The electromagnetic imaging of multi-layered circular structures can be accomplished by means of different approaches. Among these approaches, the use of synthetic aperture radar (SAR) techniques with the compensation of the Green’s function for multi-layered circular cylinders provides a trade-off between accuracy and computational complexity. Nevertheless, this approach relies on measurement points acquired uniformly. Thus, this prevents the adoption of more flexible sampling schemes, limiting the use of inaccurate positioners or manual scanners. To overcome this limitation, this paper proposes a method to handle non-uniform cylindrically acquired data, enabling multi-layered circular imaging based on non-uniformly acquired measurements. For this purpose, the presented method starts by projecting the non-uniformly measured points onto different circles with equally-spaced points. After that, the Green’s function-based circular-SAR imaging method is applied to each projection circle. Lastly, the final SAR image is obtained by the superposition of the images from the previous step. Numerical simulations and experimental results demonstrated the effectiveness and robustness of the proposed method for practical nondestructive testing (NDT) applications.

中文翻译：

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基于非均匀测量格林函数的多层圆形介电结构合成孔径雷达成像

多层圆形结构的电磁成像可以通过不同的方法来完成。在这些方法中，合成孔径雷达（SAR）技术的使用对多层圆柱体的格林函数进行了补偿，从而在精度和计算复杂性之间进行了权衡。但是，这种方法依赖于统一获取的测量点。因此，这阻止了采用更灵活的采样方案，从而限制了不正确的定位器或手动扫描仪的使用。为了克服这一局限性，本文提出了一种处理非均匀圆柱获取数据的方法，该方法可以基于非均匀获取的测量结果进行多层圆形成像。以此目的，提出的方法开始于将非均匀测量点投影到具有等距点的不同圆上。之后，将基于格林函数的圆SAR成像方法应用于每个投影圆。最后，通过叠加上一步中的图像获得最终的SAR图像。数值模拟和实验结果证明了该方法在实际无损检测（NDT）应用中的有效性和鲁棒性。