Broadband Waterborne Multiphase Pentamode Metastructure with Simultaneous Wavefront Manipulation and Energy...

Area of Science:

• Acoustic Metamaterials
• Underwater Acoustics
• Stealth Technology

Background:

• Acoustic metastructures manipulate sound waves at sub-wavelength scales.
• Previous designs primarily used single materials, limiting performance.
• Underwater acoustic stealth requires both wavefront manipulation and sound absorption.

Purpose of the Study:

• To propose and analyze a composite acoustic metastructure for enhanced underwater acoustic stealth.
• To investigate the combined effects of wavefront manipulation and sound absorption.
• To evaluate the performance compared to single-phase metastructures.

Main Methods:

• Designing a unit cell composed of metallic lattice, polymer materials, and mass balancing columns.
• Gradually modulating equivalent physical properties along the metastructure's horizontal direction.
• Utilizing the inherent damping properties of polymer materials for energy dissipation.

Main Results:

• The composite metastructure achieves simultaneous modulation of reflected wave direction and scattering acoustic amplitude.
• A significant improvement in underwater stealth effect was observed.
• The Far-Field Sound Pressure Level (FFSPL) decreased by 4.82 dB (3 kHz–30 kHz) compared to single-phase designs.
• Linearized mean stress was reduced to 1/3 of single-phase metastructures under hydrostatic pressure.

Conclusions:

• The proposed composite acoustic metastructure offers superior underwater stealth performance.
• The structure exhibits reduced stress and uniform distribution under pressure.
• Its acceptable thickness (80 mm) and low density (1100 kg/m³) indicate practical application potential.