5. Conclusions

Ferrimagnetism and ferromagnetism share many magnetic properties in common, such as hard and soft magnets, but the conductivity differentiates these two materials. Ferrites are ceramic materials and suitable for the high-frequency operation. The electromagnetic properties of ferrite materials are difficult to understand in that the magnetic susceptibility is a tensor and depends on the saturated magnetization Ms, the internal bias field H0, and the resonance linewidth ΔH. The magnetic susceptibility also depends on the frequency of the microwave ω as well as the polarization of the wave. The first two sessions explain the basic properties.

The complex permittivity ε<sup>r</sup> þ iεi, the saturation magnetization Ms, and the resonance linewidth ΔH are the most important electromagnetic properties of ferrites. How to measure the ferrite's properties are discussed in Section 3. The fullwave simulation is conducted to demonstrate how the phase shifter, circulator, and isolator work, which are shown in Section 4. Although the examples are discussed in many textbooks, Section 4 offers in-depth simulation results for the first time.

At high-power operation, the ferrite devices will be heated. The spin wave linewidth may be taken into account. Besides, the ferrites will become paramagnetism when the temperature exceeded the Curie temperature. These two factors are important for high-power operation, which are not considered in this chapter.
