Tensile tests of optical fibers and vibration tests of optical fiber rings have been conducted to measure the exact physical properties of optical fibers and optical fiber sensors. However, there have been few studies using optical fibers themselves as measurement sensors. In this study, we propose a free vibration test using an FBG sensor embedded in an optical fiber and a method to estimate the mechanical properties of the optical fiber sensor from the measured natural frequency. The proposed method does not require additional equipment such as tensile tester and can easily evaluate the mechanical characteristics even with the FBG sensor strain measuring equipment already provided. Therefore, it is expected to be used for checking the physical properties of the optical fiber itself and the properties of the recoated optical fiber. In order to analyze the natural frequency of the optical fiber, we compared the experimental results with the finite element method and evaluated the elastic modulus from the natural frequency of the optical fiber.
A solar powered aircraft is operated by converting solar energy into electrical energy. The wing of the solar powered aircraft requires a wide area to attach a number of solar cells in order to collect a large amount of solar energy. But the structural deformation and damage of the aircraft wing may occur because of bending and torsional loads induced by aerodynamic force during the operation. Therefore, the structural health monitoring of the wing is needed for increasing the operating time of the aircraft. In this study, the strain and damage of a composite wing of a solar powered aircraft were monitored by using fiber optic sensors until failure occurrence. In detail, a static loading experiment was performed on the composite wing with a length of 3.465m under a solar simulation environment, and the strain and acoustic emission (AE) of fracture signal were monitored by using fiber Bragg grating (FBG) sensors. In the results of the structural experiment, the damage occurred at a stringer when 4.5G load was applied to the composite wing, and the strain variations and AE signals were successfully measured by using FBG sensors. As a result, it is verified that the damage occurrence and location could be estimated by analyzing the strain variations and AE signals, and the fiber optic sensor would be a good transducer to monitor the structural status of a solar powered aircraft.
Optical fibers can be used as promising sensors in smart structures due to their novel characteristics. This paper presents
a wavelength division multiplexing (WDM) technique in order to improve the application capacity of single reflective
grating based fiber optic sensors to monitor large industrial structures at multiple points. The models are appropriate for
the general extrinsic fiber optic sensors such as the grating panel-based fiber optic sensor. The manufactured WDM fiber
optic sensor system was examined in order to demonstrate the feasibility for two parameter detections at two points using
mirror mounted grating based fiber optic sensor.
Optical fibers can be used as a promising sensors in smart structures thanks to their novel characteristics. In particular,
its immunity to electromagnetic interference (EMI) makes the sensor suitable for use in electronic environments. In
order to inspect the reliability of a structure, it is essential to characterize the dynamic responses of the structure. An
accelerometer associated with optical fiber makes it possible to conduct real-time structural health monitoring under high
electromagnetic environments. This paper describes an optimal design of a novel fiber optic accelerometer using one
grating panel for the application to civil engineering structures. The fiber optic sensor design was optimized to have the
best sensitivity to the motion of the reflective grating using two optical fibers in the quadrature. The reflected optical
signal of the sensor is influenced by the reflective grating pattern and optical fiber-grating distance. In this paper, several
simulations and experiments were carried out to evaluate the characteristics of the output signals according to the grating
pattern and the distance between the optical fiber and the grating for a fixed fiber core diameter. Through comparison of
the results between the simulations and the experiments, the optimum design of the grating-pattern was determined to
obtain a stable and periodic sine wave as the output signal. Furthermore, it was demonstrated that the output signals
reflected by one grating panel could be used for the final parameter-measurement.
Optical techniques are finding more and more use in the domain of nanoelectromechanical systems (NEMS). In particular, Michelson interferometry and Fabry-Perot interferometry have been employed to transduce high frequency motion of NEMS resonators. Here, we review our recent accomplishments in optical probing of NEMS. We discuss
the effectiveness of the above-mentioned optical techniques as the relevant NEMS dimensions are reduced beyond the optical probing wavelength.