Structural Monitoring Applications Research Articles

Integration of thin film giant magnetoimpedance sensor and surface acoustic wave transponder

Passive and remote sensing technology has many potential applications in implantable devices, automation, or structural monitoring. In this paper, a tri-layer thin film giant magnetoimpedance (GMI) sensor with the maximum sensitivity of 16%/Oe and GMI ratio of 44% was combined with a two-port surface acoustic wave (SAW) transponder on a common substrate using standard microfabrication technology resulting in a fully integrated sensor for passive and remote operation. The implementation of the two devices has been optimized by on-chip matching circuits. The measurement results clearly show a magnetic field response at the input port of the SAW transponder that reflects the impedance change of the GMI sensor.

Experimental and numerical studies on the sensitivity of carbon fibre/silicone rubber composite sensors

Flexible conductive composite sensors are of great importance for applications in structural monitoring due to their low cost, high durability and excellent compatibility. In this work, carbon fibre/silicone rubber composites were prepared and their sensitivity near the percolation threshold was investigated experimentally and theoretically. Results show that carbon fibre/silicone rubber composites have great mechanical and sensitivity even under high strain conditions. Two models based on the tunnelling effect and general effective medium theory were found to understand the sensitivity of composites with lower and higher fractions of carbon fibre. Moreover, the reversibility of the sensing performance is improved with the increase of carbon fibre addition.

Accurate measurement of translational shifts by adaptively masking phase correlation

The measurement of translational shifts has an impact on applications in medical imaging, remote sensing and structural health monitoring. Phase correlation (PC) is a well-known method to measure displacement. However, the PC matrix is often degraded by phase noise and aliasing. Presented is a robust PC method based on adaptive masking and essentially non-oscillatory smoothing to reduce phase noise and aliasing. With this approach, translational shifts can be measured with an accuracy of 1/300 of a pixel as shown in the experimental results.

GNSS-based multi-sensor system for structural monitoring applications

In 2007 the Centre of Applied Geomatics of the Military University of Technology started measurements aimed at the monitoring of the dynamic state of the engineering structures using GNSS. The complexity of the problem forced us to apply an integrated system architecture. This concept is based on simultaneous measuring some selected elements of the structure using various types of sensors. Measurement information from numerous instruments is numerically integrated for determining the investigated parameter, e.g., the displacement vector. The CAG team performed the tests using such a system on the two permanent 500-meters long bridges, the temporary bridge crossing for military purposes and the 300-meters high chimney of the CHP station. The information about displacement vector together with the characteristic frequencies of the structure were determined using different techniques for increasing of its reliability. This paper presents the results of such tests, gives description of the integrated system designed in the CAG and brings forward with the plans for the future.

Sensitivity analysis of piezoelectric paint sensors made up of PZT ceramic powder and water-based acrylic polymer

A strain sensor based on piezoelectric paint film has been designed to be used in structural vibration monitoring applications. The piezoelectric paint film can be considered as a piezoelectric composite constituted by two phases: lead zirconate titanate (PZT) ceramic powder (active phase) homogeneously distributed in a water-based acrylic polymer (passive phase). Two electrodes placed to both sides of the film are required to measure the electric charge generated by the sensor. Because PZT is a ferroelectric material, the film must be polarized with a high electric field across the electrodes prior to use. The sensor sensitivity, defined in this work as the electric displacement relative to the biaxial strain of the substrate surface in which the sensor is attached, has been analyzed as a function of various parameters: the electric field applied to polarize the sensor; the time during which the electric field is applied; the film thickness; the electrode area; and the concentration of PZT by weight. From the analysis of the experimental results a mathematical model has been proposed which defines the sensor sensitivity as a function of the previously mentioned parameters.

Monitoring stress changes in a concrete bridge with coda wave interferometry

Coda wave interferometry is a recent analysis method now widely used in seismology. It uses the increased sensitivity of multiply scattered elastic waves with long travel-times for monitoring weak changes in a medium. While its application for structural monitoring has been shown to work under laboratory conditions, the usability on a real structure with known material changes had yet to be proven. This article presents experiments on a concrete bridge during construction. The results show that small velocity perturbations induced by a changing stress state in the structure can be determined even under adverse conditions. Theoretical estimations based on the stress calculations by the structural engineers are in good agreement with the measured velocity variations.

In-construction vibration monitoring of a super-tall structure using a long-range wireless sensing system

As a testbed for various structural health monitoring (SHM) technologies, a super-tall structure - the 610 m-tall Guangzhou Television and Sightseeing Tower (GTST) in southern China - is currently under construction. This study aims to explore state-of-the-art wireless sensing technologies for monitoring the ambient vibration of such a super-tall structure during construction. The very nature of wireless sensing frees the system from the need for extensive cabling and renders the system suitable for use on construction sites where conditions continuously change. On the other hand, unique technical hurdles exist when deploying wireless sensors in real-life structural monitoring applications. For example, the low-frequency and low-amplitude ambient vibration of the GTST poses significant challenges to sensor signal conditioning and digitization. Reliable wireless transmission over long distances is another technical challenge when utilized in such a super-tall structure. In this study, wireless sensing measurements are conducted at multiple heights of the GTST tower. Data transmission between a wireless sensing device installed at the upper levels of the tower and a base station located at the ground level (a distance that exceeds 443 m) is implemented. To verify the quality of the wireless measurements, the wireless data is compared with data collected by a conventional cable-based monitoring system. This preliminary study demonstrates that wireless sensing technologies have the capability of monitoring the low-amplitude and low-frequency ambient vibration of a super-tall and slender structure like the GTST.

Distributed Strain Measurement along a Concrete Beam via Stimulated Brillouin Scattering in Optical Fibers

The structural strain measurement of tension and compression in a 4 m long concrete beam was demonstrated with a distributed fiber-optic sensor portable system based on Brillouin scattering. Strain measurements provided by the fiber-optic sensor permitted to detect the formation of a crack in the beam resulting from the external applied load. The sensor system is valuable for structural monitoring applications, enabling the long-term performance and health of structures to be efficiently monitored.

Dynamic characterization of piezoelectric paint sensors under biaxial strain

A piezoelectric paint film has been designed to be used as a strain sensor. The composite is a suspension of milled lead zirconate titanate (PZT) ceramic powder in a polymer binder (water-based acrylic). The sensitivity of the sensor was estimated as the electric displacement (electric charge per electrode area) generated by the sensor relative to the strain experienced by the substrate surface, under the hypothesis that the electric charge generated is proportional to the sum of the principal strains. The piezoelectric constant d 31 (conventionally used to characterize piezoelectric sensor materials for structural vibration measurement) has also been obtained. The sensor linearity has been demonstrated over a strain range of ±200 μɛ and the sensor sensitivity is shown to be flat to within ±2 dB over a frequency range of 5–500 Hz, ranges typically required for structural vibration monitoring applications.

The Tenet architecture for tiered sensor networks

Most sensor network research and software design has been guided by an architectural principle that permits multinode data fusion on small-form-factor, resource-poor nodes, or motes . While we were among the earliest promoters of this approach, through experience we found that this principle leads to fragile and unmanageable systems and explore an alternative. The Tenet architecture is motivated by the observation that future large-scale sensor network deployments will be tiered , consisting of motes in the lower tier and masters , relatively unconstrained 32-bit platform nodes, in the upper tier. Tenet constrains multinode fusion to the master tier while allowing motes to process locally-generated sensor data. This simplifies application development and allows mote-tier software to be reused. Applications running on masters task motes by composing task descriptions from a novel tasklet library. Our Tenet implementation also contains a robust and scalable networking subsystem for disseminating tasks and reliably delivering responses. We show that a Tenet pursuit-evasion application exhibits performance comparable to a mote-native implementation while being considerably more compact. We also present two real-world deployments of Tenet system: a structural vibration monitoring application at Vincent Thomas Bridge and an imaging-based habitat monitoring application at James Reserve, and show that tiered architecture scales network capacity and allows reliable delivery of high rate data. 1

Structural monitoring of wind turbines using wireless sensor networks

Monitoring and economical design of alternative energy generators such as wind turbines is becoming increasingly critical; however acquisition of the dynamic output data can be a time-consuming and costly process. In recent years, low-cost wireless sensors have emerged as an enabling technology for structural monitoring applications. In this study, wireless sensor networks are installed in three operational turbines in order to demonstrate their efficacy in this unique operational environment. The objectives of the first installation are to verify that vibrational (acceleration) data can be collected and transmitted within a turbine tower and that it is comparable to data collected using a traditional tethered system. In the second instrumentation, the wireless network includes strain gauges at the base of the structure. Also, data is collected regarding the performance of the wireless communication channels within the tower. In both turbines, collected wireless sensor data is used for off-line, output-only modal analysis of the ambiently (wind) excited turbine towers. The final installation is on a turbine with embedded braking capabilities within the nacelle to generate an impulse-like load at the top of the tower. This ability to apply such a load improves the modal analysis results obtained in cases where ambient excitation fails to be sufficiently broad-band or white. The improved loading allows for computation of true mode shapes, a necessary precursor to many conditional monitoring techniques.

2D13 A Real-time Multi-channel Wireless Sensing Network for Structural Monitoring Applications

In this paper, a newly designed wireless sensing network platform for structural monitoring applications is presented and the results of a validation test performed in the authors' laboratory are reported. The main features offered by the proposed wireless platform are the capability of real-time and multi-channel data transmission, a high compatibility to different types of sensors, a highly efficient power-supply, and low-cost. Instead of adopting the most commonly used commercial wireless modems, the wireless communication is pursued by implementing an optimized and customized solution based on a recent System on Chip wireless transceiver. The Frequency Division Multiplexing method is exploited to ensure the real-time feature of the multi-channel data transmission. A simple and practical point-to-point topology is pursued. The usage of switching regulators which feature low quiescent current, highly efficient power conversion, the adjustable output voltage, and the high output power make this platform suitable for both low-power and non low-power structural monitoring applications involving different types of sensors. In order to validate the prototyped platform, a laboratory test is performed. The measurements of the acceleration response of a simple 3-storey structure mounted on a shaking table are acquired from both a wired DAQ system and the developed wireless platform. The data comparison enables to validate the efficacy of the real-time, multi-channel wireless transmission.

In Situ Cross-Calibration of In-Fiber Bragg Grating and Electrical Resistance Strain Gauges for Structural Monitoring Using an Extensometer

This study addresses the direct calibration of optical fiber strain sensors used for structural monitoring and is carried out in situ. The behavior of fiber-Bragg-grating-based sensor systems when attached to metal bars, in a manner representative of their use as reinforcement bars in structures, was examined and their response calibrated. To ensure the validity of the measurements, this was done using an extensometer with a further calibration against the response of electrical resistance strain gauges, often conventionally used, for comparison. The results show a repeatable calibration generating a suitable geometric factor of extension to strain for these sensors, to enable accurate strain data to be obtained when the fiber-optic sensor system is in use in structural monitoring applications.

Lead-free Piezoelectric KNN-based Pin Transducers for Structural Monitoring Applications

A 2.4 mm diameter piezoelectric ceramic disc was used to construct a spring-loaded pin-type transducer for intelligent monitoring of systems. Two types of lead-free KNN-based ceramics (0.95K0.5Na0.5 (Nb0.94Sb0.06)O 3 — 0.05LiTaO3 + 1.25 mol% BaO and K0.5Na 0.5NbO3 -0.75 mol% K5.4Cu1.3Ta 10O29) were selected as a sensing element of the pin. The piezoelectric spring-loaded pins were mounted on the corners of the aluminum plate for the performance evaluation using a laser ultrasonic technique. The signals detected by transducers with different sensing elements including lead-based ceramics have been compared. The capability of impact detection of the lead-free transducers was shown to be comparable to that of the lead-based one. It is envisaged that lead-free piezoelectrics will become the important transducer materials in the next generation nondestructive evaluation technology.

Lead-free Piezoelectric KNN-based Pin Transducers for Structural Monitoring Applications

Lead-free Piezoelectric KNN-based Pin Transducers for Structural Monitoring Applications

A mobile-agent-based wireless sensing network for structural monitoring applications

A new wireless sensing network paradigm is presented for structural monitoring applications. In this approach, both power and data interrogation commands are conveyed via a mobile agent that is sent to sensor nodes to perform intended interrogations, which can alleviate several limitations of the traditional sensing networks. Furthermore, the mobile agent provides computational power to make near real-time assessments on the structural conditions. This paper will discuss such prototype systems, which are used to interrogate impedance-based sensors for structural health monitoring applications. Our wireless sensor node is specifically designed to accept various energy sources, including wireless energy transmission, and to be wirelessly triggered on an as-needed basis by the mobile agent or other sensor nodes. The capabilities of this proposed sensing network paradigm are demonstrated in the laboratory and the field.

Real-time structural damage detection using wireless sensing and monitoring system

A wireless sensing system is designed for application to structural monitoring and damage detection applications. Embedded in the wireless monitoring module is a two-tier prediction model, the auto-regressive (AR) and the autoregressive model with exogenous inputs (ARX), used to obtain damage sensitive features of a structure. To validate the performance of the proposed wireless monitoring and damage detection system, two near full scale single-story RC-frames, with and without brick wall system, are instrumented with the wireless monitoring system for real time damage detection during shaking table tests. White noise and seismic ground motion records are applied to the base of the structure using a shaking table. Pattern classification methods are then adopted to classify the structure as damaged or undamaged using time series coefficients as entities of a damage-sensitive feature vector. The demonstration of the damage detection methodology is shown to be capable of identifying damage using a wireless structural monitoring system. The accuracy and sensitivity of the MEMS-based wireless sensors employed are also verified through comparison to data recorded using a traditional wired monitoring system.

Passive wireless sensing using SWNT-based multifunctional thin film patches

This study presents a high-performance inductively coupled multifunctional carbon nanotube thin film sensor for structural monitoring applications. A versatile layer-by-layer self-assembly sensor fabrication technique is employed to encode different sensing mechanisms (e.g., strain and corrosion/pH) within one homogeneous thin film structure. Judicious selection of various polyelectrolyte species, along with the incorporation of carbon nanotubes, permits multifunctional sensing. Upon deposition of these thin films on miniature planar coil antennas to form a resonant circuit, a passive wireless sensor is realized. Unlike traditional cabled or wireless sensing systems, the proposed passive sensor does not require a constant power source, thereby rendering it ideally suited for embedment within structures.

Survey of Hardware Systems for Wireless Sensor Networks

Wireless sensor networks have been gaining interest as a platform that changes how we interact with the physical world. Applications in medicine, military, inventory management, structural and environmental monitoring, and the like can benefit from low-power wireless nodes that communicate data collected via a variety of sensors. Current deployments of wireless sensor networks (WSN) rely on off-the-shelf commodity-based microcontrollers, but the unoptimized energy consumption of these systems can limit the effective lifetimes. Ideally, researchers would like to deeply embed wireless sensor network nodes in the physical world, relying on energy scavenged from the ambient environment. This paper provides a survey of ultra low power processors specifically designed for WSNapplications that have begun to emerge from research labs, which require detailed understanding of tradeoffs between application space, architecture, and circuit techniques to implement these low-power systems.

The Potential of Locata Technology for Structural Monitoring Applications

Locata technology is becoming part of Leica Geosystems solution for the structural monitoring applications such as bridges and dams. This paper assesses the performance of the Locata technology using a test Locata network (LocataNet) established at the University of New South Wales. Using this network a long term static tests and a simulated deformation movement test, with GPS as a comparison, were conducted. This paper described the LocataNet established at UNSW and presents the results and analysis of the tests conducted. Overall the paper demonstrates the suitability of Locata for structural deformation monitoring type applications (such as bridges and dams) where there is reduced or unavailable satellite coverage.