New PI technology proposals.

[Aziz]

I will give you some more benefits to coil configurations with this universal design:

1. DD coil configuration.
TX Tesla coil as described above and seperate RX coil which are inductively decoupled to each other (k=0). In this case, we can sample just-in-time of the target signal response. Provided that the balance of the coil is perfect enough, that the clamping diodes will not clamp or clamp for a very short time period due to lower breakdown overvoltage.
DD coil configuration makes the power supply consideration easy due to galvanic decoupling of the RX coil.

2. Transformer coupled MONO coil configuration.
A small inductor (few turn windings) with small inductance is for the magnetic field energy generations. This coil need no damping resistor. It will be fired from the MOSFET. A big inductor with higher inductance of the same size and position (coupling k=1) with his damping resistor on ends is for target signal stimulation and is working as a receive coil. We have a typical transformer coil of the same size and position. Low windings to higher windings step-up transformation. Both coils are not splitted but galvanic seperated.
So power supply can be realized easy. We will have lower flyback voltage (flyback of the primary TX coil is not added).

3. Split coil (Tesla coil) MONO coil configuration.
Introduced allready above.

4. Alternating magnetic field excitation configuration (MONO/DD).
We need a symmetrical center-tapped TX coil, which the both coil ends will be driven individually from the MOSFET in alternating sequences. We have two MOSFET switching drivers. Signal can be taken as usual on both ends. The damping resistor is placed on both ends.


You see, there are many different configurations that can be made with this simple design.

Aziz

[Qiaozhi]

I have the feeling of you guys do not trust in theory and SPICE simulations

On the contrary, SPICE is an extremely useful tool to have in your toolbox. You can use it to explore many interesting ideas, or even to just understand what is really going on in a particular design. But - you cannot do this in isolation from the real world. Reality has a habit of behaving differently to theory. This doesn't necessarily mean the theory is wrong ... just that it's not a complete model. Once you have a theory, it must then be tested in practice. Then you can go back and refine the model. This is called 'engineering' and nothing to do with trust. In general, engineers don't leave things to "trust".

By the way, I note from the schematic that you are using ideal inductors (without any DC resistance). This is a small refinement you could add. It might make some difference to the results.

[Aziz]

Hi Qiaozhi,

By the way, I note from the schematic that you are using ideal inductors (without any DC resistance). This is a small refinement you could add. It might make some difference to the results.

these parasitic effects are taken into account in the inductors model. You cannot see the values. Only the {LTX/4} is visible. There is {RTX/2} for LR and {CTX/2} for LC. Only parallel shunt resistance (G) is not taken into account (loss of inductor). This can be done, as I know this value exact.

I am trusting in physics. I am trusting in Faraday, Maxwell, Tesla, Ampere, Kirchhoff and of course on my design idea.
First was the theory of the idea. Then the proof with circuit simulations. Then rechecking it with theory again.

Now, I need a real acid test. I hope somebody will proof either the falsification or the real working proof.

Aziz

[simonbaker]

spice files

Hi Aziz:

Can you post your LTSpice files and any auxiliary files/models needed to work with it? I would like to see it in action!

Also some instructions on how to install any auxiliary components, I am a little slow with understanding LTSpice setup stuff though I'm using it basic.

Good work as always!

Cheers,

-SB

[Aziz]

Hello simonbaker,

Hi Aziz:

Can you post your LTSpice files and any auxiliary files/models needed to work with it? I would like to see it in action!

Also some instructions on how to install any auxiliary components, I am a little slow with understanding LTSpice setup stuff though I'm using it basic.

Good work as always!

Cheers,

-SB

yes of course. I will provide different coil configurations with the whole projects file. This is at the moment too fresh and hot to publish. I have to tidy up my models. Maybe next weekend.
I am using LTSpice IV.
So you and others can make some experiences with LTSpice in the mean time.
Aziz

[simonbaker]

Hello simonbaker,



yes of course. I will provide different coil configurations with the whole projects file. This is at the moment too fresh and hot to publish. I have to tidy up my models. Maybe next weekend.
I am using LTSpice IV.
So you and others can make some experiences with LTSpice in the mean time.
Aziz

What do you do with the target control switch (TGTSW)? Is that just for testing without the target?

-SB

[Aziz]

Some hints for experimentators:

To get the proof of the earlier decaying, keep in mind, that the center-tapped coil will produce twice more signal levels! This means, that the target signal is already inherently amplified with factor of 2. This applies also to the decay curve.

To compare the proposed design with conventional design, use a conventional design with equal conditions but amplifing the RX signal twice. Then exact timings can be measured and compared.


Aziz

[Aziz]

What do you do with the target control switch (TGTSW)? Is that just for testing without the target?

-SB

Yes, it will be switched on on every second period. This means, target will be presented to the coil on the short circuited switch. I can see then the difference of the target response.

Aziz

[simonbaker]

Gentlemen, allow me to disagree.
I say it is the expanding magnetic field produced by the coil current, that kicks the target. The Flyback is actually reducing the eddy currents in the target.
The Flyback is too short to "saturate" for want of a better word, the target.
The Flyback induces currents of opposing polarity since the magnetic field of the Flyback expands and then collapses, that is, the field cuts across the target conductor first the one way, the the other way.
The current raising in the coil during TX, generates an expanding magnetic field that cuts across the target \ conductor and induces currents within the target. The first currents are superficial skin effect currents. It takes time for the eddy currents to expand to the core of the target.
How much time? The time needed has been named the TC of the target. High conductive and large size targets have long TC's. Large silver coins can have a TC of hundreds of uS.
If the TX pulse is short, the eddy currents will not have the time to expand to the very core of the target, so they will not reach maximum amplitude.
Now look at the Flyback. It's duration is a matter of nano seconds for the one way and a few micro seconds on the return. Its highest power is at the maximum voltage point that is about even both ways and of a duration of nanoseconds. Just too short to induce much eddy currents. And going both ways, thus canceling the eddy currents induced by the going field, with the field collapsing.
However, the eddy currents induced by the TX coil current persist for some time.
How much time? about the same time it took to generate them The TC of the charge curve equals the TC of the discharge curve.

So, how will I prove my point? I will show you that I can read the eddy currents without having a Flyback.
Better than that, I will show you that, without the Flyback, the amplitude of the eddy currents is much higher.
I will pulse the coil with a usual square wave TX pulse but will modify the circuit to eliminate the Flyback.
Below is the scope picture of the coil current.
The pulse length is about 64us, you can see a slight kink and noise spike where the TX switches OFF. Forgive me for the noise spike, I don't think it can be called a Flyback.
The scope is set at 20us \div and 10mV\div.
Note, this is the coil current, not the TX voltage wave form.

Please allow me some time to setup an RX circuit to read the eddy current. Just the preamp.
I will use US$ 1c, 5c, 10c, 25c as test targets.
Monolith

This issue seems fundamental to the workings of the PI MD. Is it really in question? Carl's Hammerhead article states it is the collapsing magnetic field that makes the eddy current -- is this not accepted?

Can we not determine this by experiment? Would not the expanding and collapsing magnetic fields induce currents of opposite polarity in the target? Can we not detect the polarity fairly easily?

(I'm just starting to take interest in PI theory, I hope you'll bear with my beginner questions)

Regards

-SB

[Carl-NC]

This issue seems fundamental to the workings of the PI MD. Is it really in question? Carl's Hammerhead article states it is the collapsing magnetic field that makes the eddy current -- is this not accepted?

I don't think Aziz is disagreeing with this. Yes, it is dB/dt that induces eddy currents in the target. And it is di/dt that produces dB/dt. I think our only disagreement is with the flyback voltage... it is an artifact of the system.

If Aziz is seeing a higher flyback that is settling faster, then I expect it is due to a faster di/dt and the arrangement of the mutually inductive coils. I doubt it is due to the higher voltage burning off the current faster. I think it is this cause & effect where we disagree.

But that's OK. The main thing is, does it Really Work? I will have an answer tomorrow. I am (right now) winding the two coils -- one center-tapped & one not -- to compare this method with the std mono. I have the mono wound and hot-glued into a TDI shell, will have the CT coil done tonight. Then I will put them on my HH board and see.

Stay tuned...

- Carl

[simonbaker]

Some hints for experimentators:

To get the proof of the earlier decaying, keep in mind, that the center-tapped coil will produce twice more signal levels! This means, that the target signal is already inherently amplified with factor of 2. This applies also to the decay curve.

To compare the proposed design with conventional design, use a conventional design with equal conditions but amplifing the RX signal twice. Then exact timings can be measured and compared.


Aziz

Something I'm not clear about:

Battery pulse is connected across LTX2, which is low resistance path. Lots of current.

Induced current in LTX1 travels through two 10K resistors, quite high resistance. Tiny current?

Even though voltage is large across both coils, the current is not the same in both coils, is it? I would think LTX2 has big current, LTX1 just small.

Target sees changing magnetic field from changing current, not voltage. How do you get twice magnetic field because current contribution from LTX1 (induced current) just a trickle -- no?

I probably misunderstand circuit, need to get LTSpice going.

Can you explain?

Thanks,

-SB

Another thought: It seems maybe what you are doing is really impedance matching through a transformer. You generate higher voltage and couple to higher resistor. But reflected back through transformer, it looks like smaller resistor to main current. Instead of using tapped auto-transformer, imagine normal transformer, what do equations tell you? I will need to see spice sim I guess.

[simonbaker]

I don't think Aziz is disagreeing with this. Yes, it is dB/dt that induces eddy currents in the target. And it is di/dt that produces dB/dt. I think our only disagreement is with the flyback voltage... it is an artifact of the system.

If Aziz is seeing a higher flyback that is settling faster, then I expect it is due to a faster di/dt and the arrangement of the mutually inductive coils. I doubt it is due to the higher voltage burning off the current faster. I think it is this cause & effect where we disagree.

But that's OK. The main thing is, does it Really Work? I will have an answer tomorrow. I am (right now) winding the two coils -- one center-tapped & one not -- to compare this method with the std mono. I have the mono wound and hot-glued into a TDI shell, will have the CT coil done tonight. Then I will put them on my HH board and see.

Stay tuned...

- Carl

Yes, it seems you and Aziz believe in collapsing field the main driver of target currents -- but I saw dissenting opinions, just wondering if proven one or other.

Look forward to your experiments!

Regards,

-SB

PS. Has anyone experimented with "assymetric" damping? In other words, use a diode and have an underdamped (very fast) first half of cycle (let it start ringing), but in the next half cycle, couple in more resistance with a diode to critically damp it out? Or something like that.

[Carl-NC]

Yes, it seems you and Aziz believe in collapsing field the main driver of target currents -- but I saw dissenting opinions, just wondering if proven one or other.

Physically, it has to be so... induction is only caused by a changing magnetic field, not a static one. What other opinions are there?

PS. Has anyone experimented with "assymetric" damping? In other words, use a diode and have an underdamped (very fast) first half of cycle (let it start ringing), but in the next half cycle, couple in more resistance with a diode to critically damp it out? Or something like that.

I've experimented with switched damping, that is, where the damping resistor is switched in during the flyback. I did this in my security wand, strictly for lower power.

- Carl

[Aziz]

Hi guys,

I could perhaps make some mistakes in my thoughts. It is difficult to compare two different configurations. Fact is, there is due to center-tapped coil the twice target signal stimulation (measureable). This is due to higher dI/dt during the flyback damping process. This stimulation will arrive the target and then back. So the target response on the receive coil should not a factor of twice of course.

I suggest to make only performance tests (what counts tests). Giving a fixed amplification factor and seeing, when the early sample time it is. The earlier, the better the sensitivity it should have. This makes the tests easy without getting confused much.

Even, when there is possibly no significant faster decaying available, what for benefits it could else have? I will not be worry about, if I have some fundamental mistakes on my thoughts.

This debate is showing purely, that not everybody has the same understanding of PI technology. So it is a big chance for us, to find a good solution and going further.

Now, what for mistakes I have made? Just feel free to correct me.

Aziz

[1843]

If Aziz is seeing a higher flyback that is settling faster, then I expect it is due to a faster di/dt and the arrangement of the mutually inductive coils. I doubt it is due to the higher voltage burning off the current faster. I think it is this cause & effect where we disagree.


- Carl

Hi,

Using a higher voltage MOSFET cuases a faster settling down. I have tried this many times and that's why the designer of www.pulsdetektor.de uses IGBTs.(1200V)

Aziz doesn't say we make the flyback voltage higher... but he says we don't limit it by a MOSFET's internal diode.

The reason for this is that when the flyback voltage goes higher than the MOSFET's breakdown voltage, the MOSFET's clamping diode is shorted and then the current flows through the diode rather than the damping resistor....

In the PIs like HH, we cannot make setteling down faster because the flyback voltage is under the MOSFET's breakdown voltage.



I hope this helps
1843