Wireless Strain Monitoring Research Articles

Highly Robust and Self-Adhesive Soft Strain Gauge via Interface Design Engineering.

Highly robust soft strain gauges are rapidly emerging as a promising candidate in the fields of vital signs and machine conditions monitoring. However, it is still a key challenge to achieve high-performance strain sensing in these sensors with mechanical/electrical robustness for long-term usage. The multilayer structural design of sensors enhances sensing performance while the interfacial connection of heterogeneous materials between different layers is weak. Herein, inspired by the efficient perception mechanism of scorpion slit sensilla with tough interface interconnections, the synergy of ultra-high electrical performance and mechanical robustness is successfully achieved via interface design engineering. The developed multilayer soft strain gauge (MSSG) exhibits a strain sensitivity beyond 105, a lower detection limit of 8.3µm, a frequency resolution within 0.1Hz, and cyclic stability over 63000 strain cycles. Also, the tough interface improves the level of heterogeneous integration in the MSSG which allows to endure different stresses. Furthermore, an MSSG-based wireless strain monitoring system is developed that enables applications on different complex dynamic surfaces, including accurate identification of human throat activity and monitoring of rolling bearing conditions.

Flexible Graphene Film-Based Antenna Sensor for Large Strain Monitoring of Steel Structures.

In the field of wireless strain monitoring, it is difficult for the traditional metal-made antenna sensor to conform well with steel structures and monitor large strain deformation. To solve this problem, this study proposes a flexible antenna strain sensor based on a ductile graphene film, which features a 6.7% elongation at break and flexibility due to the microscopic wrinkle structure and layered stacking structure of the graphene film. Because of the use of eccentric embedding in the feeding form, the sensor can be miniaturized and can simultaneously monitor strain in two directions. The sensing mechanism of the antenna is analyzed using a void model, and an antenna is designed based on operating frequencies of 3 GHz and 3.5 GHz. The embedding size is optimized using a Smith chart and impedance matching principle. Both the simulation and experimental results verify that the resonant frequency and strain magnitude are linearly inversely proportional. The experimental results show that the strain sensitivity is 1.752 kHz/με along the geometric length and 1.780 kHz/με along the width, with correlation coefficients of 0.99173 and 0.99295, respectively.

Wireless Strain and Temperature Monitoring in Reinforced Concrete Using Surface Acoustic Wave Sensors

Wireless Strain and Temperature Monitoring in Reinforced Concrete Using Surface Acoustic Wave Sensors

Fabrication and verification of vertical graphene-based strain sensor

The purpose of structural health monitoring in civil and mechanical engineering infrastructure is to make a structure safer at a lower cost. Strain, one of the crucial monitoring variables, has an innate relationship with deformation and is sensitive to the degeneration of load-bearing structural elements. In this study, a set of wireless real-time data acquisition and strain monitoring systems based on vertical graphene (VG) were developed. Both the parametric study and the feasibility of the VG-based strain sensor in crack monitoring of concrete structures were investigated. The greatest resistance difference in the cyclic tensile test is 2.99%, and the linearity is 2.4%, proving the newly designed sensor has good repeatability and stability. According to the monotonic tensile test based on a micro-displacement control platform, the relative resistance to change ΔR/R rises as applied strain rises and the repeatability error results in 0.576%. According to the notched concrete beam under the three-point bending test, the VG-based strain sensor's discrepancy from the extensometer's monitoring data is within 11.04%. The findings of this study suggest that the newly developed VG-based strain sensor has the potential for practical application in field strain monitoring, thus reaffirming the feasibility and effectiveness of this novel sensing technology.

High-Efficiency and High-Current GaN-Based Microwave Rectifier for Wireless Strain Sensing and Monitoring

In this article, a gallium nitride (GaN) Schottky barrier diode (SBD)-based microwave rectifier with high efficiency, current, and power bandwidth is proposed for wireless strain sensing and monitoring. Solutions including semiconductor devices, rectification circuits, and sensing mechanisms are discussed. A microwave rectifier working at 928 MHz is designed for wireless rectification strain sensing, with a measured power efficiency over 85% and a load resistance lower to 40 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> based on a customized quasi-vertical GaN SBD. The finger layout and TiN anode make the SBD series resistance reduced to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.81~\Omega $ </tex-math></inline-formula> , but saturation current enhanced to 11.8 nA, which significantly reduces rectification loss when the load resistance is small. Finally, a rectification strain sensor (RSS) is proposed by dielectric coupling the rectifier and a piezo-permittivity liquid metal elastomer foam (LMEF), with a measured relative output power variation and wireless working distance over 437%/mm and 3 m, respectively.

Fatigue life prediction of concrete bridges using wireless sensors - A review

This study evaluates the works carried out for fatigue life prediction of reinforced concrete girders and columns in concrete bridges, utilizing the guidelines outlined by the Indian Road Congress (IRC). To accurately predict fatigue damage on bridges, a dynamic bridge-vehicle interaction model was employed to capture the effects of trafficinduced dynamic loads. The time to the first cracking distribution function was calculated using a dedicated model, enabling the assessment of fatigue life under various amplitude loading scenarios. The model incorporates S-N curves and Miner's rule, which are widely used techniques for measuring fatigue on structures, to evaluate the cumulative damage caused by cyclic loading. Wireless sensors were used in structural monitoring systems to monitor the health of bridges. This paper describes investigations that assess the performance of wireless strain-monitoring devices. These advanced systems offer improved efficiency, cost-effectiveness, and ease of installation compared with traditional monitoring systems. The research presented herein aims to provide a comprehensive approach for evaluating and predicting the fatigue life of reinforced concrete girders and columns in bridges. The proposed model, combined with dynamic bridge-vehicle interaction simulations and wireless strain monitoring devices, offers a robust framework for bridge engineers to effectively assess the structural integrity and maintenance needs of concrete bridges, ultimately enhancing their durability and safety.

Soft Electronic Strain Sensor with Chipless Wireless Readout: Toward Real‐Time Monitoring of Bladder Volume

AbstractSensing mechanical tissue deformation in vivo can provide detailed information on organ functionality and tissue states. To bridge the huge mechanical mismatch between conventional electronics and biological tissues, stretchable electronic systems have recently been developed for interfacing tissues in healthcare applications. A major challenge for wireless electronic implants is that they typically require microchips, which adds complexity and may compromise long‐term stability. Here, a chipless wireless strain sensor technology based on a novel soft conductor with high cyclic stability is reported. The composite material consists of gold‐coated titanium dioxide nanowires embedded in a soft silicone elastomer. The implantable strain sensor is based on an resonant circuit which consists of a stretchable plate capacitor and a coil for inductive readout of its resonance frequency. Successful continuous wireless readout during 50% strain cycles is demonstrated. The sensor element has a Young's modulus of 260 kPa, similar to that of the bladder in order to not impair physiological bladder expansion. A proof‐of‐principle measurement on an ex vivo porcine bladder is presented, which shows the feasibility of the presented materials and devices for continuous, wireless strain monitoring of various tissues and organs in vivo.

Aircraft Strain WSN Powered by Heat Storage Harvesting

The combination of ultra-low-power wireless communications and energy harvesting enables the realization of autonomous wireless sensor networks. Such networks can be usefully applied in commercial aircraft where wireless sensing solutions contribute to weight reduction and increased ease of installation and maintenance. This paper presents, for the first time, a complete energy-autonomous wireless strain monitoring system for aircraft. The system is based on a multimode wireless time-division multiple access (TDMA) medium access control (MAC) protocol that supports automatic configuration and a time-stamping accuracy better than 1 ms. The energy supply depends solely on an innovative thermoelectric energy harvester, which takes advantage of the changes in environmental temperature during takeoff and landing. The system was successfully integrated and passed the functional and flight-clearance tests that qualify it for use in a flight-test installation.

Development of a distance-independent wireless passive RF resonator sensor and a new telemetric measurement technique for wireless strain monitoring

We proposed and developed a novel wireless passive RF resonator scheme that enables telemetric strain sensing avoiding the need for calibration at different interrogation distances. The specific architecture of the proposed structure allows for strong inductive coupling and, thus, a higher wireless signal-to-noise ratio. Here, in operation, the frequency scan of the sensor impedance was used to measure simultaneously both the impedance amplitude and resonance frequency. Using this wireless sensor, we further introduced a new telemetric monitoring modality that employs full electrical characteristics of the system to achieve correct strain extraction at any interrogation distance. In principle, any deformation of the sensor structure results in the resonance frequency shift to track strain. However, changing of the interrogation distance also varies the inductive coupling between the sensor and its pick-up antenna at the interrogation distance. Therefore, at varying interrogation distances, it is not possible to attribute an individual resonance frequency value solely to an individual strain level, consequently resulting in discrepancies in the strain extraction if the interrogation distance is not kept fixed or distance-specific calibration is not used. In this work, we showed that by using both the proposed passive sensor structure and wireless measurement technique, strain can be successfully extracted independent of the interrogation distance for the first time. The experimental results indicate high sensitivity and linearity for the proposed system. These findings may open up new possibilities in applications with varying interrogation distance for mobile wireless sensing.

Battery-free slotted patch antenna sensor for wireless strain and crack monitoring

In this research, a slotted patch antenna sensor is designed for wireless strain and crack sensing. An off-the-shelf RFID (radiofrequency identification) chip is adopted in the antenna sensor design for signal modulation. The operation power of the RFID chip is captured from wireless reader interrogation signal, so the sensor operation is completely battery-free (passive) and wireless. For strain and crack sensing of a structure, the antenna sensor is bonded on the structure surface like a regular strain gage. Since the antenna resonance frequency is directly related with antenna dimension, which deforms when strain occurs on the structural surface, the deformation/strain can be correlated with antenna resonance frequency shift measured by an RFID reader. The slotted patch antenna sensor performance is first evaluated through mechanics-electromagnetics coupled simulation. Extensive experiments are then conducted to validate the antenna sensor performance, including tensile and compressive strain sensing, wireless interrogation range, and fatigue crack sensing.

Design and Implementation of a Portable Wireless System for Structural Health Monitoring

In the health monitoring of large metal structure, the traditional strain measurement systems with wired and bulky instruments face the challenges of harsh environment, changing network topology and limited energy supply. To meet these requirements and improve the efficiency, a portable wireless strain monitoring system combined with wireless sensor network technology and portable design has been developed in this paper. Consisting of handheld coordinator, router and sensor, this novel system takes miniaturization, portability and low-power design as core capabilities in both software and hardware design. With tests in laboratory environment, its time domain response and power consumption have been analyzed to verify its performance and efficiency. Additionally, after calibration on an equal strength cantilever, comparative tests on quayside cranes have been explored to show that this system has an equivalent accuracy compared with the traditional measurement system. However, it improves the work efficiency and can meet the serious challenges within health monitoring of large metal structure.

Evaluation of High-Speed Railway Bridges Based on a Nondestructive Monitoring System

Recently, trains’ velocities in Korea increased more than the speed used in the design of some bridges. Accordingly, this paper demonstrates the evaluation of a railway bridge due to high-speed trains’ movement. A nondestructive monitoring system is used to assess the bridge performance under train speeds of 290, 360, 400 and 406 km/h. This system is comprised of a wireless short-term acceleration system and strain monitoring sensors attached to the bridge girder. The results of the analytical methods in time and frequency domains are presented. The following conclusions are obtained: the cross-correlation models for accelerations and strain measurements are effective to predict the performance of the bridge; the static behavior is increased with train speed developments; and the vibration, torsion, fatigue and frequency contents analyses of the bridge show that the bridge is safe under applied trains’ speeds.

Distributed Strain Sensor Networks for In-Construction Monitoring and Safety Evaluation of a High-Rise Building

The New Headquarters of Shenzhen Stock Exchange (NHSSE), currently being constructed in Shenzhen, China, is a high-rise building with a height of 245 m. One salient feature of NHSSE is its huge floating platform with an overall plan dimension of [Formula: see text] and a total height of 24 m, making it one of the largest cantilever structures in the world. In recognition of the uniqueness of the floating platform, a long-term structural health monitoring (SHM) system has been designed and implemented by The Hong Kong Polytechnic University for both in-construction and in-service monitoring of NHSSE. As part of this monitoring system, 224 vibrating-wire strain gauges have been permanently installed to measure the strain responses of key structural components of the floating platform. A wireless strain monitoring system by integrating local tethered data acquisition and long-range wireless data transmission has been developed for real-time strain monitoring and visualization. This paper presents the stress evolution of the floating platform during dismantlement of temporary supports on the basis of the real-time monitoring data and the statistical stress analysis and safety evaluation of the floating platform by use of the long-term monitoring data, as well as the effect of the welding residual stress on structural safety of NHSSE.

Wireless Strain Monitoring: A Microfluidic, Reversibly Stretchable, Large‐Area Wireless Strain Sensor (Adv. Funct. Mater. 12/2011)

Shi Cheng and Zhigang Wu demonstrate a new concept of wireless strain sensors, on page 2282, by combining microfluidic stretchable radiofrequency electronics with established integrated circuits. The implemented sensing device is capable of measuring repeated large-area strains of a human joint. The data are transferred wirelessly to a computer system for realtime healthcare or fitness monitoring.

Wireless Strain Monitoring of CFRP Laminates Using Electric Resistance Change with Oscillating Circuit

To identify a delamination crack in a CFRP laminate wirelessly, we proposed an electric resistance change method with oscillating circuit in the previous study. Although the method detects the delamination creation, it cannot monitor condition of applied strain before delamination creation because the electric resistance change due to strain changing is quite small. In the present study, a bridge circuit, two amplifiers and voltage-controlled oscillator are added to sensing circuit so that it can monitor very little change of the electric resistance change. Using proposed strain sensing system, the electric resistance change and oscillating frequency change due to strain changing are experimentally measured. As a result, the method is found to successfully monitor the applied strain.

Interdigital capacitive strain gauges fabricated by direct-write thermal spray and ultrafast laser micromachining

There is a growing demand for in situ monitoring of strain in high-temperature, harsh environment systems. Resistive strain gauges, while popular and easy to implement, have several disadvantages when used at high-temperatures. This work presents the design, fabrication, and initial testing of capacitive strain gauges for use in high-temperature, harsh environments. The gauges are fabricated using a direct-write thermal spray technology in which a computer-controlled deposition system is used to fabricate silver gauge patterns onto polymer, composite, and alumina substrates to form the strain gauges. Gauges were also fabricated using ultrafast laser micromachining of blanket NiCr coatings thermal sprayed onto an alumina substrate. The typical gauge capacitance was 4–25 pF. Mechanical measurements performed included gauge factor, linearity, and zero shift. Temperature-based measurements include the temperature coefficient of capacitance (TCC) and thermal cycling tests. The devices show promise for use in harsh environments and in wireless strain monitoring applications.

Passive wireless strain monitoring of actual tire using capacitance–resistance change and multiple spectral features

To improve reliability of automobile tires and anti-lock braking system (ABS), intelligent tires that measure strain of tires are increasingly demanded. The high stiffness of an embedded sensor like a strain gage, however, causes debonding of a sensor from tire rubber. In a previous study, the authors proposed a wireless strain monitoring method that adopts a rectangular tire specimen as a sensor with a tuning circuit. Compared to the tire specimen, an actual tire has a large hysteresis between the measured strain of the inner tire surface and the capacitance in a tire belt. The large hysteresis in the actual tire makes it difficult to measure a tire strain precisely. In the present study, to measure the strain precisely, multiple power spectrum features of the sensor output are used to estimate the strain with a statistical method. As the spectral features, a peak power spectrum and a sharpness of the resonance in addition to a tuning frequency are used for the estimating. As a result the experiments demonstrate that the method is effective for the passive wireless strain monitoring of actual radial tires.

Passive wireless strain monitoring of tyres using capacitance and tuning frequencychanges

In-service strain monitoring of tyres of automobiles is quite effective for improving thereliability of tyres and anti-lock braking systems (ABS). Conventional strain gauges havehigh stiffness and require lead wires. Therefore, they are cumbersome for tyre strainmeasurements. In a previous study, the authors proposed a new wireless strain monitoringmethod that adopts the tyre itself as a sensor, with an oscillating circuit. This method isvery simple and useful, but it requires a battery to activate the oscillating circuit. In thepresent study, the previous method for wireless tyre monitoring is improved to produce apassive wireless sensor. A specimen made from a commercially available tyre isconnected to a tuning circuit comprising an inductance and a capacitance as acondenser. The capacitance change of the tyre alters the tuning frequency. Thischange of the tuned radio wave facilitates wireless measurement of the appliedstrain of the specimen without any power supply. This passive wireless method isapplied to a specimen and the static applied strain is measured. Experimentsdemonstrate that the method is effective for passive wireless strain monitoring of tyres.

Passive Wireless Strain Monitoring of Tire Using Capacitance Change with Tuning Circuit

Reliability of automobiles is increasingly demanded. To prevent burst of tires, smart tires are currently under development. Most of the smart tires have integrated or attached sensors to measure deformation or internal pressure of tires during a long period of service. The embedded sensor enables highly precise measurement of road surface friction, and the precise friction measurements make more efficient anti-lock braking system (ABS). In a previous study, the authors proposed a new wireless strain monitoring method that adopts the tire itself as a sensor, with an oscillator circuit. This method is very simple and useful, but it requires a battery to activate the oscillator circuit. In the present study, the previous method for wireless tire monitoring is improved to produce a passive wireless sensor. A specimen made from a commercially available tire is connected to a tuning circuit comprising an inductance and a capacitance as a condenser. The proposed method enables us to measure an applied strain of a specimen wirelessly, without any power supply from outside. This new passive wireless method is applied to a specimen and an applied strain is measured. As a result, the method is experimentally proved to be effective for the passive wireless strain monitoring of tires.

Passive wireless strain monitoring of a tire using capacitance and electromagnetic induction change

Strain monitoring of tires in-service of automobiles is quite effective for improving reliability of tires and an anti-lock braking system (ABS). A previous study by the authors presented a new wireless strain monitoring method that adopts the tire itself as a sensor with an oscillator circuit. This method is simple and useful, but it requires a battery to activate the oscillator circuit. The present study proposes and investigates a new passive wireless strain measurement system using capacitance change of tires. The system consists of external antennas and strain sensor with an inductance capacitance (LC) resonant circuit. This wireless system uses electromagnetic coupling between two inductors of the antenna and the sensor. This method allows use of a part of an actual tire as a capacitor of the LC circuit. Tire deformation changes the sensor's resonant frequency. This resonant frequency change is measured as a change in the phase angle of the antenna using electromagnetic induction. Tensile tests are performed and the antenna phase angles are measured during the tests. Consequently, experiments show that this method is effective for passive wireless strain monitoring of tires.