Distributed Fiber Optic Acoustic Vibration and Sound Sensor Monitoring System

DAS technology advantages:

Continuous distributed measurement of temperature and vibration without measurement blind spots

Simultaneous detection and accurate localization of multiple events

Fiber optic is a sensor that combines transmission and sensing

60 kilometers of ultra long measurement distance, rich measurement information

Fast response speed, alarm within 1 second

Optical signal transmission, completely electrically insulated, resistant to electromagnetic interference

Intrinsic safety, suitable for long-term operation in flammable and explosive environments

Stable and reliable measurement with low false alarm rate

Long service life of optical fibers, up to 30 years maintenance free

DAS performance characteristics:

Long temperature distance: 50km

Fast response time: typical 1 second

High positioning accuracy: 2-50m

High sensitivity: can perceive vibrations within 40m around the optical cable

Simultaneous monitoring of vibration and temperature

Online monitoring function for fiber optic faults

Distributed Fiber Optic Acoustic Sensing (DAS) technology is a new type of sensing technology that can achieve continuous distributed detection of vibration and sound fields. It utilizes the highly sensitive characteristics of coherent Rayleigh scattering induced by narrow linewidth single frequency laser in optical fibers, combined with the principle of reflectometer, to perceive environmental vibration and sound field information interacting with optical fibers over long distances and with high spatiotemporal accuracy. This unique information perception ability has attracted widespread attention from both academia and industry for DAS technology. The performance of DAS technology is constantly improving, and its applications are developing rapidly. It has demonstrated its unique technological advantages and potential in perimeter intrusion detection, online monitoring of railway safety, geophysical exploration, and other areas.

Wide application requirements and technologies of distributed fiber optic acoustic sensing technology

Due to its unique advantages, DAS has attracted more and more experts from various fields to seek industry breakthroughs, while also placing increasing demands on the improvement of DAS technology.

After more than a decade of development, DAS has played an irreplaceable role in multiple fields, especially in the application scenarios of long-distance, large-scale, and spatiotemporal dense detection, including perimeter security, transportation, geophysical exploration, structural health monitoring, and other fields. Researchers are also continuously improving DAS technology to meet the personalized application needs of various fields.

In the field of perimeter security, compared to conventional methods, DAS has advantages such as strong environmental adaptability, high concealment, large monitoring range, and distributed blind spots.

Safety detection along railway lines based on DAS

In the field of railway transportation, DAS technology uses passive optical fibers as sensing and transmission devices, which can achieve spatial continuous sensing of disturbance signals along the fiber optic line. It has the characteristics of anti electromagnetic interference, long-distance distributed measurement, low cost per unit distance, and no need for on-site power supply. It can effectively compensate for the shortcomings of existing point electromagnetic sensing technology, meet the application needs of railway transportation, and can be quickly integrated into existing railway lines. It has been widely applied.

Oil and gas resource exploration is also an important application of DAS technology. The conventional oil and gas resource exploration technology uses point type electronic detectors, which have drawbacks such as low deployment efficiency and long large-scale experimental time. DAS uses conventional communication optical fibers as sensor components, which are low-cost and can play a role throughout the entire life cycle of drilling, completion, production, etc., with significant advantages.

In addition, due to the small size and light weight of optical fibers, they are easy to embed into structures such as aerospace composite materials, building materials, soil media, etc. DAS can easily obtain acoustic emission signals inside the materials, achieving permanent online monitoring of materials and structures.

The distributed acoustic vibration sensing system is a pure phase demodulation scheme based on coherent Rayleigh scattering. It utilizes the sensitivity of optical fibers to sound (vibration). When external vibrations act on the sensing fiber, due to the elastic optical effect, the refractive index and length of the fiber will undergo slight changes, resulting in simultaneous changes in the intensity and phase of the transmitted signal inside the fiber.

The DAS system only requires one core single-mode optical fiber, with a maximum measurement distance of 60 kilometers and a positioning accuracy of ± 2.5 meters. It can also achieve simultaneous detection and positioning of multiple events. It can reproduce sound wave vibration signals at any one meter position of the fiber optic, with a frequency accuracy of 1HZ and a maximum measurement frequency of 200KHZ. Every 2.5 meters of fiber optic can be transformed into a fiber optic microphone sensor, and all microphone sensors can record and demodulate the restored sound in real time. Due to its powerful positioning and sound restoration functions, it can be linked with a video camera. The video camera is equivalent to a person's "eyes", while the fiber optic acoustic vibration sensing system is equivalent to a person's "ears". When the "eyes" and "ears" are used simultaneously, the accuracy greatly increases, making security judgments more accurate. At present, it has been widely used in fields such as oil underground, national defense line safety, gas pipeline excavation prevention, communication and power line protection.