Acoustic Forces and Active Fluctuations in Levitated Granular Matter

Non-Technical Description:

A better fundamental understanding how small particles agglomerate is critical to a wide range of processes, from the very early stages of planet formation in solar nebula and interstellar media, to the nucleation and growth of small ice particles in the atmosphere, to dusty plasmas and aerosols. To address this, the project introduces a new research platform, whereby ultrasound is used to freely levitate small particles in air and manipulate their assembly into larger structures.

The activity provides training and mentoring for a research team that includes undergraduate and graduate students as well as a postdoctoral scholar. Working with artists, the project team will furthermore explore unique opportunities for using acoustic levitation in interactive performances and exhibits to increase the public engagement with science and scientists.

Technical Description:

One key experimental challenge in granular matter research has been to gain direct access to the particle dynamics without the mitigating influence of enclosing walls or other surfaces. A second experimental challenge has been to introduce attractive forces that are tunable. The project addresses both challenges by acoustically levitating the particles.

Strong sound fields can balance gravity and, at the same time, multiple sound scattering between levitated solid particles creates tunable attractive forces. This makes it possible to form freely floating structures in which large numbers of constituent particles are linked by acoustic bonds. Tightly coupling experiments with numerical simulations, a first effort is directed at designing force fields, including fields with non-conservative components that introduce torque and rotation.

A second effort develops strategies for assembling levitating structures comprised of large numbers of particles. Together, these two activities aim at introducing acoustically levitated granular matter as a powerful new research platform.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.