Dr. Jian Li Profile

Dr. Jian Li

Professor at The Univ of Kansas

SPIE Involvement:

Conference Program Committee | Author

Area of Expertise:

Structural Health Monitoring , Earthquake Engineering , Wireless Smart Sensor Networks

Websites:

Personal Website

Publications (25)

Proceedings Article | 9 May 2024 Presentation + Paper

Performance evaluation of flexible capacitive sensors on non-uniform surfaces

Emmanuel Ogunniyi, Han Liu, John White, Austin R. Downey, Simon Laflamme, Jian Li, Caroline Bennett, William Collins, Hongki Jo, Paul Ziehl

Proceedings Volume 12949, 1294916 (2024) https://doi.org/10.1117/12.3010959

KEYWORDS: Sensors, Surface finishing, Signal to noise ratio, Transducers, Capacitors, Structural health monitoring, Structural monitoring, Capacitance

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The use of strain gauges is foundational to structural health monitoring, allowing infrastructure to continuously observe strain, infer stress, and potentially detect fatigue/fracture cracks. However, traditional strain gauges have drawbacks. In addition to being costly, a single-element strain gauge will only detect strain in a single direction and must be mounted on smooth surfaces to ensure good adhesion. Soft Elastomeric Capacitors (SECs) have been proposed as a low-cost alternative to traditional strain gauges while allowing for a broader range of applications. They are flexible and can be modeled with different dimensions based on the monitored structure. Each SEC consists of three layers; the two outer layers act as electrodes and are made of a styrene-ethylene-butylene-styrene polymer in a matrix with carbon black. The inner (dielectric) layer comprises titanium oxide in a matrix with SEBS. The use of the SECs is not limited by the geometry of the surface being monitored, and it can, therefore, be adhered to a variety of surfaces as its flexibility allows it to conform to the irregularity and complexity of the monitored structure. The change experienced by a structure will correlate directly to the change in capacitance observed across the sensor, which can be used to predict the monitored structure’s state. While SECs have been studied for applications on various materials, experiments have been limited to adhering the sensor to smooth surfaces. However, concrete structures have various surface finishes that are not uniform, often deriving from an architect’s aesthetic desire. This work tests a corrugated SEC through compression tests on concrete samples with different surface finishing to investigate the effect of surface finishing on the SEC-measured strain. Each concrete sample is subjected to loading by a dynamic testing system, and the data collected from the SEC are compared to off-the-shelf resistive strain gauges. The results show that the performance of the cSEC on the different surfaces is not hindered by different concrete finishes, where a high signal-to-noise ratio of 21 dB and low mean absolute error of 22 μϵ is seen on the concrete specimen with a rough concrete surface. The strain metrics and surface effect on SEC performance are discussed.

Proceedings Article | 18 April 2023 Paper

Time-delayed joint seismic input and state estimation for building structures using incomplete acceleration measurements

Sdiq Anwar Taher, Jian Li

Proceedings Volume 12486, 124860V (2023) https://doi.org/10.1117/12.2659735

KEYWORDS: Error analysis, Matrices, Prior knowledge, Modeling, Earthquakes, Systems modeling, Sensors, Computing systems, Computation time, Algorithm development

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Proceedings Article | 18 April 2023 Paper

Soft elastomeric capacitors with an extended polymer matrix for strain sensing on concrete

Emmanuel Ogunniyi, Han Liu, Austin R. Downey, Simon Laflamme, Jian Li, Caroline Bennett, William Collins, Hongki Jo, Paul Ziehl

Proceedings Volume 12486, 1248618 (2023) https://doi.org/10.1117/12.2658568

KEYWORDS: Capacitance, Sensors, Capacitors, Polymers, Digital image correlation, Transducers, Electrodes, Dielectrics, Structural sensing, Structural health monitoring, Strain analysis

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Surface strain sensors, such as linear variable differential transformers, fiber Bragg gratings, and resistive strain gauges, have seen significant use for monitoring concrete infrastructure. However, spatial monitoring of concrete structures using these sensor systems is limited by challenges in the surface coverage provided by a specific sensor or issues related to mounting and maintaining numerous mechanical sensors on the structure. A potential solution to this challenge is the deployment of large-area electronics in the form of a sensing skin to provide complete coverage of a monitored area while being simple to apply and maintain. Along this line of effort, networks constituted of soft elastomeric capacitors have been deployed to monitor strain on steel and composite structures. However, using soft elastomeric capacitors on concrete surfaces has been challenging due to the electrical coupling between the sensors and concrete, which amplifies transduced strain signals obtained from the soft elastomeric capacitors. In this work, the authors investigate the isolation of the soft elastomeric capacitors from the concrete by extending the styrene-block-ethylene-co-butylene-block-styrene matrix of the soft elastomeric capacitors to include a decoupling layer between the electrode and the concrete. Experimental investigations are carried out on concrete specimens for which the soft elastomeric capacitor is adhered to with a thin layer of off-the-shelf epoxy and then loaded on the dynamic testing system to monitor strain provoked on the concrete samples. The results presented here demonstrate the viability of the electrically isolated soft elastomeric capacitors for monitoring strain on concrete structures. Initial comparisons between un-isolated and electrically isolated soft elastomeric capacitors showed that the nominal capacitance of the soft elastomeric capacitor is significantly lowered by adding an isolation layer of SEBS. Furthermore, strain results for the soft elastomeric capacitors are compared to ones from a resistive strain gauge and digital image correlation. The data obtained is significant for modifying soft elastomeric capacitors with the anticipation for future use on concrete structures.

Proceedings Article | 18 April 2022 Presentation + Paper

Vision-based inspection of out-of-plane fatigue cracks in steel structures

Rushil Mojidra, Jian Li, Ali Mohammadkhorasani, Fernando Moreu, William Collins, Caroline Bennett, Sdiq Anwar Taher

Proceedings Volume 12046, 120460I (2022) https://doi.org/10.1117/12.2613188

KEYWORDS: Cameras, Video, Bridges, Inspection, Distortion, Motion estimation, Motion detection, Linear filtering, Unmanned aerial vehicles, Optical filters

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Proceedings Article | 18 April 2022 Presentation + Paper

Wind-induced vibration monitoring of high mast illumination poles

Mona Shaheen, Jian Li, Sdiq Anwar Taher, Caroline Bennett, William Collins

Proceedings Volume 12046, 120460R (2022) https://doi.org/10.1117/12.2613180

KEYWORDS: Sensors, Data modeling, Video, Smart sensors, Sensor networks, Shape analysis, Data analysis, Wind measurement

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Proceedings Article | 18 April 2022 Presentation + Paper

Long-term field monitoring of fatigue cracks for steel bridges with wireless large-area strain sensors

Sdiq Anwar Taher, Jian Li, Jong-Hyun Jeong, Simon Laflamme, Hongki Jo, Caroline Bennett, William Collins, Han Liu, Austin Downey, Mona Shaheen

Proceedings Volume 12046, 1204604 (2022) https://doi.org/10.1117/12.2613072

KEYWORDS: Sensors, Bridges, Data storage, Capacitance, Wavelets, Remote sensing, Clouds, Structural health monitoring, Continuous wavelet transforms, Strain analysis, Wireless communications, Structural sensing, Smart structures, Damage detection

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Proceedings Article | 22 March 2021 Presentation + Paper

MAP-based model updating of building structures under earthquakes using limited acceleration measurements

Sdiq Anwar Taher, Jian Li

Proceedings Volume 11591, 115911J (2021) https://doi.org/10.1117/12.2583371

KEYWORDS: Earthquakes, Optimization (mathematics), Performance modeling, Data modeling, Time metrology, Inverse problems, Instrument modeling, Finite element methods, Damage detection

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Proceedings Article | 22 March 2021 Presentation + Paper

Monitoring impact damage in composites with large area sensing skins

Alexander Vereen, Austin Downey, Subramani Sockalingham, Paul Ziehl, Simon LaFlamme, Jian Li, Hongki Jo

Proceedings Volume 11591, 115911Q (2021) https://doi.org/10.1117/12.2582572

KEYWORDS: Sensors, Capacitors, Skin, Composites, Glasses, Capacitance, Sensor networks, Nondestructive evaluation, Inspection, Head

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The effect of low energy impacts can seriously impair the operational life span of composites in the field. These low-energy impacts can induce a permanent loss in the toughness of the composite without any visible indication of the material’s compromise. The detection of this damage utilizing nondestructive inspection requires dense measurements over much of the surface and has been traditionally achieved by removing the part from service for advanced imaging techniques. While these methods can accurately diagnose the damage inflicted internally by the impacts, they accrue non-trivial opportunity costs while the structure is inspected. To enable the capabilities of in-service monitoring of the composite, the novel soft elastomeric capacitor was investigated as a sensing solution. The sensor is made of three layers comprised of a styrene-ethylene-butylene-styrene (SEBS) matrix, a commercially available elastomer. These layers consist of a titania filled center layer that forms the dielectric of the capacitor and two highly conductive outer layers doped with carbon black. This simple formation allows for a capacitor that has extremely robust mechanical properties. The soft elastomeric capacitor functions by taking up deformations on the surface of the composite that is transduced into a measurable change in capacitance. This study provides an electro-mechanical model for impact damage and experimentally investigates the efficacy of these sensors for use in damage detection given their promising characteristics; that being that the sensor geometry can be arbitrarily large allowing for much fewer sensors than traditional sensor networks employed for this task at a much lower cost than installing traditional in-situ sensing solutions. To investigate these properties a set of impact trials were undertaken on a drop tower using small samples of glass fiber reinforced plate, of random orient and short fiber, with a soft elastomeric capacitor mounted directly opposite the impact site. The impactor head was only allowed one contact with the sample before being intercepted. The testing range for the samples ranged from well below the yield strength of the glass fiber reinforced plate to the ultimate strength of the plate. Experimental results reported a square root relation between the impact energy given to the plate when inducing plastic deformations and the sensor’s measured change in capacitance.

Proceedings Article | 22 March 2021 Presentation + Paper

Experimental validation of textured sensing skin for fatigue crack monitoring

Han Liu, Simon Laflamme, Jian Li, Caroline Bennett, William Collins, Austin Downey, Hongki Jo

Proceedings Volume 11591, 115911R (2021) https://doi.org/10.1117/12.2582592

KEYWORDS: Skin, Sensors, Yield improvement, Thin films, Numerical analysis, Capacitors, Capacitance

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Proceedings Article | 18 May 2020 Presentation + Paper

Online input, state, and response estimation for building structures under earthquakes using limited acceleration measurements

Sdiq Anwar Taher, Jian Li, Huazhen Fang

Proceedings Volume 11379, 1137908 (2020) https://doi.org/10.1117/12.2557712

KEYWORDS: Matrices, Filtering (signal processing), Systems modeling, Error analysis, Modeling, Data modeling, Sensors, Earthquakes, Numerical simulations, Nondestructive evaluation

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