A Study on Broadband Measurement of Complex Permittivity for Liquids Using the Open-Ended Coaxial Line Reflection Method

摘要

Various studies of specific absorption rates (SARs) have been carried out with liquid phantoms representing human body tissue to comply with safety standards. As a faithful representation of human body tissue is needed to establish an accurate SAR for measurement, knowledge regarding the precise measurement of sample materials with high permittivity and high loss is very important. In this study, the complex permittivity of a liquid phantom material was measured using the open-ended coaxial line reflection method. The effectiveness of the proposed approach for measuring a liquid phantom with high permittivity and high loss was also confirmed by comparing the measurement results with those obtained using the TM_(010) circular cavity resonator method and the open-ended cut-off circular waveguide reflection method. As a result, for example, measurement values obtained using each of the three different methods varied within 1.0 for the real part and within 1.5 for the imaginary part when tap water was inserted in the 2.5 GHz frequency band. Meanwhile, it was also confirmed that the variation in complex permittivity values exceeded 2.0 for the real part with a center conductor length of L = 0 mm at a low frequency of around 100 MHz when tap water was inserted. However, the variation in measurement values was reduced to within 1.0 by, for example, extending the length of the center conductor.