Basic Characteristics Of Magnetic Materials

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1. Magnetization curve of magnetic material

The magnetic material is composed of a ferromagnetic substance or a ferrimagnetic substance. Under the action of the applied magnetic field H, there must be a corresponding magnetization M or a magnetic induction intensity B, and their curves with the magnetic field strength H are called magnetization curves (M to H). Or B ~ H curve). The magnetization curve is generally non-linear and has two characteristics: magnetic saturation and hysteresis. That is, when the magnetic field strength H is sufficiently large, the magnetization M reaches a certain saturation value Ms, and continues to increase H, Ms remains unchanged; and when the M value of the material reaches saturation, the external magnetic field H decreases to zero, M Does not return to zero, but changes along the MsMr curve. The working state of the material corresponds to a point on the M to H curve or the B to H curve, which is often referred to as the working point.

2. Common magnetic properties of soft magnetic materials

Saturation magnetic induction Bs: The size depends on the composition of the material, and its corresponding physical state is that the magnetization vectors inside the material are arranged neatly.

The residual magnetic induction Br: is the characteristic parameter on the hysteresis loop, and the B value when H returns to zero.

Rectangular ratio: Br∕Bs

The coercive force Hc: is an amount indicating the degree of difficulty in magnetization of the material, and depends on the composition and defects (impurities, stress, etc.) of the material.

Permeability μ: is the ratio of B to H at any point on the hysteresis loop, which is closely related to the operating state of the device.

Initial magnetic permeability μi, maximum magnetic permeability μm, differential magnetic permeability μd, amplitude magnetic permeability μa, effective magnetic permeability μe, and pulse magnetic permeability μp.

Curie temperature Tc: The magnetization of ferromagnetic material decreases with increasing temperature. When a certain temperature is reached, the spontaneous magnetization disappears and becomes paramagnetic. The critical temperature is the Curie temperature. It determines the upper limit temperature at which the magnetic device operates.

Loss P: Hysteresis loss Ph and eddy current loss Pe P = Ph + Pe = af + bf2+ c Pe ∝ f2 t2 / , ρ decreases, the method of reducing hysteresis loss Ph is to reduce the coercive force Hc; reduce the eddy current loss Pe It is to reduce the thickness t of the magnetic material and increase the resistivity ρ of the material. The relationship between the loss of the core and the temperature rise of the core in free still air is: total power dissipation (mW) / surface area (cm2)

3. Conversion between magnetic parameters of soft magnetic materials and electrical parameters of devices

When designing a soft magnetic device, the voltage-current characteristics of the device must first be determined according to the requirements of the circuit. The voltage-to-current characteristics of the device are closely related to the geometry and magnetization state of the core. The designer must be familiar with the magnetization process of the material and master the conversion relationship between the magnetic parameters of the material and the electrical parameters of the device. Designing a soft magnetic device usually involves three steps: correct selection of magnetic materials; reasonable determination of the geometry and size of the magnetic core; according to the magnetic parameters, the working state of the simulated magnetic core obtains corresponding electrical parameters.

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