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Thursday, 8 August 2019

Ferrite Cores - Properties and Applications

Ferrite Cores - Properties and Applications

Ferrite cores arc moulded from a mixture of metallic oxides such that certain iron atoms in the cubic crystal of magnetite are replaced by other metal atoms such as Mn and Zn to form manganese zinc ferrite. They resemble ceramic material in production process and physical properties. Its magnetic permeability may be as high as 5000 and apparent dielectric constants in excess of 100,000. The curie point is quite low in the range of 1000 to 300°. Typical normal induction curve of soft ferrite, is shown in Fig. 4.10. The temperature dependence of a magnesium manganese core is shown in Figure.

(a) Powdered Iron Core:

Powdered Iron has a grain size of 10 microns are manufactured and coated with special insulating material upto 1 micron. The powder is mixed with binding material, compressed and baked. The product is chemically stable magnetic body. When mixed with alloy it attains superior magnetic properties and also permit the use of small cores. Some of the composition of ferrites along with its application is given in Table.

Composition and Applications of Ferrites:

Primary Characteristics
Application Areas
Nickel - zinc ferrite (15-25% ZnO)
High permeability, low coercive force, low Curie temperature, easy fabrication
Audio and TV transformers
Manganese - zinc ferrite (15 - 25% ZnO)
High permeability, low coercive force, low Curie temperature, easy fabrication, low resistivity, inexpensive materials
TV flyback transformers. cup cores, deflection yokes
Nickel - zinc ferrite (5 - 15% ZnO)
Medium permeability, medium coercive force and medium Curie temperature
Antenna rods, stable inductors (100 kHz to 10 MHz)
Magnesium manganese ferrite (5 - 10% MnO)
High resistivity, low saturation magnetization, precise processing required
Microwave gyrators, phase shifters, isolators
Magnesium - manganese ferrite (20 - 30% MnO)
Rectangular hysteresis loop, low coercive force, precise processing required
Memory cores
Nickel ferrite (50% NiO)
High resistivity and Curie point
Stable inductors (10 MHz to 100 MHz), high power microwave isolators
Barium - cobalt (5% CoO) (3 BaO . 2CoO.12Fe2O3)
High resistivity, high resonance frequency
Stable inductors (50 MHz to 500 MHz)
Barium ferrite (10% BaO) (BaO. 6 Fe203)
High coercive force, high energy product and resistivity, inexpensive materials
Permanent magnets
Oriented barium ferrite
High energy product, more expensive processing
High-energy product permanent magnets
YIG (3Y203 . 6Fe2O3)
Narrow resonance line-width, high resistivity, expensive materials
Microwave isolators, gyrators (1 GHz to 7 GHz)
Yitrium - aluminium -iron garnet
Narrow resonance line width, low saturation magnetization, low Curie temperature expensive materials
Microwave isolators, gyrators (0.2 GHz to 2 GHz)
Gamma - iron - oxide (100% Fe2O3)
High saturation magnetization, high coercive force
Magnetic tape

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