Characterization of a portable and low cost system for practical dielectric spectroscopy

A portable setup for measurements of complex permittivity based on ad-hoc arrangements is proposed and its performance compared to the ones of a bench system. The measurement setup consists of a portable spectrum analyzer (used as vector network analyzer, VNA) connected to an open-end coaxial cable for S-11 acquisition. Scattering parameters were processed using custom Labview software specifically developed to obtain complex permittivity of liquids and soft materials in real-time. A suitable calibration procedure, based on a differential principle, enables accurate measurements. Raw results showed that the portable setup provides noisier traces if compared to the performance of a high precision laboratory VNA. However, accurate permittivity data have been achieved introducing filtering to eliminate signal oscillations and spurious noise without loss of information associated to liquid dielectric relaxations. This procedure, applied to standard liquids (ethanol, ethanediol, 2-propanol) showed good performance in terms of bias and precision. Water solutions, used for cell culturing purposes, both conductive and non-conductive, were also successfully measured. The obtained results are a proof of concept that the proposed procedure is a reliable technique to perform fast, low-cost and on site permittivity measurements, useful for diagnostic or therapeutic applications.