Abstract
Shielding the microwave signature (8.2-12.4 GHz, X-band) of a locked in target is a tactically important electronic countermeasure. Herein, we report on mitigation in X-band transmission mode shielding parameters for polyurethane (PU), after incorporating graphene-like nanocarbon sheets (GNCs). Initially, PU and variable weight percent (1-25) GNCs/PU paste samples were subjected to Fourier transform infrared, Raman spectroscopy, and scanning electron microscopy. These samples were molded into toroidal shaped specimens by adiabatic hot-pressing technique, for microwave scattering measurements. Parameters, such as complex permittivity (ϵ'-jϵ″), alternating current (ac) conductivity, skin thickness, transmission (S21), effective transmission loss (SET), and shielding effectiveness were determined, in addition to direct current (dc) conductivity. The real and imaginary components are increased, respectively, by ∼5 and ∼30 times, whereas loss tangent, by ∼7, at 25 wt % loading of GNCs. The ac conductivity is enhanced from 0.248 (PU) to 7.288 S/m (25 wt %) by maximizing transmission loss to -26.45 dB (99.9%) and minimizing thickness to 1-2 mm. The dc percolation threshold is found to be low at ∼5 wt %, indicating superior dispersibility of GNCs, thereafter. In analysis, the atomic polarization (at ∼10 GHz) associated with the aromatic urethane amide rings acts as a backbone to engage incident electromagnetic field wiggles. The coupling occurs via charge transfer polarization currents at doubly bonded nitrogen, oxygen, and hydrosorpted sp3 carbon sites in GNCs. The field-matter interaction is dominant at the microvoid skin interface between GNCs and PU. Possible polarization mechanism is explained. The GNCs/PU nanocomposites are realized as an effective electromagnetic interference shielding block in the tracking band. The details are presented.
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