# Investigation of Energy Harvesting Capabilities of Metglas 2605 SA1
## 3 Energy Harvesting Application
### Experiment with Metglas 2605 SA1  
To experimentally demonstrate the energy harvesting applicability of Metglas 2605 SA1 and evaluate the considered model's relevance, the Ericsson-like cycle described in Figure 8 was experimentally implemented. Magnetic excitation consisting of several cycles of square signals (Figure 9a) was considered. The first period was used for assessing magnetic hysteresis curves and estimating the hysteresis losses without stress. The second and third periods actually implemented the Ericsson cycle, as compressive stress was applied to the sample at the maximum magnetic field (transition from state B to state C in Figure 8), and removed when the magnetic field reached a minimum value (transition from state D to state A). Magnetic hysteresis effect causing energy losses is an important factor in energy calculations. In the case of Metglas 2605 SA1, the magnetic hysteresis curves performed a counterclockwise cycle as shown in Figure 9b, denoting hysteresis losses in one unipolar cycle, while the Ericsson cycle formed a clockwise cycle confirming the actual energy conversion process. The small area of the BH curves confirmed that the hysteresis effect could be neglected in the calculation of the harvested energy. The associated area corresponded to the harvestable energy in the latter case. The estimated energy density in one unipolar cycle of Metglas 2605 SA1 is presented in Figure 10. This figure confirms that the material has a larger energy density under compressive stress. Figure 8: Ericsson cycles of the energy harvesting process under tensile and compressive stress and converted energy density. The developed model was also used to predict the converted energy of the Ericsson cycle. The estimated harvestable energy under different conditions is presented in Figure 11. Furthermore, Table 3 shows the converted energy densities calculated from the experimental Ericsson cycle and the proposed model. The difference between data and model is usually attributed to hysteresis losses, which might not be related to the used model (as the one considered in this work). However, the previous characterization of the Metglas sample revealed a very small hysteresis effect (see Section 2.2), yielding the conclusion that hysteresis does not play a significant role in the difference between predicted and measured energy density values. Instead, it has to be noted that the model of BH curves under different stress levels is fitted with the full bipolar magnetic hysteresis loops. However, the magnetic field is always positive during the measurement of Ericsson cycles. This therefore leads to a partial demagnetization and a smaller magnetic loss than a full cycle. The losses calculated from the bipolar magnetic hysteresis curves under pressure and tensile stress are all in the order of magnitude of 0.1 mJ/cm\({}^{3}\). Therefore, in the case of \(-\)6 MPa, even the predicted result of the energy density is in the same order of magnitude. Figure 10: Harvestable energy density estimated from experimental BH curves of Metglas 2605 SA1 in a unipolar cycle in the range of 0–4 kA/m. Figure 9: (**a**) Experimental magnetic hysteresis curves and energy harvesting cycle of one unipolar cycle (**b**) Comparison between BH curves and Ericsson cycle. magnitude as the magnetic losses, and the harvested energy is still positive. In addition, results indicate that the energy density predicted from the model is in the same order of magnitude as experimental measurements for both the compressive stress and tensile stress. Consequently, it is confirmed that the model could predict correctly the energy harvesting performance. In numerous reported configurations, the dynamic response around a bias field is considered, and the maximum dynamic excitations of different materials are achieved in a different magnetic field. The energy harvesting is based on a bias magnetic field and small variations around it due to reluctance variations resulting from mechanical stress application or vibrations.