Magnetic concept
Permanent magnetic material: permanent magnetic material is magnetized by an external magnetic field, the magnetism does not disappear, and the external magnetic field can be provided with a stable magnetic field. NdFeB permanent magnet commonly used indicators have the following four kinds:
The residual magnetic (Br) units are T and Gauss (Gs) 1Gs =0.0001T
When a magnet is magnetized in an enclosed environment by an external magnetic field, the external magnetic field is withdrawn after the saturation of the technique, and at this point the magnetic induction of the magnet is known as remanence. It represents the maximum magnetic flux that the magnet can supply. 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 is less than the residual magnetism in the actual magnetic circuit. NdFeB is the highest practical permanent magnetic material found in Br today.
The magnetic coercivity (Hcb) unit is an / M (A/m) and Oster (Oe) or 1 Oe = 79.6A/m
When the magnetic saturation of the magnet after magnetization is reversed, the magnetic induction intensity drops to zero, and the value of the required reverse magnetic field is called magnetic induction coercive
force (Hcb). But at this time the magnetization of the magnet is not zero, but the reverse magnetic field and the magnetization of the magnet cancel each other. When the external magnetic induction intensity is zero, the magnet still has a certain magnetic property if the external magnetic field is cancelled. The coercivity of NdFeB is usually above 11000Oe.
The intrinsic coercivity (Hcj) unit is an / M (A/m) and Oe (Oe) 1 OE = 79.6A/m
The reverse magnetic field strength required to reduce the magnetization of the magnet to zero is called intrinsic coercive force. The intrinsic coercive force is a physical quantity to measure the demagnetization resistance of a magnet. If the applied magnetic field is equal to the intrinsic coercive force of the magnet, the magnetic properties of the magnet will be basically eliminated. The Hcj of NdFeB will decrease with the increase of temperature, so it is necessary to choose high Hcj under high temperature.
Energy product (BH) unit for coke / M 3 (J/m3) or • (GOe); Austria 1 MGOe ~ 7. 96k J/m3
The product of the B and H of any point on the demagnetization curve is both BH, which we call the magnetic energy product, and the maximum value of B * H is called the maximum energy product (BH) max. Energy product is one of the important parameters of the amount of energy stored in the magnet (BH) max constant, the larger the magnet contains more magnetic energy. When designing the magnetic circuit, the working point of the magnet is as close as possible to the B and H corresponding to the maximum magnetic energy product.
Isotropic magnet: a magnet having the same magnetic properties in any direction.
Anisotropic magnets: magnetic properties in different directions are different; and in one direction, the magnets with the highest magnetic properties are oriented in that direction. Sintered NdFeB permanent magnet is an anisotropic magnet.
Direction of orientation: the direction of the optimum magnetic properties of an anisotropic magnet is called the orientation of the magnet. Also known as the "oriented axis", "easy axis"".
Magnetic field intensity: the size of a magnetic field in space, expressed in H, whose unit is an ampere (A/m).
Magnetization: the magnetic moment vector of the unit volume in a material and expressed in M. The unit is an ampere (A/m).
The magnetic induction intensity of magnetic induction intensity: the definition of B is: B= 0 (H+M), where H and M are respectively the magnetization and magnetic field strength, and 0 Mu is the permeability of vacuum. Magnetic induction is also called magnetic flux density, that is, the magnetic flux per unit area. The unit is Tesla (T).
Flux: the total magnetic induction intensity in a given area. When the magnetic induction intensity B is uniformly distributed on the magnet surface A, the general formula of flux phi is =B * A. The SI unit of magnetic flux is Maxwell.
Relative permeability: the ratio of vector permeability to magnetic permeability, that is, r = [mu / O]. In the CGS unit system, mu o=1. In addition, the relative permeability of air is often 1 in practical use, and the relative permeability of copper, aluminum and stainless steel is approximately 1.
Permeance: the ratio of flux Phi to magnetomotive F, similar to the conductance in a circuit. A physical quantity that reflects the magnetic conductivity of a material.
Permeance factor Pc: the demagnetization factor, on the demagnetization curve, the ratio of the magnetic induction intensity Bd to the magnetic field strength Hd, that is, Pc =Bd/Hd. The permeance coefficient can be used to estimate the flux values under various conditions. For the isolated magnet, Pc is only related to the size of the magnet. The intersection point of the demagnetization curve and the Pc line is the working point of the magnet. The larger the Pc, the higher the working point of the magnet, the less likely it is to be demagnetization. Generally, for an isolated magnet, the larger the orientation length is, the larger the Pc is. Therefore, Pc is an important physical quantity in the design of permanent magnetic circuit.
