What is an evanescent wave? What are its applications?

[ksmith1281]

I am reading some papers that mention evanescent waves. From what I can find, evanescent waves occur because of the Maxwell Boundary Conditions but I don't really see how. Could some please comment on this or just on the general topic. Thanks!

 

[y33t]

I am reading some papers that mention evanescent waves. From what I can find, evanescent waves occur because of the Maxwell Boundary Conditions but I don't really see how. Could some please comment on this or just on the general topic. Thanks!

That's a nice question. Evanescent fields are near field effects which are not easy to deal with. We had struggled to derive evanescent fields from Maxwell Equations to solve a problem in an hypothetical fiber network a while ago and I assure you it's not an easy task to mathematically immerse into evanescent phenomena. For general information and some of the applications ; http://www.faculty.iu-bremen.de/dknipp/c320352/Projects/Presentations%202005/CL%20Evanescent%20Fields.pdf

I would like to hear if someone comes up with the proof that derives evanescent fields from Maxwell equations step-by-step.

 

[ksmith1281]

Thanks!

 

[vanhees71]

For those who understand German, here I've written a quite complete review about fields in wave guides (in vacuo):

http://theory.gsi.de/~vanhees/faq/causality/node8.html

 

[PJC01]

An evanescent wave is a type of electromagnetic wave that exists near the boundary between two different media, such as air and a solid material. This phenomenon occurs because of the Maxwell Boundary Conditions, which state that at the interface between two media, the tangential components of the electric and magnetic fields must be continuous, while the normal components must have a discontinuity.

In simpler terms, an evanescent wave is created when an electromagnetic wave encounters a boundary between two media and some of its energy is reflected back while the remaining energy penetrates into the second medium. This energy that penetrates into the second medium is known as the evanescent wave.

The applications of evanescent waves are numerous and diverse. One of the most well-known applications is in optical fibers, where evanescent waves are used to transmit light energy through the fiber. These waves are also used in near-field microscopy, where they allow for high-resolution imaging of objects smaller than the wavelength of light. In addition, evanescent waves are used in sensing and detection techniques, such as surface plasmon resonance, which is used to detect changes in the refractive index of a material.

Furthermore, evanescent waves are also being studied for potential applications in wireless power transfer and communication. In this case, the evanescent waves are used to transfer energy between two devices without the need for physical contact.

In summary, evanescent waves are an important phenomenon in the field of electromagnetism with various applications in optics, microscopy, sensing, and wireless communication. Understanding and controlling evanescent waves can lead to advancements in these fields and potentially open up new avenues for research and innovation.