Magneto-Inductive Six Degree of Freedom Smart Sensors (MiSixthSense) for Structural and Ground Health Monitoring

桥梁、水坝、堤坝和建筑物等大型民用建筑的灾难性破坏可能会导致致命、代价高昂和对环境有害的后果。然而，周围地基也可能发生坍塌，例如山体滑坡和下沉(天坑)。施工过程中的结构倒塌也给在建筑工地工作的人带来了很高的风险。迫切需要一种能够测量结构在其整个生命周期内的性能的传感技术，以及与其相关的基础和支撑该结构的周围土壤和岩石。这将有助于提供迫在眉睫的故障的早期预警，通知维修操作和优化建筑方法。目前监测结构应力和故障的黄金标准是分布式光纤传感器，它使用细光纤电缆性能的变化来测量应变等方面。然而，光纤传感器基本上连接到结构中，需要部署工作并提供入口点，削弱了结构的完整性。然而，更重要的是，光纤传感器只能测量纤维轴线上的应变，这意味着无法直接测量结构的三维形状变形。此外，在地基和周围的土壤/岩石中安装光纤传感器既耗时又昂贵，仅限于高风险项目。这个雄心勃勃的项目寻求开发一种低成本、无线、可嵌入的传感技术，可以从结构、基础和周围地面的深处测量三维结构变形，这些变形足够小，可以添加到混凝土搅拌中或注入岩石中。每个传感器不仅可以测量其位置的变化，还可以测量方向的变化，从而产生完整的六个自由度的传感器。关键是使用低频磁场，这种磁场能够以最小的信号损失穿透岩石、土壤、混凝土和水，这与目前基于高频无线电的无线技术相比是一个显著的优势，高频无线电甚至无法穿透几厘米厚的混凝土。这些厘米级、低成本的传感器与混凝土浇注混合在一起，立即形成一个自组织和治愈的通信网络。这些设备从浇注构件(例如柱子或梁)的那一刻开始监测，提供从混凝土养护过程到加载到监测裂缝和腐蚀的特定结构构件的整个生命周期的信息。当结构元素彼此相邻放置时，网络将自动延伸，形成一个更大的、合并的通信系统。传感器可以测量它们在结构中的精确位置和方向，以及这种位置和方向随时间的变化。有了许多这样的传感器，就可以感知结构元素的实际形状，以及它如何在载荷作用下弯曲或扭曲。这是目前使用任何其他分布式传感技术不可能实现的，这是低频矢量场的关键优势，在3D中同时具有幅度和方向。在结构内嵌入传感器的问题之一是在结构的寿命期间保持运行，该寿命可以是几十年。传感器使用相同的低频磁场来收集能量，这些能量要么从周围的磁场中收集，如电源布线，要么直接注入结构的金属加固件中。这项技术有可能使建筑物和大型结构真正变得智能，使用低成本、易于部署的传感器，可以从结构内部和周围的地基进行操作。这将使得能够实时监测结构在整个生命周期内潜在故障的关键指标，为即将到来的灾难提供早期预警，并可能产生挽救生命的结果。

Catastrophic failure of large civil structures like bridges, dams, embankments and buildings can result in fatal, costly and environmentally detrimental consequences. However, failures can also occcur in the surrounding groundwork, for example landslides and subsidence (sinkholes). Structural collapse during construction also poses high risk to people working on construction sites. There is a strong need for a sensing technology that is able to measure the performance of a structure over its entire lifetime, as well as its associated foundations and the surrounding soil and rock supporting the structure. This will help to provide early warning of impending failure, inform repair operations and optimize building methods.The current gold-standard for monitoring structural stress and failure are distributed fibre optic sensors, which use the change in the properties of a thin fibre-optic cable to measure aspects such as strain. However, fibre-optic sensors are essentially wired into the structure, require deployment effort and provide a point of ingress, weakening the integrity of the structure. More importantly though, fibre-optic sensors can only measure strain along the fibre axis, meaning that the three-dimensional shape deformation of the structure cannot be directly measured. Additionally, it is time-consuming and costly to install fibre-optic sensors within the foundations and surrounding soil/rock, limiting their use to high risk projects.This ambitious project seeks to develop a low-cost, wireless, embeddable sensing technology that can measure structural deformations in 3-D from deep within a structure, its foundations and surrounding ground, that are small enough to add to the concrete mix or injected into rock. Not only can each sensor measure changes in its position, it can also measure changes in orientation, yielding a full six degree of freedom sensor. Key to this is the use of low frequency magnetic fields that are able to penetrate rock, soil, concrete and water with minimal loss of signal, a marked advantage over current wireless technology based on high frequency radio that cannot penetrate even a few cm of concrete. These cm-scale, low cost sensors are mixed in with the concrete pour, instantly forming a self-organizing and healing communication network. These devices start monitoring from the moment the element (e.g. a pillar or a beam) is poured, providing information over the entire lifetime of a particular structural element, from the concrete curing process to loading to monitoring cracks and corrosion. When structural elements are placed next to each other, the network will automatically extend to form a larger, merged communication system. The sensors can measure their precise position and orientation within the structure and how this changes over time. With a number of these sensors the actual shape of the structural element and how it is bending or twisting with loads can be sensed. This is currently impossible to achieve using any other distributed sensing technology, a key advantage of low frequency vector fields, having both magnitude and direction in 3-D.One of the issues of embedding sensors within a structure is maintaining operation over the lifetime of the structure, which can be many decades. The sensors use the same low frequency magnetic fields to harvest energy, which is either collected from ambient magnetic fields, such as mains wiring, or directly injected into the metallic reinforcement of the structure. This allows for battery-free, indefinite operation.This technology has the potential to make buildings and large structures truly smart, using low cost, easy to deploy sensors that can operate from within the structure and the surrounding groundwork. This will enable real-time monitoring of key indicators of potential failure over the lifetime of the structure, providing early warning of impending disaster, with potentially life-saving results.