The microwave measurement of the conductivity of a small fiber with an open cavity

An original method of determining the electric conductivity of spheroidal inclusions of the order of a few microns is described. The measurements are made in an open cavity at microwave frequencies. In order to produce sufficient perturbations inside the cavity, a composite made up of dielectric and conductive media had to be designed. By combining the model of the dielectric properties of the composite with the model of the operating conditions of the open cavity, we show that it is possible to determine the conductivity of a unique inclusion by using an analytical expression. Measurements are presented which concern a type of carbon fiber with several micrometers diameter and a few millimeters length. The results obtained for different samples validate the method; they can be used as a reference in the microwave range.