磁学量常用单位换算

磁学量常用单位换算

磁概念

永磁材料:永磁材料被外加磁场磁化后磁性不消失,可对外部空间提供稳定磁场。钕铁硼永磁体常用的衡量指标有以下四种:

剩磁(Br )单位为特斯拉(T )和高斯(Gs ) 1Gs =0.0001T

将一个磁体在闭路环境下被外磁场充磁到技术饱和后撤消外磁场,此时磁体表现的磁感应强度我们称之为剩磁。它表示磁体所能提供的最大的磁通值。从退磁曲线上可见,它对应于气隙为零时的情况,故在实际磁路中磁体的磁感应强度都小于剩磁。钕铁硼是现今发现的Br 最高的实用永磁材料。

磁感矫顽力(Hcb )单位是安/米(A/m)和奥斯特(Oe )或1 Oe≈79.6A/m

处于技术饱和磁化后的磁体在被反向充磁时,使磁感应强度降为零所需反向磁场强度的值称之为磁感矫顽力(Hcb )。但此时磁体的磁化强度并不为零,只是所加的反向磁场与磁体的磁化强度作用相互抵消。(对外磁感应强度表现为零)此时若撤消外磁场,磁体仍具有一定的磁性能。钕铁硼的矫顽力一般是11000Oe 以上。

内禀矫顽力(Hcj )单位是安/米(A/m)和奥斯特(Oe )1 Oe≈79.6A/m

使磁体的磁化强度降为零所需施加的反向磁场强度,我们称之为内禀矫顽力。内禀矫顽力是衡量磁体抗退磁能力的一个物理量,如果外加的磁场等于磁体的内禀矫顽力,磁体的磁性将会基本消除。钕铁硼的Hcj 会随着温度的升高而降低所以需要工作在高温环境下时应该选择高Hcj 的牌号。

磁能积(BH)单位为焦/米3(J/m3)或高•奥(GOe ) 1 MGOe≈7. 96k J/m3

退磁曲线上任何一点的B 和H 的乘积既BH 我们称为磁能积, 而B×H 的最大值称之为最大磁能积(BH)max。磁能积是恒量磁体所储存能量大小的重要参数之一,(BH)max越大说明磁体蕴含的磁能量越大。设计磁路时要尽可能使磁体的工作点处在最大磁能积所对应的B 和H 附近。

各向同性磁体:任何方向磁性能都相同的磁体。

各向异性磁体:不同方向上磁性能会有不同;且存在一个方向,在该方向取向时所得磁性能最高的磁体。烧结钕铁硼永磁体是各向异性磁体。

取向方向:各向异性的磁体能获得最佳磁性能的方向称为磁体的取向方向。也称作 “取向轴”,“易磁化轴”。

磁场强度:指空间某处磁场的大小,用H 表示,它的单位是安/米(A/m)。

磁化强度:指材料内部单位体积的磁矩矢量和,用M 表示,单位是安/米(A/m)。

磁感应强度:磁感应强度B 的定义是:B=μ0(H+M),其中H 和M 分别是磁化强度和磁场强度,而μ0是真空导磁率。磁感应强度又称为磁通密度,即单位面积内的磁通量。单位是特斯拉(T )。

磁通:给定面积内的总磁感应强度。当磁感应强度B 均匀分布于磁体表面A 时,磁通Φ的一般算式为Φ =B×A。磁通的SI 单位是麦克斯韦。

相对磁导率:媒介磁导率相对于真空磁导率的比值,即μr = μ/μo 。在CGS 单位制中,μo =1。另外,空气的相对磁导率在实际使用中往往值取为1,另外铜、铝和不锈钢材料的相对磁导率也近似为1。

磁导:磁通Φ与磁动势F 的比值,类似于电路中的电导。是反映材料导磁能力的一个物理量。

磁导系数Pc :又为退磁系数,在退磁曲线上,磁感应强度Bd 与磁场强度Hd 的比率,即Pc =Bd/Hd,磁导系数可用来估计各种条件下的磁通值。对于孤立磁体Pc 只与磁体的尺寸有关,退磁曲线和Pc 线的交点就是磁体的工作点,Pc 越大磁体工作点越高,越不容易被退磁。一般情况下对于一个孤立磁体取向长度相对越大Pc 越大。因此Pc 是永磁磁路设计中的一个重要的物理量。

Glossary of Magnet Terminology

Air Gap - The "external" distance from one pole of the magnet to the other though a non-magnetic material (usually air).

Anisotropic - An anisotropic material has different properties in different directions. For

example, wood which has a grain is stronger in some one direction than another. Like wood, neodymium magnets are also anisotropic. Even before it is magnetized, a neodymium magnet has a "preferred" magnetization direction. See our article All About Magnetization Direction for more info.

Neodymium magnets are made with a preferred magnetization direction which can not be changed. These materials are either manufactured in the influence of strong magnetic fields or pressed a specific way, and can only be magnetized through the preferred axis.Sintered Neodymium (Iron Boron) and Samarium Cobalt magnets are anisotropic.

B/H Curve - The result of plotting the value of the magnetic field (H) that is applied against the resultant flux density (B) achieved. This curve describes the qualities of any magnetic material. A graphic explanation can be found here .

BH max (Maximum Energy Product) - The Maximum Energy

Product at the point on the B/H Curve that has the most strength, expressed in MGOe (MegaGaussOersteds). When describing the grade of a neodymium magnet, this number is commonly referred to as the "N" number, as in Grade N52 magnets.

In the picture at right, it is the area inside the box, under the curve.

Br max (Residual Induction) - Also called "Residual Flux

Density". The magnetic induction remaining in a saturated magnetic material after the magnetizing field has been removed. This is the point at which the hysteresis loop crosses the B axis at zero magnetizing force, and represents the maximum flux output from the given magnet material. By definition, this point occurs at zero air gap, and therefore cannot be seen in practical use of magnet materials.

C.G.S. – Abbreviation for the "Centimeter, Grams, Second" system of measurement.

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 a magnet loses all of its magnetic

properties.

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. Find these curves for some of our most popular magnet grades on our BH

Curves page.

Demagnetization Force - A magnetizing force, typically in the direction opposite to the force used to magnetize it in the first place. Shock, vibration and temperature can also be demagnetizing forces.

Dimensions - The physical size of a magnet including any plating or coating.

Dimensional Tolerance - An allowance, given as a permissible range, in the nominal

dimensions of a finished magnet. The purpose of a tolerance is to specify the allowed leeway for variations in manufacturing.

(Magnetic) Dipole Moment (m) - a quantity that describes the torque a given magnet will experience in an external magnetic field.

Some folks (like physicists) use a magnetic dipole model to simulate or mathematically model a magnet or group of magnets. Mathematically, it's easier than considering the complexities of weird magnet shapes. It's not theoretically perfect. Using it won't always match measured field strengths near a neodymium magnet. It works great for a sphere, but isn't correct near other shapes like discs or blocks. It's a great

approximation when you're measuring far away from a magnet, but not so good close up, especially near the edges of a magnet.

Calculate the dipole moment using the formula m = dipole moment in A m2 = Br x V / μo , where:

∙ Br is Br max, the Residual Flux Density, expressed in Tesla. V is the volume of the magnet, expressed in cubic meters. μo is the permeability of a vacuum, or 4 π x 10-7 N/A2.

Electromagnet - A magnet consisting of a solenoid with an iron core, which has a magnetic field only during the time of current flow through the solenoid. Learn more in

our Electromagnets article.

Ferromagnetic Material - A material that either is a source of magnetic flux or a conductor of magnetic flux. Most ferromagnetic materials have some component of iron,

nickel, or cobalt.

Gauss - Unit of magnetic induction, B. Lines of magnetic flux per square centimeter in the C.G.S. system of measurement. Equivalent to lines per square inch in the English system, and webers per square meter or tesla in the S.I. system. 10,000 gauss equals

1 tesla.

Gauss meter - An instrument used to measure the instantaneous value of magnetic induction, B, usually measured in Gauss (C.G.S.). Also called a DC magnetometer. Gilbert - The unit of magnetomotive force, F, in the C.G.S. system.

Hysteresis Loop - A plot of magnetizing force versus resultant magnetization (also called a B/H curve) of the material as it is successively magnetized

to saturation, demagnetized, magnetized in the opposite direction and finally remagnetized. With continued recycles, this plot will be a closed loop which completely describes the characteristics of the magnetic material. The size and shape of this "loop" is important for both hard and soft materials.

With soft materials, which are generally used in alternating circuits, the area inside this "loop" should be as thin as possible (it is a measure of energy loss). But with hard materials the "fatter" the loop, the stronger the magnet will be.

The first quadrant of the loop (that is +X and +Y) is called the magnetization curve. It is of interest because it shows how much magnetizing force must be applied to saturate a magnet. The second quadrant (-X and +Y) is called the Demagnetization Curve. A graphic explanation can be found here .

Induction, (B) - The magnetic flux per unit area of a section normal to the direction of flux.

Measured in Gauss, in the C.G.S. system of units.

Intrinsic Coercive Force (Hci ) - Indicates a materials' 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.

Irreversible Losses - Partial demagnetization of the magnet, caused by exposure to high

or low temperatures, external fields, shock, vibration, or other factors. These losses are only recoverable by remagnetization. Magnets can be stabilized against irreversible losses by partial demagnetization induced by temperature cycles or by external

magnetic fields.

Isotropic Material - A material that can be magnetized along any axis or direction (a magnetically unoriented material). The opposite of Anisotropic Magnet.

Keeper - A soft iron piece temporarily added between the poles of a magnetic circuit to

protect it from demagnetizing influences. Also called a shunt. Keepers are generally not needed for Neodymium and other modern magnets. They are more commonly used with older Alnico Horseshoe Magnets.

Kilogauss - One Kilogauss = 1,000 Gauss = Maxwells per square centimeter.

Magnet - A magnet is an object made of certain materials which create a magnetic field.

Every magnet has at least one north pole and one south pole. By convention, we say that the magnetic field lines leave the North end of a magnet and enter the South end of a magnet. This is an example of a magnetic dipole ("di" means two, thus two poles). If you take a bar magnet and break it into two pieces, each piece will again have a North pole and a South pole. If you take one of those pieces and break it into two, each of the smaller pieces will have a North pole and a South pole. No matter how small the pieces of the magnet become, each piece will have a North pole and a South pole. It has not been shown to be possible to end up with a single North pole or a single South pole which is a monopole ("mono" means one or single, thus one pole).

Magnetic Circuit - Consists of all elements, including air gaps and non-magnetic materials that the magnetic flux from a magnet travels on, starting from the north pole of the magnet to the south pole.

Magnetic Field (B) - When specified on our site, the surface field or magnetic field refers to the strength in Gauss . For axially magnetized discs and cylinders, it is specified on the surface of the

magnet, along the center axis of magnetization. For blocks, it is specified on the surface of the magnet, also along the center axis of magnetization. For rings, you may see two values. B y,center specifies the vertical component of the magnetic field in the air at the center of the ring. B y,ring specifies the vertical component of the magnetic field on the surface of the magnet, mid-way between the inner and outer diameters. Some depictions of magnet fields can be found here.

Magnetic Field Strength (H) - 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.

Magnetic Flux - Is a contrived but measurable concept that has evolved in an attempt to describe the “flow” of a magnetic field. When the magnetic induction, B, is uniformly

distributed and is normal to the area, A, the flux, Ø = BA.

Magnetic Flux Density - Lines of flux per unit area, usually measured in Gauss (C.G.S.). One line of flux per square centimeter is one Maxwell.

Magnetic Induction (B) - 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 the resultant intrinsic induction. Magnetic induction is the flux per unit area normal to the direction of the magnetic path.

Magnetic Line of Force - An imaginary line in a magnetic field, which, at every point, has the direction of the magnetic flux at that point.

Magnetic Pole - An area where the lines of flux are concentrated.

Magnetomotive Force (F or mmf) - The magnetic potential difference between any two

points. Analogous to voltage in electrical circuits. That which tends to produce a magnetic field. Commonly produced by a current flowing through a coil of wire. Measured in Gilberts (C.G.S.) or Ampere Turns (S.I.).

Material Grade - Neodymium (NdFeB) magnets are graded by the magnetic material from

which they are manufactured. Generally speaking, the higher the grade of material, the stronger the magnet. We find that the Pull Force of a magnet relates directly to the "N" number. Neodymium magnets currently range in grade from N35 to N52. The

theoretical limit for Neodymium magnets is grade N64, though it isn't currently feasible to manufacture magnets this strong. The grade of most of our stock magnets is N42 because we feel that N42 provides the optimal balance between strength and cost. We also stock a wide range of sizes in grade N52 for customers who need the strongest permanent magnets available.

Maximum Energy Product (BHmax ) - The magnetic field strength at the point of

maximum energy product of a magnetic material. The field strength of fully saturated magnetic material measured in Mega Gauss Oersteds, MGOe.

Maximum Operating Temperature (Tmax ) - Also known as maximum service temperature, is the temperature at which the magnet may be exposed to continuously

with no significant long-range instability or structural changes.

Maxwell - Unit of magnetic flux in the C.G.S. electromagnetic system. One maxwell is one line of magnetic flux.

Magnetization Curve - The first quadrant portion of the hysteresis loop (B/H) Curve for a magnetic material.

Magnetizing Force (H) - The magnetomotive force per unit of magnet length, measured in

Oersteds (C.G.S.) or ampere-turns per meter (S.I). Maxwell - The C.G.S. unit for total magnetic flux, measured in flux lines per square centimeter.

MGOe - Mega (million) Gauss Oersteds. Unit of measure typically used in stating the maximum energy product for a given material. See Maximum Energy Product.

North Pole - The north pole of a magnet is the one attracted to the magnetic north pole of

the earth. This north-seeking pole is identified by the letter N. By accepted convention,

the lines of flux travel from the north pole to the south pole.

Oersted (Oe) - The C.G.S. unit for magnetizing force. The English system equivalent is Ampere Turns per Inch (1 Oersted equals 79.58 A/m). The S.I. unit is Ampere Turns per Meter.

Orientation - Used to describe the direction of magnetization of a material. Orientation

Direction - The direction in which an anisotropic magnet should be magnetized in order to achieve optimum magnetic properties.

Paramagnetic Materials - Materials that are not attracted to magnetic fields (wood, plastic, aluminum, etc.). A material having a permeability slightly greater than 1. Permanent Magnet – A magnet that retains its magnetism after it is removed from a

magnetic field. A permanent magnet is "always on". Neodymium magnets are permanent magnets.

Permeance (P) - A measure of relative ease with which flux passes through a given material or space. It is calculated by dividing magnetic flux by magnetomotive force.

Permeance is the reciprocal of reluctance.

Permeance Coefficient (Pc ) - Also called the load-line, B/H or "operating slope" of a magnet, this is the line on theDemagnetization Curve where a given magnet operates. The value depends on both the shape of the magnet, and it's surrounding environment

(some would say, how it's used in a circuit). In practical terms, it's a number that define how hard it is for the field lines to go from the north pole to the south pole of a magnet. A tall cylindrical magnet will have a high Pc, while a short, thin disc will have a low Pc.

Our online Pull Force Calculator can calculate Pc for common shapes. It assumes a single magnet in free space. Other nearby magnets or ferromagnetic materials can change matters.

Permeability (µ) - The ratio of the magnetic induction of a material to the magnetizing -force producing it (B/H). The magnetic permeability of a vacuum (µo ) is 4π×107 N/Amp2.

Pole - An area where the lines of magnetic flux are concentrated.

Plating/Coating - Most neodymium magnets are plated or coated in order to protect the

magnet material from corrosion. Neodymium magnets are mostly composed of neodymium, iron, and boron. The iron in the magnet will rust if it is not sealed from the environment by some sort of plating or coating. Most of the neodymium magnets that we stock are triple plated in nickel-copper-nickel, but some are plated in gold, silver, or black nickel, while others are coated in epoxy, plastic or rubber.

Polarity - The characteristic of a particular pole at a particular location of a permanent magnet. Differentiates the North from the South Pole.

Pull Force - The force required to pull a magnet free from a flat steel plate using force

perpendicular to the surface. The limit of the holding power of a magnet. The pull force listed is actual data acquired by testing using our state-of-the-art force test stand. A comprehensive table of the pull force for all of our stock magnets is available here: Pull Force Table.

We test for two different values of pull force using two different setups. Read more about these two pull forces here .

Rare Earth – Commonly used to describe high energy magnet material such as NdFeB (Neodymium-Iron-Boron) and SmCo (Samarium-Cobalt).

Relative Permeability - The ratio of permeability of a medium to that of a vacuum. In the

C.G.S. 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 C.G.S. system. Reluctance (R)- A measure of the relative resistance of a material to the passage of flux. It is calculated by dividing magnetomotive force by magnetic flux. Reluctance is the

reciprocal of permeance.

Remanence, (Bd ) - The magnetic induction that remains in a magnetic circuit after the removal of an applied magnetizing force.

Residual Flux Density (Brmax ) - See Br max .

Residual Induction (Brmax ) - See Br max .

Return Path - Conduction elements in a magnetic circuit which provide a low reluctance path for the magnetic flux.

Reversible Temperature Coefficient - A measure of the reversible changes in flux caused

by temperature variations.

Saturation - The state where an increase in magnetizing force produces no further increase in magnetic induction in a magnetic material.

Shunt - A soft iron piece temporarily added between the pole of a magnetic circuit to protect it from demagnetizing influences. Also called a keeper. Not needed for

Neodymium and other modern magnets.

S.I. – Abbreviation for “Système International”. Refers to the International Standard System of units. It is also known as the MKS system.

South Pole - The south pole of a magnet is the one attracted to the south pole of the earth. This south-seeking pole is identified by the letter S. By accepted convention, the lines

of flux travel from the north pole to the south pole.

Stabilization - The process of exposing a magnet or a magnetic assembly to elevated temperatures or external magnetic fields to demagnetize it to a predetermined level. Once done the magnet will suffer no future degradation when exposed to that level of

demagnetizing influence.

Surface Field (Surface Gauss) - The magnetic field strength at the surface of the magnet as measured by a Gauss meter. A comprehensive table of the surface field for all of our stock magnets is available here: Surface Field Table.

Temperature Coefficient - A factor that is used to calculate the decrease in magnetic flux

corresponding to an increase in operating temperature. The loss in magnetic flux is recovered when the operating temperature is decreased.

Tesla - The S.I. unit for magnetic induction (flux density). One Tesla equals 10,000 Gauss. Weber - The S.I. unit for total magnetic flux. The practical unit of magnetic flux. It is the amount of magnetic flux which, when linked at a uniform rate with a single-turn electric

circuit during an interval of 1 second, will induce in this circuit an electromotive force of 1 volt.

Weight - The weight of a single magnet


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