Imagine cushions that lift up instead of sinking when you sit on them. Impossible? Not according to a blueprint for new materials with "negative compressibility": these materials compress when pulled and expand when pushed. Metamaterials that do this have been built before, but the designs must be vibrated at just the right frequency to see the effect. Zachary Nicolaou and Adilson Motter of Northwestern University in Evanston, Illinois, have now designed a metamaterial that stretches when compressed, and vice versa, under any circumstances.
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