charge-based piezo drive

On a sunny day (Mon, 15 Jul 2019 10:09:11 -0500) it happened amdx wrote in :

I dunno what he means by that either. I have played quite a bit with ceramic transducers, remember in the old days TV remotes used ultrasonics, so I had a few from my repair days, and you can do a lot of fun things with those, connect to a tuned circuit etc.. measure wind speed:

Here test with 2 small 44 kHz transducers in a 'wind tunnel', see the phase shift between transmitter and receiver (a few cm away) change as I increase the airflow (PC fan not in picture blowing through the 'tunnel' (cardboard tube) ), you can see the vane moving indication wind speed. 44kHz_Doppler_phase_change_in_wind_tunnel_with_vane_MVI_4113.AVI

Very kind of you, no I am in Europe, Netherlands. But really that high a frequency is beyond my current interest, also I am flooded with experiments that I somehow have to get going if ever,,, But I really appreciate the offer, if I ever think of some application I will email you for sure. The sonoluninescence can also be done with the transducers I have, there is even a youtube video from somebody who did just that:

Interesting.

Hi,

Another way to view it is that capacitance is more closely coupled to the piezo crystal length than the drive voltage is coupled to the piezo crystal length, ie fewer external factors change the capacitance than the voltage. It would be interesting to see all the various external factors (temperature etc) related to feedback signals to get more accurate positioning.

cheers, Jamie

Not clear about the question, you don't know anti-resonance or you don't know why run the transducer at anti-resonance? Maybe as simple as easier to drive 20 ohms, maybe beam shape, maybe less susceptibility to reflections causing impedance variations. That last one seems very likely, I remember measuring impedance and watching it swing up and down as you got closer to a reflector. If my math is correct, the impedance would go from high to low just by moving the reflector 1mm.

I don't see where he has sonoluminesence. Generally you must dark accustom your eyes because it is a weak light. and it is light blue in color maybe moving towards green, but mostly blue as I recall, it's been

Jan, one hint about sonoluminescence. The water has to have to air taken out of it. We did this by boiling the water, then cooling it (with cap on) And then you've got an hour or so till the air diffuses back in. PITA of an experiment, and not really worth much over the 'Gee- Whiz' factor.

George H.

Hi George, I will have to disagree with you about degassing the water. We didn't degassed our water and didn't have any problem getting sonoluminescence. Only differing factor is, we used high frequency, but I don't think that matters. In some experiments we added air, (sparge gas) to enhance reactions. In the link below is a writeup about sparge gases by my boss, Henry. In it he starts with Ultrasound removal of Carbon Dioxide from water, but the interesting part is at about 1/3 of they way down where it says, FEATURED ARTICLE. It talks about using Noble gases as the sparge gas having increased enhancement of reactions over air.

I have more, but I get tired, maybe tomorrow.

Mikek

On a sunny day (Mon, 15 Jul 2019 12:49:20 -0700 (PDT)) it happened George Herold wrote in :

OK, got it, thank you.

On a sunny day (Mon, 15 Jul 2019 14:27:32 -0500) it happened amdx wrote in :

'anti resonance' could mean? [1] Using it out of resonance (that is easy). [2] Or some magical thing? Then it is bull. It is either in resonance or it is not, as simple as that.

I agree, maybe he just sees the bubbles forming by shining a light through the vessel. In sonoluminescence AFAIK the bubbles implode and cause a flash of light.

Not sure his bubbles really implode, but at least he has bubbles. There was a whole lot to do about those collapsing bubbles causing some radiation. I have plenty of measurement stuff around for that. But I think that experiment was refuted as radiation came from some other source in their lab.

I stopped following the endless postings about that (in sci.physics ?) long ago.

When I saw it it was from our 2" transducer, and a 2" beam of

OK.

Main reason I am not trying is I need my ears, and I could imagine standing waves forming in the fluid in my ears,,, destroying nerve cells.

And if it ain't 'nuculear' it is not so interesting anyways. Where does the light (EM radiation) come from? Non-linear medium frequency conversion? No too much frequency difference I'd think. The physics is in a way interesting.

OK thanks Mike. Perhaps the unit we had was under-powered and didn't have enough to make flashes w/o removing the air.

George H.

Ya, you have me wondering if I used the wrong term, but it is the low impedance point on a an impedance curve. When I characterized piezos I only looked at the lowest points, but this curve continues up in frequency, but it shows my point. We used them at the low impedance point rather that the high impedance point.

Obviously the collapsing bubble radiates light, so you must be bringing up some radiation I'm unaware of. I read the wiki, they get into it, but, didn't understand it.

OK, that is an advantage of using high frequency 660kHz. The 660kHz is attenuated 71.5 db per meter of air vs 40kkHz is attenuated 1.38 db per meter of air. These numbers are a bit low because, as quoted from the webpage, "this value must be added to the usual distance damping of audible sound after the 1/r law." I would assume even though 660kHz is not audible it still follows the

Yep wish would have figured that out in H.S. Mikek

Right, that's the mechanical resonance (series resonance in a quartz crystal). Antiresonance is another word for parallel-resonance.

In my ring-down calibrator thread, the toy oscillator has to resonate away the parallel capacitance to get the oscillator to run very nearly at the mechanical (series) resonance.

Cheers

Phil Hobbs

OK here's what I was working on when I quit last night. This is a graph from, Sonochemistry: Theory, Applications and Uses of Ultrasound in Chemistry.

The chart is labeled, "Bubble Formation and the Factors affecting cavitation Threshold" It plots intensity over frequency for aerated and degassed water, and shows the cavitation threshold. I added the lines for 40kHz and 660kHz and the power levels where they cross, I also added the power values. Please feel free to check my lines and values. I had to extrapolate in my own way.

Now, as to what it means. Don't know if these are positives or negatives, probably depends on what you are doing. You get much higher sonic power into solution before cavitation. You can get much higher sonic power into solution before cavitation on your faceplate causes it's problems. (faceplate erosion, cavitation in front of faceplate blocks sound transmission and alters transducer impedance) So, without further ado,

Mikek

On a sunny day (Tue, 16 Jul 2019 13:26:49 -0500) it happened amdx wrote in :

So to make the bubbles requires much less power at 40 kHz, that is why the youtube guy has all the bubbles with a simple signal source I think. I should not have any problems with my transducers and even less if I use a 75 W RMS audio amp and series resonance ?? Thanks for the chart.

Slide rules @ noon @ the Piezo Corral!

John ;-#)#

Yes, :-) But for chemistry you want higher frequency, many more bubbles, more cavitation points, much more surface area. Can anyone tell me about about Dispersion angle? Is the angle different for a 40kHz transducer vs a 660kHz transducer? I wonder, we pointed our 2" transducer at a convexed 4" air backed reflector, it caused a focus of energy about 2" in front of the reflector. At that point you had a approx 3/4" cottony froth and a hissing from the intense cavitation at the focus. I wonder if 40kHz would disperse, or would all the energy reflect from the convexed reflector. About 8" away, although in some experiments we where up to 15" away.

Here's a good video showing single bubble sonoluminesense.

Here's a video, but I am skeptical, things just don't seem right. See my comment below the video.

Mikek

On a sunny day (Tue, 16 Jul 2019 14:48:54 -0500) it happened amdx wrote in :

I have not tried it, I did some experiments with beaming at very low power (44 kHz).

There is a video somewhere where they use ultrasound and a parabolic reflector to light a match a few meters away. It was a demo outside of some exibition.

As to parabolic reflectors, it is all about wavelength, finding the wavelength is also fun, here I reflect the 44 kHz of a piece of paper, you find the zeros (combining relfected with direct):

So speed of sound in air / frequency,

Any parabolic shape that is bigger than several times the wavelength should work. Maybe an old space heater, we used that very long time ago for microwaves in the lab to make a TV link over some distance.

Mayeb even a car headlight reflector come to think of it?

Use what you have :-)

Here I do some 44 kHz doppler, frequency difference depends on the speed the reflector moves:

Just needed to add everything I did was in a water bath.

Mikek

On a sunny day (Wed, 17 Jul 2019 09:50:58 -0500) it happened amdx wrote in :

Yes swimming is cool.

OK, not everything, our 660kHz experiments were in a water solution. :-)

Mikek

No, you're talking about beepers, not about thick transducers. No bull, the thick ones have a peak *AND* a notch in their impedance graph vs freq., the resonance and the anti-resonance. As if they can act as either a parallel RLC or a series RLC depending on drive freq. IIRC, the thin PZT beepers don't do this.

Yep, a resonant notch, rather than the usual resonant peak that we all expect.

Search: transducer antiresonance

For sonoluminescence, I think they tracked that glow to the natural atmospheric Argon contamination. Then enhanced the effect by bubbling some argon through their water. Heh, modify the color of the glow by using Neon? Or Strontium salts, etc.?