High-Performance, Efficient, Low-Fresnel Number Focusing Metamirror in the D-Band

The rapid growth of wireless data traffic driven by applications such as virtual reality and artificial intelligence necessitates the development of sixth-generation (6G) wireless systems. These systems require higher data rates and lower latency, which can be achieved using terahertz carrier frequencies. However, terahertz waves present challenges such as high free-space path loss, necessitating advanced beam forming and steering technologies. One promising technology is the intelligent reflecting surface (IRS), which can be realized using metasurfaces—planar, two-dimensional metamaterials composed of sub-wavelength unit cells. This article presents a metal-insulator-metal (MIM) based metamirror operating in the D-band (0.11 to 0.2 THz) with an efficiency above 53.5% over the entire bandwidth, peaking at 77.4%. The metamirror's focusing behavior is experimentally characterized and compared to an ideal focusing mirror, showing close agreement. The study highlights the advantages of low Fresnel number optics in achieving high efficiency and broadband performance. Additionally, the article discusses the potential of metasurfaces for multifunctional IRSs, dynamic electrical controllability, and enhanced system integration. The experimental results and design strategies presented in this article offer valuable insights for the development of advanced focusing metasurfaces and their applications in 6G wireless systems.