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Angular momentum of sound pulses
1School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand.
Summary
Localized acoustic pulses in fluids carry angular momentum, with a conserved component along the direction of motion. This finding aligns with a multiphonon representation for high-frequency acoustic pulses.
Area of Science:
- Acoustics
- Fluid Dynamics
- Wave Physics
Background:
- Acoustic pulses in fluids possess momentum density.
- The presence of transverse momentum components in localized acoustic pulses is a known phenomenon.
Purpose of the Study:
- To investigate the angular momentum carried by three-dimensionally localized acoustic pulses.
- To analyze the conservation properties of acoustic pulse angular momentum.
- To explore the relationship between acoustic pulse properties and a multiphonon representation.
Main Methods:
- Analytical evaluation of pulse energy, momentum, and angular momentum.
- Utilizing a family of localized solutions to the wave equation.
- Examining the behavior of acoustic pulses in the limit of many oscillations within their spatial extent.
Main Results:
- Localized acoustic pulses in isotropic fluids inherently possess transverse momentum density.
- Acoustic pulses with azimuthal momentum density can carry angular momentum.
- The component of total pulse angular momentum along the direction of total momentum is invariant.
- Analytical results are consistent with a multiphonon representation for high-frequency pulses.
Conclusions:
- Acoustic pulses can serve as carriers of angular momentum.
- The multiphonon representation provides a valid framework for understanding high-frequency acoustic pulses.
- The study offers insights into the fundamental properties of acoustic wave propagation.
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