Electromagnetic coupling is used in communication related devices such as CB radios.
Electromagnetic coupling is a common phenomenon in electrical wiring and circuits in which an electromagnetic field in one results in an electrical charge in another. It is often called inductive coupling because the process occurs due to electrical inductance, where a transfer of electromagnetic properties from one place to another occurs without physical contact. For electromagnetic coupling to occur, there must be a change in the electromagnetic field that generates 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 common phenomenon in electrical wiring and circuits in which 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 because the two are close together, as in the electrical windings of transformers. This is not always true, and coupling at an unwanted distance, called crosstalk, can also occur with radio and telephone transmissions. Intentional electromagnetic coupling is the principle on which transformers are based, where current can increase or decrease voltage in a secondary lead 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, the couplings are also of two types. An electrical coupling occurs when the positive or negative charge density in one wire or circuit changes, and this repels charges in another wire in the circuit. The process of repelling like 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 called charge coupling or capacitance coupling.
Magnetic coupling is the flip side of this effect. As current flows in a wire, it creates a magnetic field. With alternating current, this magnetic field will fluctuate and cause a change in the magnetic field in attached 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 electrical motors, relays and transformers are based on. Electric generators also use it, as do a wide variety of communications-related devices, from Citizens Band (CB) radios to televisions and wireless door 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 called electromagnetic interference (EMI). However, not all EMI is unintentional, as it can also be used as a carrier waveform to increase signal strength.