Frequency-following RF power supply 1

[dielectric1]

I need to drive about 100 watts of RF power @ 1 MHz into a moderately resonant load (estimate Q ~ 100 - 300) whose center frequency or "desired" resonant frequency drifts. I want to (or have to) let it drift and change my drive frequency to match. Else I won't get power to couple.

I am at prototype stage but looking for a cheap, manufacturable solution ultimately. For now, in the lab, I have a linear RF amplifier and a Class E amplifier with enough "looseness" in its LC tanks that I can drive it over the required frequency range. The question is, how to tell either of these amps what frequency to put out, and automatically follow what the load wants to do? Is there standard circuitry out there for that?

 

[Warpspeed]

I have never heard that one before.
Sales managers also believers in Voodoo and snake oil.
A full moon may also be required to observe this phenomena.

In several decades of tuning radio transmitters, and other types of tuned power amplifiers. Maximum power and efficiency ALWAYS corresponds with conjugate coupling and resonance.

But that is the simple case............

Now two very closely related resonances involved with coupling significant power need the coupling coefficient to be adjustable for maximum power transfer, OR to obtain a required fairly narrow flat bandpass characteristic.

A really good example of this is tuning bass reflex loudspeaker enclosures, where cone resonance, port resonance, and box volume (coupling coefficient) are adjusted to extend acoustic coupling a half octave lower than the loudspeaker cone resonance by itself in free air is capable.

A seminal paper published by Thiel and Small totally revolutionized bass loudspeaker box design, and may not in principle be so very different to what you are trying to achieve at at other extreme end of the acoustic spectrum.

To couple acoustic power efficiently into a medium, where two very closely related resonances are involved. I urge you to seek out the original acoustic research carried out by the Australians Thiel and Small, it may be helpful.

Another application is the Tesla coil. Here there is a primary tuned tank circuit of high Q, and a secondary very high voltage tuned circuit tuned by stray capacitance.

To get maximum power transfer, the primary and secondary need to be neither under coupled or over coupled. There is a sweet spot where both primary and secondary have maximum power transfer with both at resonance.

Increasing the coupling does not increase power transfer. The higher the Q, the looser the critical coupling point is.

There are many other examples of this, but two resonant systems if severely over coupled, just fight each other.

 

[dielectric1]

Yes, we can adjust the Q of the piezo's self-resonance by damping and, maybe have some control over the load's resonances. But to know what we're looking for, you are correct, I should do the the Thiele-Small analysis. I looked at it a bit and do think it is applicable - coupling of two resonances close in freq. What I first found was a retired engineer Art Ludwig's summary of the T-S analysis, and I copied it and uploaded it here. Then I found a place where you can obtain the original papers. Actually several by Small and a couple by Thiele - apparently they never co-authored, even though both were from Australia. Here is that link:

http://jordan-usa.com/technicalpaper.html

 

[Warpspeed]

Both were not only from Australia, but were both at Sydney university together at the same time, doing very similar post graduate work.

I cannot find my copy of the original joint paper, but I know for certain that it exists. That paper is the basis for the "Thiel and Small" characteristics that every bass speaker manufacturer now routinely supply for each of their drivers.

Anyhow, with a bit of lateral thinking, I believe you will be able to effectively couple acoustic power between two closely resonant media, but the coupling coefficient needs to be optimum for highest power transfer.