We propose and study numerically a tunable and reconfigurable metamaterial based on coupled split-ring resonators (SRRs) and plasma discharges. The metamaterial couples the magnetic-electric response of the SRR structure with the electric response of a controllable plasma slab discharge that occupies a volume of the metamaterial. Because the electric response of a plasma depends on its constitutive parameters (electron density and collision frequency), the plasma-based metamaterial is tunable and active. Using three-dimensional numerical simulations, we analyze the coupled plasma-SRR metamaterial in terms of transmittance, performing parametric studies on the effects of electron density, collisional frequency, and the position of the plasma slab with respect to the SRR array. We find that the resonance frequency can be controlled by the plasma position or the plasma-to-collision frequency ratio, while transmittance is highly dependent on the latter.

Plasmas respond nonlinearly to GHz electromagnetic waves, owing to nonlinear interactions described by the electron momentum equation. These nonlinearities are especially important in high field regions of the plasma as is common in resonant structures that generate plasma discharges with intense localized amplification of the incident field. Most models treat the plasma as a linear Drude material that does not capture the nonlinear polarization terms of a plasma. In this work, we couple the nonlinear electron momentum equation to electromagnetic wave simulation in order to explore the nonlinear behavior. We develop a theoretical foundation via perturbation analysis to guide our expectations from numerical simulation. Through numerical simulation of 2D TE-polarized waves incident on a cylindrical plasma, we show that in the presence of electrical field strengths of ∼MV/m and higher, dense microplasmas have second harmonic power conversion efficiency approaching 10−6 at low pressures. The generated harmonic power is shown to arise mostly from the inertial term in the electron momentum equation. Therefore, a significant portion of the harmonic current density is generated at the surfaces of critical electron density for the fundamental frequency.

We present a multi-physics model of combustion ignition phenomena in an atmospheric pressure hydrogen-air mixture ignited by a microwave surface plasma discharge. The surface plasma is generated over a resonant metasurface structure that provides sufficient field intensification to break down and sustain a discharge. Specifically, a surface electromagnetic (EM) wave mode known as the spoof surface plasmon polariton (SSPP) is excited to yield a hybrid resonance that results from coupling of cavity and surface EM wave modes. Motivated by the need for a large, volumetric ignition kernel for applications in combustion ignition, we numerically demonstrate the volumetric surface plasma discharge enabled by the use of this particular EM wave mode in a high pressure operating regime. We discuss the transient evolution of a centimeter scale plasma kernel and subsequent ignition kernel formation. High density combustion enhancing radical species (O, H, OH) are produced throughout the bulk plasma, which leads to successful ignition. A parametric study shows that the large size of a plasma kernel is attributed to the shortening of ignition delay.

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