multiscale designed SiC_f/Si₃N₄ composite for low and high frequency cooperative electromagnetic absorption

Abstract

With the aim to design a particular material for low and high frequency cooperative electromagnetic absorption at high temperature, a multiscale design is proposed by combining the microstructure and meta‐structure in one material. The SiCf/Si3N4 composite is prepared via the chemical vapor infiltration technique with SiCf as the EM wave absorbing phase and Si3N4 as the wave‐transparent ceramic matrix. The crossing grooved meta‐structure is designed and fabricated to further improve its absorbing properties and to guarantee its absorbing capacity stability at high temperature. A minimum reflection loss of −15.3 dB and −14.8 dB can be reached at 8 and 18 GHz with a total thickness of 5 mm. The temperature‐dependent reflection loss of the designed meta‐structure keeps relative reliable high temperature absorbing performances from room temperature to 500°C. This effective enhanced EM wave absorbing property is believed to be a consequence of multiscale effect induced by combining the traditional EM absorbing materials with metamaterial structure.

Hollow Porous Bowl-like Nitrogen-Doped Cobalt/Carbon Nanocomposites with Enhanced Electromagnetic Wave Absorption

“…The rational structure design of morphological dependency can bring many advantages. − Porous structures can enhance the suppression of eddy current effects, whereas hollow structures are beneficial in promoting dielectric losses by interfacial polarization. − Che’s group synthesized yolk–shell Fe 3 O 4 @TiO 2 microspheres, hierarchical tubular CMT@CNY/Co, and multishell CoNi@Air@TiO 2 composites for highly efficient absorbers. ,, In particular, the hollow structures of the inner cavities can regulate permittivity to improve the impedance matching between the absorbers and air, leading to the precise adjustment of EMA. Meanwhile, architectures that can scatter and reflect microwaves provide opportunities for an incident microwave to be transferred to thermal energy. − More interestingly, the inner cavities decrease the specific density of the material, and unique hollow structures can enhance the multireflections and thereby absorb the incident electromagnetic waves.…”

Multioctagonal Ring Metamaterial with Broadband Microwave Absorption at Elevated Temperature

“…EAB of recently reported high-temperature microwave absorbing metamaterials. [16][17][18][19][20][33][34][35][36][37] (AB: absolute bandwidth, RB relative bandwidth).…”

“…Zhou et al used SiC f /Si 3 N 4 composites to create a crossgroove structure. [ 20 ] The RL of this composite structure reached −15.3 dB at 8 GHz and −14.8 dB at 18 GHz at 500 °C by combining the microwave absorption ability of SiC f /Si 3 N 4 with the periodic structure. The design of metamaterial improved microwave absorption bandwidth and absorptivity; nonetheless, the permittivity of the material is highly impacted by temperature, and it is unable to maintain microwave absorption over a wide temperature range.…”

A method of measuring complex ermittivity of nonmagnetic materials and selecting its initial value based on iterative inversion

“…可知，对于满足低于某一确定数值反射率的吸波材料，其输入阻抗奈奎斯特图是 一个圆心在实轴上的圆形 [18] x轴、虚部为y轴的坐标系中构成一系列圆形区域 [19] ，如图1 (a)所示，在以介电常 数实部为x轴， 虚部为y轴建立的坐标系中， 由式(5)可算得介电常数等反射率圆 [20] ， 将圆上各点代入式(1)中计算得到对应介电常数的反射率幅值和相位角，如图1 (c)、 6)所示 [21] ，ε r1 、ε ri 和d…”