Self-Powered Wireless Sensor Node for Smart Railway Axle Box Bearing via a Variable Reluctance Energy Harvesting System

In recent years, the wireless sensor node (WSN) has been used in condition monitoring of the railway axle box bearing to guarantee the safety of the high-speed train. This article proposes a variable reluctance energy harvesting system to power the WSN for extending the service life of the WSN integrated within the smart bearing. The variable reluctance energy harvesting system consists of a variable reluctance energy harvester (VREH) and a power management circuit (PMC), which is able to convert the rotation motion energy into electrical energy efficiently. The key geometrical parameters of the VREH were investigated to obtain the optimal energy harvesting performance by the theoretical modeling and the finite-element analysis. The PMC was designed in the LTspice to achieve the purposes of impedance matching, voltage boosting, rectification, and regulation. The energy harvester was prototyped and used for powering a WSN embedded in the bearing. The powering capability of the energy harvesting system was experimentally verified under the rotation speed range of 400–1200 r/min. Under the rotational speed of 1200 r/min and optimal impedance matching, the generated power of the prototype of harvester reaches 76.05 mW and the charging efficiency of PMC is 52.6%. It is proven that the designed energy harvesting system is capable of powering the WSN for detecting the rotation speed, vibration, strain, and temperature information of the bearing. The proposed smart bearing system has a great potential for improving the reliability of the high-speed train.