ACTIVE METAMATERIALS FOR CONTROL OF SOUND AND VIBRATION - A PRACTICAL SOLUTION TO CREATING NEGATIVE REFRACTION

声音和振动对整个社会和行业的影响是广泛和多样的。在某些情况下，它们是这种情况所固有的，例如音乐会和剧院。然而，它们往往是一种滋扰，例如来自车辆(内部和外部)的噪音、响亮的音乐和能源产生。在某些情况下，它们具有战略或健康重要性，例如声纳成像。声音和振动也可以被利用来完成重要的功能，如超声波成像。通过能源收集技术，它们也是一种能源，潜在地可以提高设备的效率。因此，声音和振动的控制在许多应用中都是非常重要的。传统材料的物理性能受其化学和物理结构的限制。最近超材料的出现拓宽了可能的物理性质的范围。这使得压力波(即声音和振动的传播)可以比常规方式更自由地进行控制。这些材料的新应用包括声学隐形斗篷和亚波长成像设备。该项目的主要目标是开发超材料设计，以解决当前超材料的两个重大限制。当前超材料的新特性仅限于制造时固定的窄频带。这严重限制了它们的应用。该项目旨在通过在材料中嵌入活性元素来改善这种响应性，反应可以控制和适应。这导致材料具有显著增强的灵活性，因此更加适用。大多数目前的超材料需要流体或气体作为其结构中的关键成分之一。这严重限制了它们在许多问题上的应用，例如那些嵌入运动流体中的问题。主动方法提供了使用控制系统模拟超材料关键组件的能力。通过从材料中固有地去除这些组分，消除了需要背景流体的限制条件。因此，这种积极的方法有可能创造出一种完全固体的超材料。

The effects of sound and vibration throughout society and industry are broad and varied. In some cases they are inherent to the situation, for example music concerts and the theatre. However, they are often a nuisance, for example noise from vehicles (internally and externally), loud music and energy generation. In some cases they have strategic or health importance, such as with sonar imaging. Sound and vibration can also be harnessed to accomplish important functions, such as ultrasound imaging. They are also a source of energy through energy harvesting techniques, potentially allowing the efficiency of devices to be improved. Therefore the control of sound and vibration is important in many applications. The physical properties of conventional materials are limited by their chemical and physical structure. The recent emergence of metamaterials broadens the range of possible physical properties. This allows pressure waves (i.e. the transmission of sound and vibration) to be controlled with much more freedom than is conventionally possible. Novel applications of these materials include an acoustic invisibility cloak and sub-wavelength imaging devices. The key aims of the project are to develop metamaterial designs which solve two of the significant limitations of current metamaterials. The novel characteristics of current metamaterials are limited to a narrow frequency band fixed at manufacture. This severely limits their application. The project aims to improve this repsonse by embedding active elements in the material the response can be controlled and adapted. This leads to materials which have a significantly enhanced flexibility and as a consequence are much more applicable. Most current metamaterials require a fluid or gas as one of the key components in their construction. This severely limits their application to many problems, for example those which are embedded in a moving fluid. The active approach provides the ability to emulate key components of metamaterials using a control system. By intrinsically removing these components from the material, the limiting condition of requiring a background fluid is removed. The active approach thus leads to the possibility of creating a completely solid metamaterial.