I need to locate a piece of rebar at the corner of my yard. I know the general area, but I can’t find it. I want to use a metal detector to try and find it.
I found some links on the web to make a metal detector using an AM radio and a calculator. While that is way-cool, I no longer have any AM radios.
What I do have is a voltmeter that can measure voltage, resistance, and current. Is there something I can fashion which would act as a simple metal detector? Something that would change the circuit in a measureable way when I got close to the rebar?
I am not a great source of info on this but am sorry to see your posting is hours old and without answers so will offer some possible usefulness.
Rebar is ferromagnetic and will tend to conduct additional magnetic field lines from whatever ambient magnetic field there is (probably just ghe geomagnetic field). The lines will travel along the length of the rebar and exit at the ends, where they will redirect themselves to aim at the magnetic poles of the earth. If you wind a coil, maybe a few hundred turns of wire in a loop a foot in diameter, and connect the ends of the coil to a DC voltmeter, and move the coil so it cuts the lines, there will be a voltage for the meter to measure.
By moving the coil to cut the lines, I mean the lines are shaped as I said and they stay that way, and you move the coil so lines that were outside its loop area go into the area and then go out the other side. That is, if the lines were cobwebs and the loop were a mop you’d be cleaning.
You should be able to test this by spinning the coil so the magnetic field of the earth is going through it one way and the other. Orient it like a stop sign and rotate it on its vertical axis. You may need a really sensitive range. If your voltmeter is digital, you may struggle to figure out what it is telling you, because the display will rapidly display different digits that are hard to make sense of. When your coil is not moving, it should not give you any signal, unless you park yourself over a transformer or a motor that is running or something like that.
Now take pity on me, and answer my thread about drilling holes in gadolinium. Please???
You realize, of course, that this will NEVER work - don’t you?
I mean, it sounds good in theory, but in practice it’s unworkable.
To answer the OP - there is no easy way to turn a DVM into a practical metal detector, even using stone knives and bearskins. If I was faced with this problem, I’d rent one, or find a friend who had one.
So, nobody offers anything for 3 1/2 hours, and I put something out there that might work, and it only takes 18 minutes to shoot it down, without even trying? Come on. Scanning tunneling microscopes obviously would never work, and that turned out pretty good. Rebar would be one of the easiest targets for metal detection, because it’s ferromagnetic and usually long. Rebar creates permanent stationary changes in the local geomagnetic field involving field intensities larger than that field normally has, and these changes occur on a scale around the size of a human. I already know moving wires around sometimes makes little signals because of the geomagnetic field, and a voltmeter is a pretty sensitive and versatile thing to have in hand if you are only going to have one thing at hand. It wouldn’t hurt to try!
If you want a cheap kit, try this. Years ago I got a cheapo child’s detector for one of my kids. We still have it and I’ve used it 3 times in the last couple of months to find dropped screws and such. Might cost about $30+ nowadays. Finding rebar would be a snap.
To get to the real problem, If you gave a little more detail about the rebar (I assume it’s buried? How deep? How long is it and do you know which way it’s pointing?), we might have some alternate ideas about how to find it.
I made a ‘metal detector’ once when I worked for an automated gate company. Automated gates use loops of wire embedded in the road to detect the metal of a car. I don’t remember what specific wire was used, but I wrapped some three times around a bucket to make a 9" loop, then removed the wire from the bucket and taped the loop so that it would stay a loop. The ends were connected to a 12v relay, and the relay was connected to a 12v power supply. When the loop was passed over metal it closed the relay, which would have lit a light or activated a buzzer or whatever I might have attached to it. (Of course I made some full-sized loops too.)
This was an on/off detector, and not one that sends varying voltages to create different pitches so you know you’re ‘getting warm’.
The rebar is the marker of the corner of my property. It is buried vertically and I think I remember a couple inches of it sticking up. I’m not sure how long it is. Obviously it goes some distance into the ground, but I’m not sure how long of a piece they would have used for this purpose.
I last saw it 10 years ago. That corner is now overgrown and I couldn’t find where it is. And the rebar is a nice, brown rust color which blends in nicely with the dirt.
Have you tried tying a strong Rare Earth Magnet to a string? Move it over the area where you think the rebar might be, just skimming the ground. You should notice that it behave oddly where the rebar is.