Advancing electromagnetic inversion for characterization and design

这项研究项目涉及电磁(EM)反转，其定义为根据感兴趣区域的外部EM特征推断其某些属性的过程。这一过程涉及到求解EM逆问题，这通常被视为优化问题。这一研究方案的独特之处在于，它的所有算法和技术都源于电磁反演的一致框架，然后被应用于影响不同应用领域：近场微波成像、微波海冰遥感、天线表征和电磁工程表面设计。在该研究方案中，反演算法使用的外部电磁特征要么是测量的电磁数据(如电磁场、雷达散射截面)，要么是需要实现的电磁特性。另一方面，要推断的特性是(I)散射入射电磁波的物体或区域(例如，生物组织或海冰)的介电特性，或(Ii)产生电磁波的电磁源(例如，天线)的等效电流。EM反演框架通常用于成像、遥感和无损评估应用，我们统称为表征应用。这一研究项目不仅提出了用于表征的电磁反演这一主题，而且还研究了用于设计应用的电磁反演。在用于表征的电磁反演领域，我们的主要重点是(I)开发新的算法和技术，以提高可实现的精度、空间分辨率和探测能力；(Ii)通过利用仅有震级的电磁数据来开发更实惠的反演策略。这将推动三个应用领域的发展：微波生物医学成像、微波遥感海冰溢油和无相位天线测量。在用于设计的电磁反演领域，关键挑战是如何使用反演框架来促进电磁亚表面的宏观设计，该亚表面是由亚波长元素组成的工程表面。这些表面很重要，因为它们提供了一种系统的方法，通过施加适当的边界条件将给定的电磁场转换为所需的电磁场。因此，这将推进天线工程的应用领域。本研究的长期目标是推进电磁反问题的主题，以便(1)能够系统地获得具有最大定量精度和空间分辨率的反演结果，以用于表征应用；(2)建立电磁反演作为有效的补充框架，以便于复杂电磁系统的设计。该研究计划将培养具有硬件和软件技能的高素质人才(HQP)。然后，这些HQP可以利用他们在EM反转方面的专业知识来影响各种EM表征和设计应用。

This research program is concerned with Electromagnetic (EM) inversion, which is defined as the process by which some properties of a region of interest are inferred from its external EM signatures. This process involves solving EM inverse problems, which are often cast as optimization problems. The unique aspect of this research program is that all its algorithms and techniques stem from the consistent framework of EM inversion, and are then applied to impact diverging application areas: near-field microwave imaging, microwave sea ice remote sensing, antenna characterization, and design of EM engineered surfaces.In this research program, the external EM signatures to be used by inversion algorithms are either measured EM data (e.g., EM fields, radar cross section) or desired EM properties to be realized. On the other hand, the properties to be inferred are either (i) dielectric properties of objects or regions that scatter incident EM waves (e.g., biological tissues or sea ice), or (ii) equivalent currents of EM sources that generate EM waves (e.g., antennas). The EM inversion framework is often used for imaging, remote sensing, and non-destructive evaluation applications, which we collectively refer to as characterization applications. This research program not only advances the topic of EM inversion for characterization, but also investigates EM inversion for design applications.Within the area of EM inversion for characterization, our main focus is (I) to develop novel algorithms and techniques to enhance the achievable accuracy, spatial resolution, and detection capabilities, and (II) to develop more affordable inversion strategies by utilizing magnitude-only EM data. This will be pursued to advance three application areas: microwave biomedical imaging, microwave remote sensing of oil spills in sea ice, and phaseless antenna measurements.Within the area of EM inversion for design, the key challenge to be addressed is how to use the inversion framework to facilitate the macroscopic design of EM metasurfaces, which are engineered surfaces composed of subwavelength elements. These surfaces are important as they provide a systematic means to transform a given EM field to a desired one by imposing appropriate boundary conditions. This, therefore, will advance the application area of antenna engineering.The long-term objective of this research is to advance the topic of EM inverse problems so that (1) inversion results with maximum quantitative accuracy and spatial resolution can be systematically achieved for characterization applications and (2) EM inversion is established as an effective complementary framework to facilitate the design of complex EM systems. This research program will train highly qualified personnel (HQP) with hardware and software skills. These HQP can then use their expertise in EM inversion to impact various EM characterization and design applications.