In-place rotation of particles and time-average vibrational vortex on a Chladni plate

It is traditionally believed that particles will settle at the nodes or antinodes of a vibrating plate, forming stable standard or inverse Chladni patterns. The Chladni effect has been utilized to manipulate or pattern objects such as solid particles and even biological cells. The motion of particles near the nodal point is usually considered stochastic, and the stable and orderly movement of particles is impossible. Here, we experimentally show that the aggregation of particles can keep in-place rotating with different chirality at the nodal point of a vibrating plate, by utilizing specific dual-frequency oscillating signals to a single vibrator. To understand the motion of particles, irregular whirlpool force fields are calculated by considering the function of time dependent terms of the vibration response. Our findings reveal the time averaged vibrational vortex which can trap and rotate objects or particle clusters. It offers a new controllable degree of freedom for the movement of objects on a Chladni plate.