Design of Functional Structures and Measurement Techniques for Electromagnetic Waves

Abstract: Electromagnetic fields exist all around us. Through evolution, nature has developed tools to interact and use these fields, where our eyes are a spectacular example. Humans have a long history of developing structures and objects of their own to alter and interact with these fields. Today they are important cornerstones in society, with radiating devices such as cell phones, Wi-Fi routers, or car radar and functional structures such as tinted windows, 3D glasses, and microwave oven doors. There is a high demand for these objects in various application areas. This dissertation deals with the design of functional structures along with measurement techniques of the electromagnetic field.The dissertation is centered on two parts, a general introduction and research overview (Part I) and six scientific papers, published in peer-reviewed international journals (Part II). The general introduction and research overview puts the results from the scientific papers in perspective and presents a path between them. It starts with fundamental theoretical concepts in electromagnetic theory and continues into discussing functional structures, measurement techniques, near-field measurements, and simulations of scattering media. The two primary categories of the included papers are functional structures, Papers I, II, III, V, VI, and electromagnetic measurements Paper III, IV, V, VI.Paper I investigates a functional structure in transmission through periodic sub-wavelength apertures. Fundamental limitations are presented and a functional structure is designed and optimized to reach a bandwidth close to the attainable limit. The design is manufactured and measured to verify the validity of a sum rule.In Papers II and III, functional structures exhibiting circular polarization selectivity are explored. A circular polarization selective structure is designed for satellite communication applications with dual band performance. The design is manufactured and measured through an experimental technique and post-processing scheme, specifically aimed at accurate characterization.Papers IV--VI are concerned with mm-wave imaging systems and measurement techniques of radiating devices. Techniques for reflection-based non-destructive testing measurements are developed along with techniques for measurements of the radiative near field of devices using functional structures. The measurement technique in Paper V consists of measuring the radiative near field, computing equivalent currents, and reconstructing the electromagnetic field at points of interest. This is carried out through a system calibration using a small aperture as a functional structure. In Paper VI, the functional structure is a metasurface that converts incident radiation to heat imaged with an infrared camera. The metasurface is designed for the low power levels of consumer hand-held devices.Finally, the dissertation discusses a simulation approach of full-wave solutions for highly scattering random media. The simulation tool aims to describe focusing of light into, and through, random media using wavefront shaping with functional structures to enable measurements of regions deep within tissue.