Recently, research team of Gao Fei, a researcher at College of Information Science & Electronic Engineering of Zhejiang University, Associate Professor Baile Zhang and Associate Professor Yidong Chong of Singapore Nanyang Technological University have successfully implemented a second-order topological insulator in an acoustic metamaterial on a kagome lattice, which was published on “Nature Materials” titled “Acoustic higher-order topological insulator on a kagome lattice”.

In the work, Prof. Gao and his colleagues present an acoustic two-dimensional (2D) second-order topological insulator based on a ‘breathing’ kagome lattice that has zero quadrupole polarization but a non-trivial bulk topology characterized by quantized Wanniercentres. Unlike previous higher-order topological insulator realizations, the corner states depend not only on the bulk topology but also on the corner shape; researchers show that they exist at acute-angled corners of the kagome lattice instead of obtuse-angled cornersby experiments. This shape dependence allows corner states to act as topologically protected but reconfigurable local resonances.

Such acoustic topological shape dependence has significant applications in biomedical microfluidic devices, such as accurate acoustic trapping and manipulation of cells or drug particles, or selective measurement of vibration signals in a small regionin high precision acoustic sensors.

Fig.1 Kagome lattice and its acoustic implementation.