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Related Concept Videos

Sound Waves: Interference00:53

Sound Waves: Interference

Sound waves can be modeled either as longitudinal waves, wherein the molecules of the medium oscillate around an equilibrium position, or as pressure waves. When two identical waves from the same source superimpose on each other, the combination of two crests or two troughs results in amplitude reinforcement known as constructive interference. If two identical waves, that are initially in phase, become out of phase because of different path lengths, the combination of crests with troughs...
Deriving the Speed of Sound in a Liquid01:09

Deriving the Speed of Sound in a Liquid

As with waves on a string, the speed of sound or a mechanical wave in a fluid depends on the fluid's elastic modulus and inertia. The two relevant physical quantities are the bulk modulus and the density of the material. Indeed, it turns out that the relationship between speed and the bulk modulus and density in fluids is the same as that between the speed and the Young's modulus and density in solids.
The speed of sound in fluids can be derived by considering a mechanical wave propagating...
Echo01:06

Echo

The human ear cannot distinguish between two sources of sound if they happen to reach within a specific time interval, typically 0.1 seconds apart. More than this, and they are perceived as separate sources.
Imagine the sound is reflected back to the ears. Assuming that the source is very close to the human, the difference between hearing the two sounds—the emitted sound and the reflected sound—may be more than the minimum time for perceiving distinct sounds. If this is the case, then the...
Perception of Sound Waves01:01

Perception of Sound Waves

The human ear is not equally sensitive to all frequencies in the audible range. It may perceive sound waves with the same pressure but different frequencies as having different loudness. Moreover, the perception of sound waves depends on the health of an individual's ears, which decays with age. The health of one's ears may also be affected by regular exposure to loud noises.
The pitch of a sound depends on the frequency and the pressure amplitude of the source. Two sounds of the same frequency...
Interference and Superposition of Waves01:07

Interference and Superposition of Waves

When two waves of the same nature occur in the same region simultaneously, they result in interference. Interference of waves implies that the net effect of the waves is the sum of the individual waves' effects. However, it does not imply that the individual waves affect the propagation of other waves.
Interference occurs in mechanical waves, such as sound waves, waves on a string, and surface water waves. Mechanical waves correspond to the physical displacement of particles. Hence,...
Intensity and Pressure of Sound Waves01:05

Intensity and Pressure of Sound Waves

The intensity of sound waves can be related to displacement and pressure amplitudes by using their wave expressions and the definition of intensity. The critical step to achieve this is to write the power delivered by the particles on the wave as the product of force and velocity and simplify the force per unit area as the pressure. The velocity of the medium's particles can be derived from the displacement.
Unlike the time average of a sinusoidal term, which is zero since it is positive and...

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Related Experiment Video

Updated: Jun 20, 2026

A Stable Phantom Material for Optical and Acoustic Imaging
04:54

A Stable Phantom Material for Optical and Acoustic Imaging

Published on: June 16, 2023

Sagnac interferometer for underwater sound detection: noise properties.

K Kråkenes, K Bløtekjaer

    Optics Letters
    |September 16, 2009
    PubMed
    Summary

    This study explores the Sagnac interferometer as an acoustic sensor, noting its zero path-length difference advantage. Researchers achieved a low noise-equivalent phase shift, demonstrating its potential for sensitive acoustic detection.

    Area of Science:

    • Optical physics
    • Acoustic sensing technologies

    Background:

    • Interferometers are crucial for precise measurements.
    • Traditional Mach-Zehnder interferometers have path-length differences.
    • Sagnac interferometers offer unique advantages for specific applications.

    Purpose of the Study:

    • To investigate the Sagnac interferometer's efficacy as an acoustic sensor.
    • To compare its performance against the Mach-Zehnder interferometer.
    • To quantify its sensitivity and noise performance at low frequencies.

    Main Methods:

    • Utilized a Sagnac interferometer setup.
    • Employed a passive homodyne-detection scheme.
    • Incorporated a 3 x 3 directional coupler for signal processing.

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    Main Results:

    • Demonstrated zero path-length difference, a key advantage.
    • Observed sensitivity directly proportional to frequency for low frequencies.
    • Achieved a noise-equivalent phase shift of 2.5 x 10(-7) rad/radicalHz at 10 kHz.

    Conclusions:

    • The Sagnac interferometer is a viable and advantageous acoustic sensor.
    • Its sensitivity is frequency-dependent at low frequencies.
    • Backscattered light is identified as a potential limitation to detectivity.