Timeline for Can we distinguish electric fields from magnetic fields if the whole electromagnetic field is unpolarized?
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11 events
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| Apr 27, 2023 at 11:40 | comment | added | SnoopyKid | Is it possible that it is the design of the antenna that makes the electric and magnetic fields to be perpendicular to each other, not to mention that antennas themselves act as polarizers? Is it possible to make an antenna so that the electric and magnetic fields propagate nonperpendicularly? | |
| Apr 26, 2023 at 7:41 | comment | added | hyportnex | Good question. In fact, they are not always perpendicular for example you can have the magnetic field of a bar magnet pointing in any direction relative to the eelctrostatic field of a capacitor. They are perpendicular when emitted by the same time varying current or time varying charge distribution in the far field, that is when asymptotically it is a plane wave. Maybe the "deepest" reason is because, an accelerating charge does not radiate in the direction of its acceleration., see en.wikipedia.org/wiki/Li%C3%A9nard%E2%80%93Wiechert_potential | |
| Apr 26, 2023 at 4:05 | comment | added | SnoopyKid | What makes the electric fields and magnetic fields to be always necessarily perpendicular to each other? I'm curious | |
| Apr 25, 2023 at 10:56 | comment | added | hyportnex | In a propagating field of a TEM plane wave there is never E and H component in the direction of propagation, and the E and H fields are always perpendicular to each other at every instant. But the direction at which they point is changing abruptly from one short time interval to another in a random fashion both in time and in direction within the plane orthogonal to the propagation. In fact, for a very short interval, say, femto- or pico-seconds, it is polarized but then its polarization randomly jumps to another direction. To me this is what it means to be non-polarized. | |
| Apr 25, 2023 at 3:40 | comment | added | SnoopyKid | I can't understand complicated mathematics so in layman's terms the electric fields and magnetic fields are not perpendicular in unpolarized electromagnetic field but all pointed to random directions, correct? Sorry my English is not very good | |
| Apr 24, 2023 at 10:56 | comment | added | SnoopyKid | I cannot grasp these complicated maths, do you have image examples that distinguished the electric field from magnetic field in unpolarized Electromagnetic field? Sorry. | |
| Apr 24, 2023 at 10:54 | comment | added | hyportnex | Now you can do the same with a pair of loops, one measuring $H_x$ and the other $H_y$, then a square-law detector/filter will get you the estimate of $\langle H_x^2+H_y^2\rangle$, this gives another estimate of the wave power independent of the electric field measurement. A similar idea, so-called "energy receiving antenna", in the ancient history of cell phones many years ago was promoted by Bell Labs to improve on the reception of depolarized waves; they used two orthogonal loops in whose common diameter was placed one linear dipole; they assumed fixed $E_{vert}$. | |
| Apr 24, 2023 at 10:53 | comment | added | SnoopyKid | Let's see if I get it. But because the electric fields are distributed randomly, next to the particular magnetic field will be another electric field and so on. Therefore, the electric fields and magnetic fields are distributed randomly? | |
| Apr 24, 2023 at 10:44 | comment | added | hyportnex | Fix a coordinate system. Let the direction of propagation of a plane wave be $\hat z$ Then at any given instant there is an E field in the plane perpendicular to it: $\mathbf E = E_x\hat x + E_y\hat y$ The values of $E_x$ and $E_y$ are random variates, so there is no definite direction in which $\mathbf E$ points. If you have two linear dipoles one along $\hat x$, the other $\hat y$, then the former detects $E_x$, the latter $E_y$. They could be independently measured with a square-law detector/filter and then added to form and estimate of signal power by $\langle E_x^2+E_y^2\rangle$. | |
| Apr 24, 2023 at 10:34 | comment | added | SnoopyKid | So, perpendicular is not the right word then because unpolarized EM field have electric and magnetic fields that pointed to random directions. Correct me if there is a mistake. | |
| Apr 24, 2023 at 2:17 | history | answered | hyportnex | CC BY-SA 4.0 |