How can Bi have units of Gauss if it equals B [Gauss] - H [oersted]?

[kaplandj]

In the Bi vs. H curves for magnetic property and saturation of materials, how does Bi = Intrinsic Induction have units in Gausses if it is the addition of two values that have different units.

I.E. B = flux density has units of Gauss or Wb/m^2 and H = Mag. Field Intensity is in oersteds or Amp/m, "so how can Bi equal B minus H"??

 

[hacksaw]

that question is one of the reasons for using rationalized SI.

the issue is that B is a flux density and H a field intensity, but because of the way the units are structured, B is a flux density for 1 cm2 therefore the numerical equality of B(G)=H(Oe) even though the units are different.

units just are, so deal with them...

 

[kaplandj]

Is it acceptable when using a Bi vs. H curve to just use B=Bi? Otherwise, how would you be able to find H if you need it to calculate Bi.


The reason I ask is that I am trying to do a magnetic circuit analysis by looking at the mmf drop around the cross section of a solid core solenoid.

1. I have been told to iterate values of "B" starting say at .1, then multiply that "B" by the Area for flux to travel through in each section of the circuit.

2. This new value is assumed to be Bi because then I am told to look up the corresponding H value on the Bi vs. H curve for a particular material.

3. I then multiply H*l, where l is the length of a section of the circuit.

4. Finally I add up all of the H*l values for each section of the circuit and compare it to my N*i value. When they match up after some iterations of "B" I have found the "B" value for the circuit.

Make any sense? Could anyone tell me their opinion regarding this process?

 

[hacksaw]

your "intrinsic induction" is defined as Bi=B-H. this characterizes the material response by subtracting out the externally excited field.

in making your circuit calculation you need the total flux density, so you need to work with B=Bi+H with Bi=f(H)

good luck

 

[UKpete]

kaplandj, the iterative process you describe is correct. It is necessary to iterate in that way because ferromagnetic materials are non-linear i.e. they don't have linear BH characteristics. When finite element programs do magnetostatic calculations they iterate in the same way.

As for the units, I was brought up with SI and I've never had a problem with it. B and H have different units and the two are related by the permeability 'mu' (sorry can't do the Greek letter), i.e. B=muH. In ferromagnetic materials, mu varies according to the level of saturation.

 

[hacksaw]

Uk,

Believe the orig. posting is for large signal case(non-linear) and he is working with the so-called intrinsic induction Bi that represents the material. An additional integration step would be required to solve on the basis of permeability.

 

[UKpete]

hacksaw, I think I understand now. I'm not used to the intrinsic representation, let alone in imperial units.