sci.electronics.design Re: metal dector for barbed wire fences
Robert: You mentioned a 24 bit audio card with a 1/4 inch diamater reflective antenna - could you describe that antenna? "Reflective" implies directional which is of major intrest, especially with a 1/4 in. diameter. Radar, as you mentioned, is effective but somewhat expensive. Like the retail metal detecters, radar is designed for targets that are relatively small, ie a nugget of metal. Fences, on the other hand, are very long. Nearly infinitly so in this case. Hopefully, this length can be turned to advantage but exactly how is the current question. The detector is intended for a NC tractor generally but more specifically a tractor cutting hay. Fence detection would avoid turning into a neighbor's corn when dead reckoning errs and maybe serve as a guide for the initial cut around the outer perimeter. A market for such equipment certainly exists, but the cost of a corporate structure relatively safe from government intrusion would be high.
Hul
-Passive wire detection? is a bit trickier than *if* the wire were in
-someway supplied a signal. Your technique of simple metal detection
-would work *if* you combined it with the motion of moving towards the
-fence. It would be VERY difficult to detect a fence, sitting still,
-but move towards a fence and it will 'highlight' itself. More, later.
-
-We used to do proximity fences that easily detected people at
-distances of 5-10 feet away, using the technique of supplying an
-electric field, then detect the field 'changes' caused by a person
-waliking up near to the fence. Note, again that a person moving
-EXTREMELY slowly was not detectable, but moving an inch per second set
-it off.
-
-Ground penetrating radar, probably will work. Get an old 10GHz radar
-intrusion alarm sensor - don't know if they still make them. Back in
-early 70's HP made an excellent one sold around $100. Used a splitter;
-part went to the antenna and part went to the receiver for synchronous
-detection. The side bands and that doppler shift told you a lot. I
-remember they wanted to sell to boat owners for collision avoidance,
-or such. Anyway *if* you can find a radar based motion detector, you
-can use that. You may get some false positives on large plants but
-there should be a work around for that. Radar, with multiple receivers
-probably holds the most reliable, but most expensive solution for you.
-
-Back to the passive technique using low frequency... Low frequency
-electonics are cheap and coherent detection holds a lot of power.
-
-Use a laptop with a 24 bit sound card. With a 1/4 inch diameter
-reflective antenna, I can easily 'see' over 1 inch, so let's scale
-that up. 10 inch diameter, should be able to 'see' at least 40 inches.
-With separate receivers,you should be able to extend that range to way
-over 80 inches. Yeah. that'll work. So cost is around $300 for the
-laptop, $50 extra components, six months of software and you're done!
-
-Is there a market? You gonna sell it? Is this just fence collision
-avoidance, or are you trying to robotically do a field?
-
-If you're serious about pursuing this, contact me off line.