Strain, Temperature, and Humidity Mechanisms

The same Bragg wavelength can respond to multiple physical causes. This page explains those mechanisms and why compensation is essential.

Strain, Temperature & Humidity Mechanisms

1. Concept

The same Bragg wavelength shift can result from strain, temperature, or humidity changes — or a combination of all three.

2. Mechanism

The general response formula:

Δλ/λ₀ = Kε·Δε + KT·ΔT

3. Physical Process

  • Strain: elastic elongation, photoelastic effect
  • Temperature: thermal expansion, thermo-optic effect
  • Humidity: coating absorption, moisture expansion

4. System Behavior

Cross-sensitivity means a clean signal can still represent the wrong physical quantity without proper compensation or decoupling.

5. Engineering Meaning

  • Coating selection affects humidity response
  • Packaging design determines strain isolation
  • Compensation algorithms improve accuracy
Schematic Diagram of the Sensing Principle of the UW-FBG Stress Sensor
Figure 1: Schematic Diagram of the Sensing Principle of the UW-FBG Stress Sensor
Schematic Diagram of the UW-FBG Temperature Sensing Principle
Figure 2: Schematic Diagram of the UW-FBG Temperature Sensing Principle
Mechanism Logic
Same wavelength shift ≠ same physical cause

That is why cross-sensitivity is such an important engineering issue. A signal may look clean, but still represent the wrong physical quantity if the design does not isolate or compensate the other effects.

Proper coating selection and structural design can significantly alter the effective temperature and humidity coefficients, making cross-sensitivity compensation essential for accurate measurement.

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