Department of Mechanical Engineering, University of South Carolina, Columbia, SC, 29208, USA.
Sci Rep. 2017 Jan 5;7:40004. doi: 10.1038/srep40004.
The rainbow trapping effect has been demonstrated in electromagnetic and acoustic waves. In this study, rainbow trapping of ultrasonic guided waves is achieved in chirped phononic crystal plates that spatially modulate the dispersion, group velocity, and stopband. The rainbow trapping is related to the progressively slowing group velocity, and the extremely low group velocity near the lower boundary of a stopband that gradually varies in chirped phononic crystal plates. As guided waves propagate along the phononic crystal plate, waves gradually slow down and finally stop forward propagating. The energy of guided waves is concentrated at the low velocity region near the stopband. Moreover, the guided wave energy of different frequencies is concentrated at different locations, which manifests as rainbow guided waves. We believe implementing the rainbow trapping will open new paradigms for guiding and focusing of guided waves. Moreover, the rainbow guided waves with energy concentration and spatial separation of frequencies may have potential applications in nondestructive evaluation, spatial wave filtering, energy harvesting, and acoustofluidics.
彩虹俘获效应已在电磁波和声波中得到证实。在这项研究中，通过空间调制色散、群速度和带阻的啁啾声子晶体板实现了超声波导波的彩虹俘获。彩虹俘获与逐渐减缓的群速度有关，以及在啁啾声子晶体板中逐渐变化的带阻的较低边界处的极低群速度有关。当导波沿着声子晶体板传播时，波逐渐减慢，最终停止向前传播。导波的能量集中在带阻附近的低速区域。此外，不同频率的导波能量集中在不同的位置，表现为彩虹导波。我们相信，彩虹俘获的实现将为导波的引导和聚焦开辟新的范例。此外，具有能量集中和频率空间分离的彩虹导波可能在无损评估、空间波滤波、能量收集和声学流体力学中有潜在的应用。
