多层柱状波导中后退波的传播特性及其应用

Backward wave is broadly defined as the wave that the energy flux direction that is given by the Poynting vector is opposite to the phase velocity direction. Waveguides and materials exhibit backward wave propagation that is also referred to as negative refraction have been paid considerable attention. They may be applied to control and manipulate acoustic waves for the development of Lamb wave lens, similar to superlenses. In addition, interference effects between backward and forward waves generate plate resonances in which the group velocities of Lamb waves vanish while the phase velocities have finite values. These zero-group-velocity (ZGV) resonances have been used for accurate determination of dimensional variations and material properties of plates. Numerous research works have reported properties of backward waves and ZGV points both numerically and experimentally. Most described Lamb waves in plates, multilayered thin films and coatings. Guided elastic waves in cylindrical structures, which are also commonly encountered as waveguides, also exhibit backward-propagation motions. However, little attention has been paid to the propagation properties of backward waves in multilayered cylindrical structures. This proposal has two main work packages. Firstly, the existence condition and propagation characteristics of backward waves in cylindrical waveguides with multilayered geometric structures and anisotropic materials are theoretically analyzed and numerically simulated. The aim is to thoroughly understand the influences of isotropic and anisotropic elastic constants and dimensional changes of waveguides on the behaviour of backward waves, respectively. Secondly, lab experiments will be carried out to explore both the evidence of negative refraction and possible applications. The two interested applications are the design of an acoustic isolator of the Logging-While-Drilling (LWD) acoustic tool utilizing the backward-propagation effect; and the development of a non-destructive evaluation technique to detect the bonding quality of the cased-holes using the zero-group-velocity resonance. The benefits of this research will be firstly an improved understanding of the unique propagation behaviour of backward waves in waveguides with anisotropic materials or multilayered structures; secondly an exploration of using backward waves and mode conversion in plates to control the flow of acoustic energy; and thirdly investigations of applying the zero-group-velocity resonance technique to realize non-destructive evaluations of practical multilayered cylindrical structures.

后退波是声波导中相速度与能流方向相反的模式波；在其低截止频率处，具有零群速度和有限大相速度，称为零群速度共振。利用后退波可控制声波的传播方式；用零群速度共振可提高无损检测灵敏度。近十年来对后退波的研究集中在板状波导中，但对于另一类重要的柱状波导，因其结构复杂，后退波在柱状波导中的传播特性尚不明确，急需开展多层柱状波导中后退波传播特性的理论分析、数值模拟和实验研究，探索其应用前景。本项目将通过理论和数值模拟分析多层柱状介质中声源、材料性质、几何结构和边界条件对后退波的影响，探索其存在条件和形成原因，明晰后退波的传播机理。实验上，利用激光超声技术观测和验证后退波在柱状波导上形成驻波、零群速度共振和负折射的现象。应用上，探索利用后退波改变声波传播方式，以设计随钻测井仪器的新型隔声体的可行性；探索用零群速度共振技术检测套管井界面胶结质量的原理和方法。

后退波是波导中能流方向与相速度方向相反的模式波。在后退波的低截止频率处，具有零群速度和有限大相速度，称为零群速度共振。利用后退波可控制声波的传播方式；用零群速度共振可提高无损检测灵敏度。理论方面，国内外的科学家们证实了在薄板、自由杆和薄壁空心管道中存在后退波，研究了在薄板和多层板中后退波的频散特性与材料性质和边界条件的相互关系，并初步探讨了正交各向异性板中零群速度后退波的数量。应用方面，利用后退波改变声能传播方式的应用研究仍处于初级探索阶段；零群速度共振检测技术已用于厚石灰板、薄金属板、多层粘接板和薄壁空心管的实验室测量。本项目通过理论和数值模拟分析了多层柱状介质中声源、材料性质、几何结构和边界条件对后退波的影响，重点探索了空心圆管和充液圆管中后退波的存在条件和形成原因、明晰其传播机理。实验上，利用激光超声技术观测和验证了后退波在柱状波导上形成驻波、零群速度共振和负折射的现象，完成了后退波的可视化以及负群速度的精确实验测量。应用上，探索了利用后退波改变声波传播方式，以设计随钻测井仪器的新型隔声体的可行性；初步探索了用零群速度共振技术检测充液管道的原理和方法。项目组发表了SCI收录论文5篇、EI收录论文1篇；在国内学术会议做了4次特邀报告、参加国际学术会议并发表论文12篇，与国内外后退波研究学者建立了良好的合作关系。