# Topological Insulators by Topology Optimization

## TL;DR

This paper introduces a novel acoustic topological insulator designed via topology optimization, achieving high transmission, strong field confinement, and a broad operational bandwidth without relying on traditional topological invariants.

## Contribution

It presents a new method to design acoustic topological insulators using topology optimization, bypassing the need for pseudo spin states or Chern number constraints.

## Key findings

- Achieves approximately 12.5% operational bandwidth.
- Confines over 99% of the field intensity near the interface.
- Outperforms existing designs in transmission and confinement.

## Abstract

An acoustic topological insulator (TI) is synthesized using topology optimization, a free material inverse design method. The TI appears spontaneously from the optimization process without imposing requirements on the existence of pseudo spin-1/2 states at the TI interface edge, or the Chern number of the topological phases. The resulting TI is passive; consisting of acoustically hard members placed in an air background and has an operational bandwidth of $\approx$12.5\% showing high transmission. Further analysis demonstrates confinement of more than 99\% of the total field intensity in the TI within at most six lattice constants from the TI interface. The proposed design hereby outperforms a reference from recent literature regarding energy transmission, field confinement and operational bandwidth.