Sound/Signal Propagation through glass?

[Kurama35]

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?

 

[davenn]

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

 

[Kurama35]

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

 

[davenn]

well that was a little more info 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

 

[Kurama35]

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.

 

[davenn]

OK

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

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

 

[Kurama35]

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.

 

[davenn]

I cannot help any further on this, maybe some one else will read and offer a suggestion

Dave

 

[olivermsun]

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

 

[davenn]

he's expecting to see them vibrate

 

[Kurama35]

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

Yes. Or visibly move in some way.

 

[sophiecentaur]

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.

 

[voko]

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.

 

[olivermsun]

It might be an effective way to "explore and learn" though.

 

[CWatters]

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..

 

[sophiecentaur]

It might be an effective way to "explore and learn" though.

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?

 

[olivermsun]

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 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.

 

[olivermsun]

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.

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?

 

[Drakkith]

Whether the OP is using his time efficiently is not the topic here. Please stay on topic.

 

[Kurama35]

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?

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.

 

[sophiecentaur]

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.

I was referring to random progress in a wanted direction of learning - very time consuming. I have doubts about your model of learning that way across the gamut of Science. It can work at times but there is such a vast amount of plain knowledge needed to expect to get it all via your own pathway that I can't see it providing a complete Science Education. But, there again, I have always been grateful for having being taught the value of getting down and learning stuff off by heart - on the way to actually using what I learned.

To my mind, it's an 'unexpected result' to see a piece of glass moving (i.e. vibrating) at ultrasonic frequencies at all, particularly with very moderate power levels. If there is a non linearity, then a displacement (DC) would be possible, I suppose, so the glass might be pushed away from the transducer. We'd need to have a fuller description of the movement.

 

[olivermsun]

I was referring to random progress in a wanted direction of learning - very time consuming.

I see. I thought you were talking about the OP's experiment with bread crumbs on the glass plate. It's clearer now what you meant.

I have doubts about your model of learning that way across the gamut of Science. It can work at times but there is such a vast amount of plain knowledge needed to expect to get it all via your own pathway that I can't see it providing a complete Science Education.

I don't expect people to figure it out "all on their own." But I do think some room needs to be left for exploration, or you get to the end of the Science Education and don't know the first thing about investigating something that wasn't in the textbooks.

However, since none of this is really topical to the thread, may I suggest that we continue this discussion either in a new thread, in the appropriate forum, or else in private?

 

[.Scott]

As others have said, if the glass is moving, then the water is moving.
You're real question is how can you readily detect that motion.

I would suggest putting the experiment across from a window (or other light source) in an otherwise darkened room. Then, with the water vibrating, attempt to see the reflection of the window on the surface of the water droplets.

At 40KHz, the surface waves on the water droplets should be small enough to prevent a clear reflection. What you should get is a somewhat translucent effect.

The water droplets will not hop around like bread crumbs because the glass "wets" and attracts the water, holding it down. With enough power, you could shake it loose, but you're probably a couple of orders low on amplitude.

 

[olivermsun]

One favorite way (depends if you have big enough droplets) is to shine a bright and well-directed light through a droplet and see if you can see fringing/shadowing due to the droplet. See if the shadow moves when you turn on the 'music.'

I'm really surprised that you don't notice any movement AT ALL in the droplet if the entire glass plate is visibly moving. Isn't it at least moving WITH the plate?

 

[Kurama35]

As others have said, if the glass is moving, then the water is moving.
You're real question is how can you readily detect that motion.

I would suggest putting the experiment across from a window (or other light source) in an otherwise darkened room. Then, with the water vibrating, attempt to see the reflection of the window on the surface of the water droplets.

At 40KHz, the surface waves on the water droplets should be small enough to prevent a clear reflection. What you should get is a somewhat translucent effect.

The water droplets will not hop around like bread crumbs because the glass "wets" and attracts the water, holding it down. With enough power, you could shake it loose, but you're probably a couple of orders low on amplitude.

That actually helps quite a bit. Thanks!

I believe this is off topic, but I'm not just doing this to learn. It's not just a random thing I decided to do. I have an end goal in mind with what I'm doing with this. The science behind the signal propagating through water just isn't quite what I expected. I also couldn't find much through google to explain how this should work.

 

[olivermsun]

So would you mind explaining what the end goal is?

 

[Kurama35]

One favorite way (depends if you have big enough droplets) is to shine a bright and well-directed light through a droplet and see if you can see fringing/shadowing due to the droplet. See if the shadow moves when you turn on the 'music.'

I'm really surprised that you don't notice any movement AT ALL in the droplet if the entire glass plate is visibly moving. Isn't it at least moving WITH the plate?

I think that's hard to explain. It's probably moving with the plate, but if you look at the water compared to the glass, its location doesn't seem to be changing.

 

[Kurama35]

So would you mind explaining what the end goal is?

Basically, I want to move water on the other side of the glass using sound. I'd rather not give out any more details about the why.

 

[sophiecentaur]

Basically, I want to move water on the other side of the glass using sound. I'd rather not give out any more details about the why.

In that case, you need to consider matching your power into the glass for a start - or you will not get the power transfer that you need. Also, does it have to be ultrasound and not audible sound?

 

[Kurama35]

In that case, you need to consider matching your power into the glass for a start - or you will not get the power transfer that you need. Also, does it have to be ultrasound and not audible sound?

It does not necessarily need to be ultrasound but I was under the impression that it would work better.

What do you mean by matching my power into the glass?