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

[Bill Metzenthen]

On 26/08/16 08:14, Hal Murray wrote:
> billm713 at gmail.com said:
>> If the conductor also has magnetic properties (e.g. if iron were used)  then
>> magnetic saturation could be an issue.
> Ah...  Sorry I wasn't clear.  How about
>
> Is skin depth an interesting concept if you are using materials commonly used
> for magnetic shielding, for example mu-metal?
>
> The electrical conduction is poor so the normal skin depth reasoning probably
> won't be useful in practical examples.
>
>
For skin depth, the lower conductivity of mu-metal is more than 
compensated for by its higher permeability.  At 50 Hz its skin depth is 
calculated to be around 0.3 mm assuming that the conductivity and 
permeability are real (as distinct from complex) and everything is 
linear.  I haven't needed to consider what happens when these 
assumptions aren't valid so I could only guess how rapidly the skin 
depth increases when a magnetic material such as mu-metal is pushed past 
its linear region.

The usual skin depth calculation is based upon assumptions about the 
form of the electromagnetic field and the conductor, which might not 
apply to the situation in which one is interested. Despite this, it is 
often used to get an estimate which is useful in a range of applications.