Can clock crystals be used as ultrasonic sensors?
ElectricAye
Posts: 4,561
Sorry if this seems like an idiotic question, but I'm wondering if the kind of crystal used for running clocks might also be hooked up "in reverse" to sense a mechanical vibration at about the same Hz rating as the crystal. I suppose there is the issue of mechanical coupling of vibration to the crystal itself, but what of the general concept?
thanks, oh gurus,
Mark
thanks, oh gurus,
Mark
Comments
1) You don't want external vibrations to throw off the timekeeping function
2) Coupling of the crystal to the case or leads results in the loss of energy and these crystals are intended to work using as little energy as possible.
Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
Yes, I can see your point about the crystal being isolated by design. I suspected that would be the case (no pun intended). However, I wonder what would happen if I could gently remove the casing. I suppose that because these types of crystals are designed to USE very little energy, they would also GENERATE very little energy if operated "in reverse" (trying to sense their piezoelectric effect). I'm pondering the possibility of sensing acoustic emissions in the 1MHz to 5MHz range, and it looks like off-the-shelf sensors of this sort are pretty pricey, so I am looking for a klugey miserly way of approaching the problem, at least for prototype tests. Ultimately, I'd like to use it for sensing such acoustic emissions in a fluid, so the thing would have to be coupled using silicone oil or something, and I'm sure that would REALLY knock the resonance off by a mile, perhaps even dampen it so badly as to render any output totally undetectable.
Now I'm wondering about those piezo films. I wonder if they can pick up signals in the MHz range when sunk in a few inches of water.
Hey, thanks as always for sharing the wisdom!
Mark
Thanks, Leon,
but how cheap do you think can they go? Is there a homebrew technique for working up raw piezo materials? Is that do-able for an amateur? Most of the acoustic emission sensors I've seen on the internet seem to start out at several hundred dollars. My life's dream is to turn a 40 cent clock crystal into an awesome acoustic sensor. Would that be an exercise in futility?
thanks,
Mark
As far as your idea, I think you should try it and determine if the results are suitable for your apps. I've made homebrew chips for some time now and most are successful. I think you may have something new, or at least can spin off some new technology from the extended experimentation. Let us know your results.
humanoido
Post Edited (humanoido) : 5/3/2009 1:49:49 PM GMT
"exercise in futility" are pretty strong words. Timekeeping crystals are delicate and not designed for this use. The question is what are your skills and what is your knowledge base. Handling mechanical forces in the 1MHz to 5MHz range is difficult because of the frequency involved. What do you know about materials normally used for this sort of application? What do you know about the natural movement and resonances of crystals used for timekeeping?
Amateur radio operators used to grind their own crystals back when most transmitters were crystal controlled. See if you can find an old book or old magazine article (like in QST) on the subject. Ask around at any local amateur radio club.
I don't think you're going to find someone to hand this sort of project to you on a platter. You're going to have to do some research and you're going to have to do some experimentation based on what you learn. Do you have a local university? Talk to their engineering department, maybe their physics department. You may find someone with experience working with ultrasonics ... not commercially made equipment.
Post Edited (Mike Green) : 5/3/2009 2:45:05 PM GMT
Thanks, Humanoido and Mike,
The answer to your questions about my skills and knowledge is, as Kurt Vonnegut might've put it: I know doodly squat. Which is why I was laying the question at the feet of the Masters here. The more I think about your answers, the more I suspect hacking a crystal would be a fool's errand. It would probably be better to attempt a homebrew, browse through expired patents, etc. Or to just troll for used sensors.
As for using the Vibra Film Tab, it looks like that, with or without a mass, its resonant frequency is far, far below the MHz range.
thanks again,
Mark
Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
There is one method that I can think of that goes along the lines of an FM room bug. You simply have a Coil/Capacitor "tuned" at the frequency that you want to transmit; only the capacitor doubles and performs as the Microphone. A secondary nearby transmitter (or long distance directional transmitter) at the 3rd overtone provides the energy for the L/C "room bug". This is the only thing I can think of at the frequencies of interest that might do what you are wanting.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
The science doods who asked me about making a detector for this seem to think that it might be possible to use it for acoustic detection of some sort of radiation. According to them, a nuclear particle hits their fancy fluid, the fluid squeals, and a "super-tiny microphone" picks up the squeak. Um, I don't know anything about it beyond that. The problem I see about using off-the-shelf sensors is that they appear to be "big" and I doubt the kind of localized squeak they are talking about would be picked up by something designed for non-destructive testing, etc. So a tiny piezo sensor brought to mind a clock crystal.
To Beau,
hey, that room bug thing sounds like what the Russkies planted in the concrete of the USA embassy in Moscow a couple decades ago. Is that where you heard about it? Um, and would you mind leaning toward the flower pot and speaking a little louder this time when you answer my questions?
You need really good sensors for this kind of subtle stuff, not some kludged "maybe it'll work and maybe it won't". I'm thinking of the sensors used in medical ultrasound. Some of these use the frequency range you're talking about. Do some investigating. Talk to the engineering department of your local hospitals. They may have or may occasionally come across damaged units that they can't use, but might work for your project.
They made it sound like the molecules themselves rattle around and sing when hit. I think it's a suspension of some sort, maybe little crystals in a viscous goo. So I'm not sure about the cavitation/collapse aspect of this. They aren't answering all of my questions. I like your idea of looking for medical sensors, but if the molecular "ping" is quite localized (occurring at nanoscale???) wouldn't a big ole bulbous sensor simply not detect the ping due to its relatively outlandish size? It seems to me that unless the sensor is very small, thermal noise, etc. might just overwhelm what they're looking for. I really don't have a feel for such things. Also what I'm not certain about - maybe detecting a ping doesn't actually need a MHz response. Maybe I just need something that would detect an acoustic energy burst at a tiny level for a short amount of time???
thanks always for your inputs,
Mark
"hey, that room bug thing sounds like what the Russkies planted in the concrete of the USA embassy in Moscow a couple decades ago. Is that where you heard about it? Um, and would you mind leaning toward the flower pot and speaking a little louder this time when you answer my questions?" - LOL!! close... my information is actually from "The Great Seal" listening device ...
http://images.google.com/imgres?imgurl=http://images.absoluteastronomy.com/images/encyclopediaimages/b/bu/bugged-great-seal-open.jpg&imgrefurl=http://www.absoluteastronomy.com/topics/Thing_(listening_device)&usg=__oKFfVAx19anewGPHtsHpydd8luA=&h=210&w=280&sz=16&hl=en&start=2&um=1&tbnid=W4I9lRphZrwbyM:&tbnh=86&tbnw=114&prev=/images%3Fq%3D%2522The%2BGreat%2BSeal%2522%2BBug%26hl%3Den%26um%3D1
BTW) it's interesting to point out, that a Google search for ....· "The Great Seal" Bug· ... turns up several variants of your avatar·
In principle this does work... There are many times that I have had an LC tank setup with a nearby receiver set at the same frequency of the LC, and "thumped" the coil on the LC tank only to hear the mechanical "ring" of the coil in the receiver, so the mechanical·vibration of the coil can be modulated and transmitted·in this way ... altering the capacitor as a microphone would have a similar effect.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 5/4/2009 4:12:44 AM GMT
Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
To Leon,
that's an interesting idea. What would the physical principle upon which this is based be called? Would it be a simple change of index of refraction caused by localized heating? Or is there some kind of vibronic optical phenomenon that one would look for?
And to Beau,
that's hysterical about that Great Seal Bug gizmo. It sounds like something out of a Pink Panther movie.
thanks to all,
Mark
Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
Back to your original question.... yes in theory a crystal would react to focused sound energy. The first trick is measuring the change. A great way to test it would be with an oscilloscope. This would let you hook it up, hit it with sound and see what is happening. If you don't have an oscilloscope, parallax makes one that hooks to your computer (I think it uses a javelin chip) for $99. The second trick is interpreting the results in a meaningful way. I think you would find it easier to use other means
As for doing acoustics in water..... a sealed container (think of maybe a glass jar with a plastic lid. would act as a simple acoustic pickup. Just think to when you've been underwater in a pool and you can still hear. A microphone inside the jar would pickup sounds in the water. You also could use a partially submerged container to accomplish the same thing. If your project is more industrial, you might look into a piece of PVC pipe and simply submerge your microphone.
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Callsign: NQ5I
Interests: Robotics, Embedded Systems, Computers, Machining
thanks for your idea about the modulated laser beam. It's not clear to me how that might work with a vast array of crystals all moving around randomly - seems like a possible signal to noise problem - but I'll pick other brains about your suggestion.
To Hotdog,
thanks for the ideas. Maybe when I get bored I'll Dremel the jacket off a crystal, immerse it in silicone oil and see what happens to its ability to function. Chances are it will totally choke... but only one way to tell, I spoze.
thanks to all,
Piezo film (PVDF, Polyvinylidene floride, Kynar) has modes other than the one that is implemented in the vibra-mass sensor from Parallax. Some of those are suitable in thickness mode for hydrophones up to quite high frequencies. If you want to pursue it, do download the fascinating piezo technical manual. The nice thing about piezo film is that it has a decent impedance match to fluids like water or oil. I have no idea if it would be sensitive enough for your quantum squeak detector.
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Tracy Allen
www.emesystems.com
Hey, this is excellent info! Thanks for the link!
cheers,
Mark
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Watching the world pass me by, one photon at a time.