# Evanescent Wave Coupling & Quantum Tunneling

## Main Question or Discussion Point

Hi, this is my first post here so apologies for any faux-pas I inadvertly do.

Anyways, to the subject at hand.

Evanescent Wave Coupling -> abbrv. -> EWC

Can someone explain to me evanescent (decaying) waves work?

I have been reading a wiki article about EWC, and it made many references to these waves in a magnetic field. It talked about how this waves have no energy, unless the are received by something with the same which resonates at the same frequency. Therefore using the theory of electrical resonance.

How can a wave have no energy? I realise that a simple sine wave has a net effect of zero mathematically, but its still through around positive and negative peaks; and therefore still has energy. It could be something to do with it being a magnetic field though, my knowledge is getting shakey.

It has something to do with quantum tunneling apperently.

The practical use of EWC is for wireless electricty, that does not affect other electronics (in the way that Inductive Coupling does). My understanding of it is a HF oscillating magnetic field is produced from a transmitter, and reaches a reciever where it induces a current (Lenz's Law of Induction), and the efficiency is increased by electrical resonance of the same frequency as the transmitter.

I think I've confused myself as much as anyone else, so please ask for any details I've missed.

Phinks

Related Quantum Physics News on Phys.org
*bump*

I am also interested in comments to this question.

There's a difference between having and transmitting energy.

The simple example of evanescent waves would be something like "total internal reflection" of, say, ocean surface waves encountering a (depth) boundary at an angle, and noting that if this bounding region is very narrow then the strength of reflection decreases (transmission/"coupling" occurs). My point is that it is a common classical wave effect, not something peculiar to quantum mechanics (aka. wave mechanics).

Do you have a source for that "practical use"?