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Natural Science Forum / Physics / Acoustics / June 2005A Diaphragm or A Plate?
I found a patent for a piezo-bimorph that has no center vane and is supposedly capable of producing more acoustic energy than the current design. The new design is tricky, but doable. I was wondering though, for frequencies between 10 -50 kHz would a thin plate make a better transducer than a diaphragm of some sort, sound intensity-wise? Ron -- "You see me now a veteran, of a thousand psychic wars. I've been living on the edge so long where the winds of limbo roar." > I found a patent for a piezo-bimorph that has no center vane and is > supposedly capable of producing more acoustic energy than the current [quoted text clipped - 4 lines] > > Ron What specifically is it that you are trying to do? Are you operating in air or in water? What are your target specificaitons....frequency, SPL, operating distance, directivity and/or focal spot size? Is your excitation transient or sinusoidal steady state? What are your dimensional constraints? What approaches have you tried thus far? What approaches haven't worked out and why? Which approach that you've tried comes closest to meeting your target specifications? What are your electrical drive constraints in voltage, current, power? > > I found a patent for a piezo-bimorph that has no center vane and is > > supposedly capable of producing more acoustic energy than the current [quoted text clipped - 13 lines] > to meeting your target specifications? What are your electrical drive > constraints in voltage, current, power? It's amazing what you can do with sound: focus it and start wallpaper or paint burning, or something even more spectacular like turning certain types of screws and even keys in locks. It produces no true torque, but it works all through resonance effects. Did you ever see the first Mission Impossible movie where some screws were unscrewing themselves from a grating? That's what my project does, although not nearly as quietly. In vibration engineering, it's accepted as fact that resonance effects run from 1 Hz up to 10 kHz. After that, we get into cavitation in liquids and it takes more acoustical power to affect mechanical structures: the higher the frequency the greater amount of acoustic power to do the same thing. My "sonic screwdriver" produced a nominal 143 dB at 6 to 8 inches and could spin dinner plates on it's transducer tube and open locks as well as turn keys in certain types of locks. I impressed my friends and irritated them, too, at the same time since 143 dB of audible sound at the higher frequencies (8 kHz- 10 kHz) set their teeth on edge. Since my original screwdriver either got lost or stolen, I have been trying to re-design it to work better than before and produce that same 143 dB or greater at about 15 kHz which is inaudible to most people. The electronics (an XR2206 signal generator IC, a 4046 phase lock loop IC of which, only the voltage controlled oscillator is used, a couple of power transistors, and a miniature transformer) takes 9 volts and steps it up to produce a square wave output well over a hundred volts peak-to-peak, to drive a piezo unimorph transducer. Or at least, a unimorph was my first choice. Folks say you can't do that with thin piezo-elements but they're wrong: you can and get a lot of sound from them driving them hard that way. And those are off-the-shelf unimorphs, too. One probably could get more power with a higher driving voltage (changing the turns ratio on the transformer from 1:33 to 1:40 or more), and using thin (0.001") ceramic disks of PZT-8 rather than the more sensitive PZT-5. In theory, a bimorph should produce more acoustic energy than a unimorph, but if I remember my past experiments I think the results were pretty much equal. Or rather, a bimorph with a diaphragm put out as much sound as a unimorph, but I don't know if that would be true if the bimorph was connected to a plate instead of a single ceramic disk. Like I posted, there is a patent for a bimorph that doesn't use a brass center vane, but is supposed to produce more acoustic power than traditional designs; the patent shows it used in loud speaker designs, but I'm thinking it might make for a better ultrasonic transducer if bonded to a 0.43 mm thick metal plate, maybe of aluminum. However, I've never seen bimorphs used that way either commercially or going through all the patents that I have gone through and I can't find out why. A bit of a mystery that. Small size and acoustical power are the two things I'm looking for as the screwdriver is basically a pocket-sized device (if you have deep pockets). As I said in an earlier post, I had thought about magnetostrictive rods, but since the smaller the rod, the higher the resonant frequency, I jettisoned that idea as piezo transducers can be tailored for a given frequency response a whole lot easier than a brittle piece of Terfenol-D. Not that making a transducer is a snap using piezo-ceramics. Ron > It's amazing what you can do with sound: focus it and start wallpaper or paint > burning, or something even more spectacular like turning certain types of screws > and even keys in locks. It produces no true torque, but it works all through > resonance effects. Did you ever see the first Mission Impossible movie where some > screws were unscrewing themselves from a grating? That's what my project does, > although not nearly as quietly. FWIW: I suspect that one can loosen screws this way, but not tighten them! Most 'screws loose" phenomena (in countless machines and possessions) result from jostling of an object with two or more members fastened by screws, nuts or bolts that were originally rotated in place, but the fastening force or pressure is not sufficient to prevent separation via a new superior vibration force. Thus, microscopic separation of the two fastened objects occurs. Within the time interval that separation exists, the screw may (but not always) also be free to rotate. It may also be motivated to rotate by slippage of one member vs the other, as occurs when either screw-passage hole is larger than the diameter of the screw shank. Given a choice of rotating free or tighter, it opts to be free. Sound in structures is vibration. When the vibration force is great enough to force separation, such loosening is feasible. I believe that such perturbing force is more efficiently produced at higher vibration frequencies, ergo the entry of ultrasound. The sonic screwdriver may never be harnessed for tightening screws. But it will serve an NDT function: Were harmonics to arise, separation is occurring, hence the screw must be further tightened by exterior means. The reality is that more problems arise from screws that cannot be loosened on demand such as for repair actions. Hence a sonic device that can loosen severely set screws will be welcome in all industries. The NDT method of identify screws that are not yet tight enough will also be welcome in the industry. Be sure to share with me the patent royalties resulting from such!.... Angelo Campanella I never thought about it as anything but a high-tech (well, medium tech anyway) toy. I always wanted to see it break a wine glass, but I found out a bit too late, that the glasses must have a crystalline structure with a really sharp resonance frequency. Glasses that are expensive and not so easily found. Aside from that, though, I did make screws go in but it's a lot trickier, more hit-and-miss, than making them come out. Ron > > It's amazing what you can do with sound: focus it and start wallpaper or paint > > burning, or something even more spectacular like turning certain types of screws [quoted text clipped - 40 lines] > > Angelo Campanella >I never thought about it as anything but a high-tech (well, medium tech anyway) > toy. I always wanted to see it break a > wine glass, but I found out a bit too late, that the glasses must have a > crystalline structure with a really sharp resonance frequency. Glasses that are > expensive and not so easily found. Stevie Nicks shattered a glass bedside table top in my flat a year or so ago. I was playing something sung by her, semi-loud, but not REALLY loud, on my hi-fi, and behind me, I heard a shattering, crashing noise. Couldn't work out for ages what'd happened. The windows were intact. Later, I saw that the glass top of the bedside table had shattered and the glass was in bits everywhere. There was no other explanation for it suddenly shattering like that. Martin  SignatureM.A.Poyser Tel.: 07967 110890 Manchester, U.K. http://www.livejournal.com/userinfo.bml?user=fleetie >>I never thought about it as anything but a high-tech (well, medium tech anyway) >> toy. I always wanted to see it break a [quoted text clipped - 12 lines] > >Martin Whatever it was, it most certainly wasn't sound. A glass plate lying on a table top is far too well damped. It is far more likely that it was just a very poorly tempered piece of glass that just got fed up with staying in one piece. d Pearce Consulting http://www.pearce.uk.com > Whatever it was, it most certainly wasn't sound. A glass plate lying > on a table top is far too well damped. It wasn't a glass plate lying ON A TABLE TOP. It was the table top. It was only supported at each of its 4 corners. > Whatever it was, it most certainly wasn't sound. A glass plate lying > on a table top is far too well damped. It is far more likely that it > was just a very poorly tempered piece of glass that just got fed up > with staying in one piece. Some years ago, a danish company wanted an add showing a glass braking when exposed to sound. I think it was an add for a casette tape. They had to put a small spoon in the glass to break it. The resonances in the glass made the spoon bang against its sides. Without the spoon, no tone (from a tone generator) played by a loudspeaker could do the trick. best regards Peter > Some years ago, a danish company wanted an add showing a glass braking > when exposed to sound. I think it was an add for a casette tape. > They had to put a small spoon in the glass to break it. The resonances > in the glass made the spoon bang against its sides. Without the spoon, > no tone (from a tone generator) played by a loudspeaker could do the trick. Well I've seen the wineglass trick done on TV. They had a sig gen and an amp and a speaker by the glass, IIRC. It was a while ago when I saw it. > Well I've seen the wineglass trick done on TV. They had a sig gen and > an amp and a speaker by the glass, IIRC. It was a while ago when I saw it. <http://dsc.discovery.com/fansites/mythbusters/episode/episode.html> Episode 31: Breaking Glass SignatureHerb Singleton usenet3@ross-specrtrum.com Sound & Vibration Measurements http://www.cross-spectrum.com > > Whatever it was, it most certainly wasn't sound. A glass plate lying > > on a table top is far too well damped. It is far more likely that it [quoted text clipped - 6 lines] > in the glass made the spoon bang against its sides. Without the spoon, > no tone (from a tone generator) played by a loudspeaker could do the trick. There was a website on this subject a while back and suggested what kind of "glass" to use. I suspect in your example it was a glass with a very broad resonance frequency and probably cheap glass, rather than good crystal. You have to hit the right note to within 1/4 Hz IIRC. Ron > Some years ago, a danish company wanted an add showing a glass braking > when exposed to sound. I think it was an add for a casette tape. > They had to put a small spoon in the glass to break it. The resonances > in the glass made the spoon bang against its sides. Without the spoon, > no tone (from a tone generator) played by a loudspeaker could do the trick. Some years ago, our choir was singing in our church and there was a cut glass tumbler sitting on a small table to the side of the stage. During the very last note of the song the sopranos were banging out some high note that was exactly right to shatter the glass. Quite amusing really to hear the last note of the song stop, and then almost immediately hear the glass shatter. No spoons needed... Chris W SignatureThe voice of ignorance speaks loud and long, But the words of the wise are quiet and few. --- >> > I found a patent for a piezo-bimorph that has no center vane and is >> > supposedly capable of producing more acoustic energy than the [quoted text clipped - 76 lines] > > Ron Based on your previous posts, I am aware of the history. Nonetheless, before I can comment further I need to know: 1) Are you operating in air or in water? 2) What is your SPL & operating distance requirement? 3) What is your desired operating frequency and/or frequency range? 4) What directivity and/or focal spot size do you require? 5) Is your excitation transient or sinusoidal steady state. 6) What are your dimensional constraints? 7) What approaches that you have tried haven't worked and why? 8) Which approach that you have tried had come closest to meeting your target specifications and what improvement do you need? 9) What are your practical electrical drive limitations (voltage, current, power)? Everyone who reads this newgroup is aware of > Based on your previous posts, I am aware of the history. Nonetheless, > before I can comment further I need to know. And I thoughtI was being so clear... > 1) Are you operating in air or in water? Air > 2) What is your SPL & operating distance requirement? 143 dB (or greater) at 6" distance. > 3) What is your desired operating frequency and/or frequency range? 13 -20 kHz; 16.5 kHz preferred resonance freq. > 4) What directivity and/or focal spot size do you require? I suppose a 20- 30 degree radiation pattern would suffice, but a true focal point was only just a thought: in practice, while at high frequencies focused sound could be used for heating-- if the sound intensity was great enough-- but for its principal use of turning screws, a focused source of sound is not desireable > 5) Is your excitation transient or sinusoidal steady state. square wave at 100 volts peek-to-peek > 6) What are your dimensional constraints? The transducer is no larger than 0.750" diameter; no smaller than 0.625." > 7) What approaches that you have tried haven't worked and why? Magnetostrictive rods were rejected because of previous inefficiency and also becauuse the resonant frequency of a Terfenol-D rod is way too high for a 1" rod. > 8) Which approach that you have tried had come closest to > meeting your target specifications and what improvement do you need? Using off-the-shelf Radio Shack piezo "buzzers" with no internal drive circuitry, but driven with square waves at 100 volts (or more) peek-to-peek produced a maximum of 143 dB. An unmounted, unencased bimorph produced considerably less sound output. Best results came from mounting unimorph on a short aluminum tube (1" dia. and 1.5" long) with both ends milled flat and parallel. > 9) What are your practical electrical drive limitations (voltage, current, power)? The drive circuitry requires 9 volts but gets it from 2 C cells connected to a 1.5volt to 9 volt converter. The 9 volts in the circuit is ultimately boosted to provide the transducer with 100 volts or more peek-to-peek. A better transducer would be made out of PZT-8 and handle more voltage/power. .> Everyone who reads this newgroup is aware of ??? Ron > Air > 143 dB (or greater) at 6" distance. [quoted text clipped - 3 lines] > The transducer is no larger than 0.750" diameter; no > smaller than 0.625." > Using off-the-shelf Radio Shack piezo "buzzers" with no internal drive > circuitry, but driven with square waves at 100 volts (or more) > peek-to-peek produced a maximum of > 143 dB. What characteristics (physical, electrical, other) of the Radio Shack piezo buzzer prevent you from using it in your application? Also, what was the model number of the buzzer that you used? > Best results came from mounting unimorph on a short aluminum tube (1" > dia. and 1.5" long) with both ends milled flat and parallel. Do you really mean a tube, or was it a solid rod? Also, what specifically were your "best" results (resonant frequency, distance, SPL and electrical drive)? > > Air > > 143 dB (or greater) at 6" distance. [quoted text clipped - 11 lines] > What characteristics (physical, electrical, other) of the Radio Shack piezo > buzzer prevent you from using it in your application? While the off-the-shelf unit worked okay as a prototype sound source, the size and that irregularly shaped plastic case doen't fit in with my design parameters. The ultimate design has the transducer and sound head bullet shaped and supported by a round collar. Also, what was the > model number of the buzzer that you used? Who knows? Since it was never meant to be an integral part of the design, I just picked a flat piezo-buzzer. > > Best results came from mounting unimorph on a short aluminum tube (1" > > dia. and 1.5" long) with both ends milled flat and parallel. > > Do you really mean a tube, or was it a solid rod? No, a tube. For one thing it was milled flat and parallel on each end an allowed for direct contact when needed and it also added some degree of directivity when solely acoustic, non-physical contact, use is desirable. > Also, what specifically > were your "best" results (resonant frequency, distance, SPL and electrical > drive)? That's hard to say: what I considered the most spectacular experiment used a 1" diameter dynamic speaker mounted in a copper sweat cap. The aluminum tube was epoxied into the sweat cap with J.B. Weld and a dinner plate was sitting on top of it. At the resonant frequency of the dinner plate, it would rotate. However, for turning screws, it takes considerably more acoustic power is needed and that was provided by the piezo-buzzer. Best results were at the 4.7 kHz resonance frequency of the piezo-buzzer. But sound over 120 dB at 4.7 kHz is not desirable since the ear is most sensitive at that frequency and nobody around wanted to hear that sound. Hence the need to design a piezo transducer with a peak resonance frequency of about 16.5 kHz. I ought to be able to get a transducer to be 0.750" and still have a 16.5 kHz resonant frequency by using a lighter material for the vibration plate and adjusting the thickness. I never did get an answer to my original question-- what's better a plate or a diaphragm-- but now it's moot since the plate itself determines the resonant frequency and the size also helps to determine acoustic output. Possibly with the use of either PZT-8 or a bimorph, I might conceivably get 150 dB at 6" or so at the transducer's resonance frequency with a little trial-and-error. Somebody posted a formula here once, but I don't think it's right. Ron >> > Air >> > 143 dB (or greater) at 6" distance. [quoted text clipped - 61 lines] > frequency with a little trial-and-error. Somebody posted a formula > here once, but I don't think it's right. There are only a few companies that make air ultrasonic transducers having near-audible resonant frequencies. Of the physically smaller transducers, the 25KHz transducer made by Nicera (ST/R25-16K) has the highest output which is 118dB SPL at 30cm for a 60Vp-p input (maximum). Assuming a worst- case condition of spherical spreading and assuming that the transducer is capable of handling 100Vp-p (which it is not), the extrapolated output at 6" for 100Vp-p would be 130dB SPL. Of the physically larger transducers, the 30KHz transducer made by Airmar (AR-30) has the highest output which is 119dB SPL at 100cm for 100Vp-p input (maximum input 3200Vp-p for 2% duty cycle tone burst). Because of the large size of the transducer, spherical spreading can not be assumed and the SPL at 6" is not likely to be much more than 125dB SPL. In light of these facts, your claim that you were able to produce 143dB SPL at 6" with an off-the-shelf Radio Shack buzzer is totally devoid of credibility. Your lack of credibility is further established by your flippant "who knows" reply to my request for the model number of the Radio Shack buzzer that you claim to have used. Ditto with regard to your subsequent remark "that's hard to say" in response to my request for specific details (resonant frequency, distance, SPL, electrical drive) about your so-called "best" results. There are two companies which presently have a serious big-time financial interest in generating high-intnsity ultrasound in air. They are Holosonic Research Labs and American Technology Corp. According to information on the internet, American Technology Corporation as spent $44 Million over the past seven years developing their technology. I therefore think that it is both reasonable and safe to assume that their transducer design is the best in terms of efficiency and raw acoustic output that current technology has to offer. However, using that technology, you will not likely be able to get much more than 125dB SPL at 16.5KHz for 100Vp-p input. http://www.atcsd.com/pdf/HSSWHTPAPERRevE.pdf > >> > Air > >> > 143 dB (or greater) at 6" distance. [quoted text clipped - 83 lines] > specific details (resonant frequency, distance, SPL, electrical drive) > about your so-called "best" results. I am really getting f.cking tired of every two-bit Tom, Dick, and Harry questioning my credibility. It was three years ago since I did the original experiments and I didn't-- and don't-- keep track of every part number of everything I buy. I'm not as pathetically anal retentive as you. If you have nothing constructive to say, keep your damn comments to yourself. This is the last time I intend to jump through hoops for you. Invest $2.00 and do your own goddamn research, putz! -rh >> >> > Air >> >> > 143 dB (or greater) at 6" distance. [quoted text clipped - 97 lines] > > -rh You're welcome, and have a nice day. > >> > Air > >> > 143 dB (or greater) at 6" distance. [quoted text clipped - 94 lines] > get much more than 125dB SPL at 16.5KHz for 100Vp-p input. > http://www.atcsd.com/pdf/HSSWHTPAPERRevE.pdf BTW, I can see why so many people you keep you on their killfile; it's something I'm going to do too. |
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