Acoustic Levitation from Superposition of Spherical Harmonics Expansions of Elementary Sources: Analysis of Dependency on Wavenumber and Order

Paper in proceeding, 2019

Acoustic levitation of spherical objects in mid-air is a technique that is gaining traction in various human computer interaction applications such as data visualization or interactive displays. The commonly used hardware platforms are phased ultrasonic transducer arrays, used to levitate small spheres of polystyrene. Previous works have used angular spectrum decomposition of the incident sound field to derive the radiation force exerted on an arbitrary sphere. We show an alternate formulation more suited to sound fields from transducer arrays, based on direct spherical harmonics expansions of the sound fields from the individual transducer elements in the array. Finally we investigate how the truncation order of the spherical harmonics expansion influence the calculated force, for varying sphere sizes.