Model-based adaptive locomotion and clustering control of microparticles through ultrasonic topological charge modulation

We present a novel motion control technique for microrobot clusters to exploit the characteristics of the ultrasonic field. The method comprises two steps, i.e., introducing an ultrasonic actuation (UA) linear model for three-dimensional (3D) locomotion and controlling the topological charge (TC) in the ultrasonic vortex for microrobot clustering. Here, the TC is a controllable parameter for the expansion and contraction of the pressure null space inside the vortex. We present a TC control method to cluster sporadically distributed microrobots in a specific workspace. To validate the concept, a UA system composed of 30 ultrasonic transducers with 1 MHz frequency is fabricated, and the characteristics of the generated acoustic pressure field are analyzed through simulations. Subsequently, the performances of the adaptive controller for precise 3D locomotion and the TC control method for clustering are evaluated. Finally, the UA technology, which performs both clustering and locomotion in a complex manner, is validated with a gelatin phantom in an in-vitro environment.