Results of permittivity measurements, electromagnetic interference shielding effectiveness, and heat generation due to microwave absorption in conducting polymer coated textiles are reported and discussed. Intrinsically conducting polymer, polypyrrole doped with anthraquinone-2-sulfonic acid (AQSA) or para-toluene-2-sulfonic acid (pTSA) was applied on textile substrates and the resulting materials were investigated in the frequency range 1-18 GHz. Conducting textile/polypyrrole composites interacted with incident microwaves and generated absorption levels of up to 48 % in a 0.54 mm thick substrate. A thermography station was used to monitor these composites during simultaneous subjection to microwave radiation, where absorption was confirmed via visible heat losses. Lower conductivity samples showed larger amounts of heat loss due to microwave absorption compared to samples with higher conductivity. A sample with an average sheet resistivity of 120 Ω/sq. showed a maximum temperature of 27.15ºC whilst a sample with a lower resistivity (105 Ω/sq.) reached 26.65ºC (Ambient temperature: 22.8ºC).
The dielectric behaviour of in-situ polymerized thin polypyrrole (PPy) films on synthetic textile substrates were obtained in the 1-18 GHz region using free space transmission and reflection methods. The PPy/para-toluene-2-sulphonic acid (pTSA) coated fabrics exhibited an absorption dominated total shielding effectiveness (SE) of up to -7.34 dB, which corresponds to more than 80 % of incident radiation. The permittivity response is significantly influenced by the changes in ambient conditions, sample size and diffraction around the sample. Mathematical diffraction removal, time-gating tools and high gain horns were utilized to improve the permittivity response. A narrow time-gate of 0.15 ns produced accurate response for frequencies above 6.7 GHz and the high gain horns further improved the response in the 7.5-18 GHz range. Errors between calculated and measured values of reflection were most commonly within 2%, indicating good accuracy of the method.
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