Celebrating 25 Years of the High-Impedance Surface

The high impedance surface (HIS) was introduced by Sievenpiper in 1999. It was a 2D periodic array of subwavelength unit cells and had two unique properties, namely, in-phase reflection and surface wave suppression. Sievenpiper proposed the utilization of the HIS as an in-phase reflector and for mutual-coupling/crosstalk reduction. With the passage of time, researchers found many additional applications of the HIS. They began to be used as electromagnetic absorbers as well as for radar cross section reduction. Utilizing the HIS structures along with metallic waveguides, researchers also developed the concept of impedance waveguides and gap waveguides. Recently, researchers have added PIN/varactor diodes with HIS unit cells to make their properties reconfigurable. With the increase in demand for dynamic communication systems, reconfigurable HIS designs are expected to be quite critical in many applications in the future. Flexible and lightweight graphene-based HIS structures are also expected to gain importance with the increasing focus on wearable communication systems for health monitoring and search-and-rescue operations.