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A fibre Bragg grating sensing configuration is presented for simultaneous measurement of strain and temperature. The proposed concept relies on writing a single Bragg grating on the splice region of two fibres with different levels of germanium doping. Doing so, a grating structure appears with three resonance peaks, which show distinct temperature...
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... concept underlying the simultaneous measurement of strain and temperature only requires the monitoring of two grating signatures. Therefore, the two chosen were the ones associated with the SMF28 and SM1500 fibres. The splice-FBG was not considered for this job but the associated strain and temperature sensitivities were measured for completeness, turning out to be 1.04 ± 0.08 pm/µε and 9.51 ± 0.03 pm • C −1 , respectively. These values are not far from those obtained with the grating written in the SMF28 fibre, but with sufficient differentiation in order to sustain the possibility of using this sensing head for three- parameter simultaneous measurement [15]. Figures 3 and 4 show the responses of the two sensing gratings to changes in temperature and applied strain, respectively. As expected, different temperature sensitivities are observed for the two gratings, but they exhibit similar responses to applied strain. Considering the fact that there was no observable effect on the mechanical properties of the fibre, it can be concluded that K T SMF28 = K T SM1500 and K εSMF28 ≈ K εSM1500 . Therefore, a well-conditioned system of two equations for T and ε can be written which, from the slopes indicated in figures 3 and 4, is given by (λ SMF28 and λ SM1500 in nanometres and T , ε in degrees and The relative difference between the thermal coefficients of the two selected Bragg signatures is 15.4% (referenced to K T SMF28 ). For comparison, reported solutions based on dual gratings written in Ge/Ge + B [4] and in Ge/Er + Yb doped fibres [5] have values for such relative differences of 7.3% and 13.2%, respectively. Therefore, besides its intrinsic fabrication simplicity related to the fact that only a single-step UV exposure is needed (as also happens in the configuration described in [5]), the more favourable thermal behaviour of the sensing head proposed here indicates the potential for a better discrimination between temperature and strain induced effects. The amenability of single or composed sensing heads to multiplexing is always a merit factor. When fibre Bragg gratings are involved, the most natural and advantageous choice is wavelength multiplexing. The sensing concept proposed in this paper permits the serial wavelength multiplexing of some sensors, however its number is limited by two factors: each sensing head demands a relatively large fraction of the spectrum (around 12 nm), and the losses related to splicing two different optical fibres. Combining these two factors, wavelength multiplexing would probably be limited to two or three sensing ...
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Citations
... In practical application, it is a pressing problem to eliminate the cross sensitivity between temperature and strain [8][9][10]. The current solutions include reference to fiber gratings [11][12][13], the combination of different gratings [14][15][16][17][18], the fusion of fiber gratings with different cladding diameters [19][20][21], chirped fiber gratings [22], Fabry-Perot (FP)cavities [23][24][25][26], and microstructured fiber gratings [27][28][29][30]. Among these methods, referring to fiber gratings requires that the two gratings must have identical structures and parameters, raising higher requirements for fabricating. ...
... where α and ξ are thermal expansion and thermo-optic coefficients of the optical fiber, respectively. When the strain varies at a constant temperature, the central wavelength changes under the photoelastic effect, thus obtaining Eq. 6 [16]. ...
... In addition, there is the equation of P e1 P e2 n 2 eff [P 12 − v(P 11 + P 12 )]/2 [16], in which P 11 and P 12 are photoelastic coefficients of the fiber core and cladding, respectively. ...
This work designed a dual-wavelength 2D fiber Bragg grating (FBG) engraved on the single-mode fiber to measure the temperature and strain. The FBG is composed of two sub-gratings that are not overlapped spatially at the same location of the fiber core. Experiments showed that the temperature and strain sensitivities of this grating were separately measured to be 10.64 p.m./°C and 0.882,731 p.m./μɛ at the central wavelength of 1,548 nm, and 10.74 p.m./°C and 0.916,080 p.m./μɛ at the central wavelength of 1,550 nm. These coefficients constitute a coefficient matrix that can solve the problem of cross sensitivity between temperature and strain, which has been verified by varying central wavelengths caused by the synchronous change of temperature and strain.
... This would require a temperature compensation strategy. Temperature effects can be discriminated from pure mechanical strain using a multitude of different approaches [77][78][79][80][81][82][83][84][85][86][87]. Therefore, this aspect does not imply any loss of generality of the methodology presented in this study. ...
Strain Modal Testing (SMT), based on strain sensors signal processing, is an unconventional approach to perform Experimental Modal Analysis which is typically based on data measured by accelerometers. SMT is still mainly restricted to academia and requires additional investigation for a successful transition towards industry. This paper critically reviews why the automotive sector can benefit from this relatively new approach for a variety of reasons. Moreover, a case study representative of the automotive field is analyzed and discussed. Specifically, an SMT methodology is applied to evaluate the modal properties of a reinforced composite roof belonging to a racing solar powered vehicle. In the experimental activity, signals from Fiber Bragg Grating (FBG) sensors, strain gauges, and accelerometers were simultaneously acquired and further processed. The advantages of using optical fibers were discussed, together with their weaknesses and ongoing challenges. The FBG results were compared with the conventional analysis performed with the accelerometers, emphasizing the main similarities and discrepancies.
... Two FBGs was designed using SMF28 doped with 3 mol% GeO 2 in the core and SM1500 doped with 20 mol% GeO 2 in the core, and was calculated their temperature and strain sensitivities by the matrix method. The simultaneous measurement of temperature and strain was performed by attaching these two FBGs with the same temperature sensitivity and different strain sensitivity end-to-end (Frazao and Santos 2004). Two FBGs at Bragg wavelengths of 1549 and 1551 nm were designed using the Optigrating application, both temperature and strain was applied to a 1549 nm FBG, and a 1551 nm FBG was only exposed to temperature The simultaneous measurement of strain and temperature was performed by taking the difference between the wavelength change resulting from the simultaneous application of temperature and strain and the wavelength change resulting from only temperature application (Elgaud et al. 2016). ...
Bragg wavelength is sensitive to both temperature and strain changes. Therefore, in sensors that are designed using a fiber Bragg grating (FBG), it is not possible to discriminate the cross-sensitivity of temperature and strain. The design of tilted fiber Bragg gratings (TFBG), which is a family of short-period gratings, has been one of the solutions to this problem. The core mode resonance (LP01) and cladding resonances (LPmn) appear simultaneously in the transmission spectrum. It is possible to perform the simultaneous, independent measurement of temperature and strain using only a TFBG. In this study, the design of a TFBG sensor with a tilt angle of 5° were performed by using the Optigrating 4.2.2 software in order to measure the temperature and strain simultaneously. While the varying temperature was applied to the TFBG in the first stage, the varying strain was applied to it in the second stage, and simultaneously varying temperature and strain were applied to it in the third stage, and linear shifts occurring in wavelengths were calculated using Optigrating. In the design stage of the temperature sensor, research was conducted with different thermal expansion and thermo-optic coefficients, the amounts of shifts caused by these coefficients in the wavelength were examined. It was observed that the change in the wavelength caused by the simultaneous application of temperature and strain was equal to the total change in wavelength that occurred in the non-simultaneous application of temperature and strain.
... Moreover, fabrication requirements of our design is much simpler compared with other types of PCs cavity or ring resonator temperature sensors [58,59]. Compared with these structures, performance of the proposed structure is optimum as well [47,60,61]. For example, Xing-hu et al [47] investigated a limited value of sensitivity that is not exceeding 0.0112 nm°C −1 through the temperature variation from 30 to 80°C. ...
A novel design of one dimensional annular photonic crystals with a low birefringence nematic liquid crystal as a defect layer is introduced. The output field of the sensor structure is plotted after different optimization steps on all constituents such as thickness and core radius of the starting medium. The performance of the sensor was studied using different quality parameters such as sensitivity, figure of merit, detection limit and resolution. The designed sensor exhibits a sensitivity of about 0.224 nm °C⁻¹ due to the presence of the liquid crystal material. The proposed sensor design can be used as a narrowband optical filter in the visible region around two wavelengths: 600 nm and 700 nm. As an optoelectronic device, this structure can serve as a temperature sensor with higher sensitivity than the conventional one dimensional photonic crystal structures and photonic crystals fibers.
... The transmission spectra of titled FBGs [14], superstructure [15] and dual-mode fiber based FBG [16] include too many resonance peaks which can also realize multi-parameter measurement simultaneously, but all of that sensor will take up too large spectrum range. Some other methods can achieve two peaks in spectrum after a single fabrication cycle such as using substrate flake [17] or writing FBG on fusion splice [18][19][20]. Scholars have reported a single grating schemes that FBG was written on the splice joint between two different fibers [20] or the same fibers [18][19]. The two dips have extremely similar temperature and strain sensitivity when FBG was written on the same fibers, and as a result it would cause errors in demodulation. ...
... Some other methods can achieve two peaks in spectrum after a single fabrication cycle such as using substrate flake [17] or writing FBG on fusion splice [18][19][20]. Scholars have reported a single grating schemes that FBG was written on the splice joint between two different fibers [20] or the same fibers [18][19]. The two dips have extremely similar temperature and strain sensitivity when FBG was written on the same fibers, and as a result it would cause errors in demodulation. ...
... In actual measurement for the double physical parameter, ∆λ A and ∆λ B are used to represent the shifts of two peaks, ∆T and ∆ε are the temperature and strain variation. Therefore, when the temperature and strain are applied on the hybrid structure simultaneously, the matrix form for the response of temperature and strain can be written as formula [20]: where K T A and K T B are the temperature sensitivities, K ε A and K ε B are the strain sensitivities of two peaks, respectively. If the four sensitivities mentioned above have been measured, the demodulation matrix for the two parameters can be derived as: ...
A novel hybrid fiber Bragg grating (FBG) for simultaneous measurement temperature and strain is proposed. This sensor is fabricated by inscribing fusion splice joint between two types of fibers using excimer laser and phase mask. Due to the different characteristics of the two fibers, the two resonance peaks have different responses to temperature and strain, and both physical parameters can be demodulated by analyzing the central wavelength shifts. Practical measuring results show that the hybrid FBG proposed in this paper can precisely achieve simultaneous measurement of temperature and strain. This work provides a new scheme for multi-parameter simultaneous sensing.
... Common FBG multiparameter sensors are designed to measure temperature and strain simultaneously. [52][53][54][55][56][57][58][59][60] One of the earliest dual-parameter FBG sensors was based on a single FBG. Part of the FBG was preloaded and glued to the surface (strain measuring part), while part of the FBG was unattached/free and provided a temperature measuring section, 56,57 as shown in Fig. 20. ...
... An alternative similar and interesting approach is to splice together two fibers with dissimilar temperature sensitivities (i.e., fibers with different thermo-optic coefficients), and then inscribe an FBG over the splice region. 53,54 This leads to the formation of two FBG sections having different temperature sensitivities, while the strain responses for both fibers/gratings sections remains unaltered, which provides possibilities for unambiguous strain and temperature resolution. Different temperature sensitivities of individual fibers were achieved in reported works, either using two fibers with different germanium doping levels, 54 or by combining standard germanesilicate fiber with boron-co-doped fibers (boron doping increases the coefficient of thermal expansion of silica glass, which results in string temperature-dependent stress build up in the core, which leads to high-temperature sensitivity). ...
... 53,54 This leads to the formation of two FBG sections having different temperature sensitivities, while the strain responses for both fibers/gratings sections remains unaltered, which provides possibilities for unambiguous strain and temperature resolution. Different temperature sensitivities of individual fibers were achieved in reported works, either using two fibers with different germanium doping levels, 54 or by combining standard germanesilicate fiber with boron-co-doped fibers (boron doping increases the coefficient of thermal expansion of silica glass, which results in string temperature-dependent stress build up in the core, which leads to high-temperature sensitivity). 53 Another possible use of FBGs includes chirped FBGs. ...
Needs for sensor miniaturization, versatile sensing solutions, and improved measurements' performances in difficult operating environments have recently driven considerable research in optical fiber sensor for multiparameter measurements. Multiparameter sensors not only enable new sensors' functionalities, but can also improve achievable measurement performances for some frequently measured parameters considerably. This study provides a review of work in the field of miniature fiber-optic sensors that allows independent and simultaneous measurements of two or more different physical or chemical parameters. Sensor designs and corresponding signal processing schemes are reviewed and compared. © 2019 Society of Photo-Optical Instrumentation Engineers (SPIE).
... Common FBG multiparameter sensors are designed to measure temperature and strain simultaneously. [52][53][54][55][56][57][58][59][60] One of the earliest dual-parameter FBG sensors was based on a single FBG. Part of the FBG was preloaded and glued to the surface (strain measuring part), while part of the FBG was unattached/free and provided a temperature measuring section, 56,57 as shown in Fig. 20. ...
... An alternative similar and interesting approach is to splice together two fibers with dissimilar temperature sensitivities (i.e., fibers with different thermo-optic coefficients), and then inscribe an FBG over the splice region. 53,54 This leads to the formation of two FBG sections having different temperature sensitivities, while the strain responses for both fibers/gratings sections remains unaltered, which provides possibilities for unambiguous strain and temperature resolution. Different temperature sensitivities of individual fibers were achieved in reported works, either using two fibers with different germanium doping levels, 54 or by combining standard germanesilicate fiber with boron-co-doped fibers (boron doping increases the coefficient of thermal expansion of silica glass, which results in string temperature-dependent stress build up in the core, which leads to high-temperature sensitivity). ...
... 53,54 This leads to the formation of two FBG sections having different temperature sensitivities, while the strain responses for both fibers/gratings sections remains unaltered, which provides possibilities for unambiguous strain and temperature resolution. Different temperature sensitivities of individual fibers were achieved in reported works, either using two fibers with different germanium doping levels, 54 or by combining standard germanesilicate fiber with boron-co-doped fibers (boron doping increases the coefficient of thermal expansion of silica glass, which results in string temperature-dependent stress build up in the core, which leads to high-temperature sensitivity). 53 Another possible use of FBGs includes chirped FBGs. ...
... where M = k FPε k FBGT -k FPT k FBGε is determinant of the coefficient matrix, which must be non-zero for possible simultaneous measurement [36]. ...
Strain and temperature are critical parameters to monitor in Li-ion batteries (LIBs) to improve their safety and long-term cycling stability. High local current densities can result in a massive heat release, decomposition of the electrolyte, gas evolution and even explosion of the battery cell, known as thermal runaway. However, the corrosive chemical environment in the batteries is a challenge to monitor strain and temperature. Optical fiber sensors, due to their high chemical stability and small diameter, can be embedded within the LIBs, thus becoming an interesting solution for operando and in situ measurements. In this work, a hybrid sensing network constituted by fiber Bragg gratings and Fabry-Perot cavities is proposed for the discrimination of strain and temperature. The proof-of-concept was performed by attaching the sensing network to the surface of a smart-phone battery. Afterwards, it was embedded in a Li-ion pouch cell to monitor and simultaneously discriminate internal strain and temperature variations in three different locations. Higher thermal and strain variations are observed in the middle position. The methodology presented proves to be a feasible and non-invasive solution for internal, real-time, multipoint and operando temperature and strain monitoring of LIBs, which is crucial for their safety.
... The in-line MZIs are fabricated by a splitter, combiner to observe the coupling and recouping of core-cladding modes. These kinds of sensors have been widely used to investigate the temperature [18,19], strain [20], refractive index [21][22][23], and liquid level [24]. Compared to other sensors, the sensor based on the core offset structure is more economic owing to low cost and its ease of fabrication. ...
In this paper, a high sensitive connector offset optical fiber sensor is employed to detect the refractive index of liquid. The configuration chosen for this experiment is formed by lateral core offset fusion splicing of no-core fiber (NCF) between the single mode fibers (SMF) and cladding modes are excited by misalignment. The sensing principle for refractive index detection is based on Mach-Zehnder Interferometer (MZI) principle and the experiment is carried out by immersion of device in NaCl solutions of different refractive indices. Such refractive index sensor exhibits high sensitivity 197.33 nm/RIU for the surrounding refractive index variation from 1.333 to 1.380, and the result shows the excellent agreement with theoretical analysis. Compared to other sensors, the proposed device has the potential to provide high sensitivity, ease of fabrication, low cost, compact size, and linear response. Thus, it can be used in many applications such as bio-sensors, chemical sensor, temperature sensor, and pressure sensor.
... To all of them, optical fiber sensor has attracted great attention for its many advantages, such as high sensitivity, low cost, fast response, etc. There are various types of fiber, such as no-core fiber [16], Multimode fiber [17], fiber Bragg gratings [18,19], core-offset structure [20], tapered structure [21] and photonic crystal fiber [22,23], etc. are used for temperature measurement. Fiber Bragg gratings are best for the external refractive index immunity, but its temperature response is low and long period fiber grating [24,25] has very good temperature response but it has some limitations such as complicated structure and needs expensive experimental facilities. ...
We report an experimental investigation on liquid sealed no-core (NCF) fiber based on modal interferometer and applied for temperature sensing applications. The sensor fabrication was very simple and inexpensive because that requires only a splice section of NCF in the middle of single mode fiber (SMF). After fabrication, the interferometer was packed into a liquid-sealed capillary tube and then the sensing measurements were carried out by detecting wavelength sweeping. An experimental demonstration shows that the fabricated interferometer exhibits a high linear response with sensing range and can be easily controlled by tuning the refractive index of the sealed liquid. The highest temperature sensitivity is found to be 201.17 pm/°C.
