Simultaneous Calibration of Axial and Lateral Radiation Forces of Ultra-High Frequency Ultrasound Acting on a Microrobot With Arbitrary Geometry

Acoustically actuated microrobots have attracted considerable attention, which have developed various geometries. These microrobots are powered through their interaction with acoustics. The use of ultrahigh-frequency (UHF) ultrasound yields a focus on the order of several microns, thus actuating microrobots with accurate, strong, and two-directional forces. However, to date no technique can simultaneously calibrate the actual axial and lateral radiation forces of UHF ultrasound above 60 MHz acting on a microrobot with arbitrary geometry. To address this issue, we present a force sensor based on a micropipette. The force sensor consists of the micropipette, microrobot with a marker, and fixed base, which calibrates the overall spring constants. By combining the two-directional displacements actuated by the axial and lateral radiation forces, we calibrated the forces with a resolution of hundreds of piconewtons. We calibrated the axial and lateral radiation forces on cylindrical and spherical microrobots with the same volume and further investigated the influences of the duty factor and excitation voltage. This method complements a crucial design link in UHF ultrasound actuating microrobots.