Abstract: In this paper, a high-precision liquid level microwave sensor assisted with energy dissipation control is proposed and demonstrated. The sensor achieves a micrometer-level resolution within a measurement range of 0~50 mm. Built on microwave resonators, the sensor comprises an inner conductor, an outer conductor, a resonant cavity, and a resistor. The resonant cavity is constructed of two reflection surfaces, where the first is a fixed point located inside the sensor, and the second is the measured liquid level. When the liquid level changes, the second reflection point changes accordingly, introducing cavity length shift. The liquid level change can be determined by measuring the variation of the resonant cavity shift. Meanwhile, the added resistance not only extends the liquid level measurement range, but also improves the spectral quality and measurement accuracy. Experimental results show that the liquid level sensor reaches micron resolution and a sensitivity of -1.927 2 mm/mm (resonant wavelength change/liquid level) in the range of 0~50 mm. Due to its mechanical robustness, easy fabrication process, low cost and high measuring resolution, the proposed sensor can be applied in fields such as water conservancy and hydropower weir monitoring.

Key words: microwave, resonant cavity, inner and outer conductors, reflection points, liquid level sensor