Fiber Bragg Grating Technique Research Articles

Simultaneous Measurement of Local Pulse Wave Velocities in Radial Arteries Using a Soft Sensor Based on the Fiber Bragg Grating Technique.

Arterial stiffness has been proved to be an important parameter in the evaluation of cardiovascular diseases, and Pulse Wave Velocity (PWV) is a strong indicator of arterial stiffness. Compared to regional PWV (PWV among different arteries), local PWV (PWV within a single artery) outstands in providing higher precision in indicating arterial properties, as regional PWVs are highly affected by multiple parameters, e.g., variations in blood vessel lengths due to individual differences, and multiple reflection effects on the pulse waveform. However, local PWV is less-developed due to its high dependency on the temporal resolution in synchronized signals with usually low signal-to-noise ratios. This paper presents a method for the noninvasive simultaneous measurement of two local PWVs in both left and right radial arteries based on the Fiber Bragg Grating (FBG) technique via correlation analysis of the pulse pairs at the fossa cubitalis and at the wrist. Based on the measurements of five male volunteers at the ages of 19 to 21 years old, the average left radial PWV ranged from 9.44 m/s to 12.35 m/s and the average right radial PWV ranged from 11.50 m/s to 14.83 m/s. What is worth mentioning is that a stable difference between the left and right radial PWVs was observed for each volunteer, ranging from 2.27 m/s to 3.04 m/s. This method enables the dynamic analysis of local PWVs and analysis of their features among different arteries, which will benefit the diagnosis of early-stage arterial stiffening and may bring more insights into the diagnosis of cardiovascular diseases.

Application of Fiber Bragg Grating Sensing in Bidirectional Tests of Pile Foundations

Abstract The fiber Bragg grating (FBG) technique has emerged as a new strain monitoring technique in civil engineering applications. In this paper, based on the principle of the FBG technique and the bidirectional test method, FBG sensors and conventional vibrating wire strain gauges (VWSGs) were employed to monitor the strain variation law of a pile under different loads and analyze the relationship between the side resistance and pile-soil relative displacement of soil layers in bidirectional field testing of a large-diameter cast in situ pile. Four field bidirectional test cases of cast in situ piles, prestressed high-strength concrete (PHC) and steel pipe pile, and pile-base post-grouting pile are presented. The applicability and stability of the FBG sensing technique were verified by analyzing the side resistance distribution and bearing capacity. The results showed that FBG sensors can remove the influence because of residual force and the effect of temperature change and concrete expansion photosensitive material provides an improved sensitivity to the external environment compared with a VWSG. The strain and side resistance variation tendency of the cast in situ pile were consistent between the two kinds of sensors. The FBG sensing technique had high test accuracy in the four bidirectional O-cell field test cases of the cast in situ pile, PHC and steel pipe pile, and pile-base post-grouting pile. The pile-base post-grouting technique is an effective procedure that was implemented to increase the ultimate bearing capacity. The research results of this paper reveal a new strain monitoring technique for the bidirectional test method of pile foundations and represent a new test method for measuring the bearing capacity of PHC and steel pipe piles that has a remarkable application value in practical engineering.

Deformation Monitoring for Chinese Traditional Timber Buildings Using Fiber Bragg Grating Sensors.

The Fiber Bragg Grating (FBG) sensing technique is suitable for a wide variety of measurements, including temperature, pressure, acceleration, liquid level, etc., and has been applied to many bridges and buildings in the past two decades. The fact that the FBG technique can only monitor and measure strain data for most cases when it is used for deformation measurements impedes application of the FBG sensing technique in civil infrastructures. This paper proposes FBG sensing-based deformation monitoring methods that are applicable to monitoring beam deflection, column inclination angle and mortise-tenon joint dislocation for Chinese traditional timber structures. On the basis of improved conjugated beam theory and geometrical trigonometric function relationship, the relationships between the FBG sensing strain values and the deflection of beam, inclination angle of column, as well as the amount of dislocation of mortise-tenon joint are deducted for Chinese traditional buildings. A series of experiments were conducted to verify the applicability and effectiveness of the proposed deformation monitoring methods. The results show that a good agreement is obtained between the values given by the methods proposed in this paper and other methods. This implies that the proposed deformation monitoring methods are applicable and effective in the health monitoring of Chinese traditional timber structures.

Influences of Initial Water Content and Roughness on Skin Friction of Piles Using FBG Technique

AbstractA series of pullout tests were conducted on a model pile in a soil with different initial water contents and different pile surface roughnesses to study their influences on pile skin friction. To measure axial strains and skin friction of the pile, fiber Bragg grating (FBG) strain sensors were used. Data were collected during the pullout tests and are analyzed in this paper. Test results indicate that the skin friction and axial strain of the model piles decrease with the initial water content of the soil but increase with the degree of surface roughness of the piles. The axial strain induced in the upper segment of the tested pile is considerably greater than that in the bottom segment of the pile. In addition, the skin friction is distributed nonlinearly along the length of the model piles.

Introduction to an FBG-based inclinometer and its application to landslide monitoring

This paper presents a self-designed in-place inclinometer based on fiber Bragg grating (FBG) technology and introduces its application to a landslide monitoring project in Wenzhou, China. The working principle of the FBG-based inclinometer is briefly introduced. The FBG-based inclinometers were installed into nine boreholes that were distributed over different areas of the landslide. After 4 months of monitoring, the deformation of the soil mass at different depths above the bedrock within the landslide was captured by the inclinometers. The results indicated that the soil deformation above the bedrock was relatively large whereas that below the bedrock was minor. Based on the field monitoring data, the potential sliding zones were predicted to be the areas near the bedrock. In addition, a limit equilibrium analysis was carried out to evaluate the stability of the landslide under the circumstance of rainfall. The analyses showed that the calculated failure surface was consistent with the field observations, indicating that the monitoring data recorded by FBGs were accurate. These findings demonstrate that a combination of FBG technique and limit equilibrium analysis can be used to evaluate the stability of landslides effectively.

Pullout performance of GFRP anti-floating anchor in weathered soil

Anchors are often used as anti-floating reinforcements in civil engineering structures. However, conventional steel bars present disadvantages concerning corrosion and poor adaptability to aggressive environments. Glass fiber-reinforced polymer (GFRP) components could provide a solution to these problems. In this paper the feasibility of GFRP anti-floating anchors is evaluated. Four full scale pullout tests were performed in moderately decomposed granite (MDG). Bare Fiber Bragg grating (FBG) sensors were embedded into the specimens during the pultrusion process to monitor the stress–strain distribution along their lengths. Based on the results the behavior of the anchors was assessed, including the relationships between the pullout force and the head displacement, the axial strain along anchors and the shear stress at the GFRP-grout interface. The stress distribution of anchors showing interlaminar shear failure was then analyzed based on a maximum shear stress criterion. It was proved that the load transfer mechanism of GFRP and steel anti-floating anchors differs significantly. GFRP anti-floating anchors reach failure due to interlaminar shear failure, while conventional steel anchors generally fail as a result of shear at the grout–soil interface. The test results also showed that the embedded FBG technique is reliable for monitoring the stress–strain state of an anisotropic material.

Thermal Characteristics of Temperature Sensor Using Fiber Bragg Grating for Optical Sensor Network Communication

In this paper, we present thermal characteristics of temperature sensor using fiber Bragg grating(FBG), including peak reflectivity, FWHM bandwidth and various normalized refractive index change along temperature variation. The temperature stability of FBG temperature sensor can be changed by varying the refractive index change and grating length. The proposed FBG temperature sensor can measure up to about 600℃ and heating time from 1000 hours. We can easily expect that various numerical results can be utilized as important ones when a sensor for measuring a temperature is implemented using a FBG technique.

A Novel Fiber Optic System for Measuring the Dynamic Structural Behavior of Parachutes

A novel approach has been developed for real-time characterization of a parachute during inflation. Two techniques were applied to measure static and dynamic stresses in a parachute canopy fabric material and suspension lines: the modal power distribution (MPD) technique and the fiber Bragg grating (FBG) technique. Several tests were conducted under various loading conditions, using a bi-axial tensile tester. The MPD technique was used to measure the transverse stresses in the parachute canopy fabric material and was applied using two experimental set-ups: one using a CCD camera and the other using a photo-detector. The FBG technique was used to measure the axial stresses in the parachute canopy fabric material. The tests were performed using the spectrum analyzer set-up with the bi-axial machine. Finally, a drop test was performed on the parachute canopy fabric material using the MPD technique with the photo-detector set-up.