This is a distributed sensing system that sends ultrashort laser pulses down an optical fiber and analyzes the light scattered back to detect vibration and strain along the fiber’s length. It can detect and locate acoustic and ultrasonic events at points along a fiber in real time, using standard or specialty fibers.
Description
Unmet Need - Commercial fiber-based acoustic sensing systems are largely limited to low-frequency vibration monitoring with coarse, meter-scale spatial resolution, and this technology uses ultrashort-pulse interrogation to detect and locate ultrasonic events along the fiber.
The system turns an optical fiber into a long, continuous vibration and strain sensor. A laser is shaped into ultrashort optical pulses, defined here as pulses of 10 nanoseconds or less. These are amplified, filtered, and sent into the sensing fiber through an optical circulator, a component that directs light in and out of the fiber. As the pulses travel, tiny amounts of light scatter back naturally from imperfections in the glass (Rayleigh backscatter). The arrival time of that light identifies the position along the fiber.
A photodetector converts the returning light into an electrical radio-frequency (RF) signal that preserves both its strength and its phase. A signal processing unit then separates this signal into two components (in-phase and quadrature, or I/Q demodulation) and calculates how the phase changes over time at each location. Phase changes reveal vibration or strain at that point, so the system can detect and pinpoint acoustic or ultrasonic events. The pulses can be unmodulated square pulses or frequency-swept (chirped) pulses. The fiber can be standard single-mode fiber, fiber engineered for stronger backscatter, or fiber containing fiber Bragg gratings, including ultraweak grating arrays. Both heterodyne and homodyne detection are supported.
Applications
- Pipeline and pressurized vessel integrity monitoring using ultrasonic guided wave methods
- Structural health monitoring of bridges, welds, and other civil or industrial infrastructure
- Acoustic emission detection for transformers, electric machines, and nuclear spent fuel storage systems
- Leak detection of gas or fluid in pipelines and underground storage facilities
- Subsurface monitoring of oil and gas wellbore components including tubing, casing, and valves
Advantages
- Ultrashort-pulse interrogation of the sensing fiber for detecting and locating acoustic and ultrasonic events
- Real-time calculation of dynamic phase information and real-time detection of vibration or strain
- Compatible with standard single-mode fiber, enhanced backscattering fiber, and fiber Bragg grating/ultraweak FBG array sensing media
- Flexible configuration, with square or linearly chirped pulses and heterodyne or homodyne detection
- Fiber can be placed on or adjacent to many structures, so a single system can cover pipelines, vessels, bridges, and electrical equipment
Invention Readiness
A functional minimum viable prototype has been designed, assembled, and demonstrated in a laboratory setting. Experimental data have been generated confirming ultrasonic signal detection and spatial localization along fiber links, including real-time waterfall displays of time-domain, phase, and frequency content with and without applied acoustic stimuli. Further development activities include field validation across extended fiber lengths and varied deployment environments, optimization of signal processing algorithms for robustness and computational efficiency, integration with simulation and calibration frameworks, and customization of the sensing platform for specific target application verticals.
IP Status
Patent Pending
