Ferrites for permeability tuning in the VHF region using the above resonance mode

The above resonance mode for obtaining and varying permeability in the VHF region is described. In this mode the bias field and RF magnetic field are orthogonal, and the ferrite core is always saturated or close to saturation. The bias field is larger than that required for ferromagnetic resonance. Eleven ferrites were evaluated with respect to operation in this mode. Tests included the determination of
Q
as a function of permeability, the temperature coefficient of permeability, and the effects of high RF flux densities on the
Q
of the ferrite. Application in the above resonance mode results in considerably higher permeability and
Q
values than the conventional approach at frequencies above 50 MHz. In addition, the RF power handling capabilities are substantially increased.