Basic characteristics and common magnetic properties of soft magnetic core materials

Basic properties of magnetic materials
1. Magnetization curve of magnetic material
Magnetic core material is composed of ferromagnetic material or ferromagnetic material. Under the action of external magnetic field H, there must be corresponding magnetization intensity M or magnetic induction intensity B. The curve of their change with magnetic field intensity H is called magnetization curve (M-H or B-H curve). Magnetization curve is nonlinear in general and has two characteristics: magnetic saturation phenomenon and hysteresis phenomenon. That is, when magnetic field intensity H is large enough, magnetization intensity M reaches a certain saturation value Ms, and continues to increase H, Ms remains unchanged. And when the material's M value reaches saturation and the external magnetic field H decreases to zero, M does not return to zero, but changes along the MS-MR curve. The working state of the material corresponds to a certain point on the M ~ H curve or B ~ H curve, which is often called the operating point.

Two, the common magnetic parameters of soft magnetic materials
Saturated magnetic induction intensity Bs: its size depends on the composition of the material, and its corresponding physical state is the orderly arrangement of magnetization vectors inside the material.
Residual magnetic induction intensity Br: is the characteristic parameter of hysteresis loop, B value when H returns to 0.
Rectangular ratio: Br/Bs
Coercivity Hc: indicates the degree of magnetization of the material, depending on the composition and defects of the material (impurities, stresses, etc.).
Permeability μ : is the ratio of B to H corresponding to any point in the hysteresis loop, and is closely related to the working state of the device.
Initial permeability μ I, maximum permeability μm, differential permeability μ D, amplitude permeability μ A, effective permeability μe, impulse permeability μ P.

Curie temperature Tc: The magnetization intensity of ferromagnetic material decreases with the increase of temperature. When it reaches a certain temperature, the spontaneous magnetization disappears and changes to paramagnetism. The critical temperature is Curie temperature. It determines the upper limit temperature at which magnetic devices operate.
Loss P: hysteresis loss Ph and eddy current loss Pe P = Ph + Pe = AF + BF2 + C Pe ∝ F2 T2 /, ρ decreased,
The method of hysteresis loss Ph is to reduce the coercivity Hc; The method to reduce the eddy current loss Pe is to reduce the thickness t of the magnetic material and increase the resistivity ρ of the material. The relation between the loss of magnetic core and the temperature rise of magnetic core in free still air is:
Total power dissipation (mW)/surface area (cm2)
Loss P: hysteresis loss Ph and eddy current loss Pe, the method to reduce hysteresis loss Ph is to reduce the coercivity Hc; The method to reduce the eddy current loss Pe is to reduce the thickness t and increase the resistivity R of the magnetic material. The loss of the core in free still air is related to the temperature rise of the core as follows: total power dissipation (milliwatts)/surface area (square cm).

3. Conversion between magnetic parameters of soft magnetic materials and electrical parameters of devices
When designing soft magnetic devices, the voltage and current characteristics of the devices should be determined according to the requirements of the circuit. The voltage and current characteristics of the device are closely related to the geometry and magnetization state of the magnetic core. Designers must be familiar with the magnetization process of materials and understand the conversion relationship between magnetic parameters of materials and electrical parameters of devices. The design of soft magnetic devices usually includes three steps: selecting magnetic materials correctly, determining the geometric shape and size of magnetic cores reasonably, and simulating the working state of magnetic cores to obtain corresponding electrical parameters according to the requirements of magnetic parameters.