Research on Percolation Threshold of Broadband Electromagnetic Wave Absorbing SiCN (MWCNTs) Composite Ceramics

Abstract

A simple polymer derivation method was applied in this paper to prepare a series of SiCN (MWCNTs) composite ceramics by adjusting the mass ratio of multi-walled carbon nanotubes (MWCNTs). The percolation threshold of the corresponding MWCNTs addition amount when SiCN(MWCNTs) composite ceramics exhibit the optimal electromagnetic wave (EWM) absorption performance was studied, the effect of different addition amounts of MWCNTs on reflection loss (RL), effective absorption bandwidth (EAB), electromagnetic parameters, impedance matching parameters (Z) and attenuation coefficient (α) of composite ceramics was analyzed, and the EMW absorption mechanism of the corresponding composite ceramics when MWCNTs addition amount fix at percolation threshold was discussed. The results showed that composite ceramics exhibited the best EMW absorption performance when the addition amount of MWCNTs reached the percolation threshold (10wt%): the minimum reflection loss (RLmin) was -37.9 dB, and the EAB was 2.8 GHz at a thickness of 2.4 mm; its RLmin was -21.7 dB, and the EAB reached 4.7 GHz at a thickness of 1.7 mm. By changing the sample thickness from 1.0 mm to 5.0 mm, the EAB containing the C, X and Ku bands can be acquired. Therefore, it is expected to be a promising candidate for the new generation of EMW absorbers due to its light weight, high efficiency and broad band.

Texture Regulation of Metal–Organic Frameworks, Microwave Absorption Mechanism‐Oriented Structural Optimization and Design Perspectives

“…MAMs with tunable dielectric and magnetic properties can be obtained via the aforementioned texture regulation of MOFs. Generally, the EMW absorption performance can be calculated as follows [ 109 ] $$$$\begin{equation}RL\ \left( {{\rm{dB}}} \right) = 20{\rm{log}}\left| {\frac{{{Z}_{{\rm{in}}} - {Z}_0}}{{{Z}_{{\rm{in}}} + {Z}_0}}} \right|\end{equation}$$$$ $$$$\begin{equation}{Z}_{{\rm{in}}} = {Z}_0 \sqrt {\frac{{{\mu }_{\rm{r}}}}{{{\varepsilon }_{\rm{r}}}}} {\rm{tanh}}\left( {j\frac{{2\pi fd}}{c}\sqrt {{\mu }_{\rm{r}}{\varepsilon }_{\rm{r}}} } \right)\end{equation}$$$$where ε r = ε' – jε“ and µ r = µ' – jµ” are the complex permittivity and complex permeability, respectively, whose real and imaginary parts represent storage and attenuation of dielectric and magnetic energy; [ 110 ] Z in , Z 0 , f , d , and c are the input impedance of the MAMs, free space impedance, incident wave frequency, thickness of absorber, and light velocity, respectively; [ 111 ] and RL is reflection loss (dB).When the RL value exceeds −10 dB, 90% of EMW can be absorbed, and the width of corresponding frequency band is defined as the effective absorption bandwidth ( f E ). Additionally, well‐matched impedance characteristics (| Z in / Z 0 |≈1) and high EM attenuation ( α ) are the basis for effective EMW absorption.…”