What is ferrite core?
Ferrite core is a group of sintered magnetic metal oxide made from mixtures of iron oxide. Mn-Zn ferrite and Ni-Zn ferrite are the typical examples of ferrite material. The Mn-Zn ferrite is characterized by high permeability and high magnetic flux density and feature low loss on frequencies below 1 MHz. The Ni-Zn ferrite is characterized by extremely high resistivity and low permeabilities of less than several hundred and feature loss on frequencies higher than 1 MHz. Ferrite core is applied in coils and transformers of various electronic equipment.
What is permeability?
Permeability. is the value of the permeability at very low magnetic field strength. For example, if the permeability for air (non-magnetic material) is 1, then the permeability for ferrite (magnetic material) is 10000, i.e. 10000 times magnetic flux density to pass through magnetic material when compared. In general, . is shown as initial permeability . in material characteristics table.
Why ferrite could eliminate noise in the magnetic circuit?
Apart from the initial permeability mentioned in A2, there is also another permeability, which can be written as (µ"). It means that the value of its permeability (µ") will be small at low frequency and vice versa. At that time, the high frequency noise absorbed by body of ferromagnetic material and dissipated as heat and the loss co-efficient of (µ") exists correspondingly for the purpose of stabilizing the desired frequency of the electrical appliances.
What is the permanent magnet?
Magnets have mysterious powers, like attracting iron and pointing in a north-south direction. People must have been amazed when they first found out these phenomena.
Magnet has 2 meanings - "affectionate stone" and "magnet". As a piece of iron is pulled towards a magnet, just like a child being attracted towards an affectionate mother and then "magnet" was literally written as " affectionate stone" in China.
On the other hand, as first magnetic iron ores were also mined in the Magnesia region of Greece in Europe and were therefore called Magnesia stones, from which the word "magnet" originated.
Today, magnetic parts are widely used in different kinds of hardwares which enrich our daily life and plays an increasingly indispensable role in the electronics industry. Different types of magnets were developed throughout the centuries.
If you would like to have a look on the classification of magnets in accordance with its materials.
What are the requirements for a good magnet?
Requirements for a good magnet should meet the following three conditions:
(1) To have the ability to generate a strong magnetic field in an external space of the magnet which is small in size and volume.
(2) To be stable against thermal and external demagnetization.
(3) To have good cost performance, low cost per effective magnetic energy.
Condition(1) requires the magnet to have a high maximum energy product. Metallic magnet are proved of high (BH)max. For condition(2), it is necessary to have as high a Curie temperature as possible, and for the magnet to have strong resistance to oxidation and rusting. Alnico magnet, iron-chromium-cobalt magnet and samarium- cobalt magnet have a range of temperature coefficients of magnetic flux, -0.01 ~ -0.02%/K, better than that of ferrite magnets, -0.18%/K.. Condition(3) requires the cost of the magnet to be low and the effective magnetic energy high. Raw materials for ferrite magnets are iron oxide and barium or strontium carbonate which is comparatively cheaper while the production method of these materials is relatively simple and easy as compared with that of other magnetic materials. Thus, ferrite magnet material is still accounting for the largest production volume in the worldwide magnet industry.
Although various magnet materials are available, none of them completely meets all of these requirements. A particular material is chosen for a particular application.
TDK's Magnets? With advanced technology and expertise in magnetic field, TDK can apply different materials to manufacture various kinds of magnets. The characteristics of the magnets are listed as follows:-
1. Ferrite Magnet
Being one of the leading magnet producers, our production quantity can be attained to 6,000 ton. A board array of Br type material (from isotrophic FB1A type to wet-anisotropic FB9 type) can be used for various applications.
Dry-anisotropic FB3 ones have the best cost-performance and can be formed into different complex shapes which are widely used in micro-motors.
Wet-anisotropic FB4~FB9 ones are the No.1 magnets made by High Br to high Hc and widely applicable to various fields.
2. Rare Earth Cobalt Magnet (TDK Neorec Magnet)
Neodymium-Iron-Boron Magnet acquires lower density and lighter in weight but still exhibit 10~20% superior performance than that of Samarium-Cobalt ores. Its unique advantages makes them suitable for using in smaller, lighter devices such as VCM.
3. Composite Magnet
The powder of ferrite or rare-earth magnets, which mixed with the bonding material and formed into a desired shape and then they are called bonded magnets / composite magnets.
(1) Bonded Ferrite Magnets
There are two types of bonded ferrite magnets - i.e. ferrite rubber bonded magnet (TDK material: BQA~BQC) and ferrite-plastic bonded magnets(TDK material: BPA~BPC). Ferrite-rubber bonded magnets are composed of ferrite magnet powder and bonding synthetic rubber(NBR). They have a strong magnetic anistropy and an excellent flexibility and can be formed by extrusion molding into various shapes such as sheets, boards, bars, and cylinders. On the other hand, ferrite-plastic bonded magnets are composed of magnetic ferrite powder and bonding nylon. They can be molded into highly precise and complicated shapes by injection.
(2) Rare earth cobalt bonded magnets
TDK rare earth cobalt-plastic bonded magnets (TDK material: BRA) are composed of 2-17 series Samarium-Cobalt magnetic powder which is excellent in magnetic characteristics and reversible temperature coefficient, and polyamide resin (nylon). Various shapes formed by injection molding and the products can be magnetized into the axial and transverse pressed ones.
Attached please find the Distribution Chart of the Characteristics of different magnets for your reference.
本文转自：China Industry News