Fiber optic is not only mainly used for communication signal transmission, but also for sensing and detecting various physical characteristics, including acceleration, pressure, temperature, etc. Due to the fact that optical fibers themselves do not require power supply and are not affected by electromagnetic interference, vibration optical fibers are becoming increasingly widely used in large-scale perimeter applications. A single system can achieve detection ranging from tens of meters to tens of kilometers, which has obvious advantages over traditional live detection systems (vibration cables, leakage cables, etc.).
The working principle of fiber optic vibration measurement is to generate interference of light through external strain (vibration or compression), and detect the interference signal to achieve strain detection. There are two main ways to obtain optical interference: using two independent optical fibers to transmit homologous monochromatic light and ultimately coupling to achieve optical interference, commonly known as Mach Zehnder interference; Another type is inter mode interference within multimode fibers.
Fiber optic vibration sensors have been widely used in the protection and early warning of high and steep slopes due to their advantages such as no electromagnetic interference, no need for power supply on site, good long-term reliability and stability, and long transmission distance. Dangerous rock and rockfall alarm monitoring belongs to a branch of high and steep slope protection monitoring. If dangerous rock and rockfall can be detected in advance, it will greatly reduce the economic losses caused by dangerous rock and rockfall to railways, highways, etc. Fiber optic vibration sensing technology is a type of technology that changes the characteristics of the transmitted light in the fiber optic sensor when it is affected by external interference. Through special sensing equipment, the signal is collected and analyzed to detect changes in the characteristics of the light, thereby detecting the vibration of objects.
The characteristics of fiber optic vibration sensors
The characteristics of fiber optic sensors are long transmission distance and immunity to electromagnetic interference. They have been widely used, and their modulation forms mainly include intensity modulation, fiber optic grating, and interference. Currently, there are many patented technologies in the field of fiber optic vibration sensors. These fiber optic sensors have their own advantages, some have high sensitivity, some have good frequency response, and some have high technical content, which can adapt well to common vibration signal conversion. With the continuous development of sensing technology, people’s technical requirements for sensors are also increasing. There is an increasing need for fiber optic vibration sensors that meet the conditions of high sensitivity, low cost, simple preparation process, and good stability. In the process of sensing and detection, sensitivity and stability are the main technical influencing factors, while preparation process and cost are important influencing factors in industrial production. Vibration sensors that combine these advantages are receiving increasing attention and favor.
The vibration fiber optic sensor has a simple structure, high sensitivity, large output amplitude, strong anti-interference ability, long transmission distance, good low-frequency response, low lower limit frequency, large dynamic range of the diaphragm, and good damping effect. It can adapt well to certain special occasions such as high-altitude chimney shaking, low-frequency vibration of bridges, monitoring of landslide precursors, and long-term low-frequency vibration signal monitoring under complex environmental conditions such as earthquake precursor infrasound waves.
Advantages of Fiber Optic Vibration Sensor Detection System
1. Poor environment not affected
Long term installation in harsh outdoor environments with no one on duty, stable sensor structure, and high fatigue life;
2. Strong anti-interference ability
In addition to signals caused by falling rocks, vibration signals also have a large number of complex interference signals with strong identification;
3. Fiber optic sensors have fast response speed
The monitoring range along the railway is wide, and in order to save costs and increase the monitoring range of sensors, high sensor sensitivity is required.
4. Not affected by other vibrations
At the same time as high sensitivity, it has sufficient strength to resist the damage caused by large vibrations caused by trains.