Understanding spurious modes of structures with voids using dynamic stiffness method

In another paper being presented at this symposium [1], the existence of natural frequencies and modes of a solid structure which includes an embedded negative structure is discussed. The same paper also describes the challenges associated with the presence of some spurious modes. In this paper, we explain the presence of actual and spurious modes using the exact dynamic stiffness method. We limit the analysis to structures consisting of an assembly of continuous systems (possessing both positive and negative elastic and inertial properties) which are connected at certain nodal points