Metamaterials for Acoustic Cloaking
Navy SBIR FY2008.2

Sol No.: Navy SBIR FY2008.2
Topic No.: N08-191
Topic Title: Metamaterials for Acoustic Cloaking
Proposal No.: N082-191-0693
Firm: Weidlinger Associates, Inc.
375 Hudson St FL 12
New York, New York 10014-3656
Contact: Jeff Cipolla
Phone: (212) 367-3076
Web Site:
Abstract: New metamaterials promise to improve radically the ability of structures to evade sonar detection. The physics of these "acoustic mapped metamaterials" (AMM) is novel: by careful design of their elastic properties, a coating made of AMM materials guides waves around and away from a "cloaked" internal region, rendering the object inside undetectable by active sonar. Like all technologies, AMM will require considerable effort before it becomes a practical reality. AMM theory has only recently been cast in a usable form, by Norris ("Acoustic Cloaking Theory," Proceedings of the Royal Society A, online May 2008, doi: 10.1098/rspa.2008.0076); previous theories based on extensions of electromagnetics are not physically realizable. Consequently, we propose to conduct extensive numerical experimentation and development to minimize risk. The AMM theory will be deployed to a well-verified finite element code, PZFlex . This development will enable us to test the AMM theory on submarine-like shapes. In addition, we propose to conduct finite element studies of AMM microstructures, in order to ensure that the proposed materials exhibit the desired, complicated and unique elastic properties. These unit-cell analyses will guide the design of manufacturable composites. Finally, our proposed work includes detailed consultation with established manufacturers of naval composite materials, to ensure the AMM microstructures can be manufactured at full scale and low cost.
Benefits: The AMM technology, if successful, will deliver numerous direct and indirect commercial benefits. The immediate commercial application will be to the fabrication of acoustically stealthy naval systems: submarines, torpedoes, UUVs, etc. The advantages of cloaking AMMs in these applications are considerable, and obvious. In addition, the ability to design, verify, and manufacture composite materials with carefully prescribed wave propagation behavior enables a range of previously unrealizable designs in underwater sonar and medical ultrasound to be explored. For example, it is reasonable that acoustic systems, like optical systems, can be focused at sub-wavelength scales if metamaterials with negative index of refraction can be fabricated. Realization of a negative refractive index will require similarly careful design of the elastic tensor as realization of cloaking materials.