Proc. SPIE. 9803, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2016
KEYWORDS: Transceivers, Digital signal processing, Safety, Capacitors, Sensors, Amplifiers, Control systems, Energy harvesting, Microcontrollers, Sensing systems, Integrated circuits, Motion models, Electromechanical design, Data analysis
The target of the research activity presented in this paper is to design, to realize and to test an autonomous sensor node able to measure the accelerations in correspondence of the axle box of a freight train. The final goal of the sensor is to identify the derailment conditions by observing the variations in the spectra of the box accelerations, around the frequencies associated to the wheel revolution and its multiples.
The sensor node embeds an accelerometer, a microprocessor, a transmission system, a piezoelectric bimorph energy harvester and an integrated circuit for managing the power distribution to each component of the node.
In particular, a mechanical filter to be applied to the node was specifically designed to increment the energy recovered by the harvester and to filter out the high frequency components of the axle-box acceleration, allowing the use of a more sensitive accelerometer. The harvesting system was setup by means of laboratory tests carried out with an electromechanical shaker and the sensor node was finally tested through field tests on freight trains.
The work presented aims at modeling, designing and implementing an energy harvesting system capable of generating electricity from environmental vibrations. Subject of the analysis is a piezoelectric bimorph; this particular transducer, composed of two layers of piezoceramic material, is clamped in a cantilever configuration and is dynamically bent due to vibrations. The resulting deformation ensures enough current to power the electronic circuit of a wireless sensor. An analytical model is adopted, that describes the dynamics of the mechanical system using an electrical duality. In particular the coupling of the variables is represented by an equivalent transformer. The obtainable voltage and power are investigated, focusing on the influence of the electric load on the performance of the conversion process. In addition, to overcome the limitations related to the analytical study, a finite element model is provided, capable of simulating the behavior of the system more accurately. Finally, both models are validated by means of experimental tests, showing the mutual influence between the mechanical and the electrical domain.