Active Huygens' Box: Arbitrary Synthesis of EM Waves in Metallic Cavities

Previously, it was believed that electromagnetic plane waves cannot exist in a closed metallic cavity. However, by applying the electromagnetic equivalence principle, we have demonstrated the formation of an arbitrary waveform in a region enclosed by an active Huygens' metasurface. In this paper, we apply this principle on two cavity shapes - a rectangular and a cylindrical cavity, which we call the Huygens' boxes. We present simulation results to demonstrate the generation of traveling plane waves at 0° and 45° in both Huygens' boxes. We also present measured experimental results that agrees with the simulation results for the Huygens' box. We have thus demonstrated the generation and control of waveforms in a metallic cavity at an unprecedented level. We believe that this novel discovery will find applications in a wide range of applications like imaging, communication, and medical therapy in the nearest future.