Structural effects in a composite nonwoven fabric on EMI shielding. (15th April 2017)

• Record Type: Journal Article
• Authors: Lu, Longsheng; Xing, Di; Teh, Kwok Siong; Liu, Huilong; Xie, Yingxi; Liu, Xiaokang; Tang, Yong
• Is Part Of: Materials & design. Volume 120(2017)
• Page Start: 354
• Page End: 362
• Publication Date: 2017-04-15
• Subjects: Carbon fiber -- Nonwoven fabric -- Electromagnetic interference shielding -- Shielding mechanism -- Percolation threshold -- Electromagnetic radiation; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2017.02.025
• Languages: English
• ISSNs: 0264-1275

Abstract

Abstract: A composite nonwoven fabric named CEF-NF in previous work was fabricated with carbon fibers (CFs) and polypropylene/polyethylene (PP/PE) core/sheath bicomponent fibers (denoted as ESFs). It holds great promise as an electromagnetic interference (EMI) shielding material, due to its good mechanical strength, excellent flexibility, ultra-thin thickness and remarkable electrical properties. This paper demonstrates a composite CEF-NF fabricated via two-step wet-papermaking/thermal-bonding processes. A flange coaxial test system was established to investigate the influences of material structure on EMI shielding effectiveness (EMI-SE) of CEF-NF fabrics in 30– 1500 MHz frequency range. Results indicate that the structure of a CEF-NF is highly correlated to its EMI-SE property, which increases with increasing areal density, fiber length and CF concentration. Under a set of optimal process parameters, the EMI-SE of CEF-NF with merely 40 wt% of CF and 50 g/m 2 areal density can achieve a specific overall EMI-SE as high as 30.29 dB, or 110 dB·cm 3 /g—meeting commercial EMI requirements. Lastly, the ideal and actual EMI shielding mechanism were fully investigated and analyzed. It was found that the electrical percolation threshold of CEF-NF had a great influence on the actual absorption and reflection performance. At the conductivity threshold, CEF-NF showed high absorption performance. Graphical abstract: Highlights: A composite nonwoven fabric works well in electromagnetic interface shielding. Fabric structure affects its electromagnetic interface shielding effectiveness. Conductivity percolation threshold affects the reflected and absorbed power of the fabric. Carbon fiber concentration determines whether the EMI reflection or absorption is dominant.