How Do Coherent Waves Maintain Identity in RF Systems?

In summary: When waves are said to be 'coherent', or in-phase, do they always act as a single wave, or do they maintain their individual identities?Generally, they maintain their individual identities. However, if you change or remove one, the total is different.
  • #1
sci-guy
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When waves are said to be 'coherent', or in-phase, do they always act as a single wave, or do they maintain their individual identities?
 
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  • #2
generally they are separate..in other words, if you change or remove one, the total is differenent...but that can depend on your definition and the many type of waves...there is spacial, temporal and spectral coherence for example...

See http://en.wikipedia.org/wiki/Coherence_(physics )

You might also find this intyeresting:
http://en.wikipedia.org/wiki/Noise_cancellation
Bose is one maker of earphone type noise cancellation...
 
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  • #3
sci-guy said:
When waves are said to be 'coherent', or in-phase, do they always act as a single wave, or do they maintain their individual identities?

Interesting question. I would say that fully coherent waves (that is to say, the mutual coherence function is 1) no longer have individual identities- they now form a single entangled state.
 
  • #4
Andy makes a good point..especially considering quantum mechanics...

My post was attempting a classical...everyday... perspective...
 
  • #5
Thanks, that's pretty much what I thought; I've read that quantum coherence means you can define the entire system by a single wavefunction. I assume that is like saying it acts as a single wave.

But it seems to apply even on the classical level. If you have a wave generator in a water pool pumping out synchronized waves, the output flows as a single larger wave.
 
  • #6
I have a problem reconciling this with what happens with a radio transmitting array with multiple driven elements. Do we have quantum entanglement there too?
 
  • #7
Sorry, I don't understand the technical jargon -- are you referring to a common radio broadcast signal? If so, I'm curious about that too.
 
  • #8
Any sort of radio transmission at any frequency will do. Many transmitting antennae consist of multiple elements (dipoles, for instance) which are fed from a common source. Imagine the transmitted signal or just a continuous single sine wave. Each element will be radiating the exact same signal (differing only in details of the precise phase and amplitude) and you will get an interference pattern which (usually) forms a directive 'beam' by careful choice of positions of the elements. This is totally the same as what happens a laser, in which the excited atoms release their energy in-phase with the wave that reflects up and down the cavity (stimulated emission).
As it happens, the photon energy of RF signals is exgtremely low and the vastly bigger numbers of photons can't be thought of as coming from individual atoms. But anything said about Quantum Coherence must surely apply, too, in some way.
I should like to hear how these two 'extremes' of the same phenomenon can be reconciled with a single model.
I know that RF is the 'poor relative' of light on these forums but my background is RF Engineering and I always like to square some of the Quantum Magic I have read with my own earthy experience. Stimulated emission is a minority even for light but coherent sources dominate in the RF world.
 
  • #9
I'm no scientist, but since light and radio frequencies are all part of the same electromagnetic spectrum, it seems to me that the coherence phenomena should be the same in both, as you suggest.
 
  • #10
Oh of course coherence means coherence for any system of waves - not just electromagnetic ones. My problem is the QM discussions around it which nearly always seem to involve excitation of an atom. I'd be interested to know where entanglement gets involved in an RF system with amplifiers and antennae.
 

FAQ: How Do Coherent Waves Maintain Identity in RF Systems?

What is coherence?

Coherence refers to the property of a wave or a group of waves to maintain a constant phase relationship over time. In other words, it describes the stability and predictability of the peaks and troughs of a wave.

How is coherence measured?

Coherence is typically measured using a coherence function, which compares the amplitude and phase of two waves at a given frequency. This function produces a value between 0 and 1, with 1 representing perfect coherence.

What is the difference between temporal and spatial coherence?

Temporal coherence refers to the relationship between waves at different points in time, while spatial coherence refers to the relationship between waves at different points in space. Temporal coherence is important in understanding the behavior of waves over time, while spatial coherence is important in understanding the propagation of waves through different media.

How does coherence affect interference patterns?

Coherence plays a crucial role in the formation of interference patterns. When two coherent waves superimpose, their amplitudes and phases are added together, resulting in a constructive or destructive interference pattern. Without coherence, the waves would not maintain a consistent phase relationship and interference patterns would not form.

Can coherence be created or enhanced?

Yes, coherence can be created or enhanced through techniques such as laser cooling, where atoms are slowed down and their motion is synchronized to create a highly coherent state. This is also achieved in interferometers, where the path lengths of two coherent waves are carefully controlled to maximize their interference.

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