Knowledge of basic parameters of magnets


Permanent magnet material: The permanent magnet materia […]

Permanent magnet material: The permanent magnet material does not disappear after being magnetized by an external magnetic field, which can provide a stable magnetic field to the external space. There are four commonly used indicators for NdFeB permanent magnets:
Residual magnetic (Br) units are Tesla (T) and Gauss (Gs) 1Gs = 0.0001T
A magnet is magnetized by an external magnetic field in a closed-circuit environment to technical saturation and the external magnetic field is cancelled. At this time, the magnetic induction strength exhibited by the magnet is called remanence. It indicates the maximum magnetic flux value that a magnet can provide. It can be seen from the demagnetization curve that it corresponds to the case when the air gap is zero, so the magnetic induction strength of the magnet in the actual magnetic circuit is less than the remanence. NdFeB is the highest practical permanent magnetic material with the highest Br found today.
The units of magnetic coercive force (Hcb) are ampere / meter (A / m) and Oersted (Oe) or 1 Oe ≈ 79.6A / m
The value of the reverse magnetic field strength required to reduce the magnetic induction strength to zero when the magnet after technical saturation magnetization is reversely magnetized is called the magnetic coercive force (Hcb). However, at this time, the magnetization of the magnet is not zero, but the added reverse magnetic field and the magnetization of the magnet cancel each other out. (The external magnetic induction intensity is zero.) At this time, if the external magnetic field is cancelled, the magnet still has a certain magnetic performance. The coercive force of NdFeB is generally above 11000Oe.
The intrinsic coercive force (Hcj) units are ampere / meter (A / m) and Oersted (Oe) 1 Oe ≈ 79.6A / m
The reverse magnetic field strength required to reduce the magnetization of the magnet to zero is called the intrinsic coercive force. Intrinsic coercive force is a physical quantity that measures the magnet's resistance to demagnetization. If the external magnetic field is equal to the intrinsic coercive force of the magnet, the magnet's magnetism will be basically eliminated. The Hcj of NdFeB will decrease as the temperature increases, so you should choose a high Hcj grade when you need to work in a high temperature environment.
The unit of magnetic energy product (BH) is J / m3 (J / m3) or GO • MGOe ≈ 7. 96k J / m3
The product of B and H at any point on the demagnetization curve is BH. We call it the magnetic energy product, and the maximum value of B × H is called the maximum magnetic energy product (BH) max. The magnetic energy product is one of the important parameters of the energy stored in a constant magnet. The larger the (BH) max, the larger the magnetic energy contained in the magnet. When designing the magnetic circuit, make the working point of the magnet as close as possible to B and H corresponding to the maximum magnetic energy product.
Isotropic magnet: A magnet with the same magnetic properties in any direction.
Anisotropic magnet: the magnetic properties will be different in different directions; and there is a direction, the magnet with the highest magnetic performance when oriented in that direction. Sintered NdFeB permanent magnets are anisotropic magnets.
Orientation direction: The direction in which the anisotropic magnet can obtain the best magnetic properties is called the orientation direction of the magnet. Also called "orientation axis", "easy magnetization axis".
Magnetic field strength: refers to the magnitude of the magnetic field somewhere in space, expressed by H, and its unit is ampere / meter (A / m).
Magnetization: refers to the sum of the magnetic moment vectors per unit volume inside the material, expressed by M, the unit is ampere / meter (A / m).
Magnetic induction: The definition of magnetic induction B is: B = μ0 (H + M), where H and M are the magnetization and magnetic field strength, respectively, and μ0 is the vacuum permeability. Magnetic induction is also called magnetic flux density, which is the amount of magnetic flux per unit area. The unit is Tesla (T). Zh
Magnetic flux: The total magnetic induction in a given area. When the magnetic induction intensity B is uniformly distributed on the surface A of the magnet, the general formula of the magnetic flux Φ is Φ = B × A. The SI unit for magnetic flux is Maxwell.
Relative permeability: The ratio of the medium permeability to the vacuum permeability, ie μr = μ / μo. In the CGS unit system, μo = 1. In addition, the relative permeability of air is often taken as 1 in actual use, and the relative permeability of copper, aluminum, and stainless steel materials is also approximately 1.
Permeability: The ratio of the magnetic flux Φ to the magnetomotive force F, similar to the conductance in a circuit. It is a physical quantity that reflects the magnetic permeability of a material.
Permeability coefficient Pc: It is also the demagnetization coefficient. On the demagnetization curve, the ratio of the magnetic induction strength Bd to the magnetic field strength Hd, that is, Pc = Bd / Hd. The magnetic permeability coefficient can be used to estimate the magnetic flux value under various conditions. For an isolated magnet Pc is only related to the size of the magnet, the intersection of the demagnetization curve and the Pc line is the operating point of the magnet. The larger the Pc, the higher the operating point of the magnet and the less likely it is to be demagnetized. Generally, for an isolated magnet, the larger the orientation length is, the larger Pc is. Therefore, Pc is an important physical quantity in the design of permanent magnetic circuit.