FBG Strain Sensor: Understanding Measurement Sections and Bendability for Optimal Performance

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FBG Strain Sensor: Understanding Measurement Sections and Bendability for Optimal Performance

Problem Description

A user inquired about the typical spacing range for Fiber Bragg Grating (FBG) strain sensor measurement points and the permissible bending radius for the optical fiber within these sensors.

Technical Analysis

The discussion clarifies that in FBG strain sensing, the term “measurement point” is more accurately referred to as a “measurement section”. Strain is defined as the relative displacement per unit length, with this unit length being the sensor’s measurement section. Both the length of individual measurement sections and the spacing between multiple measurement sections are highly customizable and determined by specific application requirements.

The bendability of FBG sensors is a critical characteristic influenced primarily by the sensor’s encapsulation material, outer diameter, and, to a lesser extent, the internal optical fiber properties. OFSCN employs robust encapsulation techniques, such as seamless steel tubes or high-polymer materials, which provide mechanical protection and dictate the sensor’s flexibility. Different materials possess varying elastic moduli and bending resistance. A smaller outer diameter generally correlates with a smaller achievable bending radius and increased flexibility. While encapsulation is the primary factor, extreme bending scenarios can also highlight the optical fiber’s inherent bending loss and stress tolerance.

Solution & Recommendation

For Measurement Section Spacing:

  • Measurement section lengths and their spacing are highly customizable to meet project-specific needs, including required spatial resolution and the dimensions of the object being monitored.
  • OFSCN offers flexible solutions for both single and multi-segment FBG strain sensors.
  • Typical customizable measurement section lengths range from 10cm up to 5m, with options for even longer custom designs.
  • When using a 40nm FBG interrogator, it’s recommended to limit the number of measurement segments per single sensor to ensure full-scale operation (e.g., typically no more than 5 segments for alloy tube and 1.5/2.3mm polymer-encapsulated sensors, and up to 10 segments for 0.7/1.2mm polymer-encapsulated sensors).

For Fiber Bendability:

  • The bending capability of OFSCN FBG sensors is directly related to the chosen encapsulation material (e.g., elastic alloy tube, polymer, seamless steel tube) and the product’s outer diameter.
  • Sensors with smaller outer diameters, such as the OFSCN® Polymer-encapsulated Fiber Bragg Grating Strain Sensor (0.7mm/1.2mm diameter) at ≤0.7mm (or ≤1.2mm with seamless steel tube protection), offer greater flexibility and smaller bending radii.
  • Customization is available to meet specific bending performance requirements based on application scenarios, installation space, and environmental conditions. Customers are encouraged to provide detailed project requirements for tailored solutions.

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(Original Thread: 关于光纤光栅应变传感器的测量段的间距，和传感器的弯曲半径探讨)

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