Multimodal Oscillatory Driving Forces and Precise Manipulation of Particle Motion

这个项目的目标是回答这个问题：“多模态”振荡力如何影响粒子和其他物体的运动？ 大多数先前的研究集中在“单峰”力，其可以由单个频率（例如，1 Hz）。 相反，多模态驱动力涉及多个频率的叠加（例如，1 Hz和2 Hz）。 虽然多模态振荡力更复杂，但受到多模态力的物体平均可能不会移动到任何地方，因为力本身的平均值为零。 然而，最近的实验工作表明，这种解释不一定正确。 具体地，双模式振荡电场的施加诱导颗粒优先朝向一个电极的净运动，但仅当两个频率模式是奇数和偶数的比率（例如，3 Hz和2 Hz）。 进一步的初步实验表明，净运动也观察到固体物体放置在一个平面上，使横向振动的双频模式，再次只有当模式是奇数和偶数的比例。 在两个非常不同的系统中的这些类似的观察表明，可以利用某些类型的多模态力来精确地操纵使用振荡力的物体的运动。 一系列的实验和建模研究将在三个原型系统上进行，以揭示控制净运动响应多模态场的机制。 该项目的结果将在各种技术应用中发挥作用，包括用于芯片实验室设备的粒子操纵，静电蒸发器和颗粒材料的粒子分离。基于初步观察，该项目测试了以下假设：净粒子电泳和净振动漂移都源于各自控制动量平衡的非线性驱动项中的对称性破缺，只要振荡驱动力是“非反周期的”。高速视频和粒子成像测速技术将用于精确跟踪三种不同实验系统中物体的运动：粒子电泳，带电液滴悬浮和振动固体物体。具体的实验将旨在直接测试所提出的机制产生的假设，通过系统地改变施加模式的比例，非线性电阻的大小，和驱动力的整体幅度。实验观测结果将针对每个系统的相应数值模型进行测试，为具有多模态场的非线性系统的行为提供突破性的见解。 由于非线性效应在自然界中无处不在，如果得到证实，这里提出的机制将提供基本的和广泛适用的影响，如何多模态驱动力可以用来操纵粒子motion.This奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

The goal of this project is to answer the question: how do “multimodal” oscillatory forces affect the motion of particles and other objects? Most prior research has focused on “unimodal” forces, which can be characterized by a single frequency (e.g., 1 Hz). In contrast, a multimodal driving force involves the superposition of multiple frequencies (e.g., 1 Hz and 2 Hz). Although multimodal oscillatory forces are more complicated, an object subject to a multimodal force may not move anywhere on average because the average of the force itself is zero. Recent experimental work, however, has revealed that this interpretation is not necessarily correct. Specifically, application of a dual-mode oscillatory electric field induces net motion of particles preferentially towards one electrode, but only if the two frequency modes are the ratio of odd and even numbers (e.g., 3 Hz and 2 Hz). Further preliminary experiments revealed that net motion is also observed for solid objects placed on a flat surface made to vibrate laterally with dual frequency modes, again only if the modes are the ratio of odd and even numbers. These similar observations in two very distinct systems suggest that certain types of multimodal forces can be exploited to precisely manipulate the motion of objects using oscillatory forces. A series of experiments and modeling studies will be conducted on three prototype systems to uncover the mechanism that governs the net motion in response to a multimodal field. Results from the project will be useful in a variety of technological applications, including particle manipulation for lab-on-a-chip devices, electrostatic dehydrators, and particle separations for granular materials.Based on the preliminary observations, this project tests the hypothesis that the net particle electrophoresis and the net vibratory drift both stem from symmetry breaking in the nonlinear driving terms of the respective governing momentum balances, provided the oscillatory driving force is “non-antiperiodic.” High-speed video and particle imaging velocimetry will be used to precisely track the motion of objects in three different experimental systems: particle electrophoresis, charged droplet levitation, and vibrated solid objects. Specific experiments will be aimed at directly testing the hypotheses generated from the proposed mechanism, by systematically varying the ratio of imposed modes, the magnitude of the nonlinear resistances, and the overall amplitude of the driving force. The experimental observations will be tested against corresponding numerical models specific to each system, providing groundbreaking insight on the behavior of nonlinear systems with multimodal fields. Because nonlinear effects are ubiquitous in nature, if corroborated the mechanism proposed here will provide fundamental and broadly applicable impact on how multimodal driving forces can be used to manipulate particle motion.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.