Stacked polypyrrole-coated non-woven fabric sheets for absorbing electromagnetic waves with extremely high frequencies

Conductive non-woven fabric sheets coated with polypyrrole nanoparticles and having resistivity from 1.5 × 105 to 3.0 Ω cm were prepared by immersing non-woven fabric sheets in solutions containing various concentrations of oxidizing agent and dopant and then exposing the sheets to pyrrole vapor. A stack of ten treated sheets could absorb more than 95% of electromagnetic waves in the frequency range of 75–110 GHz and more than 99% in the range of 85–105 GHz, irrespective of the resistivity of the sheet. This absorption was achieved even though the thickness of the stack was less than 10 mm. Furthermore, a conductive non-woven fabric sheet with resistivity of 7.5 Ω cm and thickness of only 0.5 mm could absorb about 90% of electromagnetic waves in the range of 75–110 GHz. These results clearly demonstrate that the stacked conductive non-woven fabric sheets prepared in this study are a new material that effectively absorbs electromagnetic waves with extremely high frequencies in the millimeter band.