*4.1. Tested Inductors*

Inductors containing cup and toroidal cores made of ferrite material F-867 [44] were used for investigations. On each core, eight turns of copper wire in the enamel of the diameter 1 mm were wound. The examined inductors with cup cores of different dimensions were mounted on the printed circuit board, which was situated vertically during measurements. The inductor with the ring core was also arranged vertically. In Figure 3, the dimensions of the examined inductor cores are shown.

**Figure 3.** Dimensions of the investigated (**a**) cup core and (**b**) toroidal core.

In Figure 4, the examined inductors with cup cores installed on the printed circuit board are shown, and in Figure 5 the examined inductor with the ring core is presented. During measurements ambient temperature was monitored and its value fluctuated between 21.9 ◦C and 23 ◦C. In both the figures, cables mounted to the ferromagnetic core are visible. These cables are indispensable to enable the current flow through the ferromagnetic core while heating this core. In Table 1 values of selected parameters of material F867 are collected, whereas in Table 2, values of geometrical parameters of the considered inductor cores are given. The inductors with the core whose parameters are collected in Table 2 are shown in Figures 4 and 5.

**Figure 4.** Tested inductors containing cup cores of different dimensions.

**Figure 5.** Tested inductors containing toroidal cores.



**Table 2.** Geometrical parameters of the tested inductor cores.

As shown in Table 1, saturation flux density *Bsat* decreases with a temperature increase from 0.6 T to 0.4 T, remanence flux density *BR* does not exceed 0.15 T, coercion force *HC* amounts to 40 A/m, initial permeability μ*i* strongly depend on temperature and increases from 2400 to 3900. Power losses per unit of volume *PV* decrease from 129 mW/cm<sup>3</sup> to 70 mW/cm<sup>3</sup> in the considered changes of temperature. In further part of this paper the considered cup cores will be denoted as: small cup core, medium cup core and big cup core, respectively. In turn, toroidal cores will be denoted as: toroidal core 16, toroidal core 20, toroidal core 30 and toroidal core 40, respectively.

Table 2 shows that the used cores are characterised by different values of such geometrical parameters as: magnetic path length *le*, cross-section area *Ae* and volume *Ve*. For example toroidal core 16 has similar value of *le* parameter to big cup core le parameter and similar value of *Ae* parameter to small cup core *Ae* parameter. Further, the toroidal core 20 has similar value of *le* parameter to big cup core.
