Analyzing and Organizing Soft Matter with Acoustic Holography

Non-Technical Description

Sound waves can exert forces that are large enough to levitate objects and move them in three dimensions. Acoustically levitated objects also influence the sound field, scattering sound waves and redirecting their forces. Scattered waves mediate interactions among the objects that cause them to organize themselves into dynamic three-dimensional assemblies.

These wave-matter composite systems constitute a largely unexplored state of matter with extraordinary and potentially useful properties. The program on “Analyzing and Organizing Soft Matter with Acoustic Holography” is dedicated to developing the fundamental principles and practical techniques needed to control acoustic forces, elucidating the physics of wave-matter composite systems, and advancing a new paradigm for materials characterization based on quantitative analysis of scattered sound.

This experimental program is motivated by the Principal Investigator’s recent breakthrough in the theory of wave-matter interactions that explains how to design and project sound waves that move matter. Principles emerging from these studies are both general and fundamental. They have practical applications, moreover, in areas as diverse as non-contact manufacturing and 3D displays.

Technology transfer for these applications already is under way, The science of acoustic manipulation through acoustic holography lends itself to effective STEM outreach in the K-12 sector. It also provides a wealth of accessible research projects for undergraduates, thereby helping to build the pipeline for diversity and inclusion in STEM research.

Technical Description

The recently-introduced acoustokinetic framework explains how the amplitude and phase profiles of a sound wave give rise to forces and torques on insonated objects. An analogous approach has proved extraordinarily fruitful for the field of optical micromanipulation by providing design principles for optical holograms that implement desired force landscapes.

Translating principles of optical manipulation into experimental realizations has benefitted from highly advanced technology for shaping the wavefronts of light. No such technology currently exists for sound. Realizing the benefits of acoustokinetics therefore requires a novel approach to computational holography.

This program bridges this technological gap by introducing spectral holography as a new paradigm for computational holography. Spectral holography is an approach to wavefront sculpting that relies on controlling the wave’s amplitude and phase at a small number of discrete emitters but over a wide range of frequencies. Whereas standard monochromatic holograms create static time-averaged force fields, spectral holograms can have dynamic content over a wide range of time and length scales.

The time-dependent behavior of individual objects and many-body systems immersed in such multi-scale landscapes represent an emerging area of research. Anticipated outcomes from studying these systems include advances in the fundamental science of classical wave-matter interactions and discovery of new principles of self-organization in soft-matter and granular materials.

The critical role of inertia in sound-mediated self-organization constitutes a particularly promising frontier for fundamental discoveries such as the remarkable dynamical behavior of wave-driven oscillators. This program also provides exciting opportunities for technology transfer to industry, including contact-free materials transport for manufacturing, rapid 3D scanning for volumetric displays and large-scale remote materials characterization.

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.