Fiber Optic Acoustic Emission Sensor for Structural Health Monitoring
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Solution Overview
Problem
Current structural health monitoring systems face challenges in effectively measuring high-frequency signals generated by structural fatigue and damage detection due to the large size and impracticality of piezoelectric sensors for widespread implementation.
Innovation Solution
The use of fiber laser acoustic emission sensors, integrated with strain and temperature sensors, which adhere to structures via shallow grooves or channels to detect ultrasonic signals and Lamb wave signals using optical fibers with fiber Bragg gratings and frequency discriminators, enabling sensitive and multiplexed monitoring without introducing structural weakness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If piezoelectric sensors are used for measuring high frequency acoustic emission signals, then measurement precision is improved, but device complexity and weight increase making large-scale implementation impractical
Solution Approach 1:
The patent replaces piezoelectric sensors (mechanical/electrical system) with fiber optic sensors (optical system). The fiber optic sensors use optical interference patterns to detect acoustic emission signals, eliminating the need for complex electronic amplification circuitry and reducing sensor size while maintaining measurement precision for high frequency signals.
Solution Approach 2:
The fiber optic sensor system can simultaneously measure multiple parameters including strain, temperature, and acoustic emission signals using the same sensor infrastructure. This multi-functionality reduces overall system complexity compared to using separate piezoelectric sensors for each measurement type.
2Measurement precision
If piezoelectric sensors are used for structural health monitoring, then measurement capability is improved, but weight increases reducing practicality for large numbers of sensors
Solution Approach 1:
The patent substitutes heavy piezoelectric sensors with lightweight fiber optic sensors. The fiber optic sensors have significantly lower weight while maintaining the capability to detect acoustic emission signals and Lamb waves through optical interference measurements.
3Measurement precision
If large numbers of sensors are implemented for comprehensive structural health monitoring, then measurement coverage is improved, but system complexity and cabling requirements increase
Solution Approach 1:
The patent merges multiple sensing functions into a single fiber optic cable that can accommodate numerous sensors along its length. Multiple fiber Bragg grating sensors are integrated into one fiber, allowing comprehensive structural health monitoring with minimal cabling and interconnects compared to traditional distributed sensor systems.
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
This approach provides high sensitivity for passive AE measurement, facilitates phased array beam forming for precise location of acoustic emission events, and rejects background noise, allowing for timely remedial actions such as repair or replacement of damaged structures.
Implementation Method 1
The first optical cavity includes two fiber Bragg gratings with a distance therebetween
Implementation Method 2
The first optical cavity includes a resonance
Implementation Method 3
measuring ultrasonic signals caused by acoustic emission for structural health monitoring
Implementation Method 4
fiber optic sensors are capable of measuring slowly varying strain
Data Source
AI summary
A method of monitoring a structure for stresses or cracks. A single mode optical fiber is adhered to a structure. The single mode optical fiber includes a first optical cavity. The first optical cavity includes two fiber Bragg gratings with a distance therebetween. The first optical cavity includes a resonance. A frequency shift of the resonance of the first optical cavity is measured with a frequency discriminator. An acoustic emission from the structure is detected based on the frequency shift.