A measuring device for the determination of the electric permittivity of conducting liquids in the frequency range 1-100 MHz

Abstract

A method is described for determination of the electric permittivity of fairly conducting solutions (specific conductivity of the order of magnitude of 1 Omega ^-1 m^-1) in the megahertz region. Use has been made of a commercial measuring bridge (the RX meter type 250-A of Boonton Radio Company) in conjunction with a cell constructed in the laboratory. The balance equations of the bridge have however been revised for this purpose. It is shown empirically that for proper evaluation of the unknown capacitance a correction term has to be introduced which is dependent on the measured conductance and is justified by a theoretical evaluation assuming a non-ideal representation of the bridge's circuit. The coaxial construction of the variable cell permits a description in terms of transmission line theory in so far as the part is considered which contains solution only. The measuring method is applicable at frequencies between 1 MHz and 100 MHz for solutions with specific conductivities smaller than 0.1 Omega ^-1 m^-1 and is limited to frequencies between 5 MHz and 20 MHz for solutions with specific conductivities of approximately 1 Omega ^-1 m^-1.