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Fiber cable can actually be a very good sensor. Some light gets reflected back from the most minute bends of the cable. By sensing reflections and comparing the
by hristov 3y ago
Fiber cable can actually be a very good sensor. Some light gets reflected back from the most minute bends of the cable. By sensing reflections and comparing them with previous reflections you can see whether the cable has experienced any new bends. By timing the arrival of reflections you can calculate exactly where the new bends are. By sensing the intensity of reflections you can calculate how sharp the bend is.
And this is not a research project anymore. Well, the fiber the article talks about is a research project, but there is a company called luna innovations that sells production fiber sensors that operate in commercial environments. There are underground fibers that sense whether someone steps in a restricted area. There are fibers stuck to pipelines that sense whether someone is trying to drill a hole in the pipeline to steal some oil (or any other vibrations or ruptures). There are fibers glued to the undersides of bridges that sense whether the bridge vibrates and bends too much.
It is a very useful sensor, because you can essentially get sensing along a large area without paying for multiple sensors and trying to figure out how you are going to power them, how they are going to communicate back, etc.
The electronics for extracting data from the fiber are complex but they do not have to be out in the wild in the area being sensed, they can be safely housed at one end of the fiber.
- isaacdl 3y agoI’ve had a fiber line for residential internet buried in my yard. At one point it stopped working and a tech was able to pinpoint the exact location that it had a slight kink using a device that measured the reflection. They just dug up that section with hand tools to unkink it.
- mlyle 3y agoYup-- an optical time domain reflectometer. Though TDRs are in common use for copper cable, too. You send the pulse down the line and get a reflection back. They're a little worse than optical ones because there's more uncertainty of the speed pulses travel down a random network cable than a piece of optical fiber.
- I_Am_Nous 3y agoThey make some really cool in-line OTDRs these days, but the one we use was about $10k I believe and it's had a broken screen for years. Still works if you plug a mouse in!
- hunter2_ 3y agoDoes varying twist rate contribute to that uncertainty? I imagine that a cable with a high twist rate is slower because the twist means the individual conductors are longer (maybe just by a couple percent) than one with a lower twist rate. And if the test equipment isn't configured for the pinout scheme being used (A vs B) then it might not even be pulsing a single pair at a time (each pair has a different twist rate) although perhaps that issue is automatically avoided.
- mlyle 3y ago> Does varying twist rate contribute to that uncertainty? Yes, but beyond the effect that you're saying. The distance between conductors affects speed down the cable. Tighter twisting also changes the distance and the amount of dielectric around, which also varies speed of propagation. These effects can be massive; a typical cat 7 cable has a velocity factor of 80% of the speed of light, varying by a couple of percent; a cat 5e cable more is often more like 65%. If you launch a pulse into a mess of mixed wiring to find out where something is unplugged or cut, you could be off by 20% or more.
- deleted 3y ago[deleted]
- shpx 3y agoHow does a cable develop a kink while it's buried?
- thsksbd 3y agoA professor I knew would measure temperature and gas species along the entire length of a fiber at refractory temperatures. Fibers are incredibly accurate devices
- nimish 3y agoAll of modern technology owes its origin to measuring light precisely. Optics is an ancient science. It's quite low tech, surprisingly so.
- closeparen 3y agoI worked for a local IT contractor in a small Midwestern city 10 years ago. We had a handheld Fluke TDR device in the truck, for locating fiber breaks.
- thrtythreeforty 3y agoI wouldn't be surprised if the Fluke cost as much as the truck.
- jes 3y ago"If you drop your DVM and it still works, it's a Fluke."
- acidburnNSA 3y agoWe use similar sensors in test flow loops to see how prototype electrically heated nuclear fuel rods jiggle.
- aaviator42 3y agoIt's insane how cool humans are to be coming up with this insane stuff.
- KineticLensman 3y ago> there is a company called luna innovations that sells production fiber sensors Luna is the current front, but acquired the technology from Optasense [0] relatively recently. There is a good timeline of Optasense commercial development in the fibre optic sensing domain at [1], going back to 2007, when Optasense was spun off from QinetiQ, which was itself the commercial spin-off (in 2001) from the UK's Defence and Evaluation Research Agency. This timeline illustrates the wide range of application areas, including pipeline and railway monitoring, border surveillance, drilling seismology, deep sea and others. [0] https://www.optasense.com/ https://www.optasense.com/ [1] https://www.optasense.com/about-us/company-background/ https://www.optasense.com/about-us/company-background/
- azepoi 3y agoI know of several compagnies in europe that do geophysical monitoring of dikes levees and dams with optical fibers
- fpierfed 3y agoIndeed and fiber cables are used to sense distant earthquakes as well. They are a very good sensor network.
- ls612 3y agoAnd as a bonus you can transmit symmetric gigabit internet over all of your sensors!