Development of a Low Loss Mn-Zn Ferrite Material for Power Applications

Abstract

Earlier Iron and its alloys were used as magnetic materials to serve the need of the electrical industry for long time. However, with the advent of higher frequencies, the standard techniques of reducing eddy current losses, using lamination or iron powder cores, were no longer efficient or cost effective. This realization stimulated a renewed interest in “magnetic Insulators” as first reported by S. Hilpert in Germany in 1909. It was readily understood that if the high electrical resistivity of oxides could be combined with desired magnetic characteristics, a magnetic material would result that was particularly well suited for high frequency operation. Research to develop such a material was being done in various laboratories all over the world, such as by V. Kato, T. Takei, and N. Kawai in the 1930’s in Japan and by J. Snoek of the Philips’ Research Laboratories in the period 1935-45 in the Netherlands. By 1945 Snoek had laid down the basic fundamentals of the physics and technology of practical ferrite materials. In 1948, the Neel theory of ferromagnetic provided the theoretical understanding of this type of magnetic material. These Ferrites are ceramic, homogeneous materials composed of various oxides with iron oxide as their main constituent. Based upon the chemical composition, soft ferrites can be divided into two major categories, manganese-zinc ferrite and nickel-zinc ferrite. In each of these categories many different MnZn and NiZn material grades are being manufactured by varying the chemical composition or by different manufacturing techniques. The two families of MnZn and NiZn ferrite materials complement each other and allow the use of soft ferrites from audio frequencies to several hundred mega-hertz. The first practical soft ferrite application was in inductors used in LC filters in frequency division multiplex equipment. The combination of high resistivity and good magnetic properties made these ferrites an excellent core material for these filters operating over the 50-450 kHz frequency range. The large scale introduction of TV in the 1950’s was a major opportunity for the fledgling ferrite industry. In TV sets, ferrite cores were the material of choice for the high voltage transformer and the picture tube deflection system.