# Effect of the Insulating Layer on the Properties of SMC Inductors
## 4 Experimental Results
### Data Presentation and Comments
#### 4.2.2 Rod Inductors' Results and Comments  
The rod inductors were measured using the RLC approach, as shown in Figure 12. Some data had to be post-processed after the measurement, such as the resistance and Q factor. The inductance values are reported in Figure 13. The reference material and soft ferrite had a high value with respect to the proposed SMC materials. The second value is represented by epoxy SMC 1-800, but after 100 kHz drastically reduced. The phospholipid SMC-800, after 100 kHz, maintained the second position up to 1 MHz. Figure 11: The Q factor of the toroid samples of the proposed SMC materials. Figure 10: The imaginary part of the initial magnetic permeability of proposed toroid samples in a frequency range of 40 kHz. Figure 14 shows the resistance values of rod inductors: after soft ferrites, the minor losses are represented by the commercial product; instead, epoxy SMC 1-800 showed the most significant losses concerning all other considered samples. The corrected quality factor trends over frequency showed a different peak value and frequency for each material, as shown in Figure 15. The differences were related to the balance between the (static) hysteresis losses and the rise in the dynamic (frequency dependent) losses. Figure 12: RCL measurement setup: detection of the DC resistance value. Figure 13: Inductance values of produced SMC and soft ferrite rod inductors in a frequency range up to 1 MHz. Two materials (nano-ferrite SMC 1-800 and epoxy SMC 2-800) reported inductance values lower than the commercial one, even at the lowest frequencies. Epoxy SMC 1-800, having the best initial permeability, also showed the highest inductance value at low frequencies (100 Hz to 100 kHz). The 50 Hz data had to be excluded from the analyses for all samples since the too-low signal and the interference with the grid frequency did not allow a precise and repeatable reading. The commercial material reported the best (lowest) resistance values, with a maximum quality factor twice the value of epoxy SMC 1-800, as reported in Figure 16. The proposed SMC inductors covered the different frequency ranges. Considering a Q factor value of 100 as the reference threshold, epoxy SMC 1-800 had a higher resistance values. The results of the proposed SMC inductors were consistent with the results of the proposed SMC inductors. Figure 14: Resistance values of produced SMC and soft ferrite rod inductors in a frequency range up to 1 MHz. Figure 15: The Q factor of the rod samples of proposed SMC materials compared to soft ferrite. valuable interval from 500 Hz to 14 kHz. Nano-ferrite SMC 1-800 and epoxy SMC 2-800 resulted in the same frequency range from 2.5 kHz to 26 kHz for the nano-ferrite coating, and 28 kHz for the epoxy SMC with 2 wt.% of the binder. The phospholipid SMC-800 showed a large interval from 400 Hz to 75 kHz. The reference material started from 100 Hz up to 340 kHz. The proposed SMC materials could be adopted up to about 20 kHz, with the sole exception of the commercial one that reached 75 kHz. The RLC measurements, once corrected by subtracting the DC resistance values, could lead to very good quality factor graphs with a clear, smooth, and symmetrical resonance peak. However, the work proved, in addition, that hysteresisraph measurements alone are not suitable to indicate the best inductor core material since they require being read together with RL measurements through a precision bridge. A further analysis, which could lead to an inversion of the ranking, with the three designed materials again on top, could be an RLC measurement with DC current bias added. Unfortunately, the adopted fluke PM6306 had a limit on the injectable DC current (20 mA), so the attempts made by the authors in this direction did not show differences between the samples.