Total internal reflection with Sound?

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Discussion Overview

The discussion explores the concept of total internal reflection (TIR) as it applies to sound waves, drawing a parallel to the optical phenomenon observed in materials like diamonds. Participants consider whether similar effects can be achieved with sound and discuss potential applications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes total internal reflection in light, particularly in diamonds, and questions if a similar effect can be achieved for sound waves.
  • Another participant suggests that sound waves can experience total internal reflection when transitioning from a slower to a faster medium, provided the angle of incidence exceeds the critical angle.
  • Examples are provided, such as sound traveling from cold air to hot air or from air to water, as potential scenarios for TIR of sound.
  • One participant expresses uncertainty about the practical applications of sound TIR, while another proposes that it could be useful for submarines utilizing layers of different salinity and temperature in water.
  • There is a discussion about whether the submarine example truly represents TIR or if it is merely reflection due to impedance mismatch.

Areas of Agreement / Disagreement

Participants express varying degrees of certainty regarding the existence and implications of total internal reflection for sound. While some agree on the theoretical possibility, there is no consensus on practical applications or the nature of the submarine example.

Contextual Notes

Participants mention specific conditions such as temperature and salinity that affect sound speed, but the discussion does not resolve the definitions or implications of TIR versus impedance mismatch.

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In Diamonds, light that enters gets trapped within due to total internal reflection, defined as:

Total internal reflection is an optical phenomenon that occurs when a ray of light strikes a medium boundary at an angle larger than the critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary no light can pass through, so effectively all of the light is reflected. The critical angle is the angle of incidence above which the total internal reflection occurs.

Diamonds have one of the highest index of refractions there is at a whopping n = 2.41.

I'm curious to know if there is a material or apparatus that can achieve the same effect as a diamond, but for sound waves instead of light.
 
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Good question. Since sound waves are waves, they obey the laws of refraction (Snell's Law) just like light. You can basically achieve total internal reflection of sound in any medium as long as it is transmitting into a faster medium above the critical angle for that boundary. For example sound travels faster in hotter air. This means if sound was moving from cold air to hot air at a shallow angle to the boundary, you would have the total internal reflection of sound.

You could even have it traveling from air (340m/s) to water (1500m/s)

I'm not sure there are any practical applications for this effect.
 
jaseh86 said:
I'm not sure there are any practical applications for this effect.
Hiding submarines?
Layers of different salinity and temperature (haloclines and thermoclines) have different densities anddifferent speeds of sound. Sonar pulses bounce off the interface between the layers allowing submarines tohide beneath/above them.
Not sure if this is really TIR or just reflection from an impedence mismatch - but it is usefull
 
mgb_phys said:
Hiding submarines?
Layers of different salinity and temperature (haloclines and thermoclines) have different densities anddifferent speeds of sound. Sonar pulses bounce off the interface between the layers allowing submarines tohide beneath/above them.
Not sure if this is really TIR or just reflection from an impedence mismatch - but it is usefull

Very interesting comments. mgb points out an example with submarines, this sounds quite fascinating, I shall look it up. Thanks.
 

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