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Definition of magnetic concept

Permanent magnetic material: Permanent magnetic material does not disappear after being magnetized by an external magnetic field, and can provide a stable magnetic field to the external space. There are four commonly used measurement indicators for NdFeB permanent magnets:

Remanence (Br): The unit is Tesla (T) and Gauss (Gs) 1Gs = 0.0001T

A magnet is magnetized by an external magnetic field in a closed circuit environment until the technology is saturated and then the external magnetic field is cancelled. At this time, the magnetic induction intensity of the magnet is called remanence. It represents the maximum magnetic flux value that the magnet can provide. It can be seen from the demagnetization curve that it corresponds to the situation when the air gap is zero, so the magnetic induction intensity of the magnet in the actual magnetic circuit is less than the remanence. NdFeB is the highest practical permanent magnet material for Br found today.

Magnetic coercivity (Hcb): The unit is ampere/meter (A/m) and Oersted (Oe) or 1 Oe≈79.6A/m

When the magnet after the technical saturation magnetization is reverse magnetized, the value of the reverse magnetic field strength required to reduce the magnetic induction intensity to zero is called the magnetic induction coercive force (Hcb). But at this time, the magnetization of the magnet is not zero, but the applied reverse magnetic field and the magnetization of the magnet cancel each other out. (The external magnetic induction is zero.) At this time, if the external magnetic field is cancelled, the magnet still has certain magnetic properties. The coercivity of neodymium iron boron is generally more than 11000 Oe.

Intrinsic coercivity (Hcj): The unit is Ampere/meter (A/m) and Oersted (Oe) 1 Oe≈79.6A/m

The strength of the reverse magnetic field required to reduce the magnetization of the magnet to zero is called the intrinsic coercivity. Intrinsic coercivity is a physical quantity that measures the resistance to demagnetization of a magnet. If the applied magnetic field is equal to the intrinsic coercive force of the magnet, the magnetism of the magnet will be basically eliminated. The Hcj of NdFeB will decrease with the increase of temperature, so you should choose a high Hcj grade when you need to work in a high temperature environment.

Magnetic energy product (BH): Unit is joule/m3 (J/m3) or high•Ou (GOe) 1 MGOe≈7.96k J/m3

The product of B and H at any point on the demagnetization curve, BH, is called 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 greater the magnetic energy contained in the magnet. When designing the magnetic circuit, try to make the working point of the magnet near B and H corresponding to the maximum magnetic energy product.

Isotropic magnet: A magnet with the same magnetic properties in any direction.

Anisotropic magnets: The magnetic properties are different in different directions; and there is a direction, and the magnet with the highest magnetic properties is obtained when oriented in this direction. 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. It is also called "orientation axis", "magnetization easy axis".

Magnetic field strength: refers to the size of the magnetic field somewhere in space, expressed by H, and its unit is ampere/meter (A/m).

Magnetization: refers to the vector sum of the magnetic moment per unit volume inside the material, denoted by M, and the unit is ampere/meter (A/m).

Magnetic induction intensity: The definition of magnetic induction intensity B is: B=μ0(H+M), where H and M are magnetization and magnetic field intensity respectively, and μ0 is vacuum permeability. Magnetic induction is also called magnetic flux density, which is the magnetic flux per unit area. The unit is Tesla (T).

Magnetic flux: The total magnetic flux density in a given area. When the magnetic induction intensity B is uniformly distributed on the magnet surface A, the general formula of the magnetic flux Φ is Φ =B×A. The SI unit of magnetic flux is Maxwell.

Relative permeability: The ratio of the medium permeability to the vacuum permeability, that is, 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 is also approximately 1.

Permeance: The ratio of magnetic flux Φ to magnetomotive force F is similar to the conductance in a circuit. It is a physical quantity that reflects the magnetic permeability of a material.

Permeability coefficient Pc: is also the demagnetization coefficient. On the demagnetization curve, the ratio of the magnetic induction intensity Bd to the magnetic field intensity Hd, namely Pc = Bd/Hd, the 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 speaking, 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 magnetic circuits.