Air Gap: A low permeability gap in the flux path of a magnetic circuit. Often air, but inclusive of other materials such as paint, aluminum, etc.
Anisotropic Magnet: A magnet having a preferred direction of magnetic orientation, so that the magnetic characteristics are optimum in one preferred direction. top
Closed Circuit: This exists when the flux path external to a permanent magnet is confined within high permeability materials that compose the magnet circuit.
Coercive Force, Hc: The demagnetizing force, measured in Oersteds, necessary to reduce observed induction, B, to zero after the magnet has previously been brought to saturation.
Curie Temperature, Tc: The temperature at which the parallel alignment of elementary magnetic moments completely disappears, and the material is no longer able to hold magnetization. top
Demagnetization Curve: The second quadrant of the hysteresis loop, generally describing the behavior of magnetic characteristics in actual use. Also known as the B-H Curve. top
Eddy Currents: Circulating electrical currents that are induced in electrically conductive elements when exposed to changing magnetic fields, creating an opposing force to the magnetic flux. Eddy currents can be harnessed to perform useful work (such as damping of movement), or may be unwanted consequences of certain designs, which should be accounted for or minimized.
Electromagnet: A magnet, consisting of a solenoid with an iron core, which has a magnetic field existing only during the time of current flow through the coil.
Energy Product: Indicates the energy that a magnetic material can supply to an external magnetic circuit when operating at any point on its demagnetization curve. Calculated as Bd x Hd, and measured in Mega Gauss Oersteds, MGOe. top
Ferromagnetic Material: A material whose permeability is very much larger than 1 (from 60 to several thousand times 1), and which exhibits hysteresis phenomena.
Flux: The condition existing in a medium subjected to a magnetizing force. This quantity is characterized by the fact that an electromotive force is induced in a conductor surrounding the flux at any time the flux changes in magnitude. The cgs unit of flux is the Maxwell.
Fluxmeter: An instrument that measures the change of flux linkage with a search coil.
Fringing Fields: Leakage flux particularly associated with edge effects in a magnetic circuit. top
Gauss: Lines of magnetic flux per square centimeter, cgs unit of flux density, equivalent to lines per square inch in the English system, and Webers per square meter or Tesla in the SI system.
Gaussmeter: An instrument that measures the instantaneous value of magnetic induction, B. Its principle of operation is usually based on one of the following: the Hall effect, nuclear magnetic resonance (NMR), or the rotating coil principle.
Hysteresis Loop: A closed curve obtained for a material by plotting corresponding values of magnetic induction, B, (on the abscissa) against magnetizing force, H, (on the ordinate). top
Induction, B: The magnetic flux per unit area of a section normal to the direction of flux. Measured in Gauss, in the cgs system of units.
Initial Permeability: Refers to the slope of the curve in the first quadrant as a material acquires magnetization. High initial permeability materials generate less hysteresis loss in an AC field. (See also Permeability)
Intrinsic Coercive Force, Hci: Measured in Oersteds in the cgs system, this is a measure of the material's inherent ability to resist demagnetization. It is the demagnetization force corresponding to zero intrinsic induction in the magnetic material after saturation. Practical consequences of high Hci values are seen in greater temperature stability for a given class of material, and greater stability in dynamic operating conditions.
Intrinsic Induction, Bi: The contribution of the magnetic material to the total magnetic induction, B. It is the vector difference between the magnetic induction in the material and the magnetic induction that would exist in a vacuum under the same field strength, H. This relationship is expressed as: Bi = B-H.
Irreversible Loss: Defined as the partial demagnetization of a magnet caused by external fields or other factors. These losses are only recoverable by re-magnetization. Magnets can be stabilized to prevent the variation of performance caused by irreversible losses.
Isotropic Magnet: A magnet material whose magnetic properties are the same in any direction, and which can therefore be magnetized in any direction without loss of magnetic characteristics.
Keeper: A piece of soft iron that is placed on or between the poles of a magnet, decreasing the reluctance of the air gap and thereby reducing the flux leakage from the magnet.
Knee of the Demagnetization Curve: The point at which the B-H curve ceases to be linear. All magnet materials, even if their second quadrant curves are straight line at room temperature, develop a knee at some temperature. Alnico 5 exhibits a knee at room temperature. If the operating point of a magnet falls below the knee, small changes in H produce large changes in B, and the magnet will not be able to recover its original flux output without re-magnetization. top
Leakage Flux: That portion of the magnetic flux that is lost through leakage in the magnetic circuit due to saturation or air-gaps, and is therefore unable to be used.
Length of air-gap, Lg: The length of the path of the central flux line in the air-gap.
Load Line: A line drawn from the origin of the Demagnetization Curve with a slope of -B/H, the intersection of which with the B-H curve represents the operating point of the magnet. Also see Permeance Coefficient. top