Classification of Fiber Bragg Grating Pressure Sensors

An FBG pressure sensor typically consists of a fiber Bragg grating attached to a diaphragm or lever structure that converts applied pressure into strain, which shifts the Bragg wavelength for measurement.

Core Components

Fiber Bragg Grating (FBG): The FBG is a short segment of optical fiber with a periodic modulation of the refractive index in the core, forming a wavelength-specific reflector. When broadband light passes through, the FBG reflects a narrow wavelength (Bragg wavelength) that shifts in response to strain or temperature changes. Diaphragm or Sensing Element: The pressure sensor usually incorporates a metallic diaphragm that deforms under applied pressure.

The diaphragm converts pressure into mechanical strain, which is then transferred to the FBG. Diaphragm-type designs are preferred for high sensitivity because they produce larger strain for a given pressure. Amplification Mechanisms: Advanced designs often include multi-hinges or lever structures to amplify the strain experienced by the FBG.

For example, a three-lever mechanism can significantly increase the strain transferred from the diaphragm to the FBG, enhancing sensitivity and allowing precise pressure measurement in the range of 0–1. 5 MPa. Temperature Compensation: To eliminate cross-sensitivity between temperature and pressure, a second FBG is often integrated.

This FB

G measures temperature independently, allowing the system to correct the Bragg wavelength shift caused by thermal effects. Packaging and Mounting: The FBG and diaphragm assembly are typically housed in a protective casing to ensure durability and stability in harsh environments, such as oil and gas pipelines or industrial settings. The fiber is carefully bonded to the diaphragm or lever structure to ensure efficient strain transfer.

Working Principle

Pressure Application: External pressure deforms the diaphragm. Strain Transfer: The deformation is mechanically amplified via levers or hinges and transferred to the FBG. Optical Response: The FBG experiences axial strain, causing a shift in the Bragg wavelength.

Signal Detection: The wavelength shift is measured using an optical interrogation system, which correlates the shift to the applied pressure. Temperature Correction: If a dual-FBG configuration is used, the temperature-induced wavelength shift is subtracted to isolate the pressure effect.

Advantages of This Structure

High sensitivity due to strain amplification mechanisms. Immunity to electromagnetic interference. Capability for simultaneous pressure and temperature measurement.

Robustness in corrosive or harsh environments. This combination of FBG, diaphragm, and lever amplification forms the fundamental structure of modern high-precision FBG pressure sensors, making them suitable for industrial, aerospace, and structural health monitoring applications.