Glossary

4.2 Refraction of sound in different media

2 min read•july 24, 2024

Sound 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 , elasticity, and 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

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  • Refraction changes wave direction passing between media due to 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
  • 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

  • for sound: sin⁡θ1c1=sin⁡θ2c2\frac{\sin\theta_1}{c_1} = \frac{\sin\theta_2}{c_2} (θ\theta: angles, cc: speeds)
  • θc=arcsin⁡(c1c2)\theta_c = \arcsin(\frac{c_1}{c_2}) when c2>c1c_2 > c_1 results in 90° refraction
  • Total internal reflection occurs beyond critical angle, all sound reflects back
  • Faster entry yields smaller refraction angle, slower medium larger angle

Applications of sound refraction

  • Underwater acoustics: 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

Key Terms to Review (17)

Critical angle: The critical angle is the minimum angle of incidence at which a wave, such as sound, is totally internally reflected when passing from a medium with a higher speed of sound to one with a lower speed. This phenomenon is crucial in understanding how sound behaves as it transitions between different materials, influencing both refraction and the behavior of waves at boundaries.
Decibel: A decibel is a logarithmic unit used to measure the intensity of sound, specifically in relation to a reference level. It provides a way to quantify sound levels, making it easier to understand the differences in loudness and intensity. By using this scale, we can compare sounds of different amplitudes, determine sound pressure levels, and understand how sound behaves in various environments.
Density: Density is defined as the mass of a substance per unit volume, often expressed in kilograms per cubic meter (kg/m³). This fundamental property of materials plays a crucial role in understanding how sound travels through different media, influencing factors such as speed, impedance, refraction, attenuation, and applications in imaging and testing technologies.
Diffraction: Diffraction is the bending and spreading of waves when they encounter an obstacle or pass through an opening. This phenomenon is essential for understanding how sound behaves in various environments, influencing aspects such as wavelength, frequency, and wave interactions with boundaries and media.
Hertz: Hertz is the unit of frequency that measures the number of cycles per second of a periodic wave, such as sound. It connects to various aspects of wave behavior, including how changes in frequency affect pitch, the relationship between frequency and wavelength, and how sound behaves in different media. Understanding hertz is crucial for analyzing sound characteristics, including infrasound and ultrasonic waves, which exist outside the range of human hearing but have significant applications in various fields.
Law of Reflection: The law of reflection states that when a sound wave encounters a reflective surface, the angle at which it hits the surface (the angle of incidence) is equal to the angle at which it bounces off (the angle of reflection). This principle is crucial for understanding how sound waves behave in different environments, influencing phenomena like echoes and sound clarity.
Longitudinal Waves: Longitudinal waves are a type of mechanical wave where the particle displacement is parallel to the direction of wave propagation. These waves are characterized by compressions and rarefactions, allowing sound to travel through different media, impacting various phenomena such as refraction, diffraction, and attenuation.
Medium: In the context of acoustics, a medium is a substance through which sound waves travel. This can include gases, liquids, and solids, each affecting how sound is transmitted based on their physical properties. The medium plays a crucial role in determining sound wave characteristics, including speed, wavelength, and how sound interacts with obstacles.
Refraction: Refraction is the bending of sound waves as they pass from one medium to another, caused by a change in their speed. This phenomenon is crucial for understanding how sound behaves in different environments, influencing aspects like wavelength, frequency, and the overall propagation of sound in various applications.
Snell's Law: Snell's Law describes how waves, including sound, change direction when they pass from one medium to another. It relates the angles of incidence and refraction to the velocities of sound in each medium, and it is essential for understanding how sound behaves as it travels through different materials and at boundaries. The law illustrates the concept that sound travels at different speeds in different media, which directly influences how waves are transmitted, reflected, or refracted.
Sonar: Sonar, short for Sound Navigation and Ranging, is a technology that uses sound waves to detect and locate objects underwater. It operates by emitting sound pulses and analyzing the echoes that return after bouncing off objects, which helps in mapping underwater environments, detecting submarines, and guiding navigation. This technology connects to various aspects of acoustics, including applications in marine biology, historical development in naval warfare, the scattering and focusing of sound waves in water, and the refraction of sound as it travels through different media such as seawater.
Sound shadow: A sound shadow is a region in which sound is significantly reduced or absent due to obstacles or variations in the medium through which it travels. This phenomenon occurs because sound waves are affected by factors such as refraction, reflection, and absorption, leading to areas where the intensity of sound is diminished. Understanding sound shadows is crucial for analyzing how sound behaves in different environments and under various conditions.
Temperature: Temperature is a measure of the average kinetic energy of the particles in a substance, directly affecting the speed at which sound travels through different media. As temperature increases, the particles move more vigorously, which allows sound waves to propagate faster. This concept connects to various phenomena in acoustics, including how sound bends when moving through different temperatures and states of matter.
Transmission: Transmission refers to the process by which sound energy travels through a medium from one point to another. It is influenced by various factors, such as the properties of the medium, frequency of the sound, and environmental conditions. Understanding transmission is crucial for analyzing how sound interacts with different materials and how it behaves in various scenarios, such as moving from air to water or encountering obstacles.
Transverse waves: Transverse waves are a type of wave where the oscillation of the medium is perpendicular to the direction of the wave's travel. These waves exhibit unique behaviors such as reflection, refraction, and diffraction when interacting with different materials, and they play a significant role in various physical phenomena.
Ultrasound imaging: Ultrasound imaging is a medical diagnostic technique that uses high-frequency sound waves to create images of organs and structures inside the body. This non-invasive method is widely used for examining various conditions, monitoring pregnancies, and guiding medical procedures, highlighting its significant role in modern healthcare.
Wave speed: Wave speed is the rate at which a wave propagates through a medium, defined mathematically as the distance a wave travels per unit of time. It is a fundamental concept that affects how waves interact with their environment, influencing phenomena such as the formation of standing waves, the refraction of sound in different materials, and resonance in various structures. Understanding wave speed is crucial in determining how sound travels in different contexts and how it can be manipulated.
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