Three (3) Different Coil Technologies ~ Which is the Deepest

[AVXVA]

Beginner question, but please be patient because I am thoroughly confused.

The application is large meteorites in western Kansas at a depth of several feet to six (6) or seven (7) feet. The detector is a White's PulseScan TDI (pulse induction.)

I am looking at three (3) different coil designs in three (3) different sizes.

1) The 22" CoilTek mono coil,
2) The 21" - 17" DeTech SEF coil,
3) The 32" DeTech concentric coil.

I don't necessarily need to pinpoint them, I just need to know something is there.

Which of these coils is consistently deepest?

The 32" concentric is impressive in transmission, but I'm thinking the small diameter return coil is maximized to target fist-sized or smaller targets.

My guess is the CoilTek mono coil is deepest.

Any insight or advice would be greatly appreciated.

Thank you.

Rob

[Carl-NC]

I would expect the SEF coil to come in third. Between the other two, it's hard to say and may depend on the size of the target. On the RX side, the target signal strength depends on area*turns of the RX coil. For the same inductance, a 22" RX coil will have over twice the sensitivity of a 12" (which is what I assume the 32" Detech coil has). This assumes parallel lines of flux from the target, but in reality they diverge and the bigger RX coil is not as efficient as the math suggests. I would expect the 32" will win on the largest deepest targets and the 22" will win on smaller targets. Just a guess.

[AVXVA]

Thank you, Carl-NC,


Credit: Minelab

IF this a realistic depiction of a concentric coil, the RX signal is dramatically smaller than the 32" TX side on that massive 32" Detech. Another beginner question (and I apologize) but what advantage does a 32" TX have if the RX is only 12"?

Also, if the target is not directly under the RX coil, the machine will not see it--even if it's under the TX circle?


Credit: Minelab

IF this a realistic depiction of a mono coil, the RX signal is the same as the TX? Thus, the detection field is much "fuller" and possibly deeper, no?

But, it doesn't pinpoint nearly as well, or not at all?


Credit: Minelab

Is this blade-like RX really what a SEF/DD coil produces?

[Carl-NC]

Those illustrations aren't at all realistic. Responses heavily depend on target size. If you have a detector with concentric & DD coils then I urge you to draw your own response curves to get a realistic idea of how they behave.

[eclipse]

These coils would need adding 1-1.5 Ohm resistance because the default Minelab resistance is a bit low for the TDI. I have the 21" - 17" DeTech SEF coil, but haven't really used it.

[Carl-NC]

These coils would need adding 1-1.5 Ohm resistance because the default Minelab resistance is a bit low for the TDI.

I doubt that will make much difference. Very slightly higher power consumption.

[Op04]

These coils would need adding 1-1.5 Ohm resistance because the default Minelab resistance is a bit low for the TDI. I have the 21" - 17" DeTech SEF coil, but haven't really used it.

Adding resistance would make faster TX ON, downside is lesser depth, so frequency needs to be higher perhaps