The magnetic core is a key component in electrical and electromechanical devices such as electromagnets, transformers and inductors. An electromagnet is a type of Magnet in which the Magnetic field is produced by the flow of an electric current. A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors An inductor is a passive electrical component designed to provide Inductance in a circuit A magnetic core is a magnetic material with a high magnetic permeability, but are usually chosen to be magnetically 'soft', that is, they are made of materials that do not maintain a significant magnetic field when external field is removed, unlike 'hard' magnetic materials. In Electromagnetism, permeability is the degree of Magnetization of a material that responds linearly to an applied Magnetic field.
The use of a magnetic core can enormously concentrate the strength and increase the effect of magnetic fields produced by electric currents and permanent magnets. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. A magnet (from Greek grc μαγνήτης λίθος " Magnesian stone" is a material or object that produces a Magnetic field. The properties of the device will depend crucially on the following factors:
- the geometry of the magnetic core. Geometry ( Greek γεωμετρία; geo = earth metria = measure is a part of Mathematics concerned with questions of size shape and relative position
- the amount of air gap in the magnetic circuit. A magnetic circuit is a closed path containing a Magnetic flux.
- the properties of the core material (especially permeability and hysteresis). In Electromagnetism, permeability is the degree of Magnetization of a material that responds linearly to an applied Magnetic field. A system with hysteresis can be summarised as a system that may be in any number of states independent of the inputs to the system
- the operating temperature of the core. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature
- whether the core is laminated to reduce eddy currents. A laminate is a material constructed by uniting two or more layers of material together An eddy current (also known as Foucault current) is an electrical phenomenon discovered by French physicist Léon Foucault in
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Commonly used magnetic core structures
Straight cylindrical rod
Most commonly made of the ferrite or similar material, and used in radios especially for tuning an inductor. Ferrite or alpha iron ( α-Fe) is a Materials science term for Iron, or a Solid solution with iron as the main constituent with a Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. An inductor is a passive electrical component designed to provide Inductance in a circuit The rod sits in the middle of the coil and small adjustments of the rod position will fine tune the inductance. A coil is a series of loops A coiled coil is a structure where the coil itself is in turn also looping In Electrical circuits, any Electric current i produces a Magnetic field and hence generates a total Magnetic flux \Phi acting Often the rod is threaded to allow adjustment with a screwdriver. A screw thread is a helical or tapered structure used to convert between rotational and linear movement or force In radio circuits, a blob of wax or resin is used once the inductor has been tuned to prevent the core from moving. Wax has traditionally referred to a substance that is secreted by Bees ( Beeswax) and used by them in constructing their Resin, not to be confused with Rosin, is a Hydrocarbon Secretion of many Plants particularly coniferous trees.
The presence of the high permeability core increases the inductance but the field must still spread into the air at the ends of the rod. In Electrical circuits, any Electric current i produces a Magnetic field and hence generates a total Magnetic flux \Phi acting Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five The path through the air ensures that the inductor remains linear. An inductor is a passive electrical component designed to provide Inductance in a circuit The word linear comes from the Latin word linearis, which means created by lines. In this type of inductor radiation occurs at the end of the rod and electromagnetic interference may be a problem in some circumstances. Radiation, as in Physics, is Energy in the form of waves or moving Subatomic particles emitted by an atom or other body as it changes from a higher energy
Single "I" core
Like a cylindrical rod but square, rarely used on its own.
"C" or "U" core
U and C-shaped cores are the simplest solution to form a closed magnetic circuit, when used alongside a I or another C or U' core.
 a U-shaped core, with sharp corners |
 the C-shaped core, with rounded banu |
"E" core
E-shaped core are more symmetric solutions to form a closed magnetic system. Most of the time, the electric circuit is wound around the center leg, whose section area is twice that of each individual outer leg.
 Classical E core |
 The EFD' core allows for construction of inductors or transformers with a lower profile |
 The ER core has a cylindrical central leg. |
 the EP core is halfways between a E and a pot core |
"E" and "I" core
Sheets of suitable iron stamped out in shapes like the (sans-serif) letters "E" and "I", are stacked with the "I" against the open end of the "E" to form 3-legged structure; coils can be wound around any leg, but usually the center leg is used. History Ancient usages Sans-serif letter forms can be found in Latin Etruscan, and Greek inscriptions for as early as 5th century BC This type of core is much used for power transformers, autotransformers, and inductors.
Pair of "E" cores
Again used for iron cores. Similar to using an "E" and "I" together, a pair of "E" cores will accommodate a larger coil former and can produce a larger inductor or transformer. An inductor is a passive electrical component designed to provide Inductance in a circuit A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors If an air gap is required, the centre leg of the "E" is shortened so that the air gap sits in the middle of the coil to minimise fringing and reduce electromagnetic interference.
Pot core
Usually ferrite or similar. This is used for inductors and transformers. An inductor is a passive electrical component designed to provide Inductance in a circuit A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors The shape of a pot core is round with an internal hollow that almost completely encloses the coil. Usually a pot core is made in two halves which fit together around a coil former (bobbin). A bobbin is a spindle or cylinder with or without flanges on which Wire, Yarn, thread or film is wound This design of core has a shielding effect, preventing radiation and reducing electromagnetic interference. Electromagnetic shielding is the process of limiting the flow of Electromagnetic fields between two locations by separating them with a barrier made of conductive material Radiation, as in Physics, is Energy in the form of waves or moving Subatomic particles emitted by an atom or other body as it changes from a higher energy
Toroidal core
This design is based on a circular toroid (topologically the shape as a doughnut). Topology ( Greek topos, "place" and logos, "study" is the branch of Mathematics that studies the properties of A doughnut (also spelled "donut" is a sweet Deep-fried piece of Dough or batter. The coil is wound through the hole in the torus and around the outside. An ideal coil is distributed evenly all around the circumference of the torus. This geometry will turn the magnetic field around into a full loop and thus will constrain virtually all of the field to the core material. Geometry ( Greek γεωμετρία; geo = earth metria = measure is a part of Mathematics concerned with questions of size shape and relative position In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges All of the core material is covered with wire, so none of the core is "wasted" on completing the magnetic circuit. This makes a highly efficient and low radiation transformer. Radiation, as in Physics, is Energy in the form of waves or moving Subatomic particles emitted by an atom or other body as it changes from a higher energy A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors It is popular for applications where the desirable features are: high specific power per mass and volume, low mains hum, and minimal electromagnetic interference. In Engineering, the term specific power can refer to power either per unit of Mass, Volume or Area, although power per unit of The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically Electric hum, Mains hum, or power line hum is an audible oscillation at the frequency of the Mains Alternating current One such application is the power supply for a hi-fi audio amplifier. Power supply is a reference to a source of Electrical power. A device or system that supplies Electrical or other types of Energy to an output load An audio amplifier is an Electronic amplifier that amplifies low-power audio signals (signals composed primarily of frequencies between 20 Hertz to The main drawback that limits their use for general purpose applications, is the inherent difficulty of winding wire through the center of a torus. Unlike a split core (a core made of two elements, like a pair of E cores), specialized machinery is required for automated winding of a toroidal core. Toroids have less audible noise, such as mains hum, because the magnetic forces to not exert bending moment on the core. The core is only in compression or tension, and the circular shape is more stable mechanically.
Planar core
A planar core consists of two flat pieces of magnetic material, one above and one below the coil. It is typically used with a flat coil that is part of a printed circuit board. A printed circuit board, or PCB, is used to mechanically support and electrically connect Electronic components using conductive pathways or traces This design is excellent for mass production and allows a high power, small volume transformer to be constructed for low cost. Mass production (also called flow production, repetitive flow production, series production, or serial production) is the production of In Physics, power (symbol P) is the rate at which work is performed or energy is transmitted or the amount of energy required or expended for The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors It is not as ideal as either a pot core or toroidal core but costs less to produce.
Core loss
In a transformer or inductor, some of the power that would ideally be transferred through the device is lost in the core, resulting in heat. A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors An inductor is a passive electrical component designed to provide Inductance in a circuit In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature There are various reasons for such losses, the primary ones being:
Hysteresis loss
The larger the area of the hysteresis loop, the more loss per cycle. A system with hysteresis can be summarised as a system that may be in any number of states independent of the inputs to the system A system with hysteresis can be summarised as a system that may be in any number of states independent of the inputs to the system Hysteresis loss increases with higher frequencies as more cycles are undergone per unit time. Frequency is a measure of the number of occurrences of a repeating event per unit Time.
Eddy current loss
The induction of eddy currents within the core causes a resistive loss. An eddy current (also known as Foucault current) is an electrical phenomenon discovered by French physicist Léon Foucault in Faraday's law of induction describes an important basic law of electromagnetism which is involved in the working of Transformers Inductors and many forms of An eddy current (also known as Foucault current) is an electrical phenomenon discovered by French physicist Léon Foucault in The higher the resistance of the core material the lower the loss. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is Lamination of the core material can reduce eddy current loss. A laminate is a material constructed by uniting two or more layers of material together
Movement of magnetic domains
As the magnetic field changes, some magnetic domains grow while others shrink, thus the walls of the domains can be said to move. A magnetic domain describes a region within a material which has uniform Magnetization. A magnetic domain describes a region within a material which has uniform Magnetization. This movement absorbs energy.
Common magnetic core materials
Having no magnetically active core material (an "air core") gives incredibly poor performance in most situations, so a wide range of high-permeability materials are used to concentrate the field. In Electromagnetism, permeability is the degree of Magnetization of a material that responds linearly to an applied Magnetic field. Most high-permeability material are ferromagnetic or ferrimagnetic. Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it A ferrimagnetic Interaction is a specific type of Antiferromagnetic interaction in which the net spin of the System is not equal to zero due
Soft iron
"Soft" iron is used in electromagnets and in some electric motors; and it can create a field as much as 50,000 times more intense than with an air core. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 [1]
Iron is desirable to make magnetic cores, as it can withstand high levels of magnetic field (up to 2. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges 16 teslas at ambient temp[2]). The tesla (symbol T) is the SI derived unit of Magnetic field B (which is also known as "magnetic flux density" and "magnetic
It's also used because, unlike "hard" iron, it does not remain magnetised when the field is removed, which is often important.
Laminated silicon steel
Although iron is a relatively good conductor, it cannot be used in bulk form with a rapidly changing field, such as in a transformer, as intense eddy currents would appear due to the magnetic field, resulting in huge losses (this is used in induction heating). Electrical steel, also called lamination steel, silicon electrical steel, silicon steel or transformer steel, is specialty Steel tailored An eddy current (also known as Foucault current) is an electrical phenomenon discovered by French physicist Léon Foucault in Induction heating is the process of Heating an electrically conducting object (usually a Metal) by Electromagnetic induction, where Eddy currents
Two techniques are commonly used together to increase the resistivity of iron: lamination and alloying of the iron with silicon
Lamination
Laminated magnetic cores are made of thin, insulated iron sheets. A laminate is a material constructed by uniting two or more layers of material together Using this technique, the magnetic core is equivalent to many individual magnetic circuits, each one receiving only a small fraction of the magnetic flux (because their section is a fraction of the whole core section). Furthermore, these circuits have a resistance that is higher than that of a non-laminated core, also because of their reduced section. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is From this, it can be seen that the thinner the laminations, the lower the eddy currents.
Silicon alloying
A small addition of silicon to Iron (around 3%) results in a dramatic increase of the resistivity, up to four times higher. Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 Further increase in Silicon concentration impairs the steel's mechanical properties, causing difficulties for rolling.
Among the two types of silicon steel, grain-oriented (GO) and grain non-oriented (GNO), GO is most desirable for magnetic cores. Electrical steel, also called lamination steel, silicon electrical steel, silicon steel or transformer steel, is specialty Steel tailored It is anisotropic, offering better magnetic properties than GNO in one direction. Anisotropy (pronounced with stress on the third syllable ˌænaɪˈsɒtrəpi is the property of being directionally dependent as opposed to Isotropy, which means homogeneity As the magnetic field in inductor and transformer cores is static (compared to that in electric motors), it is possible to use GO steel in the preferred orientation.
carbonyl iron
Powdered cores made of carbonyl iron, a highly pure iron, have high stability of parameters across a wide range of temperatures and magnetic flux levels, with excellent Q factors between 50 kHz and 200 MHz. Carbonyl iron is a highly pure (975% for grade S 995+% for grade R Iron, prepared by chemical decomposition of purified Iron pentacarbonyl. Carbonyl iron is a highly pure (975% for grade S 995+% for grade R Iron, prepared by chemical decomposition of purified Iron pentacarbonyl. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature Magnetic flux, represented by the Greek letter Φ ( Phi) is a measure of quantity of Magnetism, taking into account the strength and the extent of a Magnetic For other uses of the terms Q and Q factor see Q value. In Physics and Engineering the quality Carbonyl iron powders are basically constituted of micrometer-size spheres of iron coated in a thin layer of electrical insulation. "Globose" redirects here See also Globose nucleus. A sphere (from Greek σφαίρα - sphaira, "globe An insulator, also called a Dielectric, is a material that resists the flow of Electric current. This is equivalent to a microscopic laminated magnetic circuit (see silicon steel, above), hence reducing the eddy currents, particularly at very high frequencies. An eddy current (also known as Foucault current) is an electrical phenomenon discovered by French physicist Léon Foucault in
A popular application of carbonyl iron-based magnetic cores is in high-frequency and broadband inductors and transformers. An inductor is a passive electrical component designed to provide Inductance in a circuit A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors
Iron powder
Powdered cores made of hydrogen reduced iron have higher permeability but lower Q. They are used mostly for electromagnetic interference filters and low-frequency chokes, mainly in switched-mode power supplies. Electronic filters are Electronic circuits which perform Signal processing functions specifically intended to remove unwanted signal components and/or enhance wanted A switched-mode power supply, switching-mode power supply or SMPS, is an electronic Power supply unit (PSU that incorporates a switching regulator
Ferrite
Ferrite ceramics are used for high-frequency applications. Ferrites are a class of Chemical compounds with the formula AB2O4 where A and B represent various metal Cations usually including Ferrites are a class of Chemical compounds with the formula AB2O4 where A and B represent various metal Cations usually including The ferrite materials can be engineered with a wide range of parameters.
See also
References
- ^ Soft iron core Text - Physics Forums Library
- ^ Daniel Sadarnac, Les composants magnétiques de l'électronique de puissance, cours de Supélec, mars 2001 [in french]
External links
- Toroid Winding Calculator - Online calculator for ferrite and iron-powder coil winding calculations. An inductor is a passive electrical component designed to provide Inductance in a circuit A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors Ferrites are a class of Chemical compounds with the formula AB2O4 where A and B represent various metal Cations usually including Magnetic core memory, or ferrite-core memory, is an early form of Random access Computer memory.
- EMERF, the Electric Motor Education and Research Foundation
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