Auxetic behavior from rotating squares

A new mechanism to achieve a negative Poisson's ratio is presented. An arrangement is made which involves rigid squares connected together at their vertices by hinges. The off-axis mechanical properties obtained from the standard transformation equations show that the idealized system is isotropic. The Poisson's ratio has a value of -1 irrespective of the direction of loading. The geometry modelled is the projection of a plane in inorganic crystalline materials and involves octahedrally co-ordinated atoms.