DEEPER PI DETECTION DEPTH

[Davor]

Hi Davor:

The LTspice file did not get attached; can you try again?

Regards,

-SB

obviously I didn't check for file types. Here it goes:

[simonbaker]

Phase rotation will not occur because stimulation source energy is locked.
Moodz

Yes, if both signals same frequency and phase, which they should here, thanks. Just have to deal with interesting pattern of two coils...

Is there some way we can make a single coil "oscillate" at multiple frequencies....????

-SB

[simonbaker]

obviously I didn't check for file types. Here it goes:

Would you explain again how this is different from the normal PI circuit?

Regards,

-SB

[Aziz]

obviously I didn't check for file types. Here it goes:

Hi Davor,

thanks for sharing your TX circuit. It has minor flaws however:
Tank capacitor Cap voltage reversal (voltage at Cstore +100V -> almost -100V)!!!

You need a bipolar voltage drive (+/- 100V) and have to select the appropriate recycling path to avoid the voltage reversal. So you need two tank capacitors (+100V, -100V).

Ok, if you solve this issue, your TX circuit is a good one. It is in principle feasible.

Aziz

[Aziz]

Would you explain again how this is different from the normal PI circuit?

Regards,

-SB

The TX circuits impedance is very low (reduced to coils resistance and switch-on resistance). The reactance is zero due to LC resonant tank. Well, it's only resonating for a half period cycle.

To maintain a high current pulse, the source voltage is high (100V):
I = U/Z Z=almost coil's R
I = U/(R + switch-on R)
I -> high

Aziz

[Aziz]

Yes, if both signals same frequency and phase, which they should here, thanks. Just have to deal with interesting pattern of two coils...

Is there some way we can make a single coil "oscillate" at multiple frequencies....????

-SB

Yes. Very trivial.

Impedance matching circuit, which has two resonant frequencies.
Look at the induction heater principles.

Aziz

[Davor]

@simonbaker, I'm so glad you should ask this.
First off, pulse duration is determined solely by L and C time constant. Second, there is no stress on any active components - all switching happens at 0A, and third, over 80% of energy is conserved, just like with VLF tanks.
Pulse shape is near perfect cosine, not some square abomination.
Impedance at coil terminal is constantly low.

A way to improve this even further would be an H-bridge connection for the capacitor, so that the conserved energy could be recycled.

The circuit I'm so cryptic about uses a BJT equivalent of unijunction transistor, but when I squeeze it for efficiency I get narrow tolerances and instability problems - a no free lunch problem.

Rewiring it as I did here just gave me an insight that switching can be made incredibly simple and non-critical, and I can even get a H bridge polarity reversal for the capacitor to make it even better.

To see this rig pulsate replace Vctrl pulse statement with: PULSE(-1 1 8u 0 0 70u 10m), replace .tran command with .tran 0 50m 0 1u , and change R8 value to 10k - it will not benefit from energy conservation in this configuration, but just shows that it can be done.
Also if you wish to play with inductances up to 10mH change Vctrl pulse statement with: PULSE(-1 1 8u 0 0 200u 10m), otherwise it switches off to early.


So you think it is a PI exciter

[Davor]

Hi Davor,

thanks for sharing your TX circuit. It has minor flaws however:
Tank capacitor Cap voltage reversal (voltage at Cstore +100V -> almost -100V)!!!

You need a bipolar voltage drive (+/- 100V) and have to select the appropriate recycling path to avoid the voltage reversal. So you need two tank capacitors (+100V, -100V).

Ok, if you solve this issue, your TX circuit is a good one. It is in principle feasible.

Aziz

I'd say challenges, not flaws.
A voltage multiplier can take care of the capacitor charging, and the charging current will be very small.
A not-too-complicated H-bridge with break-before-make arrangement switches would add only twice the Ron resistance to the current path, but no switching occurs during current flow so I'm cool.
What I'm proud of is a self-maintained pulse duration that is constant even with wild variation of Vcc. Switching off just happens, and you don't have to push it. This can have some impact on PI Rx timing. As a byproduct of low impedance all the way the off transition is immaculate - try playing with the dumping resistor.

What I am looking forward is a way to interpretation of PI signal reception in VLF style. I think I'm onto it. A single coil VLF with PI excitation - how crazy is that

[moodz]

I'd say challenges, not flaws.
A voltage multiplier can take care of the capacitor charging, and the charging current will be very small.
A not-too-complicated H-bridge with break-before-make arrangement switches would add only twice the Ron resistance to the current path, but no switching occurs during current flow so I'm cool.
What I'm proud of is a self-maintained pulse duration that is constant even with wild variation of Vcc. Switching off just happens, and you don't have to push it. This can have some impact on PI Rx timing. As a byproduct of low impedance all the way the off transition is immaculate - try playing with the dumping resistor.

What I am looking forward is a way to interpretation of PI signal reception in VLF style. I think I'm onto it. A single coil VLF with PI excitation - how crazy is that

Davor .... been there and done that .... the half cosine or sine pulse you describe has already been patented by Whites ( ask Carl ) .... you cant use it ... however you can use the sinc pulse ( my proposal ) .... the spectrum of a sinc pulse is mathematically complete and balanced whereas the half cosine has discontinuities both in amplitude and phase.

read this thread.

http://www.geotech1.com/forums/showthread.php?t=15518

note particulary spectral plots in this post ....

http://www.geotech1.com/forums/showp...10&postcount=8

The problem is generating a sinc pulse with sufficient power density .....
The Asinc pulse shows promise in this post .... it is easy to generate with very high power density and spectral power distribution.

http://www.geotech1.com/forums/showp...7&postcount=60

ps the plots shown are coil current not voltage plots.

moodz

[simonbaker]

@simonbaker, I'm so glad you should ask this.
First off, pulse duration is determined solely by L and C time constant. Second, there is no stress on any active components - all switching happens at 0A, and third, over 80% of energy is conserved, just like with VLF tanks.
Pulse shape is near perfect cosine, not some square abomination.
Impedance at coil terminal is constantly low.

A way to improve this even further would be an H-bridge connection for the capacitor, so that the conserved energy could be recycled.

The circuit I'm so cryptic about uses a BJT equivalent of unijunction transistor, but when I squeeze it for efficiency I get narrow tolerances and instability problems - a no free lunch problem.

Rewiring it as I did here just gave me an insight that switching can be made incredibly simple and non-critical, and I can even get a H bridge polarity reversal for the capacitor to make it even better.

To see this rig pulsate replace Vctrl pulse statement with: PULSE(-1 1 8u 0 0 70u 10m), replace .tran command with .tran 0 50m 0 1u , and change R8 value to 10k - it will not benefit from energy conservation in this configuration, but just shows that it can be done.
Also if you wish to play with inductances up to 10mH change Vctrl pulse statement with: PULSE(-1 1 8u 0 0 200u 10m), otherwise it switches off to early.


So you think it is a PI exciter

Ok, thanks. Yes, sounds a lot like some energy recovery designs from other threads I've seen. It does seem like the right direction to go, assuming you get as good a target stimulus as conventional circuits.

-SB

[Davor]

@moodz, thank you for mentioning it. Time and again I wonder what else will get patented, and in case I ever wish to patent this exciter of mine I'll be sure to include this patent as a prior art.

Actually, the patent you mention is for a method of obtaining any kind of pulses via switched L and C arrangement, and it insists on "half-sine" - not cosine - and switches on two sides.

In any case, my exciter has one key component which makes it incredibly better than the patented solution, and it is a diode. It is an infallible solution for switch off at zero current.

Furthermore my exciter provides low-Z from beginning to the zero current, while with the patented solution it is a special case when a switch opens at the exact zero crossing, hence mine is far more reliable.

Sinc function may seem kind of sexy, but it just complicates things, and I don't need it. Perfect spectrum happens with loooong sampling times, and its spectrum goes by a popular name "brick wall" - it is exactly what I don't need, I'll be happy with periodicity in spectrum. What I do need is a perfect switch off to enable single coil operation, and diode provides. This solution is not a subset of a patented one because a diode is not some kind of a special case of a switch, but a component per se. I wanted positive pulses - I got positive pulses, a diode takes care of it. They insist on exact timings, durations etc. and I don't care about exact timings - in fact I intend to make this exciter happy as a little pig with any coil in wild range of inductances from at least 100uH to 10mH, and any kind of repetition just because I can. My solution is different from theirs, and so far I see that even as a concept mine is much better.

Lets make it official, here is a schematic of this concept where a simple diode does a timing trick. Now it is published, and for copyright information I can be contacted via e-mail or a private message on this forum. As far as I am concerned you are free to use it as ever you want for non-commercial purposes.

I'll fix the H-bridge capacitor reversal solution soon enough. It will reverse polarity to conserve the capacitor charge for subsequent pulses and reduce power consumption.

As Aziz says - patent trolls - keep off!

[simonbaker]

target models

How confident are we in our target models? It would seem that the target dynamics have some say in what is the ideal waveform to send at it.

-SB

[simonbaker]

@moodz, thank you for mentioning it. Time and again I wonder what else will get patented, and in case I ever wish to patent this exciter of mine I'll be sure to include this patent as a prior art.

Actually, the patent you mention is for a method of obtaining any kind of pulses via switched L and C arrangement, and it insists on "half-sine" - not cosine - and switches on two sides.

In any case, my exciter has one key component which makes it incredibly better than the patented solution, and it is a diode. It is an infallible solution for switch off at zero current.

Furthermore my exciter provides low-Z from beginning to the zero current, while with the patented solution it is a special case when a switch opens at the exact zero crossing, hence mine is far more reliable.

Sinc function may seem kind of sexy, but it just complicates things, and I don't need it. Perfect spectrum happens with loooong sampling times, and its spectrum goes by a popular name "brick wall" - it is exactly what I don't need, I'll be happy with periodicity in spectrum. What I do need is a perfect switch off to enable single coil operation, and diode provides. This solution is not a subset of a patented one because a diode is not some kind of a special case of a switch, but a component per se. I wanted positive pulses - I got positive pulses, a diode takes care of it. They insist on exact timings, durations etc. and I don't care about exact timings - in fact I intend to make this exciter happy as a little pig with any coil in wild range of inductances from at least 100uH to 10mH, and any kind of repetition just because I can. My solution is different from theirs, and so far I see that even as a concept mine is much better.

Lets make it official, here is a schematic of this concept where a simple diode does a timing trick. Now it is published, and for copyright information I can be contacted via e-mail or a private message on this forum. As far as I am concerned you are free to use it as ever you want for non-commercial purposes.

I'll fix the H-bridge capacitor reversal solution soon enough. It will reverse polarity to conserve the capacitor charge for subsequent pulses and reduce power consumption.

As Aziz says - patent trolls - keep off!

It will be interesting to see how fancy the circuit has to get to achieve continuous operation - and how easy to retain the diode in such a circuit. Good design challenge...

-SB

[Aziz]

Hi all,

Davor's TX circuit principle does not differ too much from the discussed TEM transmitter. But the TEM transmitter has more benefits for its simplicity as it is definitely prior art.

It's just splitting the resonant mode into different phase sections. Davor's TX just resonates for a half cycle (cap -> coil -> back to cap with voltage reversal).
The zero reactance mode (resonant mode) has the benefit of being able to push incredible more power to the coil but it's time constant is defined by pi*sqrt(LC) (half cycle period of resonance frequency).

Split the full resonant mode into two half cycle sections and then you have it.

Aziz

[simonbaker]

Hi all,

Davor's TX circuit principle does not differ too much from the discussed TEM transmitter. But the TEM transmitter has more benefits for its simplicity as it is definitely prior art.

It's just splitting the resonant mode into different phase sections. Davor's TX just resonates for a half cycle (cap -> coil -> back to cap with voltage reversal).
The zero reactance mode (resonant mode) has the benefit of being able to push incredible more power to the coil but it's time constant is defined by pi*sqrt(LC) (half cycle period of resonance frequency).

Split the full resonant mode into two half cycle sections and then you have it.

Aziz

I haven't thought this through, but there seems to be a fundamental difference between this "half-cycle" current pulse, and a traditional PI pulse which starts with a steady-state current and then suddenly switches off.

If you look at the di/dt of these two pulses, they are very different, are they not? I am wondering if the "half-cycle" works against itself by "unringing the bell" right after it strikes it. In other words, the di/dt has a quick "counter-pulse" -- could this partially cancel its effect on slower targets?

Just wondering... I guess we need to put it through the simulator.

-SB