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I would like to know of any techniques that can be used to measure the electric field strength precisely and accurately in both time and space. I know that there will be physical/ practical limitations to this and that it is not possible to measure at an infinitesimal position, but I would still be interested to know what techniques are out there.

Assume the electric field I am interested in varies significantly in all spatial directions, and in time (I believe this means the use of a typical antenna is not possible as it sort of depends on a plane wave i.e. non-varying field in the z and x directions at a point in time, if the wave propagation is in the y direction). Assume that any electric fields are oscillating at frequencies at or below microwave frequencies.

Thank you in advance for any insight.

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  • $\begingroup$ Your stated premise is wrong. Assuming a linear reciprocal medium, if "something" in there can emit a particular EM wave shape then it can also absorb the very same. $\endgroup$
    – hyportnex
    Commented Oct 6, 2023 at 13:44
  • $\begingroup$ Who said anything about linear reciprocal media... $\endgroup$
    – Christian
    Commented Oct 6, 2023 at 13:46
  • $\begingroup$ I said something about linear reciprocal media... you said nothing of the sort and that is a problem because absent a medium there is no meaningful measurement of anything including an EM field. $\endgroup$
    – hyportnex
    Commented Oct 6, 2023 at 14:51
  • $\begingroup$ Apologies I realise my comment maybe came off as flippant. But yeah the scenario I have in mind I wouldn't expect the system to behave linearly $\endgroup$
    – Christian
    Commented Oct 6, 2023 at 15:09
  • $\begingroup$ No need to apologize but you need to specify the circumstances, in this case the EM medium, before a meaningful answer can be given. If the medium is nonlinear then an infinitesimal electric dipole can sample the electric field and an infinitesimal magnetic dipole can sample the magnetic field at any given point and at the fundamental frequency but not necessarily its harmonics for its bandwidth is also infinitesimal unless some really tricky matching is employed. $\endgroup$
    – hyportnex
    Commented Oct 6, 2023 at 16:13

1 Answer 1

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Antennas are not restricted to plane waves, although they are often characterized by their plane wave response.

You may sample the electromagnetic field in a region by placing a collection of dipole antennas in different orientations at strategically chosen positions. With a lot of computation, you may solve for the field in that region.

Radio astronomers use this to image the sky: they extrapolate such measurements back to a collection of converging waves impinging on their interferometric antenna arrays.

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  • $\begingroup$ Thank you for your answer. I'm having trouble understanding how something like a dipole can be used to measure electric field if the electric field varies significantly along its length - does this method assume the dipoles are sufficiently small such that this isn't a problem? $\endgroup$
    – Christian
    Commented Oct 6, 2023 at 14:25
  • $\begingroup$ @Christian Yes, that's the simple way to do it, although the modeling necessary to reduce the results can also account for varying E field within the sensor volume if necessary. $\endgroup$
    – John Doty
    Commented Oct 6, 2023 at 16:41

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