Thickness-insensitive coding metasurface for broadband underwater acoustic radar cross section reduction

Area of Science:

• Underwater acoustics
• Metamaterials science
• Acoustic engineering

Background:

• Traditional acoustic stealth relies on material thickness tuned to specific frequencies, limiting broadband performance.
• Achieving acoustic scattering suppression requires overcoming the inherent thickness-frequency dependency.

Purpose of the Study:

• To develop a broadband acoustic metasurface that decouples thickness from frequency for enhanced stealth.
• To demonstrate effective acoustic scattering suppression over a wide frequency range (10-35 kHz).

Main Methods:

• Introduction of a 1-bit coding metasurface (CM) with two distinct deep-subwavelength units.
• Design of '0' and '1' units mimicking rigid and pressure-release boundaries, respectively.
• Optimization of spatial coding to redirect incident waves into diffuse scattering patterns.

Main Results:

• Achieved effective acoustic scattering suppression from 10 to 35 kHz with minimal sensitivity to cavity geometry.
• Demonstrated greater than 10 dB radar-cross section reduction over a broad angular span (up to 45°).
• Confirmed stable reflection phase against variations in air-cavity thickness, showcasing a thickness-decoupled design.

Conclusions:

• The developed CM offers a robust, fabrication-friendly strategy for broadband underwater acoustic signature control.
• This thickness-decoupled design paradigm opens new avenues for sonar camouflage and wavefront manipulation.
• The study presents a significant advancement in achieving stealth across diverse acoustic environments.