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SOFT FERRITES FOR ELECTRONICS - 1999
There is a growing need for soft ferrites for meeting EMI, EMC requirements in the Australian electronics industry. The single most important characteristic of soft ferrites, as compared to other magnetic materials, is the high volume resistivity exhibited in the monolithic form. Since eddy current losses are inversely proportional to resisivity and these losses increase with the square of the frequency, high resistivity becomes an essential factor in magnetic materials intended for high frequency operation. There is no other class of magnetic material that can match soft ferrites in performance, cost and volumetric efficiency, over the range from audio frequencies to above 200 MHz. During the last 25 years the basic constituents of ferrites have changed little, but purity of raw materials and process control have improved dramatically. Ferrites are ceramic materials with the general chemical formula MO.Fe2O 3, where MO is a divalent metal oxide blended with 48 to 60 mole percent of iron oxide. Manganese zinc ferrite components are used in tuned circuits and magnetic power designs from the low kilohertz range into the broadcast spectrum. The nickel zinc ferrites frequently contain oxides of other metals, such as those of magnesium, manganese, copper or cobalt. In general, they are used at higher frequencies (above 1 MHz), and are suitable for low flux density applications. The manganese ferrite is a dense, temperature stable material displaying a high degree of squareness in its hysteresis loop. This makes this material uniquely suited for such applications as multiple output control in switched-mode power supplies and high frequency magnetic amplifiers. All ferrites are useful in attenuating unwanted signal pickup or transmissions which might travel along component leads or interconnecting wires, traces or cables and are used extensively in all types of equipment to reduce the effects of Electro Magnetic Interference. The difference between hard and soft ferrite is not tactile, but rather a magnetic characteristic. Soft ferrite does not retain significant magnetization, whereas hard ferrite magnetization is considered permanent. Soft ferrites from Fair-Rite Products Corporation USA are available from Specialised Conductives Pty. Ltd., Melbourne. Specialised Conductives has many years experience supplying EMI/EMC materials to both military and commercial sectors of the Australian electronics manufacturing sector and are happy to provide information in this area.
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www.emctech.com.au |
