FERRITES

The eddy current losses in ferromagnetic materials are inversely proportional to the resistivity. Hence eddy current losses can be minimized by use of magnetic materials of high resistivity. The search for ferromagnetic materials of unusually high resistivity resulted in the emergence of ferrites. Ferrites having a resistivity of upto 107 ohm-meter as compared to 10-7 ohm-meter for iron, reduce the eddy current losses in them to negligible values, even at microwave frequencies (the eddy current power loss is proportional to the square of the frequencies and hence this high resistivity at microwave frequencies is imperative). Ferrites and materials derived from ferrites find extensive application in devices like transformers, TV Yokes, loud speakers and in many other devices. They are also one of the largely used material medium for audio/video applications and computer memories and switches. At microwave frequencies, it is used in various polarization rotators, resonance isolators and phase shifters.