Distributed Acoustic Sensing Device Variable Pulse Repetition
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional Distributed Acoustic Sensing (DAS) systems are limited by the relationship between optical sensing fiber length and maximum detectable bandwidth, restricting the ability to unambiguously detect high-frequency acoustic events due to the Nyquist frequency constraint, which requires longer time periods between interrogating light patterns, thereby limiting the detectable frequency range.
Innovation Solution
A DAS system that adjusts the time period between successively sent coherent interrogating light patterns, allowing for novel approaches to determine the frequency and location of acoustic events beyond conventional bandwidth limitations by changing the pulse repetition frequency over time, eliminating the need for additional complexity in multi-frequency or multi-wavelength methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the time period between interrogating light patterns is increased to satisfy the Nyquist criterion for long fiber lengths, then unambiguous location detection is improved, but the maximum detectable acoustic bandwidth is reduced
Solution Approach 1:
The patent applies dynamics by making the time period between interrogating light patterns variable rather than fixed. The system dynamically adjusts the pulse repetition frequency based on the specific measurement requirements, allowing it to switch between different time periods to resolve both low-frequency and high-frequency acoustic events unambiguously. This dynamic adjustment enables the system to overcome the conventional trade-off between location accuracy and bandwidth detection.
Solution Approach 2:
The patent changes the temporal parameter (time period between light patterns) to resolve the contradiction. By varying this parameter, the system can adapt to different acoustic event frequencies and fiber lengths, allowing unambiguous detection of both location and high-frequency acoustic events that would otherwise be limited by the Nyquist criterion.
2Productivity
If multiple frequency or wavelength methods are used to extend detectable bandwidth, then acoustic bandwidth detection is improved, but system complexity increases
Solution Approach 1:
Instead of adding multiple frequencies or wavelengths, the patent changes the temporal parameter (time period between pulses) to extend the detectable bandwidth. This approach achieves the goal of detecting higher frequency acoustic events without introducing additional optical components, lasers, or wavelength-division multiplexing infrastructure, thereby avoiding increased system complexity.
Solution Approach 2:
The patent uses periodic action with variable periods to achieve bandwidth extension. By adjusting the pulse repetition frequency and using different time periods between interrogating light patterns, the system can detect a broader range of acoustic frequencies without requiring multiple simultaneous interrogation channels, thus maintaining system simplicity.
3Productivity
If the pulse repetition frequency is increased to detect higher frequency acoustic events, then acoustic bandwidth detection is improved, but location unambiguity is lost
Solution Approach 1:
The system dynamically adjusts the pulse repetition frequency based on the acoustic event characteristics and fiber length. By making the time period variable rather than fixed at a high constant value, the system can maintain location unambiguity when needed while still achieving high bandwidth detection capability when the application requires it.
Solution Approach 2:
The patent employs periodic interrogation with variable periods. By using different time periods between light patterns depending on the measurement requirements, the system can achieve both unambiguous location detection (with longer periods) and high-frequency acoustic event detection (with shorter periods), resolving the contradiction between these two objectives.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables unambiguous detection and identification of acoustic event frequencies above the Nyquist limit without increasing system complexity, allowing for higher acoustic bandwidth detection and reducing ambiguity in frequency and location identification.
Implementation Method 1
Backscattered light can be the elastic Rayleigh scattering propagating in opposite direction to the pulse within the sensing fiber
Implementation Method 2
Phase analysis, for example by interfering backscattered light with coherent light coupled-out from the laser acting as a 'local oscillator'
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
Distributed acoustic sensing system (100), for coupling with an optical sensing fiber (110), which has a selectable fiber length and a down-and-up travel time for an interrogating light to travel down the fiber length and for backscattered light to travel up the fiber length, the down-and-up travel time being associated to the fiber length. The distributed acoustic sensing system (100) has: a coherent light source device (101) configured to repeatedly generate and send into an optical sensing fiber (110) a coherent interrogating light pattern (307, 507, 607, 707), which is out of a plurality of coherent interrogating light patterns and composed of coherent carrier light, during a measurement time duration, which is equal to or greater than one times the down-and-up travel time of the optical sensing fiber (110). The device (100) further has a detection device (114, 116) configured to detect over time light that is backscattered in the optical sensing fiber (110) in response to the repeatedly sent coherent interrogating light patterns and to generate and output a signal that is indicative of the detected backscattered light. The system (100) further has an evaluation device (118) configured to analyse the signal output from the detection device (114, 116). Each coherent interrogating light pattern (307, 507, 607, 707) out of the plurality of coherent interrogating light patterns has similar physical properties, wherein the similarity is in the sense that the light patterns cannot be distinguished on the basis of comparing the physical properties of the backscattered light generated from at least two successive interrogating light patterns (507, 607, 707) as such as detected. The coherent light source device (101) is capable to change the time period between successively sent the first coherent interrogating light patterns (507, 607, 707) after the passing of at least one measurement time duration.