Experimental demonstration of microwave variable-focal-length lens with single-layer metamaterial based on split-ring-resonators

We propose a variable-focal-length lens in the microwave band based single-layer metamaterial. To make the lens with single-layer metamaterial, we applied Fresnel-zone-plate theory, in which the transmission intensity distribution in the lens is controlled. In the lens, a split-ring-resonator (SRR) structure is used as a unit cell to utilize the loop-current resonance mode because it provides a small unit cell with a small aspect ratio. To electrically control the transmission characteristics, we mounted varactor diodes on the split gaps in the SRRs. Additional gaps are introduced into the SRRs to avoid breaking the asymmetry of the loop current path, which results in an 18-dB change in the intensity of the waves. By electrically controlling the location of the transparent and opaque zones according to Fresnel-zone-plate theory, we experimentally verified the dynamic control of focus and focal length with single-layer metamaterial.