Tunable Water-Based Meta-Lens

Water, the source of life, is a more abundant, low-cost, and environment-friendly candidate material for tunable meta-devices compared to conventional approaches in the microwave region. Wavefront shaping can be flexibly manipulated by adjusting the shapes and temperature of water-based meta-atoms, but individual control of each meta-atom is complicated and inconvenient, especially for continuous tunability. Here, we propose a design strategy based on the phase compensation mechanism to continuously tune the properties of water-based meta-lenses at 5 GHz. Integrated-resonant units (IRUs) with coupled water pillars are carefully designed to effectively tailor the balance between polarization conversion efficiency and phase compensation. By changing the filling height of water in the designed meta-lens from 10 to 60 mm, the focal length can be tuned from 228 to 424 mm. The off-axis focusing of the meta-lens is also demonstrated in which the deflection angle is adjustable from around 0 degrees to 5 degrees. This work will pave the way for designing tunable water-based meta-devices and facilitating their applications in microwave imaging systems.