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

[Aziz]

Measured EMI Rejection Ratio

Hi all,

my PC is a wide band EMI transmitter. I have opened it for better cooling and to create a rigid EMI environment for metal detector development.
Following measurements were taken:
RX+/RX- in serial (same winding direction) compared against RX+/RX- in anti-serial connection (opposing winding direction).

Near field EMI rejection ratio: 10+ dB (3+ times)
1 m apart from the open PC, RX+/RX- distance approx. 28 cm.
It is still subtracting a lot of EMI noise in the near field region.

Simulated far field EMI rejection ratio: 23+ dB (14+ times)
1 m apart from the open PC, RX+/RX- distance approx. 1 cm.
Comes almost to the noise floor level of the amplifier noise.

The real far field EMI rejection ratio is better of course. We can run much much bigger RX coils now.

Cheers,
Aziz

[Aziz]

Bloody Good EMI Rejection!!!

Hi all,

the two identical ribbon-cable RX coils were dryed and finished. Connected them in anti-serial: bloody good EMI rejection. Without shielding (comes later).

The "Top-Hat" Coil will be a ripper coil. Put your stakes please!

Aziz

[simonbaker]

I got that part, but is it? If you put it very close it will reduce the inductance as well, and while there is any residual inductance, there is detection as well. It can't be completely obliterated. The only part that is not affected is resistance, and in Rx it seem to be a non-problem as well.

I asked about the least viable distance for practical purposes only. This is big.

Good point about the inductance changing -- that would throw the tuning of the RX coil off as well, unless you compensated by adding more turns to beef it up -- another con for weight/bulk. Come to think about it, maybe if you simply get the total inductance back to spec by adding windings when you move the coils closer, you achieve equivalent sensitivity...??? Probably not that simple.

I guess Aziz's fancy mag field software might answer your question if you indicate what loss of depth you consider a practical trade-off.

Regards,

-SB

[Aziz]

World's Best Metal Detecting Technology

Hi all,

I'm working on the "World's Best Metal Detecting Technology". Just trying to find out more and elegant solutions in case of one particular is being patented or will be patented in the future.
Fortunately, there are many many ways of realising it. Patent trolls do not have either the chance and the bright brain to prevent us.

Aziz

[Aziz]

Hi guys,

the only "drawback" of the "Top Hat" coil I see is the increased sensitivity to magnetic minerals nearby the ground (where TX/RX+ sits). The inductive coupling will be changed differently and is therefore prone to magnetic minerals.

The RX-/TX-Bucking can be considered as a reference coil system and is less affected due to its distance to the ground.

But the "drawback" does not necessarily mean to be a drawback. All IB-coil systems, which do the continious demodulation have the same problems.

How to overcome this IB coupling problem?
Same as the standard PI does: blanking the receive signal, gating it after (almost) all magnetic response signals/mutual coupled signals died away. BTW, one could also use the mono coil design. But it would require a different detector controller. I shall consider it.

Cheers,
Aziz

[Davor]

the farther the better

I got that part, but is it? If you put it very close it will reduce the inductance as well, and while there is any residual inductance, there is detection as well. It can't be completely obliterated. The only part that is not affected is resistance, and in Rx it seem to be a non-problem as well.

I asked about the least viable distance for practical purposes only. This is big.

[simonbaker]

Rx coils in antiphase - this one cancels earth field and far field emissions. Did you check how close you may place them to retain this behaviour?

The closer the better for that behavior (cancellation)! But not for detecting targets... the farther the better for that. That is the tradeoff.

That's how it looks to me anyway.

Of course the main "con" to this idea is the cumbersome coil -- extra wire that doesn't participate in detection, only cancellation, adds weight, not to mention the bulky shape.

You can also theoretically do a "visor hat" balanced IB design that wouldn't need the bucking coils at all (which is what I was envisioning for my experiments). It would look even weirder and may be harder to physically balance on the shaft.

-SB

[Aziz]

Rx coils in antiphase - this one cancels earth field and far field emissions. Did you check how close you may place them to retain this behaviour?

This is a Magic KillerApp-Coil.

It depends on the magnetic flux of the RX+ coil part. RX+ coil should be as big as possible and should have as low inductive coupling coefficient as possible to the TX coil (0.5R .. 0.8R is reasonble radius range for RX coil, TX = 1R).

The induced magnetic flux of the RX+ coil must be compensated with the induced flux of the RX- coil. So the RX- coil should have as much inductive coupling coefficient as possible to the TX-Bucking coil. TX-Bucking coil doesn't need much turns count. The distance depends on the coupling coefficient.

To avoid a significant target response cancellation, the distance of RX+ and RX- coil should be as much as possible.

More turns count for the TX coil, less turns count for the TX-Bucking coil.

These are the basic principles.
Aziz

[Davor]

Rx coils in antiphase - this one cancels earth field and far field emissions. Did you check how close you may place them to retain this behaviour?

[Aziz]

Top Hat Coil EM Fields

This is for your eyes.

[Aziz]

Hi all,

I'm doing the new "Top Hat" coil (everyday a bit). Unfortunately, the glue must dry. That's the reason, why it takes a long time. You can make me busy with more coil analysis. It's the right time.

I have a good news for you:
Regardless of which coil driving mode you use, an universal ground balance scheme can be made. And it is an amateur coil builders heaven: it works at any coil induction balance!!! So you don't need the perfect or specific induction balance criteria.


Oh boys!, you don't know, what I have given to you!
It's going to be very very interesting soon...

Cheers,
Aziz

[Davor]

No fingers - no chocolate :duh:

[Midas]

No, the other way round.
Bzzzzzzzzzzz, bzzzzzzzz, bzzzzzzzzzzzzzzzzz
mosquite sound, it's annoying...

Aziz

PS:
"The principle of inductive brain stimulation with eddy currents has been noted since the 20th century."
Yeah!!! There is a chance to increase my IQ from 101 to much more!

I hope to increase my IQ from I think somewhere around 10 to one of those big numbers that I just don't have enough fingers to understand properly.

[Mechanic]

Hi Aziz,

You will be pleased to know that commercial coils buzz as well, even when they are potted. Although I don't exactly know how thorough the potting is.

Cheers Mick

[Aziz]

So tell me Aziz while you were listening for coil noise did you start to feel any reduction in depression, migraines or auditory hallucinations ?

http://en.wikipedia.org/wiki/Transcranial_magnetic_stimulation

Midas

No, the other way round.
Bzzzzzzzzzzz, bzzzzzzzz, bzzzzzzzzzzzzzzzzz
mosquite sound, it's annoying...

Aziz

PS:
"The principle of inductive brain stimulation with eddy currents has been noted since the 20th century."
Yeah!!! There is a chance to increase my IQ from 101 to much more!