Fiber Bragg Grating Vibration Research Articles

Adaptive Vibration Monitoring of Railway Track Structures Using the UWFBG by the Identification of Train-Load Patterns

Due to the capability of multiplexing thousands of sensors on a single optical cable, ultra-weak fiber Bragg grating (UWFBG) vibration sensing technology has been utilized in monitoring the vibration response of large-scale infrastructures, particularly urban railway tracks, and the volume of the collected monitoring data can be huge with the great number of sensors. Even though the train-induced vibration responses of urban railway tracks constitute the most informative and crucial component, they comprised less than 7% of the total operational period. This is mainly attributed to the temporal sparsity of commuting trains. Consequently, the majority of the stored data consisted of low-informative environmental noise and interference excitation data, leading to an inefficient structural health monitoring (SHM) system. To address this issue, this paper introduced an adaptive monitoring strategy for railway track structures, which is capable of identifying train-load patterns by leveraging deep learning techniques. Inspired by image semantic segmentation, a U-net model with one-dimensional convolution layers (U-net-1D) was developed for the pointwise classification of vibration monitoring data. The proposed model was trained and validated using a dataset obtained from an actual urban railway track in China. Results indicated that the proposed method outperforms the traditional dual-threshold method, achieving an Intersection over Union (IoU) of 94.27% on the segmentation task of the test dataset.

A symmetrical dual-mass block fiber Bragg grating vibration sensor based on a V-shaped flexible hinge

Real-time monitoring of vibration properties in micro-seismic applications, such as petroleum exploration, physical oceanography, and perimeter security, is important for deep exploration and the prediction of geological disasters and other fields. The fiber Bragg grating (FBG) vibration sensor with symmetrical V-shaped flexible hinges and a dual mass block is proposed. Utilizing formula derivation and simulation software, the sensor's structural parameters are optimized and subjected to analysis. These simulations inform the fabrication of the actual sensor, and subsequently, the sensor's performance is empirically tested. The results show an average sensitivity of 73.86 pm/G and a natural frequency of 800 Hz, with a working range of 20–340 Hz. Its exhibits anti-interference in the transverse direction is less than 5 % during vibration measurement. The research outcomes offer a point of guidance for the progress of FBG accelerometer development within applications that involve measuring low- to medium-frequency accelerations.

Low-frequency FBG vibration sensors for micro-seismic monitoring

Vibration sensors are key components in low-frequency micro-seismic monitoring, and their performance directly determines the accuracy of monitoring results. In response to the current problem that fiber Bragg grating (FBG) vibration sensors are difficult to effectively monitor micro-seismic low-frequency vibration signals, a rigid L-shaped beam FBG vibration sensor based on bearings is proposed. Firstly, a sensor model is established and theoretically analyzed; secondly, key parameters are optimized using differential evolution algorithm and imported into COMSOL simulation software for static stress analysis and dynamic characteristic analysis; finally, the sensor prototype is developed and a low-frequency vibration test system is set up to verify the sensor performance. The results reveal that the inherent frequency of the sensor is 57 Hz, with a flat response band of 0.3–35 Hz, a frequency lower limit of 0.05 Hz, a transverse interference degree of 4.5%, an average sensitivity of over 800 pm g−1, a dynamic range of 67.75 dB, favorable linearity, and the ability to achieve temperature self-compensation. Research findings provide new insights into low-frequency micro-seismic monitoring.

Cantilever vibration sensor based on Fiber Bragg Grating temperature compensation

To improve the sensitivity of fiber Bragg grating (FBG) vibration sensor and reduce the influence of temperature on vibration detection, an FBG vibration sensor with equal strength beam as elastic structure and temperature self-compensated is proposed. The working principle of the sensor is analyzed, the resonant frequency and the sensitivity are derived through the formula, the structural parameters are optimized, and its good response characteristics are proved by experiments. The theory of the proposed sensor is verified by experiments, and the experimental results show that the temperature impact on the sensor structure is reduced to 0.17 pm/°C in the range of 30–75°C. The sensor has a good response flat region at 20–220 Hz, the sensitivity is 149.8 pm/g. and the transverse sensitivity is only 3.95 % of the sensitivity in the working direction. Experiments show that the sensor has good comprehensive characteristics. Therefore, the sensor has great application prospect in vibration signal detection in the environment with obvious temperature changes, such as oil exploration, aerospace and so on.

Research on Feature Extraction Method of Fiber Bragg Grating Vibration Monitoring Based on FFT

Research on Feature Extraction Method of Fiber Bragg Grating Vibration Monitoring Based on FFT by Mengxing Zhang, Youming Hua, Chunbin Chen, Chenkun Chu, Xiuli Zhang * Faculty of Civil Engineering and Mechamnics, Jiangsu University, Zhenjiang, 212013, China * Author to whom correspondence should be addressed. Journal of Engineering Research and Sciences, Volume 1, Issue 7,

Exploration of Vibration Signal Measurement Method of Automobile Parts Utilizing FPGA/Photoelectric Sensor

According to the current situation of the sensor, a vibration signal monitoring system is proposed of automobile parts based on Field Programmable Gate Array (FPGA) and photoelectric sensor. FPGA controls the peripheral circuit and sets instructions to process the acquired vibration signal. The Serial Port Interface (SPI) is utilized for the data transmission and communication between the instruction set and FPGA. FPGA transmits the acquired data to the Digital Signal Processing (DSP) through the SPI and then backs up to the Secure Digital (SD) card for in-depth analysis. The Fiber Bragg Grating (FBG) is selected for the monitoring system. The sensor presents many characteristics: anti-interference, high sensitivity, lightweight, and small volume. Afterward, the FBG is used for vibration signal acquisition, and the corresponding sensor module circuit is designed. Subsequently, an Analog to Digital (A/D) conversion circuit is designed on the acquisition circuit together with the vibration conditioning circuit and FPGA peripheral circuit. In the experiment, the vibration signal is monitored in real-time through the designed monitoring system, and the changes in the Center Wavelength (CWL) of the FBG from vibration are recorded. The data are screened, and more reasonable data are produced for vibration signal processing. The vibration signal is processed through Time-Domain (TD) linear fitting and time-frequency transformation, to assess the FBG vibration sensor’s vibration response in the monitoring system.

Damage Identification of I-Beam Based on Fiber Bragg Grating Vibration Sensor and Extreme Learning Machine

Damage Identification of I-Beam Based on Fiber Bragg Grating Vibration Sensor and Extreme Learning Machine

A Novel Fiber Bragg Grating Vibration Sensor Based on Orthogonal Flexure Hinge Structure

A novel two-dimensional (2-D) fiber Bragg grating (FBG) vibration sensor based on an orthogonal flexure hinge structure has been proposed in this paper. The elastic element of this sensor which contains an inertial body, flexure hinge pair and base has been designed in small size and integrally fabricated by using wire cutting. Two FBGs are arranged in the vertical direction by two ends pasted setup to measure the vibration-induced structure displacement. The theoretical and simulation model of the FBG vibration sensor is established. The analysis shows that this structure with a 3 mm length hinge could achieve a high working frequency and low cross-interference. The dynamic characteristics of the sensor have been measured by excitation experiments. The results match the model well that the resonant frequency of the sensor in the X and Y-directions is around 1275 Hz and 1482 Hz, respectively. The third-order natural frequency of 4932 Hz, which indicates that the sensor has high torsional rigidity and strong torsional vibration resistance. The sensor has a broad flat frequency range from 20 to 800 Hz and a sensitivity 41.2/34.5 pm/g in the X/Y-direction. The cross-interference in two directions is less than 6%. The sensor has high frequency and low cross-sensitivity, which is suitable for structural health monitoring of mechanical equipment.

Study on the Sensitivity of Bare Fiber Bragg Grating for Ultrasonic Frequencies Response Under Various Temperature

This work presents a study on the sensitivity of bare fiber Bragg grating (FBG) to detect ultrasonic frequencies under various temperature. Two infrared (IR) laser with excitation wavelength, λ=1310nm and λ=1550nm were employed. Various types of FBG with operating wavelength of 1546nm, 1550nm and 1554nm were used to identify the optimum design of sensor in detecting range of ultrasonic frequencies between 5kHz until 30kHz under various surrounding temperature from 20°C until 30°C. The principle of FBG vibration detection lies in the fact that spectral shift would occur due to the acoustic-induced variations in the medium. In this study, the ultrasonic signal had been investigated by monitoring the amplitude of optical output power. At 30°C, the bare FBG with operating wavelength of 1554nm using 1310nm light source exhibits the optimum performance in detecting ultrasonic vibration frequency, in which its sensitivity was obtained as ∆P=0.10dBm. We believe that the sensitivity of the proposed sensor can be enhanced by introduce nanomaterials onto the FBG or by altering the physical structure of FBG.

Combining SDAE Network with Improved DTW Algorithm for Similarity Measure of Ultra-Weak FBG Vibration Responses in Underground Structures.

Quantifying structural status and locating structural anomalies are critical to tracking and safeguarding the safety of long-distance underground structures. Given the dynamic and distributed monitoring capabilities of an ultra-weak fiber Bragg grating (FBG) array, this paper proposes a method combining the stacked denoising autoencoder (SDAE) network and the improved dynamic time wrapping (DTW) algorithm to quantify the similarity of vibration responses. To obtain the dimensionality reduction features that were conducive to distance measurement, the silhouette coefficient was adopted to evaluate the training efficacy of the SDAE network under different hyperparameter settings. To measure the distance based on the improved DTW algorithm, the one nearest neighbor (1-NN) classifier was utilized to search the best constraint bandwidth. Moreover, the study proposed that the performance of different distance metrics used to quantify similarity can be evaluated through the 1-NN classifier. Based on two one-dimensional time-series datasets from the University of California, Riverside (UCR) archives, the detailed implementation process for similarity measure was illustrated. In terms of feature extraction and distance measure of UCR datasets, the proposed integrated approach of similarity measure showed improved performance over other existing algorithms. Finally, the field-vibration responses of the track bed in the subway detected by the ultra-weak FBG array were collected to determine the similarity characteristics of structural vibration among different monitoring zones. The quantitative results indicated that the proposed method can effectively quantify and distinguish the vibration similarity related to the physical location of structures.

A Novel Miniaturized Fiber Bragg Grating Vibration Sensor

In order to meet the needs of small space vibration detection, a novel miniaturized fiber Bragg grating (FBG) vibration sensor is proposed. With adopting the hinges and elastic plate as the elastic body, the miniaturization of sensor and suppression of transverse interference are achieved. The suspended FBG can avoid chirp phenomenon and realize distributed measurement. The structure model and principle of the sensor are introduced, the sensing characteristics of the sensor are analyzed theoretically, and the structural parameters of the sensor are determined by simulation analysis. The size of the miniaturized vibration sensor is 27 mm × 11 mm × 22 mm with a mass of only 5 g. Experimental results show that the sensor can accurately acquire vibration signals. The sensitivity is about 12 pm/g in the flat range of 0-800 Hz, and the natural frequency is 1525 Hz. Moreover, the transverse interference of the sensor is less than 3.5%, and its dynamic range is up to 86 dB. The sensor can be suitable for mechanical vibration measurement in the mid-high frequency range, which has special requirements for size, quality, and distributed measurement.

Internal Combustion Engine Fault Identification Based on FBG Vibration Sensor and Support Vector Machines Algorithm

State monitoring and fault diagnosis of an internal combustion engine are critical for complex machinery safety. In the present study, a high-frequency vibration system was proposed based on Fiber Bragg Grating (FBG) cantilever sensor and intelligent algorithm. Structural vibration signal containing fault information of engine valves and oil nozzle was identified by FBG sensors and preprocessed using wavelet decomposition and reconstruction. Moreover, vibration energy was taken as fault characteristics. Subsequently, a fault identification model was built based on multiclass υ-support vector classification (υ-SVC). Experimental tests on the valve fault and fuel injection advance angle fault were performed and presented to verify the efficacy of the proposed approach. The results here reveal that the proposed method exhibits excellent fault detection performance for ICE fault identification. Furthermore, the proposed method can achieve higher performance than other methods in the fault identification accuracy.

Distributed Weak Fiber Bragg Grating Vibration Sensing System Based on 3 \xd7 3 Fiber Coupler

A novel distributed weak fiber Bragg gratings (FBGs) vibration sensing system has been designed to overcome the disadvantages of the conventional methods for optical fiber sensing networking, which are: low signal intensity in the usually adopted time-division multiplexing (TDM) technology, insufficient quantity of multiplexed FBGs in the wavelength-division multiplexing (WDM) technology, and that the mixed WDM/TDM technology measures only the physical parameters of the FBG locations but cannot perform distributed measurement over the whole optical fiber. This novel system determines vibration events in the optical fiber line according to the intensity variation of the interference signals between the adjacent weak FBG reflected signals and locates the vibration points accurately using the TDM technology. It has been proven by tests that this system performs vibration signal detection and demodulation in a way more convenient than the conventional methods for the optical fiber sensing system. It also measures over the whole optical fiber, therefore, distributed measurement is fulfilled, and the system locating accuracy is up to 20 m, capable of detecting any signals of whose drive signals lower limit voltage is 0.2 V while the frequency range is 3 Hz‒1 000 Hz. The system has the great practical significance and application value for perimeter surveillance systems.

Cable Force Health Monitoring of Tongwamen Bridge Based on Fiber Bragg Grating

A normal cable force state of a suspension bridge is extremely vital to bridge safety. For cable force monitoring of already completed suspension bridges, it is not suitable to conduct direct parameter measurements by modifying the anchor cable structure of the bridge. Instead, using an indirect measurement would not destroy the bridge’s original structure and also meet engineering requirements. In this paper, a fiber Bragg grating (FBG) vibration sensor was developed for online monitoring of the cable vibration characteristics of Tongwamen bridge. The monitored vibration frequency was converted into cable force according to the theory of string vibration, so as to achieve an indirect measurement of bridge cable force. On both north and south sides of the bridge, FBG vibration sensors were mounted symmetrically on 8 of 19 cables for distributed measurement. The forces of two cables were found to be abnormal, which was considered worthy of attention and close inspection. This result is of great significance for the structural monitoring and safe operation of Tongwamen bridge.

String-type based two-dimensional fiber bragg grating vibration sensing principle and structure optimization

Vibration is a common phenomenon in the field of engineering, and it typically carries affluent and essential faulty information on health conditions of measured targets. Consequently, it is crucial to ensure safe and stable operations of engineering equipment through the use of effective vibration detection technologies. The increasingly and extensively advanced requirements for vibration detection make it essential to realize real-time multi-dimensional vibration information. To this end, a string-type two-dimensional (2D) fiber Bragg grating (FBG) vibration sensor has been presented through the use of both axial and transverse properties of a tightly suspended optical fiber. This sensor employs a novel mass block structure that possesses a specially designed hole pattern and introduces two stiffening beams through them to enhance the dynamic properties and remove the coupled rotational interference. The sensing principle and the proposed guidelines of cross-interference elimination have been validated by the simulation and experimental results. With the configuration of two stiffening beams, the working bandwidth of the proposed sensor has been enlarged to be respectively 10–150Hz and 10–800Hz along the x and y direction, which were consistent with both theoretical and simulation results. The rotational interference in the x direction has been significantly reduced to 15.3%. However, its complete removal requires a strict fabrication requirement and a bulky sensor size for this design. To further remove the interference and make the sensor compact, an optimized mass structure has been proposed to achieve almost complete removal of the rotational interference in the x direction.

Optical fiber grating vibration sensor for vibration monitoring of hydraulic pump

In view of the existing electrical vibration monitoring traditional hydraulic pump vibration sensor, the high false alarm rate is susceptible to electromagnetic interference and is not easy to achieve long-term reliable monitoring, based on the design of a beam of the uniform strength structure of the fiber Bragg grating (FBG) vibration sensor. In this paper, based on the analysis of the vibration theory of the equal strength beam, the principle of FBG vibration tuning based on the equal intensity beam is derived. According to the practical application of the project, the structural dimensions of the equal strength beam are determined, and the optimization design of the vibrator is carried out. The finite element analysis of the sensor is carried out by ANSYS, and the first order resonant frequency is 94.739 Hz. The vibration test of the sensor is carried out by using the vibration frequency of 35 Hz and the vibration source of 50 Hz. The time domain and frequency domain analysis results of test data show that the sensor has good dynamic response characteristics, which can realize the accurate monitoring of the vibration frequency and meet the special requirements of vibration monitoring of hydraulic pump under specific environment.

Paralleled Structure-Based String-Type Fiber Bragg Grating Acceleration Sensor

This paper has presented a novel string-type fiber Bragg grating (FBG) acceleration sensor based on directly utilizing the transversal vibrational property of a tightly suspended optical fiber. This sensor mainly consists of a mass fixed on the middle of an optical fiber embedded with an FBG element and another optical fiber or metal beam in a parallel arrangement mode, which enables to enhance the impact resistance and resonant frequency of the sensor. Compared with existing FBG-based vibration sensors, the proposed sensor possesses an excellent repeatability using a simple structure, and avoids the FBG-pasting process and the associated limitations of chirping failure. The working principle of the proposed FBG vibration sensors with two different configurations has been built with considering the rotational interference of the mass. Static experiments have been completed to show that the sensitivity of the two configurations with paralleled optical fiber and metal beam is 193.6 and 3.275 pm/g, respectively. The paralleled metal beam-based vibration sensor has a working bandwidth of 12~250 Hz, much larger than that of 4~28 Hz for the paralleled string-type optical fiber configuration. The performance of the proposed acceleration sensor can be easily adjusted by arranging different types of the parallel structure and modifying their corresponding physical parameters to satisfy different vibration measurement requirements.

A diaphragm type fiber Bragg grating vibration sensor based on transverse property of optical fiber with temperature compensation

This paper has presented a novel diaphragm-type fiber Bragg grating (FBG) vibration sensor with a small mass and an excellent sensitivity through the use of the transverse property of a tightly suspended optical fiber with two fixed ends. Two suspended optical fibers that were embedded with an FBG element each, have been arranged symmetrically along the both sides of the diaphragm in a parallel manner, and their middle points were connected with the two surfaces of the mass by rigid thin rods to sense vibration. The theoretical model of the presented sensor has been derived, and its sensing characteristics have been analyzed by numerical simulation to determine the physical parameters. Experiments have been conducted to show that its sensitivity is 31.25 pm/g within a working bandwidth range of 10~150 Hz. The linearity and relative sensitivity errors are 2.21% and ±10%, respectively. The experimental resonant frequency of 300 Hz is consistent with the theoretical value, which has verified the effectiveness of the proposed theoretical model. The temperature response of this sensor has decreased to 1.32 pm/°C in the range of 30~90°C after implementing the temperature compensation. Compared with the existing diaphragm-enabled FBG vibration sensors, the proposed sensor enables to support the easy implementation of distributed measurement, and the small mass allows for detection on mass-sensitive structures.

A non-contact FBG vibration sensor with double differential temperature compensation

This paper has presented a non-contact fiber Bragg grating (FBG) vibration sensor with double differential temperature compensation. Two FBGs and two states of the sensor have been employed to achieve double differential temperature compensation. Based on magnetic coupling and FBG sensing principle, it can be used to realize non-contact measurement of vibration of the rotating shaft. Experimental results show that the working band ranges are within 0–150 Hz; the sensitivity is −0.67 pm/µm, and the linearity is 3.87 % within a range of 2–2.6 mm. The fitting equation of temperature compensation which is caused by structural inflation can be expressed as: Δλ 1′ − Δλ 2′ = 1.51 × T − 32.97. When used to amend a temperature error, the sensor’s temperature error will be reduced to 1.19 % in the range of 25–60 °C.

Pasted type distributed two-dimensional fiber Bragg grating vibration sensor.

A pasted type distributed two-dimensional fiber Bragg grating (FBG) vibration sensor has been proposed and studied in this paper. The optical fiber is directly considered as an elastomer. The two-dimensional vibration can be separated by subtraction/addition of two FBGs' center wavelength shift. The principle of the sensor as well as numerical simulation and experimental analyses are presented. Experimental results show that the resonant frequencies of the sensor x/y main vibration direction are separately 1300/20.51 Hz, which are consistent with the numerical simulation analysis result. The flat frequency range resides in 10-750 Hz and 3-12 Hz, respectively; dynamic range is 28.63 dB; in the x main vibration direction, the sensor's sensitivity is 32.84 pm/g, with linearity 3.91% in the range of 10-60 m/s(2), while in the y main vibration direction, the sensor's sensitivity is 451.3 pm/g, with linearity 1.92% in the range of 1.5-8 m/s(2). The cross sensitivity is 3.91%. Benefitting from the two dimensional sensing properties, it can be used in distributed two-dimensional vibration measurement.