Glossary of Magnetic Terms
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.
Materials have an orientation that is aligned in a preferred direction. Anisotropic magnets have their alignment defined during the manufacturing process in a strong magnetic field. Once the preferred direction is determined, this direction cannot be changed.
The curve produced from plotting the value B (induction) against H (applied magnetic field). The curve will describe the qualities of the magnetic material.
The maximum energy product on the point of the B/H curve that has the highest strength. This is reflected as MGOe or Mega Gauss Oersted. This maximum strength is how the material grade is determined, that is, N35, N42, N48, etc.
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.
The resistance of a magnet to demagnetizing forces once an opposing magnetic field is applied to remove the residual magnetism.
The temperature at which a magnet loses all of its magnetic properties.
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.
A force that pushes the magnet pushes the magnet to demagnetize slightly or completely. These forces could include a magnetizing force in the opposite directly, shock, temperature, and vibration.
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.
The total amount of dimension may vary between the upper and lower limits. Tolerances are used to control the amount of variation in a manufactured part.
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 position. The magnetic field exists only so long as current flows through the coil.
Ferromagnetic materials can carry magnetic flux when against a magnet and is usually made of steel. These materials can act as a magnet until the magnetic material is removed.
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.
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).
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 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.
The full 4-quadrant graph showing the relationship of the induction of a magnetic material to an applied magnetic field. The first quadrant of the loop is the magnetization curve, whereas the second quadrant of the loop is the demagnetization curve.
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.
The resistance of a magnet material to demagnetization. It is equal to the demagnetizing force that reduces the intrinsic induction, Bi, in the material to zero after magnetizing to saturation; measured in oersteds.
Partial demagnetization of the magnet, caused by exposure to high or low temperatures, external fields, shock, vibration, or other factors. The losses are only recoverable by remagnetizing.
A material that can be magnetized along any axis or direction. Opposite of anisotropic magnets.
That portion of the flux, which does not pass through the air gap, or useful part of the magnetic circuit due to a shunting to the opposite pole. See also, Fringing Field.
The line drawn from the origin of the demagnetization curve with the slope of the B/H. The intersection represents the operating point of the magnet.
A piece of iron that has its component atoms oriented within the material that the material exhibits properties of magnetism. This allows the material to attract other materials containing iron, or align itself with an external magnetic field.
A combination of magnetic and/or non-magnetic materials that include the permanent magnet to generate flux. This assembly of specific materials is designed to provide a defined magnetic solution.
One or more closed-loop paths containing magnetic flux. The magnetic circuit is equivalent to an electrical circuit.
The product of the flux density (B) in a magnetic circuit and the (de)magnetizing force (H) required to reach that flux density.
The measure of the vector magnetic quantity that determines the ability of an electric current, or magnetic body, to induce a magnetic field at a given point; measured in oersteds.
A contrived but measurable concept that has evolved in an attempt to describe the "flow" of a magnetic field. Unlike electric current where there is an actual flow of electrons, a magnetic field is the result of the energy state of a series of magnetic domains. Conceptually, one could imagine that the sequential change of energy state as the result of an applied field represents a “flow”.
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.
An applied magnetic field used to drive another material to a condition of being magnetized. It may be applied by current through a coil of wire or by using permanent magnets to generate the applied field.
Magnets are graded according to strength, and as a rule, the higher the number, the “stronger” the magnet. For example, neodymium magnets (NdFeB) have grades from N35 to N55. The energy product of a magnet is specified in units of Gauss oersted. Choice of a magnetic grade for a specific application will require consideration of magnetic field required, cost, size, operating temperature, coatings, and interaction with other materials.
The maximum energy product on the point of the B/H curve that has the highest strength. This is reflected as MGOe or Mega Gauss Oersteds. This maximum strength is how the material grade is determined, that is, N35, N42, N48, etc.
The unit of magnetic flux in the centimeter–gram–second (CGS) system. One Maxwell is one line of magnetic flux.
Mega (million) Gauss Oersteds is a unit of measurement typically used in stating the maximum energy product for a given material.
The pole of a magnet which points to the north magnetic pole of the earth. All magnets have a north and south poles.
The unit of magnetic field strength, H, in the cgs electromagnetic system. One oersted equals a magnetomotive force of one Gilbert per centimeter of flux path. One oersted x 0.0796 = one kA/m.
An open circuit exists when a magnet is by itself with no return flux path due to high permeability material.
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. Although the slope is negative, by convention the values are usually referred to in the absolute value of the slope.
That point on a demagnetization curve defined by the coordinates (Bd/Hd) or that point within the demagnetization curve defined by the coordinates (Bm,Hm).
In an anisotropic magnet, the direction that the magnetic field flows. Anisotropic magnets have their direction of orientation determined during the manufacturing process and can only be magnetized in that specific direction.
A form of magnetism where certain materials are attracted by an externally applied magnetic field and form internal induced magnetic fields in the direction of the applied magnetic field.
A magnet that retains its magnetism even after it is removed from a magnetic field. Unlike an electromagnet that requires current to achieve a magnetic field, a permanent magnet remains “on” without the need for any outside field.
A measure with which flux passes through a given material or space. It is the reciprocal of the reluctance, R, measured in maxwells per gilbert.
Also called the load-line, B/H, or operating slope. Permeance coefficients can be found as the line on the demagnetization curve where a given magnet operates and depends upon both the shape and surroundings of the magnet. This number defines how hard it is for the field lines to go from the north pole to the south pole of the magnet.
The protective coating on a magnet. Neodymium magnets require a coating to protect from corrosion since their material makeup is largely iron. Depending upon the application and environment, the correct coating choice is as important as the correct selection of the magnetic material.
The north and south poles of the magnet.
The force required to pull a magnet free from a flat steel plate using a force perpendicular to the surface. This will determine the holding power of the magnet.
The permeability of a material compared with the permeability of free space. This is what normally is specified as material permeability.
A measure of the relative resistance of a material to the passage of flux, which is calculated by dividing magnetomotive force by magnetic flux.
The magnetic induction corresponding to zero magnetizing force in a magnetic material after saturation in a closed circuit; measured in gauss or tesla.
Conduction elements in a magnetic circuit that provide a low reluctance path for the magnetic flux.
The condition of a magnet where an increase in magnetizing force produces no further increase in the magnetic material. When this condition is met, all of the magnetic moments have the same alignment. A magnet should always be magnetized to saturation.
Sintered A sintered magnet is compacted powder which is then heat treated to achieve full density and orientation.
The pole of a magnet which points to the south magnetic pole of the earth. All magnets have a north and south poles.
Shaped piece of ferromagnetic material that once having been magnetized is very easily demagnetized, i.e. requires a slight coercive force to remove the resultant magnetism. Generally accepted as having a coercivity of less than 300 oersteds (24 kA/m) though most soft materials used in inductors have coercivities of under 10 oersteds.
The process of exposing a fully saturated magnet or magnetic assembly to an elevated temperature or external magnetic field to demagnetized it to a predetermined level. Once stabilized through this process, the magnet should not experience any future degradation when exposed to that level of demagnetizing influence again, or better known as preventing irreversible losses during.
The magnetic field strength at the surface of the magnet as measured by a Gauss meter.
A factor that is used to calculate the decrease in magnetic flux with an increase in operating temperature. This loss is recovered when the operating temperature is decreased. Understanding temperature requirements in an application will allow for the correct selection of magnetic material.
MKSA (SI) unit for magnetic flux density, defined by Faraday’s Law. A Tesla represents a volt-second per square meter per turn. One Tesla equals 10,000 Gauss.
The practical unit of magnetic flux. It is the amount of the magnetic flux which, when linked at a uniform rate with a single-turn electric current during an interval of 1 s1 second will induce in this circuit an electromotive of force.