Sound Field Design for Transducer Array-Based Acoustic Levitation
Doctoral thesis, 2022

Acoustic levitation is a technique where sound waves are used to hold an object at a designated position, suspending it against other external forces and keeping it stable in the desired position. Transducer arrays are an arrangement of many loudspeaker elements, tuned such that the array creates a sound field that is too complicated for the individual elements to produce on their own. Sound field design refers to the process of prescribing some target criteria for a sound field, describing these criteria mathematically, and apply some method to produce a sound field with these criteria fulfilled.

This thesis is about combining these three concepts. The necessary criteria for levitation to take place are described, using radiation pressure from sound waves in air as the physical mechanism by which the levitation forces are produced. Ultrasonic transducer arrays are modeled using analytical descriptions for the wave propagation, as well as for the predictions of the radiation forces on spherical objects of various sizes. The sound fields required to successfully levitate objects are obtained by numerically optimizing the magnitudes and phases of the elements in the mono-frequent transducer arrays. This is achieved by deriving design criteria from intuitive considerations of the conditions needed for levitation, quantifying these criteria as a
single valued cost function which is minimized with a Quasi-Newton method.

The thesis is focused on two main aspects: how to define a suitable cost function for a single levitation trap, and how to levitate multiple objects via mutual quiet zones. The design criteria for a trap are described using a vector field approach, representing properties of the force field with invariant quantities evaluated at the desired levitation position. These quantifiers are scaled by the characteristic quantities of the system and transformed to a satisficing cost function, which avoids over-optimization by reducing the prioritization of a particular criterion when closer to fulfilled. Multiple objects are levitated by superposing sound fields with mutual quiet zones, i.e. each sound field has a trap for one object and quiet zones where all the other objects will be.

Sound Field Design

Acoustic Levitation

Transducer Arrays

Numerical Optimization

Nonlinear Acoustics

Opponent: Dr. Asier Marzo, Universidad Pública de Navarra, Spain


Carl Andersson

Chalmers, Architecture and Civil Engineering, Applied Acoustics

A Method for Simultaneous Creation of an Acoustic Trap and a Quiet Zone

Proceedings of the IEEE Sensor Array and Multichannel Signal Processing Workshop,; Vol. 2018-July(2018)p. 622-626

Paper in proceeding

Minimum trap separation for acoustical levitation using phased ultrasonic transducer arrays

Proceedings of the 23rd International Congress on Acoustics,; Vol. 2019-September(2019)p. 1117-1123

Paper in proceeding

Reducing Spiraling in Transducer Array Based Acoustic Levitation

IEEE International Ultrasonics Symposium, IUS,; (2020)

Paper in proceeding

Creation of Large Quiet Zones in the Presence of Acoustical Levitation Traps

IEEE International Ultrasonics Symposium, IUS,; (2021)

Paper in proceeding

Andersson C., Acoustic Levitation of Multi-Wavelength Spherical Bodies using Transducer Arrays of Non-Specialized Geometries

Acoustic levitation is when very strong sound waves are used to make an object hover in air without any other support. For this to work, the sound waves must make very specific patterns in the space around the levitating object. One particularly powerful way to create these patterns is to use a collection of many individually controlled ultrasound loudspeakers. Different patterns can be created by modifying the sounds sent out by each of the loudspeakers, which creates forces on the levitating object in different ways. This thesis is about how to tune the loudspeakers in order to levitate the object at a desired position. The goal was partly to create design approaches which are easy to understand conceptually, while still able to reliably levitate the objects. Some new approaches for simultaneous levitation of multiple objects were developed, which is useful to enable e.g. controlled mixing of liquids in a chemical handling system or using the levitating objects as visual elements in an interactive system.

Levitation with localised tactile and audio feedback for mid-air interactions (Levitate)

European Commission (EC) (EC/H2020/737087), 2017-01-01 -- 2020-12-31.

Subject Categories

Computational Mathematics

Physical Sciences

Signal Processing



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5060





Opponent: Dr. Asier Marzo, Universidad Pública de Navarra, Spain

More information

Latest update

3/2/2022 2