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This paper demonstrates analytically and experimentally an acousticlevitation motor which has the ability to levitate and rotate an object in theair without mechanical contact. To realize such a device two core methods areapplied simultaneously; (i) resonance tracking with an Autoresonance feedbackloop, (ii) generation of controlled structural traveling waves. The purpose ofthe first method is to achieve near-field acoustic levitation, which canlevitate an object of a few kilograms. In this research, this is accomplishedthrough high amplitude vibration of an aluminum annulus at ultrasonicfrequencies (~30kHz). For high efficiency, the annulus is designed to have avery high Q value, and operating even slightly off resonance ceases levitation.Compounding this is the fact that the natural frequency constantly drifts asambient conditions and loading change. To accommodate such a drift, and producestable levitation automatically, a resonance tracking feedback loop is employedhere. Simultaneously, the purpose of the second method is to achieve propulsionforces on the levitated object by propagating and controlling traveling wavesin the aluminum annulus to create a thin layer of rotating air beneath thelevitated body. Even though a single vibration mode can produce only standingwaves, an axisymmetric structure possesses two modes per natural frequency, andexcitation of a doublet mode pair can generate effective travelling waves. Thepresent paper develops the theory behind the use of the Autoresonance feedbackmethod for achieving constant levitation and propagating travelling waves inco- and counter rotating directions. It will be shown that all this can beaccomplished with only single sensor. The result is a stable, repeatable and ahighly controllable contactless acoustic levitation motor.

Realization of a Contactless Acoustic Levitation Motor via Doublet Mode Control and Autoresonance