What Are Electromagnets?

Electromagnets are devices that generate a magnetic field through the flow of electric current, rather than through a material's permanent magnetic properties. When current passes through a conductor, it produces a surrounding magnetic field governed by Ampere's law; winding that conductor into a coil concentrates and amplifies the field along the coil's axis. Unlike permanent magnets, electromagnets can be switched on and off, and their field strength can be adjusted by varying the current, making them among the most controllable magnetic devices available to engineers.

The principle was demonstrated by Hans Christian Ørsted in 1820, when he observed that a compass needle deflected in the presence of a current-carrying wire. William Sturgeon built the first practical electromagnet in 1824, winding insulated copper wire around an iron core to produce a device that could lift many times its own weight. The iron core acts as a ferromagnetic amplifier: its high permeability channels the magnetic flux and increases field intensity far beyond what air-core coils achieve at the same current.

Coil Design and Core Materials

The magnetic field of an electromagnet depends on the number of turns in the coil, the current flowing through it, and the permeability of the core material. Engineers specify coil geometry to achieve a target field at a given location, balancing resistance, inductance, and thermal dissipation. Solenoids, Helmholtz coils, and saddle coils represent distinct configurations chosen for their field uniformity or penetration depth. Superconducting electromagnets, cooled with liquid helium or liquid nitrogen, eliminate resistive losses entirely and can sustain fields of 20 tesla or more, far exceeding the few-tesla limit of conventional copper-wound designs. The NIST Magnetic Field Metrology program maintains reference standards for field calibration across this range of coil designs.

Magnetic Confinement

One of the most demanding applications of electromagnet technology is magnetic confinement, the use of strong, precisely shaped magnetic fields to hold a plasma away from physical walls. In tokamak reactors, arrays of superconducting toroidal and poloidal coils generate the interlocking fields required to confine fusion plasma at temperatures exceeding 100 million degrees Celsius. The engineering challenge is sustaining a stable magnetic configuration against plasma instabilities while managing the enormous mechanical forces the coils exert on one another. Static magnetic trap configurations, including anti-Helmholtz coil pairs, are also used in atomic physics research to confine ultracold neutral atoms for precision measurement and quantum information experiments.

Magnetic Levitation

Electromagnets drive magnetic levitation systems by generating a repulsive or attractive force that counteracts gravity on a conducting or ferromagnetic object. Active feedback control is essential in attractive-type levitation: because the attractive force increases as separation decreases, the configuration is inherently unstable without a sensor-controller loop that modulates the coil current in real time. Electrodynamic levitation, used in some high-speed rail systems, relies instead on induced eddy currents: a moving superconducting coil induces currents in a conductive guideway, and the interaction between the two fields produces a lift force. Studies on lateral stiffness and damping in electromagnetic levitation systems have informed the design of suspension systems for both transportation and precision instrumentation. A separate approach examined in research on repulsive magnetic levitation using air-core electromagnets demonstrates that air-core designs can avoid ferromagnetic saturation at high field strengths.

Applications

Electromagnets have applications in a wide range of disciplines, including:

• Magnetic levitation vehicles (maglev trains) for high-speed ground transportation
• Medical imaging via MRI scanner magnets, which use superconducting coils to generate stable whole-body fields
• Industrial lifting and sorting of ferrous materials in recycling, steel production, and logistics
• Particle accelerators and synchrotrons, where bending and focusing magnets guide charged-particle beams
• Actuators in relays, solenoid valves, and electric motors across industrial and consumer devices