New Concentric Co-planar Coil with Strong MF.

[Aziz]

Hi Aziz,
Thanks for sharing your results.I am following you with great interest.
Best regards,
Fred.

Thanks Fred,

I made some photos of the prototype. I am going to publish this too. It may take some time.

The coarse balancing should made on the bucking coil by adding or removing 1 or 2 turn windings. This can be done of course on the TX coil. Normally, if the dimensions kept equal to my prototype, the coil configuration should be coarse balanced. It depends on the accuracy of making the coils.
I made first the TX coil. Then wounded the RX coil. The bucking coil was made in the last step. It is difficult to find a core for the bucking coil. I made on a wood plate a circle with wood pins and wound the bucking coil on this core.
More details soon...
Aziz

[Aziz]

More simulation results on the prototype.
Following image shows the induced voltage on Target. The Target is a gold ring as a coil with 1 turn winding and short circuited. The TX signal is altering at 15 kHz and Imax is 1 A. I(t) = Imax * sin(wt), w=2*PI*15kHz.
The target is moved on the y=0 plane and the induced voltage is calculated.

Next image is a prediction of sensitivity cross section on the same plane. The detection holes can be proofed by practical tests and my measurements showing exactly the same behaviour.

Aziz

[Fred]

Aziz,

Is not influence of tightening wires and shielding important?
When i build a coil there is a huge difference of inductance if i apply tape with strenght or not.
This is also a problem to calculate coils.winding is never perfect.
Regards,
Fred.

[Aziz]

Some comments on the detection holes:

Due to parallel target orientation to the coils, the magnetic field vectors have no effect because they are not perpendicular to target coil flux area. These detection holes does not exist, when the target is placed perpendicular or on some rotated angle to coil arrangement at that position.

So it depends really on the target shape, orientation, resistance, material, etc.

Aziz

[Aziz]

Aziz,

Is not influence of tightening wires and shielding important?
When i build a coil there is a huge difference of inductance if i apply tape with strenght or not.
This is also a problem to calculate coils.winding is never perfect.
Regards,
Fred.

Yes, there is much influence. Therefore I took the mean radius of the coils and this is a good approximation. Of course, the windings should be wound as tight as possible. I made this by winding a thin isolated wire around the coils. This wire has no potential and is not short circuited. Of course, a nylon thread is more convenient. I hadn't one.

Shielding is most important to RX coil. The TX and bucking coil need not to be shielded and can be neglected. If someone wants a perfect coil, then shield all of your coils.
I have not calculated the inductance of the coils yet. I have to expand the model and this would take some time for calculation. I will support different coil windings for TX and bucking coil soon. This can be better used for particular coil design.

Aziz

[Aziz]

Target is rotatet by 45 Degree on y-axis. See the difference.

[Aziz]

Now target rotated by 90 degree (less coupling to coil configuration).

[tiktak]

Hi

Hi,
Thanks
Hope see the pictures soon.
Buy the way what is the metal detector?

[Aziz]

Some photos of my prototype.

[Aziz]

My testing environment.

[tiktak]

Hi

Hi,
Still cant understand how to null this coil?I have only multimeter!
And what is the purpuse of this halfwinding and exra winding?How is all conected?What detector did you use?
Its look like you use big wire d?
Thanks for sharing the info I will try your coil ASAP!You have invested meny time in it and I respect this.Hope work as expected!
Unseen.

[Aziz]

First balancing test. Just using a multimeter and AC voltage from power supplier.

[Aziz]

Hi,
Still cant understand how to null this coil?I have only multimeter!
And what is the purpuse of this halfwinding and exra winding?How is all conected?What detector did you use?
Its look like you use big wire d?
Thanks for sharing the info I will try your coil ASAP!You have invested meny time in it and I respect this.Hope work as expected!
Unseen.

Hi tiktak,

Due to simplified computer simulation model, I expected some degree of unaccuracy. Therefore I tested the balancing with extra winding and half winding. Balancing is critical. It depends on the coil dimensions (radius, thickness, tightness, etc.).
It is a normal process, to get the first prototype balanced. Of course, it is also the proof of the calculated number of windings of the computer model. So the computer model is accurate enough.

More better can be the coil balanced on the TX coil instead of the bucking coil side. Because the TX coil has more windings (126) than the bucking coil (23), it is easier, to build to bucking coil first. Then bulding the TX coil and giving one or two turn (or removing) on the TX coil will balance the coil configuration better. But I built the TX coil first and won't willing to change it anymore.

The fine balancing coil is just for testing. A different AC signal is fed through the fine balancing coil with same frequency but different amplitude and phase.

It may be a big challenge, to get this coil running in a MD.

[tiktak]

Hi

Hi,
No Its look NICE I am shore it will work just need time!

[Aziz]

The balancing principle is quite simple.
The magnetic flux Φ, seen by the RX-coil should be exact 0.


As the inner part of the TX coil increases the magnetic flux, the outside of this will decrease it. Without the bucking coil, the magnetic flux Φ can not be made 0. And therefore a bucking coil is needed with opposite winding direction, that the B-Field vectors should show in the direction and magnitude, to get the RX-coil balanced.
See following image for details: