Editing Inductive coupling

{{Short description|Electrical circuit coupling using induction}}
{{Refimprove|date=December 2009}}
[[File:Lamp powered by induction 1910.jpg|thumb|Example of inductive coupling, 1910. The bottom coil is connected to AC power. The alternating magnetic field through the top coil induces current in it which lights the lamp.]]

In [[electrical engineering]], two [[electrical_conductor|conductors]] are said to be '''inductively coupled''' or '''magnetically coupled'''<ref>{{cite book |last=Zverev |first=A.I. |title=Handbook of filter synthesis |publisher=Wiley |orig-year=1967 |date=2005 |isbn=9780471749424}}</ref> when they are configured in a way such that change in current through one wire [[Faraday's law of induction|induces]] a voltage across the ends of the other wire through [[electromagnetic induction]].  A changing current through the first wire creates a changing [[magnetic field]] around it by [[Ampere's circuital law]].  The changing magnetic field induces an [[electromotive force]] (EMF) [[voltage]] in the second wire by [[Faraday's law of induction]].  The amount of inductive coupling between two conductors is measured by their [[mutual inductance]].  

The coupling between two wires can be increased by winding them into [[electromagnetic coil|coils]] and placing them close together on a common axis, so the magnetic field of one coil passes through the other coil.  Coupling can also be increased by a [[magnetic core]] of a [[ferromagnetic]] material like iron or [[ferrite (magnet)|ferrite]] in the coils, which increases the magnetic flux.   The two coils may be physically contained in a single unit, as in the primary and secondary windings of a [[Transformer types#Interstage and coupling transformer|transformer]], or may be separated.  Coupling may be intentional or unintentional. Unintentional inductive coupling can cause signals from one circuit to be induced into a nearby circuit, this is called [[crosstalk|cross-talk]], and is a form of [[electromagnetic interference]].

[[File: Coupling Coefficient.gif|thumb|300px|k is the [[Inductance#Coupling coefficient|coupling coefficient]], Le1 and Le2 is the [[leakage inductance]], M1 (M2) is the mutual inductance]]

An inductively coupled [[transponder]] consists of a solid state [[transceiver]] chip connected to a large coil that functions as an [[antenna (radio)|antenna]].  When brought within the oscillating magnetic field of a reader unit, the transceiver is powered up by energy inductively coupled into its antenna and transfers data back to the reader unit inductively.  

Magnetic coupling between two [[magnet]]s can also be used to mechanically transfer power without contact, as in the [[magnetic gear]].<ref>{{cite web |url=http://machinedesign.com/motorsdrives/could-magnetic-gears-make-wind-turbines-say-goodbye-mechanical-gearboxes|title= Could Magnetic Gears Make Wind Turbines Say Goodbye to Mechanical Gearboxes? |date= 19 June 2014 |publisher=machinedesign.com}}</ref>

==Uses==
Inductive coupling is widely used throughout electrical technology; examples include:
* [[Electric motor]]s and [[Electrical generator|generators]]
* [[Inductive charging]] products
* [[Induction cooker]]s and [[induction heating]] systems
* [[Induction loop]] communication systems
* [[Metal detectors]]
* [[Transformer]]s
* [[Wireless power transfer#Inductive coupling|Wireless power transfer]]
* Testing:
** [[Radio-frequency identification]]
** Presence of voltage

<gallery caption="Uses of inductive coupling" mode="packed" heights="180" >
File:Philips N4422 - power supply transformer-2098.jpg|Power [[transformer]] transfers power from one winding to the other by inductive coupling 
File:Antenna tuning coil - station WOR.jpg|Antenna transformer inductively couples antenna of AM radio station to transmitter
File:Fluke Clamp meter.jpg|[[Clamp meter|clamp ammeter]] measuring current by inductive coupling
File:Drehstromtransformater im Schnitt Hochspannung.jpg|[[Distribution transformer|Utility transformer]] cutaway shows inductively coupled coils 
File:Variometer.jpg|[[Variometer]] from radio allows inductive coupling to be varied 
File:Igncoil.jpg|[[Ignition coil]] of truck produces high spark plug voltage by inductive coupling
File:Phone wireless charge.jpg|[[Inductive charging|Inductive charger]] wirelessly charging a cellphone
File:Office of Naval Research-funded Electromagnetic Railgun launchers at the Naval Surface Warfare Center 02.jpg|Prototype [[railgun]] accelerates a projectile by inductive coupling
File:Silicon grown by Czochralski process 1956 closeup.jpg|[[Induction furnace]] heats silicon by eddy currents
File:Induction Cooktop Rolling Boil.jpg|[[Induction stove]] boiling water by inductive coupling to pan

</gallery>

==Low-frequency induction==
Low-frequency induction can be a dangerous form of inductive coupling when it happens inadvertently. For example, if a long-distance metal [[Pipeline transport|pipeline]] is installed along a [[Right-of-way (property access)|right of way]] in parallel with a high-voltage power line, the power line can induce current on the pipe. Since the pipe is a conductor, insulated by its protective coating from the earth, it acts as a secondary winding for a long, drawn out transformer whose primary winding is the power line. Voltages induced on the pipe are then a hazard to people operating valves or otherwise touching metal parts of the metal pipeline.{{citation needed|date=August 2019}}

Reducing low-frequency magnetic fields may be necessary when dealing with electronics, as sensitive circuits in close proximity to an instrument with a power transformer may pickup the [[mains frequency]]. [[Twisted pair|Twisted wires]] (e.g. in [[Networking cable#Twisted pair|networking cables]]) are an effective way of reducing the interference as signals induced in the successive twists cancel. [[Magnetic shielding]] is also an effective way of reducing unwanted inductive coupling, though moving the source of the magnetic field away from sensitive electronics is the simplest solution if possible.<ref>{{cite book |last1=Horowitz |first1=Paul |last2=Hill |first2=Winfield |title=The Art of Electronics Second Edition |date=1989 |publisher=Press Syndicate of the University of Caimbridge |isbn=0521370957 |page=456 }}</ref>

Although induced currents can be harmful, they can also be helpful. Electrical distribution line engineers use inductive coupling to tap power for cameras on towers and at substations that allow remote monitoring of the facilities. Using this they can watch from anywhere and not need to worry about changing camera batteries or solar panel maintenance.{{citation needed|date=August 2019}}

==References==
{{Reflist}}

{{DEFAULTSORT:Inductive Coupling}}
[[Category:Electronic engineering]]
[[Category:Electromagnetic compatibility]]
[[Category:Wireless energy transfer]]