A study on measurement of complex permittivity in liquids based on a combination of the open-ended cut-off waveguide reflection method and comparison of expressions with reference material

In the study reported here, a method of broadband measurement to determine the complex permittivity of liquids based on comparison to a reference material was applied to the reflection method with an open-ended cut-off waveguide as a coaxial feed. In this case, the measurement procedure was dynamically simplified, and measurement precision was guaranteed by replacing measurements with values calculated using the mode-matching method. In addition, the complex permittivity of the reference material was calculated using the Debye relaxation equation when the input impedance was calculated using the mode-matching method. This technological combination represents a major improvement in measurement precision and creates an extremely simple procedure. The effectiveness of the improved method was verified by actual measurement of the frequency characteristics of complex permittivity in certain liquid types at frequencies ranging from 500 to 1,000 MHz.