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Electromagnetic coupling occurs when an electromagnetic field in one wire induces an electric charge in another without physical contact. It is common in AC circuits and is the basis of transformers, motors, and communication devices. It can also cause interference, known as electromagnetic interference (EMI).
Electromagnetic coupling is a phenomenon common to electrical wiring and circuits in which an electromagnetic field in one causes an electric charge in another. It is often referred to as inductive coupling because the process occurs due to electrical inductance, where there is a transfer of electromagnetic properties from one location to another without physical contact taking place. For electromagnetic coupling to occur, there must be a change in the electromagnetic field that is generating it. For this reason, direct current (DC) devices do not produce the effect, but it is common in alternating current (AC) circuits. The principle of electromagnetic coupling was discovered by Michael Faraday and Joseph Henry in 1831 and is known as Faraday’s Law.
When an AC current in one circuit or wire induces a voltage in another wire, it is usually due to both being in close proximity to each other, such as in the electrical windings of transformers. This isn’t always true, however, and unintentional distant coupling, called cross talk, can also occur with radio and telephone broadcasts. Intentional electromagnetic coupling is the principle upon which transformers are based, where current can be stepped up or down in voltage in a secondary wire winding based on the current level in a primary winding on the device.
Since electromagnetic radiation is a dual condition in nature where electromagnetic waves are composed of both electric and magnetic properties, the couplings are also of two types. An electrical coupling occurs when a positive or negative charge density in a wire or circuit changes and this repels like charges in another wire in the circuit. The process of repelling how charges in the nearby wire cause them to move within the wire, and this is the definition of what electric current is. This form of current flow is often referred to as charge coupling or capacitance coupling.
Magnetic coupling is the flip side of this effect. When a current flows in a wire, it creates a magnetic field. With AC current, this magnetic field will fluctuate and cause a changing magnetic field in the coupled circuits or wires. Magnetic fields are directly perpendicular to electric fields in electromagnetic coupling, so altering a magnetic field in one circuit can alter current flow in another.
The principle of electromagnetic coupling is what all modern electric motors, relays and transformers are built on. Electric generators also use it, as do a wide variety of communications-related devices, from citizen band (CB) radios to televisions and wireless locks for buildings and cars. It can also be detrimental to the operation of a circuit and cause interference to telecommunications. In this case, it is often referred to as electromagnetic interference (EMI). However, not all EMI is unintentional, as it can also be used as a form of carrier wave to increase signal strength.
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