The paper presents the theoretical study results of the control of the spectrum of slow electromagnetic waves (EMWs) existing in a “left-handed” medium based on a magnetically active plasma metamaterial. The investigated metamaterial is a strip waveguide completely filled with a longitudinally magnetized “cold” electron plasma, containing a periodic structure of perfectly conducting split-ring resonators (SRRs). It is shown that either one (ordinary), either two (ordinary and unordinary) slow EMWs can exist in a “left-handed” medium based on the magnetically active plasma and the spectrum of these waves depends on the SRR own frequency and magnetic induction. The unordinary slow EMW possesses by the negative dispersion and the dispersion characteristic of the ordinary EMW has the sections with both the negative and positive dispersions.

The paper presents the results of a theoretical study of the dispersion characteristics of electromagnetic waves (EMW) existing in a transversely magnetized antiferromagnetic (AFM) semiconductor with loss. An AFM semiconductor is an infinite bi-gyrotropic medium, the effective material parameters of which are twice negative in several frequency ranges. It was found that these frequency regions are in the terahertz range and there are four backward EMEs in them, two of which are TE waves, and the other two are TM waves.