Electromagnetic brain?

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  • #26
Pythagorean
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I guess I had good faith in the OP's question, myself. I didn't have the slightest notion of QM or mind-reading when I read the OP.

By the by, what's the difference between a changing electric field and an electromagnetic field?

I guess I can imagine a mechanism for coupled fields that isn't coupled through the magnetic field when they're being coupled through concentration gradients... hrm.
 
  • #27
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I guess I had good faith in the OP's question, myself. I didn't have the slightest notion of QM or mind-reading when I read the OP.

By the by, what's the difference between a changing electric field and an electromagnetic field?

I guess I can imagine a mechanism for coupled fields that isn't coupled through the magnetic field when they're being coupled through concentration gradients... hrm.

The QM thing was me mixing up two threads... Lievo was right to be baffled. That was purely my error.
 
  • #28
berkeman
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By the by, what's the difference between a changing electric field and an electromagnetic field?

I guess I can imagine a mechanism for coupled fields that isn't coupled through the magnetic field when they're being coupled through concentration gradients... hrm.

An example of a changing electric field that does not launch an EM wave is the E-field between the plates of a capacitor. You can vary that field to moderate frequencies, and not launch an EM wave that propagates away from the capacitor.

I think the term "electromagnetic field" or wave would normally refer to a self-propagating EM wave, and sometimes to the energy in the near field region of an antenna (before the EM wave is truly self-propagating...there's a lot of reactance in the near field).
 
  • #29
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An example of a changing electric field that does not launch an EM wave is the E-field between the plates of a capacitor. You can vary that field to moderate frequencies, and not launch an EM wave that propagates away from the capacitor.

hrm... I guess this seems like a geometry trick to me: because you're still moving charge around the circuit (even if not through the capacitor). So the wires conducting the shuffling charges is where the magnetic field would be expected.

I think the term "electromagnetic field" or wave would normally refer to a self-propagating EM wave, and sometimes to the energy in the near field region of an antenna (before the EM wave is truly self-propagating...there's a lot of reactance in the near field).

Ok, I think I see what the convention is: utility and application (particularly with respect to communications).
 
  • #30
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"field" doesn't imply self-propagating to me, but then, i was never a radio guy. "wave" implies self-propagating to me. "changing electromagnetic field" i would interpret as something like a rotating magnetic field in a motor. thus, a changing magnetic field in a conductor could generate cross-talk in other conductors if they run parallel. but i'm not sure what effect this would have in a biological system. i think to set another nerve off and generate an action potential, you've got to trigger a voltage-gated channel. but cells work pretty hard to maintain a voltage gradient and the fluid between them is a conductor. won't the interstitial fluid act as a kind of faraday cage?

so what is the reason we don't emit radio? i'm guessing it's that our antenna is too short for all the low-frequency electrical activity we generate.
 
  • #31
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"field" doesn't imply self-propagating to me, but then, i was never a radio guy. "wave" implies self-propagating to me. "changing electromagnetic field" i would interpret as something like a rotating magnetic field in a motor. thus, a changing magnetic field in a conductor could generate cross-talk in other conductors if they run parallel. but i'm not sure what effect this would have in a biological system. i think to set another nerve off and generate an action potential, you've got to trigger a voltage-gated channel. but cells work pretty hard to maintain a voltage gradient and the fluid between them is a conductor. won't the interstitial fluid act as a kind of faraday cage?

so what is the reason we don't emit radio? i'm guessing it's that our antenna is too short for all the low-frequency electrical activity we generate.

Even more than that, our body as a whole isn't usually the antenna, just individual organs and and organ systems, even cells. IR is our big emission.
 
  • #32
berkeman
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hrm... I guess this seems like a geometry trick to me: because you're still moving charge around the circuit (even if not through the capacitor). So the wires conducting the shuffling charges is where the magnetic field would be expected.

Yes, sorry, I didn't address that point. And yes, you can definitely get EM radiation propagating away from the wires/traces that are connected to the capacitor. That's actually a very big concern in PCB and product design -- if you allow too much RF energy to propagate away from your product, you can fail the "Radiated Electromagnetic Interference" (EMI) tests that you have to pass before you can certify and ship your product.

So you keep the traces short with respect to the wavelengths involved, and you use shielding, etc. There are lots and lots of things you have to do right in order to keep the parasitic "unintentional radiation" that propagates away from your product from being a problem.
 
  • #33
Pythagorean
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Yes, sorry, I didn't address that point. And yes, you can definitely get EM radiation propagating away from the wires/traces that are connected to the capacitor. That's actually a very big concern in PCB and product design -- if you allow too much RF energy to propagate away from your product, you can fail the "Radiated Electromagnetic Interference" (EMI) tests that you have to pass before you can certify and ship your product.

So you keep the traces short with respect to the wavelengths involved, and you use shielding, etc. There are lots and lots of things you have to do right in order to keep the parasitic "unintentional radiation" that propagates away from your product from being a problem.

I have a trimeter that I used to take around with me. I'd get hits from microwaves and cellphones (no surprise there) but once when I was in a Sam's Club, I picked up a good peak from one of the freezers in a row of four. No idea what it could have been.

maybe transformer malfunction?
 
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  • #34
berkeman
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I have a trimeter that I used to take around with me. I'd get hits from microwaves and cellphones (no surprise there) but once when I was in a Sam's Club, I picked up a good peak from one of the freezers in a row of four. No idea what it could have been.

maybe transformer malfunction?

Yes, or something else that might have been causing arcing or similar.

I read a great article one time by a HAM radio operator who used to get called by the FCC to hunt down interfering transmitters. Depending on the location, strength, and frequencies, interference can be a pretty severe problem (like when it steps on EMS dispactch or police dispatch frequencies). Because of his skills at transmitter hunting, this guy got called regularly, and was usually able to find the interfering source, whether it was intentional or unintentional.

The best story of the bunch was an interfering source that seemed to be coming from a residential neighborhood, but only at certain times of the day and night. The intermittant nature of the signal made it hard to track down, but he finally knocked on a door of a home in the neighborhood, introduced himself and showed his credentials, and asked if he could look inside the home for the source. It turned out to be an electric analog wall clock which had a problem in its motor. When the second hand would start to climb up from the 30 minute mark each hour, there would be some arcing in the motor from the extra torque needed. That arcing was the source of the interfering signal (I forget what service it was interfering with, but it was a pretty important service). :tongue2:
 
  • #35
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LFP (local field potentials) can be anywhere from <1 to 40 Hz. There is currently a lot of research going into what exactly these fields are (that is, are they action potential spiking, or are they subthreshold membrane fluctuations, or are they representative of synaptic input at the dendrites), and what functional role, if any, they might have at feeding back into the neurons.
 

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