Graded phononic metamaterials: Scalable design meets scalable microfabrication

TL;DR

This paper introduces a scalable inverse design framework and microfabrication method for phononic metamaterials, enabling the creation of complex elastic waveguides with hundreds of thousands of unit cells for advanced wave manipulation.

Contribution

The authors develop a scalable design and fabrication approach for large-scale phononic metamaterials, overcoming previous limitations in size and complexity.

Findings

Successfully designed waveguides with hundreds of thousands of unit cells

Demonstrated broadband elastic wave guiding experimentally

Scalable fabrication process using photolithography and etching

Abstract

Metamaterials are a new generation of advanced materials, exhibiting engineered microstructures that enable customized material properties not found in nature. The dynamics of metamaterials are particularly fascinating, promising the capability to guide, attenuate, and focus waves at will. Phononic metamaterials aim to manipulate mechanical waves with broad applications in acoustics, elastodynamics, and structural vibrations. A key bottleneck in the advancement of phononic metamaterials is scalability -- in design, simulation, and especially fabrication (e.g., beyond tens of unit cells per spatial dimension). We present a framework for scalable inverse design of spatially graded metamaterials for elastic wave guiding, together with a scalable microfabrication method. This framework enables the design and realization of complex waveguides including hundreds of thousands of unit cells, with the potential to extend to millions with no change in protocol. Scalable design is achieved via optimization with a ray tracing model for waves in spatially graded beam lattices. Designs are fabricated by photolithography and etching of silicon wafers to create free-standing microarchitected films. Wave guiding is demonstrated experimentally, using pulsed laser excitation and an interferometer for displacement measurements. Broadband wave guiding is demonstrated, indicating the promise of our scalable design and fabrication methods for on-chip elastic wave manipulation.