Measurement and simulation of broadband radar absorption properties of polypyrrole nanotubes and their carbonaceous analogues

Abstract

The rapid development of unmanned aerial and ground vehicles (UAVs and UGVs, respectively) requires innovative means for their protection against detection and localization by radar microwave signals. Radar absorbing materials (RAMs) used in functional or structural composites of small, low-speed UAVs and UGVs can employ non-conventional fillers, such as nanostructured conductive polymers or their carbonaceous analogues. However, the work with non-conventional fillers brings difficulties in preparation and manipulation with sufficient amounts on a laboratory scale in a reasonable time and at a reasonable price. Therefore, computer simulation of filler behavior using software tools can be a vital solution to assess their ability to serve as RAMs. Here, polypyrrole nanotubes (PPy-NT) and carbonized polypyrrole nanotubes (PPy-C) were dispersed in polydimethylsiloxane matrix (PDMS) at low concentrations (1-3 % w/w) and their attenuation properties (reflection, absorption, and transmission coefficients), dielectric properties (complex permittivity and loss tangents) and apparent alternating current (AC) conductivity were evaluated between 2.6 GHz and 18 GHz. A 2 mm thin sample of the PPy-NT/PDMS composite at low concentration of 3 % w/w of the filler absorbs 28 % of the radar signal at 3.3 GHz. Using the simulation model made in CST Studio software, the evaluation of radar absorption properties was extended beyond the physical boundaries of the PPy-NT/PDMS sample, and the attenuation properties were evaluated up to a theoretical thickness of 100 mm (absorption of the signal 63 %). The presented method of simulation and the proposed model allows fast and flexible determination of attenuation properties of non-conventional RAMs of various thicknesses.