[time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Bill Metzenthen]

On 26/08/16 06:33, Hal Murray wrote:
> billm713 at gmail.com said:
>> Skin depth is probably a good place to start with in roughly estimating  the
>> thickness needed.  In copper at 50 Hz, ...
> Is skin depth an appropriate concept for magnetic shielding?  Or does it get
> messed up by saturation?
>
>
>
Skin depth is appropriate for an electromagnetic field.  It doesn't 
apply for a static electric or magnetic field but does apply for a 
varying magnetic field.  Without going into the details of 
electromagnetic field theory, the mechanism is that the varying magnetic 
field induces a current in the conductor (copper under consideration 
here) and that this current in turn produces a magnetic field which 
opposes the original magnetic field. Strictly magnetic effects, e.g. 
ferromagnetism, play no part in this scenario and hence saturation is 
not an issue.

If the conductor also has magnetic properties (e.g. if iron were used) 
then magnetic saturation could be an issue.