Sound/Signal Propagation through glass?

  1. Not sure if I'm putting this in the right place, but here's my issue:

    I'm putting a ultrasonic transducer against glass to try to vibrate/move water on the other side of the glass. I can get enough power through the transducer to physically move the glass, yet I still can't get water to move.

    I would think that the signal just isn't getting through to the other side.

    Is there a way to fix this?
     
  2. jcsd
  3. davenn

    davenn 3,975
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    hi there

    I am assuming that the water is in contact wit the other side of the glass?

    if so, if the glass is vibrating, then the water will be also
    Depending on the ultrasonic freq you are using, there may be a high attenuation in the water

    for clarity.... tell us lots more about your actual setup
    a pic or diagram showing measurements etc would be great

    Dave
     
  4. I have a thin sheet of glass sitting on top of the ultrasonic transducer. The water is on top of the glass.

    I have a 40kHz signal around 120V peak to peak
     
  5. davenn

    davenn 3,975
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    well that was a little more info :wink: but not a lot

    is the glass an actual container filled with water ? something else ?

    you are still a way too vague in your info

    please answer what I asked in my previous post

    Dave
     
  6. I'm trying. I thought I was pretty clear.

    The water (a few drops) is just directly on top of the glass, which is laying flat, which is directly on top of the transducer. There's nothing else involved other than my circuit to power it.

    Edit: What else do you need to know? The glass is 3.5mm thick. We aren't using an exact amount of water.
     
    Last edited: Aug 5, 2014
  7. davenn

    davenn 3,975
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    OK

    you didn't say a few drops in an earlier post ... hence my asking again :smile:

    in which case, as I said earlier, if the glass is vibrating, so will the water drops

    what makes you think they are not ?
    40kHz is a pretty high freq audio vibration, you are not likely to visually see it
    Tho you may see some of the sub-harmonic vibrations at lower frequencies

    Dave
     
  8. I was expecting some kind of movement in the water. The glass noticeably moves. I tried the same experiment with a piece of paper with crumbs on it and the crumbs moved, as well as the paper when I stepped up the voltage.

    Edit: I'm afraid I don't know much about how the sound/vibrations work. What will the water vibrating (in this case) do for me? My only guess is that it would decrease friction between the glass and water.
     
    Last edited: Aug 5, 2014
  9. davenn

    davenn 3,975
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    I cannot help any further on this, maybe some one else will read and offer a suggestion :smile:

    Dave
     
  10. From my understanding of your setup, the waves are propagating straight up through the glass. Are you expecting the water droplets to move sideways?
     
  11. davenn

    davenn 3,975
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    he's expecting to see them vibrate
     
  12. Yes. Or visibly move in some way.
     
  13. sophiecentaur

    sophiecentaur 14,131
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    Can you see the transducer itself moving? If you can't, then you can't expect to see the water move - unless you happen to set up a standing wave in the water.
    You may also be having a problem in coupling the transducer'e power into the glass. If the transducer is designed for use in air then it will not be matched to dense material like glass or water. There is a similar thing, the other way round, with ante natal ultrasound scanners. They use transducers that are designed (matched) for use in tissue and you need to use a gel between transducer and skin or there is a mis-match (this time) between the transducer / air / skin gap. It may be hard for you to get a match without a fair bit of specialist knowledge. Perhaps you could buy an appropriate transducer - if it's not already the right type.
     
  14. The real question here would be "what are you trying to achieve"? I am sorry if my perception is wrong, but it seems to me that your approach is this: I have this cool thing "transducer", let me try some random things with it; then you guess what the outcome of the random things will be, and when your guess does not match your observations, you ask questions here. This is not a very effective, let alone efficient, way to do science.
     
  15. It might be an effective way to "explore and learn" though.
     
  16. Perhaps look up resonance? I suspect small crumbs resonate at a higher frequency than (more massive?) drops of water that are also subject to surface tension.

    Try lower frequencies..
     
    Last edited by a moderator: Sep 25, 2014
  17. sophiecentaur

    sophiecentaur 14,131
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    Brownian Motion all over again? Random experiments are worse than random questions because the turnaround time is much longer. Hopefully, the feedback the OP is getting will save a great deal of wasted time.

    If you want to see any disturbance, the amplitude must be big enough, and the wavelength must be big enough (if you hope to see a standing wave pattern. Standing waves on the surface of water are very slow ( so that means the wavelength will probably be microscopic).
    @Kurama35 Did you try connecting an audio loudspeaker to the arrangement and feeding it with a high audible tone (say 15kHz from your computer)? That would be another suck it and see idea. Can you even see any movement of the cone at 15kHz????
     
  18. If the OP notices a physical behavior that is unexpected and then goes through the steps to understand what's causing it, then I don't think it's "wasted" time. It's learning how to learn.

    Also, I don't really expect Brownian Motion to be the important phenomenon here, although I could be wrong.
     
  19. You can notice the glass moving. What sort of movement is it? The water is sitting on a moving piece of glass but doesn't move at all?
     
  20. Drakkith

    Staff: Mentor

    Whether the OP is using his time efficiently is not the topic here. Please stay on topic.
     
  21. The sheet of glass rotates, but the water seems to remain stationary on the glass. If the glass is held in place, there's no movement in the water.
     
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