Single carbon fiber as inductor and capacitor

Carbon fibers are important for lightweight structures. The inductance and polarization are aspects of the electrical behavior that are to be distinguished from the well-studied electrical conductivity. The inductance and polarization behavior of carbon fibers are potentially valuable for rendering new functionalities to carbon fiber structures. The first report of the inductance and polarization behavior of a single fiber (whether carbon or not) is provided here. The fiber is carbon fiber, being unpoled, straight and continuous (7.0-μm diameter), as studied at 10 kHz. Prior work addressed the corresponding 12,000-fiber tow. The relative permittivity (8 × 10⁷) is much above 1.2 × 10⁴ for the tow, due to the high single-fiber resistance compared to the tow resistance and the applicable model of resistors in parallel for a tow. The single-fiber inductance per unit length is 2.3 mH/m, compared to 2.6 µH/m for the tow. The single-fiber inductance is higher than that calculated based on the dimensions by a factor of up to 1100. The tow does not comprise 12,000 capacitors/inductors in parallel, but approaches to a degree a single capacitor/inductor, due to the fiber-fiber contacts within the tow. The high single-fiber inductance is attributed to the microstructure (nanostructure) involving carbon-layer wrinkling and crumpling and interlayer contacts. Short circuiting decreases both inductance and capacitance due to discharge from the inherently charged state, and subsequent open circuiting restores the inductance and capacitance (i.e., self-charge, which is novel).