| In recent years, the promising microwave absorbing materials are supposed to have thin thickness, wide band, lightweight, good thermal stability and high absorption ratio. As a result, the metal absorbent possessing magnetic loss are often filled in with absorbing materials, because the metal absorbent can attenuate the microwave due to the spin resonance, the domain wall motion or the eddy current effect. Mainly, there are three types of absorbing materials such as dielectric loss, the magnetic loss and the conductive loss according to the absorbing mechanisms. Considering the achievement of high absorption requirement, two important conditions are supposed to be satisfied:(1) the impedance of absorbing materials should be matching the impedance of free space; (2) the incident electromagnetic (EM) wave must get attenuated rapidly through the absorbing layer. The development of microwave absorbing materials with strong absorption, high strength, lightweight, and low cost in a wide frequency range is of paramount importance to the disposal of ever-increasing EM interference. EM pollution has become a serious threat to human health and ecological environment due to an increased application of microwave absorbing materials in gigahertz mobile phones, local area networking, radar systems etc. Therefore, the protection of EM radiation has attracted much attention, which can either be achieved by absorbing or attenuating the EM radiation.To overcome EM pollution regarding the high demand in commercial and high-tech applications, a number of flat nanocomposite plates were synthesized by using the surface-modified Fe nanoparticles (NPs) as microwave absorber, carbon fibers (CFs) as reinforcement phase and epoxy resin (ER) as a matrix. The Fe NPs were synthesized by an arc-discharge plasma method, followed by a surface modification using silane coupling agent (KH-550) to improve its dispersion stability into the organic matrix (ER). In order to measure the realistic microwave absorbing properties (the reflection losses, RLs) of nanocomposites in the wave range of 2-18 GHz, a series of square plates (20×20 cm2) were made utilizing the surface-modified Fe NPs at different mass percentages (0 wt.%,20 wt.%,30 wt.% and 40 wt.%) with/(or without) oriented CFs into ER matrix. On the other hand, to study the influence of CFs on microwave absorption and mechanical properties of nanocomposite plates, a series of nanocomposite plates were manufactured fixing the contents of modified Fe NPs as 30 wt.% and using the different wt.% of CFs (1.38 wt.%,2.76 wt.% and 5.52 wt.%) into ER matrix.It is noteworthy; CFs and its appropriate direction greatly affect the microwave absorbing properties. The proper orientation of CFs and its content greatly affect the microwave absorption through impregnable reflection of microwave inwardly as the direction of CFs is vertical to the direction of incident microwave. The strong reflection of microwave inside nanocomposite by CFs can bring great probabilities to further consume it by the Fe NPs absorbent and results in an improved microwave absorption performance of the nanocomposite plate. The inevitable reflection of microwave by CFs brings the unavoidable condition for the wave absorption by Fe NPs, as well as the matching input impedance of nanocomposite plate at certain frequencies.For comparison, at the "topside" and "bottom side" modes (it means a graded distribution of Fe NPs from the top to bottom sides of the nanocomposite plate), RLs of nanocomposite plates were measured taking into account the direction of CFs to incident microwave. The RL properties are associated with structural resonance, appropriate conductivity, interfacial polarization and impedance match. Conflate of Fe NPs, CFs and its orientation into ER matrix and their effect on EM and mechanical properties are worked out and presented. |
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