Underwater metamaterial absorber with impedance-matched composite

Area of Science:

• Acoustics
• Materials Science
• Metamaterials

Background:

• Underwater acoustic absorption is crucial for various applications, including sonar and noise reduction.
• Existing acoustic absorbers often face limitations in bandwidth, thickness, or efficiency.

Purpose of the Study:

• To design and experimentally validate a novel underwater acoustic absorber.
• To achieve broadband high absorption in the 4-20 kHz range using a subwavelength structure.

Main Methods:

• Theoretical design of a structured tungsten-polyurethane composite.
• Experimental realization and measurement of acoustic absorption in a water pool using a time-domain approach.
• Engineering Fabry-Perot resonances for broad impedance matching.

Main Results:

• Achieved high acoustic absorption from 4 to 20 kHz.
• The absorber has an average thickness of 8.9 mm, significantly subwavelength (~λ/42 at 4 kHz).
• The experimental results closely match the theoretically predicted causal minimum thickness.

Conclusions:

• The structured tungsten-polyurethane composite represents a new class of acoustic metamaterials.
• The developed absorber offers high absorption, broadband functionality, and a thin profile.
• This technology holds significant promise for diverse underwater acoustic applications.