5 ms·

Large permanent magnets are a fairly minor hazard to most electronics.

by Cerium 5y ago

lostlogin 5y ago
A phone or iPad will take 3T and work ok afterwards. I’ve seen engineers photograph the cold head on an MR scanner and the phone has held up just fine. Sometimes they turn off for a bit and need a little rest.
- ska 5y ago
  Unless they are taking the photo from near or in the bore, the camera isn't seeing anything like 3T (or, for that matter 1T). Most such photos are taken from outside the 5G line which is a very different kettle of fish. You are right that lots of electronics will be safe in the sense that it will not function in the field but be ok afterwards outside the room - so long as you don't move it around too fast. On the other hand, most consumer electronics would likely fly out of your hand and smash into the bore well before you get anywhere close to the peak strength.
  - lostlogin 5y ago
    The camera is taken right up to the bore. You’re right, it wouldn’t be 3T, but it’s getting close and it’s way inside the 5g line. The iPhones I have seen go in have not had a lot of pull and can be held, even close to the bore (less than 1m). The service instructions require photographs of various component - I watched a cold head get photographed recently. I’ve also seen an engineer take a laptop pretty close. It turned off but didn’t suffer any lasting ill effects as far as we could tell. All this fits in the category of ‘don’t do this’, but with care it is done by the engineering staff.
    - ska 5y ago
      Ah, service tech makes sense. Most others aren't going see anything interesting in the photo that close. Laptop is pretty crazy, what where they (not) thinking? I guess was imagining "normal" camera not phone, but you are right that modern attempts to make phones light have removed most of the magnetic material. It doesn't take much to make it a problem (e.g. steel screws). Typical rooms are going to over 20g acceleration on ferromagnetic components in the highest gradient regions.
      - lostlogin 5y ago
        Absolutely. The engineer with the laptop had a brain fade - his area was usually CT. As magnets have got better control over their fringe fields, the issue has got worse. The field goes from nothing to 3T in a very short distance, so 10+ T/m rate of change is not uncommon.
        pvaldes 5y ago
        Not everybody has access to Computer Tomography machines but lets examine a more common situation. Moving our magnet to the fishing area. Lets imagine that we put, not a magnetic string, a standard size neodymium magnet for fishing in the front seat of our car... or we move it in the car trunk (but forgot that our car has the battery located inside the trunk (as several BMW or VOLVO models do, for example). What could happen?
        ska 5y ago
        There are basically two purely EM mechanisms at work for large static fields. First, if the field is big enough, it will saturate components that rely on EM effect to work - these will stop functioning until they are removed from the field. Permanent damage possible if other components behave badly in this situation. The other thing is if you move in the field you will induce currents on anything like a conductive loop in your device. Damage potential is really dependent on the strength, speed of motion, and how sensitive your device is. Of course, if you have magnetic materials, mechanical damage is also possible. I suspect those fishing magnets fall off fast enough you'd have to get it lined up just right to a control board to see any effect, if then.
- TeMPOraL 5y ago
  > Sometimes they turn off for a bit and need a little rest. Could it be because of a helium leak? https://hackaday.com/2018/10/31/helium-can-stop-your-iphone-maybe-other-mems-too/ https://hackaday.com/2018/10/31/helium-can-stop-your-iphone-...

Large permanent magnets are a fairly minor hazard to most electronics.

by Cerium 5y ago

Large permanent magnets are a fairly minor hazard to most electronics.

A phone or iPad will take 3T and work ok afterwards. I’ve seen engineers photograph the cold head on an MR scanner and the phone has held up just fine. Sometimes they turn off for a bit and need a little rest.

ska 5y ago
Unless they are taking the photo from near or in the bore, the camera isn't seeing anything like 3T (or, for that matter 1T). Most such photos are taken from outside the 5G line which is a very different kettle of fish. You are right that lots of electronics will be safe in the sense that it will not function in the field but be ok afterwards outside the room - so long as you don't move it around too fast. On the other hand, most consumer electronics would likely fly out of your hand and smash into the bore well before you get anywhere close to the peak strength.
- lostlogin 5y ago
  The camera is taken right up to the bore. You’re right, it wouldn’t be 3T, but it’s getting close and it’s way inside the 5g line. The iPhones I have seen go in have not had a lot of pull and can be held, even close to the bore (less than 1m). The service instructions require photographs of various component - I watched a cold head get photographed recently. I’ve also seen an engineer take a laptop pretty close. It turned off but didn’t suffer any lasting ill effects as far as we could tell. All this fits in the category of ‘don’t do this’, but with care it is done by the engineering staff.
  - ska 5y ago
    Ah, service tech makes sense. Most others aren't going see anything interesting in the photo that close. Laptop is pretty crazy, what where they (not) thinking? I guess was imagining "normal" camera not phone, but you are right that modern attempts to make phones light have removed most of the magnetic material. It doesn't take much to make it a problem (e.g. steel screws). Typical rooms are going to over 20g acceleration on ferromagnetic components in the highest gradient regions.
    - lostlogin 5y ago
      Absolutely. The engineer with the laptop had a brain fade - his area was usually CT. As magnets have got better control over their fringe fields, the issue has got worse. The field goes from nothing to 3T in a very short distance, so 10+ T/m rate of change is not uncommon.
      - pvaldes 5y ago
        Not everybody has access to Computer Tomography machines but lets examine a more common situation. Moving our magnet to the fishing area. Lets imagine that we put, not a magnetic string, a standard size neodymium magnet for fishing in the front seat of our car... or we move it in the car trunk (but forgot that our car has the battery located inside the trunk (as several BMW or VOLVO models do, for example). What could happen?
        ska 5y ago
        There are basically two purely EM mechanisms at work for large static fields. First, if the field is big enough, it will saturate components that rely on EM effect to work - these will stop functioning until they are removed from the field. Permanent damage possible if other components behave badly in this situation. The other thing is if you move in the field you will induce currents on anything like a conductive loop in your device. Damage potential is really dependent on the strength, speed of motion, and how sensitive your device is. Of course, if you have magnetic materials, mechanical damage is also possible. I suspect those fishing magnets fall off fast enough you'd have to get it lined up just right to a control board to see any effect, if then.
TeMPOraL 5y ago
> Sometimes they turn off for a bit and need a little rest. Could it be because of a helium leak? https://hackaday.com/2018/10/31/helium-can-stop-your-iphone-maybe-other-mems-too/ https://hackaday.com/2018/10/31/helium-can-stop-your-iphone-...