Stacked Polypyrrole-Coated Nonwoven Fabric Sheets for Absorbing Electromagnetic Waves with Broadband Frequencies

概要

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Microwave absorbability of electromagnetic waves in the frequency range of 1--15 GHz, which is often used in recent wireless applications, for stacks of various numbers of conductive nonwoven fabric sheets with different resistivity was evaluated to clarify their possibility as the broadband microwave absorber in the frequency range of 1--15 GHz. The conductive nonwoven fabric sheets coated with polypyrrole nanoparticles, which had resistivities from 4.6 \times 10^{3} to 1.2\times 10^{2} \Omega cm, were prepared by immersing nonwoven fabric sheets in solutions containing various concentrations of an oxidizing agent and a dopant and then exposing the sheets to pyrrole vapor. The real part (\varepsilon') and the imaginary part (\varepsilon'') of complex permittivity for each conductive nonwoven fabric sheet increased with decreasing frequency, indicating the dispersion of permittivity. In addition, the reflection loss decreased when ammonium persulfate concentration increased and/or the stack size increased. However, the stack of two conductive nonwoven fabric sheets (thickness: 6.6 mm) with a resistivity of less than 120 \Omega cm had average reflection losses of less than -10 dB in the frequency range of 1--15 GHz. From this way, it can be considered that the stacked conductive nonwoven fabric sheets prepared in this study can be a new material that effectively absorbs electromagnetic waves in the wide frequency range.
2012-08-25