Reducing Spiraling in Transducer Array Based Acoustic Levitation

Ultrasonic transducer array based levitation can be applied for non-contact manipulation of small objects. The technique can sometimes suffer from instability issues in the form of uncontrolled oscillatory movement that builds up until the levitating object moves out of the levitation trap region and drops. We propose an additional condition to the established description of the levitation trap, and describe how the condition is used in numerical optimization of a cost function to obtain the phases and amplitudes of the elements in the array. The proposed condition successfully reduces the rotational components in the force field responsible for the uncontrolled increase in kinetic energy of the levitating object.