how to build a coil for a metal detector

[Anonymous]

I would like to know how to build a coil for a metal detector and the theory of coil design ?

 

[Anonymous]

I think your question might be a little vague to give a simple answer. You might visit the following website http://tthn.com/geotech/metdet/index.html
for some good technical information on metal detectors and coils.
I will add something told to me years ago by one of the more noted designer's of VLF's, George Payne. He felt the ideal diameter of a transmit coil should be approximately 10 times the diameter of the target you are trying to find. This is probably why most VLF coils designed for coin hunting are in the 7 1/2 to 8 inch range. However, VLF's and PI's operate on somewhat different principles so I cannot give you the ideal ratio for PI's. Eric Foster is far more qualified than I am in this field.
You might want to refine your question somewhat.
I hope this helps a little.
Reg

 

[Anonymous]

I probably should qualify "ideal diameter" in my previous note. That is the maximum return target signal to depth ratio. A larger coil would give more depth but less signal return from a coin size target (target=metal object such as a coin or a ring). On VLF's where they are trying to discriminate, makes the process less accurate and more difficult. In simplified terms, a larger coil will go deeper but less likely to find very small targets.
Reg

 

[Anonymous]

Hi
Here is a nice and usefull reference about induction coils :
V. G. Welsby, "The Theory and Design of Inductance Coils", Mc Donald, 1960, 2nd Ed.
It should be available from Technical University libraries.
Lionel