Preparation of flexible microwave interactive fabric for 8.2 to 18.0 GHz frequency: Functional evaluation and validation

In this study, for the first time, coating formulation based on milled carbon fibre has been applied on textile substrate to prepare flexible covering material for microwave protection. Cotton fabric with its inherent high dielectric property and finite length with close network of carbon milled fibre has synergised to generate highly conducting surface (σ = 96.22 S/m). The samples are prepared by coating of milled carbon fibre in various concentrations with polyurethane as binder on cotton fabric. Polyurethane contains hydroxyl and hexamethylene diisocynate groups which are polar under external electric field (dielectric constant 3.2–6.5) and also contribute high dielectric properties in coated fabric. Samples were evaluated for surface resistivity and microwave properties, i.e. permittivity, scattering parameters, reflection, transmission, absorption and reflection loss. Permittivity of high level (ɛ′: 21–31, ɛ″: 60–84) and attenuation of high order (α = 1971–2354 Np/m) are achieved. The sample coated with milled carbon fibre and polyurethane in ratio of 1: 1.67 on weight basis has shown 67–70% reflection, 28–30% absorption, 0.1–0.5% transmission, and EMI shielding of 28–30 dB in X (8.2–12.4 GHz) and Ku (12.4–8 GHz) frequency band. The results were further analysed theoretically and correlated with the scattering parameters and other microwave properties.