For active noise cancelling (in for example headphones) a process called 'destructive interference' is used.

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Since Electromagnetic radiation can be described as a wave, could the same process (destructive interference) be used to 'cancel out' (or at least reduce the amplitude) of an electromagnetic radiation source?

If this is indeed possible, how would the waves (in case of EM radiation) 'cancel out' each other?

For active noise canceling the explanation given on wiki is "The waves combine to form a new wave, in a process called interference, and effectively cancel each other out" if I understand correctly the inverse sound wave compensates for the higher pressure 'compressed' zones caused by the 'ambient sound' by adding a 'low pressure' zone to decrease the pressure difference and visa versa thus dampening the sound. However I can't think of how this would work in case of EM radiation (in case it's possible).

Thank you!




2 Answers 2


certainly. accidental destructive interference of radio waves at 50MHz due to multiple-path radiation is called "picket-fencing" in the ham radio world. Deliberate destructive interference of radio waves is used in many high-directionality antenna designs to suppress reception of unwanted signals from off the main axis of the antenna.


One reason this would be difficult is velocity. To do noise-cancelling for sound, you masure the sound and respond. You can respond almost instantly because the sound travels slowly but the electric signals you use to create the response travel fast.

For electromagnetic radiation you are always behind, playing catch-up, because by the time you measure the wave you want to cancel, it has passed you. And there is no way to catch up because the signal that tells how to respond can't travel any faster than the radiation itself.

Well, but that's a negative attitude. It might work to send the radiation you want to cancel into a medium that slows it down, while the signals that say how to cancel it go through another medium that allows faster travel.

Sound is pressure waves. It has no real direction, except that it goes from high pressure to low pressure. Light travels in mostly straight lines except when it diffracts, and it mostly doesn't interact with other light. So if you make another pressure wave that cancels the first, you have elimininated the pressure. But if you make a new light wave that cancels the first everywhere, that is traveling a slightly different direction, they don't quite cancel after all. And maybe they will both get more separate with distance. I'm not sure.

It's two different things that are kind of analogous. I can't say it's impossible but it looks difficult.


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