This paper proposes a new method to develop a thermal model of an insulated gate bipolar transistor (IGBT) employing an optical fiber sensor mounted on the chip structure. Some features of the sensor such as electromagnetic immunity, small size and fast response time, allow the identification of temperature changes generated by the energy loss during device operation through direct measurement. In fact, this measurement method is considered impossible with conventional sensors. The online monitoring of the junction temperature enables identify the thermal characteristics of the IGBT. The results are used to develop an accurate model to simulate the heat generated during the device conduction and switching processes. The model showed a difference of only 0.3% between measured and simulated results, besides allowing evaluate separately the heat generated by each turn-ON/OFF process.
Fiber Bragg gratings engraved in standard telecommunications-grade single-mode fibers without previous hydrogen loading show enhanced thermal stability for high-temperature measurements up to 800 °C. The reflectivity decay at that temperature is adequate for industrial applications with a weekly change of sensing heads.
In this work, Bragg gratings were used to monitor, in real time, the temperature during the diamond deposition process obtained by hot filament chemical vapor deposition (HFCVD). Due to the instability of uniform fiber Bragg gratings (FBGs) to high temperatures, regenerated fiber Bragg gratings (RFBGs) were utilized. The results reveal that the diamond deposition process occurs at about 832 ºC (in the experimental conditions used in this case). The work also suggests that RFBGs are suitable devices to monitor processes which, as in the diamond deposition, the temperature is a critical parameter, and where other traditional methods have a little feasibility due to the own experimental setup or samples type under study.
Abstract-Thermal stability of both standard and regenerated Bragg gratings written in normal and photosensitive optical fibers was accessed. An apparent spectral wavelength stabilization of common gratings with no thermal hysteresis was reached after thermal treatments. However, after a time interval of 5 months, gratings exhibited a shift in the resonance Bragg wavelength at room temperature, as well as important changes in the thermal sensitivity above 200 ºC. Regenerated gratings proved to be stable only at temperatures below the critical regeneration temperature, with significant loss of reflectivity above that critical value. However, regeneration is performed by heating the FBG at high temperatures making the fiber brittle.A packaged RFBG sensor was recently proposed to provide mechanical stability and the sensor performance and response time were analyzed [15]. Despite the packaging does not interfere with the RFBG short term sensitivity and repeatability, the measured recovering time of 22 seconds is a direct consequence of the packaging.In this work, efficiency of thermal treatments on the spectral stabilization of both standard and Bragg and regenerated gratings written in normal and photosensitive optical fibers was accessed.FBGs were submitted to thermal cycles at temperatures up to 425 °C while RFBGs were heated up to 900 ºC. Gratings long-term performance regarding sensitivity, hysteresis and spectral stability were analyzed. Performance of a packaged RFBG was also evaluated.
II. METHODSFBGs were produced in single mode (GF-1 from Nufern) photosensitive and standard (G-652 from Fibers were hydrogenated at room temperature along 10 days in a 110 kgf/cm 2 pressure chamber. Thermal treatments (TT) were carried out in a furnace with a 1200 °C maximum temperature operation. FBGs 1, 2, 3 e 4 were submitted to 3 warm-up/cooling-down cycles. For warm-up temperature ranged from (25.0 ± 0.5) ºC to (425.0 ± 0.5) ºC in 45 minutes-long steps of 50 ºC each.FBG1 and FBG3 were slowly cooled-down (annealing) by keeping them inside the furnace after power was switched-off. FBG2 and FBG4 were removed from the furnace immediately after the last
In this work is reported the experimental and numerical results of the refractive index response of etched fibre Bragg gratings written in a graded index multimode fibre. The responses of the modes coupled by the grating inscribed in a multimode fibre are compared with the mode coupled by a grating inscribed in single mode fibre. The results of this study show that the refractive index sensitivity and the dynamical range of etched fibre Bragg gratings written in multimode fibres are higher than the ones verified in single-mode fibres. The determination of oil-biodiesel blend concentrations are also compared as an example of practical applications. It is shown that a greater core diameter of the multimode fibre enables the Bragg gratings to exhibit enhanced sensitivity without requiring further fibre diameter reduction.
This paper reports an effective method of packaging a fiber Bragg grating (FBG) for the simultaneous measurement of temperature and strain. The technique consists of embedding two fiber Bragg grating sensors inside a polymeric material with different geometrical characteristics. The mechanical and thermal characterizations of the optical transducer were performed. Then a matrix equation used measurements of the wavelength shifts from the two sensors and yielded information about the temperature and strain coefficients. The preliminary results demonstrate the feasibility of the encapsulation technique allowing measurements of temperature and strain in smart structures and harsh environments. The experimental procedure provides robustness to the sensor and the matrix equation approach has the potential to determine simultaneously the strain and temperature coefficients.
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