Electrical engineering

Physics

Geology

Impedance matching

Resonator

Acoustic impedance

Composite number

Optics

Absorption (acoustics)

Metamaterial

Oceanography

Engineering

Composite material

Acoustics

Electrical impedance

Metallurgy

Materials science

Tungsten

Optoelectronics

Broadband

Ultrasonic sensor

Underwater

Science Advances

By using a structured tungsten-polyurethane composite that is impedance matched to water while simultaneously having a much slower longitudinal sound speed, we have theoretically designed and experimentally realized an underwater acoustic absorber exhibiting high absorption from 4 to 20 kHz, measured in a 5.6 m by 3.6 m water pool with the time-domain approach. The broadband functionality is achieved by optimally engineering the distribution of the Fabry-Perot resonances, based on an integration scheme, to attain impedance matching over a broad frequency range. The average thickness of the integrated absorber, 8.9 mm, is in the deep subwavelength regime (~λ/42 at 4 kHz) and close to the causal minimum thickness of 8.2 mm that is evaluated from the simulated absorption spectrum. The structured composite represents a new type of acoustic metamaterials that has high acoustic energy density and promises broad underwater applications.

Underwater metamaterial absorber with impedance-matched composite