Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

magneto plasma
a plasma medium that in the presence of a static magnetic field behaves like an anisotropic dielectric medium whose dielectric function is a tensor.
magnetohydrodynamic MHD machine
a form of electric machine in which a stream of electrically conductive gas or liquid is passed through pairs of orthogonally positioned magnetic poles and electrodes. In an MHD generator, the fluid is forced by the prime mover to produce a DC across the electrodes. In the MHD motor, a current across the electrodes through the fluid forces the stream to flow.
magneto-hydrodynamic (MHD) generator
a heat-to-electricity conversion device with an intermediate kinetic energy stage. In the MHD generator, a partially conducting gas is heated by a fuel-fired source or a nuclear reactor to convert the heat energy to kinetic energy, and then passed between the poles of an electromagnet, which converts some of the kinetic energy to electrical energy. The electrical energy is collected through a pair of electrodes situated in the gas channel.
magnetomotive force (MMF)
a magnetic circuit term referring to that phenomenon that pushes magnetic flux through the reluctance of the circuit path. MMF is analogous to the concept of electromotive force (voltage) in an electric circuit. For a magnetic core with a single coil of N turns, carrying current I, the MMF is NI, with units of amperes (sometimes expressed as ampere-turns).
magnetoresistance
the change in electrical resistance in a conducting element experiencing a change in applied magnetic field. This is most pronounced when the magnetic field is perpendicular to current flow.
magnetostriction
a change in the length of a ferromagnetic material as the flux changes under the influence of an applied magnetic field, or resulting from domain formation after cooling from above Curie temperature. In an AC device, the steel in the core expands and contracts twice each cycle, creating audible noise (e.g., transformer hum).
magnetostrictive smart material
one of a class of materials with self-adaptively modifiable elastic properties in response to a magnetic field applied in proportion to sensed stress-strain information.
magnetotransport
motion of electrons or holes in a conducting material in the presence of an applied magnetic field.
magnetron
any arrangement of magnets in a sputter deposition or etch system that provides the magnetic field required to trap electrons in closed loops near the cathode, thus enhancing deposition/etch rates.
normal demagnetization curve
the second quadrant portion of the hysteresis loop generated when magnetic induction (B)is plotted against applied field (H ), which is mathematically related to the intrinsic curve; used to determine the performance of a magnet in a magnetic circuit.
nuclear magnetic resonance
the phenomenon in which the resonant frequency of nuclear spin is proportional to the frequency of an applied magnetic field.
See magnetic resonance imaging
permanent magnet (PM)
a magnet that produces an external magnetic field by virtue of the alignment of domains inside the material and retains its magnetism after being subjected to demagnetizing fields.
permanent magnet AC motor
a generic term used to describe both permanent magnet synchronous motors and brushless DC motors.
permanent magnet brushless DC machine
a machine that is similar in structure to a permanent magnet synchronous machine, containing armature windings on the stator and permanent magnets on the rotor. The permanent magnet brushless DC machine, however, is characterized by a trapezoidal flux density distribution in the airgap instead of the sinusoidal distribution of the synchronous machine. In operation, a DC voltage is applied sequentially to the stator coils to create a rotating field that pulls the rotor with it. To correctly operate, the brushless DC machine requires sensors to determine the rotor position so that the proper stator phases may be excited.
permanent magnet DC machine
a DC machine in which the field excitation in the stator is provided by permanent magnets instead of electromagnets.
permanent magnet DC motor

See permanent magnet DC machine
permanent magnet machine
a machine that uses permanent magnets to establish the field. In DC machines, the permanent magnets are placed on the stator, while on AC synchronous machines they are placed on the rotor.
permanent magnet stepper motor
a stepper motor that has a permanent magnet assembly on the rotor.
permanent magnet synchronous machine
a polyphase AC motor with rotor mounted permanent magnets and sinusoidal distribution of stator phase windings. The field windings in the rotor are replaced by permanent magnets to provide the field excitation in these machines.
rare-earth magnet
a magnet that has any of the rare-earth elements in its composition. Typically stronger than other magnet materials, these include neodymium iron boron and samarium cobalt.
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