New Concentric Co-planar Coil with Strong MF.

[Aziz]

Hi,

I did it. My new concentric co-planar coil has a very strong magnetic field on his center position. Balancing is possible. I made a prototype and will test the coil with my laptop detector soon.
Attached picture shows the magnetic field strength of the coil "The Coil". It has one big RX-coil. Main TX-coil is on the center position (small one).
Aziz

[ZED]

Great work Aziz,nice bit of lateral thinking.

Zed

[Aziz]

I will publish more analytical details of the coil arrangement on the coming days. It will contain more magnetic field cross-sections, target sensitivity map, how to inductively balance and finally build the coil. This coil arrangement is quite difficult to balance, because the total absolute integral of magnetic flux over the RX coil area is quite huge (strong MF).

MagFluxAbs = Integral ( Abs( _B * _dA) ) over closed surface of RX coil A.
Abs(x) = |x|
_B: Magnetic field density vector
_dA: Surface element vector with dA=Surface area and normal vector _dA' of the surface element (_dA = _dA'*dA).

A second few windings coil either on the main TX or bucking coil will enable the fine balancing with in-phase or opposite-phase resistance network from main transmit signal.

Aziz

[gwzd]

... balance and finally build the coil.

yes!, the coil, less "blah" and more substance!

MagFluxAbs = Integral ( Abs( _B * _dA) ) over closed surface of RX coil A.
Abs(x) = |x|
_B: Magnetic field density vector
_dA: Surface element vector with dA=Surface area and normal vector _dA' of the surface element (_dA = _dA'*dA).

_B is called magnetic flux density vector and is expressed in T, magnetic field is expressed in A/m and has nothing to do with areas

A second few windings coil either on the main TX or bucking coil will enable the fine balancing with in-phase or opposite-phase resistance network from main transmit signal.
Aziz

and finally, have you build it?

I think what most people here would appreciate is performance tests, depth, size, construction etc

See you around
RA

[Aziz]

yes!, the coil, less "blah" and more substance!

_B is called magnetic flux density vector and is expressed in T, magnetic field is expressed in A/m and has nothing to do with areas

and finally, have you build it?

I think what most people here would appreciate is performance tests, depth, size, construction etc

See you around
RA

Hi gwzd,

you have to carefully read, what I have written. Do not mix the magnetic field strength H [A/m] and magnetic field density B [T, Tesla].
Magnetic Flux is given by:

And this is on inductively balanced coil zero (0). This means zero coupling.
To describe the correct term, that this coil is difficult to balance, you have to look on the term: _B . _dA. The absolute value of the dotproduct _B . _dA
integrated over the flux area A (RX) gives you the information, that this coil is difficult to balance. This is followed by the strong magnetic field produced on the main TX coil.

You should bury any discrepancies between us.
Aziz

[gwzd]

Hi gwzd,

you have to carefully read, what I have written. Do not mix the magnetic field strength H [A/m] and magnetic field density B [T, Tesla].
Magnetic Flux is given by:

H is called magnetic field intensity, or strength if you prefer, I personally stick with intensity because that's how I learned it. On the other hand B is called magnetic FLUX density or just magnetic field but I haven't heard yet the term magnetic FIELD density. Perhaps it's because I'm Swedish not American or Englishman. Could any native English speaker correct me?

You should bury any discrepancies between us.
Aziz

I don't have any discrepancies with you Aziz, you are a nice person and I'm just having a cup of tea

By the way, do you already have spring over there? I'm sick of the snow already!

Have a nice evening

[Aziz]

By the way, do you already have spring over there? I'm sick of the snow already!

Have a nice evening

Yes, today we had nice sunshine. I had a cup of coffee after buying some HF-Litz wire. I have built this coil and want to replace the coils by high quality litz wire to increase the Q (Q=XL/R). Frequencies above 10/20 kHz, the eddy current effects of the coil wire became important. My effort is making a very sensitive eddy current search coil. I will design a coil for approximately 4 Ohms resistivity and ca. 6 mH for the TX-coils. So TX inner coil will be appr. 100-130, TX outer (=bucking coil) 12-22, RX ca. 100 windings. Taking the bucking coil closer to RX coil ensures that the main magnetic field of the inner TX coil is not much cancelled.

I am sure, the results of the coil will surprise many people. I am trusting on my calculated simulations.
Aziz

[Sean_Goddard]

Are you going to tune the Tx AND Rx coil to resonance (like...SORRY GUYS... Nexus) or are you going for 100% balance, or both maybe?

As usual a stunningly interesting thread Aziz, I watch with much interest .

[Aziz]

Are you going to tune the Tx AND Rx coil to resonance (like...SORRY GUYS... Nexus) or are you going for 100% balance, or both maybe?

As usual a stunningly interesting thread Aziz, I watch with much interest .

Hi Sean,

I assume, that the coils are coarse balanced: The geometry and the number of windings of the coils should be taken reasonable, that the signal on the RX coil is small as possible and can not be minimized furthermore.

There are many possibilities regarding balancing the coil:
a) on the TX coil side
Taking the in-phase or opposite-phase signal from the TX coil and feeding it via R or RC-Network to a fine balancing coil (1 or 2 turn windings placed on the same core of inner TX coil) or to the bucking coil.

b) on the RX coil side
Same as a) but feeding the signal to RX coil via RC-Network. I personally would leave the RX coil totally decoupled from the TX-coil. The RX coil should only coupled inductively.

c) extra controlled fine balance coil
This is the different way of controlling the fine balance with an external signal source controlled by a DSP or µC. As balancing depends on frequency, ground etc., the software can compensate this in a sophisticated way. Also, it could balance the coil 100.0% perfectly and would achieve ultra-sensitivity. I am allready using this technique.

d) or taking some piece wire of the TX loop and making half/quarter loops etc.
This is well-known and it is used in most search coils today.

Well, I have a working prototype now. This means, balancing of the coil configuration is 100% possible. The calculated number of windings and the geometry matches with the measured results. I am just working on the shielding the RX coil and making some fine balance network (balancing without software - just for testing).
For the balancing, I am using the method a) and c).

Aziz

PS: I have not tested the coil in resonant mode yet. Just feeding an AC signal to the coil without capacitor.

[tiktak]

Hi

Hi,
Can you please post pictures of your prototye?

[bbsailor]

Hi Sean,

I assume, that the coils are coarse balanced: The geometry and the number of windings of the coils should be taken reasonable, that the signal on the RX coil is small as possible and can not be minimized furthermore.

There are many possibilities regarding balancing the coil:
a) on the TX coil side
Taking the in-phase or opposite-phase signal from the TX coil and feeding it via R or RC-Network to a fine balancing coil (1 or 2 turn windings placed on the same core of inner TX coil) or to the bucking coil.

b) on the RX coil side
Same as a) but feeding the signal to RX coil via RC-Network. I personally would leave the RX coil totally decoupled from the TX-coil. The RX coil should only coupled inductively.

c) extra controlled fine balance coil
This is the different way of controlling the fine balance with an external signal source controlled by a DSP or µC. As balancing depends on frequency, ground etc., the software can compensate this in a sophisticated way. Also, it could balance the coil 100.0% perfectly and would achieve ultra-sensitivity. I am allready using this technique.

d) or taking some piece wire of the TX loop and making half/quarter loops etc.
This is well-known and it is used in most search coils today.

Well, I have a working prototype now. This means, balancing of the coil configuration is 100% possible. The calculated number of windings and the geometry matches with the measured results. I am just working on the shielding the RX coil and making some fine balance network (balancing without software - just for testing).
For the balancing, I am using the method a) and c).

Aziz

PS: I have not tested the coil in resonant mode yet. Just feeding an AC signal to the coil without capacitor.

Aziz,

I seem to recall another method of balancing DD coils that might apply to your new coil.

Mark Pauls, in a thread on Eric Fosters Forum, January 25, 2002 "Coplanar DD Loop Disclosure" mentioned the following balancing method that you might want to consider.

Connect a 4-80pf variable capacitor between to hot connections of the TX and RX coils at the connector inside the control box. Set the variable capacitor at mid value. Physically adjust the coils for minimal voltage. Then, once the coils are sealed up you can adjust the variable capacitor to obtain a precise null. Measure the variable capacitor value then place a fixed capacitor of that value in the control box or in the connector if you change coils.

This may or may not apply to your coil design, but I thought I would just give you one more alternative adjustment method.

bbsailor

[Aziz]

Hi,

I am going to publish all details about the new coil. Just look from time to time for more details.
I have shielded the RX coil with graphite now. It is quite dirty job. But it has a relative high resistance faraday shielding (~20-30 kOhms).
See the following sketch for the dimensions. I will post the magnetic field lines soon.
Aziz

An important announcement:
Neither German authorities nor German government may not use this coil. Due to they discriminating me, I am going to discriminate them.
"Ich will meine Kinder sehen oder geht alle zum Teufel!".

[Aziz]

Basic computer model and the magnetic field lines and strength cross section.
Current: I=1A

[Aziz]

I have mismatched the colors of the bucking and TX coil. I am sorry for this.

[Fred]

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