Centre for Nondestructive Evaluation, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, 600036, Tamil Nadu, India.
Sci Rep. 2022 Oct 29;12(1):18222. doi: 10.1038/s41598-022-23046-7.
Hyperlenses for ultrasonic imaging in nondestructive evaluation and non-invasive diagnostics have not been widely discussed, likely due to the lack of understanding on their performance, as well as challenges with reception of the elastic wavefield past fine features. This paper discusses the development and application of a cylindrical hyperlens that can magnify subwavelength features and achieve super-resolution in the far-field. A radially symmetric structure composed of alternating metal and water layers is used to demonstrate the hyperlens. Numerical simulations are used to study the performance of cylindrical hyperlenses with regard to their geometrical parameters in imaging defects separated by a subwavelength distance, gaining insight into their construction for the ultrasonic domain. An elegant extension of the concept of cylindrical hyperlens to flat face hyperlens is also discussed, paving the way for a wider practical implementation of the technique. The paper also presents a novel waveguide-based reception technique that uses a conventional ultrasonic transducer as receiver to capture waves exiting from each fin of the hyperlens discretely. A metallic hyperlens is then custom-fabricated, and used to demonstrate for the first time, a super-resolved image with 5X magnification in the ultrasonic domain. The proposed hyperlens and the reception technique are among the first demonstrations in the ultrasonic domain, and well-suited for practical inspections. The results have important implications for higher resolution ultrasonic imaging in industrial and biomedical applications.
超透镜在无损评估和非侵入性诊断中的超声成像是一个尚未被广泛讨论的领域，这可能是由于人们对其性能缺乏了解，以及在精细结构后面接收弹性波场方面存在挑战。本文讨论了一种圆柱形超透镜的开发和应用，该超透镜可以放大亚波长特征，并在远场实现超分辨率。使用由交替的金属和水层组成的径向对称结构来演示超透镜。数值模拟用于研究圆柱形超透镜在成像亚波长距离分离的缺陷方面的性能，以及它们在超声领域的构造，从而深入了解其构造。还讨论了将圆柱形超透镜的概念优雅地扩展到平面超透镜的方法，为该技术的更广泛实际应用铺平了道路。本文还提出了一种新颖的基于波导的接收技术，该技术使用常规超声换能器作为接收器，可离散地捕获从超透镜每个鳍片传出的波。然后定制制造了一个金属超透镜，并首次在超声域中展示了具有 5 倍放大倍率的超分辨率图像。所提出的超透镜和接收技术是在超声领域中的首次演示之一，非常适合实际检查。这些结果对工业和生物医学应用中的更高分辨率超声成像具有重要意义。
