Auxetic Metamaterial: Re-Entrant Honeycomb

This simulator renders a re-entrant honeycomb lattice — rigid ribs joined at hinges — and lets you set the rib hinge angle θ and the vertical-to-inclined rib length ratio h/l directly. As the inclined ribs rotate, the whole lattice's width and height are measured live from the actual node geometry and used to compute a real, numerically-measured Poisson's ratio, demonstrating exactly how a negative rib angle produces the auxetic (negative Poisson's ratio) behavior found in real re-entrant metamaterials, impact padding, and expandable stents.