Sensor-integrating gas foil bearings: real-time monitoring of temperature, lift-off state, and instantaneous angular speed

Abstract Gas foil bearings (GFBs) are widely used in high-speed rotating machinery due to their low maintenance requirements, high-speed capabilities, and contamination-free operation. However, challenges such as wear, vibrational, and thermal instabilities require advanced condition monitoring techniques. The present work introduces a sensor-integrating gas foil bearing (SiGFB) designed for real-time monitoring of key state variables, including instantaneous angular speed (IAS), temperature distribution, and friction state. The SiGFB fully incorporates all required electronics: embedded thermocouples, an accelerometer, a microphone, and an acoustic emission sensor, enabling in-situ measurement without compromising its functionality as a bearing. The measurement of acoustic emission in the bearing via a piezoelectric element on the top foil and the measurement of the sound in the gas are also new contributions. The proposed system is evaluated through experimental validation, demonstrating its ability to accurately determine the IAS to within 1 Hz, sound, and current lift-off state. While the temperature measurement is still subject to quantitative uncertainties, the results confirm that the SiGFB provides usable measurement data, laying the groundwork for future autonomous and wireless condition monitoring solutions in high-speed rotating machinery.