Active Huygens' metasurfaces for RF waveform synthesis in a cavity

Metasurfaces are engineered surfaces which exhibit unconventional electromagnetic properties. Various recent proposals of metasurfaces - many of which are constructed with micro- and nano-circuit elements - explore possible applications including arbitrary reflection, transmission, focusing, collimation, and polarization operations on incident electromagnetic waves. However, possible applications for active and non-planar meta-surfaces remain largely unexplored. In this work we report our study on active Huygens' metasurfaces which completely enclose an area. We report the theoretical groundwork, describe the metasurface element and system design, then showcase simulation and experimental results in generating an arbitrary waveform within a closed area using the proposed active closed Huygens' surfaces. The proliferation of such surfaces will find applications in medical imaging and therapy, power concentration and electromagnetic characterization.