Sound refraction is a key concept in acoustics, describing how sound waves change direction when passing between different media. This phenomenon occurs due to variations in sound speed, influenced by factors like density, elasticity, and temperature gradients in different materials.

Understanding sound refraction is crucial for various applications. From underwater acoustics and atmospheric propagation to medical ultrasound and seismic exploration, this principle plays a vital role in how we use and interpret sound in different environments.

Fundamentals of Sound Refraction

Refraction of sound waves

• Refraction changes wave direction passing between media due to wave speed differences
• Sound waves bend at interfaces between different media caused by varying sound speeds
• Density, elasticity, and temperature gradients affect sound refraction
• Refraction angle depends on incident angle and sound speed ratio in the two media

Sound behavior across media

• Air propagates sound slowest, highly compressible, affected by temperature and humidity
• Water conducts sound faster than air, less compressible, influenced by temperature, pressure, salinity
• Solids transmit sound fastest, least compressible, support longitudinal and transverse waves
• Interfaces between media cause reflection, transmitted energy depends on acoustic impedance mismatch
• Air attenuates sound highly, water allows long-distance propagation, solids vary widely

Calculations with Snell's law

• Snell's law for sound: $\frac{\sin\theta_1}{c_1} = \frac{\sin\theta_2}{c_2}$ ($\theta$: angles, $c$: speeds)
• Critical angle $\theta_c = \arcsin(\frac{c_1}{c_2})$ when $c_2 > c_1$ results in 90° refraction
• Total internal reflection occurs beyond critical angle, all sound reflects back
• Faster medium entry yields smaller refraction angle, slower medium larger angle

Applications of sound refraction

• Underwater acoustics: SONAR systems detect objects, sound channels enable long-distance communication, marine life navigate
• Atmospheric propagation: Temperature inversions increase audible distance, wind gradients affect direction and speed
• Seismic exploration maps subsurface geology
• Medical ultrasound considers refraction in imaging
• Acoustic lenses focus or redirect sound
• Non-destructive testing detects material flaws