Terahertz metasurfaces embedded into hydrogel layers

This work fabricates a metasurface embedded into a hydrogel layer using photolithography, sputtering, lift-off process, and imprinting. The split ring resonators (SRRs) of the metasurface develop cracks as the hydrogel layer is exposed to water. These cracks, which arise from the swelling of the hydrogel layer in water, increase the resistances of the SRRs, degenerating their electromagnetic resonance, and increasing the transmittance of the metasurface at its resonance frequency. The increased resonance transmittance reveals the existence of water in the hydrogel layer. As a result, the metasurface embedded into the hydrogel layer has potential for developing humidity sensors and water harvesters.