Scalable design and microfabrication of graded metamaterial waveguides

While metamaterials have emerged as a powerful tool for manipulating elastic waves, scalability remains a key bottleneck. It is challenging to model, design, and fabricate architectures with large numbers of unit cells, which restricts the design space and achievable functionalities. We present a framework for scalable inverse design of spatially graded metamaterials, accompanied by a novel microfabrication technique to manufacture planar metamaterials spanning hundreds of thousands of unit cells and beyond. To address the scalability of computational design, we present an optimization framework leveraging ray tracing for efficient forward modeling. Using this framework, we design a set of spatially graded tiles, each spanning many unit cells to guide elastic waves in a prescribed way. We then assemble the tiles like puzzle pieces to achieve complex wave-guiding objectives. To realize our designs, we developed a microfabrication technique inspired by chip manufacturing methods. This enables the manufacture of free-standing planar truss metamaterials with tens to hundreds of thousands of unit cells. Wave guiding is experimentally demonstrated using a pulsed laser to excite elastic waves and interferometry to measure the response. Surprisingly broadband wave guiding is observed, demonstrating the promise of our scalable design and fabrication methods for on-chip wave manipulation.