Coil Field Patterns

[Aurium]

I searched through the various forums on here, and haven't seen this discussion is there a source for looking at the various coils and the fields that they generate? I understand the difference between concentric coils and the D2's is primarily in the shape of the field. (as well as some benefits to cancellation, or nulling in high mineralization) But I think it's helpful to understand what type of field each coil generates, and the relative shape of that field as it helps to know why one coil is better than another in different types of soils, or search conditions. I did see a basic description of field geometry in one of the Garret publications, I'm just curious if something similar exists for whites coils. That and it's been way to long since my ExH electromagnetics classes. (I like pretty pictures they're simple for everyone to understand that way) I've also heard the D2's described as a "windshield" wiper, versus a more focused spotlight for concentric coils, implying smaller search area. (regarding the field shape, and it's area of detection)

 

[Rob (IL)]

I don't see the information being that useful, but for $30 shipped you can get one of Jeff Foster's books. He doesn't have on for the V3 but the concentric patterns are the same for all Whites concentrics and the same for their DD coils. That's the only pretty picture source I know for the Whites coils. Rob

 

[Larry (IL)]

I have seen a good drawing on the forum by someone..........and Kellyco used to have a good drawing on their loops page but I noticed it is not there any more. Maybe it is buried somewhere else now.

 

[Aurium]

I've snagged a couple of the graphics from the garret techsheet, but I think they're very useful as they show that concentric coils seem to get better depth in lightly mineralized soils, and the DD type coils get much better in heavily mineralized soils. I think it's helpful to visualize the coil fields as it helps you understand the benefits of large coils versus small coils, and how the coil covers the soil underneath it with the electric field. Which explains why concentric coils have a tendency to miss areas if you're not overlapping your sweeps. Whereas the DD coils with a windshield wiper type field, cover more area per sweep, and you can be a little more sloppy with the sweep overlaps. (I think I need to get out and do some detecting.. alas there is still snow, and frost)

 

[Taterhead]

I found a web page online from a guy who looked at coil field patterns and it was pretty informative. He used a graph system and it was pretty neet. The most dramatic difference was between disc and all metal modes on his machine, a garret. What was of great value to me was not the obvious that all metal went deeper, but the less intuitive (to me) observation that it also made a halo around the coil that did not exist with the disc mode. It was also interesting to see that his concentric coil didn't make so much of a "cone" shape as some of the lit might have you think.

Anyway, it may be specific to his coil and his machine, but it was still cool to see and I am going to consider this information when adjusting my sweep patterns between AM, mixed, and disc modes.

Also, when I think about target separation in a moderately trashy area and consider that the area being detected being smaller is a benefit, I then consider would I rather do this with a small concentric or a DD? Well, with a DD I can still have a small detection area but cover more ground, perhaps resulting in more ground covered and more targets detected.

Could be wrong, but this is how I'm thinking about it anyway.

The village idiot,

Taterhead

 

[Pulltabs by the pound]

Kellyco's link http://www.kellycodetectors.com/how-metaldetectors-work.htm shows basic idea of how a searchcoil operates but does not explain the diffences between the different coils. I found it to be helpful though.