▎ 摘　　要

We have studied the tunable properties of a hyperbolic metamaterial (HMM) composed of alternative dielectric layers and graphene sheets, and proposed a highly directional emission device working in the terahertz region. By changing the chemical potential mu(c), the equifrequency contour (EFC) of the HMM is easily switched between elliptical and hyperbolic types. Especially, when a dipole source is placed inside the structure, highly directional emission is realized provided that the EFC is a flat ellipse. Interestingly, such highly directional emission can be achieved for any frequency within a broad frequency range by tuning the chemical potential mu(c). The divergence angle of such a directional beam is lower than 12 degrees. Additionally, the influences of structural parameters (epsilon(d) and d) on the working bandwidth are also studied. These results have potential in many fields such as light coupling and spontaneous radiation antennas. Copyright (C) 2021 EPLA