Basic parameter knowledge of magnets

Permanent magnet material: permanent magnet material magnetized by external magnetic field does not disappear, can provide stable magnetic field to external space. There are four commonly used measuring indicators of Nd-Fe-B permanent magnets:

The unit of remanence (Br) is Tesla (T) and Gauss (Gs) 1Gs = 0.0001T.

When a magnet is magnetized by an external magnetic field in a closed-circuit environment to the technical saturation and the external magnetic field is withdrawn, the magnetic induction intensity of the magnet is called remanence. It represents the maximum flux 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 intensity of the magnet in the actual magnetic circuit is less than that of the remanence. Nd-Fe-B is the highest practical permanent magnet material found in Br nowadays.

The unit of magnetic inductance coercivity (Hcb) is A/m and Oe or 1 Oe_79.6A/m.

When the magnet saturated by technology is magnetized in reverse direction, the value of the reverse magnetic field intensity needed to reduce the magnetic induction intensity to zero is called the magnetic induction coercivity (Hcb). However, the magnetization of the magnet is not zero at this time, but the interaction between the reverse magnetic field and the magnetization of the magnet cancels each other out. At this time, if the external magnetic field is withdrawn, the magnet still has certain magnetic properties. The coercivity of NdFeB is generally over 11 000 Oe.

The units of intrinsic coercivity (Hcj) are A/m and Oe 1 Oe_79.6A/m.

We call it intrinsic coercive force that the reverse magnetic field intensity is applied to reduce the magnetization of the magnet to zero. The intrinsic coercivity is a physical quantity to measure the magnet's anti-demagnetization ability. If the external magnetic field equals the intrinsic coercivity of the magnet, the magnetism of the magnet will be basically eliminated. The HCj of NdFeB decreases with the increase of temperature, so the brand of high Hcj should be chosen when working in high temperature environment.

The unit of magnetic energy product (BH) is J/m 3 or GOe 1 MGOe_7.96k J/m 3.

The product of B and H at any point on the demagnetization curve is called the magnetic energy product (BH), 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. (BH) The larger the max, the larger the magnetic energy contained in the magnet. When designing the magnetic circuit, the working point of the magnet should be near B and H corresponding to the maximum magnetic energy product.

Isotropic magnets: magnets with the same magnetic properties in any direction.

Anisotropic magnet: The magnetic properties will vary in different directions, and there is a direction in which the magnet with the highest magnetic properties can be obtained. Sintered NdFeB permanent magnets are anisotropic magnets.

Orientation direction: The direction in which an anisotropic magnet can obtain the best magnetic properties is called the orientation direction of the magnet. Also known as "orientation axis" and "easy magnetization axis".

Magnetic field intensity: refers to the magnitude of magnetic field somewhere in space, expressed in H, in units of ampere/meter (A/m).

Magnetization: refers to the sum of the magnetic moment vectors per unit volume in a material, expressed in M, in ampere/meter (A/m).

Magnetic induction intensity: The definition of magnetic induction intensity B is: B = Mu 0 (H + M), where H and M are magnetic intensity and magnetic field intensity respectively, and Mu 0 is vacuum permeability. Magnetic induction intensity is also known as flux density, which is the flux per unit area. The unit is Tesla (T).

Flux: Total magnetic induction in a given area. When the magnetic induction intensity B is uniformly distributed on the surface of magnet A, the general formula of flux_is_=B*A. The SI unit of flux is Maxwell.

Relative permeability: The ratio of medium permeability to vacuum permeability, i.e. Mu r = mu/mu o. In CGS unit system, MUO = 1. In addition, the relative permeability of air is usually 1 in practical use. In addition, the relative permeability of copper, aluminium and stainless steel is approximately 1.

Permeability: The ratio of flux_to magnetomotive force F is similar to the conductivity in a circuit. It is a physical quantity reflecting the magnetic conductivity of materials.

Permeability coefficient Pc: It is also a demagnetization coefficient. On the demagnetization curve, the ratio of magnetic induction intensity Bd to magnetic field intensity Hd, i.e. Pc = Bd/Hd, can be used to estimate the flux values under various conditions. For isolated magnet, Pc is only related to the size of the magnet. The intersection of demagnetization curve and PC line is the working point of the magnet. The larger the Pc, the higher the working point of the magnet, the more difficult it is to be demagnetized. Generally, the larger the orientation length of an isolated magnet, the larger the Pc. Therefore, Pc is an important physical quantity in the design of permanent magnet magnetic circuit.