（1） Powder core

1. Magnetic particle core

Magnetic particle core is a kind of soft magnetic material made of ferromagnetic powder and insulating medium. Because ferromagnetic particles are very small (0.5 ~ 5 microns used at high frequencies) and separated by non-magnetic electrical insulating film materials, on the one hand, they can isolate eddy currents, and the materials are suitable for higher frequencies; On the other hand, due to the gap effect between particles, the material has low permeability and constant magnetic conductivity; Because the particle size is small, there is basically no skin phenomenon, and the change of permeability with frequency is relatively stable. Mainly used for high frequency inductors. The magnetoelectric properties of magnetic particle cores mainly depend on the permeability of powder materials, the size and shape of powder particles, their filling coefficient, the content of insulating medium, forming pressure and heat treatment process.

The commonly used magnetic particle cores include iron powder core, permalloy powder core and iron silicon aluminum powder core.

Effective permeability of magnetic core μ The calculation formula of E and inductance is: μ e=DL/4N2S × one hundred and nine

Where: D is the average diameter of the magnetic core (CM), l is the inductance (share), n is the number of winding turns, and S is the effective cross-sectional area of the magnetic core (cm2).

(1) Iron powder core

Common iron powder cores are composed of carbon based iron magnetic particles and resin carbon based iron magnetic particles. Among the powder cores, the price is the lowest. Saturation magnetic induction value is about 1.4T; The permeability ranges from 22 to 100; initial permeability μ I good stability with the change of frequency; Good DC current superposition performance; But the loss is high at high frequency.

Variation of initial permeability of iron powder core with DC magnetic field strength

Variation of initial permeability of iron powder core with frequency

(2) . permalloy powder core

Permalloy powder cores mainly include molybdenum permalloy powder core (MPP) and high flux powder core (highflux).

MPP is composed of 81% Ni, 2% Mo and Fe powder. The main features are: the saturation magnetic induction value is about 7500gs; The permeability ranges from 14 to 550; It has the lowest loss in the powder core; Excellent temperature stability, widely used in space equipment, outdoor equipment, etc; The magnetostrictive coefficient is close to zero, and there is no noise when working at different frequencies. It is mainly used in high-quality factor Q filters below 300kHz, induction load coils, resonant circuits, LC circuits with high requirements for temperature stability, output inductance, power factor compensation circuits, etc. it is commonly used in AC circuits, and the price of powder core is the most expensive.

High flux powder core HF is composed of 50% Ni and 50% Fe powder. The main features are: the saturation magnetic induction value is about 15000gs; The permeability ranges from 14 to 160; In the powder core, it has the highest magnetic induction intensity and the highest DC bias capacity; Magnetic core volume correction is mainly used in line filters, AC inductors, output inductors, power factor correction circuits, etc. it is commonly used in DC circuits, especially in high DC bias, high DC and low AC. The price is lower than MPP.

(3) Iron silicon aluminum powder core (koolm μ Cores）

The iron silicon aluminum powder core is composed of 9% Al, 5% Si and 85% Fe powder. It mainly replaces the iron powder core, and the loss is 80% lower than that of the iron powder core, which can be used at frequencies above 8kHz; The saturation magnetic induction is about 1.05t; The permeability ranges from 26 to 125; The magnetostrictive coefficient is close to 0, and there is no noise when working at different frequencies; It has higher DC bias capacity than MPP; It has the best performance price ratio. It is mainly used in AC inductance, output inductance, line filter, power factor correction circuit, etc. Sometimes it is used as transformer core instead of air gap ferrite.

2. Soft ferrite

Soft magnetic ferrite is a ferromagnetic oxide mainly composed of Fe2O3, which is produced by powder metallurgy. There are Mn Zn, Cu Zn, Ni Zn and other categories. Among them, Mn Zn ferrite has the largest output and consumption, and the resistivity of Mn Zn ferrite is low, ranging from 1 to 10 ohm meter, which is generally used at frequencies below 100kHz. The resistivity of Cu Zn and Ni Zn ferrites is 102 ~ 104 ohm meter, In 100kHz model ">100khz model" >100khz model ">100khz model" >100khz model ">100khz model" >100khz model ">100khz model" >100khz model ">100khz model" >100khz model ">100khz model" >100khz model ">100khz model" >100khz model ">100khz model" >100khz model ">100khz model" >100khz model ">100khz model" >100khz model ">100khz model" >100khz model ">100khz model" >100khz model ">100khz model ">100khz ~ 10 MHz radio frequency band has small loss, which is mostly used in radio antenna coil and radio intermediate frequency transformer. The magnetic core has a wide variety of shapes, including e, I, u, EC, ETD, square (RM, EP, PQ), can (PC, RS, DS) And round, etc. It is very convenient in application. Because soft magnetic ferrite can obtain high permeability without using rare materials such as nickel, powder metallurgy method is suitable for mass production, so the cost is low, and because it is sintered material with high hardness and insensitive to stress, it is very convenient in application. Moreover, the permeability changes steadily with frequency, and remains basically unchanged below 150kHz. With the emergence of soft ferrite, the production of magnetic particle cores has been greatly reduced, and many places where magnetic particle cores were originally used have been replaced by soft ferrite.

There are many ferrite manufacturers at home and abroad. Here, only Mn Zn ferrite produced by magnetics company in the United States is taken as an example to introduce its application. There are three kinds of basic materials: basic materials for telecommunications, broadband and EMI materials, and power type materials.

The permeability of ferrite used in telecommunications ranges from 750 to 2300, with low loss factor, high quality factor Q, and stable permeability with temperature / time. It is the one with the slowest decline in permeability in work, about 3% to 4% every 10 years. It is widely used in high-Q filters, tuning filters, load coils, impedance matching transformers, proximity sensors. Broadband ferrite is also known as high permeability ferrite, with permeability of 5000, 10000 and 15000 respectively. Its characteristics are low loss factor, high permeability and high impedance / frequency characteristics. It is widely used in common mode filters, saturated inductors, current transformers, leakage protectors, insulation transformers, signal and pulse transformers, and in broadband transformers and EMI. Power ferrite has a high saturation magnetic induction intensity of 4000 ~ 5000gs. In addition, it has low loss / frequency relationship and low loss / temperature relationship. In other words, the loss increases little with the increase of frequency; The loss changes little with the increase of temperature. It is widely used in power chokes, parallel filters, switching power transformers, switching power inductors, and power factor correction circuits.

（2） Wound iron core

1. Silicon steel sheet iron core

Silicon steel sheet is an alloy. The iron silicon alloy formed by adding a small amount of silicon (generally less than 4.5%) to pure iron is called silicon steel. This kind of iron core has the highest saturated magnetic induction value of 20000gs; Because of their good magnetoelectric properties, easy mass production, low price and small mechanical stress, they have been widely used in the power electronics industry, such as power transformers, distribution transformers, current transformers and other iron cores. It is the largest output and use of soft magnetic materials. It is also the largest amount of magnetic materials used in power transformers. Especially in low frequency and high power. Commonly used are cold-rolled silicon steel sheet dg3, cold-rolled non oriented electrical steel strip DW, and cold-rolled oriented electrical steel strip DQ, which are suitable for medium and small power low-frequency transformers, chokes, reactors, and inductor cores in various electronic systems and household appliances. These alloys have good toughness and can be processed by punching, cutting, etc. the cores are laminated and wound. However, the loss increases sharply at high frequency, and the general use frequency is not more than 400Hz. From the perspective of application, two factors should be considered in the selection of silicon steel: magnetism and cost. For small motors, reactors and relays, pure iron or low silicon steel sheets can be selected; For large motors, high silicon hot-rolled silicon steel sheets, single oriented or non oriented cold-rolled silicon steel sheets can be selected; Cold rolled silicon steel sheets with single orientation are often used for transformers. When used at power frequency, the thickness of common strip is 0.2~0.35 mm; When used at 400Hz, the thickness of 0.1mm is often selected. The thinner the thickness, the higher the price.

2. Permalloy

Permalloy usually refers to iron nickel alloy, with nickel content in the range of 30~90%. It is a widely used soft magnetic alloy. Through appropriate processes, the magnetic properties can be effectively controlled, such as the initial permeability of more than 105, the maximum permeability of more than 106, the coercivity as low as 2 ‰ Auster, and the rectangular coefficient close to 1 or close to 0. Permalloy with face centered cubic crystal structure has good plasticity and can be processed into 1 μ M ultra thin belt and various use forms. The commonly used alloys are 1J50, 1J79, 1J85, etc. The saturated magnetic induction intensity of 1J50 is slightly lower than that of silicon steel, but the magnetic permeability is dozens of times higher than that of silicon steel, and the iron loss is also 2-3 times lower than that of silicon steel. The transformer with higher frequency (400~8000hz) is made, and the no-load current is small, which is suitable for making small high-frequency transformers below 100W. 1J79 has good comprehensive performance and is suitable for high-frequency and low-voltage transformers, leakage protection switch cores, common mode inductance cores and current transformer cores. The initial permeability of 1J85 can reach more than 100000 105, which is suitable for low-frequency or high-frequency input and output transformers, common mode inductors and high-precision current transformers with weak signals.

3. Amorphous and nanocrystalline soft magnetic alloys

Silicon steel and permalloy soft magnetic materials are crystalline materials. The atoms are regularly arranged in three-dimensional space, forming a periodic lattice structure. There are defects such as grains, grain boundaries, dislocations, interstitial atoms, magnetocrystalline anisotropy and so on, which are detrimental to the soft magnetic properties. In terms of magnetic physics, the amorphous structure with irregular arrangement of atoms and no periodicity and grain boundaries is very ideal for obtaining excellent soft magnetic properties. Amorphous metals and alloys are a new field of materials developed in the 1970s. Its preparation technology is completely different from the traditional method, but adopts the super rapid cooling solidification technology with a cooling rate of about onemillion degrees per second. From liquid steel to the finished strip, it is formed at one time, which reduces many intermediate processes compared with the general cold-rolled metal strip manufacturing process. This new process is called a revolution to the traditional metallurgical process. Due to ultra rapid cooling solidification, the atoms of the alloy have no time to arrange and crystallize orderly during solidification. The solid alloy obtained is a long-range disordered structure, and there is no grain and grain boundary of the crystalline alloy. It is called amorphous alloy, which is called a revolution in metallurgical materials science. This amorphous alloy has many unique properties, such as excellent magnetism, corrosion resistance, wear resistance, high strength, hardness and toughness, high resistivity and electromechanical coupling properties. Because of its excellent performance and simple process, it has become the focus of research and development in the field of material science at home and abroad since the 1980s. At present, the United States, Japan and Germany have a perfect production scale, and a large number of amorphous alloy products are gradually replacing silicon steel, permalloy and ferrite to the market

China has started the research and development of amorphous alloys since the 1970s. After the completion of major scientific and technological research projects during the "sixth five year plan", "Seventh Five Year Plan" and "Eighth Five Year Plan", 134 scientific research achievements, 2 national invention awards, 16 patents and nearly 100 Alloy varieties have been obtained. The general iron and Steel Research Institute now has four amorphous alloy strip production lines and one amorphous gold component iron core production line. It produces various finalized iron-based, iron nickel based, cobalt based and nanocrystalline strips and iron cores, which are suitable for iron core components of inverter power supply, switching power supply, power transformer, leakage protector and inductor, with an annual output value of nearly 20million yuan. During the ninth five year plan, a 1000 ton iron-based amorphous production line is being established, which has entered the international advanced level.

At present, the best single performance level of amorphous soft magnetic alloy is:

initial permeability μ o=14 × one hundred and four

Maximum permeability of cobalt based amorphous μ m=220 × one hundred and four

Cobalt based amorphous coercivity hc=0.001oe

Cobalt based amorphous rectangular ratio br/bs=0.995

Cobalt based amorphous saturation magnetization 4 π ms=18300gs

Iron based amorphous resistivity ρ= two hundred and seventy μ Ω/cm

The commonly used amorphous alloys include iron-based, iron nickel based, cobalt based amorphous alloys and iron-based nanocrystalline alloys. The national brand and performance characteristics are shown in the table and figure. For comparison, the corresponding properties of crystalline alloy silicon steel sheet, permalloy 1J79 and ferrite are also listed. These kinds of materials have different characteristics and are applied in different aspects.

Basic components and characteristics of brand:

1k101fe-si-b fast quenched soft magnet base alloy

1k102fe-si-b-c fast quenching soft magnet base alloy

1k103fe-si-b-ni fast quenched soft magnet base alloy

1k104fe-si-b-nimo fast quenched soft magnet base alloy

1k105fe-si-b-cr (and other elements) fast quenched soft magnet base alloy

1k106 high frequency low loss Fe-Si-B fast quenching soft magnet base alloy

1k107 high frequency and low loss fe-nb-cu-si-b fast quenched soft magnet base nanocrystalline alloy

1k201 high pulse permeability rapidly quenched soft magnetic cobalt base alloy

1k202 high remanence ratio rapidly quenched soft magnetic cobalt base alloy

1k203 fast quenched soft magnetic cobalt base alloy with high magnetic induction and low loss

1k204 high frequency low loss rapidly quenched soft magnetic cobalt base alloy

1k205 high initial permeability rapidly quenched soft magnetic cobalt base alloy

1k206 quenched high permeability soft magnetic cobalt base alloy

1k501fe-ni-p-b fast quenched soft magnet nickel base alloy

1k502fe-ni-v-si-b fast quenched soft magnet nickel base alloy

400hz: silicon steel iron core amorphous iron core

Power (W) 4545

Core loss (W) 2.41.3

Excitation power (VA) 6.11.3

Total weight (g) 295276

(1) Fe based amorphous alloys

Iron based amorphous alloy is composed of 80%fe and 20%si, B-type metal elements. It has high saturated magnetic induction intensity (1.54t). The loss comparison permeability, exciting current and iron loss of iron-based amorphous alloy and silicon steel are better than those of silicon steel sheet, especially low iron loss (1/3-1/5 of oriented silicon steel sheet). Replacing silicon steel as distribution transformer can save 60-70% energy. The thickness of iron-based amorphous alloy strip is about 0.03mm, which is widely used in distribution transformers, high-power switching power supplies, pulse transformers, magnetic amplifiers, intermediate frequency transformers and inverter cores, and is suitable for frequencies below 10kHz

2) Fe Ni based and Co based amorphous alloy

Fe Ni based amorphous alloy is composed of 40% Ni, 40% Fe and 20% metal like elements. It has medium saturated magnetic induction strength [0.8t], high initial permeability, high maximum permeability, high mechanical strength and excellent toughness. It has low iron loss at medium and low frequencies. Heat treatment in air does not cause oxidation, and good torque can be obtained after magnetic field annealing

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