A Flexible Sandwich Structure Carbon Fiber Cloth with Resin Coating Composite Improves Electromagnetic Wave Absorption Performance at Low Frequency

In order to improve the electromagnetic wave absorbing performance of carbon fiber cloth at low frequency and reduce the secondary pollution caused by the shielding mechanism, a flexible sandwich composite was designed by a physical mixing coating process. This was composed of a graphene layer that absorbed waves, a carbon fiber cloth layer that reflected waves, and a graphite layer that absorbed transmitted waves. The influence of the content of graphene was studied by a control variable method on the electromatic and mechanical properties. The structures of defect polarization relaxation and dipole polarization relaxation of graphene, the interfacial polarization and electron polarization of graphite, the conductive network formed in the carbon fiber cloth, and the interfacial polarization of each part, combined together to improve the impedance matching and wave multiple reflections of the material. The study found that the sample with 40% graphene had the most outstanding absorbing performance. The minimum reflection loss value was −18.62 dB, while the frequency was 2.15 GHz and the minimum reflection loss value compared to the sample with no graphene increased 76%. The composites can be mainly applied in the field of flexible electromagnetic protection, such as the preparation of stealth tent, protective covers of electronic boxes, helmet materials for high-speed train drivers, etc.

Hollow MoC/NC Sphere for Electromagnetic Wave Attenuation: Direct Observation of Interfacial Polarization on Nanoscale Hetero-interfaces

Carbon-based composites with hetero-interfaces is a group of promising electromagnetic wave absorbing materials (EWAMs) for its excellent dielectric loss. For developing this kind of EWAM, in situ constructing hetero-interfaces and...

Nano-Modified Meta-Aramid Insulation Paper with Advanced Thermal, Mechanical, and Electrical Properties

Molecular dynamics simulations were used to analyze the internal mechanism for the observed improvement in performance of nano-modified meta-aramid insulation paper from a microscopic point of view. The results showed that the k-polyphenylsilsesquioxane(PPSQ) modified meta-aramid insulation paper was superior to b-PPSQ modified meta-aramid insulation paper in terms of its thermal stability and mechanical and electrical properties. The analysis of microscopic parameters showed that the stiffness of k-PPSQ was less than that of b-PPSQ, and the hydroxyl groups on the open-loop system were more likely to enter the dispersed system, resulting in higher bonding strength, meta-aramid fiber chains between k-PPSQ molecules, and the formation of hydrogen bonds. Additionally, the nano-enhancement effects of k-PPSQ and b-PPSQ resulted in various improvements, including a reduction in pores between molecules in the blend model, an increase in the contact area, the formation of interfacial polarization, and a reduction in defects at the interface.

Carbonized wood with ordered channels decorated by NiCo2O4 for lightweight and high-performance microwave absorber

Wood-derived carbon has a 3D porous framework composed of through channels along the growth direction, which is a suitable matrix for preparing electromagnetic wave (EMW) absorbing materials with low cost, light weight, and environmental friendliness. Herein, the carbonized wood decorated by short cone-like NiCo2O4 (NiCo2O4@CW) with highly ordered straight-channel architecture was successfully manufactured through a facile calcination procedure. The horizontal arrangement of the through channels of NiCo2O4@CW (H-NiCo2O4@CW) exhibits a strong reflection loss value of -64.0 dB at 10.72 GHz with a thickness of 3.62 mm and a low filling ratio of 26 wt% (with the density of 0.98 g·cm-3), and the effective absorption bandwidth (EAB) is 8.08 GHz (9.92–18.0 GHz) at the thickness of 3.2 mm. The excellent microwave absorption (MA) property was ascribed to the ordered-channel structure with abundant interfaces and defects from NiCo2O4@CW, which could promote the interfacial polarization and dipole polarization. What is more, this advantageous structure increased the multiple reflections and scattering. Finite element analysis (FEA) simulation is carried out to detect the interaction between the prepared material and EMW when the ordered channels are arranged in different directions. This research provides a low-cost, sustainable, and environmentally friendly strategy for using carbonized wood to fabricate microwave absorbers with strong attenuation capabilities and light weight.

High Absorption Electromagnetic Wave Properties of Composite CoFeO3 Synthesized by Simple Mechanical Alloying

Electronic equipment demand is strongly correlated to the electromagnetic wave interference (EMI), which causes severe effects on human health. Microwave absorbing materials (MAMs) are one method to protect human health from EMI. Cobalt nanoparticles show high performance as MAMs. Here, we have synthesized CoFeO3 by simple mechanical alloying for increased multiple reflections, interfacial polarization, magnetic domain loss, electron spin loss, internal resonance, hoping electron, conductive loss, and multiple scattering for improved absorption of EMI waves. We determined the electronic properties from the Quantum Espresso (QE) and corresponding results are discussed. The metallic character comes from the d-state of transition metal atoms Fe (II) and Co which are sufficiently large in magnitude in the Fermi level of band structure and density of state (DOS) distribution. Crystallite size in the range of 13.6 to 18.7 nm with surface morphology shows irregular shapes of the particles. For CoFeO3 as MAMs, we found that the reflection loss (RL) is -55 dB (lower than the previous reported -43.2 dB) at 10-11 GHz for a thickness of 8 mm, indicating that this study shows high potential of CoFeO3 as an alternative composite for MAMs applications.

Metal Oxide/Nitrogen-Doped Carbon Nanosheet Heteronanostructures as Highly Efficient Electromagnetic Wave Absorbing Materials

In this paper, we will discuss the excellent broadband microwave absorption behaviors of Cu/CuO/carbon nanosheet composites: traces of copper and oxide embedded in a carbon nano-sheet not only cut down the high permittivity of adsorbs but also induce more interfacial polarization centers. The results showed that at a cracking temperature of 900 °C, the fabricated material has a unique ripple-like structure, which promotes the hierarchical interfacial polarization. The prepared material has a maximum absorption bandwidth of 4.48 GHz at an exceedingly thin thickness of 1.7 mm and a maximum reflection loss of −25.3 dB at a thickness of 2 mm. It is a relatively ideal material for electromagnetic wave absorption.

The Role of ZnO as a Dopant and an Intergranular Phase in the Electrical Properties of Ca0.6Sr0.4TiO3 Ceramics

ZnO was introduced into Ca0.6Sr0.4TiO3 ceramics as a dopant and an intergrangular phase in this research, followed by detailed structure characterization, energy storage performance analysis, and electrical behavior studies. The results revealed that the existence of ZnO as a dopant led to the decrease of conduction activation energy and the deterioration of energy storage behavior, while appropriate introduction of ZnO as an intergranular phase resulted in the increase of conduction activation energy and the optimization of energy storage performance. Additionally, the inverse relation between interfacial polarization and energy storage performance was observed in this study. Finally, an increased energy storage density of 1.16 J/cm3 was achieved in 1 mol% ZnO-added Ca0.6Sr0.4TiO3 ceramics.