Why cant metal detectors have longer ranges like 100 meters or higher?

[leviterande]

Hi, everyone, I have a question. metal detectors basically work by inducing a current into a non ferro conductor, the back emf is captured by the receiving coil and thus you have a signal. What I am wondering is why is the metal detector only capable of detecting for a range of only a few feet? The metal detector is similar to any radio Tx/rx.

For example, if you have a strong magnetic pulse train from your detector, and there happens to be a a conductor somewhere around half a mile or just 100 meters etc.. out from you,. it is bound that there will be a current induced in that distant conductor which in turn of course creates a magnetic field which is also spreading out and should reach the detector receiver? Why are these common detectors limited by a few feet?

My guess: making an induced current in a distant conductor is easy. But, perhaps receiving the signal of the induced current from the distant conductor is very hard? because the signal is very low? but really in our modern era of electronics, all signals can be detected?
please enlighten me

thanks
best regards
levi karl

[FrancoItaly]

Metal detectors work with magnetic fields not with electromagnetic fields, the search coil isn't an antenna.

Best regards

[leviterande]

Metal detectors work with magnetic fields not with electromagnetic fields, the search coil isn't an antenna.

Best regards

Hi and thank you for the reply. But I am not sure I understand, because my understanding is that magnetic field is just a current or motion of charged particles. Any magnetic field associated with a copper winding comes from a current of conduction electrons. so why isnt a signal detected further by few feet from metal detectors?


Regards
Karl

[FrancoItaly]

The propagation of a magnetic field decreases with the inverse square of the distance while the electromagnetic radiation (not near field) decreases linearly with the inverse of the distance, and then goes much further than a magnetic field, at the same power.

Best Regards

[Mike(Mont)]

I guess you are new to this forum. MFD's (Molecular Frequency Discriminators) have been finding gold for decades. People who try to tell you they don't work, well maybe they just aren't as intelligent as they think. Do some reading on Konstantin Meyl and scalar waves. There are some you-tube videos.

[leviterande]

The propagation of a magnetic field decreases with the inverse square of the distance while the electromagnetic radiation (not near field) decreases linearly with the inverse of the distance, and then goes much further than a magnetic field, at the same power.

Best Regards

Alright, thanks, I think I see, so in order to get it working the way I thought it was working is basically a ground penetrating radar. Say you have a radar with medium penetration depth of 1meter, i.e. a frequency of around 300mhz. Rocks and most dielectric which is the ground would only reflect a tiny part of the radio waves. If say there is a piece of a good conductor at say 10cm depth it will reflect more than the insulators around it and thus a signature should be seen where the conductor hides.

I know these two problems however:

A-We could debunk this idea because the object itself needs to be at least 1 meter in size in order to reflect the radio energy. (But still a portion of the radio energy gets reflected even if the wavelength is bigger than the object).

B-We could also claim that even though small conductors could be distinguished and detected successfully among all the insulating earth media, we would be out of luck trying to figure out what kind of conductor it is. Why? because the reflection ability (and thus what conductor it is) of the conductor would be NEAR IMPOSSIBLE to conclude from the overwhelming noise or ambient radio reflection of the insulating earth media and because a detected strong reflection on your receiver cant differentiate between a big conductor of poor relfectivity and conductivity or a small conductor with superior conductivity and reflectivity.

Am I thinking in the right direction?

All ideas thoughts welcome. I am just seeing if I can find any possibility through sound established principles. I am aware of wallet hunters.

[Mike(Mont)]

Study Meyl and the longitudinal waves. This is the magnetic component of the wave and is about 1/6 of a wavelength.

[Mike(Mont)]

The skeptics want you to think all LRL's are wallet miners. If you subscribe to that flawed logic then you are being suckered by the skeptics (mostly people who make their living off the metal detector industry). They have motive.

Inflated prices are one thing. A few of the manufacturers actually spend thousands of hours developing the LRL's. And then there are a few who feel like they can steal that info and without any development costs charge ten times more than the thing is worth. If you want info, contact Dell Winders in Haines City, FL. He's the guy who figured out a set of L-rods can be used in place of the electronic receiver. The original MFD's did not use L-rods--they used an electronic receiver.

[leviterande]

The skeptics want you to think all LRL's are wallet miners. If you subscribe to that flawed logic then you are being suckered by the skeptics (mostly people who make their living off the metal detector industry). They have motive.

Inflated prices are one thing. A few of the manufacturers actually spend thousands of hours developing the LRL's. And then there are a few who feel like they can steal that info and without any development costs charge ten times more than the thing is worth. If you want info, contact Dell Winders in Haines City, FL. He's the guy who figured out a set of L-rods can be used in place of the electronic receiver. The original MFD's did not use L-rods--they used an electronic receiver.

Hi Mike, I am open to everything as I always was , however I read a lot too and both you and I agree that there is a lot of baloney out here. perhaps not 100% of it.. I read about Dell and saw his writings here and elsewhere. At any rate, have you had success with MFDs?
thanks

[Mike(Mont)]

I guess there is kind of a double whammy with MFD's. You have the solar magnetic interference and you have the L-rods. Both these can add significant "play" sort of like loose steering on a vehicle.

Whatever the case, if you can't use the rods you won't get too far. I tell people to learn some form of meditation, but this has fallen on deaf ears. "Don't need that.", "Don't have time.", etc., etc.

You'd do well to avoid the rabidly biased naysayers unless you are trying to convince yourself they "can't possibly work". I never understood why anyone would believe someone who can't use the L-rods.

[Qiaozhi]

What I am wondering is why is the metal detector only capable of detecting for a range of only a few feet? The metal detector is similar to any radio Tx/rx.

A metal detector coil is similar to a loosely coupled transformer, and a metal target that gets close to the coil will couple some of the TX energy into the RX coil. In effect, the metal target is acting like the core of the transformer. The main reason why a detector is restricted to a few feet in detection distance is because reactive effects cause the near field energy to fall off as a function of 1/d^3. Eddy currents generated in the target will then create their own magnetic field (Lenz's Law) and the return signal is subject to a 1/64 response.

If you haven't already read it, I would suggest you get a copy of "Inside the METAL DETECTOR" -> http://www.geotech1.com/forums/conte...metal-detector

And ... I wouldn't waste any time with L-rods or MFDs.

[leviterande]

And ... I wouldn't waste any time with L-rods or MFDs.

Exactly. And thanks for your reply.
The question perhaps doesnt have to do with metal detectors . so let me try to make an example
I have a neodymium magnet that can induce very clearly a field at any conductor hanging from a thread across the room.-the conductor moves that is- My room is about 25ft. So seemingly the first step is established into simulating a distance object. The next step is receiving the information which could be the tricky part. I may have a mental block but it looks like there can be only two solving approaches for the next step:

A-The new of course much weaker magnetic field induced in the distant conductor may be too weak for me to still detect it at the 25ft distance ? perhaps a super sensitive magnetometer could help but I understand that the field would be very low.

B-(the better solution?) Detecting by receiving the electromagnetic wave with an antenna. I.e, after we have excited our little conductor from a distance with our strong magnetic pulse train of a specific frequency from the tx, current is induced in the distant conductor at the same frequency and now we receive the weak electromagnetic wave of the same frequency emanating from the conductor. I am really not sure if my point is clear but I would love why this cant work ?
thanks

[WM6]

The skeptics want you to think all LRL's are wallet miners. If you subscribe to that flawed logic then you are being suckered by the skeptics (mostly people who make their living off the metal detector industry). They have motive.

Inflated prices are one thing. A few of the manufacturers actually spend thousands of hours developing the LRL's. And then there are a few who feel like they can steal that info and without any development costs charge ten times more than the thing is worth. If you want info, contact Dell Winders in Haines City, FL. He's the guy who figured out a set of L-rods can be used in place of the electronic receiver. The original MFD's did not use L-rods--they used an electronic receiver.

There was right answer to this already two millenia ago:

http://www.mountainman.com.au/kural/kural029.htm

[Mike(Mont)]

Did you look at the Meyl videos? He has a website with some other info on it. You see the longitudinal waves and how the flux lines "bundle" to the receiver because it is in resonance. There is little loss of energy. Of course this is totally different from the transverse wave that electrical engineers wrongly apply their principles. I have to assume they do not have a clue on this although I have suggested many times that they know and are hiding it. The thousands of hours the skeptics ave spent trying to convince people that the MFD's can't possibly work you gotta believe they have motive here.

[Mike(Mont)]

When I say that some form of meditation is essential to any L-rod work, most people run away. I'll say it again, you have to quiet the mind to be able to sense the subtle energies that create the "body response". I learned with a device that had a skin galvanometer hooked up to it. I learned to sense the body response. No doubt many of the failed L-rod wannabe's are not able to achieve this just because they think they are superior, think they know more. I call it the Natural Selection process.