SkinDepth

Screenshot of SkinDepth 1.05 (AIR) running on OS X Snow Leopard

SkinDepth is a simple utility to calculate the depth of attenuation, or skin depth, of an electromagnetic wave inside a conductive material. At the skin depth, a wave drops to around 37% its original amplitude, so by 4 times the skin depth the wave is almost completely attenuated (37% of 37% of 37% of 37% or about 98% of the original amplitude). Among other things this is an important number to know for EMI/RFI shielding, some types of nondestructive testing, and radiofrequency losses in transmission lines and transformers. The skin depth of a conductive material depends on its electrical conductivity, its magnetic permeability, and the frequency of the wave.

SkinDepth uses an approximation to the skin effect calculation – it’s valid for metals up to at least the microwave (GHz) range for the most part, but for poor conductors (insulators) it may only be applicable to a few tens of kHz. SkinDepth won’t warn you if the frequencies you’re using would make this approximation less than accurate so if you need the “real” results consult some of the above links for a more thorough background on the subject.

The SkinDepth program keeps a database of conductive materials and can automatically calculate the skin depth of a given material for a given frequency (and vice versa). SkinDepth comes with a list of some conductive materials that you can add materials to as you need them.  Even if you never need to guesstimate attenuation losses, you might find it convenient to just use it as a database of conductivities.

There are two different versions of SkinDepth available – most of the development these days is for the Python version (available on Bitbucket and GitHub), so you’ll need Python (and wxPython) installed.  I wrote the older version in AIR as an excuse to explore the platform; you can install AIR + SkinDepth as a bundled .EXE installation package.  In general I’d recommend the Python version as it’s got a few niceties the AIR version doesn’t, but you may find the installation for the AIR version a little more straightforward.  They both use the same SQLite database for storage so you can freely move material files back and forth between them.

Update Mon Jan 21 19:21:31 CST 2013: I’ve got a web version of SkinDepth up and running @ PythonAnywhere if you’d prefer not to install Python or Adobe AIR.