Microwave Power Absorption Characteristics of Ferrites

The microwave power absorption characteristics of five ferrites, BaFe 12 O 19 , SrFe 12 O 19 , CuFe 2 O 4 , CuZnFe 4 O 4 and NiZnFe 4 O 4 , have been studied by determining the average power absorption patterns of the ferrite slabs using the derived power equations with consideration of both microwave dielectric and magnetic losses. It is shown that microwave power dissipates rapidly in the ferrites with a thickness of microwave penetration depth Dp . The magnetic loss QH , av is much larger than the dielectric loss QE ,av for these ferrites in the slab thickness range of 0-3 Dp . The ratio of QH ,av to QE ,av remains above 1.5 as the slab thickness varies from Dp /4 to 3 Dp although the difference between losses decreases with increasing thickness. The power absorption patterns of these ferrites also demonstrate that microwave resonance caused by magnetic loss occurs within the materials having a thickness less than a half-wavelength in the medium λ m /2 . It is anticipated that microwave magnetic field heating of ferrites with a thickness smaller than λ m /2 can be accelerated by magnetic loss resonance which leads to a significant increase in the power absorption in these ferrites.