Theoretical approach to optimize fiber Bragg grating sensor performance using an automated new code

Multi-Functional Measurement Using a Single FBG Sensor

In this paper, characterization of the fiber Bragg grating (FBG) based on grating profile and apodization type has done. The FBG parameters considered here are grating length, grating profile and apodization type. The characteristics of FBG include reflectivity, full width at half maximum (FWHM) and side lobe power. The FBGs having high reflectivity, low FWHM and side lobe power are required for the sensing applications. A GratingMOD simulation tool based on a coupled mode theory and a transfer matrix method is used for the characterization of FBG. The effect of FBG parameters, grating length, grating profile and apodization on the characteristics of FBG is studied. The FBG parameters, grating length, grating profile and apodization type are optimized for the sensing applications. The FBG having grating length, 5 mm, sinusoidal profile and apodization type is optimized.In this paper, characterization of the fiber Bragg grating (FBG) based on grating profile and apodization type has done. The FBG parameters considered here are grating length, grating profile and apodization type. The characteristics of FBG include reflectivity, full width at half maximum (FWHM) and side lobe power. The FBGs having high reflectivity, low FWHM and side lobe power are required for the sensing applications. A GratingMOD simulation tool based on a coupled mode theory and a transfer matrix method is used for the characterization of FBG. The effect of FBG parameters, grating length, grating profile and apodization on the characteristics of FBG is studied. The FBG parameters, grating length, grating profile and apodization type are optimized for the sensing applications. The FBG having grating length, 5 mm, sinusoidal profile and apodization type is optimized.

Fiber Bragg grating (FBG) sensors are excellent transducers for collecting ultrasonic wave signals for structural health monitoring (SHM). Typically, FBG sensors are directly bonded to the surface of a structure to detect signals. Unfortunately, demodulating relevant information from the collected signal demands a high signal-to-noise ratio because the structural ultrasonic waves have low amplitudes. Our previous experimental work demonstrated that the optical fiber could be bonded at a distance away from the FBG location, referred to here as remote bonding. This remote bonding technique increased the output signal amplitude compared to the direct bonding case, however the mechanism causing the increase was not explored. In this work, we simulate the previous experimental work through transient analysis based on the finite element method, and the output FBG response is calculated through the transfer matrix method. The model is first constructed without an adhesive to assume an ideal bonding condition, investigating the difference in excitation signal coherence along the FBG length between the two bonding configurations. A second model is constructed with an adhesive to investigate the effect of the presence of the adhesive around the FBG. The results demonstrate that the amplitude increase is originated not from the excitation signal coherence, but from the shear lag effect which causes immature signal amplitude development in the direct bonding case compared to the remote bonding case. The results also indicate that depending on the adhesive properties the surface-bonded optical fiber manifests varying resonant frequency, therefore resulting in a peak amplitude response when the input excitation frequency is matched. This work provides beneficial reference for selecting adhesive and calibrating sensing system for maximum ultrasonic detection sensitivity using the FBG sensor.

Multivariate statistics based damage detection algorithms employed in conjunction with novel sensing technologies are attracting more attention for long term Structural Health Monitoring of civil infrastructure. In this study, two practical data driven methods are investigated utilizing strain data captured from a 4-span bridge model by Fiber Bragg Grating (FBG) sensors as part of a bridge health monitoring study. The most common and critical bridge damage scenarios were simulated on the representative bridge model equipped with FBG sensors. A high speed FBG interrogator system is developed by the authors to collect the strain responses under moving vehicle loads using FBG sensors. Two data driven methods, Moving Principal Component Analysis (MPCA) and Moving Cross Correlation Analysis (MCCA), are coded and implemented to handle and process the large amount of data. The efficiency of the SHM system with FBG sensors, MPCA and MCCA methods for detecting and localizing damage is explored with several experiments. Based on the findings presented in this paper, the MPCA and MCCA coupled with FBG sensors can be deemed to deliver promising results to detect both local and global damage implemented on the bridge structure.

Fiber Bragg Grating (FBG) sensors are comprehensively recognized as a structural stability monitoring device for all kinds of geo-materials by either embedding into or bonding onto the structural entities. The physical model in geotechnical engineering, which could accurately simulate the construction processes and the effects on the stability of underground caverns on the basis of satisfying the similarity principles, is an actual physical entity. Using a physical model test of underground caverns in Shuangjiangkou Hydropower Station, FBG sensors were used to determine how to model the small displacements of some key monitoring points in the large-scale physical model during excavation. In the process of building the test specimen, it is most successful to embed FBG sensors in the physical model through making an opening and adding some quick-set silicon. The experimental results show that the FBG sensor has higher measuring accuracy than other conventional sensors like electrical resistance strain gages and extensometers. The experimental results are also in good agreement with the numerical simulation results. In conclusion, FBG sensors could effectively measure small displacements of monitoring points in the whole process of the physical model test. The experimental results reveal the deformation and failure characteristics of the surrounding rock mass and make some guidance for the in situ engineering construction.

As an important factor in-service Structure health monitoring (SHM), predictions of displacement become the basis for determining the decrease of modern aircraft and aerospace structural performance. Optical fiber Bragg grating (FBG) sensors are considered an important tool for SHM , however, FBG sensors are rarely directly applied to monitor the displacement because of the intrinsic fragility. To overcome such a problem, we propose a novel method for design and curving an FBG sensor using auxiliary flexible driving function of the shape memory alloy (SMA) to monitor the displacement. The FBG sensor is curved slowly to an S shape along with SMA wire. Strain gradient of SMA which is applied by displacement loading is obtained by finite element analysis. By analyzing the spectral simulations, bandwidth of spectrum is increased and the central wavelength is changed. Spectral properties of curved FBG sensor are analyzed by stretch experiments, the results shown that its bandwidth, light intensity of peak and central wavelength are increased and the central wavelength change is linear with displacement. A new sensor based on an FBG sensor and SMA Actuators can be used to monitor displacement with displacement sensitivity of 141pm/mm.

Fiber Bragg grating (FBG) sensors are excellent transducers for ultrasonic signal detection in structural health monitoring (SHM) application. While the FBG sensors are typically bonded directly on the surface of a structure to collect signals, one of the major challenges arises from demodulating relevant information from the low amplitude signal. The authors have experimentally demonstrated that the ultrasonic wave detection sensitivity of FBG sensors can be increased by bonding optical fiber away from the FBG location. This configuration is referred to here as remote bonding. However the mechanism causing this phenomenon has not been explored. In this work, we simulate the previous experimental work through a transient analysis based on the finite element method, and the output FBG response is calculated through the transfer matrix method. We first model an optical fiber bonded on the surface of an aluminum plate with an adhesive. The consistent input signal is excited to the plate, which is detected by the directly and remotely-bonded FBGs. The effect of the presence of the adhesive around the FBG is investigated by analyzing strain and displacement along the length of the FBGs at the locations of direct and remote bonding cases, and the consequent output FBG responses. The result demonstrates that the sensitivity difference between the direct and remote bonding cases is originated from shear lag effect due to adhesive.

In this paper, one large Fiber Bragg Grating (FBG) sensor sensing network for bridge local health monitoring was studied, designed and implemented to Harbin Sifangtai Bridge, China. According to the hot point principle and finite element analysis results, FBG sensors installation scheme was made to monitor the local strain of key elements, respectively. 60 FBG sensors had been installed in monitoring points along the height of I-shape girders distributed in three main monitoring sections along the bridge. Monitoring results in load testing period was obtained, the static and dynamic results show that FBG sensors can monitoring the local strain precisely, and the local strain response is in the safe range under test vehicle load. Monitoring results in service period was obtained, 9 months after load test. Results show that maximum local strain responses in three main monitoring sections are in the safe range, under the dynamic vehicle load. Comparison of the monitoring results from FBG sensor sensing network are used to unveil the local health condition of Sifangtai Bridge reflected by local strain response.

The effectiveness of monitoring systems for composite materials is improving owing to their increasing utilisation. Abrupt failure in composite requires an effective detection method and monitoring system. The fibre Bragg grating (FBG) sensor is one of the alternative sensors used for detecting and monitoring the structural health of an engineering structure. This study evaluated the applicability of the FBG sensor for fatigue damage monitoring in the composite. This study involved composite fabrication and experimental work. The glass fibre reinforced polymer specimens were fabricated using fibre glass and resin and made into flat workpieces. The workpieces were then utilised in a series of fatigue tests. Prior to the fatigue test, tensile tests were conducted to verify the ultimate strength of the material. Commencement of fatigue tests were recorded using the FBG sensor. Once the tests were started, the signals were acquired using the FBG sensor simultaneously. Data acquisition was continued during the fatigue test progression until the specimen failed. Results show the FBG wavelength shifted from its original position during tension loading and whenever the composite was released to its original position in the cyclic test. The FBG sensor seems a promising way to monitor fatigue damage and can be utilised in fatigue monitoring. Its wavelength shifts or changes is capable to monitor fatigue damage progression effectively.

This study investigates the effectiveness of embedding fiber Bragg grating (FBG) sensors in power transmission towers to assess the remaining service life of the structures following impacts from strong winds and hurricanes. FBG sensors monitor the structural integrity of the tower using online measurement of strain variations at critical structural points. The novelty of this work lies in employing a compact long short-term memory (LSTM) framework to estimate the remaining useful lifetime (RUL) from real-time FBG sensor data under both stable and fluctuating wind conditions. To estimate RUL of the tower, LSTM neural network has been implemented, providing predictive insights for proactive maintenance and risk mitigation. A prototype transmission tower was built and experimentally evaluated in a wind tunnel to assess the effectiveness and performance of the proposed RUL model. To simulate different hurricane categories, the experiment was conducted across wind speeds between 0 and 150 mph. FBG sensors installed at critical locations continuously captured real-time strain data, which was transmitted via a low-power micro FBG interrogator to a computer for input into the RUL prediction model. The proposed three-layer LSTM converges rapidly, reducing training and validation loss by nearly two orders of magnitude within 40 epochs, and achieves robust RUL predictions with an average bias of about 50 s on the test set. To quantify structural health, a mathematical health indicator was formulated based on the observed strain responses. The FBG sensors demonstrated high effectiveness in accurately detecting strain variations and monitoring the tower's dynamic behavior under extreme wind loads. The findings support the implementation of condition-based maintenance strategies, enhance safety assessments, and enable early failure detection. This approach not only improves operational reliability but also facilitates timely intervention and maintenance during critical events. Received: 26 June 2025 | Revised: 12 September 2025 | Accepted: 11 November 2025 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data are available from the corresponding author upon reasonable request. Author Contribution Statement Yu Shi: Methodology, software, formal analysis, data curation, writing – original draft, writing – review & editing, visualization, supervision, and project administration. Abolghassem Zabihollah: Conceptualization, methodology, software, validation, investigation, resources, data curation, writing – original draft, writing – review & editing, visualization, supervision, and project administration. Yao-Chi Yu: Methodology, software, formal analysis, data curation, and writing – original draft. Arunima Pathak: Investigation, writing – original draft, and visualization. Oluwaseyi Oyetunji: Investigation.

Recently, Fiber Bragg Grating(FBG) sensors are being used in various fields. However, it has difficulty to measure at the place where it is not possible to connect fibers each other physically. In this study, using FBG a collimator, we have measured strains with a single optical fiber with many FBG sensors where FBG sensors on one optical fiber line is installed on the beam and the other optical fiber line is connected with an optical interrogator installed at stationary side. The optical fiber lines between an optical fiber line with FBG sensors on the beam and the other optical fiber line on the stationary part are connected by the collimator which makes the use of light's unique characteristic - light travels through space. The experiment showed that the wave length of the light were changed to be linear as strains increased, and the accurate strains were measured by applying the collimator collection factor, which was proposed in this paper.

We have developed a new distributed strain measurement system with a long gauge Fiber Bragg Grating (FBG) sensor based on Optical Frequency Domain Reflectometry (OFDR). This sensing system enables us to measure strain at an arbitrary position along the FBG sensor with a high spatial resolution below 1mm. However, the sensing range of this system is confined to 〜10m at present. To expand the measurement range, we have problems in several components of the measurement system, such as the signal processing capability, limitation of measurable range due to reflection properties of the FBG sensor, and the effect of length fluctuation in the arm length of the interferometer. This paper discusses these factors using a simulation model of based on coupled mode theory. The signal analysis time was shortened by confining the analyzing section. The simulated result showed that, the measurable range is approximately 1.5m, and the length fluctuation in the arm length of measurement interferometer has a significant effect on the measured result.

On the improvement of strain measurements with FBG sensors embedded in unidirectional composites

Strain measurement for composite tubes using embedded, fiber Bragg grating sensor

The advancement of age and the increased awareness of public health have resulted in increased demand for continuous vital sign monitoring devices. Therefore, we developed a noninvasive vital sign measurement device without physical resistance to the user using a fiber Bragg grating (FBG) sensor. The FBG sensor was fixed on the wrist, and a pulse wave signal was obtained. Additionally, we focused on the similarity between this pulse wave signal and the second derivative of the plethysmogram (SDPTG). Classifying this signal, we found that its shape changed according to the age and blood pressure. We found that the change in the shape of the pulse wave signal and the SDPTG have the same tendency. Therefore, it is feasible to estimate the vascular age and arteriosclerosis with the signal obtained by an FBG sensor. On the basis of these results, the FBG sensor system can measure multiple vital signs and monitor health more comprehensively.