New fiber optic system to monitor structural integrity

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New fiber optic system to monitor structural integrity
The principle of operation for a single AFO-SHM sensing node. Credit: Optics Express (2016). DOI: 10.1364/OE.24.020287

Generally, structural health monitoring systems use piezoelectric transducers. These transducers have great reliability except under high temperatures. It has limited accuracy and efficiency in harsh environments. Now scientists from the Center for Photonics Technology at Virginia Tech, Blacksburg, Virginia, USA, developed a new fiber optic system. This new fiber optic system promises to improve the ability to monitor structures under harsh conditions.

This new fiber optic system uses two optical fibers to serially connect multiple active fiber-optic non-destructive evaluation elements. Both attaches to the surface of the structure to get a monitor. Each sensing element consists of an acoustic generation unit. They embedded in between a fiber-optic cable, an acoustic detection unit, and within a fiber-optic housing.

The acoustic generation unit produces acoustic vibrations after affecting through laser pulse. These vibrations are received by the Fiber Bragg grating (FBG). FBG forms the acoustic signature of the structure. Additionally, it provides information about the strain and temperature of the structure.

Fiber optic devices have been discovered to loyally work under extremely high temperatures. Although, the discovery essentially improve health monitoring conditions of critical infrastructures under harsh environments. Thus, it will help to ensure the continuous operation of power plants and help prevent the catastrophic consequences of possible structural failures.

Chennan Hu, graduate student said, “By analyzing the acoustic signature of the structure and the additional information from FBG, we can simultaneously monitor multiple environment parameters. For example, changes in temperature, strain, and thickness, and the appearance of an artificially generated crack.”

“This system can be used in high temperature when temperature adhesive replaces low-temperature epoxy. We have already acquired promising high-temperature monitoring results,” he said.

This could be used on the outer surface of so-called P91 pipes. Generally, P91 pipe is used to transmit corrosive high-temperature, high-pressure steam.

Now scientists are planning to build a compact and robust sensor system. They will then field-test the system in a real power plant and adapt their technology for commercial use.