Acoustic Forces and Active Fluctuations in Levitated Granular Matter

非技术描述：更好地从根本上理解小颗粒如何凝聚对于广泛的过程至关重要，从太阳星云和星际介质中行星形成的早期阶段，到大气中小冰颗粒的成核和生长，再到尘埃等离子体和气溶胶。为了解决这个问题，该项目引入了一个新的研究平台，利用超声波使空气中的小颗粒自由悬浮，并将它们组装成更大的结构。该活动为包括本科生和研究生以及博士后学者在内的研究团队提供培训和指导。项目团队将与艺术家合作，进一步探索在互动表演和展览中使用声悬浮的独特机会，以增加公众对科学和科学家的参与。颗粒物质研究中的一个关键实验挑战是在没有围墙或其他表面的缓解影响的情况下直接获得粒子动力学。第二个实验挑战是引入可调的吸引力。该项目通过声学悬浮粒子来解决这两个挑战。强声场可以平衡重力，同时，悬浮固体颗粒之间的多重声音散射产生可调的吸引力。这使得可以形成自由浮动的结构，其中大量的组成颗粒通过声学键连接。紧耦合实验与数值模拟，第一次努力是针对设计力场，包括领域的非保守组件，引入扭矩和旋转。第二项工作是开发组装由大量粒子组成的悬浮结构的策略。这两项活动旨在将声悬浮颗粒物质作为一个强大的新研究平台。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.