A Fiber Bragg Grating Anchor Rod Force Sensor for Accurate Anchoring Force Measuring

Abstract

This paper presents a novel anchor rod force sensor based on fiber Bragg grating (FBG) for accurate anchoring force measurement. A special FBG strain sensor with enhanced sensitivity has been designed and embedded in the centre line of an elastic structural body, which forms the main body of the anchor rod force sensor. The mechanical structure design and measuring principle of the proposed anchor rod force sensor have been presented detailedly. Then a sensor prototype has been manufactured and fully tested. The experimental results show that the sensor provides a sensitivity of 11.58 pm/kN with a fitting linear correlation coefficient of 0.9996 in a measurement range of 50 kN, a repeatability error of 3.26%, and a hysteresis error of 3.87%. Furthermore, good resistance to bending effects of anchor rod, good creep resistance (fluctuant value is within 2 pm), and good temperature compensation capacity (maximum value is 11 pm) have also been verified. These results promise the sensor better applicability in the health monitoring of large civil engineering structures.

Fiber-Optic System for Monitoring Pit Collapse Prevention

“…(1) Microscopic characteristics of the structure or molecular characteristics presented in the form of a set of variables of the model under study ς 0 = n ∞ (U 0 ; ν 0 ; δ 0 ; n 0 ; a) [1], where U 0 is the activation energy of relaxators (centers of interaction of an electromagnetic wave (optical signal) with matter); ν 0 is the natural oscillation frequency of the relaxator (molecule, ion, cluster) relative to the equilibrium position; δ 0 is the width of the potential barrier overcome by the relaxer due to thermal activation (in this case, as a result of thermal fluctuations that significantly affect optical processes in the fiber in the field of thermoelastic deformations); n 0 is the equilibrium concentration of relaxers (in the absence of external disturbances (electromagnetic fields) in OF); a is the lattice constant (in the case of a crystal structure) [10]. For the first time, the application of the method of minimizing the comparison function in relation to theoretical studies of the kinetics of electro-optical and electrophysical processes in materials of various crystal structure complexity (in particular, in fiber-optic samples) was proposed in [10][11][12][13][14]. (2) Field characteristics: amplitude E 0 and frequency ω of the electromagnetic wave…”

“…The main methods of measuring external impacts include Tunable Wavelength Coherent Optical Time Domain Reflectometry (TW-COTDR), Phase Shift Pulse Brillouin Optical Time Domain Reflectometry (PSP-BOTDR), Pulse-Prepump Brillouin Optical Time Domain Analysis (PPP-BOTDA), Brillouin Optical Time Domain Analysis (BOTDA), Brillouin Optical Time Domain Reflectometry (BOTDR), Optical Frequency Domain Reflectometry (OFDR) or methods based on measuring losses in an OF caused by Brillouin scattering [10]. Moreover, the most widely used among FOS sensors are those built on Bragg gratings, with the measurement of losses by scattering of Brillouin, Raman, Rayleigh [11]. It should be noted that the main advantage of OF is the ability to measure not only one parameter but also two interrelated parameters [12,13], for example, displacement and mechanical stress or two parameters with a low correlation, such as temperature and mechanical stress [14,15], and in some cases, three parameters [16].…”