This chapter is organized as follows. In Section 7.2, innovative work on the optimization-enabled GST metasurfaces for sophisticated beam switching and control is highlighted. In Section 7.3, recent developments in the field of temporal artificial media are first reviewed, and then recent work on the time-varying anisotropic materials for complete polarization conversion is summarized. Finally, in Section 7.4, conclusions and a scope for future research are provided. Read more Lei Kang, Sawyer Campbell, Yuhao Wu, Jingwei Xu, Wending Mai, Eric Whiting, and Douglas H. Werner

This work introduces a new equivalent circuit generation method which can compute an accurate equivalent circuit representation for the known/measured impedance characteristics of antennas, which may assist in matching circuit design, non-Foster matching network design, and deep-learning antenna design. The method utilizes a modified Drude-Lorentz resonator representation inspired by optical material dispersion modeling to create multiple sub-circuits based on determined resonances in the impedance spectrum. Each computed sub-circuit is necessarily composed of physically realizable resistors, capacitors, and inductors, and they are connected in series to accurately reconstruct the device’s corresponding impedance characteristics over a specified region of interest. The process…

Taking lessons from epidemic contact tracing, this communication proposes a method for boosting the efficiency of a full-wave electromagnetic solver by tracking its simulated energy distribution. When the energy within a subdomain of the problem is near zero, such areas can be safely ignored by the solver, reducing computational load with negligible impact on accuracy. We show that time-domain problems can be adaptively partitioned into energy-active (infections), energy-adjacent (exposed), and energy-null (unexposed) domains. To demonstrate the high efficiency and accuracy of this method, it is successfully applied to several computational electromagnetic problems. Due to its reliance on the causality principle…

System response analysis is a powerful method for analyzing linear time-invariant (LTI) systems. In this work, we have demonstrated that a system response approach can also be applied to analyze the so-called linear space-invariant (LSI) but time-varying problems, which represent a dual of the conventional LTI problems. In this proposed approach, we perform a Fourier transform of the electric field distribution on the space coordinate, rather than in time, and express it in the wave-number domain. Specifically, we express any input signal and its corresponding output in the wave-number domain. Then, the transfer function for the LSI time-varying system can…

Time-varying materials bring an extra degree of design freedom compared to their conventional time-invariant counterparts. However, few discussions have focused on the underlying physical difference between spatial and temporal boundaries. In this letter, we thoroughly investigate those differences from the perspective of conservation laws. By doing so, the building blocks of optics and electromagnetics such as the reflection law, Snell’s law, and Fresnel’s equations can be analogously derived in a temporal context, but with completely different interpretations. Furthermore, we study the unique features of temporal boundaries, such as their nonconformance to energy conservation and causality. Read more Wending Mai, Jingwei…

As an important theoretical concept, temporal boundaries provide researchers with new insights for tailoring electromagnetic waves in the time domain. Because a temporal boundary breaks the time translation symmetry, a source is necessary to satisfy energy conservation. In this Letter, we quantify the relationship between refractive index contrast and the required energy exchange. More specifically, to realize a temporal boundary with a large refractive index contrast, a correspondingly large and abrupt energy exchange is required. Considering this practical difficulty, we propose to mimic a large-contrast temporal boundary by staggering a series of small-contrast temporal boundaries separated by carefully designed durations.