Active metasurfaces for dynamic electromagnetic wave control

Abstract

Most of the metasurfaces are composed with subwavelength building blocks of passive metallic and dielectric resonators; therefore, once the structures are designed and fabricated, their electromagnetic (EM) properties and spectral responses cannot be changed. However, dynamic control of EM wave propagation is often demanded in many practical applications, such as the dynamic beam-forming and scanning functions required by the smart antennas in the next generation 5G wireless communication system. Here in this presentation we will show our recent attempts to incorporate tunable active elements into the metasurface designs to realize arbitrary and dynamic control of EM wave propagation. We will report our attempt on equivalent principle inspired active metasurface design. It enjoys the advantage of independent tuning for the magnitude and phase in either transmission or reflection. The equivalent principle is employed to analyze the required surface electric and magnetic impedances of a Huygens metasurface to produce either arbitrary transmission magnitude and phase or arbitrary reflection magnitude and phase. Based on this general design method we will also show an application example in the microwave regime: a planar Huygens lens that is capable of dynamic focusing of the incident EM plane wave with multiple focuses, as well as tunable focal position by controlling the bias voltage on the active element embedded in the metasurface unit-cell. We believe the proposed design scheme and the demonstrated example could indicate the significant ability and potential applications of active metasurfaces for dynamic control of the electromagnetic wave propagation.