Controlling Acoustic Metamaterials with Magnetic Resonances: The Best of Both Worlds

我们周围的世界充满了从智能手机到飞机的各种设备。此外，我们的文明在很大程度上是由这些设备能够提供的功能来定义的。然而，当建造甚至构思一种设备时，工程师们在自然界或工业过程中可用材料的性质设置的限制下进行操作。这些材料属性和物理定律一起限制了该设备可能具有的功能。通过调整结构化介质中波激发的光谱，可以创建全新的动力学特性和先进的功能--所谓的超材料。最近证明和提议的这类人造材料的实际应用包括例如光纤(操纵光)、激光(操纵电子)、噪音吸收和热导引(操纵声波)。声表面波(SAW)的特性已被研究了一百多年，但正是1965年电声“叉指”换能器的发明，使声表面波设备得以开发出用于广泛和多样化的功能，包括移动电话中的模拟信号处理和传感。近年来，超材料的研究领域已经扩展到声波，有望提供一种控制和操纵声表面波传播的方法。这些所谓的声学(或声学)超材料既可以扩展现有设备的功能，又可以支撑全新的设备概念。然而，到目前为止，几乎没有建议的方法来设计可动态重新配置和调整的声学超材料，限制了它们在应用中的使用。与磁性材料的集成为实现声学超材料的非易失性调谐提供了一条令人兴奋的途径，磁性材料以其存储信息的能力而闻名，例如在磁性硬盘驱动器中。我们的项目旨在开发一种新型的磁声超材料，在这种材料中，其构建块(“元原子”)的作用是通过磁声谐振器来发挥的。这种超材料将为旨在控制表面声波传播的结构增加精致的磁场可调性，在基础科学和技术方面都带来了诱人的机会。从技术上讲，磁性固有的存储现象将显著节省非易失性磁声数据和信号处理设备的能源。例如，它们可以立即启动，并可以更容易地与现有的磁性数据存储设备集成。从基础科学的角度来看，我们项目中开发的磁声超材料将成为研究非均匀和非平稳介质中波传播物理的一个很好的试验台。该合作研究方案将由谢菲尔德大学材料科学与工程系和埃克塞特大学工程、数学和物理学院联合开展。谢菲尔德团队将为该项目贡献他们在磁致伸缩和多铁材料以及纳米技术方面的国际领先专业知识，而埃克塞特团队将在声学和磁性超材料和器件的动态表征和理论建模方面贡献他们世界领先的专业知识。通过携手合作，两个团队将确保英国在声学和磁学研究和技术方面保持领先地位，特别是开辟磁声超材料这一新的跨学科领域。

The world around us is full of devices, ranging from smartphones to airplanes. Moreover, our civilization is defined to a great degree by the functionalities that those devices can deliver. However, when constructing and indeed even conceiving a device, engineers operate within constraints set by properties of materials available, either in nature or via industrial processes. These material properties together with the laws of physics then restrict functionalities that the device may have. Radically new dynamical properties and advanced functionalities can be created by tailor-tuning the spectra of wave excitations in structured media - so-called metamaterials. Recently demonstrated and proposed practical applications of such artificial materials include e.g. optical fibres (manipulating light), lasers (manipulating electrons), and noise absorption and heat steering (manipulating acoustic waves). The properties of 'surface acoustic waves' (SAWs) have been investigated for over one hundred years, but it was the invention of electro-acoustic "interdigital" transducers in 1965 that enabled surface acoustic wave devices to be developed for a wide and diverse range of functions, including analogue signal processing in mobile phones and sensing. Recently, the field of metamaterials research has expanded to acoustic waves, promising a method to control and manipulate propagation of surface acoustic waves. These so called acoustic (or phononic) metamaterials could both extend the functionality of existing devices and underpin totally new device concepts. However, to date there have been very few suggested ways of designing acoustic metamaterials that can be dynamically reconfigured and tuned, limiting their use in applications. Integration with magnetic materials, well known for their ability to store information e.g. in magnetic hard disk drives, offers an exciting route for achieving non-volatile tuning of acoustic metamaterials. Our project aims to develop a new class of magneto-acoustic metamaterials in which the role of their building blocks ("meta-atoms") is played by magneto-acoustic resonators. Such metamaterials will add exquisite magnetic field tunability to structures aimed to control the propagation of surface acoustic waves, opening intriguing opportunities both in fundamental science and technology. Technologically, the memory phenomenon inherent to magnetism will enable significant energy savings in non-volatile magneto-acoustic data and signal processing devices. For instance, they would be instantly bootable and could be more easily integrated with the existing magnetic data storage devices. From the point of view of fundamental science, the magneto-acoustic metamaterials developed in our project will serve as an excellent test bed for studying the physics of wave propagation in non-uniform and non-stationary media. The collaborative research programme will be conducted jointly by the Department of Materials Science and Engineering at the University of Sheffield and the College of Engineering, Mathematics and Physical Sciences at the University of Exeter. The Sheffield team will contribute to the project their internationally leading expertise in magnetostrictive and multiferroic materials and nanotechnology, while the Exeter team will contribute their world leading expertise in dynamical characterization and theoretical modelling of acoustic and magnetic metamaterials and devices. By joining their forces together, the two teams will ensure that UK will remain at the forefront of the acoustics and magnetism research and technology, in particular opening the new interdisciplinary field of magneto-acoustic metamaterials.