Advanced PI coils

[Aziz]

Ok guys,

I have found an interesting paper from Geonics and their used coil configuration:

http://www.geonics.com/pdfs/technicalnotes/tn32.pdf

(see figure 1 on page 6)

The EM63-MK2 is of the same type to EM61 but the TX coil is larger. A typical PI machine. Rx1 and Rx2 are connected in anti-interference configuration. But it isn't an induction balanced coil. It's a different coil.

No wonder, the Tophat(c)(r)(tm)(blabla) coil is quite complex to be invented easily. It hasn't even been invented by the famous guys from ML.

Cheers,
Aziz

[Aziz]

BTW guys,

if you want to read more details on the so-called "Tophat" coil, here is the link (+ the following pages there):

http://www.geotech1.com/forums/showthread.php?14102-Let-s-made-a-PC-base-metal-detector-with-usb-interface-!!!&p=147055#post147055

Notice: If you make the RX+/RX-/BX coil radius smaller, it's easier to build and balance. Don't take such a bigger radius factors shown in the thread above. A reasonable radius factor is 0.4 - 0.6 (~ half of the TX radius).

Yep, it's one of the greatest recent invention in the metal detecting art.
Free to use & commercialise. A "MadLabs Inc."(c)(r)(tm) gift.

Aziz

[Aziz]

Forward to the Past.

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Hi Eric,

oh yes, it's a good coil frame design for the western australian gold fields. Such coils can be made large - very large to chase the really bigger stuff. But I'm going to build a smaller and hand-held one looking (almost) similar to the above one. (BTW, I have seen the coil already.)

I don't know, how the coil is designed in the picture above (one can't see the internals). But I can't imagine, that's an induction balanced one. The true induction balanced AI coil has been invented recently. PI's don't need induction balance as they can wait until the coil energy has been damped before the receiver gets in action. I assume, the Geonics is a plain PI type detector.
Anyway.

The concentric co-axial (Tophat) coil can be used either for VLF, PI or a PI/VLF hybrid detector. This coil type beats the standard concentric co-planar an DD coil with ease. And the "WBGB" works with such coils as well.

My recent testing was done on VLF principle detector. But it's ok to start with bench testing first. Every new coil has been bench tested before. Notice: I have placed the coil nearby my open PC (heavy noise source) and telephone/fax device. No EMI noise plaguing at all.

Cheers,
Aziz

[pigeon]

My 1968 PI which used IC's/ RTL logic and 709, 712 Linear devices. DECCO stands for Decay of Eddy Currents in Conductive Objects. Coil array is a small one for lab testing. Field coil was 1m square for TX and 0.5m RX. My initials and date are in the bottom right hand corner. EJF 2 68.

Eric.

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hi

How Can I used this coil for delta pulse ?

thank you

best time

P.

[Ferric Toes]

Forward to the Past.

[Ferric Toes]

Easy to make world records in the lab or workshop. Come again when you have that stable platform and performed field tests on a buried euro in wet mineralised soil near to power lines and a radio transmitter. Cigarette boxes no good for spacer, or health. The contents of such killed John Alldred who was also brilliant at electronics.

Are you recommending this for PI, or is it just a VLF project?

Eric.

[Aziz]

Bl00dy hell!!!,

I'm going to beat all VLF detectors...
It's quite difficult to make some bench testing with the loose coil assembly at the moment. But as far as I could see the detection depth on a 1 EUR coin, ... and it's sensitivity to small targets ...

I have used the center-tapped Tophat TX coil drive (=high power VLF) with an active RX amplifier this time.

I need a stable coil frame assembly.
I need a stable coil frame assembly.
I need a stable coil frame assembly.

It's time to make new world records...

Aziz

[Aziz]

Aziz, very interesting coil configuration and build technique. I assume you are referring to the coil's below the cigarrete boxes.

Interesting use of ribbon cable. Can see its benefit with lowering overall capacitance. Will try this method as i have lots of this ribbon cable for a convention mono PI coil.

What wire type are you using underneath the outer coil with Al foil wrapped over it?

Sid

Hi Sid,

the Tophat(c)(r)(tm)(blabla) coil is an induction balanced (IB) high performance (HP) anti-interference (AI) coil (psssst!, nobody knows this yet ). The coil consists of four coils however.

I'm using the ribbon cable for the receiver coils (RX+, RX-) as both RX coils can be made very equal (same geometry, same electrical characteristics, easy to wind and make and has perfect anti-interference feature).

To get a high transmitter efficiency and a lightweight coil, the TX coils (TX, BX) above were made of Al-foil strip (very low resistance TX coil). You know the Al-foil roll from the kitchen? Yep, the whole 30 m Al-foil roll is folded many times (30 cm width -> 5 mm width) forming an Al-strip at the end . You have to take the thicker Al-foils (12 µm thickness), fold it along the 30 m length (notice: only a certified madman can fold it without going crazy ) and isolate it with Tesa tape and you get a nice and flexible Al-strip wire. I think, I have only used the half of the 30 m for this coil above (TX coil resistance approx. 0.10 Ohm - 0.12 Ohm).

Of course, you can use standard coil wires as well.

BTW, I have just finished another but complicated Tophat(c)(r)(tm)(blabla) coil using the twin-lead loudspeaker cable (2 x 1.5 mm²) in a center-tapped coil configuration for the KISS VLF Osc. project (for the simple n-mosfet osc. controller version). And it works very well without having an active amplifier too.
TX: 2x7 turns (bifilar wound, center-tapped, total 14 turns)
BX: 2x2 turns (bifilar wound, total 4 turns)
RX+,RX-: each 5x10 turns (50 turns total, the coils shown above)

I'll make rectangular coils next time as these can be easily mounted onto a rectangular coil frame. The coil frame will be made out of wooden strips (13x13 mm). And an adjustable distance means for the coil bundle above (fine balancing).

For a PI coil you have to take other wires of course (low capacitance, low self eddy current induction, etc).

Cheers,
Aziz
the world record holder for folding at least 10 (!) 30 m Al-foil rolls...
*LOL*

[sido]

Aziz, very interesting coil configuration and build technique. I assume you are referring to the coil's below the cigarrete boxes.

Interesting use of ribbon cable. Can see its benefit with lowering overall capacitance. Will try this method as i have lots of this ribbon cable for a convention mono PI coil.

What wire type are you using underneath the outer coil with Al foil wrapped over it?

Sid

[Aziz]

Hi all,

ya wanna see my new Tophat(c)(r)(tm) coil?

Hey, I have used my folded Al foil (Al-strip 4-5 mm) for the TX coils (TX and BX). TX being 13 turns and BX 4 turns (slightly more than the optimum turns count of 3). The distance between BX and RX- (see the distance holders below) gives the rough induction balancing and adjusting the co-axial distance. The whole coil bundle BX and RX- can be very fine tuned by varying the distance to the TX, RX+ coil bundle. This coil is very easy to build and adjust and gives incredible depth performance.
The RX coils are made of ribbon cable (5 strands) and each have 10 turns giving total 5x10 = 50 turns. RX+ and RX- are connected in anti-series (anti-interference configuration). This is a super quiet coil.

See my loose coil assembly below: (it's in induction balance state)
(stop laughing.. )


Cheers,
Aziz

[Davor]

I don't expect any copyright problems if the author approves it. There are fair use provisions, but if the paper deviates from the magazine article due to the author's amendments, it is only the author's good will to approve it. It will be used for research, and in no way commercially.

BTW, this is not the first Lee I had privilege searching a paper from. There is C. Y. Lee that wrote "Elements of Cellular Mobile Radio Systems" which is a cornerstone of any serious radio propagation surveys... also quite difficult to come by.

[Ferric Toes]

Eric, will it be possible for you to nudge Mr. Lee to share his paper with us? I've already noted that it was quoted in several other papers that are full of goodies, so why not learning from the source

I could upload a .pdf of the full paper provided there are no copyright problems. It was published in Geophysics and Geophysical Prospecting in 1984 with slight differences.

Eric.

[Aziz]

Hi all,

has anyone built the Tophat(c)(r)(tm) coil yet?
I find it to be the most powerful IB coil and one of the best IB coil inventions in this century. *LOL*
(When PJ says it won't work -> take the opposite -> it will work very very well )
<Advertising and bashing mode disabled now>

It is looking very complex (four coils: TX/RX+, BX/RX-, TX = transmit coil bottom, BX = bucking coil top, RX+ = receive coil bottom, RX- = receive coil top) but is very easy to build and balance. It allows a better (mechanical) fine induction balancing feature without the need for extra loop turns too.

Just meet the following criteria:
Height (co-axial) distance between TX/RX+ and BX/RX- coil bundle > 2* RX+/RX-/BX coil radius (better more but not really required to be more than TX coil diameter)
The RX+/RX-/BX coil radius factor: 0.5 - 0.7 times the radius of TX (no problem, it works even with smaller radius factors)
A higher radius factor requires more bucking coil turns and a higher inductive coil coupling coefficient between BX and RX- coil.
The BX/RX- inductive coupling can be used as a rough IB (or adjusting the desired co-axial distance), whereas the co-axial distance offers a fine IB feature. If you add one turn more to the optimum BX coil, you have enough room to make the rough IB'ing and co-axial distance setting. It is quite easy to set the BX/RX- coil bundle distance IMHO.

Cheers,
Aziz

[Aziz]

That's not exactly fair to Lee who is well respected in the field of geophysics and who was very willing to answer some of my questions by email a few years ago. His "theories" match exactly what I have found with mono coils and concentric TX/RX on the very highly mineralised Australian ground, both thin surface layer and uniform ground. Also viscosity plots from my Magnetic Viscosity Meter add confirmation.

Eric.

There is a misunderstanding Eric. I'm not criticizing Lee.

The *LOL*'s being for people, who strictly are holding onto the 1/t response (d log(M)/dt ).
(I'm not criticizing the 1/t response as well.)

There has been written a lot. Which one is correct? Best to look at the measured data.

Aziz

[Davor]

So far I had no problems obtaining just about any kind of information/papers/sound files from all kinds of authors, and without any finances complicating the exchange. It is the corporations that force us to believe that intellectual property is difficult to come by.

Eric, will it be possible for you to nudge Mr. Lee to share his paper with us? I've already noted that it was quoted in several other papers that are full of goodies, so why not learning from the source