Home » Uncategorized » Here is the Physics for Computing the Thickness of Mild Steel Required for VLF Shielding

Here is the Physics for Computing the Thickness of Mild Steel Required for VLF Shielding

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Perhaps a physicist or radio engineer can spot an error in here:

The radio skin depth formula can be simplified to:

Image

where p is the resistivity measured in Ωm  and μ is the relative magnetic permeability of the medium. Mild steel can have a μ of around  300 (although I’ve seen some references to as high as 2000) at f=10kHz with p=0.00000015 Ωm. (My regrets, but it’s taking far too much work to write 1.5 x 10 ^-7 in scientific notation on WordPress).

Substituting for the lower magnetic permeability I get a 10kHz radio skin depth of mild steel to be about 0.1 mm. Substituting the higher permeability I get a radio skin depth of about 0.05 mm.

Thickness δ  attenuates to about 38.78% of the surface strength. What, then, counts as “complete shielding”? Using the more conservative value, a 1.2 mm thickness of mild steel provides 12 skin depths and excellent shielding,


4 Comments

  1. […] frequency sounds.   3. Help me find a radio engineer who can confirm the physics I present here: https://hummap.wordpress.com/2014/04/02/here-is-the-physics-for-computing-the-thickness-of-mild-steel…   4. Contact the authors of this paper and ask them what has happened with their theory or […]

  2. […] Last night I arrived home late after playing badminton and I was unable to sleep. I noticed that the bathroom fan wasn’t on, and I heard what seemed to be the Hum. So, after months of waiting, I put on some warm clothes, walked to where the Deming Box is located, and crawled into the box and pulled the hatch over the opening. Not that it matters at all from a scientific standpoint, but I didn’t experience any anticipation or excitement, no sense of culmination. It was simply time. My theory is that the world Hum is rooted – at least in part – in VLF radio frequencies (3 kHz – 30 kHz). The Deming Box is one piece of a classic blinded study design first envisioned by David Deming in his classic 2004 article, “The Hum – An Anomalous Sound Heard Around the World”. Full text access to this article can be unreliable, so if you find a copy of it, save it for your own personal use and reference. In that design, three identical-looking boxes are created. The first blocks VLF radio frequencies, the second box blocks to the best degree possible, all acoustic noise. The third box is a control and blocks neither. Hum hearer volunteers then enter the boxes randomly, and report their experiences. There are notable problems with the design, in particular the problem that it is impossible to not know that one has been placed inside an acoustic anechoic chamber. Blocking VLF radio frequencies is the easy part, which I think I’ve done. I used 18 gauge or thicker mild steel to create an enclosure that can block 10 radio skin depths for a 10 kHz wave. I’m waiting for a physicist to examine my physics work presented here. […]

  3. Rosemarie Mann. says:

    30 /June 2016. Hi, Glen. Interesting results from the Deming Box.
    Did you , or could you, ever get a chance to make a similar test in an empty shipping container?
    I am interested to know whether I was right quite a few years ago, when I took a small portable radio and a mobile phone into a shipping container (used by us as a storage area for engineering bits and pieces). I found that neither the radio nor the phone would not work, so had the idea that the steel of the container was blocking the radio waves/ phone signals.
    Are these the same sort of waves that you are testing for ?
    It would be fascinating and gratifying to me to have a test done with a proper meter,
    such as you mention in your experiment.
    Any chance?
    And by the way, could you please tell us the name / brand of meter that you used?
    It would be interesting to try to borrow one from say a university….we have the ‘I.S.V.R. at Southampton University…..
    Best Wishes,
    Rosemarie Mann, England
    (‘LFNS Help’,
    care of Healthwatchgloucestershire.co.uk.)

    • The phone and radio operate at high frequencies and can be easily blocked. Try wrapping your phone in foil and then calling it. VLF radio waves can penetrate much more deeply. Now, if you had a container within a container, or something along those lines, that might be an interesting test. I know that John Beaman has done something like this in BC, but I haven’t heard of too much else in that regard. One problem might be that shipping containers are often found near industrial activity, which could confound the results because of the infrasound and low frequency sound generated in the area.

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