Breaking EM Destructive Interference

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Discussion Overview

The discussion revolves around the concept of destructive interference in electromagnetic (EM) fields, particularly in the context of closely spaced RF emitters. Participants explore the implications of destructive interference on energy extraction and the nature of energy in the presence of such interference.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether energy can be extracted from the individual fields of two EM sources that exhibit destructive interference at a point far away.
  • Another participant suggests that energy can be extracted from locations outside the points of complete destructive interference.
  • A participant raises a hypothetical scenario where interference occurs everywhere in space, questioning the feasibility of such a situation.
  • Another participant asserts that it is impossible for destructive interference to occur everywhere, as there must be regions of constructive interference.
  • A participant introduces the idea of two infinitely long solenoid coils with opposing currents, suggesting that their net fields could be null throughout space.
  • Another participant counters that even in this case, regions of constructive superposition would still exist, reinforcing the impossibility of total destructive interference throughout space.
  • One participant proposes that the term "destructive interference" may be misleading, suggesting "energy redirection" as a more accurate description, and discusses practical applications of this concept, such as frequency-selective coatings on glass.

Areas of Agreement / Disagreement

Participants express disagreement regarding the possibility of destructive interference occurring everywhere in space, with some asserting it is impossible while others explore hypothetical scenarios. There is no consensus on the implications of destructive interference for energy extraction.

Contextual Notes

Participants acknowledge the complexity of energy behavior in the context of interference, with discussions highlighting the need for clarity in terminology and the conditions under which energy can be redirected or extracted.

MTtylerb
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Hi, I have a question about destructive interference. Suppose I have two very closely spaced EM sources, e.g two RF emitters. At a point far away from the sources the arbitrarily orientated magnetic field due to source one is: B1(t)=sin(ωt) and source two: B2(t)=sin(ωt+pi) so the total field is null due to destructive interference B(t)=B1(t)+B2(t)→0 (the same is true for the electric fields). Is there anyway to extract energy from the nonzero energy wound up in the individual fields? Or does destructive interference of the two fields make this impossible?
 
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Hi MTtylerb, welcome to PF!

You can extract energy from the field at other locations, just not from the locations where there is complete destructive interference.
 
What if the interference occurs everywhere in space?
 
MTtylerb said:
What if the interference occurs everywhere in space?

This is not possible, there must be areas with constructive interference.
 
How about two infinitely long solenoid coils wound in between another but with opposing currents? The net fields throughout space would be null as it is composed of the non-zero individual fields.
 
If you wind them in between one another then you will still have regions of constructive superposition. It is simply impossible to have destructive interference everywhere in space.
 
The term "destructive interference" can be misleading when you are talking about energy. A better name might be "energy redirection". The fields of the waves add together mathematically to destroy each other at certain points, but there is no actual physical destruction happening. The energy is redirected. (Waves can destroy objects, such as a laser cutter, but this is through high-energy absorption, not through wave interference.) This energy redirection can be quite useful. For example, frequency-selective coatings on glass can be made using interference. Certain frequencies are reflected instead of transmitted.
 

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