Piezoelectric polymeric nanowires for energy harvesting devices in wireless sensor networks of smart bridges

City infrastructures are essential for the sustainable growth as well as for the economic, social and territorial cohesion. Health, resilience and proper operation of city infrastructures are essential premises to ensure the long-term public safety as well as to ensure economic growth, productivity and environmental sustainability. In this perspective, the sensing system is the heart of all smart city infrastructures because it allows the monitoring of the structures and enables their intelligent adaptation to changing conditions. Moreover, the data collected from several city infrastructures can be elaborated in order to estimate the resilience or the residual fragility after extreme events at different spatial scales (i.e., either for the single city infrastructure or a network of city infrastructures). Realizing the importance of installing large arrays of sensors to achieve these goals, the inherent scalability, flexibility and minimum interference with the construction make wireless technologies an appealing solution for smart city infrastructures. With the deployment of large wireless networks in smart cities, however, replacing the batteries in all devices becomes a problematic task. Conversely, harvesting the energy from alternative sources in the surrounding environment would be greatly beneficial. Examples of these alternative energy sources include thermal, light (solar), wind, mechanical (vibration). Amongst them, harnessing energy from ambient vibrations is probably the most attractive approach for smart bridges, but its feasibility strongly depends on the use of low power technologies as well as on the capability of generating as much energy as possible. Within this framework, the present contribution considers a new class of piezoelectric textiles to scavenge the energy required for the wireless structural monitoring of smart bridges from ambient vibrations. Specifically, the devised energy harvester exploits a power generator built using arrays of electrospun piezoelectric nanofibers. Numerical analyses have been performed using experimental data in order to demonstrate that it provides higher energy levels than a standard scavenger employing a conventional piezoelectric film. Finally, the output energy levels have been discussed to assess the potentialities of such energy harvesting strategy for wireless structural health monitoring of smart bridges.