Energy-harvesting WSNs for structural health monitoring of underground train tunnels

The main goal of this work is to investigate the feasibility of a WSN with energy-harvesting capabilities for structural health monitoring, specifically targeting underground tunnels. To assess the energy availability in a real-life scenario, we instrumented an underground train tunnel in Rome with Telos B motes interfaced with wind micro-turbines, collecting air-flow data for more than a month. The paper analyse the collected data to quantify the energy availability in terms of typical WSN operations, including communication, storage and sensing. In addition, the energy requirements of a typical sensor for underground tunnels SHM was investigated, namely a vibrating wire strain gauge. Strain gauges are used to monitor concrete and steel deformations, which are critical factors to evaluate the stability of a tunnel and its expected shape deformation. Vibrating wire strain gauges consist of a length of steel wire, tensioned between two end-blocks embedded within the structure being studied, such that deformations of the structure will alter the tension of the steel wire. The tension of the wire is determined by using an electromagnet to excite the wire, and then by measuring its resonant frequency of oscillation.