Monitoring of silicone adhesive in space solar cells with an embedded multi-parameter TFBG sensor in a simulated space environment

Abstract

In this research the ageing of a silicone adhesive in a simulated space environment is monitored through an embedded three parameter tilted Fibre Bragg Grating (TFBG) sensor. Here, the silicone is used as an adhesive between two thin cover glasses, and the space environmental ageing is simulated by thermal cycles in high vacuum conditions (better than 10-5 mbar). These operational conditions can induce variations in the silicone adhesive with respect to its original properties such as dimensional stability, chemical composition, generated contaminants, discoloration and, mechanical or optical degradation. Therefore, surrounded by the adhesive, in the centre of the cover glass sandwich, a weakly tilted FBG sensor was placed to obtain information from its spectra on the state of the polymer during the test. Specifically, the temperature, strain and refractive index (RI) of the silicone can be, simultaneously and separately, measured from the spectrum of a single TFBG from selected resonance peaks. These parameters can be used to evaluate the “health” state of the silicone during the vacuum thermal cycles. The simultaneous TFBG thermomechanical measurements gave a solution to the non-localized measuring issues when using classical fibre optic or electrical strain-gauges and a thermocouple (TC) to compensate the temperature and to better understand the material behaviour. The trends of the measured parameters are reported during the entire testing time, and at the end of the test, the optical fibre sensor measured a negative strain of ~100 με and a positive RI variation of ~0.002.

Enhanced Strain Measurement Sensitivity with Gold Nanoparticle‐Doped Distributed Optical Fibre Sensing

“…Because of these advantages, FOS has been used for SHM in felds such as aerospace engineering (for example, SHM in aerospace structures [9,10]) and civil engineering (for example, the monitoring of the railway infrastructures [11] and the pavement layers [12]). Te most commonly used optical fbre sensing methods for SHM include distributed fbre optic sensing [13] and fbre Bragg gratings sensing [14,15]. Compared with fbre Bragg gratings, distributed fbre optic sensors (DFOS) have the advantage that they can obtain strain information along the length of the sensing fbres.…”

A Wavelet Derivative Spectrum Length Method of TFBG Sensor Demodulation

“…Tilted fibre Bragg grating (TFBG) has an interesting transmission spectrum that is sensitive to changes in several physical quantities such as temperature [ 1 ], bending [ 2 ], strain [ 3 ], and polarisation state [ 4 ]. TFBG gratings can also be used to measure several parameters simultaneously [ 5 , 6 , 7 , 8 ]. As with any fibre optic sensor, the main advantage is the small size of the sensor.…”

Space Silicone Adhesive Monitoring Via Minimally Intrusive Optical Fibre Sensing During Vacuum UV/VUV Radiation Exposure

“…The strain-temperature measurements give an indication on the dimensional and physical condition of the material. At the same time, the variations of its refractive index (RI) are linked to the chemical changes in the polymer [6,7]. Hence, since some chemical reactions may be induced by UV/VUV radiation, the silicone RI may undergo a variation detectable by the TFBG sensor.…”