Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

magnetic dipole
an arrangement of one or more magnets to form a magnet system that produces a magnetic field with one pair of opposite poles.
magnetic drive

See magnetic torque coupling
magnetic field
magnetic force field where lines of magnetism exist.
magnetic field intensity
a force field that is a measure of the magnitude and direction of the force imparted upon an elemental current normalized to the elemental current's value. Depends on material characteristics. The units are amperes per meter.
magnetic flux
the integral of the component of magnetic flux density perpendicular to a surface, over the given surface.
magnetic flux density
a vector quantifying a magnetic field, so that a particle carrying unit charge experiences unit force when traveling with unit velocity in a direction perpendicular to the magnetic field characterized by unit magnetic flux density. It has the units of volt-seconds per square meter in the SI system of units.
magnetic induction
the flux density within a magnetic material when driven by an external applied field or by its self demagnetizing field, which is the vector sum of the applied field and the intrinsic induction.
magnetic leakage

See leakage
magnetic length
the effective distance between the north and south poles within a magnet, which varies from 0.7 (alnico) to 1.0 (Nd-FeB, SmCo, hard ferrite) times the physical length of the magnet.
magnetic levitation
(1) noncontact support of an object using magnetic forces. Abbreviated as maglev.

(2) a method of melting metals without contacting a surface. A cone-shaped high-frequency coil produces eddy currents in the metal which are strong enough to both suspend and melt it, generally in a neutral atmosphere.

(3) one of several techniques of suspending a driveshaft within a bearing so that no contact is made between the shaft and other surfaces. magnetic bearing

(4) one of several techniques for suspending a railroad train above its tracks so that wheels are not needed. Typically, superconducting magnets are needed, and propulsion is by a linear induction motor cf whose armature lies along the rails.
magnetic loss
losses in magnetic flux in a magnetic circuit, primarily due to magnetic leakage and fringing.
See core loss
magnetic moment
for a current-carrying coil in an external magnetic field, the ratio of the torque sensed by the coil to the flux density of the external field. In permanent magnets, the product of the polar flux and the magnetic length; the product of the intrinsic flux density and the magnet volume.
magnetic monopole
a magnet system that produces a magnetic field of a single polarity. Although nonexistent, may be approximated by one pole of a very long magnet.
magnetic motor starter
motor starter that uses electromechanical devices such as contactors and relays.
magnetic orientation
the preferred direction of magnetization for an anisotropic magnetic material.
magnetic overload
an overload sensor in a motor controller used to shut off the motor in event of an over current condition. With a magnetic overload, the sensor uses a magnetic coil to sense the overload condition, then trips the overload contact(s).
See overload relay
magnetic permeability tensor
relationship between the magnetic field vector and the magnetic flux density vector in a medium with no hysteresis; flux density divided by the magnetic field in scalar media.
magnetic polarization vector
an auxiliary vector in electromagnetics that accounts for the presence of atomic circulating currents in a material. Macroscopically, the magnetic polarization vector is equal to the average number of magnetic dipole moments per unit volume.
magnetic resonance imaging (MRI)
(1) a form of medical imaging with tomographic display that represents the density and bonding of protons (primarily in water) in the tissues of the body, based upon the ability of certain atomic nuclei in a magnetic field to absorb and reemit electromagnetic radiation at specific frequencies. nuclear magnetic resonance

(2) an imaging modality that uses a pulsed radio frequency magnetic field to selectively change the orientation of the magnetization vectors of protons within the object under study. The change in net magnetic moment as the protons relax back to their original orientation is detected and used to form an image.
magnetic saturation
the condition in a magnetic material when an increase in the magnetizing force does not result in a useful increase in the magnetic induction of the material.
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