- Available Technology
High sensitivity distributed sensing method for both dynamic and static measurement is needed for structural health monitoring, seismic wave detection, and in situ underground deformation monitoring for geophysical and geotechnical applications. These systems are immune to electromagnetic interferences, can operate longer, and perform better in harsh environments. Current methods include phase optical time domain reflectometry (phase-OTDR) and optical frequency domain reflectometry (OFDR). Both methods are complicated, time consuming, and have a limited measurement range of around 100m. The distributed acoustic sensing market is projected to reach $792 million by 2025, growing at a CAGR of 11.4% from 2020 to 2025. Clemson University researchers have developed a CMPI system and method that allows for faster signaling processing time and a higher measurement rate of more than 100 km. This method is expected to cost significantly less than other distributed acoustic sensing methods.
Distributed Sensing, Static Measurement, Distributed Acoustic Sensing, Optical Interference, Frequency Domain
This sensing system includes an optical fiber with a series of any two reflectors from a Fabry Perot Interferometer (FPI), which records the localized change in distance between the reflectors in the form of optical interference. The microwave photonics interrogation unit is configured to prepare a microwave modulated low coherence light wave. By scanning the microwave frequencies, the complex microwave spectrum is obtained and converted to a time domain signal at a known location by complex Fourier transform. The values of these time domain pulses are a function of the optical path differences of the distributed FPI’s, which are used to read the displacement between pairs of measurement reflectors.
• Lower cost than other strain sensing methods
• CMPI measures strain directly so it can measure sharper spatial resolution with clear, defined uncertainty
• Allows for a faster temporal resolution
Proof of Concept
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