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

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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.