Refraction of a sound wave occurs if it travels between tissues with different propagation speeds. As the incident pulse or returning echo strikes an interface of different density or elasticity and therefore a different propagation speed, the direction of the wave changes according to Snell’s law 1 :

  • sin θ1/sinθ2 = c1/c2


  • sin θ1 = incident angle of the sound wave at the interface
  • sinθ2 = refraction angle of the sound wave in the new medium            
  • c1 = propagation speed in the initial medium
  • c2 = propagation speed in the new medium

Ultrasound machines assume all pulsed waves and returning echoes travel along a direct path, therefore refraction can cause refraction artifact 2 .

Ultrasound - general index
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rID: 46913
Section: Physics
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