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Introduction
This article provides everything you will need to know about electromagnetic coils and their use.
You will learn:
What is an Electromagnetic Coil?
Types of Electromagnetic Coils
How Electromagnetic Coils Work
Components of an Electromagnetic Coil
And much more …
Chapter 1: What is an Electromagnetic Coil?
An electromagnetic coil is an electrical coil that generates an electromagnetic field when electric current passes through it. The structure of an electromagnetic coil consists of a length of wire that is wound around a core, which can be a cylinder, bobbin, oval, or other shape that is made of metal, plastic, or no material and just air. The wire winding of an electromagnetic coil carries electrical current, which makes it possible for the coil to serve several distinct and unique functions.
The wires for electromagnetic coils are made of copper or aluminum that are wound around ferromagnetic material made of iron, nickel alloys, or cobalt, which are responsive to magnetization and increase the coils electromotive force (EMF) and its magnet flux. Each of the various metals is ferromagnetic that delivers a dense magnetic flux that enhances and amplifies the magnetic field of an electromagnetic coil.
Electromagnetic coils are an essential part of many electrical circuits. They control high power or high voltage circuits with a low power circuit. Transformers transfer electrical energy between circuits using an electromagnetic inductor.
Chapter 2: Types of Electromagnetic Coils
Electromagnetic coils are made by winding wire in a coil, spiral, or helix shape around a core. When electricity passes through the wires of the coil, it generates a magnetic field in the core. Electromagnetic coils are a type of inductor that is the simplest form of electric component since they consist of a conductor, or wire, that is wrapped around a ferromagnetic core. Regardless of their simplicity, electromagnetic coils are an essential part of a wide range of technological and electronic components due to their ability to adapt to a wide range of applications and their versatility.
Solenoid
A solenoid consists of wire wound around a cylindrical core and generates a magnetic field when electric current is applied to it. They are mechanical devices that are used to change electrical energy into linear mechanical energy. The central component of a solenoid is its plunger or armature, which produces the linear movement. They control the flow of fluids by opening and closing valves and are a normal part of hydraulic and pneumatic systems.
The mechanism of a solenoid is as simple as that of other electromagnetic coils. When a solenoid receives electric current, a movable rod is pulled toward one end of the solenoid activating the action by the solenoid. When the electric current is stopped, the magnetic field stops and the rod returns to its original position. As simple as this process is, it is a vital part of several mechanisms and devices.
Toroidal Electromagnetic Coils
The distinguishing characteristic of toroidal electromagnetic coils is their shape, which is that of a donut or circle. The typical electromagnetic coil has a cylinder-like core with aluminum or copper wire wrapped around it. When the coil receives electric current, it activates magnetic flux in the core.
Electromagnetic toroids are made of ferromagnetic metals including iron, ferrite, and other alloys, which have a toroid shape that contains the magnetic field. Their circular design minimizes magnetic interference from external magnetic sources and prevents loss. It is a more efficient design for energy transfer and provides far better performance. Aside from preventing leakage, the core shape significantly reduces electromagnetic interference from other electronic components.
The high efficiency, compact size, and reduction of electromagnetic interference makes toroidal electromagnetic coils the perfect choice for powering electronics, telecommunications, and audio equipment applications. The use of toroidal electromagnetic coils improves the performance of electronic systems.
U-Shaped Electromagnetic Coils
A U-shaped electromagnetic coil has two coils that operate separately and are located at each end of the U-shape. The two excitation coils have wires that are wrapped around the ends of the U-shaped core that is made of ferromagnetic material. The magnetic field for a U-shaped electromagnetic coil is centered at the tips or poles of the U-shape. When the coils of each arm of the U-shape are connected, a complete electromagnetic field is created.
For high magnetic permeability, the cores of U-shaped electromagnetic coils are made of iron or some form of magnetic alloy. As with all forms of electromagnetic coils, the wires for U-shaped coils are made of copper or aluminum, which are insulated to prevent short circuits and electrical losses.
Choke Electromagnetic Coil
A choke electromagnetic coil has the same structure as all forms of electromagnetic coils and is used to block high frequency AC current by limiting the rate of change over a frequency range. Although a choke blocks high frequency AC current, it allows lower frequency AC current and DC current through. They are often used in circuits where AC current has to be converted to DC current.
With DC power, chokes filter AC ripples in DC power supplies for steady and smooth DC output. With radio frequencies, chokes block all forms for current except for DC current. Chokes are also used to protect insulation from steep rises in current in a circuit by allowing a gradual rise.
Chokes are a unique form of inductor that is designed to block or choke high frequencies. They are a critical part of mode switching by filtering low and high frequencies in a circuit. In addition to their blocking function, chokes are used to separate different frequencies. The two broad classes of chokes are audio and radio where audio chokes block power line frequencies while radio chokes block radio frequencies and allow audio and DC current to pass.
Electromagnetic Coil Chuck
An electromagnetic coil chuck is a special form of electromagnetic coil that is used as part of a machining process. During the machining, grinding, and processing of workpieces, an electromagnetic chuck holds a workpiece in place during machining. It clamps the workpiece using magnetic force, which can be easily turned on and off when switching workpieces.
The surface of an electromagnetic chuck has a pattern of magnetic poles that are parallel or concentric, which ensures even distribution of the magnetic force for a secure and tight grip on the workpiece. The magnetic force has a control circuit that regulates the electric current for precision control of the chuck. The uses of electromagnetic chucks include grinding the surface of a ferromagnetic workpiece, milling, lathe operations, and electrical discharge machining.
C-Core Electromagnetic Coil
The coil for a C-core electromagnetic coil is wrapped around a ferromagnetic core that is in the shape of the letter C, a design that creates a concentrated magnetic field. Like a U-shaped core, the magnetic flux is highest at the end of the C-shape where the gap between the pole points will have a strong magnetic field.
Magnetic flux resistance is high at the air gap in the C-shape due to the resistance of magnetic flux to travel across the air gap since it prefers to move through the ferromagnetic iron core. The reluctance of the magnetic flux to travel across the air gap is similar to electrical resistance and the reason the magnetic field is stronger at the ends of the C-shape.
E-Shaped Electromagnetic Coils
The term E-shaped refers to a group of electromagnetic coils that have the shape of the letter E with the middle leg of the metal E having differing shapes including a cylinder, cube, rectangular cube, and stretched oval. The middle leg is generally where the wire winding is applied since its area is larger than the other two legs of the E-shape.
E-shaped cores for electromagnetic coils are easy to wind and have low core loss. Their air gap makes E-core electromagnetic coils ideal for switching regulator inductors, flyback transformers, and power inductors. The problem with E-shaped electromagnetic coils is their high leakage, a factor that limits their use and placement.
The many varieties of E-cores are used for a wide range of applications including transformers, inductors, and chokes. Planar E-core electromagnetic coils are thin and flat and ideal for gapped inductors where there is limited space.
Although there are disadvantages to E-shaped core electromagnetic coils, they are widely used due to their low cost and simple assembly. They are made of various ferromagnetic materials and have copper or aluminum wound wiring. E-shaped core electromagnetic coils can be quickly assembled for a variety of applications.
Potted Electromagnetic Coil
Potted electromagnetic coils are sealed with a liquid, such as silicone rubber, epoxy, and polyester. The potting of the core and wire winding protects an electromagnetic coil from exterior magnetic fields. The structure of a potted core is an easy way for adjusting the ferromagnetic core to meet the specific requirements of an application. They have good high circuit and temperature stability and are constructed around a wound bobbin.
The key to potted electromagnetic coils is their isolation from stray magnetic fields and the effects of surrounding circuit elements. Potted electromagnetic coils are used for differential induction, power transformers, power inductors, converter and inverter transformers, and transformers for telecom inductors.
Helmholtz Electromagnetic Coil
Helmholtz electromagnetic coils are used for scientific research and the calibration of magnetometers since they provide precision control and a uniform magnetic field. They do not follow the traditional structure of an electromagnetic coil but are made up of two identical, parallel, coaxial coils at a distance from each other that is equal to their radius. They produce a magnetic field between the coils when they receive electric current. The uniformity of the magnetic field is the reason that Helmholtz electromagnetic coils are used for experiments and calibration purposes.
The coils for a Helmholtz electromagnetic coil are wired in a series such that the current flowing through them moves in the same direction and are positioned such that the axis of each coil is aligned. The magnetic field that is generated simulates the effects of magnetic fields on electronic devices and systems, which is useful for electromechanical compatibility (EMC) testing.
Superconducting Electromagnetic Coils
The coils for superconducting electromagnetic coils are unlike the copper or aluminum coils found in all other types of electromagnetic coils. The wire for superconducting coils is made of niobium titanium or niobium tin alloys, which have no electrical resistance when cooled below critical temperatures. A cryogenic cooling system is used to keep the windings cold that uses helium or liquid nitrogen. Since superconducting electromagnetic coils do not generate heat, they do not lose energy.
The wires for superconducting electromagnetic coils have no electrical resistance, which makes it possible for them to generate larger electrical currents and create intense magnetic fields. Regardless of the high amount of electrical currents and magnetic fields generated, superconducting electromagnetic coils are inexpensive to operate because there is no loss of energy.
Superconducting electromagnetic coils are used to shape and direct particle beams and to determine the energy reach of an accelerator. The key to their use is their wires, which are made of niobium titanium, a highly resilient wire alloy. Niobium titanium magnet wire is made by forming the alloy into fine filaments that are embedded in solid copper. The fine structure carries current on its surface and is assisted by its copper surface.
In the 100 years since their discovery, superconducting magnets have found use in several industrial and medical applications. For many years, superconducting magnets have been used for magnetic resonance imaging (MRI), which enables doctors to observe the inner workings of the body. They produce magnetic levitation to power trains and are part of the operation of particle colliders.
Bobbin Coils
Bobbin electromagnetic coils have a ferromagnetic body to support their conductive wire winding that is wound around a cylindrical bobbin, which creates a compact and efficient electromagnetic coil. The design of bobbin coils maximizes energy conversion due to their precision windings. Bobbins for bobbin electromagnetic coils are made of many different types of ferromagnetic materials. They have a long life span and are a cost-effective industrial solution.
The versatility of bobbin electromagnetic coils is due to their many sizes, which can range from ones for speakers to ones for superconducting electromagnetic coils. The many varieties of bobbin electromagnetic coils make it possible to find a bobbin electromagnetic coil for any size and type of application.
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Chapter 3: Components of Electromagnetic Coils
The structure of electromagnetic coils is rather simple since it consists of a core around which wires are wound. Variations in the core material, core shape, and winding method differentiates the various types of electromagnetic coils. Most electromagnetic coils have copper or aluminum wires wound around their core with aluminum being used for its lightweight.
Cores
The cores of electromagnetic coils are made of ferromagnetic materials such as iron, nickel, and cobalt that are attracted to magnets. The ferromagnetic materials concentrate the magnetic flux to make a denser and more amplified magnetic field. Electromagnetic coil strength varies in relation to its type of core due to the number of flux lines that pass through the core.
When the core material of an electromagnetic coil has high permeability, the flux lines easily pass through. Core permeability is a measure of how easily a core can be magnetized and is the ratio of its magnetic flux density to the intensity of its magnetic field.
The type of core material can result in eddy current losses and hysteresis losses. Eddy current losses are caused by induced currents that generate heat and reduce coil efficiency. Hysteresis losses also generate heat caused by magnetization and demagnetization. The effectiveness and efficiency of an electromagnetic coil is severely damaged by the amount of heat it generates.
Iron Core – Iron cores, also known as magnetic cores, have a high level of magnetic permeability and can easily magnetize and demagnetize. As electric current passes through the coiled wire of an electromagnetic coil, the iron core creates a magnetic field and helps to concentrate and strengthen the magnetic field.
Powdered Metal Core – Powdered metal cores are normally made of iron powder and are made by combining grains of metal with insulating material. The performance of this type of core depends on the size of the grains and powdered metal.
Laminated Iron Alloy Cores – Laminated iron alloy cores are made up of sheets of metal that are pressed together in stamped layers that are laminated with insulation. The layered construction reduces eddy currents. They are constructed from various iron alloys such as nickel iron and silicon iron with silicon iron used for high power transformers.
Tape Wound Cores – Tape wound cores are made with strips of permeable alloys in thicknesses from 0.0005 in to 0.0004 in (0.0127 mm to 0.010016 mm) and are wound into toroidal shapes or bobbin cores. The air gap in tape wound cores is so small that it minimizes losses, fringing, leakage, distortion, and decreases the necessary magnetizing force. The magnetic path is within a single electrical winding.
Ferrite Cores – Ferrite cores are made of metal oxide ceramic and iron oxide that are mixed with nickel, manganese, cobalt, copper, or zinc. Of the various types, manganese zinc ferrite and nickel zinc ferrite are the most widely used. Ferrite cores have low permeability, low Curie temperature, and saturated flux density with high resistivity to help reduce eddy currents.
Wire
The wires for electromagnetic coils are made of copper or aluminum, which is wrapped around the ferromagnetic core. The wire of an electromagnetic coil is called the winding with each loop of the wire being referred to as a turn. In windings where the wires touch, the wires have to be insulated. When there is more than one winding, they are said to be magnetically coupled. Current passes from one winding to the other winding. To receive electrical current, the wires from the winding are connected to an external circuit.
Coils are classified by the frequency of current they receive, which are DC current, audio frequency (AF) current, or radio frequency (RF) current or by their function. Coil functions include electromagnets, inductors, transformers, machinery, micro coils, and transducers.
Copper Wire – The wide use of copper wire for the manufacture of electromagnetic coils is due to the wire’s high electrical conductivity, strength, and ductility and malleability that makes it easy to wind. Copper has low resistance and allows for easy flow of current. Of the various choices of wire for electromagnetic coils, copper is one of the least expensive after aluminum.
Aluminum Wire – The reason aluminum may be chosen for the manufacture of an electromagnetic coil is its weight and cost, which is much lower than copper. Like copper, aluminum is a soft malleable metal that can be easily shaped and wound. It is resistant to corrosion, like copper, due to its thin oxide layer. The use of aluminum wire in the manufacture of electromagnetic coils is in the production of speakers and voice coils.
Silver Wire – Silver wire has the highest electrical conductivity of all metals and the most common conductive metal. The cost of silver is the reason that it is not widely used for the production of electromagnetic coils and its susceptibility to oxidation.
Gold Wire – Like the other wire metals, gold is ductile and malleable, which makes it easy to form into wire. Gold doe not react with other elements and is resistant to corrosion and tarnishing, which makes it an ideal metal for producing electromagnetic coils. Aside from its tendency to contact surrounding components, gold is not widely used for electromagnetic coils due to its cost, limited availability, and weight, which is the heaviest of all metal types.
Niobium Titanium – Niobium titanium wire is a superconducting alloy that is used for electromagnetic coils and is normally wrapped in copper. It is an alloy of niobium and titanium, which has low magnetic field conducting properties, stable mechanical properties, flexibility, and low cost.
Assorted Other Metal Wires – Carbon, manganin, titanium, nickel chromium, kanthal, and nickel are other wire metals that are seldom used for the production of electromagnetic coils. The reason for the lack of use of these metals include cost, their resistivity, and low conductivity.
Winding
The manufacture of electromagnetic coils involves winding conductive wire around a ferromagnetic core, which is a simple and straightforward process. As with all forms of electrical components, the production of electromagnetic coils requires precision planning and close attention to details, which includes how the wire is wound. The winding of electromagnetic coils can take several forms and determines the efficiency and effectiveness of the coil.
The types of winding include cylindrical, disk, continuous, twisted, and helical. The choice of windings depends on the number of turns, size, cross sectional shape, number of parallel wires, cooling method, and electrical power. The winding has to be carefully planned to ensure the highest quality performance from electromagnetic coils.
Cylindrical Winding – Cylindrical winding is made up of coils that are laid closely in an axial direction. The turns are one or more parallel wires with the connections between the layers of wire being completed by transition. Cylindrical windings are simple, have good cooling, and have a low probability of short circuits. It is a compact winding with good insulation layers.
Disk Winding – Disk winding is separately wound single or paired coils with several turns wound one on another helically in a radial direction. The disk winding method is different from layered winding due to its increased mechanical strength in the axial direction.
Continuous Winding – Continuous winding is a series of coils wound in the axial direction and connected to each other with turns that are flat on top of each other in spiral order. The winding process of continuous winding provides a large end bearing surface and cooling surface with greater stability.
Helical Winding – Helical winding consists of turns wound along a helical path with oil channels between the wires. The coils have identical parallel rectangular wires laid flat in a radial direction. It is a multi-parallel winding due to the many parallel wires, which are laid concentrically at different distances from the axis.
Micro Coil Winding – The winding of micro coils requires special equipment, which necessitates reducing the thickness of the wires to reach the designed number turns. Micro windings can have over 1000 windings that are as small as the head of a pin.
Chapter 4: Electromagnetic Induction
Electromagnetic induction is a process where electric current can be induced or made to flow because of a changing magnetic field. Force in current carrying wire is due to electrons in the wire that move when a magnetic field is present. Moving wire through a magnetic field or changing magnetic field strength causes current to flow. There are two ways used to describe electromagnetic induction, which are Faraday’s law and Lenz’s law.
Faraday’s Law
Michael Faraday was an English scientist who is known as the father of electric motors, generators, transformers, and electrolysis and wrote the law of induction, which is known as the Faraday effect. He discovered that changing magnetic influence creates electric current while stationary magnetic influence does not. Current is the flow of electrons and is how electricity is carried. The flow of currents creates magnetic fields and induces or creates current in wires.
A magnet exerts force on electrons and moves them, which is easy with copper wire since it does not provide any resistance. For this to work, wires have to form a closed loop or complete circuit. The magnetic field works on all parts of the loop in different ways because of the direction of the magnetic field that pushes the current in different directions depending on the pole of the magnet.
Lenz’s Law
Faraday’s law explains the magnitude of the electromotive force (EMF) produced by electromagnetic induction. Lenz’s law explains the direction of the flow of electrons or current. His law says that the direction of current flow will oppose the change in flux that produced it. Any magnetic field produced by induced current flow will move in the opposite direction to the change in the original field.
Electromagnetic Coils
Electromagnetic coils are wire coils with one or more turns that are electrical conductors used to produce a magnetic field. As the number of turns of the wire increase, the strength of the magnetic field increases. Faraday learned that passing current through a wire creates a magnetic field due to charged particles in the wire. Since electrons in a wire move in one direction, a well-defined magnetic field is created around the wire. The strength of the magnetic field changes as the amount of current flowing through the wire changes.
In addition, the number of loops of the wire also affects the strength of the magnetic field, which is directly proportional to the number of wire loops. As with the amount of current, the strength of the magnetic field increases as more loops are added to the wire.
Faraday’s law of induction points out that changing the magnetic field induces an electromotive force (EMF) in the looped wire, which causes electrons to form and move. By adjusting the loop of wire and the angle between the loop and magnetic field, induces current flow. The property that induces the EMF is known as magnetic flux, which is the measure of the magnetic field running through the looped wires. When the field changes, electromotive force is induced.
Using magnets and coils of wire make it possible to generate electric current. As the movement of the magnet increases, the amount of current produced increases. It is this factor that has led to the wide use of electromagnetic coils in so many applications from electric motors and generators to transformers and sensor coils.
Of the many technical discoveries over the centuries, Faraday’s discovery has had the greatest impact on society and has changed society’s ability to produce and use electricity.
Chapter 5: Uses for Electromagnetic Coils
The types of electromagnetic coils change in relation to their size, shape, and material depending on the application for which they are designed. The industries that depend on electromagnetic coils the most are the medical, military, automobile, and aerospace industries. The use of electromagnetic coils for all industries, and these four in particular, is a critical aspect of the efficiency, effectiveness, and quality of their products.
Medical Industry
In medicine, transcranial magnetic stimulation (TMS) uses a magnetic field to stimulate nerve cells in the brain using a noninvasive method to help with symptoms of depression. The process includes placing an electromagnetic coil against the scalp. Magnetic pulses from the electromagnetic coil stimulate nerve cells.
Other medical uses for electromagnetic coils include heart rate monitors, radiation therapy systems, and MRI systems. Electromagnetic coils are used as diagnostic tools such as electrocardiograms (EKG) and electroencephalogram (ECG) to noninvasively capture images of the organs of the body.
Military
The days of soldiers sitting in foxholes preparing to charge the enemy are slowly fading away as technological advances change the face of combat. Electromagnetic environments (EME) have become an essential element in the tactics of modern warfare. EME is used to jam communications, protect communications, and missile defenses. In weaponry, electromagnetic coils are used for high velocity rail guns.
Auto Industry
In the auto industry, electromagnetic coils are found in every aspect of a vehicle from the engine and transmission to the electrical systems. This is especially true for electric vehicles that use a set of electromagnetic coils mounted on a shaft while another set in a housing that surrounds the shaft. A closed electrical circuit sends electrons along a wire coil that generates an electromagnetic field with a north and south pole. When the north and south polarity reverses on one of the electromagnetic coils, an EV motor uses the energy to rotate the shaft and convert electricity into torque, which turns the wheels of an EV car.
Other systems that use electromagnetic coils include ignition coils, alternators, starter motors, and power steering. Every aspect of the effective operation and performance of modern vehicles is dependent on electromagnetic coils.
Aerospace
Every part that goes into an aircraft has to adhere to a strict set of standards that ensure the proper performance and safety of an aircraft. In the aerospace industry, electromagnetic coils are used for transformers, inductors, and other electromagnetic parts, each of which follow Federal Aeronautics Administration (FAA) guidelines.
Conclusion
An electromagnetic coil is an electric coil that generates an electromagnetic field when electric current passes through it.
The wires for electromagnetic coils are made of copper or aluminum that are wound around ferromagnetic material made of iron, nickel alloys, or cobalt, which are responsive to magnetization and increase the coils magnet flux.
Electromagnetic coils are a type of inductor that is the simplest form of electric component since they consist of a conductor, or wire, that is wrapped around a ferromagnetic core.
Variations in the core material, core shape, and winding method differentiates the various types of electromagnetic coils.
As with all forms of electrical components, the production of electromagnetic coils requires precision planning and close attention to details, which includes how the wire is wound. The winding of electromagnetic coils can take several forms and determines the efficiency and effectiveness of the coil.
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