Fiber Bragg Grating Vibration Sensor Research Articles

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.

A fiber Bragg grating vibration sensor based on crossed variable section beam

This paper presents a triaxial vibration sensor that can be used for vibration acceleration detection. The main body of the elastic structure of the sensor is a variable section beam. The fiber Bragg gratings (FBG) are applied to the surface of the crossed variable section beam. The theoretical equation for the sensitivity of this sensor is given by the theoretical analysis of material mechanics. The simulation of modal analysis was carried out by means of the finite element method. The resonant frequencies of the proposed fiber Bragg grating triaxial sensor in the Z, X, and Y directions are 363.01 Hz, 466.34 Hz, and 466.82 Hz, respectively. Finally, the sensor was calibrated and tested in each direction of vibration, and the results showed that the sensitivity of Z, X, and Y directions were 6.66 pm/g, 4.61 pm/g, and 4.61 pm/g respectively, which proved that the FBG sensor has good sensing response for vibration in three directions.

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.

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.

A novel fiber Bragg grating vibration sensor with double equal-strength cantilever beams

A novel fiber Bragg grating vibration sensor with double equal-strength cantilever beams

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

Design and analysis of high-frequency fiber Bragg grating vibration sensor

The fiber Bragg grating vibration sensor has received a lot of attention due to its unique performance. However, the natural frequency of the sensor limits its development and application. This paper presents an acceleration sensor with an isosceles triangular cantilever and mass block structure, which has high natural frequency and high sensitivity. The optical fiber sensing system consists of two fiber gratings. One section of the fiber grating is pasted on the cantilever and serves as an accelerometer; the other is used as a reference grating. The first-order natural frequency of the accelerometer is 8356 Hz, and its sensitivity is 0.46 pm g−1. A vibration test confirms the reliability of the sensor, and the resonant frequency of the sensor is 8193 Hz. The principle of light intensity demodulation is adopted in the sensor system and its sensitivity is 45.82 mV g−1 with a linearity of 0.997. The sensor has the advantages of high frequency and sensitivity, and thus can be applied to the rail transit bearing systems

Fiber Bragg Grating Sensor Based Vibration Monitiring for Foreign Matter Invasion of Protective Barrier

A vibration monitoring system based on fiber Bragg grating is proposed to meet the need of protective barrier along the railway to monitor the foreign matter invasion. A high sensitivity fiber Bragg grating vibration sensor based on cantilever structure is developed. Three vibration sensors were deployed to a protective barrier with a length of 20 meters to conduct intrusion vibration monitoring test. Test results show that: 1) the fiber Bragg grating vibration sensor can well monitor the vibration signal; 2) the vibration intensity decreases obviously with the distance impact position increasing; 3) the response time of vibration measurement of different sensors is also in sequence when the distance impact location is different. Therefore, the magnitude of the external impact and the impact position in the protective barrier can be analyzed through the response amplitude distribution of each sensor and the response time sequence of the sensors.

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.

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.

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.

Doppler Effect-Based Optical Fiber Vibration Sensor Using Frequency-Shifted Interferometry Demodulation

A novel optic-fiber vibration sensing system based on frequency-shifted interferometry (FSI) is proposed and demonstrated in this paper. The sensor is based on the phenomenon that the light frequency transmitted through a segment of bent fiber can be Doppler shifted by vibration. The Doppler frequency shift is measured using FSI demodulation. Compared to traditional fiber Bragg grating vibration sensor, the proposed sensor is easy to fabricate, of low cost and without directional dependency. The application of FSI demodulation allows for custom tailoring of measurement sensitivity, and has superior signal stability due to its same-path interference nature. The measured Doppler frequency shift using the FSI system agrees well with the calculated one, derived from strain measurements. The results show that the system has a high sensitivity and wide frequency range, limited only by the excitation apparatus used in the experiment.

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.