A Simplified Measurement Procedure for Dielectric Measurement of Liquids, Including Calibration via the Cut-Off Circular Waveguide Reflection Method

In this study, a simplified procedure for extension of the measurable range for the low-frequency band was investigated for dielectric evaluation of liquids using the cut-off circular waveguide reflection method. An RF LCR meter was used to evaluate input impedance, and a formula involving comparison with short/open conditions and one reference material (referred to here as SOM) as standard was used in determination of complex permittivity for an unknown material. Subsequent research was then conducted to determine the validity of permittivity evaluation based on the proposed procedure. Specifically, S-11 at the tip of the jig of the coaxial-feed-type cut-off circular waveguide with an N connector was calibrated using the SOM standard based on comparison with a theoretical value calculated using electromagnetic analysis for the analytical model in the frequency band of 10 - 1,000 MHz. The complex permittivity of various liquids was also determined by substituting the measured S-11 value after SOM calibration into a formula involving comparison with SOM termination at frequencies of 20, 50 and 1,000 MHz. Complex Permittivity determined via this procedure was compared with that established by substituting measured S-11 values after calibration with short/open and loaded conditions (referred to here as SOL) directly into a formula involving comparison with SOM termination without moving the reference plane. The results showed good agreement between the two procedures at all frequencies. Accordingly, the effectiveness of the formula for analysis of unknown substances involving comparison with SOM termination including the S-11 calibration procedure was confirmed. The results for frequency characteristics of permittivity in various liquids at 10 - 1,000 MHz showed the feasibility of the proposed simplified dielectric evaluation method including SOM calibration in the low frequency band.