FDTD analysis of positive-index plasma–metamaterials combining overdense plasma and high–permittivity ceramic inclusions

The efficiency of plasma-based material processing could be enhanced by producing larger plasma volumes with high electron density, n e . In most material plasma-processing technologies, plasmas are sustained by electromagnetic waves, such as microwaves at 2.45 GHz. However, when n e exceeds the critical density n e , c , the plasma permittivity becomes negative and transverse electromagnetic (TEM) waves cannot propagate through the plasma. This work demonstrates that the insertion of high-permittivity ceramic cylinders can balance the negative permittivity of the plasma, restoring electromagnetic wave propagation over larger distances through the plasma. The viability of this plasma metamaterial design was confirmed by finite-difference time-domain simulations of a square lattice of ceramic cylinders with relative permittivity ∊ r = 40 , a spatial period of 10 mm, and an overdense plasma density n e = 4 n e , c . Effective permittivity, permeability, and refractive index of the metamaterial were retrieved from the transmitted and reflected fields, confirming propagation for a positive refractive index. For a radius of the ceramic cylinders of 1.6 mm, the plasma–ceramic composite exhibits true metamaterial behavior at 2.45 GHz. This metamaterial design, which tailors microwave absorption, could enable the generation of larger, more homogeneous, high-density plasmas, opening routes to faster and more efficient plasma-based material processing.