A 1–8-GHz Miniaturized Spectroscopy System for Permittivity Detection and Mixture Characterization of Organic Chemicals

In this paper, a miniaturized broadband dielectric spectroscopy system is presented for permittivity detection, chemical sensing, and mixture characterization for 1-8-GHz frequency range. A sensing capacitor exposed to the material under test (MUT) is part of a true time-delay (TTD) cell excited by a microwave signal at the sensing frequency of interest. The phase shift of the microwave signal at the output of the TTD cell compared to its input is a measure of the permittivity of MUTs. For wideband and accurate sensing, TTD cells are cascaded in a reconfigurable fashion to increase the detected phase shift, especially at low frequencies. TTD cells are designed to detect permittivities within the range of 1-30 considering nonideal effects, such as electromagnetic coupling between adjacent TTD cells. Calibration using reference liquids is applied to the fabricated sensor and sensor characteristics are extracted. Permittivity detection of organic chemicals is performed in the range of 1-8 GHz with an error less than 2%. The measured permittivities in the 1-8-GHz range are used to estimate the sub-1-GHz permittivities of MUTs using extrapolation. The sensing system is also used for mixture characterization to find the mixing ratios in binary mixtures with an accuracy of 1%.