In
electrical engineering
Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...
, two
conductors are said to be inductively coupled or magnetically coupled when they are configured in a way such that change in current through one wire
induces
Electromagnetic or magnetic induction is the production of an electromotive force (emf) across an electrical conductor in a changing magnetic field.
Michael Faraday is generally credited with the discovery of induction in 1831, and James Clerk ...
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 or
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...
) 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
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 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
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the 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
cross-talk
In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, indu ...
, and is a form of
electromagnetic interference.
An inductively coupled
transponder consists of a solid state
transceiver chip connected to a large coil that functions as an
antenna
Antenna ( antennas or antennae) may refer to:
Science and engineering
* Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves
* Antennae Galaxies, the name of two collid ...
. 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
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nicke ...
s can also be used to mechanically transfer power without contact, as in the
magnetic gear.
Uses
Inductive coupling is widely used throughout electrical technology; examples include:
*
Electric motor
An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate f ...
s and
generators
*
Inductive charging products
*
Induction cookers and
induction heating systems
*
Induction loop communication systems
*
Metal detectors
*
Transformer
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
s
*
Wireless power transfer
* Testing:
**
Radio-frequency identification
** Presence of voltage
Low-frequency induction
Low-frequency induction can be a dangerous form of inductive coupling when it happens inadvertently. For example, if metal long-distance
pipeline is installed along a
right of way
Right of way is the legal right, established by grant from a landowner or long usage (i.e. by prescription), to pass along a specific route through property belonging to another.
A similar ''right of access'' also exists on land held by a gov ...
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.
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 could begin to display 60Hz pickup. Twisted wires are an effective way of reducing the interference as signals induced in the successive twists cancel. Using 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.
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.
References
{{DEFAULTSORT:Inductive Coupling
Electronic engineering
Electromagnetic compatibility
Wireless energy transfer