NSF: CCSS: Precision Positioning for Structural Monitoring by Embedded RFID Tags

结构完整性的准确无损监测对于土木工程研究至关重要，并且在健康的基础设施和公共福利方面具有很高的国家利益。桥梁、大坝倒塌等灾害不仅在灾害修复和救灾方面，而且在预防性维护预算和公众恐慌因素方面，都给社会带来了非常高的社会成本。以前的无损低应变桩完整性检测方法，如核辐射，超声波，声波，雷达，光纤和加速度计可以检索标记位移和材料的变化，但都有适用性的限制，在其各自的长期发展历史。迄今为止，结构完整性保证将从一种方便、非侵入性、可靠和具有成本效益的方法中获益匪浅，该方法可以广泛部署，用于结构整个寿命期的长期监测。本计画提出一种以被动式射频辨识标签（RFID）为基础的超高精度定位系统，可直接量测特定结构点因蠕变与变形所产生的内部位移。这些标签可以嵌入到新的桩和建筑材料中，为结构完整性测试提供一种新的替代方案，取代或补充现有的方法。由于无源标签不需要维护或充电，因此其寿命与结构一样长。 完整性测试可以通过将定制RFID阅读器放置在指定的外部点来简单地执行，以报告埋置标签的精确位置或振动。适当地选择感测无线电频率，使得其不会太高而导致不良的材料穿透，或者不会太低而导致不良的测距精度。这个拟议的结构“雷达”使以前看不见的结构问题，并激发学生的工程奇迹，将对社会产生积极影响的兴趣。 本计画旨在建立一种新的高精度射频测距定位方法，以进行结构完整性的非侵入性长期监测。超高频信号可以深入建筑材料，以定位埋在结构中的特定标记标签，空间精度约为20微米，时间分辨率低于毫秒。该方法基于无源谐波RFID平台和碰撞信号的后向散射二次谐波，以最小化自干扰的相位噪声。剩余的相位噪声通过频率策略、稳定参考、移动平均和零点校准进一步减轻。研究任务包括射频前端改进、系统级改进和土木结构演示，将在现实场景中验证新的非侵入式传感方案，并具有目标性能和可靠性。在射频前端将采用多个非相干频率，以同时提高操作距离和空间分辨率。通过随机化天线和人工波束形成可以进一步减轻多径变化容限。三维定位中的几何精度衰减将通过天线放置和到达角评估来减轻，使得系统可以实现5微米精度和每秒100万个样本的三维定位。该系统将在混凝土混合物和承重梁的现实土木结构中进行实验证明。通过使用已知标签分离的多标签方法，将研究由于温度和金属腐蚀感测引起的介电常数变化。如果成功的话，由此产生的高精度应变传感器可以带来一种具有成本效益的非侵入性方法，将大大提高结构完整性监测。精确定位方法还可以应用于精密仪器、基础工程和人机界面等许多其他应用。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Accurate noninvasive monitoring of structural integrity is critical for civil engineering research and has a high national interest on healthy infrastructure and public welfare. Disasters such as the collapses of bridges and dams have very high social cost for the society not only for the disaster repair and relief, but also in terms of preventive maintenance budget and public panic factors. Previous nondestructive low-strain pile integrity testing methods such as nuclear radiation, ultrasound, sonic, radar, optical fibers and accelerometers can retrieve marker displacement and material changes, but all have applicability limitations in each of their long history of development. To date, structural integrity assurance would take great benefits from a convenient, non-invasive, reliable and cost-effective method that can be broadly deployed for long-term monitoring throughout the lifetime of the structure. In this project, a new marker-based ultra-high precision positioning system is envisioned, which employs the passive radio-frequency identification (RFID) tags to directly measure internal displacement of specific structural points caused by creep and deformation. These tags can be embedded in new piles and building materials to provide a novel alternative to structural integrity testing, replacing or complementing existing methods. As the passive tag never needs maintenance or recharging, it can have a lifetime as long as the structure. Integrity testing can be simply executed by placing the custom RFID reader at designated external points to report the precise location or vibration of the buried tags. The sensing radio frequency is selected properly so that it is not too high that would result in poor material penetration or too low that would result in poor ranging precision. This proposed structural "radar" enables the seeing of the previously unseen structural concerns and stimulates students' interest of engineering wonders that will have positive impacts to society. This project aims to establish a new precision radio frequency (RF) ranging and locating method for noninvasive long-term structural integrity monitoring. The ultra-high frequency signal can penetrate deep into the building materials to locate specific marker tags buried in the structure with spatial accuracy around 20 microns and temporal resolutions below millisecond. The method is based on the passive harmonic RFID platform and backscattered 2nd harmonic of the impinging signal to minimize the phase noise from self-jamming. The remaining phase noises were further mitigated by frequency strategy, stable reference, moving average, and zero-point calibration. The research tasks include RF frontend improvement, system-level improvement, and civil structure demonstration, which will bring forth verified demonstration of the new noninvasive sensing scheme in realistic scenarios with the targeted performance and reliability. Multiple incoherent frequencies will be employed in RF frontend to simultaneously improve both operational distance and the spatial resolution. Multi-path variation tolerance can be further mitigated by randomizing antennas and artificial beamforming. Geometrical dilution of precision in 3D locating will be mitigated by antenna placement and evaluation of angle of arrival, so that the system can achieve 3D locating with 5-micron accuracy and 1 million samples per second. The system will be experimentally demonstrated in realistic civil structures of concrete mixes and weight-bearing beams. By using multi-tag method with known tag separation, permittivity change due to temperature and metal corrosion sensing will be investigated. If successful, the resulting high-precision strain sensor can bring forth a cost-effective noninvasive method that will greatly improve the structural integrity monitoring. The precision locating method can also be applied to many other applications in precision instrument, foundation engineering, and human-machine interface.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.