Optical fiber sensor is the best method for earthquake monitoring

2021-05-02

The massive human casualties and property losses caused by the Wenchuan 8.0-magnitude earthquake made the earthquake prediction become a hot spot for the scientific community and the entire society.
At the Xiangshan Science Conference on the "Mechanism of the Great Wenchuan Earthquake and Follow-up Disasters" that was held in an emergency on May 19th, many scholars proposed to carry out "group survey and prevention" of earthquakes; at the same time, they should use a multidisciplinary comprehensive preparatory period. Early warning The method for predicting earthquakes, such as using infrasonic waves, ground stress, geoelectrical pulses, and earth micro-motion to predict earthquakes, improves the prediction level of earthquakes.
"Because of the long-range telemetry, resistance to harsh environments (high temperatures above 500°C), high sensitivity, and ease of networking, fiber-optic sensors may be the best means of earthquake monitoring at the moment, once established permanently near the seismic zone The optical fiber sensor network for monitoring earthquakes can timely monitor underground anomalies and give early warning of possible earthquakes, thereby maximally avoiding casualties and property losses.” Rao Yunjiang, Dean of the School of Telecommunications, University of Electronic Science and Technology of China who has long been engaged in the research of fiber optic sensors. The professor said.
Robust Fiber Sensor Research
Modern information technology consists of information acquisition, transmission, and processing technologies, so sensors, communications, and computer technology have become the three pillars of information technology. The advent of the optical fiber invention is a major achievement in the history of the world's science and technology. It has caused a series of modern scientific and technological revolutions in the information field. One of its greatest successful applications is fiber optic communications and fiber optic sensing.
In recent years, sensors have developed in the direction of miniaturization, digitization, intelligence, and networking. In this process, new members of the sensor family of optical fiber sensors have become popular. Optical fiber sensors have many excellent properties such as resistance to electromagnetic interference and atomic radiation, light weight, small size, insulation, high temperature resistance, corrosion resistance, etc., and can respond to changes, pressure, temperature, vibration, sound field, refractive index, acceleration, voltage, gas, etc. Various parameters are accurately measured and can adapt to extremely harsh environments. At the same time, due to the low fiber transmission loss and frequency bandwidth, the optical fiber sensor has unparalleled advantages compared with traditional sensors in terms of networking and transmission distance.
Rao Yunjiang said that fiber-optic sensors can be buried deep in the formation of temperatures up to 250 °C or more, so the distance can be measured up to several hundred kilometers. It can be used to detect dynamic changes of underground physical quantities such as seismic waves, internal stress of geological blocks, temperature, displacement and inclination, underground fluid pressure, and underground magnetic field.
Because fiber-optic sensors have many unique advantages that can solve many of the measurement problems that traditional sensors cannot solve, they have been widely used in medical, transportation, power, machinery, petrochemicals, aerospace, geology and rock since its inception. Soil engineering and other fields.
Applied to earthquake monitoring has a technical basis
Under the support of the National Outstanding Young Scientists Fund, the National Natural Science Key Fund, and the National Natural Science Foundation of China, Rao Yunjiang led his research group to conduct extensive and in-depth research in the field of fiber optic sensors, solving many key and difficult problems. Their research results lay a solid foundation for the application of fiber optic sensors in the field of seismic monitoring.
According to Rao Yunjiang, in the research of multi-parameter sensing of optical fiber, with the development of science and technology, in many important occasions, it is necessary to simultaneously measure the change of two or more parameters. For example, simultaneous measurement of strain, vibration, and temperature in smart materials and structural health monitoring, internal stress, temperature, displacement, and tilt of seismic blocks in earthquakes, and underground physical quantities such as vibration, underground fluid pressure, and underground magnetic fields; pressures in oil and natural gas production , temperature and flow measurement at the same time. Therefore, the application of composite fiber optic sensors to achieve multiple parameters at the same time, measurement technology is not only a field of fiber optic sensing is also a very important and challenging scientific research topics in the field of sensors.
In order to solve this problem, Rao Yunjiang's research group first proposed a series of fiber-optic multi-parameter sensing methods for the first time, and the integrated sensor is used to implement a new method for simultaneous measurement of multiple parameters.
In addition, integrated fiber optic sensors are also used in the health monitoring of national defense and large bridges. At present, this kind of sensor has been successfully applied to the real-time monitoring of five bridges in Chongqing. The experience gained by applying such fiber-optic sensors in civil engineering structures is very helpful for seismic monitoring.
Excellent networking capability is one of the characteristics of the new generation of fiber-optic sensors. In response to this challenge, Rao Yunjiang’s research group has for the first time introduced a large-capacity fiber-optic sensor network based on multiplexing methods. By transforming traditional fiber-optic sensors into cavity lengths, Several millimeters of sensors, combined with some scientific methods, established a network capable of reusing more than 1,000 fiber-optic sensors, which was the first in the world to solve the bottleneck of poorer multiplexing capabilities of traditional fiber-optic sensors, for the large-scale application of such sensors. Laid the technical foundation. This type of sensor is currently being used for health and safety monitoring of oil (gas) pipelines.
The task force also turned ultra-long-distance fiber sensing into reality. Remote distance telemetry is another feature of the new generation of fiber optic sensors. How to achieve a distance of more than 100 kilometers is another challenge in the field of fiber optic sensing. Facing this challenge, Rao Yunjiang’s research team also prepared for the first time in the world a measurement system with an ultra-long-distance measurement capability of 250 kilometers. This system has been used as an optical fiber fence in practical facilities for security protection and counter-terrorism in important facilities. Obtained important applications in seismic monitoring.
In addition, Rao Yunjiang’s task force has also made major breakthroughs in the research of micro-nano fiber sensing technology. They solved many problems with conventional electrical sensors in their ability to withstand harsh environments.
Many related achievements of Rao Yunjiang's research group have been successfully used to monitor the stress, displacement, inclination and vibration of bridges, and they have been industrialized, so they have a good foundation.
Research on Safety and Health Monitoring for Major Infrastructure
"The support of the National Fund for Distinguished Young Scientists, the National Natural Science Key Fund and the General Program has provided us with a guarantee for the smooth development of the above-mentioned research work with advanced international standards. With the support of these projects, we have supported the national '211 Project' and The vision of the advanced scientific research platform built on the 985 project and our construction of a world-class optical fiber sensing technology research center is becoming a reality step by step. At the same time, it also enables China’s research level in the field of fiber optic sensing to achieve a leap forward: continuous in the first The 17th and 18th International Optical Fiber Sensing Conference made a special report and became the only member of TPC (Transaction Processing Performance Committee) in China Mainland for the International Optical Fiber Sensing Conference.
Rao Yunjiang added: “A variety of fund projects have also played a good role in promoting China’s international reputation in the field of fiber optic sensing. For example, we hosted the first international seminar on the status quo and future trends of fiber optics development, the fifth The International Conference on Fiber Optic Communications and Networking and the Second International Symposium on the Status Quo and Future Trends of Fiber Optics Development have achieved very good academic exchanges.”
For the status quo, Rao Yunjiang is not satisfied. He pointed out that China still needs to strengthen its original research in the area of ​​fiber optic sensors and put forward more new concepts, new principles and new methods in order to further enhance China’s international status in the field of fiber optic sensing; on the other hand, it must satisfy the national economy and The major needs of national security have led to the development of a number of optical fiber sensors and systems with independent intellectual property rights that have been applied in practice.
Rao Yunjiang emphasized: “We must face the major needs of China's major infrastructure safety and health monitoring to address the issues of earthquake monitoring and forecasting, as well as national major arteries, national energy infrastructure, industrial energy conservation and emissions reduction, and safety monitoring of aerospace vehicles and engines. Deeply develop the basic research work of the next-generation optical fiber sensor network and key devices through the system, and solve the key scientific issues of multiplexing and networking of large-capacity optical fiber sensor units and ultra-long-distance optical fiber sensor networks, and implement new generation optical fibers. The important breakthroughs in key sensor devices have laid the foundation for China’s first-ever establishment of a new generation of fiber-optic sensor systems and the resolution of major scientific issues in the large-scale application of fiber-optic sensors. The realization of these goals is inseparable from the support and guidance of the National Natural Science Foundation of China.” After the Wenchuan Earthquake, Rao Yunjiang proposed to the Committee of the Fund a proposal for a key project of “Basic Research on Fiber-optic Seismic Multi-parameter Sensing Technology”. He hopes to be able to transmit the fiber under the support of the National Natural Science Foundation of China. Is applied to seismic monitoring of this scientific issue has important practical and historical significance of in-depth study.

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