Symbol

Definition

Units

A_e

Effective cross-sectional area -In a structure containing a non-uniform cross section, the effective magnetic cross section is the area of a structure with uniform cross section which is equivalent to the first for purposes of magnetic calculations.

Also called A_c.

 mm²

A_L

Inductance factor—Industry standard method of expressing the inductance of a magnetic core, independent of turns. The inductance (in µH) of a coil with N turns wound on a core with known A_L is N²•A_L/1000. A_L is established at low flux density (<1mT) and at a low enough frequency to avoid error from resonance or frequency response.

mH/1000T
or
nH/T²

awg

American wire gauge  - also known as the Brown & Sharpe wire gauge, is a standardized wire gauge system

B

Magnetic Flux Density - The number of lines of magnetic force per square centimeter of material. Also called Induction or Magnetic Induction.

Gauss

Tesla

BH Curve

BH Curve -  Relation between magnetic induction B and magnetizing force H for a magnetic material.  Also called Magnetization Curve or Hysteresis Loop.

B_r

Remanence - The residual flux level in a core at H = 0. The measured B_r depends on the recent magnetization history of the core. B_r/B_max is the squareness.

Gauss

Tesla

B_max

Saturation Flux Density - The maximum flux density a magnetic material can accommodate.  At B_max, further increases in H result in no significant increase in B

Gauss

Tesla

H

Field Strength - The externally applied magnetic field.  Also called Magnetizing Force or mmf (Magnetomotive Force.)

Oersted

Amp-Turns/cm

H_C

Coercive force - The reverse magnetic field needed to reduce a previously magnetically saturated core from B=B_r to B=0. H_c is a measure of the width of the hysteresis loop at low frequency.

Oersted

Amp-Turns/cm

L

Inductance - The magnetic flux linkage in Maxwell-turns per ampere of magnetizing current.

Henries

l_e

Magnetic path length -  The effective length along which field strength is applied for a particular core shape and dimension.

T_C

Curie Temperature - Temperature at which a ferromagnetic material loses its ferromagnetism and becomes paramagnetic (μ_e approaches 1).  For ferrites, the effects of exceeding Curie temperature are fully reversible.

^ºC

μ

Permeability—The ratio of magnetic flux density in gauss to magnetic field strength in oersteds.

μ_e

Effective Permeability—If a magnetic circuit is not homogeneous (i.e., contains an air gap), the effective permeability is the permeability of a hypothetical homogeneous (ungapped) structure of the same shape and dimensions that would give an inductance equal to the gapped structure.

V_e

Effective magnetic volume: Product of A_e and l_e.

mm³

W_aA_c

Area Product: Product of winding window area and A_e. Also called A_p.  Area product is a useful parameter for estimating the power handling capability of a core, if the frequency and circuit topology are known.

cm⁴