▎ 摘　　要

TM surface plasmon (SP) characteristics of a four-layer structure, consisting of air as the superstrate, a monolayer of graphene, a dielectric buffer layer and metal as the substrate are analyzed at sub-THz frequencies. TM SPs in such case are represented by metal-like and graphene-like branches. For small frequencies the metal-like plasmon splits up into two branches depending on the graphene electron concentration; one of the branches goes into cutoff at the point where the branch features Brewster-type characteristics. Graphene-like plasmon modes are converted into short-range modes for small buffer thicknesses. Brewster-type SP modes can be effectively modulated in the vicinity of their cutoff thicknesses by means of the graphene electron concentration.