Frenzel Tobias, Köpfler Julian, Jung Erik, Kadic Muamer, Wegener Martin
Institute of Applied Physics, Karlsruhe Institute of Technology, 76128, Karlsruhe, Germany.
Institute of Nanotechnology, Karlsruhe Institute of Technology, 76021, Karlsruhe, Germany.
Nat Commun. 2019 Jul 29;10(1):3384. doi: 10.1038/s41467-019-11366-8.
Optical activity requires chirality and is a paradigm for chirality. Here, we present experiments on its mechanical counterpart, acoustical activity. The notion "activity" refers the rotation of the linear polarization axis of a transversely polarized (optical or mechanical) wave. The rotation angle is proportional to the propagation distance and does not depend on the orientation of the incident linear polarization. This kind of reciprocal polarization rotation is distinct from nonreciprocal Faraday rotation, which requires broken time-inversion symmetry. In our experiments, we spatiotemporally resolve the motion of three-dimensional chiral microstructured polymer metamaterials, with nanometer precision and under time-harmonic excitation at ultrasound frequencies in the range from 20 to 180 kHz. We demonstrate polarization rotations as large as 22° per unit cell. These experiments pave the road for molding the polarization and direction of elastic waves in three dimensions by micropolar mechanical metamaterials.
旋光性需要手性，并且是手性的一个范例。在此，我们展示了其力学对应物——声活性的实验。“活性”这一概念指的是横偏振（光学或力学）波的线性偏振轴的旋转。旋转角度与传播距离成正比，且不依赖于入射线性偏振的方向。这种互易偏振旋转不同于非互易法拉第旋转，后者需要时间反演对称性破缺。在我们的实验中，我们在20至180kHz的超声频率下，在时间谐波激励下，以纳米精度对三维手性微结构聚合物超材料的运动进行时空分辨。我们展示了每个单元胞高达22°的偏振旋转。这些实验为通过微极性机械超材料在三维空间中塑造弹性波的偏振和方向铺平了道路。
