A high transmission broadband gradient index lens using elastic shell acoustic metamaterial elements

Abstract

The use of cylindrical elastic shells as elements in acoustic metamaterial devices is demonstrated through simulations and underwater measurements of a cylindrical-to-plane wave lens. Transformation acoustics (TA) of a circular region to a square dictates that the effective density in the lens remain constant and equal to that of water. Piecewise approximation to the desired effective compressibility is achieved using a square array with elements based on the elastic shell metamaterial concept developed in [30]. The size of the elements are chosen based on availability of shells, minimizing fabrication difficulties. The tested device is neutrally buoyant comprising 48 elements of nine different types of commercial shells made from aluminum, brass, copper, and polymers. Simulations indicate a broadband range in which the device acts as a cylindrical to plane wave lens. The experimental findings confirm the broadband quadropolar response from approximately 20 to 40 kHz, with positive gain of the radiation pattern in the four plane wave directions.

11 pages, 10 figures

References in corpus (7)

• Acoustic cloaking theory
• Acoustic metafluids
• Sonic Gradient Index Lens for Aqueous Applications
• Focusing and directional beaming effects of airborne sound through a planar lens with zigzag slits
• Transparent gradient index lens for underwater sound based on phase advance
• Acoustic scattering from an infinitely long cylindrical shell with an internal mass attached by multiple axisymmetrically distributed stiffeners
• Tunable cylindrical shell as an element in acoustic metamaterial

Cited by in corpus (2)

• Gradient index phononic crystals and metamaterials
• Acoustic Cloak Design via Machine Learning