Collaborative Research: Conformal Gradient-Index Lenses for Ultrasonic Wave Amplification and Improved Diagnostics

目前的结构系统是由同质材料制成的，如铸铁、熟铁、裸钢和脆性塑料，这些材料极易失效，因此需要加速检查和修复。超声波是一种基于弹性波在结构中传播的无损评估方法，这种弹性波受结构缺陷的影响，因此可以用于损伤诊断。然而，在传统结构中，弹性波的振幅由于扩散/散射而随距离衰减，这限制了临界缺陷的可探测性。在这项研究中，新的结构系统将设计一个嵌入或外部添加的透镜，以便超声波信号在结构中传播时可以聚焦和放大。通过这种方式，超声波能量可以远距离传输和保存。这项研究将允许在早期阶段检测缺陷并防止意外故障。目标应用将是管道系统，因为它们非常容易发生故障。因此，这项研究的结果将有利于美国的经济和社会。这项多学科研究包括超材料、传感器、增材制造、结构监测和设计。该项目以协同教育为特色，整合了两所院校在招收工程专业学生方面的优势。特别是，两所大学的女本科生和研究生将通过相互研讨会和女工程师协会（SWE）联系起来。本研究将引入共形梯度折射率（GRIN）超材料透镜作为结构系统的一部分，使弹性波在通过非平面结构时被放大。使用GRIN透镜，不同的超声波模式（即纵向、弯曲或扭转）将被聚焦和传输，从而使更高的频率(50？（200khz）将能够随着对结构损伤灵敏度的增加而传播。通过改变单胞的折射率来设计GRIN透镜，并对现有的用于平面的GRIN透镜模型进行改进，使其适用于共形表面。超材料透镜层将通过3D打印创建，这将允许更实用和重量轻的结构轻松集成到主机结构中。此外，采用多材料增材制造技术生产的新型复合管道结构将采用嵌入式超材料透镜进行设计，以解决管道中使用的传统材料造成重大事故的最高风险。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Current structural systems are made of homogenous materials such as cast iron, wrought iron, bare steel, and brittle plastic, which are highly susceptible to failure and therefore require accelerated inspection and repair. Ultrasonics is a nondestructive evaluation method based on propagating elastic waves in structures, which are affected by defects in the structure and can therefore be used for damage diagnostics. However, in conventional structures, the amplitude of elastic waves decays with distance due to spreading/scattering, which limits the detectability of critical defects. In this research, new structural systems will be designed with an embedded or externally added lens so that ultrasonic signals can be focused and amplified as they propagate in the structure. In this way, ultrasonic wave energy can be transmitted and preserved over long distances. The research will allow detecting defects at their earliest stage and preventing unexpected failures. The target application will be pipeline systems due to their high susceptibility to failure. Therefore, results from this research will benefit the U.S. economy and society. This multi-disciplinary research encompasses metamaterials, sensors, additive manufacturing, structural monitoring, and design. The project features a synergistic educational component that integrates the strengths of two institutions in recruiting students who are underrepresented in engineering. In particular, female undergraduate and graduate students at both institutions will be connected via mutual workshops and the Society of Women Engineers (SWE).This research will introduce a conformal gradient-index (GRIN) metamaterial lens as part of a structural system such that elastic waves will be amplified as they propagate through the non-planar structure. With the GRIN lens, different ultrasonic wave modes (i.e., longitudinal, flexural, or torsional) will be focused and transmitted such that higher frequencies (50?200 kHz) will be able to propagate with the increased sensitivity to structural damage. The GRIN lens will be designed by varying the refractive index of unit cells, and the existing model of the GRIN lens for flat surfaces will be modified for conformal surfaces. The metamaterial lens layer will be created with 3D printing, which will allow more practical and light weight structures to be easily integrated into the host structure. Additionally, a novel composite pipe structure, produced with multi-material additive manufacturing technologies, will be designed with the embedded metamaterial lens to address the highest risk of major incidents from the conventional materials used in pipelines.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.