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Distributed vibrational and acoustic sensing technology

Periodic Reporting for period 1 - DIVAS (Distributed vibrational and acoustic sensing technology)

Reporting period: 2016-06-08 to 2018-06-07

Light is largely used to investigate matter using several basic principles, in the same way a driver uses car headlights to obtain information of the road in the darkness. Often light is used for monitoring the condition of the leading communication medium, the optical fiber. For example, an infrared light pulse is used to measure fiber losses through backscattering or to evaluate the temperature and strain stress along the fiber through Brillouin scattering.
The project DIVAS (DIstributed Vibrational and Acoustic Sensing technology) developed a system that turns the standard communication optical fiber in a distributed, point resolved, acoustic sensor through the Phase-OTDR (i.e. Phase-sensitive Optical Time Domain Reflectometry) principle. This method uses highly coherent pulses of light that turn each infinitesimal segment of the optical fiber into an interferometric device that provides an incredible sensitivity to vibrations through light backscattering phenomena. We can imagine the optical fiber as a km-long and extremely sensitive distributed microphone with a very wide bandwidth. Each infinitesimal segment contributes to the creation of an interferometric signal, the amplitude of which is proportional to the change of stress or temperature in the corresponding segment of the optical fiber. The change of stress occurs due to the propagation of vibrations through the fiber. Therefore, if the fiber is attached to a long structure, such as a bridge or a wind turbine, we can use it to monitor the vibrations through this structure and interrogate its integrity in order to monitor its condition and prevent damages.
The high level of sensitivity of the DIVAS system renders it capable of the detection of very low amplitude acoustic and ultrasonic vibrations, which is useful for the detection of seismic events, high-speed train location and identification, security systems for intruder detection, fluid flow monitoring in pipelines, or the structural health monitoring of bridges, wind turbines, nuclear plants, dams, and electric power transmission lines, among others. The system was developed by a series of innovative engineering solutions, which decreased dramatically its cost to below 10 k€ with a spatial resolution in vibration detection below 6 m and a detection range over 5 km. The combination of the system’s performance and cost will help distribute the, so far uncommon, Phase-OTDR technology widely, in order to take advantage of its capabilities.
The main objective of the project DIVAS is to provide a low-cost Phase-OTDR system and eventually a network of partners interested in its applications. The system designed and developed during the DIVAS project bears a cost more than two orders of magnitude less than current commercial alternatives with no significant sacrifice in the spatial resolution for vibration detection, which remains below 6 m.
First, the initial specifications of the system were defined, taking into account the current Phase-OTDR market. Then, the system setup was designed and optical and optoelectronic components that meet performance and economic requirements were identified. The system was assembled and customized software was developed for its operation. Finally, the system was tested in a civil application using a scaled laboratory bridge (a scaled copy of a demountable military bridge), in collaboration with the School of Civil Engineering and the School of Rural and Surveying Engineering at the National Technical University of Athens. The distributed Phase-OTDR sensing system was calibrated and assessed against commercial point sensors for structural monitoring. The system demonstrated its value for applied research and Structural Health Monitoring, showing its capability to detect structural damages and structural aging.
Regarding the dissemination and exploitation of the project results, industrial partners who are interested in a collaboration as soon as the prototype will be fully developed and intellectual property rights will be managed were identified. The researcher also joined two collaboration networks, one for device development and future research, and one for further integration through the PIC4ALL European Action. Indeed, we foresee the possibility of a substantial further reduction of cost of the system through the use of Photonic Integration in mass production. The project results were disseminated in several occasions, including general public events (Athens Science Festival, Open Laboratory Day for Master’s students) and scientific events (seminars, workshops, conferences, and journal publications).
The Phase-OTDR system of the project DIVAS is the first distributed acoustic sensor interrogator bearing a cost well below 10 k€ and assuring a resolution less than 6 m and a sensed optical fiber range more than 5 km. The cost of the system is more than two orders of magnitude less than that of current commercial alternatives with no significant sacrifice in performance. Phase-OTDR is a quite mature technology, but it still struggles to reach the applied research field and several civil applications due to its prohibitively high costs. The results of the DIVAS project will help distribute the Phase-OTDR technology widely, in order to take advantage of its capabilities. A detailed description of the system design and development is submitted for open-access publication in order to facilitate its spread in society.