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I Way of producing 600kHz longitudinal waves - Piezo or siren

  1. Nov 3, 2015 #1
    Hello! My name is Nick and I have an MSc in Computer Science, I'm also Physics enthusiast and amateur/independent researcher. I would like to ask for your help on something. I'm currently trying to find a way to study ultrasonic waves' effects on water and I'd like to find a means of transferring a specific frequency (that would be 600 khz) to water. Unfortunately I was not able to find a cheap ultrasonic transducer working at that high frequency. The ones I found start from many hundreds of $. The wave type I'm trying to transfer is longitudinal waves (like sound waves), not transverse waves. So I was thinking of like a metallic tank, on which I would apply the transducer and that would transfer the waves to the water. Another way I thought of to produce this kind of waves at that high frequency is by making a custom siren type generator. But based on my calculations, this is also difficult because I'd need a siren with around 370 holes on every disc, spinning at 10.000rpm to produce only 60.000 and 600.000Hz would be the 10th harmonic. I was about to completely abandon the idea but I recently was told of a man who has succeeded in using a siren for the same job in the past and he was able to reach that high frequency. Unfortunately I don't have any way to contact him to ask, so I'm instead asking kindly for your help because this seems to be a dead end to me. I don't own or have access to any special kind of tools like laser cutters or anything like that but I would be able to use plexi glass for a custom made siren. Any thoughts please? :-)
     
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  3. Nov 3, 2015 #2

    berkeman

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    Welcome to the PF.

    The issue is not just the generation of the 600kHz longitudinal waves, it is coupling them effectively to the water. If you start with sound waves at that frequency, I doubt that you will be able to couple that energy from the air into the tank of water very effectively. That will waste the majority of the sound energy that you would have created with your mechanical siren setup.

    I think you just need to go ahead and use the least expensive medical ultrasound transducer you can find that works in your 600kHz band. They are specifically designed to couple their transmitted energy well into water (or flesh). Here is a large manufacturer that you may already know about:

    http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=3&cad=rja&uact=8&ved=0CDMQFjACahUKEwjHjPCEtfXIAhVV-GMKHYAzCm0&url=http://www.blatek.com/PDF/Brochures/BLT0706_Medical_091407B.pdf&usg=AFQjCNFzJxDQQ1h-4a2WBwRo09IFb1SNZw

    Please also consider safety issues when working with ultrasound experiments. You should do some reading about safety considerations and ultrasound equipment. :smile:
     
  4. Nov 3, 2015 #3

    sophiecentaur

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    I would imagine that the cost of a suitable siren (design and construction) could be pretty high unless you have access to some pretty good workshop equipment and skills.
    Usually, when you see that people generally choose a particular method for doing a job, it is because it is cheapest or most convenient. Now, whilst that isn't always the case, you need some special circumstances to make it worth while going against the trend. It may be worth looking a bit more into piezo methods. although I see what you mean about the prices suddenly shooting up at the high frequency end of things.
    The actual spec could be relevant here. What power do you want to operate at, for instance?

    I notice that Fishfinder transducers sometimes use 200kHz. They are not ridiculous prices and it may be worth while buying one and seeing if you can get it to operate at third harmonic. You could even consider approaching a manufacturer and asking about that possibility. Once you get chatting to Technical departments, you can often get some really good free advice - as long as you can avoid sounding completely clueless and expect them to do all the thinking for you. You sometimes need to be a bit cheeky.
     
  5. Nov 3, 2015 #4
    Thank you both for your fast replies and before I begin I'd like to say I'm sorry but English is not my first language, so please excuse me if some things of what I write are incomprehensible! Well, first of all Berkeman I'd like to say I totally agree with you as far as energy wasting goes but I'm thinking, if the siren could produce something like 80db, the energy coming from it, even in the 10th harmonic, even through a poor coupling through a plastic or metallic tank would be enough for me to observe the resonance phenomenon I'm looking for. This phenomenon could be observed even from as low as 30 watts. At that frequency the water tends to heat abnormally and this is what I'm trying to observe. Also thanks for the suggestion about safety issues, I really appreciate it.
    I have also looked around for medical grade transducers but the ones commercially available (not custom made ones) usually work up to 200kHz and from 1MHz and above. For some reason I don't know (maybe the demand is low at those frequencies, who knows) they tend to skip almost the whole kHz band and the only transducers I have found to work in those ranges are the ones used for underwater sonars. But those are really expensive (unless I haven't done a proper research yet). Also those used in medical applications tend to be very narrow band. I haven't found anything cheap, even at 1MHz that could work down at 600khz.
    And now comes the answer to a very good question dear sophiecentaur made. The power I need is something around 30-50W. At first I thought I could try and see if those cheap chinese ultrasonic face cleaners from ebay work at 1MHz but then again I though 50W would be wayy too much power for them.
    About coupling with the siren, I thought if the water was held in a plastic pipe and I could attach the siren to a hole before that, the vibrations could easily be transferred to the water...I think... Something like that:

    p l a s t i c w a t e r PVC p i p e
    v
    I-----------------------I----------------
    Iwater tank I HOLE <--------- siren attached here
    I-----------------------I----------------

    Well the hole wall is somewhat righter, I don't know why it keeps showing it like that but anyway, I think you're getting my point...
     
  6. Nov 3, 2015 #5
    Also, what do you think about the Hartman oscillator - whistle that could be used along with an air compressor?
     
  7. Nov 3, 2015 #6

    berkeman

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    So it looks like you are aiming for a wavelength in the water of about 1 inch, correct?

    http://www.ctgclean.com/tech-blog/2011/10/ultrasonics-sound-wave-length-vs-frequency/

    30 Watts is a lot of power to be dealing with. I don't think even the medical grade transducers will go that high, but I could be wrong. It still may be worth calling the Technicalo Support folks at a couple of the bigger transducer suppliers to see if they even have anything available in your target range of frequency and power. And geeze be careful please.
     
  8. Nov 3, 2015 #7
    Yes berkemen, I didn't do the math but judging from the chart in the link, the wavelength in the water would be close to that...And seeing the word "steel" in there, I thought of another idea...What if I attached an electromagnet to a stainless steel tank? Wouldn't that make the job a lot easier? I don't know if the electromagnet would be able to vibrate at such high frequencies though, but still...I could play with the harmonics...
    About big transducer suppliers, unfortunately, because I live in Europe, the few of them that are able to manufacture something like that are very expensive...I already made some calls but the prices start from $400-500 and go up to thousands for lab grade transducers...
     
  9. Nov 3, 2015 #8
    About electromagnets, I think of the same principle of working as in loudspeakers.
     
  10. Nov 4, 2015 #9
    If the signal is dissipated rapidly (in comparison at least) into heat, I can't justify any standard use for it other than a water heater.

    Maybe you could look for a water tank heater based on this effect or something? - you never know.
     
  11. Nov 4, 2015 #10
    Thank you elegysix for your response to my issue. Well, it's not just "a heater"...It's THE heater! We are talking about great efficiency here. For example, supposedly, if water tank with 4lt of water needs 10.000 watts of energy to raise the temperature from 40 to 80C degrees in 3 minutes, this device would need half of that power! The phenomenon belongs to sympathetic vibratory physics sector and a guy called Peter Davey, who used to play sax, has done the same thing using two pieces of metals, cut properly and inserted one inside the other so they resonate and the two of them, when plugged to mains, produce almost infinite harmonics. It boils a glass of water almost instantly! This is what I'm trying to study, with more precision though. So it's not a common phenomenon and not one that is commercially available yet, that's for sure. Thanks for asking though :-)
     
  12. Nov 4, 2015 #11

    sophiecentaur

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    Overall efficiency (Heatout/kWhin) you would need to consider the efficiency of the 600kHz source, the transducer and the matching system. For sheer efficiency, you really have a hard job to beat an electrical element immersed in the water in a lagged tank. Where else can the heat escape to? You couldn't expect to do better than Heat out = Power In
    An absorption phenomenon due to resonance is an interesting thing to study and wouldn't require high powers. If the efficiency of your transducer is not important then you could try a number of electro-acoustic ideas. I wondered about a 600kHz RF tuned circuit with the inductor bolted to a diaphragm. But there again, you have to ask why that's not already been done for cheap commercial devices. A piezoelectric transducer is, effectively, just an equivalent RLC circuit, to which the driver will (presumably) be tuned, if they want efficiency.
    600kHz is either not popular to make because it is a difficult frequency range or because "there's no demand for it Sir". A chat with a technical department could leave you very well informed about these matters and could result in some useful advice. Techies are real suckers when you ask them about what they know. (To wit, PF :wink:)
    PS
    You must mean Joules of energy?
     
  13. Nov 4, 2015 #12

    CWatters

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    Great efficiency? Your figures suggest it would take around 5kW to put 3.7kW into the water. That's about 74% efficient.

    Have you considered a immersed resistive heating element which should be close to 100% efficient?

    Edit: For completeness...

    Power = 4186 * 4 * 40 / 180 = 3.7kW
     
  14. Nov 4, 2015 #13

    Vanadium 50

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    Yes you are. You're claiming almost 200%. This is impossible. If Davey claims this, then Davey is a crackpot.
     
  15. Nov 4, 2015 #14

    Vanadium 50

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    I agree, those numbers don't work out. But he's claiming twice as efficient, and given that electrical heaters are 98-99% efficient, those numbers are even more impossible.
     
  16. Nov 4, 2015 #15

    DrClaude

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    Closed pending moderation.
     
  17. Nov 4, 2015 #16

    berkeman

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    We do not discuss crackpottery at the PF. Your thread will remain closed.
     
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