New PI technology proposals.

[Carl-NC]

The flyback voltage isn't an artifact! It is an essential process for "kicking the target". It is the process (damping), where the target's eddy currents will be actually generated.

No, it is the di/dt of the turn-off that kicks the target. The flyback voltage is a side effect (L*di/dt) that is only useful near the end, where we look at it for small variations.

Of course, during TX on-time there is also some eddy currents in the target. But they have no real role in the PI technology as supposed. The effects of the damping process predominating this.

Finally, someone who agrees with me on this! Yes, the "on-time" eddy currents are negligible, even if the current is still ramping up at the point of turn-off.

The higher the flyback voltage is, the more efficiently and faster will be the damping process.

Sorry, but it is a faster turn-off settling that produces the higher flyback, not the other way around.

The transmitter coil will therefore be a splitted winding coil. Either a center-tapped or a step-up coil. The step-up coil will produce high flyback voltages beyond the hell. ... My proposal is using only the small part of the splitted coil. If we use the center-tapped coil, this will allow double current flow (half resistance -> I = 2 A) on a half coil (Lhalf = 300µH/4 = 75µH).

You'll need to post a schematic to clarify, but I suspect you are getting a faster turn-off simply because of L/4.

- Carl

[Aziz]

I have the feeling of you guys do not trust in theory and SPICE simulations. During the last days, I also did not. Because it changes my knowledge about PI detectors. The theory is older than 100 years old. It is well proofen.

But I have learned much more with SPICE simulations rather than with soldering iron. Particularly when the SPICE simulation says "The flyback process is kicking the target! That's matters!". And you can see the targets induced voltage and current. Provided that, you have modeled the circuit right.

So the theory says, "practice won't work without my permission. If so, then practice is believing it has the permission for.".


Just some advises for practical testing:
Do not try this without the background knowledge. You may fry your circuit or getting electric shocks from the coil ends otherwise.

Aziz

[Aziz]

Hi Carl,

No, it is the di/dt of the turn-off that kicks the target. The flyback voltage is a side effect (L*di/dt) that is only useful near the end, where we look at it for small variations.
- Carl

We are talking almost about the same thing. Almost.

Let's give to some process points names:
toff = exact turn-off time
toff- = the time just before turn-off
toff+ = the time just after turn-off

At toff we have maximum flyback voltage. The magnetic field energy is still there and the nature is getting into heavy stress. It is protesting. The coil says: "Damn, I have loaded much energy. Where to damp it?".

At toff+ starts the damping resistor to convert this magnetic field energy into heat. The current through the coil and damping resistor, in which is converting to heat, is killing the magnetic field density around the coil. The target see's a magnetic flux change! The dI(t)/dt in the damping process is necessary, to convert this energy as fast as possible. Now the damping resistor gets into heavy stress (producing heat). But it is his profession to do this and the resistor likes this process. The more the flyback voltage, the more the heat production (until the resistor goes up in smoke).

Sorry, but it is a faster turn-off settling that produces the higher flyback, not the other way around.

You'll need to post a schematic to clarify, but I suspect you are getting a faster turn-off simply because of L/4.

- Carl

At toff, the coil surrounding has the same magnetic field energy got from the half part of the coil (L/4). At toff we have also now the full coil windings (L=300µ). Now, it is the same state as the full coil would do anyway. The turn-off process applies to both alternatives: either single full coil or half driven coil plus the step-up conversion on the other end. They have to damp the same magnetic field energy. Who willl win the race?

Now the benefits of the lucky side effects (nice to have effects):
Mosfet see's only the half coil capacitance (switching of course faster off). Mosfet see's only less coil voltage while the damping resistor see's the full coil voltage.
Damping process is now 4 times efficiently.


Who can follow me?

Aziz

[Aziz]

To ease the imagination of the idea, I will put the schematics of this idea. Then you can make your own thoughts.

Aziz

But the idea is somehow genius that it never considered at this unconventional way.

The following picture shows the MONO coil configuration.

[Aziz]

To All:

Just some words about the intellectual property:
I have published this design idea to many other available sources. It is a public domain invention and be so kind and try not to register any patents relating this idea.

This is a gift from me, provided that it's a novel invention. Watch out, if someone tries to steal the idea from the public domain.


Aziz

[Carl-NC]

Spice is a wonderful tool, been using it for 25 years. But it's important to have a fundamental understanding of what is going on, so that you interpret the sim results correctly.

I agree, the flyback process kicks the target, but it is the di/dt that matters, and the flyback voltage follows from this. If you cut the L from 300uH to 75uH, you will get a 4x faster turn-off, all else being equal. You will also get a faster turn-on, which will typically result in a higher peak current if you are still running on the slope (most are). Also, the lower RL will help even more.

The lower L does mean a lower RD but with a root-2 relation so you still keep a faster turn-off. And the lower L probably means a lower parasitic C which adds another boost via a higher RD.

So, yes, running L/4 will give you wonderful gains in di/dt and therefore effective TX field strength, and also faster settling. BUT... you get a correspondingly weaker RX signal from the target. There is no free lunch, and that's why everyone is not off to the races reducing their coil inductance.

At toff, the coil surrounding has the same magnetic field energy got from the half part of the coil (L/4). At toff we have also now the full coil windings (L=300µ). Now, it is the same state as the full coil would do anyway. ... To ease the imagination of the idea, I will put the schematics of this idea.

Ah, OK, I see now what you did. Truly you have L/4 at turn-on. That helps per discussion above. At turn-off you are dumping the damping current through an additional L/4. I'll have to give this some thought, but it might be a clever improvement. What mutual inductance are you using?

One benefit is that for RX you have the whole L value. It's equivalent to a separate 75u TX coil and 300u RX coil, but has the benefit of lower weight and the mutual inductance during decay possibly helps. I might build up a quick test coil & see what happens "in real life".

- Carl

[gwzd]

gwzd said that history is not his favorite subject, but without studying history we are doomed to make the same mistakes over and over again.

Skip the mistakes, go directly to the end and make things work. History is for people with too much time. Anyway, everybody is writing it in its own way.
Regards,

[gwzd]

But I have learned much more with SPICE simulations rather than with soldering iron.

It shows! The deep understanding you have obtained is as futile as a spice simulation without knowing what's happening in the reality.
I saw once a student running a TO-220 at 450 degrees Celsius, in spice of course. He was convinced it would work in real life, I encouraged him to build the circuit just to see his face when the whole thing started to smoke!
Regards,

[gwzd]

To ease the imagination of the idea, I will put the schematics of this idea. Then you can make your own thoughts.

Aziz

But the idea is somehow genius that it never considered at this unconventional way.

The following picture shows the MONO coil configuration.

I'm speechless, you really did it! You copyrighted the 3-opamp instrumentation amplifier! I'll have to be careful in the future when using that, one never knows you might come after me ;-)
One word of advice for you genius, use 1N914 or something faster in place of those 1N4148, why? well, try spice!
Regards,

[Aziz]

Hi Carl,

What mutual inductance are you using?
- Carl

The transmitter coil parts are fully coupled to each other (k=1). They sharing the same geometrics. A typical center-tapped coil. It is confusing in the model. It shows two inductors. But this is necessary to model a split coil.

We have then the total coil inductance L:
L = L1 + L2 + 2*k*sqrt(L1*L2), where L1 = LTX1 = 75µH, L2 = LTX2 = 75µH and k is the coupling factor of the coils between L1 and L2.

The formula ends with the total coil inductance of L = 300µH.

The coil coupling factors are defined in the text area with K1, K2, K3..

The target model has equal amount of coupling to the coils. It is of course very small to simulate a small signal response. Imagine, it could be yellow color. Despite of this, it is generating distinct target response in the model to the decay curve.

Aziz

[gwzd]

I might build up a quick test coil & see what happens "in real life".

- Carl

Yeah, that would be wise, "in real life".
Regards,

[Monolith]

Does the Flyback kick the target?

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

[Aziz]

Hi gwzd,

I'm speechless, you really did it! You copyrighted the 3-opamp instrumentation amplifier! I'll have to be careful in the future when using that, one never knows you might come after me ;-)
One word of advice for you genius, use 1N914 or something faster in place of those 1N4148, why? well, try spice!
Regards,

nice try! But the amplifier section is not the invention. It shows only, how you should extract the target signal.

I will try 1N914 next time (isn't 1N4148 a substitude for this?). But I need some low Rdson 800/1000V N-MOSFET's and high current ultra-fast recovery diodes (improvement for BYV28-200). Do you know some good parts?

Aziz

[gwzd]

Hi gwzd,



nice try! But the amplifier section is not the invention. It shows only, how you should extract the target signal.

Well, one can throw a joke, right?!

I will try 1N914 next time (isn't 1N4148 a substitude for this?). But I need some low Rdson 800/1000V N-MOSFET's and high current ultra-fast recovery diodes (improvement for BYV28-200). Do you know some good parts?

Aziz

Yes, it is a substitute in "theory" if you use the exact bias they say. I think some manufacturers actually have the same datasheet for the two. But, for some reasons the 1N914 is better choice for handling transients like the one you are trying to attenuate there. I have tried several of them and the result is always the same, the reverse recovery time of the 1N914 is significantly better than the 1N4148, even though both are specified for a few nanoseconds.
Regards,

[gwzd]

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.
Monolith

Now we are talking! Less blah and more scope shots and real data!!
Regards,