It is widely known that materials exposed to the severe low earth orbit (LEO) environment undergo degradations. For the
evaluation of fiber Bragg grating (FBG) sensors in the LEO environment, the reflective spectrum change and the Bragg
wavelength shift of FBG sensor were measured during aging cycles simulating the LEO environment. The LEO
environment was simulated by high vacuum (~10<sup>-5</sup> Torr), ultraviolet (UV) radiation (<200nm wavelength), temperature
cycling (-30°C~100°C), and atomic oxygen atmosphere (AO flux of 9.12×10<sup>14</sup> atoms/cm<sup>2</sup>/s and kinetic energy of ~0.04
eV). FBG sensor arrays were embedded into the graphite/epoxy composite material. Through the aging cycles simulated
for the LEO environment, the change in the reflective spectrums and the Bragg wavelengths from FBG sensors were
For the translation stage of nanometer scale, fiber optic EFPI sensor is suggested for the feedback control system on account of its high sensitivity, small size, simple system and relatively low cost. The novel signal processing algorithm for the real-time demodulation of EFPI output signal was developed and verified. The local linearity in the adjacent fringe values was shown, and used for the sinusoidal approximation of the nonlinear output signal. The real-time signal processing program was designed and the intensity signal of the EFPI sensor was demodulated to the phase shift with this program. The theoretical resolution of 0.36~8.6 <i>nm</i> in the displacement range of 0~200 <i>μm</i> was obtained. The sensor system was applied to the 1-D nano-positioner with a Piezo-electric actuator. The positioner successfully reached to the desired destination within 1 <i>nm</i> accuracy.
Impact location monitoring is one of the major concerns of the smart health monitoring. For this application, multipoint ultrasonic sensors are to be employed. In this study, a multiplexed FBG sensor system with wide dynamic range was proposed and stabilization controlling system was also developed for the maintenance of maximum sensitivity of sensors. For the intensity demodulation system of FBG sensors, Fabry-Perot tunable filter (FP-TF) with 23.8 nm FSR (free spectral range) was used, which behaves as two separate filters between 1530 ~ 1560 nm range. Two FBG sensors were attached on the bottom side of the graphite/epoxy composite beam specimen, and low velocity impact tests were performed to detect the one-dimensional impact locations. Impact locations were calculated by the arrival time differences of the impact longitudinal waves acquired by the two FBGs. As a result, multiplexed in-line FBG sensors could detect the moment of impact precisely and found the impact locations with the average error of 1.32 mm.