# Effect of the Insulating Layer on the Properties of SMC Inductors
## 4 Experimental Results
### Data Presentation and Comments
#### 4.2.1 Toroid Results and Comments  
The first analysis concerns comparing the typical data obtained using characterization at a low frequency [24]. In fact, the tests were performed up to 1000 Hz. As previously mentioned, the specific iron losses and magnetic induction saturation of the selected materials show better values compared to the materials procured on the market. Such results are reported in Table 1, where the best results show the toroid ring produced with 1 wt.% of the epoxy binder. Similar considerations were implemented for maximum permeability, measured until 20 kHz. Figure 7 shows the maximum permeabilities of the proposed toroid samples: epoxy SMC 1-800 displayed high values but decreased rapidly versus high-frequency values; on the other hand, epoxy SMC 2-800 showed a minor reduction in maximum permeability along the considered frequency interval. Figure 8 provides information on the specific iron losses of produced SMC toroids. The measurement was conducted at 0.1 T because the supply system could not deliver the necessary power to obtain 1 T at a high frequency. On the other hand, tests for inductance applications are usually performed at low magnetic induction. Phosphatized SMC-800 showed higher losses than the other SMC materials, which had energetic behaviors very close to each other. However, epoxy SMC 1-800 has the lowest iron losses, but a possible crossover is possible for a frequency greater than 20 kHz. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & _Frequency (Hz)_ & **Epoxy SMC 1-800** & **Epoxy SMC 2-800** & \begin{tabular}{c} **Nano-Ferrite** \\ **SMC 1-800** \\ \end{tabular} & \
\begin{tabular}{c} **Phosphatized** \\ **SMC-800** \\ \end{tabular} \\ \hline \multirow{4}{*}{
\begin{tabular}{c} **Specific Iron** \\ **losses@1T (W/kg)** \\ \end{tabular} } & _50_ & 8.8 & 10.2 & 9.1 & 17.4 \\  & _200_ & 40.3 & 49.3 & 42.9 & 88.8 \\  & _400_ & 92.4 & 117.6 & 100.9 & 223.5 \\  & _1000_ & 300 & 405 & 340 & 635 \\ \hline \multirow{4}{*}{B @5000 A/m (T)} & _50_ & 1.35 & 1.09 & 1.12 & 0.64 \\  & _200_ & 1.33 & 1.09 & 1.11 & 0.64 \\ \cline{1-1}  & _400_ & 1.32 & 1.09 & 1.11 & 0.63 \\ \cline{1-1}  & _1000_ & 1.32 & 1.06 & 1.10 & 0.62 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The specific iron losses at 1 T and magnetic induction at 5000 A/m for produced toroid rings. Figure 7: The maximum magnetic permeability of proposed toroid samples in a frequency range of 20 kHz. Some materials obtained favorable results for the initial magnetic permeability of the proposed SMC toroid samples, as shown in Figure 9, for the real part of the initial magnetic permeability. For example, epoxy SMC 1-800 showed values around 90, while commercial material was the lowest, exhibiting a good value of about 50. A high initial magnetic permeability is generally required for audio and telecommunication applications or instrument transformers where the magnetizing current is low. Commonly, the imaginary part of initial magnetic permeability is considered null; on the other hand, Figure 10 demonstrates that some materials have considerable values, which turn into losses. The low values are obtained in the case of commercial and high-resin-content materials. From this point of view, the inductor quality factor Q is calculated through Equation (1), and the results are reported in Figure 11. Phosphatized SMC-800 showed the best Q factor at around 7000 Hz. On the other hand, epoxy SMC 2-800 had modest data in the same frequency range. Regarding epoxy SMC 1-800 and nano-ferrite SMC 1-800, the high Q factor was reached at around 100 Hz, suggesting the use of these materials for low-frequency applications. Therefore, an SMC inductor in the toroid shape can operate in frequency  
Figure 8: The specific iron losses at 0.1 T of proposed toroid samples in a frequency range of 20 kHz. Figure 9: The real part of the initial magnetic permeability of proposed toroid samples in a frequency range of 40 kHz. intervals up to 10 kHz.