Energy harvesting for railway IoT applications

• Autor(a) principal: Nunes, Ana Luísa Vicente Ruivo
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/36655
• topic: Vibration energy harvesting; Railway; Low-power; Electromagnetical harvester; Rectification; Inductive sensor; Piezoelectric harvester; Lead-free piezoelectric material

The subject of this dissertation comes from the urgent need of finding alternatives to the conventional way of powering devices: batteries. However, this issue is more significant than it may appear, because the lack of energy and its costs not only affect who plans a simple sensor network for a railway application, but also the entire human population. Therefore, this work focus on how to create energy from vibration that is present all around us. There were two types of harvesters considered: electromagnetic and piezoelectric. Within the electromagnetic harvester, there were three different harvesters built (coil with a moving magnet inside). During a running test, the maximum power achieved was 9 mW, with a coil of 170 turns, 20 cm long with a 2 cm diameter. It was possible to observe that the voltage produced was very low, which made rectification of a signal with these characteristics a challenge. In order to solve this problem two rectifier circuits were considered: bridge and doubler rectifier. The doubler rectifier allowed to achieve the most voltage, an average output voltage of 23 mV for an input signal with peaks of 160 mV . Given that the power produced by the prototypes built were not satisfactory, it is clear that none of them could function as an harvester. However, these harvesters could work properly as a battery-free inductive sensor. The second harvester considered were piezoelectrics. A characterization along frequency of PZT (lead based) and KNN (lead-free) piezoelectric materials was performed. A comparison based on their piezoelectric properties was made, it is clear that PZT piezoelectrics are more efficient than KNN ones, but KNN power production is still promising despite the fact that they have inferior properties. The maximum power achieved for a PZT piezoelectric was 54 nW for a frequency of 500 Hz and for a KNN a power around 4.5 nW was obtained at a frequency of 200 Hz.