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。颗粒声学超材料是由周期性和无序排列的粒子构成的。该项目寻求从根本上了解颗粒填料的声学和机械响应，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，即声学带隙。带隙阻止某些频率的声音传播。具有声学带隙的超材料在隔振、声波通信、声学超透镜、声学二极管和声学隐身设备等方面都有应用。该项目将工程设计的颗粒形状和材料与特殊设计的颗粒空间布置相结合，以允许对材料的声学特性进行详细控制。该项目将通过合作机构之间的合作伙伴关系，每年让几名本科生参与研究，其中之一是为少数群体服务。外联举措包括每年举办一次关于颗粒状媒体的系列讲座。将开发供国际理论物理中心使用的教学单元，向发展中国家的研究生讲授基本的计算研究技能。在颗粒状介质中，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-颗粒接触区域的变化引起的围压。这项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整机械响应。将利用围压的变化来主动控制颗粒超材料的声学特性。新的直接可视化技术和对单个粒子运动和力的离散元模拟将使预测的机械响应和测量的机械响应之间能够实现密切的反馈。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属性、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中构建无序和结晶的颗粒状填料。该团队还将探索边界条件对颗粒填料内部应力网络的影响，目的是调整其声学特性。通过直接测量得到的真实粒间力定律将被实施到机械响应的离散元模拟中，并与实验结果进行比较。这些目标的实现将为颗粒超材料的声学特性提供前所未有的洞察力。

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.