Let's made a PC-base metal detector with usb interface !!!

[Aziz]

The Ultimate Magic Coil!

Hi all,

it seems, my ultimate detector has the ultimate magic coil now!

You must see the magic elegance and genius of the new coil design.

Oh man!, it's the end of ...

Aziz

[Aziz]

Further evolution of the idea:
(difficult to build however)

You could reduce the RX-/TX-bucking coil size slightly (0.5R .. 0.8R). The RX- coil needs more turns in this case (see the above equation condition). In this case, you wouldn't need more distance of the RX coils.

Aziz

Ok, this idea fails! It doesn't give a benefit after calculating a coil configuration (less sensitivity). It is quite difficult to build such a coil too. We should focus to the K.I.S.S.-principle (easy to build to the amateurs - like me).

Aziz

[Aziz]

Further evolution of the idea:
(difficult to build however)

You could reduce the RX-/TX-bucking coil size slightly (0.5R .. 0.8R). The RX- coil needs more turns in this case (see the above equation condition). In this case, you wouldn't need more distance of the RX coils.

Aziz

[Aziz]

Hi Aziz,

What do you think of adjusting the gain of the cancelling rx coil preamp? Then you could have a smaller cancelling rx coil at the same inductance and just increase the gain until it cancels the emi from the rx coil. Or would you prefer the cancelling be done before the preamps? I tried making a 25" rx coil for my 25" mono on the weekend, but the wire I used was not suitable it was detectable by the tx coil. I have some litz here might have to try that.

As far as the gap (height)between the rx coil and the cancelling rx coil I believe it would not have to be too far above. 10~20cm would be sufficient. A weak signal will be detected in the rx coil but not(or only a tiny bit) in the cancelling coil. A strong signal will be somewhat cancelled by the cancelling coil, but there will still be a signal none the less. You will never entirely loose the signal unless the 2 coils are too close together. The other advantage is that it will cancel out some strong ground signal as well

Cheers Mick

Cheers Mick

Hi Mick,

sure you could do that. With minor disadvantages (higher amplifier noise, not perfect EMI cancellation..). But it would in principle work.

It is always better and easier to build identical RX coils. TX-Bucking coil should be placed as close as possible to the RX- coil (high inductive coupling coefficient).

But the latter coil proposal above is nice, very nice and I'm very very amused.

Aziz

[Mechanic]

Hi Aziz,

What do you think of adjusting the gain of the cancelling rx coil preamp? Then you could have a smaller cancelling rx coil at the same inductance and just increase the gain until it cancels the emi from the rx coil. Or would you prefer the cancelling be done before the preamps? I tried making a 25" rx coil for my 25" mono on the weekend, but the wire I used was not suitable it was detectable by the tx coil. I have some litz here might have to try that.

As far as the gap (height)between the rx coil and the cancelling rx coil I believe it would not have to be too far above. 10~20cm would be sufficient. A weak signal will be detected in the rx coil but not(or only a tiny bit) in the cancelling coil. A strong signal will be somewhat cancelled by the cancelling coil, but there will still be a signal none the less. You will never entirely loose the signal unless the 2 coils are too close together. The other advantage is that it will cancel out some strong ground signal as well

Cheers Mick

Cheers Mick

[Aziz]

Breakthrough Modification

Hi all,

the sketch below is illustrating the first modification I have suggested:
Bigger RX+/RX-/TX-Bucking coil. Below is the 1.2 times radius of TX coil. It works very very nice (better than the original design). But it needs more distance of the coils as illustrated below.

Free cutting edge coil science & invention to the people to make the world more smart (not greedy). Patent trolls!, please hold on your breath and keep holding it.

Aziz

Thanks Midas, you have stimulated this idea!!

Cheers,
Aziz

[Aziz]

..
Now of course the optimum coil proportions need to be determined. I suspect that being freed of the cancelling effect of the bucking coil the RX will probably grow larger in relation to the TX compared to a concentric. Could be wrong... its happened before.

Yup, the RX can be quite large now (up to ~0.95 times of the TX radius). I prefer 0.8R of TX.

There is a slight modification possible to make even much larger RX coil:
Make the RX+/RX-/TX-Bucking size bigger than the TX coil. It works too. A radius factor of 1.2R is (almost) equivalent to 0.8R. 1.3R equivalent to 0.7R.

To make it easy, the RX+/RX-/TX-Bucking size should be identical of course. RX+/RX- needs to be identical.

Another slight modification to the professionals (difficult to build however):
RX-/TX-Bucking can be made smaller too (not identical to RX+ size).
One must meet the following equation condition:

N(RX+) * Fluxarea(RX+) = N(RX-) * Fluxarea(RX-), where
N = number of coil winding turns
Fluxarea = pi*radius*radius (mean radius of the coil)

This means, if you have a small coil, you need more turns to get the required same magnetic flux compared to the other coil. The EMI cancellation works, because the noise is considered to be an uniform far field EM nearby the coil.

Cheers,
Aziz

[Midas]

Hi Midas,

I agree with your brilliant view.


It obviously took me a while to evolute the co-axial coil into this magic coil design. We can crank up the pre-amplifier gain now. So the amplifier resistor noise becomes relevant. That's the reason, why I would like to test some better dual op-amps.

You can call the coil's name whatever you prefer.

Cheers,
Aziz

Sorry I didn't mean that to come out sounding like such sour grapes. What matters is you posted it first, full credit and naming rights go to you. I only meant that whatever you call it, it will highly likely end up being colloquially called, a Top Hat Coil.

I think you mean evolve btw, evolute means something very different.

Now of course the optimum coil proportions need to be determined. I suspect that being freed of the cancelling effect of the bucking coil the RX will probably grow larger in relation to the TX compared to a concentric. Could be wrong... its happened before.

Midas

[Aziz]

Damn you Aziz! You stole my idea!
Lol, it was probably hints from you that got me thinking about it anyway..
But yeah its brilliant. Anti interference, no bucking coil field partially cancelling your main TX and unlike the coaxial coil you can get your RX and TX right up next to the ground.
Win, win win!

I'll have to get rich some other way..

BTW I'm pretty sure we have to call this a 'Top Hat Coil' No other name is going to stick so well.

Midas

Hi Midas,

I agree with your brilliant view.


It obviously took me a while to evolute the co-axial coil into this magic coil design. We can crank up the pre-amplifier gain now. So the amplifier resistor noise becomes relevant. That's the reason, why I would like to test some better dual op-amps.

You can call the coil's name whatever you prefer.

Cheers,
Aziz

[Aziz]

Hi all,

according to the magnetic field cross-section view, one can exactly see, where to set external parts (screws, coil stem mounting, coil cable, tuning capacitors, etc.).

That's the small region with the two blue points nearby the RX-/TX-Bucking coil. Well, this is a ring-region with less EM field of course.

Aziz

[Aziz]

Magnetic Field Cross-Section

Coil upside down now (the right operating orientation).

[Aziz]

Preparing Coil Prototypes

Hi all,

BTW, I am preparing two coil prototypes at the moment.

TX:
- 26 cm to 34 cm diameter Al-strip spiral coil (30 m folded Al-foil roll )
- 42 cm to 48 cm diameter Al-strip spiral coil (30 m folded Al-foil roll )

RX+/RX-
approx. 20.5 cm diameter and 50 turns each, wound at the same coil former (pot).

TX-bucking:
Have to be found yet. I'll see, how many turns count I need. But I'll use a cheap loudspeaker cable.

Both TX coils are finished and I am waiting for their drying (resin). It could take some time.

Aziz

[Aziz]

APRIL, APRIL!!!

Hi all,

did I fool you with an April joke?
No way! This ain't a joke. This is a "MadLabs Inc." brilliant mind work.
(I'm sure, a lot of people are thinking, that this is an April joke.)

Ok, how is the coil working?

Part 1:

EMI-Cancellation:

EMI (noise) is usually a far field response. The noise source is far away from the RX coils. The term "far" means several coil radius distances (distance > R or 2*R). The EMI far field nearby the search coil becomes an uniform EMI EM field.

So both coils nearly detect the same amount of EMI noise but with different polarity. As both RX coils (RX+, RX-, =identical coils) have the same turns count, size, orientation, but opposite winding direction, the induced EMI noise adds to zero, when both RX coils are connected in series.

To get best performance, both RX coils must be identical. It's better to wind the RX coils on the same coil former.

Induction-Balance Principle:

The idea behind the coil does not differ to other IB-coil types. The RX coils induced magnetic flux have to sum to zero somehow.

TX vs. RX+

As the RX+ coil size is smaller than the TX coil, both coils are relatively low inductive coupled. The RX+ coil is detecting a voltage from the TX coil however. The amount of the voltage is dependend of the coil coupling coefficient. The smaller the RX+ coil size, the less voltage is induced. The RX+ coil size should be smaller than the TX coil size to reduce the coil coupling coefficient between both coil parts. Otherwise, we would require more turns count in the TX-Bucking coil part.
We have to cancel the induced voltage from the TX coil now.

TX-Bucking vs. RX-

Both coil parts have the same size. Due to high inductive coupling of both coil parts (mounted close to each other), a few turns of TX-Bucking winding is enough to chancel the induced voltage in the RX+ coil part. Notice, the RX- is opposite winding direction of RX+ and hence inducing opposite polarity from the TX coils (TX/TX-Bucking).
The higher the inductive coupling between TX-Bucking and RX-, the less turns count for the TX-Bucking coil is necessary. If you have a small RX+/RX-/TX-Bucking coil size, the lesser turns count for TX-Bucking coil is nessary.

Distance of TX/RX+ vs. TX-Bucking/RX-

It is obvious, that we need some distance between the coil parts. The induced target response in the RX+ and RX- coil must differ significantly, to avoid it's effective cancellation. So the RX- coil must be placed as far as possible to the targets. The less the distance, the more target response will get cancelled. The more distance, the less target response will be lost. You should use large distance, whenever you can (distance > coil radius).

The distance however is dependent on the coil coupling coefficients between the coils. But the slight distance variation is an essential part of the coil balancing procedure.

To be continued...
Aziz

[Aziz]

APRIL, APRIL!

..
What happened to the KISS method,this is one difficult coil to make when one can use a figure eight coil for the same result
..
PS: Nice APRIL FOOL'S DAY joke!!!!!

Hi Ron,

this coil is challenging the equivalent mono size coil (size of TX). With little compensation to the RX side, this coil outperforms the equivalent mono size coil with ease.

It is primarily destined to relative large coils, where the mono size coils can't be used well due to noise.

Such a coil isn't difficult to build. When I compare it to the concentric co-planar IB coil, this one is much easier to make and balance.

With the convenient anti-coil-shock algorithm (due to mechanical vibration of the IB-coil), one can use very large frame IB-coils, which can go deep, very very deep.

Cheers,
Aziz

[Midas]

Hi all,

I'll write more detailed infos later how the magic coil works. The shown coil above is only an example of course. You can make the outer TX coil much bigger of course (getting almost a ground loop coil *LOL*). Or the inner coils smaller. Or vary the distance. You can use spirally wound TX coils. You can use rectangular (frame) coils instead of round coil. Or elliptical.

On your imagination, there is no limit.

Aziz

Damn you Aziz! You stole my idea!
Lol, it was probably hints from you that got me thinking about it anyway..
But yeah its brilliant. Anti interference, no bucking coil field partially cancelling your main TX and unlike the coaxial coil you can get your RX and TX right up next to the ground.
Win, win win!

I'll have to get rich some other way..

BTW I'm pretty sure we have to call this a 'Top Hat Coil' No other name is going to stick so well.

Midas