On the feasibility of pentamode mechanical metamaterials

TL;DR

This paper explores the potential of pentamode mechanical metamaterials for advanced applications, demonstrating through numerical and experimental methods that near-ideal properties can be achieved with current lithography techniques.

Contribution

It provides the first experimental approximation of the ideal pentamode material, showing a feasible high figure of merit using state-of-the-art fabrication.

Findings

Achieved a figure of merit (bulk/shear modulus ratio) of about 1,000.

Validated numerical models with fabricated microstructures.

Demonstrated potential for three-dimensional transformation acoustics.

Abstract

Conceptually, all conceivable three-dimensional mechanical materials can be built from pentamode materials. Pentamodes also enable to implement three-dimensional transformation acoustics - the analogue of transformation optics. However, pentamodes have not been realized experimentally to the best of our knowledge. Here, we investigate inasmuch the pentamode theoretical ideal suggested by Milton and Cherkaev in 1995 can be approximated by a metamaterial with current state-of-the-art lithography. Using numerical calculations calibrated by our fabricated three-dimensional microstructures, we find that the figure of merit, i.e., the ratio of bulk modulus to shear modulus, can realistically be made as large as about 1,000.