Fiber-Optic Distributed Acoustic Sensor Achieving Ultrasonic Resolution Over Kilometer-Scale Ranges

This invention is a coherent optical fiber-based distributed acoustic sensing system that detects and localizes ultrasonic vibration events along the full length of a sensing fiber with sub-meter spatial resolution. By combining ultrashort optical pulse interrogation with real-time digital signal processing, it delivers sensing capabilities far beyond what conventional distributed acoustic sensing systems can achieve.

Description

The system operates by launching ultrashort optical pulses (≤10 ns) into a sensing fiber, generating Rayleigh backscatter signals that carry information about the fiber's acoustic environment along its entire length. A heterodyne coherent detection scheme mixes the backscattered light with a local oscillator reference signal using a balanced photodetector, preserving both amplitude and phase of the return signal. The resulting RF signal is digitized and processed through in-phase/quadrature (I/Q) demodulation, which converts the high-frequency beat signal into a complex baseband representation. A real-time phase-tracking algorithm then extracts dynamic phase changes at each spatial location along the fiber — directly corresponding to local acoustic or ultrasonic disturbances — and produces time-distance maps of vibration activity across the full sensing range. The system is compatible with standard single-mode optical fiber, enhanced backscattering fiber, and ultraweak fiber Bragg grating arrays, providing flexibility across deployment scenarios. It supports both unmodulated square wave pulses and linearly chirped frequency-modulated pulse formats, and can employ homodyne or heterodyne detection architectures depending on application requirements.

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

- Sub-meter spatial resolution (~60 cm using 6 ns pulses), dramatically exceeding the meter-scale limitations of conventional commercial distributed acoustic sensing systems
- Ultrasonic frequency sensing capability (50 kHz and above), enabling detection of guided waves and mechanical vibrations relevant to non-destructive testing
- Real-time phase tracking supports live data visualization and dynamic sensing applications
- Compatible with standard optical fiber infrastructure, minimizing deployment cost and complexity
- Digital I/Q demodulation improves signal-to-noise ratio and enables robust, high-fidelity phase recovery

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