Fiber Bragg grating sensor for earthquake detection

Fiber Bragg Grating (FBG) sensors can detect seismic activity by measuring strain and displacement in structures and soil with high precision and real-time monitoring capabilities.

Principles of FBG Sensing

FBG sensors consist of periodic variations in the refractive index inscribed along the core of an optical fiber. When light passes through the fiber, a specific wavelength—called the Bragg wavelength—is reflected, while other wavelengths pass through. Changes in strain or temperature alter the reflected wavelength, allowing precise measurement of physical parameters. This principle enables FBGs to detect minute deformations in structures or the ground, which are critical indicators of seismic activity .

Advantages for Earthquake Monitoring

FBG sensors offer several benefits over traditional seismic sensors:

• High sensitivity: Capable of detecting micro-strains and subtle structural movements .
• Electromagnetic immunity: Optical fibers are unaffected by electromagnetic interference, making them suitable for urban or industrial environments .
• Multiplexing capability: Multiple FBGs can be inscribed along a single fiber, enabling distributed sensing over long distances for real-time monitoring of bridges, buildings, or soil layers .
• Durability: Resistant to harsh environmental conditions, including temperature extremes and corrosive soils .

Applications in Earthquake Detection

FBG sensors can be deployed in structural health monitoring (SHM) and geotechnical systems to detect seismic events:

• Building and bridge monitoring: FBG arrays measure strain and vibration in structural elements, providing early warning of stress accumulation or damage during earthquakes .
• Soil and foundation monitoring: FBG-based inclinometers and strain sensors can track lateral earth pressure, soil heave, and differential settlement, which are critical for detecting ground movement during seismic events .
• Automated real-time systems: Integration with wavelength-division multiplexing (WDM) allows high-density, quasi-distributed sensing, enabling continuous monitoring and rapid detection of seismic-induced deformations .

Recent Innovations

Recent research has enhanced FBG sensitivity using exceptional point engineering, achieving nearly an order-of-magnitude improvement in strain detection. This allows FBGs to detect extremely small perturbations, which is valuable for early earthquake detection and multi-parameter monitoring . Advanced fabrication techniques, such as femtosecond laser inscription, further improve sensor precision and durability .

Conclusion

FBG sensors provide a highly effective platform for earthquake detection by monitoring strain, displacement, and structural integrity in real time. Their combination of sensitivity, multiplexing, and environmental resilience makes them ideal for both urban infrastructure and geotechnical applications, offering a promising approach for early warning systems and seismic risk mitigation .