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

目前的结构系统是由铸铁、锻铁、裸钢和脆性塑料等均质材料制成的，这些材料非常容易失效，因此需要加速检查和维修。超声波是一种基于结构中传播的弹性波的无损评估方法，受结构中缺陷的影响，可用于损伤诊断。然而，在常规结构中，由于传播/散射，弹性波的幅度随距离衰减，这限制了对关键缺陷的检测。在这项研究中，新的结构系统将被设计成嵌入或外加透镜，以便超声信号在结构中传播时能够被聚焦和放大。这样，超声波能量就可以远距离传输和保存。这项研究将允许在缺陷的最早阶段发现缺陷，并防止意外故障。目标应用将是管道系统，因为它们对故障的敏感性很高。因此，这项研究的结果将有利于美国的经济和社会。这项多学科的研究涵盖了超材料、传感器、添加剂制造、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学专业人数不足的学生方面的优势。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学会(SWE)联系在一起。这项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，这样弹性波在非平面结构中传播时将被放大。使用GRIN透镜，不同的超声波模式(即纵波、弯曲波或扭转波)将被聚焦和传输，从而使更高的频率(50-200 kHz)能够随着对结构损伤的敏感性而传播。GRIN透镜将通过改变晶胞的折射率来设计，现有的平面GRIN透镜模型将针对共形表面进行修正。超材料透镜层将用3D打印来创建，这将允许更实用和更轻的结构轻松地集成到主体结构中。此外，一种采用多材料添加剂制造技术生产的新型复合管道结构将与嵌入的超材料透镜一起设计，以解决管道中使用的常规材料发生重大事故的最高风险。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.