The Spark and Magnetism of Electric Coils

by Rebekah Fuller, IQS Editor

From hobby to industry, conductive devices called electric coils serve as key connections and transmitters within a myriad of circuits. In the most basic construction, a metal wire is wound around a core insulator, and the two ends are made into electrical connection terminals called “taps.” Without these devices, electrical current would not be able to be controlled, directed or transformed in electronics, automotive, medical, computer, appliance, telecommunications and industrial manufacturing applications. You wouldn’t be able to start your car without the spark that induction coils, or ignition coils, provide for operation of ignition systems. And, manufacturing would cease if the workers couldn’t even turn on the machinery that makes everything the modern world relies on. No matter how big, complex or high-tech the equipment is, electrical current would be lost and useless to operate it without coils of conductive metal, most popularly copper and aluminum. These electrical coils can transmit heat, sound, electricity, magnetism and movement essential in electric motors, MRI machines, power plants and much more, including my grandpa’s metal detector, as he was a hobbyist of the metal detecting sport.

Photo courtesy of Sag Harbor Industries, Inc.

Metal detecting relies on a specialized coil called a search coil, also known as the Garrett coil, as it is used in this brand of popular ground search metal detectors. Electric coils don’t just transfer energy from the actual wires and connections, but from an applied magnetic field as well, since magnetism is a non-contact force. So, the flat circular coil at the end of a metal detector sends a magnetic field out into the ground and acts as a transmit coil and a receive coil. A transmit coil generates a magnetic field, and when a metallic object is within this field it creates a distortion that the receive coil senses. When the hobbyist hears the beeping signal he knows to start digging to possibly discover some old coins, someone’s long lost ring, or any number of items that fall out of pockets and are forgotten. My grandpa liked to search the sand dunes near his summer cottage, as all kinds of things are lost on bumpy dune buggy rides!

Metal Detector.

Magnetism is an essential component of an electric coil assembly, as its construction serves as an inductor or a reactor that can store magnetic energy when an electric current is passed through it. The loops of the coil help to create a strong magnetic field. This magnetism is used to actuate and cause movement in mechanisms, as in copper relay coils. Solenoid coils are smart devices that allow for remote activation of machinery. From simple voice coils used in loudspeakers to high-voltage generator stator windings, the construction of electrical coils ranges from the most basic single winding to the addition of secondary and even tertiary windings. An electric transformer, for example, is an electromagnetic component that consists of a primary and secondary winding that enables it to transfer electrical energy from one electric circuit to another by means of a magnetic coupling with no moving parts.

Photo courtesy of Sag Harbor Industries, Inc.

When coils have multiple windings, interlayer capacitance can be a problem. Think of this as interference between the layers. Spiral or helical shaped windings and flat wire are utilized to decrease interference. Other dangers that can occur in electrical coil construction involve unprotected wires in harsh environments. This is why manufacturers offer molded coils or encapsulated coils. Molded coils are encased in plastic coverings which seal the entire coil unit, and encapsulated coils are made from wire which has itself been enclosed in a polymer epoxy. From simple bobbin wound coils to high voltage coils and toroids that amplify inductance in power generation applications, electricity could not be regulated without these electromagnetic devices.

Photo courtesy of Sag Harbor Industries, Inc.

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