Ultrawide phononic band gap for combined in-plane and out-of-plane waves

TL;DR

This paper develops a genetic algorithm-based method to optimize silicon-based phononic crystal unit cells, achieving record-wide band gaps for in-plane, out-of-plane, and combined elastic waves, advancing wave control technologies.

Contribution

It introduces a specialized genetic algorithm combined with reduced Bloch mode expansion for efficient design of phononic crystals with maximal band gaps.

Findings

Record normalized band-gap size exceeding 60% for combined waves

Optimized unit cell designs for all three wave categories

Efficient search method for large design spaces

Abstract

We consider two-dimensional phononic crystals formed from silicon and voids, and present optimized unit cell designs for (1) out-of-plane, (2) in-plane and (3) combined out-of-plane and in-plane elastic wave propagation. To feasibly search through an excessively large design space (10e40 possible realizations) we develop a specialized genetic algorithm and utilize it in conjunction with the reduced Bloch mode expansion method for fast band structure calculations. Focusing on high symmetry plain-strain square lattices, we report unit cell designs exhibiting record values of normalized band-gap size for all three categories. For the combined polarizations case, we reveal a design with a normalized band-gap size exceeding 60%.