The influence of fiber orientation on electromagnetic shielding in liquid-crystal polymers

Abstract

The influence of conductive carbon-fiber orientation and weight percentage on the electromagnetic (EM) shielding effectiveness (SE) in liquid-crystal polymer (LCP) composites was investigated experimentally and theoretically. The experimental results show that the SE of LCP composites with longitudinal fiber orientation is higher than random fiber orientation under the same weight percentage of carbon fibers filled. This is because longitudinal fiber orientation is parallel to the electric field of the incident EM wave, and most of the energy of the incident wave is reflected by the longitudinal fiber. In comparison with nylon66 composites, the SEs of LCP composites with longitudinal fiber orientation are also higher than nylon66 composites with the same content of carbon fibers. Furthermore, the SE of 20% conductive carbon-fiber-filled LCP composites was measured to be 50 dB at a frequency of 0.3 GHz and 53 dB at 1 GHz, which is at least 10 dB higher than that of nylon66 composites. The SE predicted by theoretical models and measured by experiments was in good agreement for carbon-fiber-filled LCP composites of longitudinal and random fiber orientations.

A novel structure of woven continuous-carbon fiber composites with high electromagnetic shielding

“…For an idealized, coaxial holder transmission-line circuit model, the theoretical model for SE measurement was proposed in the previous study. 1,2 The characteristic impedance (Z o ) of a 50 Ω coaxial line holder and tested samples are modeled by the combination of the lumped circuits of Z o and Z L (sample characteristic impedance). Ideally, contact between the sample and the holder of the coaxial-line conductors is good and the ideal effective circuit is shown in Fig.…”

“…1 The SE can be theoretically calculated by considering all of the effects. The modified effective circuit is shown in Fig.…”

“…Low-cost, high EM shielding, optical laser modules made with modified thermosets using compression molding technology were reported, 3,7 and a systematic investigation on the EM shielding effectiveness (SE) of injection-molded thermoplastic packaging using nylon66 and LCP composite was conducted in previous works. 1,2 With an optimized weight percentage of CF mixed in the Nylon66 and LCP composite, high EM shielding can be obtained. The weight percentage of CF was 10% less (from 30% to 20%) for LCP composites with well-orientated discontinuous CF.…”

“…According to the result in this study, the SE of the woven composite is much higher than that of conventional, discontinuous CF-filled polymer composites under the same content as in our previous work. 1,2 It has also shown that, if small conductive particles can be segregated in a network within the composite, lower concentrations of filler are needed to form conductive composites. 14 Therefore, the most practical method of producing a conductive network with fillers at a low concentration is to use continuous fibers.…”

Polarized wave electromagnetic shielding of anisotropic carbon nanomodifier-based LLDPE composites

“…Moreover, due to the possibility of producing composites with very thin-walls, such as films and microinjection molded parts (as thin as 25 mm), the study of the shielding performance of composites containing nanomodifiers (diameter < 0.5 lm) is of relevance [13]. The orientation effect of carbon-based conductive modifiers such as nanofibers, nanotubes, and fibers in polymer composites on their electrical properties have been previously reported [10,12,14,15]. Modifier alignment produces anisotropic electrical networks in the composites, which typically reduce their EM SE [16].…”