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Total internal reflection with Sound?

  1. Aug 25, 2008 #1
    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.
  2. jcsd
  3. Aug 25, 2008 #2
    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 travelling from air (340m/s) to water (1500m/s)

    I'm not sure there are any practical applications for this effect.
  4. Aug 25, 2008 #3


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    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
  5. Aug 29, 2008 #4
    Very interesting comments. mgb points out an example with submarines, this sounds quite fascinating, I shall look it up. Thanks.
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