I've been reading about Transcranial Magnetic Stimulation (TMS) which can activate neurons using a magnetic field, which got me thinking... what if we can pick and choose exactly which neurons to activate? Then we'd be able to create true non-invasive in-brain virtual reality.

For that to be possible, we'd need to be able to make a magnetic field of any shape, probably by combining the magnetic fields of hundreds of different electromagnets and having them "sum" to the final desired vector field...

Also, we would have to be able to pick and choose the "dead zones" so we don't stimulate every single neuron within range. Are there even dead zones in magnetic fields? Is this possible?

  • $\begingroup$ Nope. Maxwell's equations limit us greatly in the kinds of fields we can make. $\endgroup$
    – CuriousOne
    Dec 29, 2014 at 9:03
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    $\begingroup$ Trivially no: the field must be always divergence-less until someone finds a monopole (or several). $\endgroup$ Dec 29, 2014 at 9:08
  • $\begingroup$ Which shape would you create? And I might be of some help $\endgroup$ Mar 8, 2016 at 1:52
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    $\begingroup$ In some way it is possible, see Halbach array. $\endgroup$ Sep 22, 2016 at 4:53

1 Answer 1


yes. the usage of steering static magnets on a larger or smaller field are employed in the old crt's and accelerators. these are some times referred to as focusing magnets. both static and electric magnets.

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    $\begingroup$ Any comment on the "dead zones" aspect? $\endgroup$
    – Kyle Kanos
    Oct 27, 2015 at 18:10
  • $\begingroup$ Maybe dead zones aren't necessary if you can focus them enough. But they'd have to be focusable on a point of space which seems hard $\endgroup$
    – pete
    Nov 7, 2015 at 1:33

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