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Medical Are Strong Oscillating Magnetic Fields Safe?

  1. Apr 17, 2012 #1
    Hi, I am doing some research into magnetic fields and I have a question. Are strong oscillating magnetic fields safe for human bodies? I am referring to the type of magnetic field in a speaker just a lot bigger.

    If you have any info that would be great.
  2. jcsd
  3. Apr 17, 2012 #2


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    Staff: Mentor

    Welcome to the PF.

    Are you familiar with how MRI works?
  4. Apr 19, 2012 #3
    Yes I understand MRI's (Magnetic Resonance Imaging). I know that they use strong magnetic fields to image your body. I also know that they affect any metal in a close vicinity. I'm wondering if the magnetic fields in your earbuds are strong enough to endanger you. If not how bid of a field is dangerous. One last question, how do you measure magnetic fields?
  5. Apr 20, 2012 #4
    ATM - it depends on the oscilatory speed and strength of the magnetic field. There are a couple of dangers with fluctuations and strong fields. The biggest dangers are with eddy currents that can form during fast switching fields. Imagine that you are are inside a uniform magnetic field of say 1.5T (15,000 Gauss - Earth field ~=0.5 Gauss), a typical clinical MRI scanner. If you begin to change the magnetic field quickly due to additional fields being added or subtracted to the main field (MRI Gradients), then you will have regions in the body that experience 1.5T + delta and 1.5T - delta fields. If you do this very quickly, you can develop eddy currents in the neurons that can cause muscles to twitch spontaneously. The +- delta is usually small (~40G/cm) over a length of 1 meter or so.

    Magnetic fields at strengths over 7Tesla and higher 14T 21T, etc, cause blood to act weird because of the iron in the hemoglobin. Blood becomes more viscus and can affect the body.

    You last question though, magnetic fields in earbuds strong enough to danger you - absolutely not. The field strenghts of earbud electromagnets are extremely small (and do not need to be large because the speaker resonator is tiny).

    Measure magnetic fields with a magnetometer.
  6. Apr 26, 2012 #5
    Could that explain why I felt light twitching in my neck/face muscles during an MRI? I mentioned something to the tech about it and they waived it off as if it had no correlation...
  7. Apr 26, 2012 #6

    That's exactly where the twitching came from. The tech is an idiot if they don't know about eddy current muscular stimulation occurs during MRIs. All ( I think ) MRI techs need to be certified by https://www.arrt.org/ and I would assume that this concept is on their tests.

    They aren't that dangerous (actually some like it because it is like a deep tissue massage) but can be dangerous if focused on the heart and AV node. But in reality, the only real bad thing from twitching is that your head was moving during the scan (if you were getting a head scan). You would distort the image - image taking a digital photo of a moving object and it gets blurred.
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