[HN Gopher] The Non-Radiating Antenna
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The Non-Radiating Antenna
Author : ithkuil
Score : 57 points
Date : 2021-08-08 16:38 UTC (6 hours ago)
(HTM) web link (physicsworld.com)
(TXT) w3m dump (physicsworld.com)
| [deleted]
| madengr wrote:
| RF & antenna engineer here. I'd like to know the input impedance
| at resonance. If you take two closely spaced, parallel dipoles
| and drive them out of phase, you get the same effect of nulling
| the far field. The issue is the impedance drops substantially.
|
| Now take one dipole and insert a 1/2 wavelength delay (an
| additional resonator), and you end up with the same. So what they
| have done is synthesize the second dipole with the disk, so two
| dipoles along a common axis rather than parallel.
|
| Dipole near fields drop off at 1/r^3, so yes, this is a method of
| near field coupling for power transfer or localized beating.
| [deleted]
| jpmattia wrote:
| > _I'd like to know the input impedance at resonance._
|
| The lack of radiated energy means the real part of the
| impedance must be zero (or close to it?) There's some energy
| being stored, but no guesses as to sign of the imaginary part.
| exporectomy wrote:
| Can someone explain if the introduction about quantum states is
| in any way the same effect or just an analogy? Could it be that
| discrete energy levels in atoms exist because those are the non-
| radiating states and they're non-radiating for a somehow-similar
| reason?
| jpmattia wrote:
| > _an someone explain if the introduction about quantum states
| is in any way the same effect or just an analogy?_
|
| Not the same effect, and not an analogy; it's more about the
| history of non-radiating accelerating charges. When it was
| first understood that hydrogen was composed of a positive
| nucleus and an orbiting electron, there was quite a bit of head
| scratching as to how the electron orbit was stable and didn't
| just radiate its orbital energy away.
|
| Bohr's model was somewhat ad hoc, but it said that the only
| allowed orbits would fit integral numbers of the electron's
| wavelength and would not radiate its energy away. The model got
| the right numbers for the orbital energies so it explained the
| spectral lines of hydrogen, though details of the hydrogenic
| orbitals would have to wait until Schrodinger's equation.
| jbay808 wrote:
| By the principle of reciprocity, such an antenna also shouldn't
| couple at all to the far field of a distant radiating source...
| Right?
|
| So this should work well for a near-field coupling device, but
| not as some kind of distant silent receiver.
|
| The "macroscopic atom" analogy makes me wonder, because atoms can
| absorb traveling photons just fine. But then again, only as well
| as they also radiate.
| petschge wrote:
| If it only receives the near field, can I used that to subtract
| the near field from a close-by regular antenna? That should
| make it more immune to local influences and improve the SNR of
| a far away signal?
| jpmattia wrote:
| Unless I'm missing something, I don't think reciprocity helps
| you much here. There is a contained radiation field when the
| antenna is excited; there are no fields far away. Now when you
| start with no fields far away, it doesn't tell you much about
| the excitation near the antenna.
|
| You can envision some radiation pattern from far away antennas
| which have overlap with the near-field modes. As a consequence,
| some amount of energy will be received by this antenna.
| Naturally it depends on how well the near-field mode is excited
| as to how much coupling occurs.
| [deleted]
| MrYellowP wrote:
| Serious:
|
| They've discovered a new form of metaball?
|
| How do I calculate this?
| IshKebab wrote:
| So that was a really bad explanation but it sounds like it makes
| evanescent waves? Otherwise I don't see how it could work. Also I
| don't really understand how you can make a symmetric point source
| sort of thing that makes evanescent waves.
|
| Very unclear article. A single animation would have helped
| massively.
| Animats wrote:
| Where does the energy go? Can you use this as a dummy load? What
| gets hot then?
| madengr wrote:
| There will be losses in the dipole conductor and resonator
| dielectric, so you have a finite input impedance, but that's
| where the energy should go; into heat. You could use it as a
| dummy load over very narrow bandwidth.
| jpmattia wrote:
| I'm spitballing, but there is a small amount of energy stored
| in the field around the structure. Since there's no
| dissipation, it would not make for a decent dummy load.
| [deleted]
| [deleted]
| Gravityloss wrote:
| A picture would be nice.
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