metal dector for barbed wire fences

What are you actually trying to do? Is this an operator aid, to keep from driving into the fence, or for a robotic tractor, or what?

You may be able to make a metal detector directional simply by backing up the detection coil with a metal plate, one or two feet back. Metal detectors work with near-field radiation of a low frequency signal (in the 100's of kHz, if I recall correctly), and look for changes in the coil inductance caused by nearby metal. Placing the coil a foot or two from the metal backing will leave the detector "detecting" the backing -- but it'll be constant; as long as there's enough change from the metal you want to detect, things should work.

Alternatively use the barb wire fence as an antenna for LF low power signal and get the strength detection of carrier to denote when too close.

Ultra sonic projected on the fence wire should make it vibrated. A ultrasonic mic just behind the transducer should detect this.

Fence wire is a hard surface and the only thing I can see that may hamper this is rust..

If you transmit a low frequency magnetic wave in the vicinity, surface rust on the metal may produce some nice G/T hz signals. Of course, you need a detector for that. Maybe IR . who knows.. ;)

Jamie

Paul - that's definite possibility but, as you say, an alternative if "plan a" doesn't prove feasible.

Hul

need

there

other

type

sci.electronics.components metal dector for barbed wire fences

Anybody here have any suggestions for possible ways to detect fence wire, mostly 1, 2 or 3 levels of barbed wire but also some 8 inch square matrix? Typical mounting would be on a tractor or trailer, so the detector would need a sense of direction, ie looking outward not inward. Minimum range would be around one foot with 4 feet probably optimum. Typical retail metal detectors have a short range and need a metal free environment, leaving the methods they use somewhat doubtful. Evidently, there are detectors with seperate heads/coils and 1-5 foot ranges but, once again, require a metal free environment. One possible area would utilize rf antenna's, one transmiting and the other recieving a reflection from the wire(s). A parabolic or corner reflector type antenna maybe if not for the high frequency - two 12 inch antenna's would be about max size and that's in the gigaherts range, which might be a problem. Any suggestions along this line will be appreciated.

Hul

"Hul Tytus" skrev i nyhetsmeldingen: jri79h$opj$ snipped-for-privacy@reader1.panix.com ...

This application makes my head shouts "radar!".. not metal detector..