FLEXIBLE STRAIN SENSORS
by
Aditya Vijay Mane
MIS: 612302034
Under Guidance of
Prof. Vishwajeet More
Department of Mechanical Engineering
COEP Tech University, Pune
CONTENTS
Intoduction
Literature Review
Importance of Flexible Strain Sensors in SHM
Structural Health Monitoring(SHM)
Fiber Optic Sensors
Fiber Bragg Grating (FBG) Sensors
Construction
Working Principle
Applications
Conclusion
Introduction
• Flexible strain sensors are advanced
devices designed to measure the
deformation, bending, or stretching of
materials when subjected to stress.
• Unlike rigid sensors, they are
lightweight and adaptable, making them
ideal for applications where surfaces are
irregular or prone to movement.
• These sensors can operate effectively in
dynamic and harsh environments,
providing real-time data with high
precision.
• Their adaptability has made them
essential in engineering, healthcare,
robotics, and infrastructure monitoring.
Literature Review
Sr.No Reference Name Seed Idea/Work Description
1. Temperature-compensated flexible strain Proposes temperature-compensated flexible strain
sensors for bridge monitoring,2019. sensors that enhance the reliability of bridge
monitoring by eliminating thermal effects.
2. Multifunctional flexible sensors for Explores multifunctional flexible sensors capable of
integrated SHM: Strain, temperature, and simultaneously detecting strain, temperature, and
humidity,2021. humidity for integrated SHM applications.
3. Durability and scalability challenges in Analyzes the challenges related to the durability and
flexible strain sensors for SHM,2020. scalability of flexible strain sensors, providing
solutions for enhanced long-term performance.
4. Real-time monitoring using FBG sensors in Demonstrates the use of FBG sensors for real-time
complex environments, 2021. monitoring in complex environments, emphasizing
their adaptability and precision in SHM applications.
Importance of Flexible Strain Sensors in SHM
• Flexible strain sensors can continuously measure strain, deformation, and stress in
structures, providing real-time feedback on their condition. This is critical for
early detection of structural issues such as cracks, fatigue, or overloading.
• Unlike traditional rigid sensors, flexible strain sensors can conform to irregular,
curved, or moving surfaces of structures. This makes them highly versatile for
applications like monitoring bridges, pipelines, or even aerodynamic structures.
• Particularly in ensuring the safety, reliability, and longevity of critical
infrastructures like bridges, buildings, and other civil structures.
Structural Health Monitoring(SHM)
• Structural Health Monitoring (SHM)
is a process of assessing and
monitoring the condition of
structures like bridges, buildings,
dams, and pipelines in real time to
ensure their safety and functionality.
SHM uses advanced sensing
technologies to detect damage,
assess performance, and predict
failures before they become critical.
Fiber Optic Sensors
Fiber optic sensors are advanced sensing
devices that use the principles of light
transmission and reflection to measure
strain, temperature, or other physical
changes. These sensors are built using
optical fibers, which are thin, flexible
strands of glass or plastic designed to
guide light over long distances.
Fiber Bragg Grating (FBG) Sensors
Fiber Bragg Grating (FBG) sensors are a
specific type of fiber optic sensor that
operate by reflecting specific
wavelengths of light within a fiber optic
cable. They are widely used in various
applications due to their precision,
durability, and ability to measure both
strain and temperature.
Construction
• Sensing Layer: Detects strain or
deformation through changes in electrical,
optical, or mechanical properties.
Substrate: Provides structural
support while maintaining
flexibility.
• Protective Coating: Ensures durability
against environmental factors like humidity,
temperature, or corrosion.
Working Principle
• Fiber Bragg Grating (FBG) sensors operate based on the principle of light
reflection at specific wavelengths, which is influenced by external factors such as
strain or temperature.
• FBG sensors are created by inscribing periodic variations in the refractive index
along the core of an optical fiber.
• These variations form a grating that reflects light at a specific wavelength, called
the Bragg wavelength.
• A broad spectrum of light is sent through the optical fiber.
• The grating reflects a specific wavelength corresponding to the spacing of the
grating, while the rest of the light continues through the fiber.
• When strain (stretching or compression) or temperature changes occur, the spacing
of the grating is altered.
•This causes a shift in the
reflected wavelength, which
can be detected by optical
analyzers.
•The change in the reflected
wavelength is directly
proportional to the strain or
temperature affecting the
sensor.
•This allows precise
quantification of these
parameters.
Applications
• FBG sensors detect strain at key
points such as joints, beams, and
decks.
• By measuring micro-
deformations, they provide early
warnings of potential structural
damage.
• They monitor how loads (e.g.,
from vehicles) are distributed
across the bridge.
• This data is used to assess the bridge's performance under dynamic and static
conditions.
• FBG sensors are embedded near expansion joints to measure stress caused by
temperature fluctuations and movement.
• Helps prevent damage due to improper joint functioning.
• FBG sensors can identify fatigue and the initiation of cracks by monitoring strain
accumulation over time.
• Provides critical insights to prevent catastrophic failures.Bridges expand and
contract with temperature changes.
Conclusion
• Flexible strain sensors, particularly Fiber Bragg Grating (FBG) sensors, have
revolutionized the field of sensing technology with their exceptional sensitivity,
adaptability, and durability.
• These sensors are highly effective in addressing the challenges of real-time
structural monitoring across a range of applications, especially in bridges and
other critical infrastructures.
• FBG sensors offer unparalleled advantages, such as high precision, immunity to
electromagnetic interference, and the ability to operate in harsh environmental
conditions.Their unique capability to multiplex multiple sensing points along a
single optical fiber reduces installation complexity and cost, making them an ideal
choice for large-scale monitoring systems.
Reference
➢ S. Kumar, T. Singh, and J. Verma, "Temperature-compensated flexible strain
sensors for bridge monitoring”,2019.
➢ M. Patel, A. Sharma, and P. Gupta, "Multifunctional flexible sensors for
integrated SHM: Strain, temperature, and humidity",2021.
➢ H. Lee, K. Park, and D. Choi, "Durability and scalability challenges in flexible
strain sensors for SHM," IEEE Sensors Journal,2020.
➢ Y. Liu, C. Wang, and X. Deng, "Real-time monitoring using FBG sensors in
complex environments," Optical Engineering, 2021.
