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1. Initial permeability, μi
The initial permeability μi is the limit value at the initial magnetization curves origin point and is given by the following formula:


2. Effective permeability, μe

This is usually defined as the permeability of a core forming a closed circuit where leakage flux is negligibly small.



L: Self-inductance of core with coil (H)

        N: Number of turns

        Le: Effective magnetic path length (m)

        Ae: Effective cross-sectional area (m2)
3. Saturation flux density, Bs (T)
The magnetic flux density at a magnetic field where his up to a approximate saturation magnetic field value. (Fig.1)
4. Remanence, Br (T)

The value of density retained by the core when the magnetic field is reduced from the saturation magnetic flux density to zero.(Fig.1)

5. Coercivity, Hc (A/m)
The value of magnetic field strength where by the flux density becomes zero under the intensification, in the opposite direction, of the magnetic field. (Fig.1)
6. Loss factor, tanδ

This is the sum of the hysteretic loss factor, eddy current loss factor and residual loss factor.

tanδ= tanδh + tanδe + tanδr


tanδh is the hysterias loss factor

tanδe is the eddy current loss factor

tanδr is the residual loss factor

7. Relative loss factor, tanδ/μi

This is the ratio of loss factor to permeability.

tanδ/μi (for materials)

tanδ/μe (for cores with gaps in the magnetic circuit)

8. Quality factor, Q

This is the reciprocal of the loss factor and is given by

Q = 1/ tanδ
9. Temperature coefficient, αμ (1/K)
This is the fractional difference of permeability per 1K in a temperature range of from T1 to T2.


μ1: Permeability at temperature T1

μ2: Permeability at temperature T2
10. Relative temperature coefficient, αμr (1/K)
This is the temperature coefficient per unit permeability and is given by the following equation:
11. Discommendation factor, DF
This is the factor representing the variation of permeability through time after a complete demagnetization of the core at a constant temperature.
12. Curie temperature, Tc (℃)
It is the critical temperature level at which the ferromagnetic state of the material changes to paramagnetic state. (Fig.2)
13. Electrical resistively, r (Ω.m)

This is the electrical resistance per unit length and cross-sectional area of a magnetic core.

14. Density, d (kg/m3)   

This is the weight per unit volume of a magnetic core as expressed below.  

d =W/V


W: Weight of magnetic body (kg)

V: Volume of magnetic body (m3)

15. Power loss, Pc (kW/ m 3)
Power loss denotes the loss by an electrical transformer, such as a switching power supply, under a magnetization condition featuring a high frequency and large amplitude. Operating magnetic flux density is given by the following equation.


E: voltage effective value applied to coil

Bm: peak value of magnetic flux density(T)

f: Frequency (Hz)

N: Number of tunes

Ae: Effective cross-sectional arum (m2)

16. Inductance factor, AL (nH/N2)

This is the inductance per turn of the coil would around the ferrite cores with definite shape and dimension.

AL = L/N2


L: Inductance of the coil with ferrite core,

N: Number of tunes