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Wired Fencing

In a regular (wired) fencing system (for sabre and foil,) contact is determined simply by applying a current to the weapon through a wire and forming a circuit between a conductive jacket called a lame which is in turn connected to a wire - naively, the circuit contains a light which indicates a current flowing.

An image of a sabre lame is shown:

A Lame

Wireless Fencing

It is desirable to eliminate the wires - this has been done however how this is done is a trade secret. Each fencer wears a pack on their waist which connects to their lame and weapon.

Some wireless fencing systems are pretty bad, some are not, which suggests there is some variation in how they operate.

The Task

Therefore, I need to determine whether two (conductive! - this is a wireless fencing system, to give an idea of scale) objects are in contact, the catch is that there is no return path for a simple DC circuit. As far as I'm aware, this can be done using time domain reflectometry, however this would require a fairly complicated ADC + FPGA setup (reflections would be on the order of 10nS or less.)

I think this is also possible by treating the conductors as antennae/waveguides: Send a radio signal from one side and detect it on the other, as a single wire transmission line.

Does this sound feasible (there seems to be a patent documenting a similar system but that doesn't mean it works,) and does this problem have a name that I've missed (i.e. existing literature?)

JRE
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mhh
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  • Can your device contact both of the objects at the same time? Why can't you use one of the objects as the return path? – The Photon Mar 24 '20 at 16:50
  • This can be abstracted to a metal stick touching a conductive cloth, there isn't a return path available. – mhh Mar 24 '20 at 17:01
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    The cloth is the "signal" path, the stick is the "return" path. I still don't see the problem. – The Photon Mar 24 '20 at 17:15
  • @mhh abstracting things is a dangerous business, when you don't exactly know yet what the important properties of the system are, yet :) Could you elaborate on what the obejcts are, and where exactly your sensing system would be? – Marcus Müller Mar 24 '20 at 17:28
  • The Abstraction is valid, I have included a description of how a sport fencing (I suspect there is some ambiguity here, I only mentioned it in passing) system works. – mhh Mar 24 '20 at 17:38
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    OK, it's very helpful that you clarified when you said "fencing" you meant the sport and not the means of restraining livestock. – The Photon Mar 24 '20 at 17:40
  • Ha. I realized too late that it's a niche hobby, although I suppose if you wanted to see if your perfectly spherical metal cow nudged a metal fence there could be a similar method – mhh Mar 24 '20 at 17:43
  • In the commercial system, which controller lights up when a hit is scored? The one who struck, or the one who was struck? Or do they send a signal back to a base station and the indication is made there? – The Photon Mar 24 '20 at 17:49
  • The lights are not on the fencers and there is a millisecond precision requirement on the timing, so the data is sent to a base station. This replaces the whole wired system so the lights are then controlled by the computer receiving the data. – mhh Mar 24 '20 at 17:55
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    @mhh, there is no mention of the base station in your post ....... anyway, each foil could be an antenna of a radio transmitter .... the receiver is the base station .... touching the lame changes the received signal property – jsotola Mar 24 '20 at 18:19
  • I'd guess you could transmit low level RF and measure the VSWR which would change when the saber contacted the lame. – John D Mar 24 '20 at 18:40

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