Suppose I route coax through a strong DC magnetic field, such as in an
MRI, with the magnetic field perpendicular to the cable axis. Will the
current distribution in the center conductor then become biased "up"
with respect to the field (right hand rule), and the current
distribution in the shield then become biased "down," thereby
destroying symmetry?



I assume you only ask, in theory? First thought coming to my mind is
what is going to happen with that coax near the MRI when it is turned on!




Ed :^)

Thanks, all, for your helpful responses.

The general consensus appears to be that a tiny electric dipole will be
induced that oscillates transverse to the cable at the same frequency
as the carrier. It might possibly leak a tiny amount of energy to the
area immediately surrounding the coax, but probably not a significant
amount compared to that which is already lost due to imperfections in
the cable.

I'm not planning any installation in an MRI, but I do have an
application where the cable is routed through some fairly strong
permanent magnetic fields, and I wondered if I needed to magnetically
shield the cable to avoid substantial losses. Sounds like I don't need
to worry.

I suppose I could actually run a test, but it's a lot easier just to
freeload off all your experience!

Tracy Hall
hthalljr'gmail'com

I would read the manufacturers data, attempt to get a 100% braid (silver
plated copper tubing for a shield would be GREAT! grin), and limit
exposure to the fields in as much as it is possible..
But hey, I am a natural paranoid--but that trait kept me alive when I was
younger and carrying on with women of questionable character in cheap
bars... grin

Warmest regards,
John

"Tracy Hall" wrote in message
ups.com...
Thanks, all, for your helpful responses.

The general consensus appears to be that a tiny electric dipole will be
induced that oscillates transverse to the cable at the same frequency
as the carrier. It might possibly leak a tiny amount of energy to the
area immediately surrounding the coax, but probably not a significant
amount compared to that which is already lost due to imperfections in
the cable.

I'm not planning any installation in an MRI, but I do have an
application where the cable is routed through some fairly strong
permanent magnetic fields, and I wondered if I needed to magnetically
shield the cable to avoid substantial losses. Sounds like I don't need
to worry.

I suppose I could actually run a test, but it's a lot easier just to
freeload off all your experience!

Tracy Hall
hthalljr'gmail'com

In sci.electronics.design Tracy Hall wrote:
Thanks, all, for your helpful responses.

The general consensus appears to be that a tiny electric dipole will be
induced that oscillates transverse to the cable at the same frequency
as the carrier. It might possibly leak a tiny amount of energy to the
area immediately surrounding the coax, but probably not a significant
amount compared to that which is already lost due to imperfections in
the cable.

Hmm.
I suppose that for largish low frequency components in the signal, you
might also get the cable bits physically moving, both together, and in
relation to each other, which might screw up the impedance a little.