Fig. 2. Device design and characterization of the wave number–spiral acoustic tweezers.

(A) A schematic of the designed proof-of-concept wave number–spiral acoustic tweezers, which are composed of five pairs of IDTs divided into two groups. In each group, five IDTs are interlinked so that only two input channels are needed for powering and controlling all the IDTs. If 2D standing SAWs are generated by two pairs of IDTs, then the resultant acoustic radiation force will trap micro-objects in the potential wells. By adjusting the phases, amplitudes, and frequencies of excitation signals, we can dynamically reshape the wavefields of standing SAWs, thus achieving dynamic and reconfigurable particle manipulation. (B) A photo of a fabricated chip with five pairs of IDTs deposited on an X-cut LiNbO₃ substrate. A disposable microfluidic chamber is bonded on top of the substrate and filled with red dye for visualization. Y and Z are crystallographic axes for illustrating the orientation of the X-cut LiNbO₃ substrate; x, y, and z are local coordinate axes as references for the wave number–spiral acoustic tweezers. The wave numbers (C), frequencies (D), and slowness values (E) at different angles obtained from the experiment (red circles) agree well with their theoretical values (blue asterisks).