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工业的影响是广泛而多样的。在某些情况下，它们是情况所固有的，例如音乐会和剧院。然而，它们通常是令人讨厌的，例如来自车辆（内部和外部）的噪音、嘈杂的音乐和能量产生。在某些情况下，它们具有战略或健康重要性，例如声纳成像。声音和振动也可以用来完成重要的功能，如超声成像。通过能量收集技术，它们也是一种能量来源，有可能提高设备的效率。因此，声音和振动的控制在许多应用中是重要的。传统材料的物理性能受到其化学和物理结构的限制。最近出现的超材料拓宽了可能的物理性质的范围。这允许以比常规可能的自由度大得多的自由度来控制压力波（即，声音和振动的传输）。这些材料的新应用包括声学隐身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，解决当前超材料的两个重大局限性。目前的超材料的新特性仅限于制造时固定的窄频带。这严重限制了其应用。该项目旨在通过在材料中嵌入活性元素来改善这种反应，从而可以控制和适应这种反应。这导致具有显著增强的柔性的材料，并且因此更加适用。目前大多数超材料都需要流体或气体作为其结构的关键成分之一。这严重限制了它们在许多问题中的应用，例如嵌入运动流体中的问题。主动方法提供了使用控制系统来仿真超材料的关键部件的能力。通过从材料中固有地去除这些组分，去除了需要背景流体的限制条件。因此，主动方法导致创建完全固体超材料的可能性。

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.