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magnetic flux

A

Anonymous

Guest
As I understand it a pattern of magnetic flux eminates from the planar surface of a circular coil in a cone shape below the coil,with whats refered to as a mirror image above the coil.Does this mean that any distortion in the lower field,when a coin is in range for example,will cause a similar,mirror image distortion in the field which is above the coil?
Please accept my appologies for posting such a basic question on this group,but I,ve wondered about this for years now.
 
I would say no. The mirror image of the undisturbed field is caused by the symmetry of the original system. The coin disturbs mostly just the lower portion of the field. The system is no longer symmetrical, the top portion remains almost as it originally was.
 
Thats what I thought.Shame though,it would have been very easy to implement an imaging system if the opposite was true.Thanks for the quick response RiverDon.
 
What confused me was Charles Garett's book "Modern Metal Detectors".He kept refering to the upper field as a "mirror image",so my simplistic mind came up with this idea of a bottle of baby lotion containing short strands of wire wool which,when placed in the vicinity of the upper field gave you a perfect 3D image of the target in the lower field.Guess its just wishfull thinking,but wouldn't it be great to get a 3D image?
 
does anyone know of a system which gives a graphic display of the object detected.Even,if it was only an outline on an lcd screen discrimination would be a piece of cake.
 
From what I gather from my pre-purchase research, imaging is tough. You need radiation finer than the target. Present detectors use audio waves to penetrate the ground. Their wavelength is much too long to form a clear image. You could add radar or even xrays to form an image, but that would be complex, costly, heavy, use too much power and even maybe dangerous. Phase detection with digital signal processing in conjunction with PI could do it, but will also add complexity. Many experienced detectorists prefer the simplicity of using their skilled ears on tones to form an "image" with the best processor around--their trained brains. Imaging is coming Alan, but don't hold your breath. I will buy something long before it happens. But it's a nice wish.
 
Thanks Don,Maybe they,ll bring out an add-on for a mobile phone so we can do our imaging on that,should be high enough frequency,hehe.Until then good luck with your new detector when u get it.
 
Sorry, but getting images of buried targets from a metal detector is currently investigated by a couple of research teams in both Europe and US.
Even though the radiated waves are very long (few km), it is possible to get an image of metallic pieces. It makes use of signal processing together with magnetic induction theory. First results in our team are quite encouraging. For instance, we were able to get a sharpen image of thin rods. Current work deals with more complex shapes.
 
Congratulations on your research. Don't feel sorry. I'm all for it.
Shape discrimination is a big step towards imaging. I didn't say it was impossible, just difficult. DSP is the way to go. How big was the rod and what aspect ratio did it have? And when do you hope to have a product? Should I wait instead of buying now?
 
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