“Topological” and “defect” rainbow trapping effects and particle manipulation based on two-dimensional gradient valley-Hall topological insulator defect states

Acoustic microfluidics is an important technique for particle manipulation in biomedical analysis and detection. However, particle manipulation based on surface acoustic waves is limited to thin fluid layers, as energy loss prevents it from reaching deeper solutions. Traditional bulk-wave methods can operate in deep solutions, but energy dissipation makes long-distance particle manipulation difficult. In this work, we introduce line defects into two-dimensional gradient valley-Hall topological insulators and achieve the rainbow trapping of defect states. The results show a point-like concentration of acoustic pressure along the waveguide, and the location of maximum pressure can be tuned by changing the frequency of the incident wave. Based on this mechanism, we demonstrate long-distance movement and trapping of particles in deep solutions. The findings provide a reliable method for continuous long-distance particle manipulation, which is useful for multi-step processes in biochemical analysis and detection.