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Old 01-04-2011, 03:39 PM   #1
Mark R
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Default What effect does a magnetic field have on electronics?

In this case, I mean a static (but strong) magnetic field. I'm aware of Faraday induction, and have seen some electronics damaged by it when carried close to a powerful magnet. But does a strong static field disturb electronic components?

I recently saw a new MRI scanner with a 3 Tesla magnet. One of the new features was a redesign of the RF receiver. Previously, the antenna array (which goes into the main field of the scanner) was connected via coax cables to a receiver outside of the main field. This new scanner integrates the RF receiver and digital processing module into the antenna array - boasting improved SNR due to removal of the relatively lossy coax.

The same scanner also comes with EKG monitoring. Normally, this would be done by a conventional monitor placed away from the magnet. This scanner, however, comes with a wireless monitor that goes on the chest, and communicates with a wireless receiver placed elsewhere in the room.

So, is a static field disruptive at all? What about if the electronics contain magnetic components - e.g. inductors/transformers? Is there a way to avoid magnetic saturation of such components when exposed to the field?
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Old 01-04-2011, 04:58 PM   #2
William Gaatjes
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Quote:
Originally Posted by Mark R View Post
In this case, I mean a static (but strong) magnetic field. I'm aware of Faraday induction, and have seen some electronics damaged by it when carried close to a powerful magnet. But does a strong static field disturb electronic components?

I recently saw a new MRI scanner with a 3 Tesla magnet. One of the new features was a redesign of the RF receiver. Previously, the antenna array (which goes into the main field of the scanner) was connected via coax cables to a receiver outside of the main field. This new scanner integrates the RF receiver and digital processing module into the antenna array - boasting improved SNR due to removal of the relatively lossy coax.

The same scanner also comes with EKG monitoring. Normally, this would be done by a conventional monitor placed away from the magnet. This scanner, however, comes with a wireless monitor that goes on the chest, and communicates with a wireless receiver placed elsewhere in the room.

So, is a static field disruptive at all? What about if the electronics contain magnetic components - e.g. inductors/transformers? Is there a way to avoid magnetic saturation of such components when exposed to the field?
That is a good question. IIRC, I do remember that in the past oscillators where made where the core of the coil of an inductor could be magnetized with a permanent magnet and as such could be tuned(changing saturation point). But there is a way to shield from magnetic radiation : mu metal, it works with static fields as well. Old CRT televisions had speakers with a mu metal shield to prevent the electron beam from being deflected and as a result color distortion..

http://en.wikipedia.org/wiki/Mu-metal
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Old 01-04-2011, 10:55 PM   #3
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In general I don't believe a static magnetic field is an issue for electronics (though I'm not an expert in the effects of strong magnetic fields). However, in the use case you mentioned, if the sensor is mounted in vivo with a wireless transmitter, it would seem likely that it is intended to move with the patient. However, if the patient moves (causing the sensor to move), that would imply the magnetic field the sensor sees will change, which could conceivably cause problems.
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Old 01-05-2011, 02:32 PM   #4
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I know that ferrous materials can be saturated, so in that vein I would assume transformers would stop working.

Also if I recall magnets will also affect electron flow, as the electron flow itself causes its own magnetic field, which means the huge magnet might affect or stop the electron flow.
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Old 01-05-2011, 02:56 PM   #5
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Magnets are used in a lot of electronics where you wouldn't normally think they should be without ill effects. It is all in how you shape the field of the magnet. Inside hard drives there are two very strong magnets. People often use that example to say that magnets like this exist in hard drives so you can't erase a drive with magnets like them. What they don't understand is that the field of the magnets is not directed at the platters but is directed vertically not horizontally towards the platters. The same thing can be done in other electronics.

I imagine with something like a MRI you have such a controlled environment that you can plan for exactly what you want to effect. To do EKG you could set up a master clock system where the transmitter transmits during the intervals where the MRI is preparing for the next sample.

How magnets effect electrons I think is still being researched . They are doing a lot of research with effecting mood and emotions using magnets that stimulate the brain in some way. They are not sure exactly what the magnetism is effecting but I'm guessing there is some sort of electrical connection.
http://en.wikipedia.org/wiki/Transcr...ic_stimulation
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Old 01-05-2011, 03:48 PM   #6
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Originally Posted by Modelworks View Post

How magnets effect electrons I think is still being researched . They are doing a lot of research with effecting mood and emotions using magnets that stimulate the brain in some way. They are not sure exactly what the magnetism is effecting but I'm guessing there is some sort of electrical connection.
http://en.wikipedia.org/wiki/Transcr...ic_stimulation
Interesting that you mention that because if i am not wrong, hydrogen is electrically polarized because of 1 proton and 1 electron. If i understand correctly, if an hydrogen atom is rotated along its electrical axis it should also create a weak magnetic field. However, the electron and the proton of a single hydrogen atom are not fixed at position, or are they ? I do not know. According to current theories it is not, ( Heisenberg).

A better example :
If we take a watermolecule, it is electrically polarized as well. As such when a water molecule is moved around, should it also not create a magnetic field ? I honestly do not know.

But i do remember this, when electrons flow as a current in a plasma, they cause an magnetic field. This is used as explanation of the helical shaped birkland currents known as filaments.
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Last edited by William Gaatjes; 01-05-2011 at 03:54 PM. Reason: Type errors in my text.
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