New Sensor Technology for Level Measurement of Dielectric Liquids Such as Cryogenic Liquids

This paper introduces a novel technique for measuring liquid levels in harsh environments, including cryogenic settings with low-permittivity dielectric liquids. The approach employs a coplanar waveguide sensor that transmits a low-power microwave signal. Unlike traditional radar techniques that detect the liquid surface, this sensor measures the shifts in the signal frequency, directly correlating to the liquid level, providing more precise measurements. Two prototypes were developed using flame retardant woven glass-reinforced epoxy resin and polytetrafluoroethylene substrates and tested on cyclohexane and liquid nitrogen. The results showed a frequency variation of around 30 MHz for a 220 mm level change in liquid nitrogen. The first model demonstrated 1.29 MHz/cm sensitivity for cyclohexane and 1 MHz/cm for liquid nitrogen. The second prototype exhibited sensitivity of 0.6 MHz/cm and 0.8 MHz/cm respectively.