Compressor Blade Vibration Measurement Using Radio Frequency Amplitude and Frequency Modulation

Abstract Radio Frequency (RF) sensors are a novel, non-contact, low-power measurement technology that offers potential for engine health monitoring. A series of experiments were conducted in a single-stage compressor to study the RF sensor response to blade vibrations. Dual-polarized 18 GHz waveguide antennas were placed over the rotor while synchronous and asynchronous vibrations were induced. A mathematical model based on amplitude and frequency modulation is proposed. The RF signal is amplitude modulated by the blade passage and blade vibrations, and frequency modulated due to Doppler shift from blade passage. The model showed qualitative agreement with the RF data in the frequency domain. The RF data was pre-conditioned based on the mathematical model and used as the input into a simple, multi-layer neural network for regression analysis. The results demonstrated that blade vibration deflection by nodal diameter can be predicted from RF measurements using a simple, artificial neural network based regression algorithm.