Multiplexed parametric vortex beams for underwater communications

Area of Science:

• Underwater acoustics
• Acoustic communication
• Wave physics

Background:

• Underwater acoustic communication faces bandwidth and aperture limitations at low frequencies.
• Parametric acoustic arrays offer directive low-frequency fields from compact sources.
• Acoustic vortex beams encode information in phase structure via topological charge (TC).

Purpose of the Study:

• To model the simultaneous generation and propagation of multiple TCs.
• To encode and recover digital information using TC channels.
• To improve underwater acoustic communication efficiency and data capacity.

Main Methods:

• Developed a 3D mixed-domain split-step solver for the Westervelt equation.
• Modeled self-demodulation of vortex-bearing primary waves for multiple TC generation.
• Encoded 8-bit ASCII characters mapped to TC channels and recovered using two metrics.

Main Results:

• Successfully recovered six representative ASCII characters over meter-scale distances.
• Demonstrated recovery from a ~40 cm circular aperture in water at 4 kHz carrier frequency (40 kHz).
• Introduced a Fourier series-based demultiplexing metric to improve higher-order TC detectability.

Conclusions:

• The developed model enables simultaneous generation and propagation of multiple TCs for enhanced data encoding.
• Simulations confirm the feasibility of acoustic vortex beams for robust underwater data recovery.
• The new demultiplexing metric aids in optimizing amplitude weighting for improved communication performance.