Role of coating add-on and substrate material on microwave and EMI shielding properties of coated fabric

Abstract

Role of coating add-on and nature of textile substrate have been studied on microwave and EMI shielding properties of coated cotton fabric. Coated fabric samples have been prepared with coating formulations containing carbon black and milled carbon fibre in polyurethane matrix, using cotton (non-conducting) and conducting fabric (warp: SS20%/PET80%, weft: SS 55% / PET 45% ) substrate simultaneously. A high precision lab coating machine (Mathis Lab Coater, UK) has been used to produce coated fabric of uniform thickness (0.31- 0.67 mm). Coated fabrics are studied for microwave and EMI shielding properties in 8.2-18.0 GHz (X & Ku) frequency band in vertical and horizontal polarisation of electromagnetic wave. The microwave properties of coated fabric based on cotton substrate are found due to coating add-on only, as the cotton itself does not have any role to play. Cotton - based coated fabric with add-on of 257.7% exhibits 32-43% reflection, 22-39% transmission, 37-42% absorption and EMI shielding of 5.23-7.93 dB in 8.2- 18.0 GHz. On the other hand, microwave properties of coated fabric prepared on conducting substrates are found to produce synergetic effect of substrate material and coating add-on. Coated fabric on conducting substrate with add-on of 185.5% displays 92-82% reflection, 0.17-0.36% transmission, 7.20 - 26.310% absorption and EMI shielding of 23.98- 21.64 dB. Apart from this, coated fabrics are also prepared with gradual increase of coating add-on in order to understand the effect of ultimate coating add-on loading and to obtain optimum threshold combined effect of coating add-on and substrate materials. Sample with coating add-on of 237.9% acquires high surface conductivity (σ = 46.34 S/m) and low surface resistivity (34.25 Ω/□). Coated fabric offers 93.47-79.47% reflection, 6.39-22.07% absorption, <0.2% transmission, and EMI shielding of 28.86- 26.68 dB.