[3dem] Slowly varying magnetic fields

[Henning Stahlberg]

Hi John,

Do you have NMR or MRI machines nearby?

Henning.


___________________________________________________

Henning Stahlberg
Center for Cellular Imaging and Nanoanalytics (C-CINA)
Structural Biology and Biophysics, Biozentrum,
WRO-1058, Mattenstrasse 26
University Basel, CH-4058 Basel, Switzerland
Tel: +41 - 61 - 387 32 62 (office)
Tel: +41 - 61 - 387 32 27 (administrative assistant)
Fax: +41 - 61 - 387 39 86
mailto:Henning.Stahlberg at unibas.ch
Skype:henningstahlberg
http://stahlberglab.org
http://2dx.org
___________________________________________________


On Jun 3, 2009, at 9:23 PM, John Rubinstein, U of T wrote:

> Dear Colleagues,
>
> We recently identified a slow varying magnetic field (e.g. changes  
> on the time scale of ~1 second) in our microscope room.  Looking at  
> our FEI engineer's EMF meter, the minimal 60 Hz AC fields in the  
> room appear to be carried on a (much larger) background that  
> resembles the rising and falling of an ocean surface (but less  
> regular).  This pattern would be quite pretty to look at if the  
> fields did not cause random displacement of our electron beam of up  
> to  ~5 mm on the phosphor screen at 600 kx magnification (Tecnai F20  
> operating at 200 kV).  These fields were not present 2 years ago  
> when we installed the microscope.  We are not near any elevators and  
> our room is on the 3rd floor so we know we are far from any subway  
> tracks.  These "DC" fields are strongest as you go up in our room,  
> but are stronger in our room than in the room above ours.  The only  
> ductwork and wires in our ceiling are those we put in for our air  
> conditioner and dehumidifier and the fields persist with this  
> equipment turned off.  Naturally, I am concerned that something has  
> changed far away in the building causing these effects and that the  
> fields are being transmitted to our room via metal beams or rebar.
>
> Has anybody come across this sort of problem before, identified the  
> source of the fields, and/or solved the problem in some way?  Any  
> insight from experience would be greatly appreciated.
>
> Best regards,
> John
>
> -- 
> John Rubinstein
> Molecular Structure and Function Program
> The Hospital for Sick Children
> 555 University Avenue, Rm. 3330
> Toronto, ON
> Canada
> M5G 1X8
> Tel: (+001) 416-813-7255
> Fax: (+001) 416-813-5022
> www.sickkids.ca/research/rubinstein
>
>
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