Abstract:

Objective The electromagnetic (EM) wave pollution and its secondary reflection bring great threat to human health and to information security. To reduce the secondary reflection pollution of carbon fiber fabric composites, enhancing the impedance matching of carbon fiber fabric is a feasible method.
Method Glass fiber has low dielectric properties; the impedance matching of carbon fiber fabric could be improved by using glass fiber to regulate the fabric structure of the carbon fiber fabric. In this work, five different fabric structures of glass fiber/carbon fiber (G/C) fabric were designed and were compounded with waterborne polyurethane. The morphology, electromagnetic interference (EMI) shielding, dielectric and photothermal conversion properties of glass fiber/carbon fiber composites were characterized by an ultra-depth of field microscope, vector network analyzer, simulated solar xenon lamp light source system and infrared thermal imager.
Results Glass fiber and carbon fiber interweave with each other to form the G/C fabrics structure which was arranged smoothly as illustrated in Fig. 1. The EMI shielding efficiency (SE) of the five G/C fabric composites showed effective EMI shielding. Their average EMI SE was greater than 20.0 dB in the X band (8.2-12.4 GHz) as can be seen in Fig. 3(a). The EMI total shielding efficiency(SE_T) curves of C fabric (its weft yarns are all carbon fiber) composites was relatively stable, with its SE_T being 33.4 dB at 9.6 GHz(Fig. 2(a)). The SE_T curves of G/C fabrics composites decreased firstly and then increased with the increasing frequency within X band after the introduction of glass fiber. The EMI SE value of G2C1 fabric (glass and carbon yarns were woven into the fabric alternately as weft) composite was up to 38.7 dB at 12.1 GHz, as shown in Fig. 2(a). The power coefficients values of absorptivity of G/C fabric composites increased by adding glass fiber. The structural changes in G/C fabric composites effectively regulate various dielectric polarization relaxation mechanisms (Fig. 5), which indicated that the use of G/C fabric structure could improve the impedance matching with the EM wave and reduce the second reflection. The surface temperature of G/C fabric composites responds rapidly under simulated solar xenon lamp light source as shown in Fig. 6. The surface temperature of G/C fabric composites gradually reached equilibrium after rapidly increasing under 2 kW/m² light intensity and decreased rapidly when the light source was turned off at 300 s and this was demonstrated in Fig. 6(a). With the increase of glass fiber content, their surface equilibrium temperature was decreased, which is consistent with the results of the SE_T. The fabric structure of G1C1 fabric composite was clear, indicating its rapid response to the light. The equilibrium temperature of G1C1, as shown in Fig. 6(a), reached 71.8 ℃ at 300 s under 2 kW/m² light intensity. In addition, the time-temperature curves of G1C1 fabric composite under different light intensities (1,1.5,2 kW/m²) showed that the equilibrium temperature (average temperature from 200 s to 300 s) |ΔT₁|,|ΔT₂| and |ΔT₃| were 8.0, 20.6 and 28.6 ℃, respectively. It is indicated that G/C fabric composites have significant differences in response to different light intensities. Light is also a type of electromagnetic wave. It can be inferred that G/C fabric composite material can quickly convert the energy of electromagnetic wave into joule heat dissipation to achieve excellent electromagnetic shielding performance.
Conclusion In this work, five G/C fabric composites were fabricated, each possessing efficient EMI shielding and photothermal conversion properties. The dielectric properties of G/C fabric composites were adjustable by structural parameters of G/C fabrics, and the research results demonstrated that such composites could effectively regulate various dielectric polarization relaxation mechanisms. The impedance matching performance of G/C fabric composites increased to match that of the electromagnetic waves and the secondary reflection of the EM wave was reduced. The method of designing fabric structure has great application potential in EMI shielding materials.

Key words: carbon fiber, glass fiber, fabric composite, electromagnetic interference shielding, photothermal conversion