Gengkai Hu, email@example.com Co-authors: Xiaoning Liu, Yi Chen, Guoliang Huang Elastic metamaterials with chiral microstructure By carefully designing microstructures of composites to promote internal resonances under wave loading, elastic metamaterials with negative material parameters (density, bulk and shear modulus) can be obtained over a certain frequency. This property may have a great potential to control low-frequency elastic waves. In the first part of the talk, we will explain how to realize elastic metamaterials with chiral microstructure to trigger rotational resonance. Chiral lattice with embedded resonators and thin plate with chiral microstructure are designed and the both are demonstrated to have simultaneous negative effective mass density and bulk modulus over certain frequency, negative refraction of the latter is also verified experimentally by a transient elastic wave tests. In the second part of the talk, we will present a homogenization method for planar chiral lattices such as tetrachiral lattices (isotropic chiral lattice as a special case), a bi–dimensional orthotropic chiral micropolar model is developed based on the theory of irreducible orthogonal tensor decomposition. The material constants of the continuum model are analytically derived by a homogenization process. By comparing with discrete lattices, the proposed continuum model is shown to be able to characterize correctly the wave properties of the chiral lattices.