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Re: [TCML] Skin effect



Christopher Karr wrote:
Hello, everybody,

I've been reading up on the skin effect, and there's nothing that's
very conclusive on it. I have seen arguments that go either way, but
no actual studies. I'm in the process of testing this. If you'd like
to read about my test set-up, and, possibly, donate to the cause, you
may go to my website at


Huh? Skin effect is exceedingly well understood (it's Maxwell's equations, after all).

All you need to know is the EM properties of skin and other tissues, and those are very well known (at least in terms of usual ranges).

Once you know that you can calculate the current density and distribution for any applied field.

As a practical matter, skin "depth" in humans at TC frequencies is in the tens of cm to meters. (something you can easily calculate knowing the dielectric constant and resistivity). The actual "skin depth" term is actually a convenient approximation, where instead of calculating the actual current distribution, you assume that the current is carried in a uniform layer of a particular depth. In reality, it's highest at the surface and gradually tapers off (reaching 1/2.71828 (exp(-1)) at the skin depth in a uniform slab).




I was wondering if anybody knew of any group that had tested the skin
effect on biological conductors.

I don't know that this group has done any testing (except accidentally...) But there's literally hundreds of pages of peer reviewed journal articles from people who have.



The theory for the skin effect is simple, but it is hard to
understand exactly what forces are to blame.

Indeed, a good conceptual understanding of why current distributes the way it does is non-trivial to come by, but rest assured that the physics is very, very well understood. There are a variety of finite element analysis programs that do the calculations for arbitrary objects and fields.

 It's also difficult to
determine what amperage is enough to cause RF burns over extended
periods.

That's because "RF burn" is somewhat subjective. As is the tissue damage threshold, which varies from person to person, etc.

I suggest you take a look at the RF exposure safety literature, perhaps starting with the ANSI/IEEE standards. They're about 100 pages long and have more information on experimental data, etc, than you can imagine, as well as a list of hundreds of references.

Jim
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