Talk:Induction loop

Untitled
I have cleaned up this article as much as I could. From 1979 until 1993 I was in the USAF and was a telecommunications technician, so I knew what he was talking about. The person who wrote this article was obviously an engineer of some kind becuase he was talking about some really deep subjects. Perhaps the person who wrote this piece could go back through and look at it again.

--TracyRenee 12:32, 30 Mar 2005 (UTC)
 * I've looked at the cleaned-up version as well as the first version and I'm still baffled. Most of the discussion sounds like it should be under electromagnetism and it doesn't get around to defining its subject. I'd VfD or redirect this to electromagnetism, I don't think it's salvageable. --Wtshymanski 21:07, 16 Apr 2005 (UTC)


 * Having a specific page for this is probably a good idea, though it should be retitled. inductive proximity sensors are used everywhere (just about every stoplight out there). They are definitely a notable subject.Fake0Name (talk) 07:05, 12 November 2010 (UTC)

Temporary Home for material NOT about induction loops
Just cant think what this stuff is doing here. Can someone write something about induction loops?Light current 02:30, 15 August 2005 (UTC)
 * Trying to integrate this material into electromagnetism or inductance could be verry tricky and time consuming unless you really know the difference between 'conservative' and 'non conservative' etc.. Anyway is there anything here that is not already covered on other pages? I think not. VfD Light current 02:40, 15 August 2005 (UTC)

Description
There are two kinds of fields: conservative and non-conservative. For a conservative field, the integration around a loop is zero. In a conservative field the work done by the force that generates the field depends on end points only and is independent of the path. Fields associated with the electric static force and the gravitational force are examples of conservative fields. For a non-conservative field, an electrical field is induced by a changing magnetic field. The force in a piston of a thermal engine is also non-conservative.

Since the electrical field induced by a changing magnetic field is non-conservative, the work done by this electrical field depends on the path. The inductance is associated with this path dependent work. It is for this reason that inductance is very sensitive to paths. To translate this into electrical engineering concepts, an inductance is very sensitive to the shape of the devices because the shape will effect the path of the current flow and thus the non-conservative work involved.

Since the work done by a non-conservative field depends on the path, it is not practical to talk about potential. If one tries to define a potential for given end points, there would be an infinite number of potentials involved. It is for this reason that we talk about the non-conservative work associated with a given loop. Here is how inductance comes into play.

Mathematically, inductance, indicated by the symbol "L", can be defined in two different ways:


 * 1) The total magnetic flux in a closed loop divided by the current that generates the flux
 * 2) The total work done by the vector potential when going around a loop divided by the current that generates that vector potential

If the current belongs to the same loop, we call the inductance self inductance. If the current belongs to another loop, we call it mutual inductance, using symbol "M".

While inductance is defined in terms of loops, not all examples must actually form a loop, i.e. a solenoid. A geometry that does not form a loop, one can always determine a loop that will have the same inductance effect. For example, in the case of a straight line, one may add two lines at both ends that are perpendicular to the current and let both lines be infinitely long. At infinity, one adds another line of any shape to close the loop. The justification for this is that a line perpendicular to the current will not have inductance associated with the current because it is penpendicular to the vector potential given by the current. As for the line at the far end, there is no inductance since the vector potential is zero at infinity.

The same principle can be applied to general shapes. Mathematically, it is a matter of numerical computation. In principle, for any 3D geometrical configuration, inductance can be calculated.

Based on the definition of inductance, the larger the loop, the larger the inductance. In the example above, the straight line is equivalent to an infinitely large loop. In general, a non-closed geometry has larger inductance than a closed loop.

This fact is quite important in high frequency electronic designs. At very high frequencies inductance contributes to total impedance. Thus it has an impact on crosstalk and reflection and strongly affects signal quality and signal delay. Therefore, correct loop concepts can help in improving the design of better circuits. For example, high frequency design demands small current loops.

Inductance also plays an interesting role in quantum mechanics, particularly the Aharonov-Bohm effect. This effect states that when a pair of charges pass around a long solenoid, the relative phase of the two charges will change. The change can be verified by the interference patterns on a screen. The implication is that a nonlocal quantum effect takes place. Although there is no magnetic field outside the solenoid, the particles are somehow affected by the field. Nonlocal effects plays an important role in current quantum information science.

introduction for laypeople?
I still have no idea what one of these does aside from that it's used in metal detectors and traffic systems. Can someone smarter than me write an intro? Lot49a (talk) 19:07, 17 April 2008 (UTC)

Missing material
Wow - some major clean-up is still required. Large parts of this article are barely in English! Grammar, syntax, and so on need some serious work. In addition, there are some major holes in the historical introduction. I know, for example, that a massive amount of research in this area was carried out by the British Army (Royal Artillery) post-world war two, with a particular emphasis on how induction loops might enhance commands in gun installations during the noise of battle. If there is anyone out there with more detailed knowledge, please add it to the article.  Timothy Titus Talk To TT  19:33, 28 March 2009 (UTC)

Disambiguation
May I propose that the term Induction loop should be the subject of a Disambiguation Page. At present, there is clearly a severe confusion in the page over the use of the term - probably resulting from it's use as a shorthand description in a number of different fields of application.

The possible applications/links might reasonably be:

The only problem I can see is that some of these might need creating, and that would need to be done by the original contributors to the Induction loop page.

I'd also add that the initial entry about the history of induction loops is possibly referring to carrier communications by induction loop, or the use of the system on military / naval applications? Whatever, it's not a useful layman's introduction to the general concept. So an update is needed.

If there is support for the disambiguation route, I'd be willing to assist. --TechTom (talk) 13:18, 11 June 2009 (UTC)

Whether or not we go disambiguation, there is (2019) another usage - for charging, from tooth brushes thru phones to "WiFi" EV chargers. There seem to be three broad categories: Sensing, Data Transmission (including baseband = audio) and Power Transmission. Shannock9 (talk) 01:28, 2 January 2019 (UTC)

Car detector
The description about how this is used to detect cars makes no sense. Cars are not magnets. Moving a magnet near a piece of conductive material will generate a voltage. Moving a non-magnetic piece of steel (e.g. a car) near a conductive loop will do nothing. Therefore, inductive proximity sensors cannot not be purely passive.

As I understand their function, The proximity detectors in road-surfaces are actually used as inductor in an oscillator, and the proximity of a piece of steel near the loop affects the flow of the magnetic field-lines from the inductor, therefore changing the inductance of the coil. Since the coil is used in an oscillator, the oscillator frequency then changes, which can easily be detected by other electronics.

Critically, this is very much not a passive system. The coils in the road-surface are constantly emitting a small magnetic field, which is what is used to detect the car's presence. Also, motion of the car is not required or relevant to the sensor detecting the car, which is somewhat critical since cars can be stopped at stop-lights.

Furthermore, there seems to be an ongoing conflation of two subjects going on in this article. The discussion of the use of inductive coupling to transfer information (e.g. the Discussion of the "Telecoil", which really should be called a coupled inductor, telecoil is just a brand-name used apparently exclusively in hearing-aids), and the use of inductors to detect the presence of objects are very different things, and use very different systems. Apparently someone has confused the two, since they both *do* use inductors.

I will sit down and do some research about the specifics in a few days (I need to confirm I understand everything precisely. I currently just have a general idea). If anyone has any preferences before I re-write the article a bit, please let me know. Fake0Name (talk) 07:05, 12 November 2010 (UTC)

The current description of function is wrong. The Inductance of the loop increases when the core of the coil is filled by the vehicle which contains a significant amount of steel as opposed to the air and concrete that was there without the vehicle. There are a number of ways that the system could detect this increase in inductance. Could someone who works in traffic signal design comment on how this is done and complete the article? — Preceding unsigned comment added by 74.200.4.237 (talk) 12:57, 5 August 2015 (UTC)

Inductive loop
This article is inspired by a story at How Stuff Works on traffic sensors. Today a link was placed to that story in preparation for an overhaul. I came looking for "inductive loop", essentially the topic of inductive coupling, one of the means of coupling (electronics). The term "loop" is frequently found in physics texts in connection with inductance. The two particular applications constituting this article today (traffic detection and audio telecoil) provide too narrow coverage of an essential means of developing Faraday's law of induction. There is significant readership of this article, so improvement would be appreciated.Rgdboer (talk) 22:36, 18 July 2012 (UTC)

The term "inductive loop" is used by the Federal Highway Administration in their manual on vehicle detection. See Manual. Details of operation, including opposite influences of ferromagnetism and eddy currents on the inductance of the sensing loop, are noted. The device relies on a variable inductor which can be used in a band-pass filter with an electronic oscillator input. The output of the filter signals the presence or absence of a vehicle. There is no use of the term "induction loop" in the FHA reference. Rather, this term stems from the Ampetronic Corporation in promoting their audio broadcasting system and the How Stuff Works site.Rgdboer (talk) 21:28, 19 July 2012 (UTC)

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