Using Optical Tweezers to Assemble Micro-spheres within Metamaterials that Achieve Engineered Wave Propagation Properties

Here we present a new way to fabricate metamaterials that consist of carefully organized micro-spheres using optical tweezers. Due to the nonlinear stiffness that results at the junction between such micro-spheres, these metamaterials give rise to nonlinear stress-wave propagation properties that enable a variety of applications (e.g., acoustic lenses, sound scramblers, and armor that mitigates impacts by dispersing shock waves). To achieve control of such properties, however, it is necessary that specific micro-spheres of customized sizes and materials can be positioned within lattice tessellations as desired. Such fabrication flexibility can be achieved by automating optical tweezers such that many individual optical traps can be simultaneously and independently controlled to assemble each micro-sphere individually. This paper reviews our group's progress toward automating the assembly of such metamaterials.