Fiber grating sensing system in different fields

Foreword: The FBG sensing system is mainly composed of a broadband light source, a fiber grating sensor, and signal demodulation. The broadband light source provides light energy for the system. The fiber grating sensor uses the light wave of the light source to sense the measured information of the outside world, and the measured information of the outside world is reflected in real time by the signal demodulation system. According to the analysis, the future fiber grating sensor system will be able to meet the single-point high-precision real-time measurement, and can adapt to the network of quasi-distributed multi-point, multi-parameter test requirements, in the future to play a greater role in the field of sensing effect.

Application of Fiber Bragg Grating Sensing System in Different Fields 1. Applications in Geodynamics In the field of geodynamics such as earthquake detection, the principle of surface sudden change and its danger assessment and prediction are very complicated. The changes in stress and temperature in the volcanic area are the most effective means to reveal the evolution of volcanic activity and the range of its key activities so far. The application of FBG sensors in this field is mainly in the detection of rock deformation, vertical seismic waves, and use as a geophone and optical seismograph. The strain in the active area usually contains static and dynamic strains. The static strain (including the static deformation generated by the volcano, etc.) is generally located close to the geological deformation source, while the dynamic strain represented by the seismic wave of the source can be It is detected in the surroundings of the earth far away from the source. In order to obtain a fairly accurate source of seismic or volcanic sources and better describe the geometry and evolution of the source region, densely arranged stress-strain gauges need to be used. Fiber Bragg Grating Sensor is a broadband and highly networked sensor that can achieve long-distance and densely-arranged multiplexed sensing, and meets the requirements of seismic detection. Therefore, it has undoubtedly more potential applications in the field of geodynamics. It has been reported that FBG sensors have successfully detected rocks and surface dynamic strains with a frequency of 0.1Hz to 2Hz and a size of 10-9e.

2. Application in spacecraft and ships The advanced composite materials have better fatigue resistance and corrosion resistance, and can reduce the weight of the hull or spacecraft, which is of great significance for fast shipping or flying, so the composite materials are increasingly It is used to make aviation navigation tools (such as aircraft wings).

In order to fully measure the condition of the hull, it is necessary to understand the deformation moments, shear pressures, and slamming forces on the deck in different parts. The general hull requires approximately 100 sensors, so the FBG sensor with extremely high wavelength reproducibility is most suitable for the hull. Testing. The FBG sensor system can measure the bending stress of the hull and measure the slamming force of the waves on the wet deck. The 16-channel fiber grating multiplexing system with interferometric detection performance successfully achieved a dynamic strain measurement with a bandwidth of 5 kHz and a resolution of less than 10ne/(Hz) 1/2.

In addition, in order to monitor the strain, temperature and vibration of an aircraft, landing and driving conditions, ultrasonic fields, and acceleration conditions, more than 100 sensors are usually required. Therefore, the weight of the sensors should be as light as possible and the size should be as small as possible. Therefore, the most dexterous fiber grating sensors are used. Is the best choice. In addition, there are actually two directions of strain in the composite material of the aircraft. The fiber grating sensor in the embedded material is an ideal intelligent component for realizing multi-point multiaxial strain and temperature measurement.

3. Application in Civil Engineering Structures Structural monitoring of civil engineering is the most active area of ​​fiber grating sensors. For bridges, mines, tunnels, dams, buildings, etc., by measuring the strain distribution of the above structures, it is possible to foresee the load and conditions of the structures, and facilitate maintenance and condition monitoring. The FBG sensor can be attached to the surface of the structure or embedded in the structure in advance. Simultaneously, the structure is subjected to impact detection, shape control, and vibration damping detection, and the defect condition of the structure is also monitored. In addition, a plurality of fiber grating sensors can be connected in series into one sensor network to perform quasi-distributed detection of the structure and remotely control the sensor signals through a computer.

One of the building structures that fiber grating sensors can detect is a bridge. In application, a set of fiber gratings is glued to the surface of the composite bar of the bridge, or a small groove is made on the surface of the beam, so that the bare core portion of the grating is embedded in the groove (for protection). If more perfect protection is needed, it is best to bury the grating in the composite ribs when building the bridge. At the same time, in order to correct the strain caused by the temperature effect, a separate stress and temperature sensor arm can be used and the two arms can be mounted on each beam.

Two fiber gratings with the same center wavelength replace the mirrors of the Fabry-Perot interferometer to form an all-fiber Fabry-Perot interferometer (FFPI), which minimizes the phase noise of the interference with low coherence. One method realizes a highly sensitive dynamic strain measurement. Combining two other FBGs with FFPI, one of the gratings is used to measure the strain and the other is protected (free from stress) to measure and correct the temperature effect while achieving three measurements: temperature, static strain, Instantaneous dynamic strain. This method combines the coherence of the interferometer and the advantages of the fiber Bragg grating sensor. Within the measurement range of 5me, it achieves a static strain measurement accuracy of less than 1me, a temperature sensitivity of 0.1°C, and less than 1 ne/(Hz) 1/2 Dynamic strain sensitivity.