Coil

Coil

Overview
A coil is a series of loops. A coiled coil is a structure in which the coil itself is in turn also looping.


An electromagnetic coil (or simply a "coil") is formed when a conductor (usually an insulated solid copper wire
Wire
A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...

) is wound around a core or form to create an inductor
Inductor
An inductor is a passive two-terminal electrical component used to store energy in a magnetic field. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...

 or electromagnet
Electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...

. One loop of wire is usually referred to as a turn, and a coil consists of one or more turns.
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Encyclopedia
A coil is a series of loops. A coiled coil is a structure in which the coil itself is in turn also looping.

Electromagnetic coils



An electromagnetic coil (or simply a "coil") is formed when a conductor (usually an insulated solid copper wire
Wire
A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...

) is wound around a core or form to create an inductor
Inductor
An inductor is a passive two-terminal electrical component used to store energy in a magnetic field. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...

 or electromagnet
Electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...

. One loop of wire is usually referred to as a turn, and a coil consists of one or more turns. For use in an electronic circuit
Electronic circuit
An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow...

, electrical connection
Electrical connection
An electrical connection between discrete points allows the flow of electrons . A pair of connections is needed for a circuit.Between points with a low voltage difference, direct current can be controlled by a switch...

 terminals called taps are often connected to a coil. Coils are often coated with varnish and/or wrapped with insulating tape to provide additional insulation
Electrical insulation
thumb|250px|[[Coaxial Cable]] with dielectric insulator supporting a central coreThis article refers to electrical insulation. For insulation of heat, see Thermal insulation...

 and secure them in place. A completed coil assembly with taps is often called a winding. A transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...

 is an electromagnetic device that has a primary winding and a secondary winding that transfers energy from one electrical circuit to another by inductive coupling
Inductive coupling
In electrical engineering, two conductors are referred to as mutual-inductively coupled or magnetically coupled when they are configured such that change in current flow through one wire induces a voltage across the ends of the other wire through electromagnetic induction...

 without moving parts. The term tickler coil usually refers to a third coil placed in relation to a primary coil and secondary coil. A coil tap
Coil tap
A coil tap is a wiring feature found on some electrical transformers, inductors and coil pickups, all of which are sets of wire coils. The coil tap are points in a wire coil where a conductive patch has been exposed .When the coil taps are disconnected, the coil operates as normal...

 is a wiring feature found on some electrical transformers, inductors and coil pickups, all of which are sets of wire coils. The coil tap(s) are points in a wire coil where a conductive patch has been exposed (usually on a loop of wire that extends out of the main coil body). As self induction is larger for larger coil diameter the current in a thick wire tries to flow on the inside. The ideal use of copper is achieved by foils. Sometimes this means that a spiral
Spiral
In mathematics, a spiral is a curve which emanates from a central point, getting progressively farther away as it revolves around the point.-Spiral or helix:...

 is a better alternative. Multilayer coils have the problem of interlayer capacitance
Capacitance
In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...

, so when multiple layers are needed the shape needs to be radically changed to a short coil with many layers so that the voltage between consecutive layers is smaller (making them more spiral like).

Analysis


The inductance
Inductance
In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit...

 of single-layer air-cored cylindrical coils can be calculated to a reasonable degree of accuracy with the simplified formula



where Henry [µH] (microhenries) are units of inductance, R is the coil radius
Radius
In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...

 (measured in inches to the center of the conductor), N is the number of turns, and L is the length of the coil in inches. In case you need to input coil dimensions in mm
MM
-Computers:* .mm, the Myanmar's Internet country code top-level domain* mm tree, the Andrew Morton's Linux kernel tree* Columbia MM, an early e-mail client* MediaMonkey, a digital media player and media library application-File extension :...

, you can multiply the formula result with 1/25.4. The online Coil Inductance Calculator calculates the inductance of any coil using this formula. Higher accuracy estimates of coil inductance require calculations of considerably greater complexity.

Note that if the coil has a ferrite core, or one made of another metallic material, its inductance cannot be calculated with this formula.

Coil examples



Some common electromagnetic coils include:
  • A bifilar coil
    Bifilar coil
    A bifilar coil is an electromagnetic coil that contains two closely spaced, parallel windings. In engineering, the word bifilar describes wire which is made of two filaments or strands. It is commonly used to denote special types of winding wire for transformers. Wire can be purchased in bifilar...

    is a coil that employs two parallel
    Parallel (geometry)
    Parallelism is a term in geometry and in everyday life that refers to a property in Euclidean space of two or more lines or planes, or a combination of these. The assumed existence and properties of parallel lines are the basis of Euclid's parallel postulate. Two lines in a plane that do not...

     windings.
  • A Barker coil is used in low field NMR imaging.
  • A Balun
    Balun
    A balun is a type of electrical transformer that can convert electrical signals that are balanced about ground to signals that are unbalanced , and the reverse. They are also often used to connect lines of differing impedance...

    is set of transformer coils for transmission lines.
  • A Braunbeck coil is used in geomagnetic research.
  • A degaussing coil is used in the process of removing permanent magnetism (magnetic hysteresis
    Hysteresis
    Hysteresis is the dependence of a system not just on its current environment but also on its past. This dependence arises because the system can be in more than one internal state. To predict its future evolution, either its internal state or its history must be known. If a given input alternately...

    ) from an object.
  • A choke coil
    Choke (electronics)
    A choke is a coil of insulated wire, often wound on a magnetic core, used as a passive inductor which blocks higher-frequency alternating current in an electrical circuit while passing signals of much lower frequency and direct current by having an impedance largely determined by reactance, which...

    (or choking coil) is low-resistance
    Electrical resistance
    The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...

     inductor
    Inductor
    An inductor is a passive two-terminal electrical component used to store energy in a magnetic field. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...

     used to block alternating current
    Alternating current
    In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

     while passing direct current
    Direct current
    Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

    .
  • A Flat coil is used in thin electric motors.
  • A Garrett coil is used in metal detector
    Metal detector
    A metal detector is a device which responds to metal that may not be readily apparent.The simplest form of a metal detector consists of an oscillator producing an alternating current that passes through a coil producing an alternating magnetic field...

    s.
  • A Helmholtz coil
    Helmholtz coil
    A Helmholtz coil is a device for producing a region of nearly uniform magnetic field. It is named in honor of the German physicist Hermann von Helmholtz.- Description :A Helmholtz pair consists of two identical circular magnetic...

    is a device for producing a region of nearly uniform magnetic field
    Magnetic field
    A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

    .
  • A hybrid coil
    Hybrid coil
    A hybrid coil is a transformer that has three windings, and which is designed to be configured as a circuit having four branches, that are conjugate in pairs....

    (or bridge transformer) is a single transformer that effectively has three windings.
  • An induction coil
    Induction coil
    An induction coil or "spark coil" is a type of disruptive discharge coil. It is a type of electrical transformer used to produce high-voltage pulses from a low-voltage direct current supply...

    (or ignition coil
    Ignition coil
    An ignition coil is an induction coil in an automobile's ignition system which transforms the battery's 12 volts to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel...

    ) is an electrical device in common use as the ignition system
    Ignition system
    An ignition system is a system for igniting a fuel-air mixture. Ignition systems are well known in the field of internal combustion engines such as those used in petrol engines used to power the majority of motor vehicles, but they are also used in many other applications such as in oil-fired and...

     (ignition coil or spark coil) of internal-combustion engines.
  • A loading coil
    Loading coil
    In electronics, a loading coil or load coil is a coil that does not provide coupling to any other circuit, but is inserted in a circuit to increase its inductance. The need was discovered by Oliver Heaviside in studying the disappointing slow speed of the Transatlantic telegraph cable...

    is, in electronics, a coil (inductor) inserted in a circuit to increase its inductance
    Inductance
    In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit...

    . Archaically called Pupin coils.
  • A multiple coil magnet is an electromagnet
    Electromagnet
    An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...

     that has several coils of wire connected in parallel.
  • A Maxwell coil
    Maxwell coil
    A Maxwell coil is a device for producing a large volume of almost constant magnetic field.-Description:A constant-field Maxwell coil set consists of three coils oriented on the surface of a virtual sphere...

    is a device for producing almost a constant magnetic field.
  • A Micro coil use in security devices.
  • A Oudin coil
    Oudin coil
    An Oudin coil, also called an Oudin oscillator or Oudin resonator, is a disruptive discharge coil wired as a transformer designed to produce high voltage arcs and discharges, similar to a Tesla coil...

    is a disruptive discharge coil.
  • The polyphase coil
    Polyphase coil
    Polyphase coils are electrical coils connected together in a polyphase system such as a generator or motor. In modern systems, the number of phases is usually three or a multiple of three. Each phase carries a sinusoidal alternating current whose phase is delayed relative to one of its neighbours...

    s
    are connected together in a polyphase system such as a generator or motor.
  • A relay coil is the copper winding part of a relay
    Relay
    A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...

     that produces a magnetic field that actuates the mechanism.
  • A Repeating coil
    Repeating coil
    In telecommunications, a repeating coil is a voice-frequency transformer characterized by a closed magnetic core, a pair of identical balanced primary windings, a pair of identical but not necessarily balanced secondary windings, and low transmission loss at voice frequencies...

    is a voice-frequency transformer.
  • A Rogowski coil
    Rogowski coil
    A Rogowski coil, named after Walter Rogowski, is an electrical device for measuring alternating current or high speed current pulses. It consists of a helical coil of wire with the lead from one end returning through the centre of the coil to the other end, so that both terminals are at the same...

    is an electrical device for measuring alternating current.
  • A Rook coil is a high Q
    Q factor
    In physics and engineering the quality factor or Q factor is a dimensionless parameter that describes how under-damped an oscillator or resonator is, or equivalently, characterizes a resonator's bandwidth relative to its center frequency....

     coil wave wound cylindrical coil often used for crystal sets.
  • A single coil
    Single coil
    A single coil pickup is a type of magnetic transducer, or pickup, for the electric guitar and the electric bass. It electromagnetically converts the vibration of the strings to an electric signal...

    is a type of pickup for the electric guitar
    Electric guitar
    An electric guitar is a guitar that uses the principle of direct electromagnetic induction to convert vibrations of its metal strings into electric audio signals. The signal generated by an electric guitar is too weak to drive a loudspeaker, so it is amplified before sending it to a loudspeaker...

    .
  • A solenoid
    Solenoid
    A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create...

    is a mechanical device, based on a coil of wire, that usually converts energy into linear motion, however solenoids also come in a rotary motion (normally up to a turn of 90 degrees).
  • A Spider coil is a high Q
    Q factor
    In physics and engineering the quality factor or Q factor is a dimensionless parameter that describes how under-damped an oscillator or resonator is, or equivalently, characterizes a resonator's bandwidth relative to its center frequency....

     wave wound flat coil often used for crystal sets, that somewhat resembles a spider's web.
  • A telephone
    Telephone
    The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

     cord
    is usually manufactured in a coiled fashion, as to allow maximum length while taking up minimum space when not in use.
  • A Tesla coil
    Tesla coil
    A Tesla coil is a type of resonant transformer circuit invented by Nikola Tesla around 1891. It is used to produce high voltage, low current, high frequency alternating current electricity. Tesla coils produce higher current than the other source of high voltage discharges, electrostatic machines...

    is category of disruptive discharge coils, usually denoting a resonant transformer that generates very high voltages at radio frequencies.
  • A Universal coil or a Dual Lateral coil is a self supporting coil used for high voltage applications.
  • A voice coil
    Voice coil
    A voice coil is the coil of wire attached to the apex of a loudspeaker cone. It provides the motive force to the cone by the reaction of a magnetic field to the current passing through it...

    which is mounted to the moving cone of a loudspeaker
    Loudspeaker
    A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...

    .


Other applications of coils exist in the field of electromagnetic devices. A coilgun
Coilgun
A coilgun is a type of projectile accelerator that consists of one or more coils used as electromagnets in the configuration of a synchronous linear motor which accelerate a magnetic projectile to high velocity...

 is a type of cannon that uses a series of electromagnetic coils to accelerate a magnetic shell to very high velocities. The filament of an incandescent light bulb
Incandescent light bulb
The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...

 has usually the shape of a coiled coil, in order to fit the long filament in a small space.

Further reading
  • Querfurth, William, "Coil winding; a description of coil winding procedures, winding machines and associated equipment for the electronic industry" (2d ed.). Chicago, G. Stevens Mfg. Co., 1958.
  • Weymouth, F. Marten, "Drum armatures and commutators (theory and practice) : a complete treatise on the theory and construction of drum winding, and of commutators for closed-coil armatures, together with a full résumé of some of the principal points involved in their design; and an exposition of armature reactions and sparking". London, "The Electrician" Printing and Publishing Co., 1893.
  • "Coil winding proceedings". International Coil Winding Association.
  • Chandler, R. H., "Coil coating review, 1970-76". Braintree, R. H. Chandler Ltd, 1977.


External links

Chemistry, biology and medicine


A chemistry coil
Coil (chemistry)
A coil, in chemistry, is a tube, frequently in spiral form, used commonly to cool steam originating from a distillation and thus to condense it in liquid form. Usually it is of copper or another material that conducts heat easily. Coils are often used in chemical processes in batch reaction or...

 is a tube of spiral form, used commonly to cool originating steam of the distillation and thus to condense them in liquid form. In the study of how molecules interact with each other
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

, there are a few specific references to organic coils. During self-assembly
Self-assembly
Self-assembly is a term used to describe processes in which a disordered system of pre-existing components forms an organized structure or pattern as a consequence of specific, local interactions among the components themselves, without external direction...

, organic elements organize to form this structural pattern. Molecular self-assembly
Molecular self-assembly
Molecular self-assembly is the process by which molecules adopt a defined arrangement without guidance or management from an outside source. There are two types of self-assembly, intramolecular self-assembly and intermolecular self-assembly...

 assembles the molecules, without guidance or management from an outside source, into these shapes.

Examples of these structural patterns include:
  • A coiled coil
    Coiled coil
    A coiled coil is a structural motif in proteins, in which 2-7 alpha-helices are coiled together like the strands of a rope . Many coiled coil type proteins are involved in important biological functions such as the regulation of gene expression e.g. transcription factors...

    is a structural motif
    Structural motif
    In a chain-like biological molecule, such as a protein or nucleic acid, a structural motif is a supersecondary structure, which appears also in a variety of other molecules...

     found in many proteins.
  • A random coil
    Random coil
    A random coil is a polymer conformation where the monomer subunits are oriented randomly while still being bonded to adjacent units. It is not one specific shape, but a statistical distribution of shapes for all the chains in a population of macromolecules...

    is a polymer
    Polymer
    A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

     conformation where the monomer
    Monomer
    A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...

    s are arranged at random.


As an acronym, COIL denotes the Chemical Oxygen Iodine Laser
Chemical oxygen iodine laser
Chemical oxygen iodine laser, or COIL, is an infrared chemical laser. As the beam is infrared, it cannot be seen with the naked eye. It is capable of output power scaling up to megawatts in continuous mode...

.

In medicine, the Guglielmi Detachable Coil
Guglielmi Detachable Coil
A Guglielmi Detachable Coil, or GDC, is a platinum coil commonly used in intracranial non-invasive surgery for the occlusion of brain aneurysms. It was invented by Italian interventional neuroradiologist Dr...

is a platinum coil commonly used in intracranial non-invasive surgery, for the occlusion of brain aneurysms.

Pottery


Coiling
Coiling (pottery)
Coiling is a method of creating pottery. It has been used to shape clay into vessels for many of thousands of years. It ranges from Africa to Greece and from China to New Mexico. They have used this method in a variety of ways. Using the coiling technique, it is possible to build thicker or taller...

 is an old and wide spread technique to form relatively tall and thin-walled vessels with good control over shape and wall thickness.

Seafaring


In sailing terms, a rope is said to be "cheesed down" when it needs to be stowed away neatly.

External links


  • For the definition of Coil and words related to it, see Wiktionary.