Property Measurement Errors Based on Application of an Estimation Equation Using the Coaxial Probe Method

Abstract

EM (electromagnetic) analysis was applied to calculate dielectric constants estimation errors caused by non-consideration of radiation resistance in an equivalent circuit. This supported the derivation of an equation for the estimation of such errors with dielectric measurement for an unknown material compared to the S 11 value with a reference material in contact with a coaxial probe. Frequencies of 0.50, 1.5 and 3.0 GHz were applied for calculation. Specifically: 1. The dielectric constants of various liquids were initially set on the basis of reference and unknown materials previously examined by the author. 2. S 11 values were calculated via the MoM (method of moments) approach based on transverse EM analysis using a model with the assumption of actual measurement using a coaxial probe and various liquids in contact with the jig. 3. The dielectric constant and S 11 values were substituted into the equation used to estimate the dielectric properties of an unknown material as compared with a reference material. 4. The dielectric constant difference between values estimated using this equation and the values set for S 11 computation was calculated. 5. Complex permittivity errors caused by differences in the physical structure of the equivalent circuit in derivation of the estimation equation were determined under various conditions of frequency and unknown materials. The results showed that the complex permittivity of methanol estimated using the equation with pure water as the reference material, by way of example, became smaller than the true value as the frequency increased. The estimation error was also found to increase with frequency, showing values between 4.012 and 11.456% at 3.0 GHz.