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On Wed, 28 Jun 2006 19:10:50 +1000, "Phil Allison"
<philallison@xxxxxxxxxx> wrote:
>
>>> There is ZERO attenuation of low frequency magnetic induction.
>>
>> Almost.
>
>
> ** Exactly.
>
>
>> The currents induced in the conductor take
>> energy off the field and thus attenuate it.
>
>
> ** Crapology.
>
>
>
It takes a good deal of copper, several mm roughly as I recall, to
produce enough eddy-current effects to cut a 60 Hz magnetic field in
half. Skin depth in copper is about 8 mm at 60 Hz, so that sort of
brackets the attenuation numbers. 1 oz copperclad FR4 starts being a
useful shield at some 10's of KHz.
John
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