Frequency Shift Baseline Removal for Improved Flow Measurement using Microwave Cavity Resonator

The flow velocity of the coolant in the high-temperature fluid advanced reactor is an important variable for reactor performance monitoring. However, due to the harsh environment inside the nuclear reactors, there are limited options for measuring flow velocities. A microwave resonant cavity-based flow sensor is a novel sensing approach that measures flow velocity through deflection of the structure due to dynamic pressure. Hollow metallic resonator offers resilience to high temperature and radiation. A key technical challenge of the microwave resonant cavity-based flow sensor is the measurement of the resonant frequency shift due to membrane displacement. This research proposes a baseline removal technique that overcomes the large baseline in the forward gain of the S
21
parameter frequency sweep introduced by nonideal components in the microwave system. The signal processing technique allows locating the microwave resonances, thus enabling the enhanced measurement of flow velocities. Several smoothing filters that can remove the baseline, while preserving the resonant frequency are implemented and evaluated. This approach is then realized in the LabVIEW for an actual experiment. The experimental results show the measured frequency shifts match with theory, which indicates the proposed method provides a reliable way to measure the frequency shift for flow measurement.