[FoRK] Annihilation from within...

Eugen Leitl < eugen at leitl.org > on > Mon Dec 11 04:43:06 PST 2006

On Mon, Dec 11, 2006 at 12:33:20PM +0100, Dave Long wrote:

> Without shielding, you're trying to pick up 100 fT variations while 
> sitting in a 50 uT field.  1e-8 is not the strongest of signals.  My 

Metal vapor magnetometers are being uses in archaeometry, and the MEG
application is eventually expected (=I don't know, that's what the researchers
claim) to achieve a better sensitivity than SQUIDs.

Neural processes are relatively quick, I don't see nonregular processes
in that time domain which can't be removed by signal filtering. If
shielding is required, there's always the mu-metall option.

> guess as to why the pictures in the PDF only show the device fitting 

Can you send me that paper?

> over the top of the head is that the rooms in which they are installed 
> have been wrapped in mu-metal[2] (not the most mobile of solutions).
> 
> Given all the above objections to squids, I'll agree that atomic 
> magnetometers have more promise, subject to the following questions: 
> (a) do they have the resolution for MEG? (b) are they any easier to 

The current device mentioned is supposed to have 256 channels. With
MEMS I don't see why you can't use 10 um sized cells, or smaller.

> shield?

I must profess ignorance here. I know that these things are being operated
in the wild (in the field, literally), so I presume you can remove magnetic
field background (50/60 Hz, etc.) by DSP.
 
> [0] kind of like for an MRI, one didn't take metal objects into the 
> squid closet -- but failure to observe that precaution would only ruin 
> your data, not your day

I need to read up on the physics to look at the dynamics range of the
detector cell, my QM is rustly. If you don't have to tirate the field
threshold, it should be able to have plenty of dynamics.
 
-- 
Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
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