Abstract:

Objective Carbon fiber has strong electromagnetic shielding ability because of its good conductivity. With the development of electronic informatization, the design of carbon fiber fabrics with electromagnetic shielding performance has been widely supported and explored. At present, the research on the influence of fabric structural parameters on electromagnetic shielding performance mainly focuses on traditional metallized fabrics or mixed fabrics, while the research on carbon fiber electromagnetic shielding fabrics mainly focuses on single-layer fabric structures, and its shielding effectiveness has certain limitations. It is necessary to evaluate the electromagnetic shielding performance of different structural parameters and multi-layer carbon fiber composites.

Method The electromagnetic shielding properties of plain weave structure, twill weave structure, biaxial structure and spread fiber structure carbon fiber fabrics and thermoplastic polyurethane(TPU) composites were studied, and their electromagnetic shielding mechanisms were analyzed. Four kinds of structural fabrics were used as reinforced structures, and were molded by hot pressing assisted by hot pressing at 190 ℃ and 5 MPa for 20 s. The electromagnetic shielding performance of composites in X-band was tested, and the difference of shielding efficiency of different structures was analyzed. The carbon fiber fabric with fiber spreading structure was hot-pressed and compounded by the number of layers and the angle of layers, and the effects of the change of the number of layers and the angle of layers on the electromagnetic shielding properties of the composites were explored.

Results The results show that the fabric structure has a significant influence on the electromagnetic shielding properties of CF/TPU composites. Plain fabric shows the highest total shielding effectiveness (S_SE), reaching 28 dB, which is significantly better than twill fabric (26.8 dB) and biaxial fabric (24.5 dB). The reason why plain fabric can achieve the best electromagnetic shielding effectiveness is mainly due to the dense distribution of interweaving points between fiber bundles in its fabric structure, which effectively enhances the overall coherence and stability of the fiber network, thereby reducing the scattering and transmission paths of electromagnetic waves inside the material. In addition, under the same area density condition, the plain fabric structure has smaller porosity than the other two types. This characteristic further limits the leakage of electromagnetic waves through the pores, reduces the occurrence of leakage waves, and ultimately improves the electromagnetic shielding effectiveness of composite materials. Furthermore, the electromagnetic shielding efficiency can be significantly improved through carbon fiber spreading treatment. The 80 g/m² spread fabric achieves an S_SE value of 34 dB, which is better than the unspread 150 g/m² fabric (28 dB). The multi-layer layup structure has a significant impact on the electromagnetic shielding performance of CF/TPU composites. Although the fiber spreading treatment reduces the interweaving times of warp and weft yarns per unit area, the full spreading of carbon fiber tows promotes the full contact between warp and weft tows and significantly increases the number of contact points. In addition, the higher tightness of spread fabric compared with traditional plain fabric is also one of the key factors to improve electromagnetic shielding performance. With the increase of the layup angle, the S_SE value shows a significant upward trend. When the included angle reaches 90°, the S_SE value reaches a peak of 50 dB, which is about 12 dB compared with 37.2 dB at the included angle of 0°. This is because with the increase of the layup angle, the fiber bundles in the middle layer gradually tend to be arranged in parallel, the interlayer gap is effectively filled, and the porosity is reduced, thus significantly improving the electromagnetic shielding performance of the composite material and reducing the leakage phenomenon. Further analysis shows that under the condition of the optimal composite angle of 90°, with the superposition of layers layer by layer, the S_SE value continues to increase steadily, but the increment gradually decreases, showing a decreasing trend. When five layers are superimposed, the S_SE value reaches the maximum value of 64.57 dB. This observation reveals a nonlinear relationship between electromagnetic shielding effectiveness and the number of layers. Therefore, in practical applications, it is necessary to comprehensively consider the balance between cost and efficiency to optimize the structural design of electromagnetic shielding composites.

Conclusion The electromagnetic shielding efficiency of plain woven carbon fiber reinforced composite materials reaches 28 dB, which is slightly higher than that of twill and biaxial reinforced structures, and the shielding efficiency of plain woven CF/TPU after fiber expansion is improved by nearly 50% compared with that of ordinary plain woven. At the same time, the layup structure of carbon fiber fabric has a significant influence on the electromagnetic properties of CF/TPU. With the increase of layup angle, its electromagnetic shielding efficiency also increases, and its electromagnetic shielding efficiency reaches 50 dB at 90° layup; With the increase of the number of layers, its electromagnetic shielding efficiency gradually increases, but the gain effect of the number of layers gradually decreases

Key words: carbon fiber, fabric structure, expansion, layered structure, electromagnetic shielding, flexible composite, thermo plastic polyurethane