Carbon black/ polyurethane nanocomposite-coated fabric for microwave attenuation in X & Ku-band (8–18 GHz) frequency range

Abstract

In the present study, coating formulations based on carbon nanoparticle (125–150 nm) and two component polyurethane resin [Polyester polyol-8 and hexamethylene diisocyanate [C8H12N2O2 (NCO-(CH2)6–NCO)] have been prepared in concentration of 5,6,7,8, 9 and 10 g of carbon black in 100 ml of polyurethane solution and was applied on cotton fabric adopting knife over roller coating technique. The coated fabrics were evaluated for surface resistivity and relevant microwave properties i.e. permittivity, scattering parameters, reflection, transmission, absorption, reflection loss and electromagnetic interference shielding in HVS free-space microwave measurement system. It is observed that increasing the carbon content increases the permittivity values and decreases the impedance. It is seen that with increase of carbon content up to 7 g, absorption increases due to increase of permittivity while with further increase of carbon content from 8 to 10 g, absorption decreases due to increase of conductivity and thereby increased reflection. The coated fabric at 6.55 wt% carbon and 93.45 wt% PU in thickness of 1.3 mm has shown about 46% absorption, 29.49% transmission and 24.5% reflectance in X (8.2–12.4 GHz) and Ku (12–18 GHz) frequency band. When electrical thickness of coated fabric equals λ/4, a peak of reflection loss is observed due to Salisbury absorption mechanism. Highest reflection loss of –31.39 dB at 17 GHz, more than 20 dB in bandwidth of 16–18 GHz and more than 10 dB in entire Ku- band is achieved. Coated fabric may be used as apparel for protecting human being from hazardous microwave and for radar absorbing structural materials for defence applications.