Mechanical mode engineering with orthotropic metamaterial membranes

TL;DR

This paper demonstrates how nanopatterning silicon nitride membranes induces anisotropic elastic properties, enabling control over mechanical modes and enhancing their application potential in sensing technologies.

Contribution

It introduces a method to engineer anisotropic elasticity in membranes via nanopatterning, achieving high anisotropy comparable to natural crystals, with tunable pattern orientation.

Findings

Nanopatterning induces anisotropic elasticity in membranes.

Achieved anisotropy ratio of 1.568, comparable to natural crystals.

Pattern rotation allows arbitrary anisotropy axis definition.

Abstract

Metamaterials are structures engineered at a small scale with respect to the wavelength of the excitations they interact with. These structures behave as artificial materials whose properties can be chosen by design, mocking and even outperforming natural materials and making them the quintessential tool for manipulation of wave systems. In this Letter we show how the acoustic properties of a silicon nitride membrane can be affected by nanopatterning. The degree of asymmetry in the pattern geometry induces an artificial anisotropic elasticity, resulting in the splitting of otherwise degenerate mechanical modes. The artificial material we introduce has a maximum Ledbetter-Migliori anisotropy of 1.568, favorably comparing to most bulk natural crystals. With an additional freedom in defining arbitrary asymmetry axes by pattern rotation, our approach can be useful for fundamental investigation of material properties as well as for devising improved sensors of light, mass or acceleration based on micromechanical resonators.