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A fiber Brag grating-based temperature sensor FBG together with high accuracy, resolution and compact size interrogation system using a short period grating was presented in this work. The designed sensor measures the temperature from 35 °C temperature to 41 °C which is represented the ranges of human body temperature for use in medical applications. In this paper, we present some results obtained from experiments within a measurement range from (35°C to 40°C) which is from hypothermia to hyperthermia) that the sensor has high sensitivity and high resolution of (85.9%) for FBG sensor. After the results we obtained and the features that the sensor enjoys, such as small size, immunity from electrical influence, and the ability to work in environments Magnetic Resonance Imaging (MRI) environments. The sensor can be used in hospitals and clinics for improvement and monitoring of patients. The importance of this work increases due to the COVID-19 pandemic we are going through, so this work can be proposed to contribute to monitoring patients’ cases and considered as a new equipment in studying temperature sensor in human.

The performance of packaged Fiber Bragg grating (FBG) sensors with carbon fiber reinforced plastic (CFRP) may degraded even functional failure with the working time increases. The reliability of this kind of packaged FBG sensors has been analyzed by using the FMEA method in this paper. Considering the working environment of FBG sensor, such as alternating loads and ageing, the related failure modes are discussed. The risk index of each failure mode is calculated. The relationship between different failure modes is analyzed, and as well as the weak links of the packaging design and process of the FBG sensor. The results are helpful to improve the availability and the reliability of packaged FBG sensor by CFRP.

This article successfully applied fiber bragg grating sensors to multi-parameter online monitoring of various objects such as substation equipment and important structures, where using various types of sensors including static level, displacement meter, inclinometer and strain gauge to remotely monitor the safety status of substation equipment and important structures in real time. It is conducive to safe and stable operation of substations. The results show that the FBG sensor can realize the automatic and real-time measurement of multi-physical quantities in the substation safety monitoring. This technology provides data support for the substation disaster prevention and reduction, and has important practical application value.

The bending deformation of Carbon Fiber Reinforced Polymer (CFRP) shaft is one of the important indicators reflecting its performance. Monitoring the deformation of CFRP shaft under different loads is of great significance for the optimal design of CFRP shaft. Fiber Bragg Grating (FBG) sensor is small in diameter, easy to be embedded inside the CFRP shaft, which has little influence on the structure itself. In addition, it can realize "one fiber multi-point" measurement, which is very suitable for the internal monitoring of anisotropy composites. This paper proposes a pre-embedded FBG sensor to monitor CFRP shaft strain. Prepared CFRP shaft test piece. Four FBG sensors are embedded inside the shaft, and four FBG sensors and four strain gauges are pasted on the surface of the shaft. The CFRP shaft was subjected to three-point bending loading on a universal testing machine. The strain data obtained by FBG sensor and strain gauge under various loads were compared and analyzed. The feasibility and accuracy of the embedded FBG sensor to monitor CFRP shaft strain were verified.

The Vibration detection is one of the key technologies of structural reliability. Traditional detection methods mainly focus on the analysis under single excitation, while the actual engineering problems mostly present the resonance phenomenon of multi-source excitation. Therefore, in this paper, based on the characteristics of FBG sensor, the vibration response characteristics under multi-source excitation are studied, including theoretical simulation and experimental research under multi-source excitation. On this basis, the experimental system for damage detection is built and its results show that this method by multi-excitation detection is feasible and it is sensitive to crack damage.

Being the main and safest oil and gas transportation method globally, the integrity and condition of pipeline system is very crucial. The offline existing maintenance method might have consumed more time and risky as it does not detect the flaws immediately after it is formed. This paper focused on the detection of the leak detection in pipes using the Fiber Bragg Grating pressure transducer. Two different sizes of artificial leak were introduced on the pipe in order to measure the applicability of the FBG sensor in detecting the leak in a pipe. The FBG signals were acquired on a galvanized steel pipe in lab scale size equipped with 5 pairs of valve. During the experimental work execution, the FBG sensor was attached on the pressure transducer that is linked to the pipeline. Findings showed that bigger leak size contributed to higher voltage drop in the pipe which was 0.0075 V compared to 0.0017 V. This study shows that FBG is a reliable method to be utilised in leak detection because it is very sensitive towards pressure changes in pipe. The results also showed that FBG exhibits good uniformity.

Today, research on steel corrosion issues are still widely debated and revived scientific attention. In order to detect steel corrosion, an idea to explore the relationship of corrosion potential using half-cell potential related to the variations in strain change on embedded steel measured by FBG sensor were explored. In this study, the steel was embedded in various types of concrete consist of NPC, HPC, UHPC and a series of nano metaclayed-UHPC. It was observed that the steel embedded in NPC is very low in corrosion resistance. Conversely, nano metaclayed-UHPC can delay the embedded steel to corroded. It was also noticeably that the corrosion readings for steel embedded in NPC specimens possess the highest possibility of corrosion potential as well as the large strain was observed by using FBG. Inclusion of 1% nano metaclay in UHPC shows a superior performance in term of corrosion resistance and protected the steel from corrosion. The RSM analysis was found that the R2 values are strong relationship between corrosion potential and strain changes. The R2 obtained for NPC, HPC, UHPC, UHPC1, UHPC3 and UHPC5 models associated with corrosion potential with respect to strain changes were found to be 0.95, 0.99, 0.87, 0.93, 0.98 and 0.97, respectively.

Fibre optic Bragg gratings (FBGs) written in normal and reduced diameter high birefringence (HiBi) fibres are studied. Chemical etching is used to reduce the diameter of fibres while the optical properties of the FBG spectrum are measured. The results obtained agree qualitatively with the stress enhanced chemical etching. The birefringence of the fibre is determined as a function of the diameter. Optical characterization of the FBG under transverse strain and temperature is also performed. The results obtained show the feasibility of the simultaneous measurement of those parameters with a HiBi FBG sensor.

The civil engineering community is becoming increasingly interested in monitoring structural behavior and in assessing its corresponding integration. In this paper, fiber Bragg grating (FBG) sensors were installed to investigate the in situ characteristics of the hydration progress period and the curing process of highway bridge construction. Moreover, the security and serviceability of a bridge can be changed by material proprieties such as shrinkage and creep, which is correlated with the prestressing strain and settlement during the support frame removal. The response and effectiveness of the schedule at every step during the prestressing process, and during the support frame removal, were also examined. It appeared that an FBG sensor was clearly shown to be a smart sensor candidate for function integration and response of a highway bridge during both its construction and service life.

Using the spectral selectivity and adjustable reflectivity FBGs are predestined for serial networking. Presently the addressing is realised by time division multiplex (TDM) or wavelength division multiplex (WDM). But these technologies have big disadvantages regarding the effective use of the prevailing resources time and wavelength, respectively. In this paper a new scheme capable of addressing a large number of FBGs in a single serial network is proposed and compared to TDM and WDM. Using all optical sequence inversion keyed (SIK) direct sequence (DS) code division multiplex (CDM) it overcomes the restrictions handling the resources time and wavelength without losing accuracy.

The authors have applied newly developed small-diameter fiber Bragg grating (FBG) sensors, whose cladding is 40 µm in diameter, for the detection of transverse cracks in carbon fiber reinforced plastic (CFRP) laminates. In previous research, the small-diameter FBG sensors were embedded in CFRP cross-ply laminates. When transverse cracks occurred, reflection spectra from the FBG sensors broadened with an increase in the crack density. Thus, the authors showed that small-diameter FBG sensors had the potential to detect the occurrence of cracks. In the present research, this technique is applied to the detection of the transverse crack evolution in CFRP quasi-isotropic laminates, whose laminate configuration is more suitable for practical use. Through the experiment and the theoretical calculation, it was found that the small-diameter FBG sensor could also detect transverse cracks in quasi-isotropic laminates quantitatively.

In this paper, we demonstrate a multipoint fiber Bragg grating (FBG)-based sensor system by using intensity and wavelength-division-multiplexing (I-WDM) technique to enhance the sensing capacity and capability. In the proposed multipoint sensor system, a three output port optical splitter with different output ratios of 50%, 35% and 15% is proposed to connect each intensity coding FBG sensor for strain and temperature sensing simultaneously. Different output ratios of connected ports can produce different intensity-coding for I-WDM application. Nine FBGs with different Bragg wavelengths are employed for demonstration. The proposed FBG sensor system not only can sense the strain and temperature simultaneously, but also can increase the capacity and capability.

We propose a novel optical bistable device (OBD) in frequency-domain with which we can perform optical bistable operations in a number of fibre Bragg gratings (FBGs) which are included in the same OBD. Such an OBD may bring more opportunities in applications and, as an example, we show the possibility of using it in an FBG sensor demodulating system. By use of a tunable light source, consisting of a broad band source and a scanning fibre F–P (FFP), we demonstrate the above-mentioned operations experimentally.

In-fibre Bragg grating (FBG) sensors are one of the most exciting developments in the field of optical fibre sensors in recent years. Compared with conventional fibre-optic sensors, FBG sensors have a number of distinguishing advantages. Significant progress has been made in applications to strain and temperature measurements. FBG sensors prove to be one of the most promising candidates for fibre-optic smart structures. This article presents a comprehensive and systematic overview of FBG sensor technology regarding many aspects including sensing principles, properties, fabrication, interrogation and multiplexing of FBG sensors. It is anticipated that FBG sensor systems will be commercialized and widely applied in practice in the near future due to the maturity of economical production of FBGs and the availability of cost effective interrogation and multiplexing techniques.

This paper presents a single fiber Bragg grating (FBG) sensor that is capable of measuring the axial load and temperature simultaneously. The FBG sensor is coated with a block of recrystallized Lophine, which introduces the bandwidth modulation of the FBG reflectance spectrum. Thermal-mechanical testing of the Lophine-coated FBG sensor under different load and temperature combinations was carried out. It was discovered that the FBG bandwidth is linearly proportional to the applied load and temperature. By fitting the measured FBG bandwidths and central Bragg wavelengths as linear functions of the axial load and temperature, we demonstrated that the axial load and temperature can be inversely determined from the measured reflectance spectrum of a single Lophine-coated FBG sensor. The measurement errors for the axial load and the temperature were found to be ±4 gm and ±4 °C, respectively.

A novel technique for simultaneous measurement of static strain, temperature and vibration in health monitoring of structures is demonstrated using an integrated in-fibre Bragg grating (FBG)/extrinsic Fabry-Perot interferometer (EFPI) sensor. The EFPI sensor provides static strain and vibration information simultaneously by using the channel-spectrum method and the low-coherence interferometric technique, respectively. The FBG sensor is used for temperature measurement. The experimental results show that a static-strain accuracy of ±20µe, a temperature accuracy of ±1°C and a vibration resolution of 1 nm have been achieved with a good repeatability.

This paper presents an aircraft health and usage monitoring system (HUMS) using fiber Bragg grating (FBG) sensors. This study aims to implement and evaluate the HUMS for in-flight strain monitoring of aircraft structures. An optical-fiber-based HUMS was developed and applied to an ultralight aircraft that has a rectangular wing shape with a strut-braced configuration. FBG sensor arrays were embedded into the wing structure during the manufacturing process for effective sensor implementation. Ground and flight tests were conducted to verify the integrity and availability of the installed FBG sensors and HUMS devices. A total of 74 flight tests were conducted using the HUMS implemented testbed aircraft, considering various maneuvers and abnormal conditions. The flight test results revealed that the FBG-based HUMS was successfully implemented on the testbed aircraft and operated normally under the actual flight test environments as well as providing reliable in-flight strain data from the FBG sensors over a long period of time.

The model of force analysis on a uniform strength beam is built by the general finite element program (ANSYS software). The flexivity profile produced by uniform strength beam with different forces is simulated by ANSYS software. In experiment, a fiber Bragg grating sensor is fixed on the uniform strength beam with modified acrylate. The flexivity and strain are varied by changing the load on the end of the beam. The strain of the uniform strength beam is measured with FBG when applied force is varied from 2.45N to14.7N with a step of 2.45N. Both the simulated and experimental results show that, the strain induced by the uniform strength beam is linear with the load force. The sensitivity is 18.32μ/N for experimental measurement, and 19.72μ/N for simulation. The experimental results are consistent with the simulation results, with the maximum measurement error of strain being 7.4%. It indicates that, the FBG sensor fixed with modified acrylate is proved to be effectively and reliably in the applications of civil engineering.

Online strain measurement of rotating blades has been achieved with fiber Bragg grating (FBG) sensors and a rotary optical coupler constituted by two lenses and an air gap between them. In addition to the FBG sensors installed in blades, a FBG sensor having a minimal effect on the deformation of a blade was introduced and utilized to compensate the inevitable light intensity loss change due to shaft rotation. The rotary optical coupler enables continuous transmission of optical information about local deformation on a blade to a signal processing unit at the stationary side. Strains at five different locations along the blade were successfully measured online, while the rotating speed is changed rapidly.