Energy harvesting based on magnetoelastic materials

In the last decades, many researches have been focused on sensor networks, especially with the help of new technologies like GPS, GSM and, in general, wireless communications. To make these systems autonomous a power supply is needed, but batteries require at least an annual maintenance and the periodic replacement makes such systems less autonomous. Energy harvesters, having a lifespan of 10 or 20 years, are an interesting alternative to batteries because they do not need human intervention and are environmentally friendly. Different types of energy harvesters have been proposed such as piezoelectric, electrodynamic harvesters and so on. This work focuses on electromagnetic harvesters, based on giant magnetostrictive materials and electrical steels. The goal of this project was the study and the analysis of the performance and, when possible, the efficiency of three types of energy harvesters. Moreover, a deep investigation of the parameters that can influence the performance of such devices is in the thesis purpose. The first setup, which has been designed in the framework of the European project, EMRP ENG02 "Metrology for energy harvesting", was suitable for investigation on direct force harvester based on bulk materials. A deep investigation was done on Terfenol-D, and the parameters influencing the performance have been highlighted. A numerical modeling approach has been also utilized to deep the analysis of the device. In particular, the role of the mechanical preload and excitation amplitude and their interaction have been explained. A maximum power of 82 mW has been generated, corresponding to a specific power of 5.2 mW/cm3. The second setup was useful for low energy systems; in this setup the core material was an amorphous alloy. The test rig has been designed in order to have a simple structure, avoiding the use of high permeability materials. A plastoferrite has been utilized as permanent magnet, and a shielding technique has been implemented in order to have uniform magnetization on the sample. This setup highlighted the capability of amorphous materials in low vibration energy harvesting. Also in this case, a numerical modeling approach has been used for comparison and validation purposes. Finally, a third setup based on a cantilever structure has been specifically design and realized during this project. In this device, Fe-Si and Fe-Co have been used as core materials. The setup is able to generate power of the order of 5.2 mW in the power frequency range. Fe-Co reveals to be superior with respect to Fe-Si. The study highlighted the importance of the magnetic bias pattern. To show this, four different magnets configurations have been considered around the device. A simplified 2D FEM approach has been successfully used to explain the device behavior. In conclusion, this work has provided a deep insight on the behavior of three types of electromagnetic harvesters.