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Sound/Signal Propagation through glass?

by Kurama35
Tags: glass, propagation, sound or signal
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Drakkith
#19
Aug6-14, 09:13 AM
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Whether the OP is using his time efficiently is not the topic here. Please stay on topic.
Kurama35
#20
Aug6-14, 10:41 AM
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Quote Quote by olivermsun View Post
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
#21
Aug6-14, 10:54 AM
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Quote Quote by olivermsun View Post
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
#22
Aug6-14, 11:15 AM
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Quote Quote by sophiecentaur View Post
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
#23
Aug6-14, 11:25 AM
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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
#24
Aug6-14, 11:29 AM
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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
#25
Aug6-14, 11:29 AM
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Quote Quote by .Scott View Post
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
#26
Aug6-14, 11:30 AM
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So would you mind explaining what the end goal is?
Kurama35
#27
Aug6-14, 11:31 AM
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Quote Quote by olivermsun View Post
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
#28
Aug6-14, 11:31 AM
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Quote Quote by olivermsun View Post
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
#29
Aug6-14, 01:02 PM
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Quote Quote by Kurama35 View Post
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
#30
Aug6-14, 01:43 PM
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Quote Quote by sophiecentaur View Post
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?
sophiecentaur
#31
Aug6-14, 03:45 PM
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Quote Quote by Kurama35 View Post
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?
When a wave passes across a boundary between two media with different wave speeds (acoustic impedance), energy is reflected. The bigger the ratio of the two speeds, the more energy is reflected - hence the jelly that is excludes the air between ultrasound head and tummy - to exclude air. The scan works because of the small amount of power, reflected at the boundary between different tissue densities (speeds).

Any ultrasound transducer will be designed for a particular medium, to avoid the problem of getting power in, in the first place. Water /glass etc have very different speeds from air so reflections are particularly problematic when air is involved. This is why I asked about the original purpose for your transducer. Also, what is the sort of power it produces? A transducer used in an ultrasonic cleaning bath would be matched to the water (natch) but a School Demo ultrasound transducer would be suited to air. Matching the 'wrong one' involves a 1/4 wavelength layer of an intermediate density material not trivial.

If there is a particular job you want this to do then a few more details could be useful.


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