Metamaterials are artificial materials engineered to have properties that may not be found in nature (wikipedia), which usually gain their properties from structure rather than composition, using small inhomogeneities to create effective macroscopic behavior. Over the past decade, metamaterials have seen rapid growth, starting from electromagnetic metamaterials to acoustic metamaterials and elastic metamaterials. The unusual properties of a metamaterial greatly enhanced the possibly of wave manipulation and broadened the applications, such as negative refraction, super-resolution, subwavelength imaging, cloaking, etc. 
We are aiming at designing new metamaterials exhibiting intriguing properties that might lead to various applications and have successfully designed the following two types:

  • Exotic Solids:  the ability to withstand shear is a trait that distinguishes a solid from a liquid. In this new design of elastic metamaterial whose components are all solids, we achieved that at certain frequencies only compressional waves are allowed, blurring the distinction between a solid and a liquid, and in another frequency regime the material becomes super anisotropic that compressional and shear waves are propagating along different directions. The secret of the design is the utilizing of the multiple resonances in the building blocks of the metamaterial.
  • Negative shear band: negative shear band requires negative values for shear modulus and mass density simultaneously. It is well-known that negative shear modulus is hardly achievable.  In this research, we devised a structure with solid-coated-liquid cylinder embedded in a foam host that exhibits a negative shear band. It leads to the elastic analogue of the Brewster angle.  


​Prof. Zhaoqing Zhang, Prof. Ping Sheng, Prof. Yun Lai


Ying Wu, Yun Lai, and Zhao-Qing Zhang, “Elastic metamaterials with simultaneously negative effective shearmodulus and mass density” Phys. Rev. Lett., 107, 105506 (2011)
Yun Lai,Wing Wu, Zhao-Qing Zhang, and Ping Sheng “Hybrid Elastic Solids”  Nature Materials, 10, 620 (2011), featured in Nature Materials