Vapor-Phase Polymerization of Polypyrrole on Carbon Cloth: Simultaneous Tuning of Surface Resistance and Dielectric Permittivity for High-Performance Flexible RF Antenna Electrodes.

Carbon cloth is a lightweight and mechanically robust fibrous substrate with strong potential for value-added flexible electronic applications. In this study, carbon cloth/polypyrrole (CC/PPy) composites were fabricated via vapor-phase polymerization (VPP) and evaluated as radiating electrodes for flexible monopole patch RF antennas. By varying the polymerization time, the surface resistance and complex permittivity of the CC/PPy composites were systematically tuned, enabling simultaneous optimization of electrical conductivity and dielectric response. Among the prepared samples, the composite polymerized for 20 s exhibited the most balanced properties, with a sheet resistance of 1.86 Ω/sq, a real permittivity (ε') of 5.78, and an imaginary permittivity (ε″) of 0.23. When applied as the antenna electrode, this material delivered a return loss of -34.81 dB, a radiation efficiency of 84.32%, a peak gain of 3.30 dBi, and a peak directivity of 3.91 dBi at 1.74 GHz. In addition, the antenna maintained stable performance after 5000 bending cycles, demonstrating excellent mechanical durability. These results show that simultaneous control of surface resistance and dielectric properties is critical for high-performance flexible RF electrodes and provide a practical surface-functionalization strategy for upgrading carbon-cloth-based fibrous materials into value-added electronic products.