DD and Concentric

[Unregistered]

Hi Tinkerer,

sorry for my late answers. I started with the improvement of my coil software. I also took my Laptop-MD-Hardware from my basement and started to work on.

On the new coil software, I will support Postscript (+PDF) output for the PCB-coils. I also want to develop a much bigger PCB-Coil (30 .. 40 cm diameter). The coil software and especially my printer was former restricted to DIN A4 (210 x 290 mm) format. I want to manufacture some bigger PCB-IB-Coils next year.

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

I took also a high resistance graphite shield.

You should keep the TX-coil resistance as low as possible to get a good coil Q. I soldered my TX-coils on the PCB to lower the resistance. I tried with 10 - 20 W Power Amplifier to feed my TX coils and got some improvement. But on the other hand, you will have more instability, signal deformations (distortion factor), more power consumption, more noise, more unwantend resonance of coil signals etc. Of course, balance of IB-coil will change.

If the resistance of the coil can not be minimized, you could use higher voltage for signal feeds (12 .. 24 V).

I do this by feeding two signals: High-Current TX-coil feed, Low-Current balance correction feed. Balance will change on different soils and ground conditions. So, the second feed is also used as a ground canceling signal.

But you can not do this technique with simple electronics. You need a DSP or high performance number crunching computer (e.g. Laptop).

Aziz

[Tinkerer]

DSP and IB coils

Hi Aziz,
again many thanks for the info.
Your Postscript/pdf output will make it much easier to print the traces.
Double sided PCB should also help getting more turns on the same space. Thick board and designing the traces so that the trace of the one side falls in the space between the turns on the other side should reduce the capacitance.
The fact that the balance changes with humidity , ground etc. is my biggest worry, so your info about the feeding of different current to the two coils should be a big help.
I understand that you are using the IB coil for a VLF system. I am using it for a PI system, however, the balance problems are the same.
Do you write DSP source code for PIC? I would like to use some DSP filtering, but am too old to start learning that.
Tinkerer

[Aziz]

Hi Tinkerer,

you're welcome.

My 20 cm PCB-IB coil for instance is a double sided PCB-coil and I found the corresponding project files (they were lost in my hard disk). But double sided PCB-coil is very difficult to build (because of the balance problems). Double sided PCB-coils has more mechanical and temperature stability.

The interleaved spacing of the cu-traces is a good idea to lower the capacitance. I have not tried this yet. But on the next design, I will consider this (soon).

I made also one PCB-IB-PI coil (simulation), that only has one winding for the tx-coil and one for the canceling tx-coil. The balance is made by geometry (radius) and coil resistances (different current flow through tx-coils) by connecting an amount of thin parallel wires. This lowers the eddy currents on the (thick) cu-traces. I have not practical experiences with such coil yet. But I can make some PCB-IB-PI designs for experimenting (but have to code a little bit on my software).

If you have the possibility of computerized processing, then you will not want do PI technology. You will try the better VLF technique using multiple frequencies. So therefore my experiences are restricted on IB-VLF (1 - 48 kHz).

Many years ago, I tried the MD with a 40 MIPS DSP. But DSP coding is very difficult, time and money consuming and has many other restrictions. So I gave this up and started to code on simple personal computers (Laptop, PC) using simple Windows XP operating system. It is easy, fast and low-cost. The next generation of small Laptops or tablet-pcs are most convenient for this purpose and they have enough processing power (more than you really need). Also the Hi-Fi-sound capabilities are predeterminded to lower the noises and to increase the SNR (signal-noise-ratio). This enables up to -100 .. -110 dB rx-signal for processing (24 Bit / 96 or 192 kHz sampling rate).
The main advantage of this is, you have only simple and small detection hardware and the front end is the software on the PC. Easy update and change of processing is possible.

I just coded the software on Visual C/C++ 6 and most parts of it are available through the internet (Digital signal processing, Filters, FFT, Sound-Card-Driver sources, GUI sources, etc.).

In few weeks, I will post some PCB coils as postscript and PDF files (coil software is working now). Every of you should then able to start with the Laptop MD. I made the experiments for you and proved the realisation. It is really possible.
I will also show you some pictures about the hardware and software. This could take some weeks (next year probably).

Aziz

[Aziz]

Here is a high resolution of the Induction Balanced PCB coil of shown one.

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

2400 x 2400 dpi resolution, dimensions are displayed in mm on top.

Just click and look/save the file. If you want to build this PCB, you should print the mirrored in horizontal direction for the negative disposure foil.
Aziz

[Aziz]

Ok, www.tripod.com causes problems sometimes. I will try attachements.