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not clear from explanation why kz is larger than k when total internal reflection occurs.
Could someone please add references to the electric section? Sorry - I don't know how to tag it as needing references. 137.215.6.53 ( talk) 07:40, 18 July 2008 (UTC)
We should delete the reference [5] on "evanescent wave coupling". Since I'm not really active on wikipedia, I would leave this to someone else. However, this paper by Yong et.al. seems to give a reference for a general physical phenomenon, yet it is a relatively new, specialiced and totally unknown paper. I recommend one of the standard textbook, such as:
- Jackson, J.D., 1999. Classical Electrodynamics, 3rd ed. Am. J. Phys. 67, 841. - Novotny, L., Hecht, B., 2006. Principles of Nano-Optics. Cambridge University Press. - Meschede, D., 2008. Optik, Licht und Laser. Springer DE. — Preceding unsigned comment added by 141.84.253.1 ( talk) 12:31, 20 March 2013 (UTC)
Isn't this page lacking the information (or at least needing to put it more clearly) that the direction of the evanescent electric field is the same of the exponential decaying? I have the impression sometimes that people care much about the fact that the evanescent waves "evanesce" exponentially, but this is by no means its most notable characteristic. The fact that the field is in the same direction of this decay is the one worth noting. -- NIC1138 ( talk) 05:18, 13 January 2009 (UTC)
As the separate page on "evanescent wave coupling" is quite short, and concentrates on practical applications, it seems to me that it would be better to merge it into this page. Is anybody opposed to this idea ? ( RGForbes ( talk) 21:43, 11 March 2009 (UTC)).
I found this article while preparing an exam in photonics and I think a correction might be necessary. My understanding is that an evanescent wave appears when a wave crosses from a denser to a thinner material, in my case optically denser/thinner. This is one of the prerequisites for total reflection, which is connected to the appearance of evanescent waves. Is this true for any electromagnetic wave? Everything I've read seems to imply so, however I'm rather a layman in the field so I'd like to be sure :)
Longbowman3 ( talk) 13:57, 16 April 2009 (UTC)
Can I take it that "with an intensity that exhibits exponential decay with distance" means "of an intensity which diminishes exponentially with distance"? Or is something subtler being implied here, something to do with "exhibit" or "decay"? Unfree ( talk) 04:56, 7 March 2010 (UTC)
I find "Evanescent waves are a general property of wave-equations" confusing. Surely, an equation is something a human being can write down in pencil on paper. Surely, evanescent waves must be physical phenomena. Surely, "property" and "general property" must have quite well established meanings in science. Can it be said that evanescent waves are phenomena which can be seen to emerge naturally from the wave equations, are implicit in them, or can be accounted for by them? Unfree ( talk) 05:19, 7 March 2010 (UTC)
Considering the direction of movement and the surface of the medium, one would naturally expect the incident angle of the photon, phonon, or whatever, to refer to the angle between the two, rather than between the photon and the normal to the surface. So "they strike it at an angle greater than the so-called critical angle" would seem to imply less shallow rather than shallower. A rewording is called for, or at least a clarification. (Also, how is "so-called" called for?) Unfree ( talk) 05:31, 7 March 2010 (UTC)
"EM waves", I take it, is an abbreviation for electromagnetic waves? If so, let's insert "(EM)" after the first occurrence of "electromagnetic", or even better, spell it out each time. Unfree ( talk) 05:38, 7 March 2010 (UTC)
Just a hunch, but thinking about "in the nearfield region within one-third wavelength" makes me wonder whether this might be two ways of saying the same thing. Is it? If so, let's state so explicitly and eliminate a layer of logical abstraction. Unfree ( talk) 05:44, 7 March 2010 (UTC). I feel it would be more precise to use the terms induction field or reactive near field and this would avoid the need for mentioning one-third wavelength. Beamtube ( talk) 23:56, 24 January 2011 (UTC)
The way "in quantum mechanics" enters the discussion suggests (considering quantum mechanics to be valid) that all that has gone before is phony. It's as if we weren't discussing the real world, but an erroneous, prehistoric notion of it. I'm sure this is a familiar situation to those who learn Maxwell's equations before Schroedinger's, and being unfamiliar with any of them, I'm out of my league here, but an introductory sentence or two ought to suffice to explain why quantum mechanics is unnecessary at the outset, but ought to crop up later. Unfree ( talk) 06:08, 7 March 2010 (UTC)
Explaining "the unit vector in the z direction" crops up a little late, after we've been exposed to the unit vectors in the x and y directions without any explanation. Also, we're told that alpha is a real number, which, when multiplied by i, gives an imaginary result. That's clear. But it isn't clear at the outset (especially without understanding the unit vector notation) exactly what the "components" are, and what alpha and beta are. Unfree ( talk) 06:19, 7 March 2010 (UTC)
The caption of the pictures of the refracted versus evanescent wave in the "Total internal reflection of light" section incorrectly called the refracted wave the "diffracted wave." I fixed this and also removed a link in that caption to Diffraction limit because I didn't see how it was relevant (admittedly that page does talk about evanescent waves being used to beat the diffraction limit in imaging, but that didn't seem relevant to the picture). If I am wrong in these things, please revert. 165.124.205.144 ( talk) 08:13, 27 May 2010 (UTC)
The history of the discovery should be mentioned. I think two men discovered the wave at about the same time. — Preceding unsigned comment added by 92.27.109.117 ( talk) 15:37, 26 February 2013 (UTC)
In a standing wave, the nodes don't move. However, in the case of total internal reflection, the nodes move in a direction that is parallel to the reflecting surface. Constant314 ( talk) 18:01, 8 April 2013 (UTC)
The near field article is entirely about antennas. That near field decreases with the cube of distance whereas the evanescent field decreases exponentially with distance. Constant314 ( talk) 18:05, 8 April 2013 (UTC)
Sorry to point this out and cause consternation. But an evanescent field is not a wave, for instance according to the definition of wave in Wikipedia. A wave travels in space (or a medium) unless and until it is attenuated or deflected, and carries energy away from the source. By definition an evanescent field does neither. Yes I know that "evanescent wave" is a common expression, and I hear it more than "field" where I work from people who understand what I am saying but don't care about semantics (I've even caught myself saying it!). There is already a redirect page from "evanescent field" to this one. My suggestion would be to reverse them!
Also, on a different subject: a standing wave is not a "wave" either. It is two waves. What is "standing" is the oscillation of the electric (or magnetic) field. Another misnomer but not one that causes confusion.
Evanescent wave is a confusing term because it sounds like something exotic. Actually evanescent fields are ubiquitous, and most electric and magnetic fields in everyday life fall in this category. In your house you are surrounded by 50 (or 60) Hz fields very little of which is radiated into space. It is only when you are very far from all currents (many wavelengths away) that fields are dominated by traveling waves (since, again by definition, any evanescent fields have greatly decayed, whether exponentially or otherwise). Interferometrist ( talk) 18:39, 17 October 2015 (UTC)
When the second object is introduced into the evanescent field of the first object the field stops being evanescent. The field reflects off the second object, re-reflects off the first object, etc. The field between the objects must become non-evanescent or there will no power flow. Evanescent-wave coupling means there is coupling where an evanescent field would exist if the object being coupled were not there. Constant314 ( talk) 22:42, 27 October 2015 (UTC)
Nice job. I'd like to see the zero phase shift attribute brought back in. It is in the definitions and there is a nice tie-in with other knowledge. Zero phase shift means infinite phase velocity and zero group velocity which dovetails nicely with zero energy transport. Constant314 ( talk) 23:27, 28 October 2015 (UTC)
I am, like many others before, not comfortable with the modern use of the term evanescence. The bad direction it takes is to replace well known phenomena by fuzzy descriptions allowing some researchers to pretend making new discoveries and to patent already known ideas. For instance it is suggested that the near-field of a quasi-static dipole is made of evanescent waves whereas it simply decreases as 1/r3. So why discard the Coulomb's field and says that all charges are surrounded by an evanescent wavelike field? Why not going further and say that magnets and electrostatic charges are attracted and repelled by evanescent wavelike forces? I think (as suggested by many others in various section of this talk), that evanescent fields or waves should be limited, as they were originally, to the exponential decay of the field (or its envelope); Evanescent field, if there is no visible envelope (when decay is much shorter than the wavelength if any) and evanescent wave if an envelope can be seen. Such situations arise when an infinite number (at least a large amount) of charges or small dipoles (optionally oscillating ones) interacts in some distributed manners. As a result, evanescent fields and waves will still concerns some near-field optics situations and wave propagation inside conductors as well as many other situations, but will not pervade the whole quasi-static frame. Henri BONDAR ( talk) —Preceding undated comment added 13:19, 22 January 2016 (UTC)
Constant314 ( talk) 20:48, 29 January 2016 (UTC)
The usage of evanescent field is pervading situations that were well described using classical near-fields a few years ago. To my knowledge the field for a single charge, the Coulomb field, is decreasing as 1/r2 and is not evanescent or the gravity field should also be considered as an evanescent one. If you admit that the dipole field in 1/r3 is directly obtained using the Coulomb one, it should not be considered as evanescent too. By extension you cannot consider that non-radiating dipole-dipole interactions used for WPT transfer as evanescent.
If anything decreasing with distance is evanescent then the radiation of an antenna is also evanescent. Should we say that evanescence starts for a decreasing higher than 1/r, 1/r2, 1/r3?
As many contributors here I prefer to use the term "evanescent" to describe 'specific processes where the field is decreasing exponentially'. As in such situation the average Poynting vector is zero "evanescent wave" is then also an improper expression as previously said. I don't like the growing dogmatism introduced by Soljacik, Witricity and followers to defend that their non-radiative near-field device involves a kind of magic quantum focalisation process. These ideas pervade many wikipedia pages and articles whereas the device is only a modern declination of Tesla coupled coils associated to resonant circuits (resonances do not alter the link as falsely suggested but reduce the losses in the devices). They also renamed the coupling index kQ used since around 1930 to described capacitive and magnetically coupled resonant circuits into "factor of merit". It is now common to see in the literature as a first example of evanescent field the Witricity system of coils. The dogmatic pictures showing a kind of magic concentration of field lines coming with it are the first you see when you use the words "resonant circuits", "WPT" on Google search. Even worse in this page you can read that the interaction between the two plates of the capacitor is evanescent.
Is anyone ready to fight against obscurantism or do we have to say goodbye to Charles-Augustin de Coulomb and several centuries of science. Henri BONDAR ( talk) 21:07, 11 January 2019 (UTC)
There seems to be excessive hand wringing over whether an evanescent wave is a wave. The article is about evanescent fields. I propose that we change all instances in the article to evanescent field (except in direct quotes) an give the alternate names one time in the lede. Constant314 ( talk) 22:15, 15 January 2019 (UTC)
In the introduction section, a definition of evanescent field is presented. In the literature, it is presented a novel methodology to analyse this type of waves, regarding its excitation and its propagation. I think it is important to add a simply description about this in this introduction. I suggested the following:
A novel methodology to analyse the excitation and propagation of this type of waves is proposed in
[1], based on geometry.
References
{{
cite journal}}
: Check date values in: |date=
(
help)
This is the
talk page for discussing improvements to the
Evanescent field article. This is not a forum for general discussion of the article's subject. |
Article policies
|
Find sources: Google ( books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL |
![]() | Text and/or other creative content from Evanescent wave coupling was copied or moved into Evanescent wave with this edit. The former page's history now serves to provide attribution for that content in the latter page, and it must not be deleted as long as the latter page exists. |
![]() | This ![]() It is of interest to the following WikiProjects: | |||||||||||||||||||||||||||||||||
|
not clear from explanation why kz is larger than k when total internal reflection occurs.
Could someone please add references to the electric section? Sorry - I don't know how to tag it as needing references. 137.215.6.53 ( talk) 07:40, 18 July 2008 (UTC)
We should delete the reference [5] on "evanescent wave coupling". Since I'm not really active on wikipedia, I would leave this to someone else. However, this paper by Yong et.al. seems to give a reference for a general physical phenomenon, yet it is a relatively new, specialiced and totally unknown paper. I recommend one of the standard textbook, such as:
- Jackson, J.D., 1999. Classical Electrodynamics, 3rd ed. Am. J. Phys. 67, 841. - Novotny, L., Hecht, B., 2006. Principles of Nano-Optics. Cambridge University Press. - Meschede, D., 2008. Optik, Licht und Laser. Springer DE. — Preceding unsigned comment added by 141.84.253.1 ( talk) 12:31, 20 March 2013 (UTC)
Isn't this page lacking the information (or at least needing to put it more clearly) that the direction of the evanescent electric field is the same of the exponential decaying? I have the impression sometimes that people care much about the fact that the evanescent waves "evanesce" exponentially, but this is by no means its most notable characteristic. The fact that the field is in the same direction of this decay is the one worth noting. -- NIC1138 ( talk) 05:18, 13 January 2009 (UTC)
As the separate page on "evanescent wave coupling" is quite short, and concentrates on practical applications, it seems to me that it would be better to merge it into this page. Is anybody opposed to this idea ? ( RGForbes ( talk) 21:43, 11 March 2009 (UTC)).
I found this article while preparing an exam in photonics and I think a correction might be necessary. My understanding is that an evanescent wave appears when a wave crosses from a denser to a thinner material, in my case optically denser/thinner. This is one of the prerequisites for total reflection, which is connected to the appearance of evanescent waves. Is this true for any electromagnetic wave? Everything I've read seems to imply so, however I'm rather a layman in the field so I'd like to be sure :)
Longbowman3 ( talk) 13:57, 16 April 2009 (UTC)
Can I take it that "with an intensity that exhibits exponential decay with distance" means "of an intensity which diminishes exponentially with distance"? Or is something subtler being implied here, something to do with "exhibit" or "decay"? Unfree ( talk) 04:56, 7 March 2010 (UTC)
I find "Evanescent waves are a general property of wave-equations" confusing. Surely, an equation is something a human being can write down in pencil on paper. Surely, evanescent waves must be physical phenomena. Surely, "property" and "general property" must have quite well established meanings in science. Can it be said that evanescent waves are phenomena which can be seen to emerge naturally from the wave equations, are implicit in them, or can be accounted for by them? Unfree ( talk) 05:19, 7 March 2010 (UTC)
Considering the direction of movement and the surface of the medium, one would naturally expect the incident angle of the photon, phonon, or whatever, to refer to the angle between the two, rather than between the photon and the normal to the surface. So "they strike it at an angle greater than the so-called critical angle" would seem to imply less shallow rather than shallower. A rewording is called for, or at least a clarification. (Also, how is "so-called" called for?) Unfree ( talk) 05:31, 7 March 2010 (UTC)
"EM waves", I take it, is an abbreviation for electromagnetic waves? If so, let's insert "(EM)" after the first occurrence of "electromagnetic", or even better, spell it out each time. Unfree ( talk) 05:38, 7 March 2010 (UTC)
Just a hunch, but thinking about "in the nearfield region within one-third wavelength" makes me wonder whether this might be two ways of saying the same thing. Is it? If so, let's state so explicitly and eliminate a layer of logical abstraction. Unfree ( talk) 05:44, 7 March 2010 (UTC). I feel it would be more precise to use the terms induction field or reactive near field and this would avoid the need for mentioning one-third wavelength. Beamtube ( talk) 23:56, 24 January 2011 (UTC)
The way "in quantum mechanics" enters the discussion suggests (considering quantum mechanics to be valid) that all that has gone before is phony. It's as if we weren't discussing the real world, but an erroneous, prehistoric notion of it. I'm sure this is a familiar situation to those who learn Maxwell's equations before Schroedinger's, and being unfamiliar with any of them, I'm out of my league here, but an introductory sentence or two ought to suffice to explain why quantum mechanics is unnecessary at the outset, but ought to crop up later. Unfree ( talk) 06:08, 7 March 2010 (UTC)
Explaining "the unit vector in the z direction" crops up a little late, after we've been exposed to the unit vectors in the x and y directions without any explanation. Also, we're told that alpha is a real number, which, when multiplied by i, gives an imaginary result. That's clear. But it isn't clear at the outset (especially without understanding the unit vector notation) exactly what the "components" are, and what alpha and beta are. Unfree ( talk) 06:19, 7 March 2010 (UTC)
The caption of the pictures of the refracted versus evanescent wave in the "Total internal reflection of light" section incorrectly called the refracted wave the "diffracted wave." I fixed this and also removed a link in that caption to Diffraction limit because I didn't see how it was relevant (admittedly that page does talk about evanescent waves being used to beat the diffraction limit in imaging, but that didn't seem relevant to the picture). If I am wrong in these things, please revert. 165.124.205.144 ( talk) 08:13, 27 May 2010 (UTC)
The history of the discovery should be mentioned. I think two men discovered the wave at about the same time. — Preceding unsigned comment added by 92.27.109.117 ( talk) 15:37, 26 February 2013 (UTC)
In a standing wave, the nodes don't move. However, in the case of total internal reflection, the nodes move in a direction that is parallel to the reflecting surface. Constant314 ( talk) 18:01, 8 April 2013 (UTC)
The near field article is entirely about antennas. That near field decreases with the cube of distance whereas the evanescent field decreases exponentially with distance. Constant314 ( talk) 18:05, 8 April 2013 (UTC)
Sorry to point this out and cause consternation. But an evanescent field is not a wave, for instance according to the definition of wave in Wikipedia. A wave travels in space (or a medium) unless and until it is attenuated or deflected, and carries energy away from the source. By definition an evanescent field does neither. Yes I know that "evanescent wave" is a common expression, and I hear it more than "field" where I work from people who understand what I am saying but don't care about semantics (I've even caught myself saying it!). There is already a redirect page from "evanescent field" to this one. My suggestion would be to reverse them!
Also, on a different subject: a standing wave is not a "wave" either. It is two waves. What is "standing" is the oscillation of the electric (or magnetic) field. Another misnomer but not one that causes confusion.
Evanescent wave is a confusing term because it sounds like something exotic. Actually evanescent fields are ubiquitous, and most electric and magnetic fields in everyday life fall in this category. In your house you are surrounded by 50 (or 60) Hz fields very little of which is radiated into space. It is only when you are very far from all currents (many wavelengths away) that fields are dominated by traveling waves (since, again by definition, any evanescent fields have greatly decayed, whether exponentially or otherwise). Interferometrist ( talk) 18:39, 17 October 2015 (UTC)
When the second object is introduced into the evanescent field of the first object the field stops being evanescent. The field reflects off the second object, re-reflects off the first object, etc. The field between the objects must become non-evanescent or there will no power flow. Evanescent-wave coupling means there is coupling where an evanescent field would exist if the object being coupled were not there. Constant314 ( talk) 22:42, 27 October 2015 (UTC)
Nice job. I'd like to see the zero phase shift attribute brought back in. It is in the definitions and there is a nice tie-in with other knowledge. Zero phase shift means infinite phase velocity and zero group velocity which dovetails nicely with zero energy transport. Constant314 ( talk) 23:27, 28 October 2015 (UTC)
I am, like many others before, not comfortable with the modern use of the term evanescence. The bad direction it takes is to replace well known phenomena by fuzzy descriptions allowing some researchers to pretend making new discoveries and to patent already known ideas. For instance it is suggested that the near-field of a quasi-static dipole is made of evanescent waves whereas it simply decreases as 1/r3. So why discard the Coulomb's field and says that all charges are surrounded by an evanescent wavelike field? Why not going further and say that magnets and electrostatic charges are attracted and repelled by evanescent wavelike forces? I think (as suggested by many others in various section of this talk), that evanescent fields or waves should be limited, as they were originally, to the exponential decay of the field (or its envelope); Evanescent field, if there is no visible envelope (when decay is much shorter than the wavelength if any) and evanescent wave if an envelope can be seen. Such situations arise when an infinite number (at least a large amount) of charges or small dipoles (optionally oscillating ones) interacts in some distributed manners. As a result, evanescent fields and waves will still concerns some near-field optics situations and wave propagation inside conductors as well as many other situations, but will not pervade the whole quasi-static frame. Henri BONDAR ( talk) —Preceding undated comment added 13:19, 22 January 2016 (UTC)
Constant314 ( talk) 20:48, 29 January 2016 (UTC)
The usage of evanescent field is pervading situations that were well described using classical near-fields a few years ago. To my knowledge the field for a single charge, the Coulomb field, is decreasing as 1/r2 and is not evanescent or the gravity field should also be considered as an evanescent one. If you admit that the dipole field in 1/r3 is directly obtained using the Coulomb one, it should not be considered as evanescent too. By extension you cannot consider that non-radiating dipole-dipole interactions used for WPT transfer as evanescent.
If anything decreasing with distance is evanescent then the radiation of an antenna is also evanescent. Should we say that evanescence starts for a decreasing higher than 1/r, 1/r2, 1/r3?
As many contributors here I prefer to use the term "evanescent" to describe 'specific processes where the field is decreasing exponentially'. As in such situation the average Poynting vector is zero "evanescent wave" is then also an improper expression as previously said. I don't like the growing dogmatism introduced by Soljacik, Witricity and followers to defend that their non-radiative near-field device involves a kind of magic quantum focalisation process. These ideas pervade many wikipedia pages and articles whereas the device is only a modern declination of Tesla coupled coils associated to resonant circuits (resonances do not alter the link as falsely suggested but reduce the losses in the devices). They also renamed the coupling index kQ used since around 1930 to described capacitive and magnetically coupled resonant circuits into "factor of merit". It is now common to see in the literature as a first example of evanescent field the Witricity system of coils. The dogmatic pictures showing a kind of magic concentration of field lines coming with it are the first you see when you use the words "resonant circuits", "WPT" on Google search. Even worse in this page you can read that the interaction between the two plates of the capacitor is evanescent.
Is anyone ready to fight against obscurantism or do we have to say goodbye to Charles-Augustin de Coulomb and several centuries of science. Henri BONDAR ( talk) 21:07, 11 January 2019 (UTC)
There seems to be excessive hand wringing over whether an evanescent wave is a wave. The article is about evanescent fields. I propose that we change all instances in the article to evanescent field (except in direct quotes) an give the alternate names one time in the lede. Constant314 ( talk) 22:15, 15 January 2019 (UTC)
In the introduction section, a definition of evanescent field is presented. In the literature, it is presented a novel methodology to analyse this type of waves, regarding its excitation and its propagation. I think it is important to add a simply description about this in this introduction. I suggested the following:
A novel methodology to analyse the excitation and propagation of this type of waves is proposed in
[1], based on geometry.
References
{{
cite journal}}
: Check date values in: |date=
(
help)