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

桥梁、水坝、堤防和建筑物等大型土木结构的灾难性破坏可能导致致命的、昂贵的和对环境有害的后果。然而，周围的地基也可能发生故障，例如山体滑坡和下沉（天坑）。建筑施工过程中的结构倒塌也对在建筑工地工作的人员构成了很高的风险。迫切需要一种传感技术，能够测量结构在其整个生命周期内的性能，以及其相关的基础和周围的土壤和岩石支撑结构。这将有助于提供即将发生故障的早期预警，通知维修操作和优化建造方法。目前监测结构应力和破坏的黄金标准是分布式光纤传感器，它利用细光纤电缆特性的变化来测量应变等方面。然而，光纤传感器本质上是连接到结构中，需要部署工作并提供一个入口点，从而削弱了结构的完整性。更重要的是，光纤传感器只能测量沿纤维轴的应变，这意味着不能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，限制了它们在高风险项目中的应用。这个雄心勃勃的项目旨在开发一种低成本、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，可以添加到混凝土混合物中或注入岩石中。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，从而产生一个完整的六自由度传感器。其中的关键是使用低频磁场，它能够穿透岩石、土壤、混凝土和水，而信号损失最小，这是目前基于高频无线电的无线技术的一个显著优势，因为高频无线电甚至不能穿透几厘米的混凝土。这些厘米级、低成本的传感器与混凝土混合在一起，立即形成一个自组织和愈合的通信网络。这些设备从构件（如柱或梁）浇筑的那一刻开始监测，提供特定结构构件整个生命周期的信息，从混凝土养护过程到加载，再到监测裂缝和腐蚀。当结构元素彼此相邻放置时，网络将自动扩展，形成一个更大的合并通信系统。传感器可以测量它们在结构中的精确位置和方向，以及它们如何随时间变化。有了许多这样的传感器，结构元件的实际形状以及它是如何弯曲或扭曲与负载可以被感知。这是目前使用任何其他分布式传感技术都无法实现的，这是低频矢量场的一个关键优势，同时具有3-D的幅度和方向。在结构中嵌入传感器的问题之一是在结构的整个生命周期内保持运行，这可能是几十年。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，比如电源线路，要么直接注入到结构的金属加固中。这允许无电池，无限期操作。这项技术有潜力使建筑和大型结构真正智能，使用低成本，易于部署的传感器，可以从结构内部和周围的基础工作。这将能够实时监测结构生命周期内潜在故障的关键指标，为即将发生的灾难提供早期预警，从而可能挽救生命。

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.