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I know that polarization only occurs in transverse waves and polarization of light occurs as EM wave is a transverse wave. But sound waves are both transverse and longitudinal in solids. So can polarization occur for the transverse part? But we cannot stop the sound wave from propagating by any medium except vacuum. Because it will propagate through the stopping medium(like an analyzer but for sound).

Even if it gets polarized somehow(I don't think it can get polarized) then how can we observe it, since any sound reaching our eardrums will be longitudinal as the medium in front of our eardrums will be air, and so no polarization will occur in longitudinal waves.

See the 7th and 8th line in this image(source:- https://en.wikipedia.org/wiki/Polarization_(waves)). enter image description here

I am a little confused now.

P.S. This may seem as a possible duplicate but all other answers didn't clarify my doubt.

EDIT:- Based on the answers, it seems that shear waves can be polarized. So my question is how to polarize these shear waves?

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  • $\begingroup$ The concept of polarization doesn't really make sense when applied to sound waves. Sound waves are a change in pressure through the medium, whereas any wave that can be polarized is more like a change in position through a medium. One can cause the other, but they're not quite the same thing. Imagine a bomb going off next to a dangling chain; the pressure from the bomb will cause a transverse wave through the chain, which will be polarized "away" from the blast, but the blast isn't polarized. $\endgroup$ – bendl Aug 14 '17 at 19:53
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"Sound" is a pressure phenomenon, and has no polarization.

It is possible to send acoustic shear waves through an elastic solid (and that transverse component can have a direction) - but not through a gas.

Just to confuse you more - in an anisotropic medium, different directions of shear may propagate at different velocities, resulting in an apparent rotation of the direction over time (and in fact it can go from linear to circular polarization, etc).

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  • $\begingroup$ If it possible to send shear waves through an elastic solid, and if polarization is a property of transverse waves, then theoretically, it should be possible for that transverse sound waves to get polarized, right? $\endgroup$ – Dark Vader Aug 14 '17 at 16:33
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    $\begingroup$ @QuamosM87 Shear waves can get polarized. I think what Floris is saying is that these shear waves aren't 'sound' waves as such, and so 'sound' can't be polarized. $\endgroup$ – CooperCape Aug 14 '17 at 16:36
  • $\begingroup$ @CooperCape thanks for translating what I intended. You are exactly right. $\endgroup$ – Floris Aug 14 '17 at 16:47
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    $\begingroup$ Hmmmm .... shear waves can couple (both ways) to compression waves in surrounding media so I'm not entirely comfortable with simply defining them out of category "sound": it just doesn't seem to be a useful distinction. And I'm pretty sure that when I use a screwdriver to listen to an engine by bone conduction (as my mechanic grandfather taught me) that sheer waves are part of what I "hear". $\endgroup$ – dmckee Aug 14 '17 at 16:54
  • $\begingroup$ If shear waves are part of the sound wave in the solid medium, can it be concluded that sound waves can get polarized? I am asking whether these polarized shear waves can be converted to 'sound' waves as such. $\endgroup$ – Dark Vader Aug 14 '17 at 18:08
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These transverse waves are known as S-waves or shear waves and yes they can be polarized. Waves that are polarized in the horizontal direction are known as SH-waves and those in the vertical direction are known as SV-waves. These waves exhibit the property that when they meet a boundary between two mediums (say solid -> air) they can turn into P-waves, which are the more well know compression waves.

When they are polarized as SH-waves it means that the particle motion in the solid is contained in the horizontal plane, and the same goes for SV-waves except in the vertical plane.

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  • $\begingroup$ Yes I agree with you that theoretically it seems transverse sound waves can be polarized but in an analyzer the vibrations which are not in the direction of the transmission axis gets blocked. But how can you block a sound wave with anything other than vacuum? $\endgroup$ – Dark Vader Aug 14 '17 at 16:39
  • $\begingroup$ "But how can you block a sound wave with anything other than vacuum" I think with this you're still assuming that these waves are longitudinal... $\endgroup$ – CooperCape Aug 14 '17 at 16:42
  • $\begingroup$ umm.. okay. so suppose a shear wave is travelling in medium 1. then it comes in contact with medium 2. what will happen then? can it be possible to make an analyzer for this shear wave with medium 2 $\endgroup$ – Dark Vader Aug 14 '17 at 16:50
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    $\begingroup$ If medium 2 is air or liquid then it will turn into a P-wave, which can be detected. Otherwise you get mode conversion $\endgroup$ – CooperCape Aug 14 '17 at 16:52
  • $\begingroup$ We know that the Earth has a liquid core, because we see some seismic transmission paths that do not have any S-wave polarization. They lost that when the wave propogated through liquid. Seismometers DO exist which can sense P waves, S waves, and polarization. $\endgroup$ – Whit3rd Aug 15 '17 at 0:06

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