Timeline for Why does an MRI machine or other EMP generating machine not damage humans, but it will fry computers?
Current License: CC BY-SA 4.0
22 events
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| May 10, 2023 at 15:36 | comment | added | Aron | Also, doesn't make x-ray not a high frequency EM radiation. | |
| May 10, 2023 at 15:27 | comment | added | Aron | @JohnDoty Right, but it can't be different frequencies of microwave, IR, visible light, ultra violet? | |
| May 9, 2023 at 11:51 | comment | added | John Doty | @Aron You hardly ever see x-rays characterized by frequency. Where do you see EHz used as a unit? We usually use keV. | |
| May 9, 2023 at 4:42 | comment | added | Aron | @JohnDoty No. High frequency means different things in different context. In the context of radio communication, high frequency means high frequency radio (duhhh). When talking in terms of medical imaging (where x-rays and positrons are routinely used), the context is high energy physics. | |
| May 8, 2023 at 21:37 | comment | added | John Doty | @Aron "High frequency" means different things to different people. In radio communication, where it has an internationally standardized definition, it means 3 MHz to 30 MHz. In other contexts, it's less well defined. | |
| May 8, 2023 at 13:30 | comment | added | LorenzoDonati4Ukraine-OnStrike | @Aron I know Planck relation, but I was using engineering jargon, not a specific QM relation. I'm sorry if this was confusing. The adjective "high" is definitely imprecise and context-dependent. About your "about EM, not frequency radio" objection, I can't get it. Radio-frequencies are just a part of EM spectrum. What's the objection here? I'm starting to suspect we are saying the same things, but with different POV. Mine is that of an engineer (EE specifically). I guess yours is the POV of a physicist? | |
| May 8, 2023 at 12:55 | comment | added | Aron | @LorenzoDonatisupportUkraine High energy == high frequency. It is literally the Plank relation. You were talking about EM, not high frequency radio. High frequency EM is hard x-ray or gamma. OP was stating that for the intents of addressing the Magnetic field of the electromagnet, an MRI is nothing like an EMP. Adding the weak sauce radio waves to the mix does not make it any more like an EMP. | |
| May 8, 2023 at 11:41 | comment | added | LorenzoDonati4Ukraine-OnStrike |
@ntoskrnl Excerpts: The regenerative braking effect drops off at lower speeds and cannot bring a vehicle to a complete halt reasonably quickly with current technology. and Current regenerative brakes do not immobilize a stationary vehicle; physical locking is required, for example to prevent vehicles from rolling down hills.
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| May 8, 2023 at 11:40 | comment | added | LorenzoDonati4Ukraine-OnStrike | @ntoskrnl I'm not knowledgeable to the latest innovations, but as far as I know what Wikipedia says about this is still correct. | |
| May 8, 2023 at 11:37 | comment | added | LorenzoDonati4Ukraine-OnStrike | @Aron Moreover I added a very clear note to the end of my comment, i.e. "(Very rough explanation)." That was clearly to hightlight that mine wasn't an attempt to explain what is NMR. So your comment about "worst explanation" is really out of place. I know how NMR works, but I didn't want to put a wikipedia page in a comment. The point is that I was objecting to the statement that "The MRI is just a big magnet", which is clearly wrong even with all the possible approximation, since without the RF excitation you can't have NMR. | |
| May 8, 2023 at 11:32 | comment | added | LorenzoDonati4Ukraine-OnStrike | @Aron When did I say "high energy"?!? I said "high frequency". Radio frequency in electronics is, broadly speaking, considered "high frequency", as opposed to "low frequency" (anythin in audio bands and below). That's a bit approximate, but in engineering the difference is quite clear. Essentially we engineer talk about "high frequency" when the wave propagation aspects of signals in the circuit begin to become relevant. | |
| May 8, 2023 at 7:57 | comment | added | Aron | @LorenzoDonatisupportUkraine "EM high frequency radiation"? I would hardly call radio waves "high energy". The point of OP, is that the magnetic component of the MRI is in fact NOT an EMP source. Also, worst explanation of NMR I've heard. The point of the B field is to break symmetry between the various spin states. The radio waves are there to pump the spin states to the higher state. The imaging is done by watching for the decay of those high spin states (called relaxation). | |
| May 7, 2023 at 15:52 | comment | added | ntoskrnl | @LorenzoDonatisupportUkraine "regenerative braking in EVs becomes irrelevant at very low speed" This is not correct. The motor in an EV is driven by a variable frequency drive (VFD) that can apply any torque at any speed in either direction. | |
| May 7, 2023 at 10:52 | comment | added | LorenzoDonati4Ukraine-OnStrike | "The MRI is just a big magnet and because the field is static there is no induced currents in the brain." That's not entirely correct: MRI scan works by irradiating you with EM high frequency radiation while you are subjected to a static magnetic field. This latter serves to align atomic dipoles so that when the tissues are irradiated the difference in the response to the variable EM field (the atomic resonance) will highlight differences in tissues composition and state. (Very rough explanation). | |
| May 7, 2023 at 10:49 | comment | added | LorenzoDonati4Ukraine-OnStrike | @d3jones The movement of the bed in an mri scan is too slow to make induced currents and potentials relevant. The intensity of the induced fields are proportional to the relative speed between the static field and the moving object. That's why regenerative braking in EVs becomes irrelevant at very low speed and they still need mechanical brakes to bring the vehicle to a full stop or to keep it stationary. | |
| May 7, 2023 at 9:14 | comment | added | D Duck | The main static field, $B_0$, is approximately 1 or 2 T, wheras $B_1$ is on the order of a mT. | |
| May 7, 2023 at 6:50 | comment | added | Stian | The field isn't static through the procedure. Those "clunk" noises come when they flip the polarity. | |
| May 6, 2023 at 22:50 | comment | added | d3jones | The field may be static, but while you are being moved into the machine the field is time-varying, from your point of view. A time-varying magnetic field induces an electric current. Why aren't you electrocuted? | |
| May 6, 2023 at 20:53 | comment | added | ShoulO | So it is a matter of scale then. The more powerful EMP,- the more messed up brain would be. | |
| May 6, 2023 at 20:47 | vote | accept | ShoulO | ||
| May 6, 2023 at 10:25 | comment | added | D Duck | Video is Transcranial Magnetic Stimulation of the Brain - Royal Institution Christmas Lectures 2011 - BBC Four | |
| May 6, 2023 at 10:04 | history | answered | D Duck | CC BY-SA 4.0 |