Mechanical vibrations of railway vehicles were converted to electric power by means of a piezoelectric energy harvester, a rectification circuit, and a storage battery. The power harvested is used to supply one node of a sensor network for the structural monitoring and safety improvement on railway vehicles. The dynamic dimensioning of the piezoelectric generator is presented, for the mechanical and electric viewpoints; the resonance tuning is described and the experimental validation of the performances of the node is provided. The tests were conducted on a scaled railway bogie, which is able to simulate the real working conditions of a train. The efficiency and the duty cycle of the autonomous sensing platform are measured.

The constant spread of commercial trades on railways demand development of alternative diagnostic systems, which are suitable to applications without electric supply and convenient for the industrial development and diffusion, which means low cost, good reliability, and high integrability. Similarly, it is possible to install navigation and traceability systems (for instance, by the use of global positioning systems—GPS—transmitters) to control on demand the travel history of the train and even that of each coach separately. Recent studies demonstrated the possibility to generate directly onboard the electric power needed to the supply of simple diagnostic systems based on low power sensors and integrated wireless transmission modules. The design of this kind of generators is based on the idea of converting the kinetic energy of train vibration to electric energy, through appropriate energy harvesters containing electromechanical transducers dimensioned ad hoc. The goal of this work is to validate the design procedure for energy harvesters addressed to the railway field. The input vibration source of the train has been simulated through numerical modeling of the vehicle and the final harvester prototype has been tested on a scaled roller rig. The innovative configuration of magnetic suspended proof mass is introduced in the design to fit the input vibration spectra of the vehicle. From the coupled study of the harvester generator and the vehicle, the effective output power of the device is predicted by means of a combination of experimental and simulation tests. The generator demonstrated the ability to supply a basic sensing and transceiving node by converting the kinetic energy of a train vibration in normal traveling conditions. The final device package is 150 × 125 × 95 mm, and its output voltage and current are 2.5 V and 50 mA, respectively, when the freight train velocity is 80 km/h. The corresponding output power is almost 100 mW.

This paper proposes a new strategy for detecting material strength loss under mechanical fatigue on the basis of the pull-in voltage of the test device. Gold microbeam specimens are tested for mechanical fatigue using an electrostatically actuated dedicated device. The design of the fatigue device is discussed, providing the analysis of stress distribution inside the specimen. The finite-element method is used to simulate the electromechanical coupling. The fatigue limit is estimated through the ldquostaircaserdquo method, and a Wohler curve is obtained from experiments. The surface topography evolution is monitored by scanning electron microscope images; specimen failure modes and material degradation are discussed, revealing the local yield of the material on the upper surface of the beam. The type of degradation appears to be in agreement with the established literature as a consequence of fatigue.