Electromagnet Technologies

Summary

Electromagnetic technology is fundamental to the maintenance and progress of modern society. Electromagnetism is one of the essential characteristics of the physical nature of matter, and it is fair to say that everything, including life itself, is dependent upon it. The ability to harness electromagnetism has led to the production of most modern technology.

Definition and Basic Principles

Magnetism is a fundamental field effect produced by the movement of an electrical charge, whether that charge is within individual atoms such as iron or is the movement of large quantities of electrons through an electrical conductor. The electrical field effect is intimately related to that of magnetism. The two can exist independently of each other, but when the electrical field is generated by the movement of a charge, the electrical field is always accompanied by a magnetic field. Together, they are referred to as an electromagnetic field. The precise mathematical relationship between electric and magnetic fields allows electricity to be used to generate magnetic fields of specific strengths, commonly through the use of conductor coils, in which the flow of electricity follows a circular path. The method is well understood and is the basic operating principle of both electric motors and electric generators.

When used with magnetically susceptible materials, this method transmits magnetic effects that work for a variety of purposes. Bulk material handling can be carried out in this way. On a much smaller scale, the same method permits the manipulation of data bits on magnetic recording tape and hard disk drives. This fine degree of control is made possible through the combination of digital technology and the relationship between electric and magnetic fields.

Background and History

The relationship between electric current and magnetic fields was first observed by Danish physicist and chemist Hans Christian Oersted (1777–1851), who noted, in 1820, how a compass placed near an electrified coil of wires responded to those wires. When electricity was made to flow through the coil, these wires changed the direction in which the compass pointed. Oersted reasoned that a magnetic field must exist around an electrified coil.

In 1821, English chemist and physicist Michael Faraday (1791–1867) found that he could make an electromagnetic field interact with a permanent magnetic field, inducing motion in one or the other of the magnetized objects. By controlling the electrical current in the electromagnet, the permanent magnet can be made to spin about. This became the operating principle of the electric motor. In 1831, Faraday found that moving a permanent magnetic field through a coil of wire caused an electrical current to flow in the wire, the principle by which electric generators function. In 1824, English physicist and inventor William Sturgeon (1783–1850) discovered that an electromagnet constructed around a core of solid magnetic material produced a much stronger magnetic field than either one alone could produce.

Since these initial discoveries, the study of electromagnetism has refined the details of the mathematical relationship between electricity and magnetism as it is known today. Research continues to refine understanding of the phenomena, enabling its use in new and valuable ways.

How It Works

The basic principles of electromagnetism are the same today as they have always been because electromagnetism is a fundamental property of matter. The movement of an electrical charge through a conducting medium induces a magnetic field around the conductor. On an atomic scale, this occurs as a function of the electronic and nuclear structure of the atoms, in which the movement of an electron in a specific atomic orbital is similar in principle to the movement of an electron through a conducting material. On larger scales, magnetism is induced by the movement of electrons through the material as an electrical current.

Although much is known about the relationship of electricity and magnetism, a definitive understanding has so far escaped rigorous analysis by physicists and mathematicians. The relationship is apparently related to the wave-particle duality described by quantum mechanics, in which electrons are deemed to have the properties of both electromagnetic waves and physical particles. The allowed energy levels of electrons within any quantum shell are determined by two quantum values, one of which is designated the magnetic quantum number. This fundamental relationship is also reflected in the electromagnetic spectrum, a continuum of electromagnetic wave phenomena that includes all forms of light, radio waves, microwaves, X-rays, and so on. Whereas the electromagnetic spectrum is well described by the mathematics of wave mechanics, there remains no clear comprehension of what it actually is, and the best theoretical analysis of it is that it is a field effect consisting of both an electric component and a magnetic component. This, however, is more than sufficient to facilitate the physical manipulation and use of electromagnetism in many forms.

Ampere's circuit law states that the magnetic field intensity around a closed circuit is determined by the sum of the currents at each point around that circuit. This defines a strict relationship between electrical current and the magnetic field that is produced around the conductor by that current. Because electrical current is a physical quantity that can be precisely controlled on scales that currently range from single electrons to large currents, the corresponding magnetic fields can be equally precisely controlled.

Electrical current exists in two forms: direct current and alternating current. In direct current, the movement of electrons in a conductor occurs in one direction only at a constant rate that is determined by the potential difference across the circuit and the resistance of the components that make up that circuit. The flow of direct current through a linear conductor generates a similarly constant magnetic field around that conductor.

In alternating current, the movement of electrons alternates direction at a set sinusoidal wave frequency. In North America, this frequency is 60 hertz, which means that electrons reverse the direction of their movement in the conductor 120 times each second, effectively oscillating back and forth through the wires. Because of this, the vector direction of the magnetic field around those conductors also reverses at the same rate. This oscillation requires that the phase of the cycle be factored into the design and operating principles of electric motors and other machines that use alternating current.

Both forms of electrical current can be used to induce a strong magnetic field in a magnetic material that has been surrounded by electrical conductors. The classic example of this effect is to wrap a large steel nail with insulated copper wire connected to the terminals of a battery so that as electrical current flows through the coil, the nail becomes magnetic. The same principle applies to all scales in which electromagnets are utilized to perform a function.

Applications and Products

The applications of electromagnetic technology are as varied and widespread as the nature of electromagnetic phenomena. Every possible variation of electromagnetism provides an opportunity for the development of some useful application.

Electrical Power Generation. The movement of a magnetic field across a conductor induces an electrical current flow in that conductor. This is the operating principle of every electrical generator. A variety of methods are used to convert the mechanical energy of motion into electrical energy, typically in generating stations.

Hydroelectric power uses the force provided by falling water to drive the magnetic rotors of generators. Other plants use the combustion of fuels to generate steam that is then used to drive electrical generators. Nuclear power plants use nuclear fission for the same purpose. Still other power generation projects use renewable resources such as wind and ocean tides to operate electrical generators.

Solar energy can be used in two ways to generate electricity. In regions with a high amount of sunlight, reflectors can be used to focus that energy on a point to produce steam or some other gaseous material under pressure; this material can then drive an electrical generator. Alternatively, and more commonly, semiconductor solar panels are used to capture the electromagnetic property of sunlight and drive electrons through the system to generate electrical current.

Material Handling. Electromagnetism has long been used on a fairly crude scale for the handling and manipulation of materials. A common sight in metal recycling yards is a crane using a large electromagnet to pick up and move quantities of magnetically susceptible materials, such as scrap iron and steel, from one location to another. Such electromagnets are powerful enough to lift a ton or more of material at a time. In more refined applications, smaller electromagnets operating on exactly the same principle are often incorporated into automated processes under robotic control to manipulate and move individual metal parts within a production process.

Machine Operational Control. Electromagnetic technology is often used to control machinery. Operation is normally achieved through the use of solenoids and solenoid-operated relays. A solenoid is an electromagnet coil that acts on a movable core. When current flows in the coil, the core responds to the magnetic field by shifting its position as though to leave the coil. This motion can be used to close a switch or to apply pressure according to the magnetic field strength in the coil.

When the solenoid and switch are enclosed in a discrete unit, the structure is known as a relay. It controls the function of electrical circuitry and operates valves in hydraulic or pneumatic systems. In these applications, the extremely fine control of electrical current facilitates the design and application of many solenoids. These solenoids range from very small (used in micromachinery) and those used in typical video equipment and CD players to very large ones (used to stabilize and operate components of large, heavy machinery).

A second use of electromagnetic technology in machine control utilizes the opposition of magnetic fields to affect braking force for precision machines like high-speed trains. Normal frictional braking in such situations would have serious negative effects on the interacting components, resulting in warping, scarring, material transfer welding, and other damage. Electromagnetic braking forces avoid any actual contact between components and can be adjusted continuously by control of the electrical current being applied.

Magnetic Media. The most important aspect of electromagnetic technology is also the smallest and most rigidly controlled application. Magnetic media began with the magnetic wire and progressed to magnetic recording tape. In these applications, a substrate material in tape form, typically a ribbon of an unreactive plastic film, is given a coating that contains fine granules of a magnetically susceptible material, such as iron oxide or chromium dioxide. Exposure of the material to a magnetic field imparts the corresponding directionality and magnitude of that magnetic field to the individual granules in the coating. As the medium moves past an electromagnetic “read-write head” at a constant speed, the variation of the magnetic properties over time is embedded into the medium. When played back through the system, the read-write head senses the variation in magnetic patterns in the medium. It translates that into an electronic signal converted into the corresponding audio and video information. This is the analog methodology used in the operation of audio and videotape recording.

With the development of digital technology, electromagnetic control of read-write heads has come to mean the ability to record and retrieve data as single bits. This was realized with the development of hard drive and floppy disk-drive technologies. In these applications, an extremely fine read-write head records a magnetic signal into the magnetic medium of a spinning disk at a strictly defined location. The signal consists of a series of minute magnetic fields whose vector orientations correspond to the 1s and 0s of binary code; one orientation for 1, the opposite orientation for 0. Also recorded are identifying codes that allow the read-write head to locate the position of specific data on the disk when requested. The electrical control of the read-write head is such that it can record and relocate a single digit on the disk. Given that hard disks typically spin at 3,000 rpm (revolutions per minute) and that the recovery of specific data is usually achieved in milliseconds, one can readily grasp the finesse with which the system is constructed.

Floppy disk technology never reached the scale of hard disk technology, but it provided a means to make data readily portable. Other technologies, particularly USB (universal serial bus) flash drives, replaced the floppy drive as the portable data medium. Still, the hard disk drive remains a modern staple in data storage. New magnetic media and electromagnetic methods technology continue to increase the amount of data storage space on hard disks. This has progressed from merely a few hundred megabytes (106 bytes) of storage to average systems commonly storing two or more terabytes (two trillion bytes). The largest storage capacity is twenty terabytes on a single drive.

Social Context and Future Prospects

Electromagnetic technologies and modern society are inextricably linked, particularly in communications. Despite modern telecommunications swiftly becoming entirely digital, the transmission of digital signals is still carried out through electromagnetic carriers. These can be essentially any frequency, although regulations control what range of the electromagnetic spectrum can be used for what purpose. Cellular telephones, for example, use the microwave region of the spectrum only, while other devices are restricted to operate in only the infrared region or the visible light region of the electromagnetic spectrum.

Electromagnetic technologies, materials, and methods continue to emerge, impacting many sectors of society, including transportation and the military. For example, high-speed Maglev trains use the repulsion between electrically generated magnetic fields to levitate the vehicle so that there is no physical contact between the machine and the track. Electromagnetic technologies work to control the acceleration, speed, deceleration, and other motions of the machinery. High-speed transit by such machines, first popularized in Asia, was integrated globally in the 2020s along with electric-powered buses.

Electromagnetic technologies are essential in military communications, intelligence, and analytical reconnaissance. Weaponry is an important field of military electromagnetic technology, including lasers and electromagnetic pulse (EMP) devices. The US military has successfully demonstrated a tactical high-power operational responder (THOR) and the Mjölnir, which use high-energy microwave lasers to defend against drones and other attacks. Other technology includes jamming, jamming detection, and anti-jamming devices as well as satellite radio navigation suppression and electronic masking.

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