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

Abstract

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%.

Complex Permittivity Detection of Organic Chemicals and Mixtures Using a 0.5–3-GHz Miniaturized Spectroscopy System

“…As in [21], [22], and [24], the effect of the complex permittivity of a MUT on an interdigitated capacitor appears as the change in the frequency-dependent model of the sensing element, as shown in Fig. 1(a).…”

“…This method requires relatively large sensing structures if used for sensing frequencies below 10 GHz. In [21] and [22], capacitance variation of a sensing element exposed to the MUT and placed as a part of a wideband true time-delay element is used to find the real part solely, but in a wider frequency range. This system can be considered miniaturized and self-sustained if a wideband frequency synthesizer is mounted on board.…”

“…The magnitude and phase of the voltage variations are detected using on-board surface-mount quadrature down-conversion mixers associated with sensor calibration and unique detection algorithms. Similar to [21] and [22], this system tends to be self-sustained if the frequency sweep generator is implemented on the same board. However, compared to [14], [21], and [22], it has the advantage of detecting both real and imaginary parts of the complex permittivity simultaneously within a wide frequency range.…”

“…Similar to [21] and [22], this system tends to be self-sustained if the frequency sweep generator is implemented on the same board. However, compared to [14], [21], and [22], it has the advantage of detecting both real and imaginary parts of the complex permittivity simultaneously within a wide frequency range. Moreover, due to the use of vertical tubes instead of microfluidics, the volume needed for liquid characterization is 150 L, which can be considerably reduced with the use of microfluidics.…”

A 24 GHz dielectric sensor based on distributed architecture

“…Several techniques for dielectric sensing in biological and medical applications have been proposed and investigated. In recent years, microwave and radio frequency dielectric sensors have been demonstrated in several one-port and two-port sensing applications using different sensing and read-out approaches like de-embedding S-parameters [5], measuring the phase of transmission co-efficients [6], measuring the phase of reflection co-efficients [7], using dielectric probes [8], sensing resonator based oscillators, synthesizers and PLLs [9]- [10]. The proposed dielectric spectroscopy system is aimed to sense, characterize and differentiate bio-materials.…”