Measurement Method for Dielectric Property of Lossy Liquid Using Waveguide Well for SAR Probe Calibration

In this article, we propose a method for estimating liquid dielectric property with a waveguide well (LDP2W method), using the transmission characteristics to evaluate the dielectric property of a tissue-equivalent liquid employed for measuring a specific absorption rate (SAR) in human exposure assessment. To realize the LDP2W method, an SAR probe calibration system was converted to a dielectric property measurement system. To verify the measurement system, the dielectric properties for different types of liquids were estimated by numerical simulation and actual measurement at 1950 and 3500 MHz. The estimation result was within around 4% of a reference value obtained from a theoretical formula or by a coaxial probe method. We also discuss the uncertainty factors in our proposed method. One of the factors is a reflected wave from the liquid surface at low frequencies. It can be removed using a time domain gating technique, which reduces the estimation error in the measurement of pure water at 900 MHz. The other factor was antenna misalignment, which caused a maximum estimation error of around 0.5%.