Measurement of Tip Clearance Based on Microwave Resonance Method

This study provides a tip clearance measurement system based on open coaxial cavity. According to the principle that the distance between the blade and the resonant cavity varies its resonant frequency changes, the single frequency of VNA is extracted to measure the S21 time-domain signal of the rotating blade. The tip clearance is measured by the attenuation of the |S21| (the magnitude of transmission coefficient). At the same time, the uniformity of the blade spacing can be tested by the period of a single peak curve. The system consists of an open coaxial resonator, a drive motor, a computer, a vector network analyzer and a simulated engine blade. According to the measured results, the system can be used to measure tip clearance and blade spacing uniformity according to the change in amplitude of the resonance frequency and the periodicity of the test curve, respectively.