What is an electromagnetic coupling?

Electromagnetic coupling is used in communication-related devices such as CB radios.

Electromagnetic coupling is a phenomenon common to electrical wiring and circuits where an electromagnetic field in one results in an electrical charge in another. It is often referred to as inductive coupling because the process occurs due to electrical inductance, where a transfer of electromagnetic properties from one location to another occurs without physical contact occurring. 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.

Electromagnetic coupling is a phenomenon common to electrical wiring and circuits where an electromagnetic field in one results in an electrical charge in another.

When an AC current in one circuit or wire induces a voltage in another wire, it is usually due to the two being close together, as in the electrical windings of transformers. This is not always true, and coupling at an unintended distance, called crosstalk, can occur with radio and telephone transmissions as well. Intentional electromagnetic coupling is the principle on which transformers are based, where current can be increased or decreased in voltage in a secondary wire winding based on the level of current in a primary winding of the device.

As electromagnetic radiation is a dual condition in nature, where electromagnetic waves are composed of electrical and magnetic properties, couplings are also of two types. An electrical coupling occurs when a positive or negative charge density on one wire or circuit changes, and this repels charges on another wire in the circuit. The process of repelling similar charges on nearby wires causes them to move within the wire, and this is the definition of electric current. This form of current flow is often referred to as load coupling or capacitance coupling.

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Magnetic coupling is the flip side of this effect. As current flows in a wire, it generates a magnetic field. With AC current, this magnetic field will fluctuate and cause a change in the magnetic field in coupled circuits or wires. Magnetic fields are directly perpendicular to electric fields in electromagnetic coupling, so changing a magnetic field in one circuit can change 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 door locks for buildings and automobiles. It can also be harmful to the operation of a circuit and cause interference to telecommunications. In this case, it is often called electromagnetic interference (EMI). However, not all EMI is unintentional as it can be used as a carrier waveform to boost signal strength as well.

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