What is magnetic permeability ?

- Oct 31, 2017 -

The magnetic properties represent the physical quantities of magnetic properties. Represents the resistance of the magnetic flux in the space or in the core space, or the ability to turn on the magnetic field in the magnetic field. The formula μ = B / H, where H = magnetic field strength, B = Magnetic induction strength, commonly used symbol μ said, μ is the dielectric permeability, or absolute permeability.



The magnetic permeability μ is equal to the ratio of the magnetic induction intensity B to the magnetic field strength H in the magnetic medium, that is, μ = dB / dH.

The relative permeability of the magnetic medium is usually used, which is defined as the ratio of the permeability μ to the vacuum permeability μ0, that is, = μ /.

The relationship between the relative permeability and the magnetic susceptibility χ is: = 1 +.

The permeability μ, the relative permeability and the magnetic susceptibility are all physical quantities that describe the magnetic properties of the magnetic medium.

    For paramagnetic> 1; for antirust <1, but both are almost identical to 1. In most cases, the relative permeability of the conductor is equal to one. In the ferromagnetic, the relationship between B and H is a nonlinear hysteresis loop, not a constant, and H, its value is much greater than 1.

For example, if the relative permeability of the air (non-magnetic material) is 1, the relative permeability of the ferrite is 10,000, that is, when compared, the magnetic flux density through the magnetic material is 10,000 times. Cast iron for 200 to 400; silicon steel sheet for the 7000 ~ 10000; nickel-zinc ferrite is 10 to 1000.

Involved in the permeability of the formula:

Magnetic field energy density = B ^ 2 / 2μ

In the International System of Units (SI), the relative permeability μr is a dimensionless pure number, and the unit of the permeability μ is Henry / m (H / m).

Commonly used vacuum permeability


Common parameters

(1) initial permeability μi: refers to the basic magnetization curve when H → 0 when the permeability

(2) Maximum Permeability μm: After the initial section of the basic magnetization curve, the slope μ = B / H increases with the increase of H, and the magnetic density reaches the maximum at a certain magnetic field (Hm) Bm)

(3) saturation permeability μS: basic magnetization curve saturation section of the permeability, μs value is generally small, the depth of saturation, μs = μo.

(4) Differential (incremental) Permeability μΔ: ΔΔ = ΔB / ΔH. ΔB and ΔH are the increments taken at (B1, H1) points as shown in Fig. 1 and Fig.

(5) differential permeability, μd: μd = dB / dH, in (B1, H1) point to take the differential, available μd.

We can see: μ1 = B1 / H1, μ △ = △ B / △ H, μd = dB1 / dH1, although the three are at the same point on the permeability, but the value is not equal.

Non-magnetic materials (such as aluminum, wood, glass, free space) B and H ratio is a constant, with μ. To represent the magnetic permeability of the non-magnetic material, i.e., μ. = 1 (in CGS unit system) or μ. = 4πX10o-7 (in RMKS unit system).

In a large number of materials, if the free space (vacuum) μo = 1, then △ slightly larger than the material called paramagnetic materials (such as platinum, air, etc.); slightly smaller than the material, known as the magnetic Materials (such as silver, copper, water, etc.). The magnetic element μ1 described in this chapter is of great use. Only when the need for magnetic shielding, will be made of copper and other magnetic materials made of magnetic shield magnetic field will not radiate the magnetic field to the space.


blob.png   blob.png


The measurement of the permeability is measured indirectly, the inductance of the winding coil on the core is measured, and the magnetic permeability of the core material is calculated by the formula. Therefore, the permeability of the test instrument is the inductance tester. It is emphasized that some simple inductive test equipment, the test frequency can not be adjusted, and the test voltage can not be adjusted. For example, some of the bridge, the test frequency of 100Hz or 1kHz, the test voltage of 0.3V, given the 0.3V is not the voltage across the inductor coil, but the signal generator voltage. As for the voltage across the measured coil is unknown. If you use high-end instruments to measure inductors, such as the Agilent 4284A precision LCR tester, not only the test frequency is adjustable, and the measured inductor coil voltage and magnetization current are adjustable at both ends. Knowing these functions of the test instrument is a great help to the correct measurement of the permeability.

Related Products