The Skin Game

[sully]

fde..

Why skin depth?

[fdegrove]

Hi,

Why skin depth?

Electrons tend to travel on the outside diameter of a conductor, hence the term skin depth which refers to the depth of conductor penetration.

In the context of oxides on the surface of conductors it should be obvious that this will increase resistance at high frequencies as higher frequencies occupy the outside diameter and are said to not even penetrate the conductor but pass as an electron cloud at the outside....which in turn brings up the issue of DA in insulators.

For indepth reading on this topic I'd recommend papers by Dr. Malcolm Hawksford, a British scientist who publicised well founded papers on this phenomenon.

Cheers,

[sully]

I asked about skin depth because I wasn't sure if you were referring to the typical exponential depth profile used in the literature, or the complete bessel function analysis required when the skin depth for flat infinite width plates is invoked.

The flat plate exponential functions are inaccurate for round conductors when the skin depth approaches 1/5th of the conductor diameter, so there you gotta switch to bessels..they are a p.i.t.a..

BTW..When oxidation prevents interstrand conduction, they interrupt the radial eddy currents that are responsible for skinning..So, when a stranded conductor oxidizes, the skin depth increases..that is typical of lower resistivity materials..Superconductors have very high skinning, for example..

Hawksford.. If you examine the inductance formula, there are three components..geometry related, you know, the diameter/spacing log ratio thing..a loop length compensation component part, which is really small for typical lengths, and the self inductance component..which is Mu time delta..delta is .25 at dc, and goes to zero at hf..end result, internal energy storage is based on .03 microhenries per inch for copper twisted pair..That is approximately 18% of a #18awg zip cord..

Hawksford, of course, did analysis on copper wire...then used steel for his test...steel has mu's up to 1000, even to 10,000. Meaning the use of steel hugely compromises the results..as, the internal self inductance of the steel can exceed the parallel wire geometric inductance by two to three orders of magnitude..

If you wish more details, perhaps a new thread? I apologize for keeping it so non technical, but it's not a skin thread..

Sully

[millwood]

Originally posted by fdegrove
Electrons tend to travel on the outside diameter of a conductor, hence the term skin depth which refers to the depth of conductor penetration.

Cheers,

I am afraid that this is one of those "scientific" discussions that turned out to be nothing but discussions. Yes, skin effect is real. But it is only real at high frequencies (shall we say over 100Khz?) and on bare wires.

I challenge anyone to find measured increase of skin-effect at audio frequency (say 20Khz tops) that is more than 10 or 20%.

and I challenge anyone to find the same thing to be even remotely material for multi-strand wires at audio frequency.

anyone having worked on an AM receiver will be able to tell you how thin those wires are and how many strands they are. for a good reason.

On a 2nd thought, I have seen people here spending far more resources on less useful things so maybe being concerned about skin effect at audio frequency isn't bad, relatively speaking.

My next project is to build a neutrino-shielf for my amps and enjoy neutrino free sound,

[sully]

I said: ""or the complete bessel function analysis required when the skin depth for flat infinite width plates is invoked.""

I meant..or the bessels when the skin depth compared to conductor diameter does not allow the flat plate approximation equations..

Sully

[millwood]

Originally posted by sully
If you wish more details, perhaps a new thread? I apologize for keeping it so non technical, but it's not a skin thread..

Sully

Sully, I would love to learn more. the more math and the merrier.

thanks.

[fdegrove]

Hi,

If you wish more details, perhaps a new thread? I apologize for keeping it so non technical, but it's not a skin thread..

As I don't think this topic was really discussed indepth before ( pun intended) then yes, please do.

I'm by no means a scientist so don't expect major scientific contributions from me but it could make for very interesting reading/discussions nonetheless.

If you like it could even extend to DA issues, cable geometry, whatever you fancy.

Cheers,

[sully]

Luckily, even with 3 billion neutrinos passing through every square inch of your body every second (solar nutrinos, of course)... none interact with your mass.

I worry bout the inductive energy storage and current profile..as skinning is current slew dependent..

Course..I still use my #12 extension cord wire for my speakers..at least they don't go up in flames at 1500 w/ch..

Sully

[sully]

New thread on skinning...soon

going through an abode change, so my test setup is in total disarray..

The Hawksford article does have some interesting things which are inconsistent with electromagnetic field theory, as that subject is understood spanning the last five decades (plus 6). I love the switching of steel for copper, and the TEM wave propagation theory that "magically" goes right by the amp and speaker binding posts without reflections...and people who believe that transport current signals travel at 2.93 meters per second along the wires...

Ah, I digress...

Another thread...another time..soon, hopefully


Sully

[millwood]

Originally posted by sully
transport current signals travel at 2.93 meters per second along the wires...

Sully

even a dumb banker can tell that's not right.

Through electrons do travel at fairly modest speed. It is just the EM signal the electrons "carry" goes much faster.

Either way, I would love to see a real discussion on skin effect.