Distributed Acoustic Sensing for Civil Infrastructure Natural Frequency Measurement

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Solution Overview

Problem

Current methods for measuring natural frequencies of civil infrastructures are time-consuming and costly, requiring multiple accelerometer sensors and complex algorithmic analysis, and struggle to detect weak 'normal' vibrations effectively.

Innovation Solution

A distributed acoustic sensing (DAS) system using a low frequency shaker and existing fiber optic cables to directly measure natural frequencies of structures without post-processing or algorithmic analysis, enhancing mechanical vibrations for quick and cost-effective monitoring.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If multiple accelerometer sensors and complex algorithmic analysis are used to measure natural frequencies, then measurement precision may be improved, but device complexity and cost increase significantly

Engineering Contradiction:

Improvenatural frequency measurement precisionVSAvoidsensor array and data processing complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent combines multiple sensing functions into a single distributed fiber optic cable that acts as both the excitation source and the sensing element. The fiber optic cable replaces multiple accelerometer sensors and integrates the functions of vibration excitation and vibration measurement into one component, significantly reducing device complexity while maintaining measurement capability

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The fiber optic cable serves multiple functions simultaneously: it acts as the excitation source through the shaker, serves as the sensing element for detecting vibrations, and provides the measurement medium for natural frequency determination. This multi-functionality eliminates the need for separate sensors and processing systems

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Measurement precision

If multiple accelerometer sensors are deployed to detect weak vibrations, then measurement capability improves, but the cost and time for installation and data processing increase

Engineering Contradiction:

Improveweak vibration detection capabilityVSAvoidinstallation and post-processing time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The distributed fiber optic sensing system is self-sufficient, requiring no external power sources, calibration procedures, or complex setup. The fiber optic cable inherently detects vibrations along its entire length without requiring individual sensor installation at multiple points, eliminating time-consuming installation and calibration processes

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The fiber optic cable is divided into multiple sensing segments along its length, with each segment independently detecting vibrations at its location. This segmentation allows the system to monitor multiple points simultaneously using a single continuous cable, reducing installation time compared to deploying multiple discrete sensors

Inventive Principle:

Principle #1Segmentation

3Measurement precision

If complex algorithmic analysis with assumptions is used to determine natural frequencies, then measurement capability is achieved, but the process becomes time-consuming and requires undesirable assumptions

Engineering Contradiction:

Improvenatural frequency determinationVSAvoidpost-processing time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent replaces complex computational algorithms with a direct physical measurement approach. The fiber optic sensing system directly measures vibration characteristics and natural frequencies through optical interference patterns, eliminating the need for time-consuming post-processing algorithms and assumption-based analysis

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 continuous, real-time determination of natural frequencies, facilitating structural health assessment without the need for extensive sensor arrays or complex data processing, while being sensitive enough to detect minor vibrations and external sources.

Implementation Method 1

employing a low frequency shaker/transducer as part of the overall DAS system to enhance mechanical vibrations of these structures

Methodology Applied

Scientific EffectResonance: Resonance

Implementation Method 2

distributed fiber optic sensing (DFOS)—distributed acoustic sensing (DAS) systems

Methodology Applied

Scientific EffectDistributed Acoustic Sensing:

Data Source

PatentUS11619542B2Distributed acoustic sensing based natural frequency measurement of civil infrastructures

Publication Date: 2023.04.04 NEC CORP

AI summary

Aspects of the present disclosure describe distributed fiber optic sensing (DFOS)—distributed acoustic sensing (DAS) based systems, methods, and structures that advantageously enable and/or facilitate the determination of natural frequency(ies) of civil infrastructures.