Collaborative Research: Mechanics of Granular Acoustic Meta-materials with Engineered Particles and Packings

声学超材料是一种能够控制声波的工程材料。粒状声学超材料是由周期性和无序排列的粒子构成的。该项目旨在从根本上了解颗粒填料的声学和力学响应，其中颗粒具有特定的工程特性。这些材料表现出一个关键的声学特性，即声带隙。带隙阻止某些频率的声音传播。具有声波带隙的超材料可用于隔振、声波通信、声学超级透镜、声学二极管和声学隐形装置。该项目将结合工程颗粒形状和材料与特别设计的颗粒空间安排，以便对材料的声学特性进行详细控制。该项目将通过合作院校之间的伙伴关系，每年让几名本科生参与研究，其中一所院校为少数民族服务。外展活动包括关于颗粒介质的年度系列讲座。将开发供国际理论物理中心使用的教学模块，以便向发展中国家的研究生教授基本的计算研究技能。在颗粒介质中，材料的离散性质允许在颗粒和网络尺度上进行优化。此外，颗粒材料中的声速取决于颗粒-颗粒接触面积变化引起的围压。本研究的目的是了解工程颗粒超材料的声学响应，并利用其独特的特性来调节机械响应。围压的变化将被用来积极地控制颗粒状超材料的声学特性。新颖的直接可视化技术和单个粒子运动和力的离散单元模拟将实现预测和测量机械响应之间的密切反馈。该团队将使用3D打印和其他制造技术来设计具有不同弹性特性、表面处理和复杂形状的颗粒。在实验和模拟中，该团队将使用直接组装方法在二维和三维上构建无序和结晶颗粒填料。该团队还将探索边界条件对颗粒填料内应力网络的影响，目标是调整它们的声学特性。从直接测量中获得的真实粒子间力定律将被应用到机械响应的离散单元模拟中，并与实验结果进行比较。这些目标的实现将为粒状超材料的声学特性提供前所未有的见解。

Acoustic meta-materials are engineered materials enabling the control of sound waves. Granular acoustic meta-materials are constructs of particles in periodic and disordered arrangements. This project seeks a fundamental understanding of the acoustic and mechanical response of granular packings where the particles possess specific engineered properties. These materials exhibit a key acoustical property, that is acoustic band gaps. Band gaps prevent sound of certain frequencies to propagate. Meta-materials exhibiting acoustic band gaps have applications for vibration isolation, sound wave communication, acoustic super-lenses, acoustic diodes, and acoustic cloaking devices. This project will combine engineered particle shapes and materials with specially designed spatial arrangements of the particles to allow detailed control over the acoustic properties of the material. This project will involve several undergraduates in research each year through partnerships between the collaborating institutions, one of which is minority-serving. Outreach initiatives include an annual lecture series on granular media. Teaching modules for use by the International Centre for Theoretical Physics will be developed for teaching basic computational research skills to graduate students from developing countries. In granular media, the discrete nature of the material allows optimization on both the grain and network scales. Also, the speed of sound in granular materials depends on the confining pressure due to changes in the particle-particle contact area. The objective of this research is to gain understanding of the acoustic response of engineered granular meta-materials, and to exploit their unique features to tune the mechanical response. Variations of the confining pressure will be employed to actively control the acoustic properties of granular meta-materials. Novel direct visualization techniques and discrete element simulations of individual particle motions and forces will enable close feedback between the predicted and measured mechanical response. The team will use 3D printing and other fabrication techniques to engineer particles with varied elastic properties, surface treatments, and complex shapes. In both experiments and simulations, the team will construct disordered and crystalline granular packings in both two- and three-dimensions using direct assembly methods. The team will also explore the effects of boundary conditions on the internal stress networks of granular packings with the goal of tuning their acoustic properties. Realistic inter-particle force laws obtained from direct measurements will be implemented into discrete element simulations of the mechanical response and compared to the results from experiments. Attainment of these goals will provide unprecedented insight into the acoustic properties of granular meta-materials.