Transparent Transmitters and Programmable Metasurfaces for Transport and Beyond-5G (TRANSMETA)

随着通信朝着更高频率的更高数据速率发展，与窗户相比，混凝土结构和建筑物将显著降低电磁信号强度。TRANSMETA的总体愿景是创建透明的智能反射元表面，可以放置在建筑物或车辆的窗户上，并将来自基站的入射电磁波智能地直接反射到用户（内部或外部），以提高信号接收质量。超表面还可以过滤某些频率，改变极化，或减少雷达反射。实现这一点的挑战是：1.对于透明导体，在层厚度和频率响应方面，在光学透明度和导电性之间存在需要量化的折衷。如何将这些材料与传统的不透明电子器件进行电连接和物理连接也是一个实际的挑战。TRANSMETA将通过研究两种导体方法来解决这个问题：i）亚微米尺度的金属网格，其中的线条太小，人眼无法看到; ii）如果结果不符合要求，还将研究使用氧化铟锡的补充技术。为了测试它们的性能，透明天线和静态超表面，如频率选择表面，将被制造和测量。必须根据材料特性设计新的超颖表面。TRANSMETA将通过使用商业电磁软件进行广泛的研究来解决这个问题，这些软件的输入来自早期的测量。将研究超颖表面后部的地平面的效果，并且我们将致力于最大化光学透明度。作为反射超颖表面的替代方案，还将在不需要后接地层的地方设计透射表面。必须研究制造这些超颖表面的实际挑战。TRANSMETA最初将制造静态（非智能）超颖表面，这些超颖表面可以反射两个固定位置之间的信号，并在拉夫堡大学的消声室中通过阻断直接信号进行测试。如果建筑物中存在已知的通信死区，这将是适用的，随着我们向更高的频率发展，通信死区将变得越来越普遍。当然，光学透明度对于这些新的超颖表面并不总是必不可少的，但它增加了应用范围。4.为了使超颖表面智能化，必须将可重构性集成到系统中。TRANSMETA将通过两种技术来解决这一问题：i）二氧化钒，当施加直流电时，其属性从绝缘体变为导体，ii）PIN二极管。将这些技术整合到系统中，同时最大限度地提高透明度，这是一个挑战。直流偏置线可以做成透明的，但是它们的最佳位置和方向对整体性能至关重要.实现智能化的另一个挑战是能够感知发射机和用户的位置，以便将信号反射到正确的方向。TRANSMETA将开发一种传感系统，该系统使用来自基站和用户的导频信号，然后应用信号处理来检索方向。现场可编程门阵列（FPGA）将相应地控制元表面行为。最后，所有这些元素将集成在一起，创建元表面演示器，并在我们12个工业项目合作伙伴的支持下在真实环境中进行测试。成功完成该项目的影响将是提高超5G通信系统的能力。利用透明导体将使这些智能元表面能够用于车辆和建筑物窗户。

As communications move towards higher frequencies for higher data rates, concrete structures and buildings will significantly reduce the electromagnetic signal strength compared to windows. The overarching vision of TRANSMETA is to create transparent intelligent reflecting metasurfaces that could be placed on the windows of buildings or vehicles, and which would intelligently reflect the incoming electromagnetic wave from a base station directly to the user (either inside or outside) to improve signal reception quality. Metasurfaces can also filter certain frequencies, change the polarisation, or reduce the reflections from radar.The challenges to achieving this are: 1. For transparent conductors there is a trade-off between optical transparency and electrical conductivity in terms of layer thickness and frequency response which needs to be quantified. There are also practical challenges in how to connect these materials electrically and physically to the conventional opaque electronics.TRANSMETA will address this by investigating two approaches for the conductors: i) metallic meshes on the sub-micron scale where the lines are too small for the human eye to see; ii), if the results are not as required, a complementary technique using indium tin oxide will also be investigated. To test their performance, transparent antennas and static metasurfaces, such as frequency selective surfaces, will be fabricated and measured.2. Novel metasurfaces must be designed based on the material properties. TRANSMETA will address this by carrying out extensive studies using commercial electromagnetic software with input from the earlier measurements. The effect of the ground plane at the rear of the metasurface will be investigated and we will aim to maximise the optical transparency. As an alternative to the reflecting metasurfaces, transmitting surfaces will also be designed where no rear ground plane is required.3. The practical challenges of fabricating these metasurfaces must be investigated.TRANSMETA will initially make static (non-intelligent) metasurfaces which can reflect the signal between two fixed positions, tested by blocking the direct signal in the anechoic chambers at Loughborough University. This will be applicable if there were known communication dead zones in buildings which will become increasingly common as we move towards higher frequencies. Of course, optical transparency is not always essential for these novel metasurfaces, but it increases the scope of applications.4. To make the metasurface intelligent, reconfigurability must be integrated into the system.TRANSMETA will address this with two techniques: i) vanadium dioxide where the properties change from being an insulator to a conductor when a direct current is applied, ii) PIN diodes. There are challenges in integrating these techniques into the system while also maximising the transparency. The direct current bias lines can be made transparent, but their optimum position and orientation are critical to the overall performance.5. A further challenge in achieving the intelligence is being able to sense where the transmitter and user are located in order to reflect the signal in the correct direction.TRANSMETA will develop a sensing system that uses the pilot signals from the base station and user and then applies signal processing to retrieve the directions. A field-programmable gate array (FPGA) will control the metasurface behaviour accordingly.Finally, all these elements will be integrated together to create metasurface demonstrators which will be tested in real-world environments with support from our 12 industrial Project Partners.The impact of successfully completing this project will be improved capability for beyond-5G communication systems. Utilising transparent conductors will enable these intelligent metasurfaces to be employed in vehicles and building windows.