  Rotationally resonant metamaterials are leveraged to answer a longstanding
question regarding the existence of transformation-invariant elastic materials
and the ad-hoc possibility of transformationbased passive cloaking in full
plane elastodynamics. Combined with tailored lattice geometries, rotational
resonance is found to induce a polar and chiral behavior; that is a behavior
lacking stress and mirror symmetries, respectively. The central, and simple,
idea is that a population of rotating resonators can exert a density of body
torques strong enough to modify the balance of angular momentum on which hang
these symmetries. The obtained polar metamaterials are used as building blocks
of a cloaking device. Numerical tests show satisfactory cloaking performance
under pressure and shear probing waves, further coupled through a free
boundary. The work sheds new light on the phenomenon of resonance in
metamaterials and should help put transformation elastodynamics on equal
footing with transformation acoustics and optics.
