DD and Concentric

[Fred]

Exactly, its not a smart game.

[Tinkerer]

IB coils

DD Coils are very easy to build and balance. But they are due to geometric variant type of coils, any mechanical distortion will cause balance asymmetry. Especially, when temperature effects will occur. Further on, any mechanical load will cause asymmetry. To overcome this, a motion-mode is more convenient.

On the other side, concentric coils are very difficult to build. But they have many advantages.

Look to the following concentric coil: (PCB-IB-Coil)
http://ibcoils.tripod.com/album/inde...b-coil?i=0&s=1

Have you ever seen such a coil?

I looked at the pictures at ibcoils.tripod. This is very interesting, specially the pictures of the magnetic fields. Did you use the "Maxwell"software by Anvil for that? I find it very hard to make precise coils for IB. Your system seems to be the perfect answer.
How do you calculate the exact number of turns needed to achieve balance?
Is there a way to make final adjustments once the PCB has been etched?
Tinkerer

[Aziz]

I looked at the pictures at ibcoils.tripod. This is very interesting, specially the pictures of the magnetic fields. Did you use the "Maxwell"software by Anvil for that? I find it very hard to make precise coils for IB. Your system seems to be the perfect answer.
How do you calculate the exact number of turns needed to achieve balance?
Is there a way to make final adjustments once the PCB has been etched?
Tinkerer

The software for this purpose is developed by me for more than 10 years. It is based on simple wire-by-wire calculation using the biot-savart law. I implemented an optimizer for this purpose and can find the optimum balance parameters (geometry, number of turns, etc.). There are many ways to find an optimum balanced IB-coil. Often, I decide to set the number of turns for the tx-coils and then calculating the rx-coil (number of turns, radius start, radius end, etc.). And sometimes, if I can not find a good coil, I change the number of turns for tx-coils. Only the limitation is the surface area (diameter) and the thickness and gap of the wire on the pcb.
On the picture shown, you can see, that almost all of the area of the coil is used. Especially the rx-coil has a transformation function (like transformer) and is built-in hardware amplifier.
All the integrated area of the rx-coil will induce no signals (due to balance). This balance will be disturbed by the environment (metal, ground, mechanical shock, etc.). The rx-coil is kept very thin to get more windings (higher transformation). The tx-coils are thicker, to provide more current and therefore higher magnetic flux.

For the fine and ground adjustment, there is one turn coil between two tx-coils. This will compensate all the effects, caused by ground and manufacturing tolerance. So, you need two signal feeds: one for the tx-coils (connected serial) and one low-power for the compensation coil. With this technique, I can achive a very good balance and get more sensitivy. The place for compensation coil is not important. But the gap between the two tx-coils is a good place for this because this gap is physically needed.

Here comes: I realized this metal detector with only a Laptop + 24Bit/96kHz sound card and very simple amplifiers.
The complexity of the detector is really high and you need very good software techniques. Especially to compute a real-time signal for the compensation coil. You need a big number crusher for this. It is possible to realize a good and very cheap detector usung a Laptop.

You all should start working now. I gave you too many hints.

[Aziz]

Some pictures on my album are too big to be displayed correctly.

Here is a compressed file, containing more pictures:

http://ibcoils.tripod.com/wien2.rar

Aziz

[plboy]

I should imagine that it was fairly tricky to calculate the parameters for this coil. How good was the nulling? i.e. what was the residual voltage in the RX with no target present?

I've also written a calculator for concentric coils, and that was difficult enough to get an accurate result. How many prototype boards did you build, before you got one that worked properly?

what about concentric

[Qiaozhi]

what about concentric

I will post the concentric coil calculator soon. Just give me a few days to tidy-up the code.

[Aziz]

I will post the concentric coil calculator soon. Just give me a few days to tidy-up the code.

How do you calculate your induction balanced concentric coils?

[Tinkerer]

IB coils

Aziz,
I could not access the page http://ibcoils.tripod.com/wien2.rar but I admired your pictures of the coil magnetic fields that you posted earlier.

Here is the link for download of the free version of MAXWELL SV software by Ansoft.
I understand this software is great for calculating magnetics and for visualizing the magnetic fields.
http://www.ansoft.com/membership/login.cfm?campaign=26


I feel it is very important to have the magnetic fields of the 3 coils interacting in just the right way to obtain maximum sensitivity and depth.
Tinkerer

[Aziz]

I do not know, whether Maxwall SV is able to calculate balanced IB-coils. I can not image that. It is application specific.

But to understand how IB-coils are working, it is usefull to study the EM-field of coils. I have simulated hundreds of different coils and the result of many years is the coil what I showed you.

Here is another 3d EMF of a coil:

(real 3D magnetic fields of other coil)

(real 3D magnetic fields of other coil)

[Qiaozhi]

How do you calculate your induction balanced concentric coils?

There is an article on this site that discusses constructing concentric coils, where the number of turns on the TX and nulling coil are assumed to be related to the area contained by each coil. In practice I found that this was not correct, and my own tests indicate that they are in fact related to the radii of the two coils.
The calculator uses a modified version of Brook's equation, since the original equation was estimating the inductance about 10% lower than the actual measured value.
Hopefully I will be ready to post the software here sometime this weekend.

[Tinkerer]

I do not know, whether Maxwall SV is able to calculate balanced IB-coils. I can not image that. It is application specific.

But to understand how IB-coils are working, it is usefull to study the EM-field of coils. I have simulated hundreds of different coils and the result of many years is the coil what I showed you.

Here is another 3d EMF of a coil:

(real 3D magnetic fields of other coil)

(real 3D magnetic fields of other coil)

Hi Aziz,

again I have no luck with the tripod website. It does not open for me. I agree with you that a good understanding of the EM field of the IB coil is necessary to be able to design such a coil. This is why I like your pictures so much.
I am new to IB design and am amazed how different the IB coil behaves from a usual PI coil. So much to learn.
Here are some questions:
With a standard PI coil, the best depth/sensitivity is roughly equal to the diameter of the coil.
How does it relate to the IB coil? To the diameter of the TX coil or the RX coil?
I wound some coils in the spiral way. I found that the capacitance can be reduced that way. However, more turns and more wire are needed to obtain the same inductance. This again increases the capacitance. I feel that somewhere there is an ideal compromise, but how do I calculate that? The number of turns are not indicative, since the small diameter turns near the center of the coil, add very little inductance, while the last turns with the largest diameter add much more inductance and capacitance.
Another problem is the larger surface of the shield for the spiral wound coil. It adds more capacitance too.
Tinkerer

[Unregistered]

There is an article on this site that discusses constructing concentric coils, where the number of turns on the TX and nulling coil are assumed to be related to the area contained by each coil. In practice I found that this was not correct, and my own tests indicate that they are in fact related to the radii of the two coils.
The calculator uses a modified version of Brook's equation, since the original equation was estimating the inductance about 10% lower than the actual measured value.
Hopefully I will be ready to post the software here sometime this weekend.

OK...humor&other things aside.
What you saying here is confusing!? Radii of coils are defining area contained by each coil?
So? You are practically saying here "no 2+2 are not 4, but 2+2 are 4"????
You should read more in those patents you have. Kerr for example...

[plboy]

Next thing you will post here is how i didnt understand what you saying.
It is pretty hard to understand somebody so enthusiastic like yourself.
You want to discover "hot water" again and become famous. I can understand you wish to prove yourself here and be respectfull expert. I do respect you young man. Dont guess me wrong on this.
There is no proper way to establish "all in one" calculation method for coils. Due so many complex reasons. Learn more and you will see.

concentric for PI

[Aziz]

Hi Tinkerer,

Hi Aziz,
again I have no luck with the tripod website. It does not open for me.

I am sorry for that case. May be it depends on your provider or on tripod. Try the click right and save the file into your hard disk.

Here are some questions:
With a standard PI coil, the best depth/sensitivity is roughly equal to the diameter of the coil.
How does it relate to the IB coil? To the diameter of the TX coil or the RX coil?

It depends on the size of the target and the pyhsical effects of the target (intensity of the distortion of the balance). Of course, it depends on many other factors: Size of the TX coils, integrated surface area of the RX coil. The advantage of the PI coils are, that they do not need a canceling coil. Therefore the magnetic flux is higher. On IB-coils, you create a local canceling area. As you can see the magnetic field direction vectors on my pictures, you can see a change of direction (from centerpoint to first TX-coil (up/down-change)). The search coil (RX) is placed somehow to add all of the integrated area, to induce 0 Volt. That means, all added magnetic fields inside would cause zero vector. The RX-coil can only detect the disturbances inside of the rx-coil-windings. As a physical effect of magnetic fields, disturbances outside the rx-coil, will also cause disturbances inside of the rx-coil.

I wound some coils in the spiral way. I found that the capacitance can be reduced that way. However, more turns and more wire are needed to obtain the same inductance. This again increases the capacitance. I feel that somewhere there is an ideal compromise, but how do I calculate that? The number of turns are not indicative, since the small diameter turns near the center of the coil, add very little inductance, while the last turns with the largest diameter add much more inductance and capacitance.

Spiral coils are relative inefficient. The magnetic flux will be cancelled slightly from the first radius to the last radius of the coil windings. So the total result is lower than on ideal circle-coils. But how the make an easy and cheap coil on the pcb? I am restricted to spriral coils. But they have a big advantage: small coils, big coils, easy to build, balanced. Detection for different sized objects. Of course, the inductance will be low. But the resistance is high.
Spiral coils are compromise.

It is also possible, to place the rx-coil outside of the tx-coils. But difficult to realise (post processing of the signals).

Another problem is the larger surface of the shield for the spiral wound coil. It adds more capacitance too.
Tinkerer

Coils, especially thin on pcb, need an enough gap to the shield, to reduce the capacity. Otherwise, it will act as a resonant circuit. A higher resistance shield (5-10k or even higher) can be a good solution (with graphite).

[Tinkerer]

PCB coils

Thanks Aziz for the very useful information.
I have used graphite composition coatings with a PP spacer of 5 mm. That seemed to work OK. I will try with the TX inside and RX outside.
Somehow the capacitance does not seem as critical with the IB coil as it is with the traditional PI coil.
The higher resistance of the winding will only become a problem for high power TX. So far I have not tried above 1.2 A TX current. Have you tried much more power than that?
It seems to me that the balance changes somewhat when increasing the power. Did you observe the same?
Is there a way to compensate for changes in balance?
thanks for the help
Tinkerer