Multistable Elastic Pixels based on Nematic Colloids for Reconfigurable Metasurfaces

Metamaterials are engineered to modulate incident electromagnetic (EM) waves in novel ways. We are developing a versatile approach for reconfigurable metasurface design where reversible changes between device states correlate to significant changes in EM response. Our approach relies on multistable elastic pixels (MEPs) which are discrete nematic liquid crystal (NLC)-filled structures containing colloids whose positions are controlled by the NLC elastic energy landscape. MEPs have two or more well-defined elastic energy minima, which correspond to stable colloid positions, separated by significant energy barriers. Once stably placed, a colloid can be repositioned to another stable location by the application of an external electric or magnetic switching field. Upon removal of the switching field, the system will persist in the new stable state. Colloids will serve as scatterers; hence, metasurfaces with judiciously placed MEPs will have strong changes in EM response upon colloid repositioning. Colloids can be returned to their original locations by reversing the switching field; thus, changes in the EM responses are reversible. We design MEPs to generate complex director fields and defect interactions that define colloid multistable sites and energy barriers between them.