Microscale Architected Materials for Elastic Waveguiding: Fabrication and Dynamic Characterization across Length and Time Scales

We present an experimental protocol for the fabrication and characterization of scalable microarchitected elastic waveguides. Using silicon microfabrication techniques, we develop free-standing 2D truss-based architected waveguides with a maximum diameter of 80 mm, unit cells size of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:mn>100</a:mn> <a:mtext> </a:mtext> <a:mtext> </a:mtext> <a:mi mathvariant="normal">μ</a:mi> <a:mi mathvariant="normal">m</a:mi> </a:mrow> </a:math> , and minimum beam width of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mrow> <e:mn>5</e:mn> <e:mtext> </e:mtext> <e:mtext> </e:mtext> <e:mi mathvariant="normal">μ</e:mi> <e:mi mathvariant="normal">m</e:mi> </e:mrow> </e:math> , thus achieving scale separation. To characterize elastic wave propagation, we introduce a custom-built scanning optical pump-probe experiment that enables contactless excitation of elastic wave modes and full spatiotemporal reconstruction of wave propagation across hundreds of unit cells with subunit cell resolution. Results on periodic architectures show excellent agreement with finite element simulations and equivalent experimental data at larger length scales. Motivated by scalable computational inverse design, we fabricate a specific example of a spatially graded waveguide and demonstrate its ability to guide elastic waves along an arbitrary predesigned path.