h a l f b a k e r y
Contrary to popular belief
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In the movies, military compounds often get broken into by cunning individuals who snip a convenient hole in the chicken-wire fence.
These intruders could easily be detected through the application of DSP. A device at one end of the fence would transmit an electrical impulse or sweep signal into the
metal structure, and listen for the echoes both transmitted and reflected. Even a single snip into the wire mesh structure would alter the received signal, which in many cases, perhaps through iterative reconstruction, could pinpoint its exact location.
This seems like something that would already have been invented, but all I could find were vibration-detection systems which involve attaching extra sensors to the fence.
Senstar FlexZone Locating Fence-Mounted Intrusion Detection Sensor
Mentioned in my anno. A TDR-based system that "detects and locates any attempt to cut, scale, or somehow get through a fence", locating the intrusion to within 3 m. [notexactly, Oct 03 2019]
Southwest Microwave Intrepid MicroPoint II Fence Detection System [PDF]
Mentioned in my anno. A system "using proprietary Digital Signal Processing (DSP) algorithms to precisely locate intrusion attempts to within 3 meters (10 ft) while ignoring harmless disturbances caused by wind, rain or vehicle traffic". Also runs its power and communications over the same cables. Can have sensitivity set individually for each 1.1-meter section of fence. [notexactly, Oct 03 2019]
Future Fibre Technologies: The Boundaries of Security [PDF DL]
Mentioned in my anno. See page 30 for a description of the special coax-with-sense-wires-in-keyways cable. [notexactly, Oct 04 2019]
||This is definitely Baked but possibly not WKTE (for obvious reasons). Systems certainly existed and were deployed as early as 1993.
||Did you use the term 'time-domain reflectometry' in your
||Some previous colleagues of mine have been
deploying this kind of system, and closely-related
fibre-acoustic systems in undisclosed locations
since about 2008.
||Sorry, that sounded like I was dissing the idea, Im
not. Its a very good idea! [+] but there are
implementations, not widely known, that do exist.
||Curse my spelling! Before opening, I was imagining all sorts of ways of tracking in utero baby position ... and pinging when correct position closest to predicted birth date...
To avoid false triggers, wouldn't the sensors have to be quite close together, and the tension maintained in the wire (which expands in summer/contracts in winter)? <pops along to Area 51, to see how they might do it>
||A quick Google search for [ tdr fence intrusion detection ]
turns up several relevant pages and PDF documents. These
systems seem to typically use real cable instead of sending
the signal directly through the fence, and they can detect
people climbing the fence, not just cutting through it! See
[links] for details.
||Another relevant search term turns out to be Perimeter
Intrusion Detection System (PIDS).
||The nearest I can think of is the Fibre Bragg Grating sensor,
where the frequency of light reflected varies with strain,