Design of Non-contact Microwave Level Measurement System for Corrosive Radioactive Liquid at High Temperature Environment

Abstract

This paper presents the design and preliminary validation of a non-contact microwave level measurement system tailored for corrosive and radioactive liquids in high-temperature environments, such as lead–bismuth eutectic at 800°C. The primary objective was to develop a safe, reliable, and long-life alternative to conventional contact-type sensors, which are prone to rapid degradation under such extreme conditions. A 24 GHz frequency-modulated continuous-wave (FMCW) radar configuration was selected due to its superior short-range accuracy. The system incorporates several novel design features: a conical horn antenna optimized for narrow beamwidth, a quartz-based microwave window, and a stainless-steel S-shaped circular waveguide that simultaneously enables efficient microwave propagation and effective gamma radiation shielding. Signal processing combines fast Fourier transform (FFT) and chirp Z-transform (CZT) algorithms to enhance intermediate frequency estimation, thereby improving range resolution. Experimental validation on a laboratory test bench demonstrated input matching of antenna better than 15 dB and confirmed the feasibility of centimeter-level resolution. FFT-based processing showed limited sensitivity to small distance variations, whereas the CZT approach successfully detected 1 cm positional changes, though with non-linear response linked to oscillator control voltage non-linearity. Future work will focus on correcting non-linearities and deploying the system in harsh environments.