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Could non-Newtonian fluids be used in the future as a kind of percussive ear protection? (leminal.space)

submitted 5 months ago by [email protected] to c/askscience

11 comments fedilink hide all child comments

I feel like we are ways out from seeing anything like it. From what I've seen non-Newtonian fluids typically take a decent amount of energy to stop something and sound wouldn't have much energy compared to something like a bullet.

On a sidenote does Decibullz own a patent on percussive hearing protection or am I looking up the wrong term? I feel like there must be other hearing protection out there that is effective against sudden loud sounds.

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[–] [email protected] 26 points 5 months ago (2 children)

"Sudden" doesn't matter. "Loud" does.

I don't see how anything non-Newtonian would be better against sudden sounds. In fact it would be worse, as they'd get more solid and thereby transmit MORE of the noise you're trying to block out. Or maybe they only get more rigid but their sound transmission properties don't change at all. Either way, sounds somewhat pointless.

The only way I can think that something like this would work would be to have a molded vacuum chamber as an ear plug, with a specifically engineered sound transmission bridge inside. With too much energy trying to go through, it would break. But I doubt it would be quick enough to be effective, and they'd also be one time use, and extremely fragile.

[–] [email protected] 9 points 5 months ago (1 children)

Thanks I think this was the answer I was looking for.

[–] [email protected] 1 points 5 months ago* (last edited 5 months ago)

It's a bit oversimplified, actually. Sound bounces off of discontinuities in the medium, which is why foam works. You just have to control the scattering somehow.

The big problem with using oobleck or whatever is it responds to shear, and shear can't travel through air. You could use it for earthquake protection, though, or if you could channel compressive waves from the air into shear form using a fancy bridge like in OP.

Also, shear-thinning fluid is a thing too.

[–] [email protected] 2 points 5 months ago* (last edited 5 months ago) (1 children)

There are lots of strange options besides newtonian fluids. Would be interesting to see how dilatant, peusdoplastic, thixotropic etc react to sounds. Perhaps there is a way to make a material that allows quiet sounds to pass through and blocks all the loud ones. My guess is that dilatant liquids should be a good candidate.

[–] [email protected] 2 points 5 months ago (1 children)

A quick search tells me this have to do with shear forces. Sound would be entirely compressive, so those material properties would have no effect, or at least not change due to sound levels.

[–] [email protected] 1 points 5 months ago

That’s unfortunate. Just like OP, I would have really liked the idea of using a non-newtonian fluid to filter out certain types of sounds without using electricity. Well, I guess, we’re back to active noise canceling then.

[–] Brokkr 5 points 5 months ago

From some quick searches (so not a definitive answer, but a place to start), it seems that sound waves are most likely longitudinal which doesn't cause shear. However, shear forces can be created by sound waves when they hit a surface.

From that information, I don't think the shear energy imparted by a sound wave is very large. Since non-newtonian fluids only thicken under shear, they may not actually behave very differently than a regular fluid in these conditions. Preventing sound waves from traveling is usually accomplished by causing lots of scattering (open cell foam) or by absorbing the energy in a viscoelastic material (usually polymers).

[–] [email protected] 5 points 5 months ago

Not that any of that would work, but just as a thought experiment: under sudden sonic pressure the fluid would become more crystaline and would then actually make the sounds travel with less resistance, so maybe that would actually make it worse?

[–] [email protected] 2 points 5 months ago (1 children)

We already have computers that can determine which sounds to cancel out. That's pretty cool.

Sound isn't going to be like a bullet or an electrical storm hitting the grid. I don't think you can just make a material that blocks out sound when it reaches a certain level and allow it below the threshold. Definitely an interesting theory but I am not sure how it would be designed.

[–] [email protected] 1 points 5 months ago* (last edited 5 months ago)

Compression thickening/thinning, which only starts after a certain rate of change. I'm not sure what materials have such a property. Then, you'd incorporate it into a composite which dissipates sound selectively in one state. One idea is a fibers of a material that matches the impedance of the fluid during quiet periods, but scatters it as impedance shifts during high-energy periods.

Maybe you could use standard shear thickening somehow, but it would be a lot harder as sound only travels through air compressively.

[–] [email protected] 1 points 5 months ago

I think a fluid that you put in your ear muffles everything and makes it hard to hear. Being newtonion or non-newtinion. I can't imagine a way for it to be useful as a general solution. You'd need to take it out anyways in order to hear normally. And then I don't know how this would compare to an already existing high quality hearing protection. There are some available that supposedly are somewhat linear in the frequency spectrum.