Inductance and superconductors

I have a question about inductors and superconductor's.

I have read that superconductor's expel all magnetic fields (or at least most )

so if a you had a inductor made out of a superconductor then how could it produce a inductance since each field generated by each wire could not induce a voltage in the next. if it would then why exactly since the field is expelled by the next wire?

Also what would the inductance be for it if say it's inductance would normally be 1 mh in a normal state but in a superconducting state what would it be?

Shoot, I used to know some of this stuff but I can tell some of the reading you've been doing hasn't explained things thoroughly enough.

If I recall the inductance still exists, it just has no resistive component to it.

I'm guessing that means it doesn't act as a classical inductor, since the magnetic fields are forced out of the super conducting region there is no interaction electrically but it still produces a magnetic field around the wire? That's my guess at least.

Actually it will be the classic inductor squared, with no resistance there goes a lot of pesky negligible factors that aren't. It will also store energy indefinitely (IE, forever) if you short the leads while conducting current, thus forming a permanent electromagnet. Basically the Q of the circuit will be exceedingly high.

It will be fun to play with.

Remember, they are using superconducting electromagnets for many industrial and scientific uses. Electromagnets is just another word for inductor.

An ideal wire, or coil of wire, carrying a current will have a magnetic field in space dependant on the geometry of the wire. At the wire surface, the electric field doesn't penetrate the wire, because there is zero resistance throughout the wire corss-section. Hence there is no field in the wire itself - it is all external.

When the wire has resistance then the field extends in to the wire, reducing as you go in further, and the term 'skin depth' describes how far in the field extends. In normal wire the skin depth is frequency dependant. Superconductors have a very small 'skin depth' that is not frequency dependant, for normal superconducting conditions.

Skin depth is a term readily appreciated by the early HAM and rf transmitter community, and lately by switchmode designers - and maybe some other exotic applications (?).

Ciao, Tim

timrobbins said:

Skin depth is a term readily appreciated by the early HAM and rf transmitter community, and lately by switchmode designers - and maybe some other exotic applications (?).

Click to expand...

I have noticed an increase in availability of Litz wire lately at some of the parts websites.

marshallf3 said:

I have noticed an increase in availability of Litz wire lately at some of the parts websites.

Click to expand...

That's funny you say that. I have had a funny feeling about seeing much more lately. It seems during times of war and major innovations, companies make more odd items. If you figure that they set up a factory tooled to produce litz, they would start marketing to sell inventory.

Dunno. Odd you noticed too.

Ok so if anything then the superconductor inductor, lol would create a larger inductance for the same size inductor as a normal one

same number of turn
same size in all directions
everything is the same except the one is normal wire and the other is superconducting wire


also anyone heard of bifilar coil
they are supposed to create 0 inductance (well almost 0 )
is there still a net magnetic field produced by the coil even though each wire's current is in the opposite direction? I would think there would still be a small field since the very end wire's magnetic field on one side is not being opposed

http://www.allaboutcircuits.com/vol_1/chpt_8/12.html

I'll being using the technique soon for a 0.1Ω resistance.

retched said:

That's funny you say that. I have had a funny feeling about seeing much more lately. It seems during times of war and major innovations, companies make more odd items. If you figure that they set up a factory tooled to produce litz, they would start marketing to sell inventory.

Dunno. Odd you noticed too.

Click to expand...

Makes sense when you think about it. Switching PS ICs are operating at higher frequencies and producing more amps. Litz wire has another advantage than just minimizing the skin efect - it's easier to wind the equivalent AWG on a toroid form.

I assume you've seen this relatively new IC? LTC3788

No, no I have not.

Interesting. If I had time before work, I would play with it in LTspice...

I guess after work it is.

Very interesting.

2 separate outputs of up to 60V @ 10A each and no heat sinks required - even on the MOSFETS.