Ag Area of the air gap, or the cross sectional area of the air gap perpendicular to the flux path, is the average cross sectional area of that portion of the air gap within which the application interaction occurs. Area is measured in sq. cm. in a plane
normal to the central flux line of the air gap.
Am Area of the magnet, is the cross sectional area of the magnet perpendicular to the central flux line, measured in sq. cm. at any point along its length. In design, Am is usually
considered the area at the neutral section of the magnet.
B Magnetic induction, is the magnetic field induced by a field strength, H, at a given point. It is the vector sum, at each point within the substance, of the magnetic field strength and resultant intrinsic induction. Magnetic induction is the flux per
unit area normal to the direction of the magnetic path.
Bd Remanent induction, is any magnetic induction that remains in a magnetic material after removal of an applied saturating magnetic field, Hs. (Bd is the magnetic induction at any point on the demagnetization curve; measured in gauss.)
Bd/Hd Slope of the operating line, is the ratio of the remanent induction, Bd, to a demagnetizing force, Hd. It is also referred to as the permeance coefficient, shear line, load line and unit permeance.
Bi (or J) Intrinsic induction, is 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 relation is expressed by the equation:
Bi = B –H
where: Bi = intrinsic induction in gauss; B = magnetic induction
in gauss; H = field strength in oersteds.
F Leakage factor, accounts for flux leakage from the magnetic circuit. It is the ratio between the magnetic flux at the magnet neutral section and the average flux present in the air gap. F = (Bm Am)/(B Ag).
F Magnetomotive force, (magnetic potential difference), is the line integral of the field strength, H, between any two points, p1 and p2.
F = ∫ H dl
F = magnetomotive force in gilberts
H = field strength in oersteds
dl = an element of length between the two points, in centimeters.
H Magnetic field strength, (magnetizing or demagnetizing force), is the measure of the vector magnetic quantity that determines the ability of an electric current, or a magnetic body, to induce a magnetic field at a given point; measured in oersteds.
Hci Intrinsic coercive force of a material indicates its resistance to demagnetization. It is equal to the demagnetizing force which reduces the intrinsic induction, Bi, in the material to zero after magnetizing to saturation; measured in oersteds.
ℓm/D Dimension ratio, is the ratio of the length of a magnet to its diameter, or the diameter of a circle of equivalent crosssectional area. For simple geometries, such as bars and rods, the dimension ratio is related to the slope of the operating line of the magnet, Bd/Ha.
R Reluctance, is somewhat analogous to electrical resistance. It is the quantity that determines the magnetic flux, ¿, resulting from a given magnetomotive force, F.
where: R = F/¿
R = reluctance, in gilberts per maxwell
F = magnetomotive force, in gilberts
¿ = flux, in maxwells
ø magnetic flux, is a contrived but measurable concept that has evolved in an attempt to describe the “flow” of a magnetic field. Mathematically, it is the surface integral of the normal component of the magnetic induction, B, over an area, A.
ø = ∫ ∫ B • dA
ø = magnetic flux, in maxwells
B = magnetic induction, in gauss
dA = an element of area, in square centimeters
When the magnetic induction, B, is uniformly distributed and
is normal to the area, A, the flux, ø = BA.
A gaussmeter is an instrument that measures the instantaneous value of magnetic induction, B. Its principle of operation is usually based on one of the following: the Halleffect, nuclear magnetic resonance (NMR), or the rotating coil principle.
A hysteresis loop is a closed curve obtained for a material by plotting (usually to rectangular coordinates) corresponding values of magnetic induction, B, for ordinates and magnetizing force, H, for abscissa when the material is passing through a
complete cycle between definite limits of either magnetizing force, H, or magnetic induction, B.
Irreversible losses are defined as partial demagnetization of the magnet, caused by exposure to high or low temperatures external fields or other factors. These losses are recoverable by remagnetization. Magnets can be stabilized against irreversible losses by partial demagnetization induced by temperature cycles or by external magnetic fields
A keeper is a piece (or pieces) of soft iron that is placed on or between the pole faces of a permanent magnet to decrease the reluctance of the air gap and thereby reduce the flux leakage from the magnet. It also makes the magnet less susceptible to demagnetizing influences.
The operating line for a given permanent magnet circuit is a straight line passing through the origin of the demagnetization curve with a slope of negative Bd/Hd. (Also known as permeance coefficient line.)
The temperature coefficient is a factor which describes the reversible change in a magnetic property with a change in temperature. The magnetic property spontaneously returns when the temperature is cycled to its original point. It usually is expressed as the percentage change per unit of temperature.