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Described is a device acting on an acoustically levitated object bymanipulating the pressure and flow of a thin layer of air such that itsrotation can be precisely controlled without mechanical contact. Virtual workanalysis assists in simplifying the multi-actuator control problem into aproblem governed by a controllable parameter. Actuation is done with avibrating ring capable of producing ultrasonic standing and traveling waves,creating the acoustic excitation that affects the pressure in a thin,intermediate layer of gas. A distinctive vibration pattern is required togenerate the temporal and spatial pressure field of the squeezed air layer thatgives rise to both acoustic levitation force and rotational torque. Describedare the physical and design development stages leading to an optimizedstructure, all followed by verifying and dynamics-calibration experiments.Moreover, by precisely controlling the ratio of standing and traveling waves ina closed-loop, one can affect the shear forces applied by the squeezed airlayer, thus creating a non-contacting manipulation mechanism. An over-actuatedset-up is converted via an algebraic transformation, into a simplified singlecontrol-parameter problem. The transformation ties the standing waves ratio,and hence the rotational torque, to the amplitudes and phases of the actuators.This arrangement leads to an effective closed loop methodology that wasimplemented experimentally showing good performance and exhibiting rapidangular positioning.

A rotational traveling wave based levitation device - Modeling, design, and control