Time-Varying Components for Enhancing Wireless Transfer of Power and Information

Temporal modulation of components of electromagnetic systems provides an exceptional opportunity to engineer the response of those systems in a desired fashion, both in the time and frequency domains. For engineering time-modulated systems, one needs to thoroughly study the basic concepts and understand the salient characteristics of temporal modulation. In this paper, we carefully study what time-varying circuit elements -- capacitors, inductors, and resistors -- mean and study their effects in the case of periodically varying time modulations. We develop a solid theory for understanding these elements, and apply it to two important applications: wireless power transfer and antennas. For the first application, we show that by periodically modulating the mutual inductance between the transmitter and receiver, the fundamental limits of classical wireless power transfer systems can be overcome. Regarding the second application, we consider a time-varying source for electrically small dipole antennas and show how time modulation can enhance the antenna performance. This paper establishes the relevance of "electromagnetic systems engineered by temporal modulation" from radio frequencies to even optical wavelengths.