to shield against DC and low frequency magnetic field usually high
permeability magnetizable material -- Permalloy, Mu-metal or similar is
used, the field concentrates in the high permeability material and
"behind it" is no left over magnetic field
73
Alex
On 8/25/2016 11:10 AM, Magnus Danielson wrote:
Hi,
On 08/25/2016 11:04 AM, Bill Metzenthen wrote:
On 25/08/16 18:25, Poul-Henning Kamp wrote:
--------
In message
<1057836989.2088307.1472104857885.javamail.ya...@mail.yahoo.com>, Br
uce Griffiths writes:
You'd need a rather thick copper jacket to shield effectively
against the 50Hz magnetic field.
As in: A good-sized fraction of the wavelength if I recall :-)
Electric fields are so much easier...
One interesting thing here is that across distances like this,
there would be significant longitudal currents in such a shield.
Not as bad as metal spanning the Mississippi, but getting there.
Skin depth is probably a good place to start with in roughly estimating
the thickness needed. In copper at 50 Hz, a quick calculation suggests
9.5 mm, but this just the depth at which the E-M field decreases by 1/e
or 8.7 dB. Thus to get 20 dB attenuation this implies a thickness of
about 22 mm, etc.
While interesting, I think you are going overboard. The easy remedy is
to move the fiber of the power-cable and put it on some distance, just
choose a different path for it in the building.
Cheers,
Magnus
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2016.0.7752 / Virus Database: 4647/12877 - Release Date:
08/25/16
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
