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The permeability of a magnetic material expressed in actual physical units, not relative to permeability of free space. The permeability of magnetic materials is rarely expressed in terms of absolute permeability. The usual mode is in terms of relative permeability.
A non-magnetic discontinuity in a ferro-magnetic circuit. For example, the space between the poles of a magnet, although filled with brass or wood or any other non-magnetic material, is nevertheless called an air gap.
The MKSA unit of magnetizing force, H. Ampere’s Law defines it. The ampere-turns are per meter of magnetic path length.
A high-temperature conditioning of magnetic material to relieve the stresses introduced when the material was formed. To prevent oxidation, the anneal is usually performed in a vacuum or inert-gas atmosphere.
The magnetic field induced by a field strength, H. It is the vector sum, of 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.
The average value of magnetic induction over the area of the air gap, Ag; or it is the magnetic induction measured at a specific point within
the air gap; measured in Gauss.
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 – Hem where; Bi = intrinsic induction in gauss (or tesla); B = magnetic induction in gauss (or tesla); Hem = field strength in oersteds (or kA/m).
The magnetic induction corresponding to zero magnetizing force in a magnetic material after saturation in a closed circuit; measured in gauss or tesla.
The frequency range over which an inductor or a capacitor exhibits low impedance.
A hysteresis loop of four quadrants. In practice, usually only the first and second or, more typically, only the second quadrant is shown.
Two strands of magnet wire wound side-by-side.
A switch-mode power supply (SMPS) that switches the input voltage to a higher output voltage. Also called an “up switcher.”
Centimeter-Gram-Second system, the oldest system of units and the one used for presenting powder core data. Only the units for magnetizing force, magnetic flux density, length, mass and time are utilized. Statvolts and abamperes can be avoided by using the simple
conversions and the magnetizing force equation provided in the Group Elite Powder Cores catalog.
A relatively expensive iron powder used in low-permeability, highfrequency powdered iron cores.
A process for making laminations from thin-gauge sheet. The lamination design is silk-screened onto the magnetic material, and lightsensitive chemicals are used to etch away the excess. This process is popular for low-volume laminations where tooling costs normally would be prohibitive.
Exists when the external flux path of a permanent magnet is confined within high permeability material.
The resistance of a magnetic material to demagnetization. It is equal to the value of H where the intrinsic curve intersects the H axis in the second quadrant of the hysteresis loop. It is expressed in oersteds or kiloAmps per meter (kA/m).
An often-used type of EMI filter, which is wound with both conductors of the power source in such a way that noise not common to both
conductors is filtered. The desired signal passes through the common mode filter unimpeded.
Power lost in a magnetic material when flux density changes. Also called iron losses or excitation losses.
The amps per unit of cross-section in the conductor.
Cores that are impregnated for mechanical rigidity.
A filter circuit that removes the AC ripple from a mostly DC current.
Refers to a magnetic circuit where comparatively more of the flux generated by the MMF fringes around the magnetic material instead of entering it.
That portion of the hysteresis loop which lies between the residual induction point, Br, and the coercive force point, Hc (normal curve) or
Hci (intrinsic curve). Points on the normal curve are designated by the coordinates Bd and Hd.
Mechanical air gap created by a small number of breaks in the magnetic path. In a standard C-core this number is generally two.
Major feature of powder cores. It is the cumulative effect of many small gaps distributed evenly throughout the core. In a typical MPP core, the number of separate air gaps results from the use of powder to construct the core and numbers in the millions. The result is minimal fringing flux density compared to a core with one or two air gaps in the magnetic path. (Flux that passes around a discrete air gap and through the sides of a core is “fringing.” Fringing flux enters the surrounding winding and causes a substantial amount of eddy current loss.)
A low-power isolation transformer used in electronic circuits to control semiconductors.
Core loss associated with the electrical resistivity of the magnetic material and induced voltages within the material. Eddy currents are
inversely proportional to material resistivity and proportional to rate of change of flux density. Eddy current and hysteresis losses are the two
major core loss factors. Eddy current loss becomes dominant in powder cores as the frequency increases.
A magnet formed by current flowing through a conductor. The electrical conductor may be wire, copper plate or strips of foil and may exist with a permeable material such as steel to conduct the field to desired areas. The magnetic field exists only so long as current flows through the coil.
Filter unwanted noise (EMI = electromagnetic interference).
Inductors used for power conversion rather than filtering or tuning.
A standardized method of evaluating unprocessed thin-gauge alloy for core loss and permeability.
The law that defines the relationship of the voltage induced across the winding of a core to the flux density within the core.
Ferromagnetic materials have atomic fields that align themselves parallel with externally applied fields creating a total magnetic field much greater than the applied field. Ferromagnetic materials have permeabilities much greater than 1. Above the Curie temperature, the ferromagnetic materials become paramagnetic.
In magnetics, the magnetic field. Flux implies flow which is not the case in magnetics. That is, no one has measured a magnetic “flow”. Flux is represented conceptually as “magnetic lines of force”. Flux density is measured in gauss or tesla.
In the special pulse test used to evaluate bobbin tape wound cores, this corresponds to Bₘ – Bᵣ
The numeric ratio of the amount of flux intercepted by the secondary winding and the total flux created by the applied amp-turns.
A device that functions as an inductor and a transformer.
An adhesive applied to the gap surfaces of C and E -cores to reduce mechanical noise levels. On small cores, it occasionally is used instead of banding to hold the two halves together.
See energy product and maximum energy product (BHmax).
A unit of magnetomotive force, F, in the CGS system.
MPP and HF cores are graded into increments of permeability within their normal ± 8% tolerance. It is expressed as a per cent deviation
from the nominal value.
A device that detects very low-level currents in the neutral conductor of an electrical line. This requires a very high-permeability core; generally Ni-Fe alloys are used.
Equal to the demagnetizing force required to reduce residual induction, Bᵣ, to zero; measured in oersteds (or kA/m). The material characteristic of coercivity is taken as the maximum coercivity — that value of H required to reduce the residual induction to zero after the material has been saturated (fully magnetized).
Indicates a material’s resistance to demagnetization. It is equal to the demagnetizing force which reduces the intrinsic induction, Bᵢ, in the material to zero; measured in oersteds (or kA/m). As for coercivity, the
maximum value of intrinsic coercivity is obtained after the material has been saturated (fully magnetized).
The magnetizing force required in the material, to magnetize to saturation; measured in oersteds (or kA/m).
A “permanent” magnet material that has an intrinsic coercivity greater than or equal to about 300 oersteds (24 kA/m).
A filter circuit (inductor and/or capacitor) that exhibits high Q. It is very frequency-sensitive and filters out or allows to pass, only those
frequencies within a narrow band.
Common symbol for maximum applied magnetizing force.
A closed curve obtained for a material by plotting (usually to rectangular coordinates) corresponding values of magnetic induction, B, for ordinate 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. If the material is not “driven” to saturation, it is said to be on a minor loop.
A filter circuit that removes unwanted frequencies (harmonics) from a mostly AC current. This would include some EMI filters.
Refers to magnetic materials that are metallurgically non-crystalline in nature.
Having properties which are dependent upon direction within the
material. See also, “isotropic” and “grain oriented”.
American Wire Gauge. A gauging system used to size magnet wire.
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 or tesla.)
Indicates the energy that a magnetic material can supply to an external magnetic circuit when operating at the Bd, Hd point on its demagnetization curve; measured in megaGauss-Oersteds (MGOe) or kiloJoules per cubic meter (kJ/m3).
The maximum product of (Bd x Hd) which can be obtained on the demagnetization curve, i.e. in the second quadrant of the hysteresis loop.
The maximum intrinsic induction possible in a material.
The frequency range over which an inductor or a capacitor exhibits high impedance.
Maximum induction.
The injection molded form upon which the coil is wound on many Ccores, pot cores, and laminations.
See Inductance bridge.
The process of reducing the magnetic output of a saturated permanent magnet to a precise value. Usually achieved by applying a reverse
magnetic field in stepped increments until the desired output is achieved. Also referred to as “tuning”.
A device that stores electrical energy in a manner similar to the way an inductor stores magnetic energy. The unit of capacitance is the farad.
The enclosure surrounding a toroidal tape core, which protects it from being stressed by the environment of the application. Sometimes
called a core “box.” Standard materials are nylon, glass-nylon, and aluminum.
An inductor.
The value of demagnetizing force that reduces residual induction to zero. The maximum coercive force, as measured on a saturated
magnet, is proportional to the remanent flux density. See “flux density.” It is expressed in oersteds or kiloAmps per meter (kA/m).
For larger cores, where injection molded bobbins are not available, fabricated coil base tubes are used on which to wind the turns of wire.
The winding on a mag amp or a saturable reactor used to control the amount of magnetic energy the core will absorb before saturating.
A core cross-section that has been “stepped” so it approximates a circle. This is desirable on high-voltage devices because it allows the
use of circular cross-section coils without the loss of coupling that would be apparent if the core had a squared cross-section. The round
coil is preferred because of corona.
Tc or Tc: The temperature above which ferromagnetic materials become paramagnetic, losing substantially all of their permanent
magnetic properties. Some references state materials become nonmagnetic above the Curie temperature.
Direct Current (DC) applied to the winding of a core in addition to any time-varying current. Inductance with DC bias is a common specification for powder cores. The inductance decreases or “rolls-off” gradually and predictably with increasing DC bias.
Annealing a magnetic material in the presence of a DC magnetic field to enhance magnetic properties.
A material condition where a ringing AC field has reduced the remanent induction to or near zero. A ringing AC field is a continually decreasing sinusoidal field. A pulsed DC field can be used to achieve gross demagnetization, but with much effort and with residual local magnetization.
Any deviation from the mathematical ideal of a real-world periodic waveform, which is specified as a per cent of the desired signal. Distortion can be expressed mathematically in terms of the harmonics of the fundamental frequency. This parameter is of considerable importance in instrumentation transformers.
The transformer that is immediately “upstream” of the wall outlet.
Maximum recommended usage (cycles) per unit time. Alternatively, the fraction of percent of “on” time, between 0 and 1 or 0 to 100%.
A method of observing the dynamic hysteresis loop properties of a soft magnetic core. This test is frequently used when cores are to be
matched in pairs, etc.
The electrical resistance to current flow in ohms per unit length of the material being evaluated.
The energy that a magnetic material can supply to an external magnetic circuit when operating at a point on its demagnetization curve; measured in megaGauss-Oersteds (MGOe). See also BHmax.
Cut cores are impregnated with an epoxy to make the core rigid. No insulative purpose is intended.
The current which produces magnetic energy (or flux) in an inductor.
A soft ferrite material that has lower permeability with very low eddycurrent loss. The common ferrites are nickel-zinc, manganese-zinc and magnesium-zinc ferrite.
A capacitor, quite often used in conjunction with an inductor, that filters unwanted frequencies by storing electrostatic energy.
In the special pulse test used to evaluate bobbin tape cores, this corresponds to Bₘ – Bᵣ.
Magnetic (B) – The fundamental magnetic force field. “Flux” means to flow (around a current carrying conductor, for example) and “density”
refers to its use with an enclosed area and Faraday’s Law to determine induced voltage. Also called the “induction field.” From Faraday’s Law, the MKSA unit of flux density is a volt-second per square meter per turn or “Tesla.” (The CGS unit of magnetic flux density is the Gauss. There are 10,000 Gauss per Tesla).
Remanent or residual ~ – The flux density that remains in a magnetic material after an applied magnetic field (magnetizing force) is removed.
Saturation – This is the flux density of maximum material magnetization. Magnetization (M) is the contribution of a magnetic material to the total flux density.
B = µo(H+M) in MKSA units.
B = H+4πM in CGS units.
Saturation magnetization is the maximum value of magnetization. Also, the term “saturation” is sometimes used as a reference to the decrease
of permeability with increasing magnetizing force. In an inductor, this corresponds to a decrease of inductance with current.
Magnetic (B) – The fundamental magnetic force field. “Flux” means to flow (around a current carrying conductor, for example) and “density”
refers to its use with an enclosed area and Faraday’s Law to determine induced voltage. Also called the “induction field.” From Faraday’s Law, the MKSA unit of flux density is a volt-second per square meter per turn or “Tesla.” (The CGS unit of magnetic flux density is the Gauss. There are 10,000 Gauss per Tesla).
Remanent or residual ~ – The flux density that remains in a magnetic material after an applied magnetic field (magnetizing force) is removed.
Saturation – This is the flux density of maximum material magnetization. Magnetization (M) is the contribution of a magnetic material to the total flux density.
B = µo(H+M) in MKSA units.
B = H+4πM in CGS units.
Saturation magnetization is the maximum value of magnetization. Also, the term “saturation” is sometimes used as a reference to the decrease
of permeability with increasing magnetizing force. In an inductor, this corresponds to a decrease of inductance with current.
An instrument that measures the change of flux linkage with a search coil. The current in the search coil caused by relative motion with the
magnet is integrated (totalized). Using a calibrated coil allows calculation of field and magnet properties.
The field(s) associated with the divergence of the flux from the shortest path between poles in a magnetic circuit. Where flux passes from a
high permeability into a lower permeability material, the flux redistributes. See also, Leakage Flux.
The unit of magnetic induction, B, in the CGS electromagnetic system. One gauss is equal to one maxwell per square centimeter or 10⁻⁴ tesla.
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.
1,000,000,000 Hz (gigaHertz).
Silicon steel or other granular magnetic material that has a preferred direction of magnetization.
(magnetizing or demagnetizing force) 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 (or kA/m)
The value of H corresponding to the remanent induction, Bd; measured in oersteds (or kA/m). See also BdHd.
A device which produces a voltage output dependent upon an applied DC voltage and an incident magnetic field. The magnitude of the
output is a function of the field strength and the angle of incidence with the Hall device.
A unit of inductance.
Hysteresis is the tendency of a magnetic material to retain its magnetization. Hysteresis causes the graph of magnetic flux density
versus magnetizing force to form a loop rather than a line. The area of the loop represents the difference between energy stored and energy
released per unit volume of material per cycle. This difference is called hysteresis loss. It is one of two major loss mechanisms in inductor
cores; the other is eddy current loss. Hysteresis loss is measured at low frequency to distinguish it from eddy current loss.
The property of a magnetic material by virtue of which the magnetic induction for a given magnetizing force depends upon the previous
conditions of magnetization.
