Active Huygens' Box: Arbitrary Electromagnetic Wave Generation With an Electronically Controlled Metasurface

This work investigates the generation of arbitrary electromagnetic waveforms inside a geometrical area enclosed by an active metasurface. We introduce the Huygens' box, where a region of space is enclosed by an active Huygens' metasurface. We show that, upon generating the necessary electric and magnetic currents, we can create any desired electromagnetic field inside Huygens' box. Using this method, we demonstrate, through simulation and experiment, the generation of traveling plane waves, a standing plane wave, and a Bessel wave inside a metallic cavity. These waves are generated using the same (reconfigurable) metasurface by aptly controlling the electronic excitations. By linear superposition of these unconventional traveling-wave "modes," we experimentally demonstrate, for the first time, a subwavelength superoscillation focal spot formed without involving evanescent EM waves and without an accompanying region of exorbitantly high waveform energy. The Huygens' box brings controlled waveform generation to an unprecedented level, with far-reaching implications to imaging, wireless communication, and medical therapy.