Carbon-fiber/polymer-matrix composites as capacitors

A continuous carbon-fiber/epoxy-matrix composite with a paper interlayer (0.04 mm thick after composite fabrication) was found to exhibit a capacitance of 1.2 μF/m2 at 2 MHz, in contrast to a value of 0.21 μF/m2 for epoxy-impregnated paper (0.10 mm thick). The high capacitance is partly a consequence of the large area of the surface of a fiber layer sandwiching the paper interlayer. This area is twice the flat area. Without a paper interlayer, the composite failed to serve as a capacitor, because of the conductivity in the through-thickness direction.