Prada Claire, Clorennec Dominique, Royer Daniel
Laboratoire Ondes et Acoustique, ESPCI-Universite Paris, 7-CNRS UMR 7587, 10 rue Vauquelin, 75231 Paris Cedex 05, France.
J Acoust Soc Am. 2008 Jul;124(1):203-12. doi: 10.1121/1.2918543.
Elastic plates or cylinders can support guided modes with zero group velocity (ZGV) at a nonzero value of the wave number. Using laser-based ultrasonic techniques, we experimentally investigate some fascinating properties of these ZGV modes: resonance and ringing effects, backward wave propagation, interference between backward and forward modes. Then, the conditions required for the existence of ZGV Lamb modes in isotropic plates are discussed. It is shown that these modes appear in a range of Poisson's ratio about the value for which the cutoff frequency curves of modes belonging to the same family intercept, i.e., for a bulk wave velocity ratio equal to a rational number. An interpretation of this phenomenon in terms of a strong repulsion between a pair of modes having a different parity in the vicinity of the cutoff frequencies is given. Experiments performed with materials of various Poisson's ratio demonstrate that the resonance spectrum of an unloaded elastic plate, locally excited by a laser pulse, is dominated by the ZGV Lamb modes.
弹性板或圆柱体能够在波数不为零的情况下支持零群速度（ZGV）的导模。利用基于激光的超声技术，我们通过实验研究了这些ZGV模式的一些迷人特性：共振和振铃效应、反向波传播、反向和正向模式之间的干涉。然后，讨论了各向同性板中ZGV兰姆波模式存在所需的条件。结果表明，这些模式出现在泊松比的一个范围内，该范围围绕着属于同一族的模式的截止频率曲线相交时的泊松比值，即当体波速度比等于一个有理数时。给出了根据截止频率附近具有不同奇偶性的一对模式之间的强排斥对这一现象的解释。用不同泊松比的材料进行的实验表明，由激光脉冲局部激发的无载弹性板的共振谱由ZGV兰姆波模式主导。
