(BH) max Maximum energy product The BH is the maximum product of (BdHd) which can be obtained on the demagnetization curve.
A closed circuit condition A closed circuit condition exists when the external flux path of a permanent magnet is confined with high permeability material.
magnetic flux Magnetic flux is a contrived but measurable concept that has evolved in an attempt to describe the flowof a magnetic field. Mathematically, it is the surface integral of the normal component of the magnetic induction, B, over an area, A. A = B A, where: 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.
permeability Permeability is the general term used to express various relationships between magnetic induction, B, and the field strength, H.
recoil permeability Recoil permeability the average slope of the recoil hysteresis loop. Also known as the minor loop.
Air Gap An air gap is a low permeability gap in the flux path of a magnetic circuit. Often air, but inclusive of other materials such as paint, plating material, plastic, etc. In a linear solenoid, often the dominant part of the air gap is the distance between the front end of the actuator (plunger) and the bottom end of the solenoid (end core), also referred to as the STROKE.
Am Area of the magnet 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 magnet design, Am is usually considered the area at the neutral section of the magnet.
Ampere Turns Ampere Turns relates to the force produced by the solenoid or electromagnet which is the product of the current passing through the coil multiplied by the number of turns of wire inside the coil. The force of a solenoid is generally defined as Ampere Turns which resembles a graph that changes its value as the stroke changes. For each device the value of Ampere Turns is limited by the Duty Cycle.
Anisotropic Magnet An Anisotropic magnet having a preferred direction of magnetic orientation, so that the magnetic characteristics are optimum in one preferred direction.
Anisotropy Anisotrophy means having different properties depending on the inspected direction. Magnets which are anisotropic, or have an easy axis of magnetization, have their anisotropy developed by two methods: Shape and Magnetocrystalline.
Armature Armature is tthe moving part of a solenoid. This part is also referred to as the plunger in a linear solenoid.
Air Gap Area Air Gap Area, 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.
AT AT is the same as Ampere Turns.
B Magnetic induction B magnetic induction is 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 Remnant induction Bd Remnant 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 (Bd/Hd) is the ratio of the remnant induction, Bd, to a demagnetizing force, Hd. It is also referred to as the permeance coefficient, shear line, load line and unit permeance.
BdHd Energy product BdHd 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; measured in megagauss-oersteds.
Bg (Magnetic induction in the air gap) Magnetic induction in the air gap, (Bg) is the average value of magnetic induction over the area of the air gap, A; or it is the magnetic induction measured at a specific point within the air gap; measured in gauss.
Bi (or J) Intrinsic induction 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 .
Bis Bis ,or J Saturation intrinsic induction, is the maximum intrinsic induction possible in a material.
Bm, Recoil induction, Recoil induction (Bm) is the magnetic induction that remains in a magnetic material after magnetizing and conditioning for final use; this is measured in gauss.
Bo, Magnetic induction Magnetic induction (Bo) at the point of the maximum energy product (BH)max; measured in gauss.
Bobbin The spool on which the magnet wire is wound. Bobbins are usually made of plastic.
Br, Residual induction (or flux density), Residual induction is the magnetic induction corresponding to zero magnetizing force in a magnetic material after saturation in a closed circuit; measured in gauss.
Closed Circuit A closed circuit exists when the flux path external to a permanent magnet is confined within high permeability materials that compose the magnet circuit.
Coercive Force, Hc Coercive Force is 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 Tc is the temperature at which the parallel alignment of elementary magnetic moments completely disappears, and the material is no longer able to hold magnetization.
Demagnetization Curve The Demagnetization Curve is the second (or fourth) quadrant of a major hysteresis loop. Points on this curve are designated by the coordinates Bd and Hd.
Domains Magentic domains are areas in a magnetic alloy which have the same orientation. These are regions where the atomic moments of atoms cooperate and allow for a common magnetic moment. It is the domains which are rotated and manipulated by an external magnetizing field to create a useful magnet which has a net magnetic moment. In un-magnetized material the domains are un-oriented and cancel each other out. In this condition there is no net external field.
Duty Cycle Duty cycle is the ratio of “ON” time over the “ON + OFF” time (“TOTAL” time) for any one cycle of operation. Duty cycle is usually expressed in percentage. For example, the duty cycle of a solenoid being cycled “on” and “off” at the rate of 2 seconds ON and 18 seconds OFF is 2/(2+18)= 1/10 or 10%. The duty cycle for a unit being left in the ON position for an extended period of time (depending on the size of solenoid this could be ranging from a few seconds to a few minutes) would be considered 100% or CONTINUOUS. As the duty cycle of the application becomes smaller, the allowance for the input power increases. This is because the device is allowed to cool down in between ON times. The increase in input power will result in an increase in force generation. The specifications in this catalog generally show the force values for duty cycles of CONTINUOUS (100% or C), INTERMITTENT (50% or I), LONG PULSE (25% or L) and PULSE (10% or P).
Eddy Currents Eddy currents are circulating electrical currents that are induced in electrically conductive elements when exposed to changing magnetic fields, creating an opposing force to the magnetic flux. They 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 An electromagnet consists 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 Energy Product refers to when the magnetic material energy can supply to an external magnetic circuit when operating at any point on its demagnetization curve. This can be calculated as Bd x Hd, and measured in Mega Gauss Oersteds, MGOe.
F Leakage factor This is the ratio between the magnetic flux at the magnet neutral section and the average flux present in the air gap. F=(B mA m)/(B, A g). It accounts for flux leakage from the magnetic circuit
F Magneto motive force, (magnetic potential difference) The magnetic potential difference is the the line integral of the field strength, H, between any two points, p1 and p2. p2; F=? H dl; p1; F = magneto motive force in gilberts; H = field strength in oersteds; dl = an element of length between the two points, in centimeters.
F Reluctance factor The F Reluctane factor measuresthe apparent magnetic circuit reluctance. This is a result of the treatment of H, and H, as constants.
Ferromagnetic Material A material is considered ferromagnetic if the permeability is very much larger than 1 (from 60 to several thousand times 1), and has hysteresis phenomena.
Flux When a medium is subjected to a magnetizing force, it is in a condition of flux. This condition is characterized when 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.
Flux Meter An instrument that measures the change of flux linkage with a search coil.
Fringing Fields Fringing Fields are leakage flux; it is usually associated with edge effects in a magnetic circuit.
Gauss The gauss is the unit of magnetic induction, B, in the cgs electromagnetic system. One gauss is equal to one maxwell per square centimeter.
Gauss meter A gauss meter 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 Hall effect, nuclear magnetic resonance (NMR), or the rotating coil principle.
Gilbert The unit of magneto motive force, F, in the cgs electromagnetic system is known as a gilbert.
H Magnetic Field Strength 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. This is measured in oersteds.
Hc Coercive force Hc Coercive force of a material, is equal to the demagnetizing force required to reduce residual induction, Br to zero in a magnetic field after magnetizing to saturation; measured in oersteds.
Hci Intrinsic coerecive force The Hci Intrinsic coercive force of a material determines its demagnetization resistance. 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.
Hd Hd is the value of H corresponding to the remnant induction, Bd; on the demagnetization curve. This is measured in oersteds.
Hmv Hmv is the value of H corresponding to the recoil induction, B. This is also measured in oersteds.
Ho The magnetic field strength at the point of the maximum energy product (BH)max is known as Ho; measured in oersteds.
Hs Hs is the magnetizing force required in the material to magnetize to saturation measured in oersteds. This is the Net effective magnetizing force.
Hysteresis Loop 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.
Induction, B The magnetic flux per unit area of a section; must be normal to the direction of flux. This is measured in Gauss in the cgs system of units.
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 intrinsic induction is the contribution of the magnetic material to the total magnetic induction, B. This 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 Irreversible loss is deteredmind as partial demagnetization of a magnet caused by external fields or other factors. Irreversible loss is recoverable by re-magnetization only. 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 keeper is a piece (s) of soft iron that can be 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. This also allows the magnet to be less influenced to demagnetizing influences.
Knee The part of the demagnetization curve is the point at which the B-H curve ceases to be linear. All magnet materials develop a knee at some temperature, even if their second quadrant curves are straight line at room 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.
Knee of the Demagnetization Curve The point at which the B-H curve ceases to be linear. All magnet materials develop a knee at some temperature – even if their second quadrant curves are straight line at room 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.
Leakage Flux Leakage flux is the 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 (Lg).
Lg The length of the airgap (LG) is the length of the path of the central flux line of the air gap. The Lg is measured in centimeters.
Lm The Lm is defined as the length of the magnet. This is the total length of magnet material traversed in one complete revolution of the centerline of the magnetic circuit. This is measured in centimeters.
Lm/D The lm/D Dimension ratio is the ratio of the length of a magnet to its diameter, or the diameter of a circle of equivalent cross-sectional area. In simple geometries like bars and rods the dimension ratio is related to the slope of the operating line of the magnet, BdHa.
Load Line The 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.
Magnet Wire Copper or aluminum wire covered with thin insulation is considered a magnet wire, while the insulation material can typically be made of thin enamal. Magnet wires are used in the construction of many applications, including electromagnets and solenoids. The wire itself is most often copper, but aluminum wire is not uncommon.
Magnetic Assemblies A combination of materials, magnetic and non-magnetic, which form a particular solution. Incorporates a permanent magnet as the flux generator and usually relies on mild steel to conduct the flux to the workface. Allows for better means of mounting-tapped holes, threads, press fits, etc.
Magnetic Circuit A magnetic circuit is an assembly consisting of some or all of the following: electrical currents, ferromagenetic conduction elements, permanent magnets, and air gaps.
Magnetic Flux The total magnetic induction over a given area. When the magnetic induction, B, is uniformly distributed over an area A, Magnetic Flux = BA.
Magnetic Length Magnetic Length, The physical length of the magnet dimension which corresponds to the direction the magnet is magnetized. This may or may not be the magnet’s orientation direction.
Magnetizing Force, H The magnetomotive force per unit length at any point in a magnetic circuit. Measured in Oersteds in the cgs system.
Magnetomotive Force, F Analogous to voltage in electrical circuits, this is the magnetic potential difference between any two points.
Major Hysteresis Loop The major hysteresis loop of a material is the closed loop obtained when the material is cycled between positive and negative saturation.
Maximum Energy Product, BHmax The point on the Demagnetization Curve -measured in Mega Gauss Oersteds, MGOe – in where the product of B and H is a maximum and the required volume of magnet material required to project a given energy into its surroundings is a minimum.
Maximum ON Time The maximum length of time a solenoid or an electromagnet can be left in the ON position at a given power input. Exceeding the maximum value may potnetially cause damage such as overheating. Maximum ON time overrides the Duty Cycle. The actual ON time of an application should not be longer than the ON time allowed for the operating duty cycle. For example, if in an application the duty cycle is 25% and the allowed ON time is 10 seconds, while the actual ON time is 15 seconds, then a longer duty cycle, perhaps 50%, should be considered to ensure that the allowed ON time is not exceeded.
Maxwell The maxwell is the unit of magnetic flux in the cgs electromagnetic system. One maxwell is one line of magnetic flux.
Neutral Section A permament magnet’s neutral section is determined by a plane passing through the magnet perpendicular to its central flux line at the point of maximum flux.
North Pole The pole of a magenet that when freely suspended, would point to the north magnetic pole of the earth.
Oersted The oersted is the unit of magnetic field strength, H, in the cgs electromagnetic system. One oersted equals a magneto motive force of one gilbert per centimeter of flux path.
Open Circuit Condition This condition occurs when a magnetized magnet is by itself with no external flux path of high permeability material.
Operating Line 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. This is also known as permeance coefficient line.
Operating Point On a permanent magnet, the operating point is the demagnetization curve defined by the coordinates (BdHd) or that point within the demagnetization curve defined by the coordinates (BmHm).
Orientation Direction This is the direction in which an anisotropic magnet should be magnetized in order to achieve optimum magnetic properties. This is also known as the “axis”, “easy axis”, or “angle of inclination”.
Oriented Anisotropic Material An oriented (anisotropic) material is one that has superior magnetic properties in a given direction.
P Permeance Measured in maxwells per gilbert, P Permeance is the reciprocal of the reluctance, R.
Paramagnetic Material A material having a permeability slightly greater than 1 is considered a paramagnetic material.
Permeameter A permeameter is an instrument that can measure and perhaps record a specimen’s magnetic characteristics.
Permeance The inverse of reluctance; this is analogous to conductance in electrical circuits.
Permeance Coefficient,Pc Ratio of the magnetic induction, BD, to its self demagnetizing force, HD PC = BD / HD This is also known as the “load line”, “slope of the operating line”, or operating point of the magnet, and is useful in estimating the flux output of the magnet in various conditions. As a first order approximation, BD / HD = Lm/Lg, where Lm is the length of the magnet, and Lg is the length of an air gap that the magnet is subjected to. PC is therefore a function of the geometry of the magnetic circuit.
Plunger The moving part of a linear solenoid.
Pole Pieces Ferromagnetic materials placed on magnetic poles used to shape and alter the effect of lines of flux.
Reluctance, R Analogous to resistance in an electrical circuit, reluctance is related to the magnetomotive force, F, and the magnetic flux by the equation R = F/(Magnetic Flux), paralleling Ohm’s Law where F is the magnetomotive force (in cgs units).
Relative Permeability Relative permeabolity is the ratio of permeability of a medium to that of a vacuum. In the cgs system, the permeability is equal to 1 in a vacuum by definition. The permeability of air is also for all practical purposes equal to 1 in the cgs system.
Remanence, BD The magnetic induction that remains in a magnetic circuit after the removal of an applied magnetizing force. If there is an air gap in the circuit, the remanence will be less than the residual induction, Br.
Residual Induction, Br: The residual induction is where the hysteresis loop crosses the B axis at zero magnetizing force, and represents the maximum flux output from the given magnet material. This point occurs at zero air gap; therefore this cannot be used practically in magnet materials.
Return Path The conduction elements in a magnetic circuit. A return path can provide a low reluctance path for the magnetic flux.
Reversible Temperature Coefficient The measure of the reversible changes in flux caused by temperature variations is the reversible termpature coefficient.
Saturation Saturation is the condition in which elementary magnetic moments have become oriented in one direction. A ferromagnetic material is saturated when an increase in the applied magnetizing force produces no increase in induction. Example – saturation flux densities for steels are in the range of 16,000 to 20,000 Gauss.
Search Coil A coiled conductor, generally of known number of turns and area, that is used with a flux meter to measure the change of flux linkage with the coil.
Sintered A sintered magnet consists compacted powder which is then subjected to a heat treat operation. This achieves magnetic orientation and full density.
Stabilization The exposure of a magnet to demagnetizing influences is known as stabilization. This is expected to be encountered in use in order to prevent irreversible losses during actual operation. High or low temperatures or external magenetic fields can cause demagnetizing influences.
Stroke The stroke is the distance a plunger must travel before it is stopped. The starting point is usually defined by the external components within the mechanism outside the solenoid whereas the end (stopping) point is within the solenoid when the plunger reaches the bottom of the solenoid and cannot go any further. This is for both pull and push type linear solenoids. Generally, the force initially developed by a linear solenoid (starting force for both pull and push types) is dependent upon the stroke; i.e., the longer the stroke, the smaller the force.
T max Maximum Service Temperature T max Maximum service temperature, is the maximum temperature to which the magnet may be exposed with no significant long-range instability or structural changes.
Temperature Coefficient This 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. Generally this is described as the percentage change per unit of temperature.
Unoriented Isotropic Material An unoriented isotropic material has equal magnetic properties in all directions.
Vg Air Gap Volume Vg Air gap volume, is the useful volume of air or nonmagnetic material between magnetic poles. This is measured in cubic centimeters.
Weber A Weber is the practical unit of magnetic flux as well as the amount of magnetic flux. When linked at a uniform rate with a single-turn electric current during an interval of 1 second, will induce in this circuit an electromotive of force of 1 volt.