Ultrasound

Engineering

Radiation pressure

Optical tweezers

Radiation

Acoustic radiation

Vortex

Computer science

Acoustics

Acoustic wave

Geology

Oceanography

Physics

Optics

Particle (ecology)

Spurious relationship

Topology (electrical circuits)

Acoustic radiation force

Mechanics

Tweezers

Machine learning

Electrical engineering

Annual Review of Fluid Mechanics

Acoustic tweezers powerfully enable the contactless collective or selective manipulation of microscopic objects. Trapping is achieved without pretagging, with forces several orders of magnitude larger than optical tweezers at the same input power, limiting spurious heating and enabling damage-free displacement and orientation of biological samples. In addition, the availability of acoustical coherent sources from kilo- to gigahertz frequencies enables the manipulation of a wide spectrum of particle sizes. After an introduction of the key physical concepts behind fluid and particle manipulation with acoustic radiation pressure and acoustic streaming, we highlight the emergence of specific wave fields, called acoustical vortices, as a means to manipulate particles selectively and in three dimensions with one-sided tweezers. These acoustic vortices can also be used to generate hydrodynamic vortices whose topology is controlled by the topology of the wave. We conclude with an outlook on the field's future directions.

Acoustic Tweezers for Particle and Fluid Micromanipulation