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Headings/claims

I have reworded these heading changes. "Principles of wireless energy transfer" would be a misnomer as worded, part of the section shows a history similar wireless telegraphy, people coming up with systems based on a miss-understanding of the physical world, they didn't come up with any "Principles" used later on.

"Tesla's abandoned work" makes it sound like Tesla was on to something. The larger worldwide system was not based on any know principle, it came from an aether theory fantasy in Tesla's mind. It was not "abandoned" in so much as it never worked. Fountains of Bryn Mawr (talk) 18:49, 27 October 2016 (UTC)

I beg to agree on disagreement, especially, "abandoning work" is no statement about it being "on to something", imho. If "foundational efforts" would have suited better compared to "principles"? Even if I prefered the structure, which I intended to establish, I won't care until further notice. Just let me know, when I could be of some help. :)- Purgy (talk) 07:13, 28 October 2016 (UTC)
If you can see better wording please add it. I find it hard to characterize things before microwave because most sources I find on Wireless Power/history do not cover any of this, and they treat Tesla as a footnote[1][2][3], i.e. we are are working outside RS. I think we can go beyond that as a way of adding context by describing it. Fountains of Bryn Mawr (talk) 13:32, 28 October 2016 (UTC)

Edited "Tesla" section for improved readability and factual accuracy

  • Tesla's patented high frequency "System of Electric Lighting" was one wire, not wireless.
  • Tesla selected Colorado Spring as the location for the Experimental station because of the availability of electric power, not because of its elevation.
  • The C/S oscilator developed just over 1 megavolts electrical output, not 10 megavolts.

GLPeterson (talk) 04:30, 28 October 2016 (UTC)

Being fully aware of your opposed perspective, I want to explicitely make note of me not perceiving your edits as furthering improved readability, and also that I perceive them as (intentionally?) introducing biased POVs. I won't care until further notice. Purgy (talk) 07:00, 28 October 2016 (UTC)
Reason for move to Colorado Springs? We have to go with secondary sources:
  • Tesla: Inventor of the Electrical Age by W. Bernard Carlson, page 264 - "Moreover, by being in the mountains, Tesla could study how currents were conducted through both the earth’s crust and the atmosphere at high altitude."
  • Tesla, Master of Lightning by Robert Uth, page 92 - "What of Tesla's scheme to transmit electrical energy through the upper atmosphere — the very idea that brought him to the foot of Pikes Peak?"
Tesla floated the idea that he simply went to Colorado Springs for the AC power supply in his 1916 testemony[4] when pressed by his own lawyer. Primary source so not usable as such and we have to take into account the purpose of this testimony; Tesla was trying to make a claim on inventing radio and down-playing the fact that he had built a conduction based system, not a radio system.
"one wire, not wireless" could be refined and wording could be changed to "in the megavolts range" unless nailed down to a better source (just haven't looked). Fountains of Bryn Mawr (talk) 14:57, 28 October 2016 (UTC)

Protected edit request on 2 November 2016

Early on he seemed to borrow from the idea's of Mahlon Loomis,

Should read 

Early on he seemed to borrow from the ideas of Mahlon Loomis,

Schemathings (talk) 16:52, 2 November 2016 (UTC)

Done — Martin (MSGJ · talk) 09:25, 3 November 2016 (UTC)

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Non- vs. Radiative and Near- vs. Far-Field

I have no idea about the specific terms of this topic, but to my abstract knowledge near- and far-field are mathematical constructs, describing the dominant part of the EM-wave in the respective region of the emitter (having of course also other, most relevant differences, like energy coupling). The "measure" for "near" and "far" is thereby given by the ratio of the wavelength of the EM-wave and the distance. So for each setting there is a specific distance, where the contributions of near- and far field to the EM-wave are of equal magnitude. This distance might be considered as a natural boundary between those regions.

In any case, both "fields", near- and far-, are inherently bound to radiation, and so -not knowing about the local habits- talking about the use of "near field effects" as "non-radiative" takes me by surprise. Even when the exploited effects are physically confined to the "near neighbourhood", they are inherently based on "radiation".

I do not dare to touch the tangled mass of notions like capacitive, inductive, magnet/o-dynam/ic, (electro/magneto)-"static", especially in connection with "resonant", but I think there are still many skeletons in the closet, all in need of some contemporary EM-refreshing. -Purgy (talk) 07:33, 30 November 2016 (UTC)

Read the Field regions section. It's all laid out there. Everything in the section is supported by modern mainstream wireless power texts; check the copious sources cited. For example, on near-fields being "nonradiative" and far-fields being "radiative", see Agbinya, p.1. Cheers --ChetvornoTALK 11:32, 30 November 2016 (UTC)
The part of your statement above I disagree with is: "...both "fields", near- and far-, are inherently bound to radiation... Even when the exploited effects are physically confined to the "near neighbourhood", they are inherently based on "radiation"". Radiation means electromagnetic waves (radio waves). The characteristic of radiation is that it leaves the transmitter whether or not a receiver is present to receive it, while the energy in near fields stays with the transmitter unless there is a receiving coil nearby to absorb it. Power can be transmitted by near fields without any being radiated. For example, consider two coils of wire near each other, one powered by current from the 60 Hz wall plug, the other connected to a light bulb which is lit. There is no "radiation" going on here; the power is crossing the space from the transmitting to the receiving coil through the (near field) magnetic field, by inductive coupling (electromagnetic induction), as in a transformer. If you separate the two coils, the light goes out and then no power is drawn from the source by the transmitting coil, indicating that no power is being radiated as radio waves. --ChetvornoTALK 12:53, 30 November 2016 (UTC)
May I point you to the first part of my very first sentence? :) Our notions on "radiation" do not conform. Your "radiation" is my "far-field approximation" of radiation. personally, I prefer to call EM-effects per "radiation", when their propagation does not macroscopically involve some medium. So in my nomenclature, if some device is charged via a cable it is not radiative, however when it is charged, read out, modified, ... across some distance, to me radiation is involved. To be more precise, radiation happens to me whenever there is some non-zero d/dt, so along a high voltage 60Hz transmission line you have heavy radiation losses, and in a near-field communication environment you do not only have power supply, but also information interchange across the EM-fields.
I admit that considering a transformer a radiative device is somehow bewildering, but I think, in this article the term near-field interaction to be far more physically appropriate than the -to my measures- factually wrong term non-radiative, which stems imho from aged mind maps of Maxwell's equations.
I certainly do not want to change the habits and the common lingo, but I felt urged to mention the theoretical background. The view of inductive coupling is just an approximation of the radiative process, unified in the relativistic field tensor, where motors, transformers, inductive and capacitive coupling, ... are all the same. -Purgy (talk) 10:12, 1 December 2016 (UTC)
I see your point, you are saying that any transfer of power across space by time-varying electromagnetic fields could be called "radiative". But you are using the term "radiative" in a way different from its use in the wireless power field, and indeed in all electromagnetics. In electromagnetics the term "radiation" is reserved for the far-field components, which travel as electromagnetic radiation, and the transfer of power by near fields is called "induction" (electrostatic induction, electromagnetic induction). It is important for WP articles to use the correct terminology for their field. The terms "radiative" and "nonradiative" are used as categories of wireless power systems in most textbooks on the subject [5], [6], [7], [8], [9] so my feeling is they need to be in the article. --ChetvornoTALK 00:43, 2 December 2016 (UTC)
I strongly disagree with your claim "In electromagnetics the term "radiation" is reserved for the far-field components". It may well be so in the wireless power field, and I certainly won't move a single finger to change any habits in this important, highly practical field, and also not to change any wordings in Wikipedia articles on these topics. However, I sensed the need to point to the rather arbitrary discrimination between near- and far-field, governing the quite obvious term "radiation" to be unnecessarily vague. How do you think about a wave guide, transmitting microwave power across a single conductor? You cannot identify near and far field in this setting, and it is "non-conductive" either, because this all is derived for some simple, highly theoretic boundary conditions, allowing for this well known separation in "components", which have no physical significance beyond their decay rate in exactly these boundary conditions (vertical lambda/2-dipole above a halfplane). The advances in wireless power are to be expected in finding similarly interesting boundary conditions as the waveguide with circular cross section offers.
Please, remember also what I called these terms: tangled mass of notions like capacitive, inductive, magnet/o-dynam/ic, (electro/magneto)-"static", especially in connection with "resonant". These are all remnants of early understanding of EM, focused on parts of the whole theory.
Why use "non-radiative", if "near-field" is available, more correct and even more precise, at all? Need of "soothing" caused by excluding "radiation"? Holy marketing! ;) -Purgy (talk) 08:58, 2 December 2016 (UTC)

Archives not listed

The archives of this Talk page are not listed at the top for some reason by the archiving bot. Does anyone know how to make it do that? I don't know enough about archiving to find what's wrong. Thanks. --ChetvornoTALK 01:47, 6 May 2017 (UTC)

Fixed. It was a complicated (and interesting to me!) situation...feel free to ignore the following technical analysis if you don't care:) Many years ago, the page was at Wireless energy transfer, whose talkpage was archived normally at Talk:Wireless energy transfer/Archive 1 and then continuing as /Archive 2. The page was then renamed (in several steps) eventually landing here at Wireless power transfer. The editors who moved the page moved the talkpage itself but didn't move the talkpage archives, so they were stranded at their old name. The archive bot then continued to archive normally, continuing to fill /Archive 2 and subsequent as subpages of the new name, leaving Talk:Wireless power transfer/Archive 1 vacant. The talk-header with archive search noticed that there was no /Archive 1 of the current name, so it didn't think there were any archives. I inserted the old-name's talk archives and now we're all set. DMacks (talk) 05:06, 6 May 2017 (UTC)
Thanks so much! It looked to me like the bot was working ok, but that problem you found would never have occurred to me. I'll have to remember it in case I run across it again. Thanks again. --ChetvornoTALK 07:39, 6 May 2017 (UTC)

Good Mention of Inventor Nikola Tesla Wireless Power Experiments

glad a mention of nikola teslas experiments to transmit wireless eleltric power. July 4th 2017 will be the 100th anniversary of the destruction of the 300 foot wodend power tower by the order of the us overment suppossely because erman spies could have used to thoer to spy on us shippin off long island .america was at war in world war 1 at the time. july 4th 1917.hoefully the world will not have to wait another 100years for wireless power to be in use. also, no mention in article aout ELETRIC ROADS in south korea and now sweden usein wireless power transfer to power and rechare a ev electric vechicle thanks.Edson andre' johnson d.d.ulc,amm — Preceding unsigned comment added by TheStilletoKid (talk • contribs) 03:48, 18 June 2017 (UTC)

Recent edits on "2nd resonance" systems

I am concerned about the text and image Discharger1016 recently added to the Resonant inductive coupling section:

Only the resonance on the secondary side is effective.　This is called 2nd-resonance technology.
"Power transfer is performed only by the resonance of the secondary side. This is called phase synchronization."

This confusing text seems to imply that in resonant inductive power systems resonant circuits are not necessary in both the transmitter (primary) and receiver (secondary) circuits as the rest of the article indicates, but would work just as well with a resonant circuit only in the receiver. The cited sources do not support this. They show that such "single-tuned" power systems work and are used in cases such as railway power systems where the transmitting coil cannot be a tuned circuit. This should be mentioned in the article. But there is no indication that they are as efficient as double-tuned systems:

  • [10] - Powerpoint presentation may describe such a single-tuned inductive power system for a railway (its hard to tell because the circuit is not given) but it does not compare single-tuned and double-tuned systems or say single-tuned is as efficient.
  • [11] - entirely in japanese and does not render in my browser
  • [12] - Apparently an abstract of a japanese article behind a paywall. Can't tell whether it's an article from a reliable technical magazine or a promotional article from a commercial site.
  • [13] - An abstract of a paper presented at a conference. It says "...it is possible to achieve highly efficient wireless power transfer with a resonant structure in only the secondary side." However, there is no indication it compares single-tuned and double-tuned power systems or that a single-tuned system can be as efficient as double-tuned.
  • [14] - Just an advertisement for a japanese electronics magazine, without access. If there is an article in this magazine which supports the editor's position, he doesn't indicate which one.
  • [15] - A brief single page japanese description of railway inductive power system. No circuit or technical specs.

Unless adequate sources supporting it are found, I think this addition should be reverted. --ChetvornoTALK 09:58, 16 May 2017 (UTC)

Let's review the history of wireless power transfer again. The world's first practical use was in 1993. This is the achievement of John Boys. Please refer to the website of the Japanese company. A Brief History of Development
The Tutorial of John Boys can be understood that if you read it carefully, he is analyzing the coupling of resonance on the secondary side . In particular, you should refer to P13, P14, P89 etc.
Next, why he does not adopt dual resonance is in P29 and P30, this is because the phase characteristic Zp becomes complicated at heavy loads.
And there are many references from P94 to P96. Originally we should read all of them, but the easier way is to find out about patents of Japanese companies that partnered with John Boys. There is no concept of dual resonance in the patent applications of them and their competitors from 1990 to 2000 when they were invented. Those are resonance of the secondary side only.
What I'd like to say is that it should be responsible for the comparison of single and dual resonances by WiTricity who appears later and presented dual resonance.
WiTricity has not fulfilled its responsibility. However, one of other Japanese company is comparing single resonance and dual resonance. These data are on a verifiable website. Anyone can download it for free. I show you extractions those explanations.Extractions,Catalog download (red bar)
According to 【Exhibition Report】 Techno Frontier 2017 - New Energy Newspaper, it is :written as follows.
- Summary -
The "2nd-resonance" technology, which was demonstrated at the booth of OMRON, maintained about 90% without drop in efficiency, even if the axis of the coil was shifted by 10 cm.
The point is to construct the resonance circuit only on the secondary side. If constructed on both the primary side and the secondary side, transfer distance become long, but if axis of the coil shifts, the efficiency drops extremely.
Next, There is also an interesting description in A Brief History of Development. It is said that these descriptions are quoted from DAIFUKU NEWS No. 161 (August 2001), and this DAIFUKU NEWS No. 161 seems to be a pretty well-known report. And when search it on the net, it is being referenced many times. But I have not read it yet.
Referenced documents are as follows.
That is, SCMaglev's wireless power transfer technology of Japan Railway Technical Research Institute is referring to this (DAIFUKU/John Boys) technology. And Not only is it being referred to, but also presence of contact between key persons are written.
I present it for reference.
In any case, these patent applications are considered to be evidence that John Boys realized practical using of wireless power transfer technology before MIT.
I never meant to dismiss the achievement of Marin Soljačić. However, I would like everyone to understand that the true pioneer of the wireless power transfer is John Boys.--Discharger1016 (talk) 19:51, 18 June 2017 (UTC)

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Coupling in WPT

Apologies for being sloppy. First, with the deleted sentence I intended to address situations like e.g., radio or TV broadcasting, where the coupling, in the usual sense of mutual interaction, of receiver(s) and transmitter via the EM- field is absolutely negligible (non-reciprocity?). The transmitter is in no way appreciably concerned when some receivers' antennae within its transmission range are removed or added. In reasonable WPT however, afaik, adding a receiver or switching off one will result in a change in load of the transmitter, so that they may be considered as noticeably coupled. Second, I did not intend to deny broadcasting of power. Regards, Purgy (talk) 18:50, 17 May 2018 (UTC)

Okay, I see what you mean, you have a point. However I really don't think this minor technical point belongs in the introduction. Many (most) of the readers coming to the introduction will be general readers with no technical knowledge. They need to understand the more fundamental point that wireless communication and wireless power are alike, they use the same underlying technologies. My feeling is the appropriate place for the sentence would be in the 3rd paragraph of the "Overview" section, where this is explained. --ChetvornoTALK 19:16, 17 May 2018 (UTC)
Please, allow for my disagreement. Imho, it is the most important task in WPT to find scenarios (resonance?) of wireless, but "most strong" coupling, to overcome the effects of near/far-field, which are well established only for extreme cases, the transformer and the dipole field over a half plane. I think it is worth to mention that the former is broadly used in WPT (this is done already), but the latter is useless, and that the main task is to search for settings (signal forms and boundary conditions?) which allow for a coupling like with the transformer, but avoids certain inconveniences or disadvantages like with the capacitive analogs. Certainly, anything wireless rests on the propagation of EM waves without medium, but a strong energy/power coupling across this propagation is a formative property for WPT, and not a minor technical point.
I won't interfere about this in the article. Purgy (talk) 06:34, 18 May 2018 (UTC)

Power penetration of different materials

Wireless power transfer can penetrate some materials better than others. The extent to which each type of power transmission can penetrate common materials (eg glass, normal plastics, wood, copper, aluminium, iron, steel, brick, unreinforced concrete) would be a useful addition to this article (ideally in the table that contrasts the different mechanisms of transfer). If anyone knows this information, please add it. Thanks. FreeFlow99 (talk) 14:35, 29 November 2018 (UTC)

This is a fairly complicated subject. A certain amount of the electromagnetic energy reflects from the surface, which varies with angle of incidence and polarization, then some of the transmitted energy is absorbed passing through the material, which depends on thickness, then additional energy reflects from the exit surface. The waves reflected from the front and rear surface of the material superpose, so the reflected energy depends sinusoidally on thickness. When the path length difference equals an even multiple of a half-wavelength you get constructive interference and a strong reflected ray; when it is an odd multiple of a half-wavelength you get destructive interference and weak reflection and more transmission. All of these attenuation coefficients vary with frequency. I'm not sure a single absorption number representing an "average" over a wide frequency band, polarization states and material parameters would tell much. Also, most wireless power transmission is through air. --ChetvornoTALK 18:46, 22 December 2018 (UTC)

Evanescent wave or classical near field coupling between dipoles ?

Martin Soljacick had suggested that in the witricity patented device their might be some king of evanescent wave coupling. However evanescent coupling only arise at the interface between two mediums. The coupling coefficient between near-by coils as well as for nearby electrical dipoles can be computed in a classical way (through a coupling matrix) it leads to fields decreasing as 1/r^2, 1/r^3, 1/r^n. Besides the amplifying effect of resonances is also well known and described for a wide range of domains (magnetic and electric but also acoustical, mechanical). It is linked to an amplification of the field amplitude near resonance (that can be seen as a cumulative recycling of non-transferred energy in the generator and load side) and has nothing to do with the field geometry, no one as ever observed that the field distribution is affected by frequency as falsely suggested in the corresponding drawing (or you should prove it with actual data). According to my expertise, the Witricity system uses two core-less transformers on both sides of the link for the impedance adaptation function and a classical near-field coupling with a wider distance (improved by the resonance effect on both sides). Following Okkam razor principle there is no need to introduce some kind of evanescent concept that is moreover in contradiction with any accurate measurements on coupled coils(resonant or not), except if you want to patent a century old idea.

I suggest that the dogmatic chapter "inductive resonant coupling" should be removed, that a correct figure showing actual field-line should be used for magnetic coupling and that the resonance effect (increasing fields level without altering the field lines) should be introduced separately in a way to cover in a balanced manner both electric and magnetic near-field coupling.--Henri BONDAR (talk) 11:34, 4 January 2019 (UTC)

I wrote that section and drew the diagram. I appreciate the informed criticism. I basically agree that the diagram should be either replaced or supplemented with a circuit diagram of a more typical resonant inductive wireless power system. At the time I drew it the Soljačić experiment was high profile, so I felt we needed a drawing of it. I believe most modern wireless power systems don't use the "Witricity" self-resonant coils shown in the diagram, but the transmitter and receiver coils are in tank circuits direct-coupled to the oscillator and rectifier circuits, is that right? The magnetic field lines were not meant to be accurate; I was trying to suggest strong coupling. I'm not sure what you mean by "No one has...observed that the field distribution is affected by frequency as falsely suggested in the...drawing". But I'll remove the diagram until I can draw up a more representative one. --ChetvornoTALK 19:22, 4 January 2019 (UTC)
I included the term "evanescent fields" just because it was used in the Soljačić paper (and a few others). I agree it seems misleading and the fields are just induction fields. If you say it is not used in this application I will remove it. --ChetvornoTALK 19:22, 4 January 2019 (UTC)
As for removing the "Resonant inductive coupling" section, I think it is clearly needed to explain this important technology. The text is thoroughly sourced. Although I am just a BSEE and not expert in wireless power, I don't see any technical errors (beyond use of the word "evanescent"); maybe you can point them out. I also don't see that it is "dogmatic"; if you mean it overemphasizes the "Witricity" approach, I disagree; it seems to me the text in the section applies to all resonant inductive systems. Keep in mind that this is not a technical explanation for engineers but an encyclopedia article that attempts to be comprehensible to general readers. --ChetvornoTALK 19:22, 4 January 2019 (UTC)
As you probably know I have published a few articles concerning non-radiating near-field situations. Beside I am the inventor of the longitudinal configuration for the wireless capacitive resonant coupling. The first subject I'd like to discuss with you is the use of the unipolar/dipolar terms for capacitive coupling. According to me they suggest a difference in essence with the magnetic coupling case instead of a clear duality between the two. The idea that two coils as well as two electrical dipoles can be arranged in a longitudinal way (along the same axis in the direction of the energy transfer) or in a transverse way (perpendicular to the direction of the energy transfer) is much more in agreement with the duality principle (an with the transverse character of the far field). Beside in one of our articles we have demonstrated that for near-field conditions the coupling in both cases (magnetic or electrical) are twice higher for the longitudinal configuration than for the transversal one. In the electrical case the coupling can be further increased using electrode asymmetry. The dual case for magnetic coupling is the use of conical coils with the smaller diameter sides facing.
The second aspect that worries me much more is the incorrect suggestion that resonance has something to do with the coupling whereas it has not. The coupling coefficient can be obtained using the ideas of self and mutual inductance or equivalently self and mutual capacitance. The problem in the current page is that you suggest that these quantities are modified according to frequency whereas they are not at all frequency dependent (if the medium in between in not dispersive). All the quantities involved in the coupling computation depend only on the distribution of charges and currents then only on the geometries of electrodes or coils and the distance between them (with an extremely small influence of the skin effect in the magnetic case). If you want to make an appropriate picture of the field lines you should represent the field lines of a source coil nearly unaffected by the distant load coil with only a very small amount of field lines intercepted by the distant load coil.
The practical coupling coefficients for WPT systems are usually extremely small (often below one percent) as it can be easily measured for instance using the effective coupling coefficient obtained as the difference of the square of the anti-resonance and resonance frequencies divided by the square of the anti-resonance frequency (there is a very nice wiki page on this topic). Of course resonances improve the situation to a very large extent, however it doesn't affect the link but are only internal to the source and load devices. Resonance works as a cumulative effect inside the devices. For instance in the well known case of the Tacoma bridge, the small energy transfer due to the wind is progressively amplified with time in the bridge structure. A simple demonstration is to visualize the oscillation levels for resonant situations. It is very easy to show that the energy increases linearly with time until destruction arises. The amplitude levels are very large if the Q-factor of the circuit is large enough leading to both a larger energy transfer for the same coupling and smaller losses. Outside resonance frequencies energy is dissipated in the fastening structure (in the generator or load circuit in the electrical case, more accurately in the switching transistors or the rectifying diodes). So the only cause of power increase for resonant coupling (whatever electric magnetic, mechanic...) is not the change in coupling coefficient but the increase of amplitudes in the devices themselves. The critical quantity for coupled resonant circuits is the quantity kQ that was called coupling index in some old articles (somewhere in early 1900). When the coupling index is above unity, the efficiency is high. Said otherwise a small coupling can be compensated by large Q-factors (a larger possibility to recycle non-transferred or received energy to increase the amplitudes). All this is well explained for instance if you look in the technical pages of the Q-alliance (the non dogmatic approach of the resonant magnetic coupling and happily also much more successful on the market). The key aspect is to understand that resonance is a general internal process not related to the coupling link whatever its nature.
There is an other dogmatic aspect originated from Witricity and Marin Soljacik reinvention of the wheel that now pervades many wiki pages and articles: the idea that nearby coils or dipoles are coupled through evanescent waves but this is another story.Henri BONDAR (talk) 14:25, 7 January 2019 (UTC)
For the students, to explain the difference between coupling and resonance I often use the example of guitar cords: Two nearby guitar cords are weakly coupled (coupling coefficient is about 10^-4) moreover they are tuned to different frequencies, then when you move one cord, the other one stays nearly at rest. But if you tune two cords at the same frequency you will see with bare eyes that nearly all the energy given to one cord is progressively transferred to the other one and back and forth several times before the energy is totally dissipated. This highly efficient transfer through a weak coupling takes of course quite a long time (only an extremely small amount of energy is transferred at each alternation) and is due to the very high Q-factor involved (around 10^5) and then to the large value of the coupling index kQ=10. When the Q are different in the two coupled devices (the two cords here), the coupling index is k.sqr(Q1Q2),then better results are observed if the two sides have large Q factors (this gives a simple answer to the idea of second resonance).
Another clear explanation of the effect of resonance is to use the impedance adaptation theorem that states that the power transfer is optimized when the reactance of the link is compensated by the appropriate conjugate reactance; leading to a resonant circuit. One illustration of this idea is given on one of my didactic videos: https://www.youtube.com/watch?v=YegIW-1hbvQ&t=3s. Henri BONDAR (talk) 21:35, 7 January 2019 (UTC)
What specific text do you think should be changed in the article? And what do you think it should be changed to? In the capacitive coupling section I changed the terms "bipolar" and "unipolar" to "transverse" and "longitudinal" to address your concern. --ChetvornoTALK 23:19, 7 January 2019 (UTC)
I think the page is well structured in particular the far-field (radiative) and the non-radiative near-field are well described (good job indeed). I suggest, if not already done, that in non-radiative near-field chapter, you should explain first that there is no directive effect (no antenna gain) and that the field decreases more quickly for quadripoles or more complex structures than for dipoles. That in contrary to far-field were dipoles are always set transverse to the propagation direction, in non-radiative near-field dipoles could be arranged in longitudinal and transverse manner (electric and magnetic coupling treated on equal footing a reference to the electromagnetism duality theorem welcomed). An illustration of the two possible configurations is also welcomed (at least for coils). You may also explain that the longitudinal arrangement leads to higher coupling coefficients at least for intermediate distances and add a reference to support the idea (our article on this topic can provide other ref. if you don't use it directly) https://www.sciencedirect.com/science/article/abs/pii/S0304388613000314. The picture for the magnetic field lines in the longitudinal configuration that is already on the page is OK for me. Maybe a similar drawing for two electrical dipoles should be inserted, the picture should show a few shared field lines instead of all of them (in your two pictures for capacitive coupling some fields lines not linked to the load are missing to illustrate the idea that the coupling is usually weak (I will seek the web for a neutral illustration if any).
According to me the general resonance mechanism should follow in a separate paragraph for instance using the impedance tuning theorem (a conjugate reactance to cancel the natural reactance of the link). The idea that resistance should also be optimized on both sides could also be introduced. Ideally a picture showing up and down transformers to adjust the resistance on both sides, down in the generator side and up in the load side for inductive coupling because the link impedance is very small, and up-down for capacitive coupling because the link impedance is very large (see the examples in my didactic videos). An introduction of the key importance of the coupling index kQ is also welcomed (unfortunately the Qi consortium didactic pages have been removed, I found this https://phys.org/news/2014-09-versatile-pilotage-wireless-power.html but it point to a MIT introduction in 2007 whereas the introduction of the concept was done a century ago at least. I will search for another neutral and clearer source).
Then you may introduce some implementations. Among them the Witricity patent with its specific embedded core-less impedance adapters (the only original input according to me), some other implementations and references to the Qi WPT consortium if not done, some examples of transverse capacitive coupling; Tesla with its transverse vertical dipoles arrangements and his fortuitous discovery of standing waves (Telsa was working in intermediate distances between near and far field). More recently (around 1950 if I am not wrong) the New Zealand team and their first powered vehicle using transverse capacitive coupling, followed by a lot of other implementations (I remember of a Philips toothbrush in the years 1970). Finally, if you like, a reference to our more recent introduction of the asymetric longitudinal capacitive coupling with the only common root (expectedly) our 2006 patent, the following ones and Murata work on the subject.
Be careful, most recent articles (IEEE) do not cite our original patents and the following ones by Murata and more generally all our work. For instance there is a team in Detroit Michigan (now in San Diego) that we visited four years ago under a non disclosure agreement that published two years later several thesis and papers on the longitudinal capacitive coupling for car charging without citing their original source. More generally they have published in IEEE papers all the content of our patents and articles (including very technical aspects patented in Japan) without ever citing their sources (Their bad excuse was that they only cite IEEE sources). They won some innovation prices and earn several founding from Ford and the automotive market. Their main researcher pretend to be the word specialist in capacitive coupling whereas he doesn't even grasp the notions of self and mutual capacitance. Its how many structures works now; personal interest above moral rules and good practice, leading somehow to the evanescence of the structured knowledge !.Henri BONDAR (talk) 08:48, 8 January 2019 (UTC)
For the coupling index kQ, I found the proper link: https://en.wikipedia.org/wiki/Double-tuned_amplifier. The name coupling index is not explicitely written but you find it easily in french documents ("indice de couplage") http://philipperoux.nexgate.ch/Resources/Circuits_couples_VP1.pdf . I am certain that it originated before the years 1940 when the first vacuum tube HF amplifiers were made.
For the electric field lines in case of two coupled dipoles (a quadripole field in the strong coupling case) I found: http://xaktly.com/ElectricField.html but it is probably not the best illustration as the shared field lines corresponding to the mutual capacitance are not clearly separated from the field lines associated to the self capacitances of the two dipoles (the field lines starting on one charge/electrode and ending on the second charge/electrode of the same dipole).
Beside I have a problem with the following page that is more advertising for Witricity than anything else: https://en.wikipedia.org/wiki/Resonant_inductive_coupling. The corresponding pictures are also the first one that you see when you make a WPT search on Google.Henri BONDAR (talk) 11:25, 8 January 2019 (UTC).
Note that the Resonant inductive coupling page was perfectly free of any dogmatic content up to the 23 January 2017. Before the progressive migration of the content since this date; the addition of the incorrect field line pictures, the introduction of the evanescent wave coupling...., the resonance mecanism was correctly explained and the "coupling index" called "factor of merit" was correctly introduced (since 2012).Henri BONDAR (talk) 12:02, 8 January 2019 (UTC)
For a first accurate description of both capacitive and inductive resonant couplings see [1]. Older work (originating around 1932) concerning double tuned resonant circuits is summarized in the chapter 5 (pp 201 to 226), the coupling coefficient and coupling index are introduced in the bottom of page 202, for a direct access see: https://www.jlab.org/ir/MITSeries/V18.PDF.Henri BONDAR (talk) 15:53, 8 January 2019 (UTC)
Let me see if I understand your argument about frequency. The coupling coefficient k for a given geometry is not dependent on frequency. Resonant coupling can transmit more power at greater range because the coupling device (coil or capacitor) is in a resonant circuit. When driven at its resonant frequency, the current in the transmitter coil of a resonant inductive system will be Q times the current in a nonresonant system. Similarly in a resonant capacitive system the voltage on the capacitor plates will be Q times the voltage in a nonresonant system. Therefore the field strength in the resonant systems will be Q times the field strength in a corresponding nonresonant system. Therefore the resonant system will have the same power transfer efficiency as a nonresonant system with coupling coefficient kQ. Is that basically right? --ChetvornoTALK 21:13, 8 January 2019 (UTC)
Yes, you can also say that; when reactance tuning is made, the impedance seen by the generator is resistive instead of being inductive/capacitive, the energy doesn't oscillate back and forth in the generator/load structure leading to large induced losses and you have much less losses in the device. Quantitatively in the worst case current/voltage are increased Q times for the same amount of losses. The key point is to understand that this process is only device specific and has nothing to do with the link itself. So calling the product kQ a 'factor of merit' instead of a 'coupling index' as historically introduced is awkward but not totally inappropriate. This mechanism is known since at least a century (and perhaps more in acoustics) and has been formulated correctly since 1935 at least in electronics. Tesla was perfectly aware of it when he tried to destroy is hosting building using a mechanical resonance around 1890. Please note that reactance tuning is only the first step in the general impedance matching problem (see https://en.wikipedia.org/wiki/Impedance_matching and go to Maximum power transfer matching subsection)."They are no great discoveries, only a great ignorance of the past" and we are here to avoid that as far as possible.Henri BONDAR (talk) 05:21, 9 January 2019 (UTC)
Sorry I talk too much, it is one of my bad habits (quantity instead of quality). I have read the article again, after your last corrections there are no more urgent issues. However, I suggest that instead of using the inductive/resonant inductive, capacitive/resonant capacitive separation it would be much clearer to use a strong coupling/ weak coupling separation. In strong coupling situations (very close devices) the impedances are mostly resistive, the only reactive contributions are due to leakage inductance and leakage capacitance (more often called stray capacitance) so that impedance matching reduces to resistance tuning (choice of appropriate voltage ratio according to conditions). When the coupling gets smaller (devices set farther apart) the impedance matching process becomes critical to reach high power transfer or good efficiencies. In this case the link impedance is dominantly reactive and using an appropriate matching in the devices is critical. In this section the coupling index can be introduced as well as the importance of the Q-factors. I can send you my pictures for reactance tuning and resistance tuning process illustration if you like (down-up or up-down scheme according to situations). For the Witricity patent, according to me, it should remain only the idea that using subsidiary coils to provide the resistance tuning function provides an elegant way to reduce the number of windings (compared for instance to separate transformers used in my didactic videos) and that large coils lead generally to large Q-factors. Another aspect that we may introduce later is to define the relative range (separation divided by dipole size), in our article we have demonstrated that the maximum practical range for such near-field systems is limited to relative distances of about 10 due to maximum Q-factor considerations.Henri BONDAR (talk) 08:52, 10 January 2019 (UTC)
I appreciate all the expert technical information! I don't know the best sources for learning about this, so I'd really appreciate any links or sources you can give me. Here are my feelings about the points you raise above:
  • The point you made about the coupling not being frequency-dependent, and the improvement in efficiency of resonant systems being due solely to the increased amplitude of sources due to resonance, and the "coupling index" k(Q1Q2)1/2 should be in the article.
  • On changing the current section names from Inductive coupling / Resonant inductive coupling and Capacitive coupling / Resonant capacitive coupling to Strong coupling / Weak coupling, I oppose this. I think the current organization is good for introducing nontechnical readers to resonant coupling. General readers are likely to be familiar with nonresonant inductive coupling in the form of transformers and cordless toothbrushes, and this type of wireless power is easy to explain. With this background the article introduces resonant coupling as a modification which increases the currents and voltages in the coils and thus increases the strength and range of the fields. The differences you mention between strong resonant coupling and weak resonant coupling are kind of technical and might be better left to a separate mathematical section.
  • Resonant inductive coupling article: I absolutely agree with your above criticisms; it is a very poor article. As you mentioned, in Jan 2017 it was rewritten by an editor who not only introduced a lot of WP:UNDUE WEIGHT Witricity material, but made other unfortunate changes:
    • The editor for some reason emphasized single-tuned systems over double-tuned, in which only the receiver coil is a tuned circuit, while the transmitter coil is untuned. He seemed to think that these circuits were better and that industrial wireless power systems were increasingly using them (although all the supporting references he gave were in Japanese). Is this true? What is the advantage of a single-resonant system? It would seem to me that a system in which both coils are resonant circuits is always going to have higher power transfer efficiency than one with only one resonant circuit.
    • More generally, the article overemphasizes wireless power applications. Resonant inductive coupling is widely used in all kinds of areas besides wireless power: impedance matching in radio transmitters and antenna tuners, IF transformer bandpass filters in receivers, inverters and power supplies, ferroresonant transformers. These are the main applications and should be given the most emphasis in the article and listed first.
I plan to rewrite that article when I get a chance. If you could leave a note on the Resonant inductive coupling Talk page with your criticisms that would help improve the article.
  • Your point that to maximize power throughput the impedances must be conjugate-matched in the transmitter and receiver (more generally through the entire power chain) is important and should be in the article.
I view the existing sections on inductive and capacitive coupling as introductions for general (non technically educated) readers, and as such I think there is a limit to the amount of detailed technical/mathematical information which should be included in them. It seems to me that there should be an additional section for the mathematical details, something like Theory of near-field power transfer, which could include a derivation of the power transfer equations for resonant inductive and capacitive wireless systems, and a lot of the great points you mention above could be made in that section. --ChetvornoTALK 01:09, 15 January 2019 (UTC)
I agree with all your suggestions, will contribute actively for the theoretical side and will try to provide more historical references.
  • For the general presentation of non-radiating near-field couplings, I continue to think that introducing the idea that dipoles could be arranged either longitudinally or transversely, with up a too time larger coupling for the first case, should be great. A picture with core-less coils will be fine as the introduction of a dual capacitive situation will not be obvious for many readers. Beside it appears later in the capacitive coupling sub-section. Most non-radiative near-field devices are arranged longitudinally (two Tesla coils structures arranged longitudinally in case of the Witricity patent) by the way we should be careful that a correct balance is made between all participants (Witricity, Qi consortium and others).
  • Because Witricity has, according to me, a tendency to present their technology as brand new and well above any standard, they have a lot of aggressive followers leading to a form of proselytism over the web. One example is the case of asymmetric resonance, more generally the resonant induction page but also some other pages (see evanescence below). You are right when you think that the Q factors have similar weights on both side of the link as indicated by the coupling index. However, if for some reasons one coil is going to be better than the other one; using the best one on the load side has an advantage in term of field level. When the high-Q coil is used on the generator side, for the same power transfer you have a higher field level and lower energy extraction on the load side, whereas in the second case the field level is lower and the extraction of energy on the load side higher. This is important when you want to fulfill some field regulations while still hiding it under a quasi-magical frame.
  • I have some difficulties in the evanescent field page: https://en.wikipedia.org/wiki/Evanescent_field where Witricity dipole-dipole interaction is suggested as an example of evanescent field as well as the capacitor and transformers internal fields (Already removed). Soljacik non-neutral position is according to me not sustained by any other reliable secondary sources. Your opinion welcomed.
  • If you have some remaining time, your opinion is also welcomed in the Q-factor page: https://en.wikipedia.org/wiki/Q_factor where I suggest a reorganization of the presentation and an improved initial picture. Henri BONDAR (talk) 06:45, 15 January 2019 (UTC)

References

  1. ^ VACUUM TUBE AMPLIFIERS Copyright, 1948, by the McGraw-Hill Book Company, Inc
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