Organizing and Characterizing Soft Matter with Acoustic Holography

About This Grant

Non-technical Abstract Waves push and pull small objects, causing the objects to recoil and scattering the waves. This interplay causes mobile objects to reorganize themselves in any context where waves interact with matter. This program will use sound as a model wave to uncover general principles of wave-mediated self-organization in common materials such as droplets, powders and biological cells. The experimental initiative will expand on recent breakthroughs to create structured sound waves that can move objects freely in three dimensions. The project will use these structured sound fields to measure wave-mediated interactions and to discover how those interactions induce materials to self-organize. The same approach will used to develop an innovative form of acoustic imaging that can characterize physical objects while tracking their movements in three dimensions. These activities will be used to train graduate and undergraduate students and will serve as a focal point for the PI’s award-winning K-12 STEM outreach program. Real-world applications for non-contact acoustic manipulation will be patented and brought to market through the Principal Investigator’s entrepreneurial activities.   Technical Abstract This program will advance the science of wave-mediated interactions in soft and granular matter using acoustic holography as a platform both for manipulation and also for characterization. The core innovation is the development and application of a new acoustokinetic framework for acoustic forces, which builds on the team’s earlier theoretical work on photokinetic forces in holographic optical trapping. While optical holography has enabled precise manipulation of micrometer-scale colloidal particles, acoustic holography creates complementary opportunities across a much larger range of length scales and force scales. Sound’s spectral content also opens up new pathways to dynamical control that are not available with light. This program will realize these opportunities through initiatives in spectral acoustic trapping. A key scientific focus is on nonreciprocal and nonconservative interactions mediated by structured sound fields. Unlike typical pairwise interactions that are constrained by Newton’s third law, wave-mediated forces can be nonreciprocal, enabling passive particles extract energy from scattered waves to power their own collective motion. Wave-matter composite systems therefore display a form of activity that is an emergent property of their state of organization and does not require the individual particles to be inherently active. Through a combination of experiment, theory and simulation, this project will develop the statistical mechanics of emergent activity and apply it to wave-guided self-organization of hierarchically structured materials. This program also will study the waves scattered by systems of particles with the goal of extracting information from the spatial and spectral structure of the scattered wavefronts. This approach complements standard numerical reconstruction of acoustic holograms and builds on the PI’s earlier success in direct analysis of optical holograms. Direct analysis of the scattered sound field will complement acoustic manipulations and eliminate the need for conventional imaging in applications such as acoustodynamic mass determination. All these activities will address the national need for a well-trained technical workforce by providing outreach opportunities in the K-12 sector and for the general public, by providing research experience and professional development for undergraduate and graduate students, and by disseminating new knowledge and technology through publication, patenting and entrepreneurial activities. 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.