# Investigation of Energy Harvesting Capabilities of Metglas 2605 SA1
## 2 Magnetic Behavior
### Experimental Setup  
The variation of the magnetic flux density (\(B\)) when applying an excitation magnetic field (\(H\)) was measured with a dedicated test bench. Measurements under several constant tensile and compressive stresses were performed. The schematic of the setup is shown in Figure 2. The magnetic excitation part was composed of two U-shaped yokes, the considered sample, and two coils. The U-shaped yokes ensured the closing of the magnetic circuit to maximize the magnetic flux density in the sample. The primary coil of 110 turns \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Materials**} & \multirow{2}{*}{**Magnetostriction**} & **Saturation** & **Range of Bias** & **Price** \\  & & **Magnetic Field** & **Excitation** & **1000 EUR/kg** \\ \hline \multirow{3}{*}{Galfenol} & \multirow{3}{*}{400 ppm [35]} & \multirow{3}{*}{20 kA/m} & 3.58 kA/m [36] & \multirow{3}{*}{5–10 [33]} \\ \cline{1-1} \cline{5-5}  & & & 40 kA/m [37] & \\ \hline Terfenol-D & 1100 ppm [38] & 10 kA/m & 24 kA/m [28] & 10–20 [33] \\ \hline Metglas 2605 SA1 & 41 ppm [31] & 0.5 kA/m & \textless{}1 kA/m [39] & 0.1 [32] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characteristics of different magnetostrictive materials used for energy harvesting. was wound on the two yokes separately and equally (55 turns each) and ensured the generation of the magnetic excitation from an electrical input. A sinus excitation voltage was generated by a waveform generator (TEKTRONIX AFG1062) and amplified through an amplifier (YOKOGAWA 7058). To obtain the value of the current in the primary coil (and thus the applied magnetic excitation level), a resistance of 20 \(\Omega\) was connected in series with the coil. A second sensing coil of 500 turns was also wound around the Metglas 2605 SA1 sample to measure the induced magnetic flux density in the material through the coil voltage using an acquisition system (DEWESoft SIRIUSi). From the measured current through the resistance and the voltage across the sensing coil, the magnetic excitation \(H\) and flux density \(B\) could be derived from Equations (1) and (2), where \(N_{P}\) and \(N_{S}\), respectively represent the number of turns of the primary coil and the number of turns of the sensing coil, \(I\) the current through the primary coil, \(l\) the length of the sample, \(S\) the cross-section of the sample, and \(U\) the voltage measured across the sensing coil. \[H=\frac{N_{P}I}{l} \tag{1}\]  
\[B=\frac{1}{N_{S}S}\int Udt \tag{2}\]  
In the case of tensile stress, the complete structure of the tensile setup is depicted in Figure 3. The sample consisted of five layers of 25 \(\upmu\)m thick Metglas 2605 SA1 foil cut with dimensions of 13 mm \(\times\) 60 mm and glued together with acrylic resin leading to a much lower cross-section than that of the yoke (37 mm \(\times\) 13 mm), in order to reduce the magnetic flux leakage. The mechanical stress was applied equally on both sides of the sample through cables. The application of the displacement was carried out using actuators (MISUMI RSDC306) that were controlled by MATLAB simultaneously through a dedicated controller (MISUMI EXRS-C1). This displacement was then converted into tensile stress by the cables. A force sensor (RS Pro 204-2773) was connected with a strain gauge converter (WACHENDORFF Z-SG, Italy) to measure the real time mechanical input. In this study, the magnetic characteristics under tensile stress of 0 MPa, 6 MPa, 18 MPa and 30 MPa (corresponding to 0 N, 10 N, 30 N and 50 N, respectively) were recorded. Figure 3: Setup for the measurement of Metglas 2605 SA1 under tensile stress. Figure 2: Main circuit of the measurement setup. This setup was also used for measuring magnetic hysteresis response curves under compressive stress as depicted in Figure 4. This was achieved through slight modifications of the tensile testbench by adding 3D printed components, springs, and linear guides. The linear guides were added to ensure that the forces on both sides are on the same horizontal line.