Experimental study and application of a self-powered wireless health monitoring system for railway bridges based on piezoelectric energy harvesting

Harvesting the renewable ambient energy to power the wireless sensor nodes (WSNs) is a promising technology for realizing long-term health monitoring of engineering structures. In this work, a self-powered wireless health monitoring system (SP-WHMS) is introduced and successfully applied to the railway bridge. In the SP-WHMS, multiple vibration-based piezoelectric energy harvesters (VB-PEHs) are mounted on the bridge to convert the train-induced bridge vibration energy into electrical energy, and a storage capacitor is used to store the harvested energy. An energy management circuit (EMC) monitors the voltage across the storage capacitor and outputs astable voltage to the WSN once the capacitor voltage exceeds a threshold. The effectiveness of the SP-WHMS is verified through a field test, where two WSNs are used to monitor the settlement of the bridge pier and the strain of the bridge, respectively. The result shows the average activation intervals of the tested WSNs are 59 min and 57 min, respectively. For each activation, both WSNs require about 2.6 J of energy. In addition, some strategies for improving the energy harvesting efficiency of the SP-WHMS are provided, such as (1) Rectify the VB-PEHs before parallel connection; (2) Increase the charging current by increasing the layers or decreasing the thickness of the piezoelectric patch in the stack. This work provides a practical case and technical guidance for the application of the SP-WHMS on railway bridges.