Time-modulated reactive elements for control of electromagnetic energy

Accumulation of electromagnetic field energy in classical passive structures, such as resonators and reactive circuit elements, is limited by the amplitude of time-harmonic external sources. In the steady-state regime, all incident power that is not absorbed is fully re-radiated (reflected), and the time-averaged stored energy is constant, even though the external source continuously supplies energy. We have recently shown that lossless objects can continuously accumulate energy if their properties are properly modulated in time. Here, we discuss this possibility, and study means to release this accumulated energy in the desired moment or moments of time in the form of pulses of the desired shape. Furthermore, we discuss a possibility of keeping the energy inside the load, turning off the incident wave and changing the modulation function of the load. Finally, instead of a single time-reactive element, we consider a parallel time-varying LC circuit that gives the same functionality, in addition to allowing engineering currents flowing through the load's circuit elements. This paper is an extended version of [1].