Resonant Measurement of Coaxial Probe Based on Tunable Impedance Matching Network

In this work, we first present a tunable impedance matching network (IMN) to produce an outstanding resonance for improving the sensitivity of coaxial probes. A two-port network based on a three-line coupled (TLC) structure along with a tunable phase shifter is designed to realize conjugate matching. The calculated shape factor for characterizing the sharpness of resonance can be up to
$1.4\times 10^{5}$
when deionized (DI) water is loaded. The minimum measurable concentration level of ethanol is 0.005 mole fraction. The conventional probe’s sensitivity is enhanced to be comparable with those achieved by other resonance-based sensing methods. Using calibration liquids, the complex permittivity of a liquid can be extracted.