# Investigation of Energy Harvesting Capabilities of Metglas 2605 SA1
## 1 Introduction
Terfenol-D and Galfenol are among the materials with the highest energy conversion potential and are commercially available [28]. Terfenol-D is brittle under tension [29] but shows higher admissible compressive stress around 300-880 MPa [30]. Hence, this material is usually used in harvester systems in the shape of rods and mainly works under compressive stress. Galfenol is usually used in unimorph or bimorph cantilevers. However, the costs of Galfenol and Terfenol-D remain too prohibitive for them to be considered realistic constituents of energy harvesters aiming at replacing batteries. Figure 1: Mechanisms during the process of magnetization. (**a**) Sample in initial state, (**b**) Sample in the bias magnetic field, (**c**) Sample in the bias magnetic field under tensile stress. Hence, the question behind the actual and realistic use of magnetostrictive materials as microgenerators lies in finding a cost-effective solution with decent performance. As listed in Table 1, Metglas 2605 SA1 is a soft magnetic material saturating at 500 A/m with a magnetostrictive coefficient of 41 ppm [31], both being much lower than Galfenol and Terfenol-D. However, its much lower price, around 100 EUR/kg [32] compared to 10,000-20,000 EUR/kg for Terfenol-D and 5000-10,000 EUR/kg for Galfenol [33], makes the mass production and cost-effectiveness possible with respect to battery-powered solutions. To be considered as a conversion material, the intrinsic conversion abilities of such materials should be investigated independently of the structure. Therefore, the conversion ability of Metglas 2605 SA1 was measured experimentally and estimated by a biphasic model in this study. Then, Ericsson cycles [34] were assessed on Metglas 2605 SA1 foils under different stresses. The Ericsson cycle, in the case of magnetostrictive energy harvesting process, includes two constant stress paths and two iso-magnetic field paths. The constant stress path can be simplified to the unipolar anhysteretic BH curves in this study as explained in Section 3. Therefore, it can easily be assessed from magnetic characterization and models, while being quite easy to achieve experimentally. The Ericsson cycle can also give a formal and clear basis for comparison purposes in terms of energy conversion abilities, as the area enclosed by the cycle represents the converted energy under a given stress level and magnetic conditions. In this work, the experimentally measured energy densities obtained by performing the Ericsson cycle were compared with the predicted results from a dedicated model to evaluate the energy conversion capabilities of Metglas 2605 SA1. Results confirmed the validity of the model along with the relevance of Metglas for energy harvesting applications. We also give the orders of magnitude of the converted energy density under various excitation magnetic fields and applied mechanical stresses, yielding insights with respect to conventionally used materials. The paper is organized as follows: Section 2 describes the experimental methods for determining the magnetic properties, and Section 3 gives the energy conversion using Ericsson cycles, followed by the conclusions.