Abstract

The fiber Bragg grating has been one of the most widely used sensors in the field of optical fiber sensors in recent years. Significant progress has been made in fiber Bragg grating sensor applications to measure environmental parameters such as strain and temperature. The fiber Bragg grating is sensitive to the temperature as well when it is measuring the strain change, which is ignored in most measurement applications, including perimeter protection sensors. Since the fiber Bragg grating is affected by both strain and temperature changes, cross-sensitivity compensation is required to accurately measure and reduce noise. In this paper, what we believe to be a novel intrusion detection technique is proposed based on a tilted cantilever beam, which is very effective for temperature compensation in fiber-Bragg-grating-based security fences. With this technique, temperature and strain can be measured simultaneously and completely independently of each other. For this work, we place a ramp with an angle of θ, similar to a tilted cantilever beam, on the fence and stick a fiber Bragg grating on the ramp. A uniform strain applied to the fence creates a strain gradient along the cantilever beam and of course along the fiber Bragg grating causing a change in the full width at half maximum of the reflection spectrum. This full width at half maximum change along with the Bragg wavelength shift are used to obtain the strain and temperature simultaneously. In our simulation results, the temperature sensitivity of the fiber Bragg grating is 14.2 pm/°C for the Bragg wavelength with no change in the full width at half maximum, and the strain sensitivity is 0.453 pm/µɛ for the Bragg wavelength and a nonlinear sensitivity according to a quadratic function for the full width at half maximum variation.

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