High-precision permittivity measurements of liquids are essential for specifying the specific absorption rate (SAR) of radio frequency power into human tissue. At VSL, a commercial unit is used for these measurements, but for reaching a low uncertainty some inherent disadvantages need to be overcome. In this paper, a multi-step approach is proposed using a combination of curve fitting, nonlinear progressive technique and an improved transmission line model. This approach is applicable even without a priori knowledge of the liquid properties. Using this approach, the applicable frequency range of the commercial unit is successfully extended from 200MHz-3GHz to at least 100MHz-4GHz, and the accuracy is improved from 2 percent to 0.2 percent - 0.3 percent.
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