Lokesh A. Gupta

Wireless temperature microsensors integrated on bearings for health monitoring applications

This paper reports the performance of a wireless MEMS bimorph temperature sensor integrated on a bearing for component health monitoring applications. The sensor consists of a robust array of bimorphs consisting of gold and thermally-grown oxide operable to at least 300°C. Fabrication details are included, as well as the hermetic packaging information. Speed of actuation results from a high-speed camera is included showing the actuation time is less than 600 µs. Reliability testing of the bimorph array up to 400 million thermal cycles is also shown, after which the bimorphs still yield consistent behavior. Finally, dynamic testing is performed showing actual bearing temperature values at different speeds on a real-world helicopter bearing

Wireless Temperature Sensor Operating in Complete Metallic Environment Using Permanent Magnets

This paper presents the first wireless temperature sensor operating in a complete metallic environment using permanent rare-earth magnets. The sensor is based on change in magnetic field strength with temperature, which is detected using commercially available Hall Effect sensors. Temperature of a hot plate at a distance of 19 mm in air and through a 9.5-mm-thick nonmagnetic austenitic stainless steel plate is successfully detected from 5 °C to 80 °C as a proof-of-concept demonstration. The curve fit values show excellent response with R2 value greater than 98% for both the cases.

Remotely powered wireless strain telemeter

This paper presents a wirelessly powered strain telemeter for mechanical health monitoring applications. The telemter is integrated with a rectenna tuned at 2.4 GHz. The rectenna is comprised by a resonant printed dipole antenna, microstrip transmission line filters and commercially available high-frequency diodes. The experimental results demonstrate that the rectenna is able to deliver 8 mW of DC power to the wireless telemeter when illuminated by a 10-W Yagi transmitter with a gain of 15 dB placed at a distance of over 2.5 m.

Wireless temperature and vibration sensor for real-time bearing condition monitoring

This article presents a unique sensor capable of simultaneously measuring the bearing cage temperature and vibration signature using inductive coupling. The temperature sensing is based on thermal-induced shift in resonant frequency of an inductive coil and a temperature-sensitive capacitor mounted on a bearing cage. This shift is detected remotely by placing an interrogator coil in close proximity to the sensor coil and the bearing cage. Bearing cage vibrations, result in change in the coupling factor between the sensor and interrogator coils along the bearings axial direction. This leads to amplitude modulation of excitation frequency by a signal proportional to bearing cage vibration. In this article the authors present bearing cage temperature measurements from 20°C to 90°C for Timken MMC9112K at 1280 rpm to 3250 rpm. The corresponding vibration frequencies at each speed are measured and compared with theoretical values calculated using standard bearing frequency equations. A good agreement between measurement and theory is observed for various vibration components such as ball spin, fundamental train and ball pass-outer race frequencies with average variation of 2.8%.

Application of ball bearing cage RF temperature sensor in high speed turbocharger

The application of a radio frequency ball bearing cage temperature telemeter in a high speed turbocharger is demonstrated. A temperature dependent LC tank circuit is adhered to the bearing cage and wirelessly monitored using an axially displaced stationary receiver coil. The cage sensor is installed in a turbocharger rotor-bearing system and is able to withstand the harsh conditions of being tested at speeds up to 77,000 r/min. The sensor tracks the transient temperature response within the bearing due to mechanical losses and external heating. This sensor concept may be utilized to monitor bearing performance at high speeds, detect loss of lubricant and impending failure, and implement predictive analytics using measured data.

Multi-point bearing cage wireless temperature sensor

In this article, a multi-point bearing cage wireless temperature sensor for mechanical health monitoring applications is presented for the first time. Two insulated inductive coils and two temperature sensitive capacitors are attached along the circumference of the cage. The resonant frequencies of these LC circuits shift linearly with temperature as sensed by the capacitors. An interrogator coil placed axially at 3-mm distance is then able to detect the individual resonant frequencies corresponding to a localized temperature sensed by the individual capacitors on the cage. This allows the user to have a more detailed knowledge of the temperature profile along the bearing circumference and allows the detection of localized faults caused by defects such as shaft imbalance, misalignment, and spalls on individual balls.