Applicability of the microwave cavity perturbation method for conductivity measurements on carbon fibers

A microwave cavity perturbation technique has been used to measure the resistance per unit length of carbon fibers. These materials and other test materials used in these measurements such as copper, evenohm, and tungsten, have much higher conductivities than polymeric materials which have been investigated previously with this technique. The 1500–5000-Ω resistance of the carbon fibers lay in the region near the limit of applicability of the perturbation technique, thereby affording a means of investigating this limit. The condition Rs/Zc>2 where Rs is the sample resistance and Zc is the characteristic impedance of the cavity, appears to be a useful condition for estimating the limit of applicability.