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Novel schemes for sensors and absorbers in linear time-variant systems and exceptional points of degeneracy

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This dissertation focuses on a new class of electromagnetic devices and sources, whose working principle relies on the engineering of their operating point condition into the so-called exceptional point of degeneracy (EPD). An EPD is a point in the state space of a dynamical system that refers to the condition at which two or more eigenmodes of the system coalesce into a single one and bifurcate as a system parameter changes. The surge of interest towards the EPD concept has led to different and unique properties associated with the emergence of these points in a system which has various potential applications such as enhancing the gain of active systems, enhancing directivity and tunability of antennas, and enhanced-sensitivity sensors.

A comprehensive investigation of EPDs in periodically time-varying systems, in analogy to the EPDs found in spatially periodic structures, is presented in this dissertation. We derive the conditions for EPDs to exist in time-periodic systems and show that even a single resonator with a time-periodic component develops EPDs. Furthermore, we experimentally demonstrate the existence and high sensitivity of such an operating point to external perturbation. Moreover, we propose a design of a biosensor based on a temporally induced EPD and show the ultra-sensitivity and scalability of the designed biosensor to different bio samples. Furthermore, we show that introducing time variation into an absorber structure could potentially increase the bandwidth beyond the physical bound, breaking the bandwidth limit of standard absorbers.

In this dissertation we also design metasurfaces for different wave manipulations. We design a chiral metasurface for simultaneous perfect bending and polarization rotation of the incident wavefront, and we also present a general synthesis method of cylindrical metasurface design for exotic wave manipulation.

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