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<title>Inductive coupling</title>

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<p>In <a href="Electrical_engineering" title="Electrical engineering">electrical engineering</a>, two <a href="Electrical_conductor" title="Electrical conductor">conductors</a> are said to be <b>inductively coupled</b> or <b>magnetically coupled</b><sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> when they are configured in a way such that change in current through one wire <a href="Faraday's_law_of_induction" title="Faraday's law of induction">induces</a> a voltage across the ends of the other wire through <a href="Electromagnetic_induction" title="Electromagnetic induction">electromagnetic induction</a>. A changing current through the first wire creates a changing <a href="Magnetic_field" title="Magnetic field">magnetic field</a> around it by <a href="Ampere's_circuital_law" class="mw-redirect" title="Ampere's circuital law">Ampere's circuital law</a>. The changing magnetic field induces an <a href="Electromotive_force" title="Electromotive force">electromotive force</a> (EMF) <a href="Voltage" title="Voltage">voltage</a> in the second wire by <a href="Faraday's_law_of_induction" title="Faraday's law of induction">Faraday's law of induction</a>. The amount of inductive coupling between two conductors is measured by their <a href="Mutual_inductance" class="mw-redirect" title="Mutual inductance">mutual inductance</a>.

</p><p>The coupling between two wires can be increased by winding them into <a href="Electromagnetic_coil" title="Electromagnetic coil">coils</a> 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 <a href="Magnetic_core" title="Magnetic core">magnetic core</a> of a <a href="Ferromagnetic" class="mw-redirect" title="Ferromagnetic">ferromagnetic</a> material like iron or <a href="Ferrite_(magnet)" title="Ferrite (magnet)">ferrite</a> 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 <a href="Transformer_types#Interstage_and_coupling_transformer" title="Transformer types">transformer</a>, 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 <a href="Crosstalk" title="Crosstalk">cross-talk</a>, and is a form of <a href="Electromagnetic_interference" title="Electromagnetic interference">electromagnetic interference</a>.

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<p>An inductively coupled <a href="Transponder" title="Transponder">transponder</a> consists of a solid state <a href="Transceiver" title="Transceiver">transceiver</a> chip connected to a large coil that functions as an <a href="Antenna_(radio)" title="Antenna (radio)">antenna</a>. 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.

</p><p>Magnetic coupling between two <a href="Magnet" title="Magnet">magnets</a> can also be used to mechanically transfer power without contact, as in the <a href="Magnetic_gear" title="Magnetic gear">magnetic gear</a>.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>

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<p>Inductive coupling is widely used throughout electrical technology; examples include:

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<ul><li><a href="Electric_motor" title="Electric motor">Electric motors</a> and <a href="Electrical_generator" class="mw-redirect" title="Electrical generator">generators</a></li>

<li><a href="Inductive_charging" title="Inductive charging">Inductive charging</a> products</li>

<li><a href="Induction_cooker" class="mw-redirect" title="Induction cooker">Induction cookers</a> and <a href="Induction_heating" title="Induction heating">induction heating</a> systems</li>

<li><a href="Induction_loop" title="Induction loop">Induction loop</a> communication systems</li>

<li><a href="Metal_detectors" class="mw-redirect" title="Metal detectors">Metal detectors</a></li>

<li><a href="Transformer" title="Transformer">Transformers</a></li>

<li><a href="Wireless_power_transfer#Inductive_coupling" title="Wireless power transfer">Wireless power transfer</a></li>

<li>Testing:

<ul><li><a href="Radio-frequency_identification" title="Radio-frequency identification">Radio-frequency identification</a></li>

<li>Presence of voltage</li></ul></li></ul>

<li class="gallerycaption">Uses of inductive coupling</li>

<div class="gallerytext">Power <a href="Transformer" title="Transformer">transformer</a> transfers power from one winding to the other by inductive coupling </div>

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<div class="gallerytext">Antenna transformer inductively couples antenna of AM radio station to transmitter</div>

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<div class="gallerytext"><a href="Clamp_meter" class="mw-redirect" title="Clamp meter">clamp ammeter</a> measuring current by inductive coupling</div>

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<div class="gallerytext"><a href="Distribution_transformer" title="Distribution transformer">Utility transformer</a> cutaway shows inductively coupled coils </div>

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<div class="gallerytext"><a href="Variometer" title="Variometer">Variometer</a> from radio allows inductive coupling to be varied </div>

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<div class="gallerytext"><a href="Ignition_coil" title="Ignition coil">Ignition coil</a> of truck produces high spark plug voltage by inductive coupling</div>

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<div class="gallerytext"><a href="Inductive_charging" title="Inductive charging">Inductive charger</a> wirelessly charging a cellphone</div>

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<div class="gallerytext">Prototype <a href="Railgun" title="Railgun">railgun</a> accelerates a projectile by inductive coupling</div>

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<div class="gallerytext"><a href="Induction_furnace" title="Induction furnace">Induction furnace</a> heats silicon by eddy currents</div>

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<div class="gallerytext"><a href="Induction_stove" class="mw-redirect" title="Induction stove">Induction stove</a> boiling water by inductive coupling to pan</div>

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<div class="mw-heading mw-heading2"><h2 id="Low-frequency_induction">Low-frequency induction</h2></div>

<p>Low-frequency induction can be a dangerous form of inductive coupling when it happens inadvertently. For example, if a long-distance metal <a href="Pipeline_transport" class="mw-redirect" title="Pipeline transport">pipeline</a> is installed along a <a href="Right-of-way_(property_access)" class="mw-redirect" title="Right-of-way (property access)">right of way</a> 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.

</p><p>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 <a href="Mains_frequency" class="mw-redirect" title="Mains frequency">mains frequency</a>. <a href="Twisted_pair" title="Twisted pair">Twisted wires</a> (e.g. in <a href="Networking_cable#Twisted_pair" title="Networking cable">networking cables</a>) are an effective way of reducing the interference as signals induced in the successive twists cancel. <a href="Magnetic_shielding" class="mw-redirect" title="Magnetic shielding">Magnetic shielding</a> 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.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup>

</p><p>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.

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<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite id="CITEREFZverev2005" class="citation book cs1">Zverev, A.I. (2005) [1967]. <i>Handbook of filter synthesis</i>. Wiley. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>9780471749424</bdi>.</cite></span>

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<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://machinedesign.com/motorsdrives/could-magnetic-gears-make-wind-turbines-say-goodbye-mechanical-gearboxes">"Could Magnetic Gears Make Wind Turbines Say Goodbye to Mechanical Gearboxes?"</a>. machinedesign.com. 19 June 2014.</cite></span>

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<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><cite id="CITEREFHorowitzHill1989" class="citation book cs1">Horowitz, Paul; Hill, Winfield (1989). <i>The Art of Electronics Second Edition</i>. Press Syndicate of the University of Caimbridge. p. 456. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0521370957</bdi>.</cite></span>

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