Measurements of the complex permittivity of highly concentrated aqueous NaCl solutions and ferrofluid employing microwave cylindrical cavities

Few resonance cavities operating on different modes have been used for the accurate multi-frequency determination of the complex permittivity of highly concentrated aqueous NaCl solutions at a frequency range of 2.5 GHz to 24 GHz. It has been shown that the use of the perturbation method would lead to significant measurement uncertainties especially for lossy samples and should be avoided especially for TE0n1 mode cavities. At frequencies that are smaller than 15 GHz the imaginary part of the permittivity of NaCl solutions increases while at frequencies larger than 15 GHz it decreases, with the increasing conductivity of the electrolyte. In the last case the total dielectric losses for the saturated electrolyte are noticeably smaller than for pure water. The complex permittivity and complex permeability of ferrofluid, liquid that exhibits diamagnetic properties at microwave frequencies, were measured by employing two cylindrical cavities operating on complementary modes. (paper)