Question for Eric

[Anonymous]

Eric,
How much of a depth increase over a circular coil does one get in theory / practice by using a rectangular coil with a length to width ratio of 4:1 I understand that 4:1 is optimuum for depth. Are there any special tricks that we need to know? Dave. * * *

 

[Anonymous]

Hi Dave,
I will scan some formulae at have a go at posting them. 3 : 1 is the minimum that gives any depth gain. Anything greater than this gives an improvement, although greater than 5 : 1 would show diminishing returns. Basically it is the formula for a parallel wire where the field falls of as the square of the distance rather than the cube.
Eric.

 

[Anonymous]

Eric, does this happens with IB as well?

 

[Anonymous]

Hi Jeff,
Fundamentally, yes. However, it is easy to make large coils for a PI as there are no tuned circuits and you are usually dealing with one coil. But for multiple balanced and tuned coils in an IB, it becomes very difficult.
Eric.

 

[Anonymous]

Hi Eric,
Have you made any actual measurements as to the depth increase lets say on a typical coin using the 11" round versus the corresponding rectangular coil which I would assume to be about 4" by 13+.
Also, does the general theory hold true for an elliptical coil also or is a true rectangular design far superior?
Thanks,
Reg

 

[Anonymous]

Hi Reg,
The width of the rectangular coil has to be the same as the diameter of the circular one e.g. An 11in circular would be compared with a 11in x 33in rectangular. I have not done any detailed measurements but the theory says it should happen and users have reported increases in range. The whole subject of coil design is very complex and most coils on treasure hunting detectors are below optimum size anyway. It would be nice if a computer guru could devise a program into which you can put all the parameters both of the detector and the type of object to be detected, and come up with the optimum shape, number of turns, type of wire, shielding etc etc.
Eric.