Trainiti Giuseppe, Xia Yiwei, Marconi Jacopo, Cazzulani Gabriele, Erturk Alper, Ruzzene Massimo
Daniel Guggenheim School of Aerospace Engineering Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
Phys Rev Lett. 2019 Mar 29;122(12):124301. doi: 10.1103/PhysRevLett.122.124301.
Elastic waveguides with time-modulated stiffness feature a frequency-periodic dispersion spectrum, where branches merge at multiple integers of half the modulation frequency and over a finite wave number range. In this range, frequency becomes complex, with its real part remaining constant. The vanishing group velocity associated with these flat bands leads to frequency-selective reflection at an interface between a nonmodulated medium and a time-modulated one, which converts a broadband input into a narrow-band output centered at the half modulation frequency. This behavior is illustrated in an elastic waveguide in transverse motion, where modulation is implemented experimentally by an array of piezoelectric patches shunted through a negative electrical capacitance controlled by a switching circuit. The switching schedule defines the modulation frequency and allows the selection of the output frequency. This implementation is suitable for the investigation of numerous properties of time-space modulated elastic metamaterials, such as nonreciprocity and one-way propagation, and can lead to the implementation of novel functionalities for acoustic wave devices operating on piezoelectric substrates.
具有时间调制刚度的弹性波导具有频率周期性色散谱，其中各分支在调制频率一半的多个整数倍处且在有限波数范围内合并。在此范围内，频率变为复数，其实部保持恒定。与这些平带相关的消失群速度导致在非调制介质和时间调制介质之间的界面处产生频率选择性反射，这将宽带输入转换为以半调制频率为中心的窄带输出。这种行为在横向运动的弹性波导中得到了说明，其中调制通过由开关电路控制的负电容分流的压电贴片阵列实验性地实现。开关时间表定义了调制频率并允许选择输出频率。这种实现方式适用于研究时空调制弹性超材料的众多特性，例如非互易性和单向传播，并且可以导致在压电基板上运行的声波器件实现新功能。
