Portable System for Practical Permittivity Measurements Improved by Homomorphic Deconvolution

This paper presents a versatile low-cost procedure for complex permittivity measurements of liquids from 400 MHz to 5 GHz. Our procedure uses handheld instrumentation and custom software for data acquisition and postprocessing. The purpose is to replace the benchtop vector network analyzer (VNA) generally used in such applications with a portable and cheaper handheld spectrum analyzer used in the VNA mode. Postprocessing software based on homomorphic deconvolution is used to remove possible inaccuracies in the permittivity spectra coming from the reduced performance of the handheld VNA with respect to benchtop models. Our measurements are evaluated by comparison with those of the National Physical Laboratory (NPL). The results of the real and imaginary parts of the permittivity spectra of two well characterized organic compounds, ethanediol and 2-propanol, are in very good agreement with the NPL reference standards, showing a relative root-mean-square error (RRMSE) always less than 5%. Low values of the RRMSE, together with an expanded uncertainty less than 3%, ensure that our permittivity measurements are repeatable and accurate. Thanks to its versatility, portability, and at least half of the cost of commercial models, our system is suitable for on-site measurements in different applications, including food quality monitoring and control of medical treatments and biological procedures.