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Simultaneous Measurement of Liquid Level and Temperature Using Tilted Fiber Bragg Grating
Abstract
We present a tilted fiber Bragg grating (TFBG)-based fiber optic sensor for the simultaneous measurement of liquid level and temperature. Due to different responses of cladding modes and core mode in TFBG spectrum to liquid level and temperature changes, both values can be measured independently. The examined 3.5° TFBG exhibits linear liquid level, as well as temperature, responses and sensitivities of-0.456 ± 0.009 dB/mm and 11.4 ± 0.2 pm/°C, respectively. In addition, greater sensor applicability is proposed for liquids having lower refractive indexes using TFBG with greater tilt angle. The presented system is capable of being applied in chemical, food, and automotive industries as well as, thanks to its all-fiber structure, in potentially hazardous environments where the immunity to electromagnetic fields or/and electric isolation is required.
... In the past thirty years, fiber optic temperature sensors have been employed due to their inherent characteristics and advantages. [1][2][3][4][5][6][7][8][9][10] Many optic fiber temperature sensors have been reported composed of fiber Bragg gratings (FBG), [3][4][5] long-period fiber gratings, [6,7] photonic crystal fibers, [8,9] and polarizationmaintaining fibers. [10] However, the sensitivity of temperature sensors based on fiber Bragg gratings is limited to only 0.01 nm/ C and expensive femtosecond lasers are needed. ...
... In the past thirty years, fiber optic temperature sensors have been employed due to their inherent characteristics and advantages. [1][2][3][4][5][6][7][8][9][10] Many optic fiber temperature sensors have been reported composed of fiber Bragg gratings (FBG), [3][4][5] long-period fiber gratings, [6,7] photonic crystal fibers, [8,9] and polarizationmaintaining fibers. [10] However, the sensitivity of temperature sensors based on fiber Bragg gratings is limited to only 0.01 nm/ C and expensive femtosecond lasers are needed. ...
... Recently, optical fiber sensors with interferometers have been reported. Various temperature sensors have employed optical fiber structures, [3][4][5][6][7][8][9][10] splicing methods, [11,12] filling materials, [13,14] and filling methods. [15,16] According to their main structural characteristics, [17][18][19][20] including Sagnac, Michelson, Mach-Zehnder (MZ) and Fabry-Perot (FP), the specific requirements of applications can be met. ...
A simply fabricated, highly sensitive, and inexpensive optical fiber temperature sensor is reported with a Fabry–Perot (FP) microcavity of controlled length. The microcavity with controllable length is fabricated by single-mode fiber (SMF) and polydimethylsiloxane (PDMS) for temperature sensing. After the PDMS is cured, the SMF is connected to the supercontinuum light source (SCLS) and the optical spectrometer analyzer (OSA) for online observation of the reflection spectrum. The micro-displacement platform is used to pull the SMF to form an air cavity. After the air cavity is stabilized, ultraviolet (UV) activated glue is used for packaging outside the PDMS. The FP microcavity is formed by the end face of the SMF and the face of PDMS. The length of the FP microcavity can be controlled online by the micro-displacement platform to a minimum of 15 µm. The free spectral range (FSR) may reach 74.8 nm and the interference fringe contrast (IFC) is up to 19.8 dB to allow sensitive measurements across a wide temperature range. The experiments demonstrate a high temperature sensitivity of 5.388 nm/°C from 33 to 93 °C with high repeatability and linearity (R²=0.9937). Stability experiments showed that the maximum changes in wavelength and intensity are only 45 pm and 0.035 dB, respectively. It is anticipated that the easily constructed, compact, and inexpensive fiber-optic temperature sensor will be employed in practical applications.
... The processing equation of a multi-parameter sensor written in matrix form, with the sensitivities of the measured quantities determined for different wavelengths or for different modes of light, allows the measured quantities to be reconstructed by calculating the inverse sensitivity matrix, subject to the condition that the determinant of the sensitivity matrix has a value different from zero. The most common two quantities measured simultaneously are strain and temperature [1,2], refractive index and temperature [3], fluid level and M. Detka temperature [4], and force and temperature [5]. The most commonly simultaneously measured three quantities are torsion, strain and temperature [6]. ...
... The T matrix describing the entire grating structure can be described by the equation: (4) where T1, T2 ... TM are matrices of uniform sections 1, 2 ... M of the grating. Relationships for the calculation of matrices of uniform sections are specified in [12,13]. ...
... Optical fiber sensors (OFSs) for detecting the above parameters have attracted considerable attention, as they offer various advantages over mechanical and electric transducers [1]. These sensors are based on fiber Bragg gratings (FBGs) [1][2][3], long-period fiber gratings (LPFGs) [4,5], Michelson interferometers [6,7], Mach-Zehnder interferometers [8][9][10][11][12], Sagnac loops [13], fiber Fabry-Perot cavities [14], etc., or a combination of them [15][16][17]. Osuch et al. present a tilted FBG-based sensor for simultaneous liquid-level and temperature measurement, which exhibits sensitivities of −0.456 ± 0.009 dB/mm and 11.4 ± 0.2 pm/ • C, respectively [2]. ...
... These sensors are based on fiber Bragg gratings (FBGs) [1][2][3], long-period fiber gratings (LPFGs) [4,5], Michelson interferometers [6,7], Mach-Zehnder interferometers [8][9][10][11][12], Sagnac loops [13], fiber Fabry-Perot cavities [14], etc., or a combination of them [15][16][17]. Osuch et al. present a tilted FBG-based sensor for simultaneous liquid-level and temperature measurement, which exhibits sensitivities of −0.456 ± 0.009 dB/mm and 11.4 ± 0.2 pm/ • C, respectively [2]. Enriquez et al. proposed a configuration of a hybrid fiber Bragg grating together with a long-period grating sensor used for simultaneous RI and temperature detection [15]. ...
An all-fiber Mach–Zehnder interferometric sensor capable of measuring liquid level, refractive index (RI), temperature, and axial strain is proposed and experimentally demonstrated. The proposed sensor is based on a fiber ball–thin fiber (TF)–core-offset structure sandwiched between two standard single-mode fibers. The variations of ambient liquid level, RI, temperature, and axial strain cause the change of phase difference between the cladding modes and the core mode, which leads to the shift of interference spectrum. The wavelength shifts of three resonant dips in the transmission spectrum are used to investigate the sensing characteristics of the sensor. Experimental results show that the sensor with TF length of 20 mm exhibits high RI and liquid-level sensitivities of and at a wavelength of 1589.5 nm. Meanwhile, the sensor is insensitive to temperature and axial strain, and the maximum sensitivities are 0.0390 nm/°C and - {4}.{84}\; \times \;{{10}^{ - 4}}\;{\rm nm}/\unicode{x00B5} \varepsilon , respectively. In addition, the sensor shows superiority in measuring multiple parameters simultaneously.
... Osuch et al. [48] investigate the application of tilted Bragg gratings for utilization in sensors of simultaneous measurement of temperature and liquid level. After the modifications with the gratings, the researchers observed that it was possible to identify values in wider coverage ranges, differently from when utilized without the Bragg gratings. ...
... As optical fibers are generally utilized in telecommunications [61], when they are mentioned industrial sensors, it comes to mind the image of a fragile fiber which would not have applicability in a hostile environment as industrial. Jiang et al. [44], Osuch et al. [48], Bremer et al. [52], and Werneck et al. [60] make it clear in their work the excellent relationship of Bragg grating sensors and the heavy industrial environment. ...
... LPFBGs also allow for design of sensors that combine measurements of parameters that are otherwise difficult to measure by fiber-optic approaches, e.g., sensors for simultaneous measurements of liquid level and temperature. 87 The most frequently reported combination of parameters sensed by multiparameter LPFBG sensors are RI and temperature sensor. There are several approaches to distinguish those two parameters. ...
... Access to cladding modes through tilted FBGs also allows for a design of sensor for simultaneous measurement of liquid level and temperature. 87 In this case, both parameters can be measured avoiding undesired crosstalk by tracking the difference in responses of core and cladding modes' resonances. In particular, temperature variations are related to the core mode resonance wavelength, while the variation in the liquid level is correlated to an integral of amplitudes of all cladding modes that are present in the sensor's transmission spectrum. ...
... Previously, fiber optic liquid-level sensors have mostly operated by detecting the reflected light from the liquid's surface or a curved cantilever beam [15,16]. Various approaches have since been proposed, including the use of cladding-less fiber [17], long period grating [7], fiber Bragg grating (FBG) [18], tilted fiber Bragg grating [19,20], leaky mode attenuation [21], coreless multimode fiber [22], single mode-multimodesingle mode (SMS) structure [23], tapered structure [24], etc. While the aforementioned techniques can be operated effectively in the ambient temperature, specific intricate applications (e.g., superconducting magnets and wires, aerospace, and biological experiments) may require the use of fiber-optic sensors that have the capability to monitor the cryogenic temperature. ...
A novel analytical technique for the level detection of cryogenic liquids like liquid nitrogen using wave theory and employing a Gaussian beam, a zeroth-order Bessel-Gauss (BG) beam, and a radially polarized Bessel-Gauss (RPBG) beam is presented here. At first, this wave theory-based analytical model is shined by the Gaussian (G) beam, and the observations are validated with the already reported experimental data. The obtained results are in good concurrence with the experimental findings presented by J. E. Antonio-Lopez et al. in the year 2011. With this validation of the proposed theory, this idea next extended to the utilization of Gaussian, BG, and RPBG beams as input sources for the proposed structure. The performance of this sensor with the change in refractive index according to the cryogenic temperature and the level of liquid nitrogen is investigated using the propagation of these beams inside the sensor structure. A comparative assessment has also been presented utilizing the Gaussian and non-Gaussian beams. By irradiating the RPBG beam, the discerned sensitivity is 4.517 dB/°K, 18458.8 dB/RIU, 9.759 dB/cm, and 0.176 dB/nm, with a resolution of 5.5 × 10⁻⁷ RIU. This is 3.8 times more sensitive than the published ray theory-based publications till date that are based on the Gaussian beam. Due to its better sensing performances, with the ease of fabrication processes, the proposed sensing technology opens new avenues to develop high-performance fiber optic-level sensors with the scope of multiple input sources for physical, biological, and chemical sensing in cryogenic environments.
... Currently, optical fiber liquid leak detection technologies rely on sensors such as Rayleigh scattering, Raman scattering, and Bragg grating [5][6][7][8]. However, these detection methods have several limitations: they are only sensitive to changes in stress and temperature and cannot directly measure liquid leakage events, resulting in poor real-time effectiveness. ...
In order to address the issues of high light loss and low coupling efficiency in quasi-distributed leak monitoring fiber-optic sensors, a micro-focusing Fresnel lens is employed to enhance the power reception of the fiber. First, a simplified method is utilized to derive the Fresnel lens formula, enabling the design of a compact-sized lens with short focal length and superior convergent performance. Second, Trace Pro simulation software is employed for meticulous design and optimization, facilitating prediction of the lens’ performance, light gathering efficiency, and spot uniformity. Finally, the comparison of experimental data between systems with and without the lens shows that, without impairing other sensing properties, the total power of the light’s conductive mode in the fiber can be increased by 65% by this lens, thereby enhancing the signal discrimination ability and enabling the sensor to exhibit higher consistency and reliability when responding to external environmental interference.
... In 2016, Y. Hen et al. designed a sensor based on the modulation principle of fiber Bragg grating (FBG) for broad-spectrum light source, calculated the change of refractive index by wavelength bias. The standard deviation of the measured value of refractive index change is [15]. In 2018, J. Chen et al. developed a compact refractive index sensor based on total internal reflection (TIR) method with a sampling frequency of 0.1 Hz, and a standard deviation of in measuring results is obtained [16]. ...
The refractive index of seawater is one of the essential parameters in ocean observation, so it is necessary to achieve high precision seawater refractive index measurement. In this paper, we propose a method for measuring the refractive index of seawater based on a Position Sensitive Detector (PSD). Theoretical model is established to depict the correlation between laser spot displacement and refractive index change, utilizing a combination of position sensitive detector and laser beam deflection principle. Based on this optical measurement method, a seawater refractive index measurement system was established. To effectively enhance the sensitivity of refractive index detection, a focusing lens was incorporated into the optical path of the measuring system, and simulations were conducted to investigate the impact of focal length on refractive index sensitivity. The calibration experiment of the measuring system was performed based on the relationship between refractive index of seawater and underwater pressure (depth). By measuring laser spot displacement at different depths, changes in displacement with respect to both refractive index and depth were determined. Experimental results demonstrate that the system exhibits a sensitivity of 9.9277×10−9RIU (refractive index unit), the refractive index deviation due to stability is calculated as ±7.545×10−9RIU. Thereby the feasibility of highly sensitive measurement of seawater refractive index is verified.
... In the work [15], there was developed an aerial method, which in addition to the SRI definition, as well, might be used, applying TFBG grating to specify the liquid level. ...
The article describes the optical elements of signal demodulation and polling systems from photonic pressure sensors on inclined fiber Bragg gratings, which are often used to measure the refractive index (RI). A new design of a photonic fiber-optic Bragg pressure sensor with an inclined lattice has been developed, which is connected to standard multimode fibers with an inclined Bragg lattice connected to a metal diaphragm, which is a deformed inclined cantilever. The light source is polarized using the first polarizer and directed to the photonic crystal fiber in such a way as to excite multimode fibers. In this work, a method was developed for determining the optical elements of the spectral contour length system, which consists of setting the cut-off wavelength and then determining the accompanying refractive index. An experimental study determined the curve of the chain length change in the set. To process random signals, the spatial correlation method is used in combination with an approach to digital images based on the number of lanes and the direction of movement. The experimental results differ from the theoretical ones by about 4%. The developed correlation method reflects frequency as well as randomness, it is used in the photographic process together with the image correction given in this document.
... Mechanicaland electrical-based liquid level sensing techniques have shown excellent performance in conventional liquid level measurement [1,2], but their utility in conductive, flammable, and explosive environments is limited. In recent years, various fiber-optic sensors have been widely used for liquid level sensing due to their unique advantages such as anti-electromagnetic interference, no explosion hazard, and long life cycle, including Mach-Zehnder interferometric fibers [3], fiber Bragg grating technology [4], tilted fiber Bragg grating technology [5], and long-period fiber grating (LPFG) technology. Among them, the LPFG has attracted the attention of many researchers because of its high sensitivity. ...
A new, to the best of our knowledge, type of liquid level sensor with -phase-shifted long-period fiber grating operating near the phase-matched turning point is proposed. The sensor introduces a -phase shift at the center of the grating, which can generate three attenuation peaks due to the mode interference effect in the transmission spectrum of the sensor operating near the phase-matched turning points. According to the different liquid level and temperature sensing characteristics of three attenuation peaks, simultaneous detection of liquid level and temperature can be realized through wavelength modulation and intensity modulation detection. In this paper, the structural parameters of this liquid level sensor, such as grating period and grating length, are designed optimally based on the fiber grating coupled mode theory, and the wavelength spacing of the attenuation peaks on both sides and the intensity of the center attenuation peak are analyzed in relation to the liquid level and temperature. The simulation results show that the liquid level sensitivity is 5.58 nm/mm and for wavelength modulation and intensity modulation, respectively, for the liquid level variation range of 0 to 18 mm; and the temperature sensitivity of wavelength modulation and intensity modulation is and 0.171 dB/°C, respectively, over the temperature variation range of 20°C to 80°C. Therefore the simultaneous detection of liquid level and temperature can be realized by establishing a measurement inversion matrix. Compared with other liquid level sensors, this sensor is expected to be widely used in the field of liquid level sensing due to its simple structure, high liquid level sensitivity, large liquid level measurement range, and narrow monitoring peak bandwidth.
... The spectrum of cladding modes of the TFBG grating changes under the influence of many quantities. These quantities can be: refractive index [15], bending [16], liquid level [17][18][19], temperature and strain [20]. The state of polarization can have a negative effect on the measurement of these quantities if it is uncontrolled or it can be used to increase the sensitivity of measurements of some quantities [21][22][23]. ...
... As the refractive index increases, the extinction ratio of each cladding mode resonance is decreasing, that is, the envelope area will correspondingly decrease, as shown in the inset of Fig. 6(b). The envelope area method for TFBG proposed by C. Caucheteur et al. [34] shows a resolution of 2*10 −4 RIU as well as a temperature-insensitive property, the method has been widely studied, including the sensing of liquid level, temperature and so on [39,40]. The value of the envelope area was obtained by calculating the integral area contained in the upper envelope and the lower envelope, which was based on the demodulation algorithm we coded. ...
A high sensitive aqueous ammonia sensor based on tilted fiber Bragg grating (TFBG) had been reported. The sensors were fabricated by a 10 ° TFBG coated by a membrane receptor named as Polyaniline/Graphene oxide on the surface of the fiber. The correlative concentrations of aqueous ammonia were demodulated by global monitoring of the envelope area of cladding modes in the transmitted spectrum of the TFBG. Tests have shown that the proposed sensor can provide a linear and rapid response of aqueous ammonia within 22 seconds, in a concentration range from 1-12 ppm. Moreover, the limit of detection can even reach 0.08 ppm, through the theoretical analysis of our experimental results. The proposed sensor has good performance, is easy to manufacture and of small size, making it a good choice for real-time, in-situ, label-free detection of aqueous ammonia in the future.
... Meanwhile, they can be applied in harsh environments. Currently, the most widely used fiber-optic sensors for liquid-level sensing are mainly focused on long-period grating (LPG) [5], [6], [7], [8], Fabry-Perot interferometer (FPI) [9], [10], [11], Mach-Zehnder interferometer (MZI) [15], [16], [17], fiber Bragg grating (FBG) [12], [13], [14], multimode interference (MMI) [18], [19]. In 2007, a fiber-optic etched FBG sensor for liquid-level monitoring was proposed. ...
High-resolution monitoring of liquid level over a wide range has always been a great challenge. In this paper, a fiber ring laser (FRL) sensor system with Fabry-Perot interferometer (FPI) is proposed for the high-resolution measurement of liquid level. The FPI fabricated with a polyimide film is embedded in a FRL for intracavity sensing. It is used as a reflective sensing head, which generates different reflection losses at different liquid levels to modulate the output power of the FRL. With the intracavity sensing, the resolution of the liquid level sensing system has been significantly improved from 37.5 mm to 1.5 mm. The measurement range of the liquid level sensing system is obtained as 0.6 m. The output stability and measurement error of the sensing system have been discussed. The sensor has a compact structure and a broad application prospect in the field of wide-range and high-resolution liquid level monitoring, such as in chemical and marine applications.
... Due to the tilt of the grating and the related coupling between the core and cladding modes, TFBG is sensitive to fiberrelated parameters (temperature, axial strain, pressure, bend-ing, among others) and outside medium parameters, such as surrounding refractive index (RI) [32]- [35]. TFBGs have also been proposed for the simultaneous measurement of different quantities, benefiting from the difference in responses of cladding modes and core mode in the TFBG spectrum [36]. ...
In this work, we investigate the application of tilted fiber Bragg grating (TFBG) sensors during
ex vivo
laser ablation of porcine hepatic tissues. Initially, TFBG’s ability to measure the surrounding refractive index (RI) for different sucrose concentrations and the possibility to measure the RI of the targeted tissue during laser ablation (LA) is analyzed. After, the temperature sensing modality of TFBG is investigated in detail. We have implemented an algorithm for quasi-distributed spatial temperature profile reconstruction along TFBG. The algorithm models the TFBG core mode spectrum as a chain of Bragg gratings (each Bragg grating is modeled
via
coupled mode theory), where each grating is sensitive to local temperature changes. After, the Gaussian-shape temperature profile along the TFBG is reconstructed using the iterative optimization technique. Temperature measurements have been compared with highly-dense FBG array measurements and with conventional TFBG point temperature measurements based on the core mode tracking techniques (maximum tracking, X-dB Bandwidth, centroid methods). Overall, the proposed reconstruction algorithm is able to provide a quasi-distributed temperature profile along TFBG, which is not possible to obtain using conventional point temperature measurements based on the TFBG’s core mode tracking. The resulted root-mean-square error in comparison to FBG array reference measurements is 7.8±1.7 °C. In general, the results show that the main reliable sensing modality of TFBG during LA is temperature monitoring, which can be significantly improved by the proposed algorithm.
... Given this form, any error in the measurement of ∆λ will lead to increasingly large errors in the parameters to be measured for smaller values of the determinant of M. Several examples of this can be found in the literature, but rarely with more than two parameters [6,24,35,47,[203][204][205][206]. ...
The aim of this paper is to provide a comprehensive review of mode-division and spatial-division optical fiber sensors, mainly encompassing interferometers and advanced fiber gratings. Compared with their single-mode counterparts, which have a very mature field with many highly successful commercial applications, multimodal configurations have developed more recently with advances in fiber device fabrication and novel mode control devices. Multimodal fiber sensors considerably widen the range of possible sensing modalities and provide opportunities for increased accuracy and performance in conventional fiber sensing applications. Recent progress in these areas is attested by sharp increases in the number of publications and a rise in technology readiness level. In this paper, we first review the fundamental operating principles of such multimodal optical fiber sensors. We then report on the theoretical formalism and simulation procedures that allow for the prediction of the spectral changes and sensing response of these sensors. Finally, we discuss some recent cutting-edge applications, mainly in the physical and (bio)chemical fields. This paper provides both a step-by-step guide relevant for non-specialists entering in the field and a comprehensive review of advanced techniques for more skilled practitioners.
... In both cases, the analysis may consist in determining changes in the intensity of the amplitude of a single mode or a group of modes (modal strength spectroscopy [16]). For the group of modes, the most popular here is the envelope method [9], which is used not only for the measurements of the refractive index but also for the determination of the liquid level [21] and the bending curvature [18]. This method also has a more advanced version in the form of approximation of the area using a triangle mesh [22]. ...
Tilted fibre Bragg grating (TFBG) are used as sensors to determine many quantities such as refractive index, temperature, stress, rotation and bending. The TFBG spectrum contains a lot of information and various algorithms are used for its analysis. However, most of these algorithms are dedicated to the analysis of spectral changes under the influence of the refractive index. The most popular algorithm used for this purpose is to calculate the area occupied by cladding modes. Among the remaining algorithms, there are those that use the determination of the cut-off wavelength as a surrounding refractive index (SRI) indicator. Projection on the wavelength axis can also be used to calculate the bending radius of the fibre. However, this is a more difficult task than with SRI, because the mode decay in bending is not so easy to catch. In this article, we propose a multi-step algorithm that allows to determine the impact of bending on mode leakage. At the same time, the place on the wavelength from the side of the Bragg mode and the ghost mode is determined, which represents the cladding mode radiated from the cladding under the influence of bending. The developed algorithm consists of the following operations carried out on the transmission spectrum: Fourier filtering, calculation of the cumulative value of the spectral length, low-pass filtering of the cumulative curve or its corresponding polynomial approximation, determination of the first and second derivative of the approximated curve, and projection of the second derivative of the curve on the wavelength axis. The shift of the wavelength determined in this way indirectly indicates the bending radius of the optical fibre. Based on multiple measurements, we prove that the presented algorithm provides better results when determining the bending radius compared to other algorithms adopted for this purpose and proposed for SRI measurements. Additionally, we analyse the method of determining the shift of a fragment of the spectrum using the phase of the discrete Fourier transform.
... Sun et al. proposed a polyimide coated FBG for salinity sensing, which is based on the surface plasmon resonance effect but the sensitivity is only 35.8 pm/% [13]. Meanwhile, FBGs sensors have also been proposed for liquid surface height sensing [14,15], while the sensitivity is still needed to be improved. Since FBGs have good stress sensitivity, which can be used to realize highly sensitive measurement. ...
A double fiber grating sensor system is proposed and experimentally demonstrated for a highly sensitive measurement of water salinity and surface height simultaneously. The system consists of one horizontal and one vertical fiber grating, which are fabricated by the femtosecond laser direct writing. The horizontal fiber with a 20-mm-long grating structure can realize an 18.3-dB extinction ratio and a 300-nm/RIU sensitivity for refractive index sensor, which can be used for water salinity measurement with a 375-pm/% sensitivity. As for the vertical fiber with similar grating structure, it can realize a 0.62-dB/mm sensitivity for the surface height sensing with a resolution of 0.125 mm, which can be used for the water surface height monitoring. The presented sensor system is easy fabrication and cost effective, which would have a great application potential for water environment monitoring.
... Compared to the conventional FBG sensors discussed above, Tilted Fibre Bragg Grating (TFBG) sensors have a special configuration which leads to the enhanced sensitivity to the surrounding refractive index (SRI). Thus, the TFBG sensors have been advantageously employed in sensing temperature [53], liquid level [54], SRI [55], relative humidity (RH) [56] and pH [57] in the chemical and biochemical areas. Among the applications, Lao et al. [33] adopted a TFBG sensor to detect the SoC of supercapacitors. ...
Batteries have rapidly evolved and are widely applied in both stationary and transport applications. The safe and reliable operation is of vital importance to all types of batteries, herein an effective battery sensing system with high performance and easy implementation is critically needed. This also requires the sensing system to monitor the states of batteries in real time. Among the available methods, optical fibre sensors have shown a significant advantage due to their advanced capabilities of which include the fast measurement of multiple parameters with high sensitivity, working without interfering the battery performance, being able to be composited in multiplexed configurations and being robust to various harsh environment conditions. This paper mainly discusses the current optical fibre sensing methods for batteries in terms of the working principles and critical reviews the sensing performance corresponding to different sensing parameters. Moreover, the challenges and outlooks for future research on battery sensing are derived.
... To date, there are many efforts devoted to the development of fiber-optic liquid-level sensors owing to their excellent features, such as high sensitivity, small size, immunity to electromagnetic interference, and resistance to harsh environments [4][5][6]. Recently, a number of fiber grating sensing structures, including fiber Bragg gratings (FBGs) [7,8], long period gratings (LPGs) [9,10], and tilted fiber Bragg gratings (TFBGs) [11,12], have been demonstrated for liquid-level measurement. However, the liquid temperature variation will affect the measurement accuracy. ...
We propose and demonstrate an all-fiber liquid-level sensor using an in-line multimode-single-mode-multimode (MSM) fiber structure. A piece of single-mode fiber (SMF) is spliced to two sections of equivalent multimode fiber (MMF) which are used as both mode splitter and mode coupler. The cladding mode will be excited when the light propagates from MMF to SMF, and then it will be combined with fundamental mode to form a Mach-Zehnder interferometer (MZI) when the light propagates from SMF to the other MMF. The liquid level is detected by the selected resonant dips shift of the transmission spectrum. A sensing sensitivity of 264.6 pm/mm is achieved for the proposed sensor with an SMF length of 26mm. Due to its compact structure, easy fabrication, and high sensitivity, the proposed liquid-level sensor is attractive for practical applications in a variety of fields, such as marine detection and chemical processing.
... Also, FBGs are inherently sensitive to strain and temperature [3], and it measures all other physical parameters which can be mapped into strain or temperature domain. Further, several grating modulation techniques, such as tilting [4], [5], phase-shifting [6], [7], chirping [8], [9], tapering [10], [11], and apodization [12], [13], have been proposed to enhance the sensing characteristics of traditional FBG sensors. Moreover, FBG sensors exhibit inherent advantages over its electronics counterparts, such as small in size, immune to electromagnetic and radio frequency interferences, easily embedded into the structure, fast response, corrosion-free, and remote sensing etc. ...
In this paper, we present an apodized Fiber Bragg
grating (FBG) for the single and quasi-distributed sensing applications. Optical characteristics, such as reflectivity, Full-Width at
Half Maximum (FWHM), and side-lobes of FBG critical for an
efficient quasi-distributed sensing networks are optimized for the
proposed grating. The coupled-mode theory and transfer matrix
method are utilized to establish numerical modeling of apodized
FBGs for single and quasi-distributed sensing networks. All the
simulations are performed using MATLAB. Simulation results
illustrate that for the optimized grating parameters L = 10 mm
and δn = 0.8 × 10−4, the proposed grating is characterized
with reflectivity of 0.532, FWHM of 0.132 nm, Maximum SideLobe (MSL) of -36.25 dB, and Side-Lobe Suppression Ratio
(SLSR) of -33.51 dB. Comparative performance analysis of the
proposed grating with the elite apodization profiles, Gaussian and
Tanh4z, is carried out through simulation. These results illustrate
that the proposed grating has better reflectivity and FWHM
as compared to Gaussian. It has better side-lobes suppression
than Tanh4z apodized FBG structure as well. Generally, an FBG
sensor characterized by the high reflectivity, narrower FWHM,
and better side-lobes suppression is of great importance in Wavelength Division Multiplexing (WDM) quasi-distributed sensing
networks. The optimized grating is utilized for five-stage WDM
quasi-distributed strain and temperature sensing networks. A
high dynamic strain/temperature range of 1450 µǫ/131.6◦C is
obtained using this optimized grating. This dynamic range of
strain is very suitable for real-field structural health monitoring
applications making our proposed grating a suitable candidate
for the above mentioned application.
... Fiber Bragg Grating (FBG) is a kind of sensor widely used for measuring strain and temperature in engineering application [12][13][14][15]. Bare FBG sensor can be embedded into a variety of sensing elements to measure a wide range of physical parameters, because bare fiber grating sensors are known to have small size and light weight [16][17][18]. There are a number of water pressure sensors fabricated using FBG sensors, while they indeed verified to own the characteristics of good application performance [19,20]. ...
... An extension of this method is the use of skewness and kurtosis parameters calculated from the spectrum to increase the range of SRI determination below the SRI of pure water [11]. This method, calculating the area of the TFBG cladding modes' envelopes, is also used for liquid level monitoring [15]. The SRI can also be indicated by the transmission spectrum area changes, defined as follows [16]: ...
Tilted fiber Bragg grating (TFBG) is a very popular fiber optic element that is used as a sensor for various physical quantities. The calculation of the refractive index of a substance surrounding the TFBG is based on its spectrum demodulation, which consists of determining a certain parameter that is correlated with the sought quantity. The most commonly used parameter is the area created by the maxima and minima of the cladding mode resonances. In this article, we propose a new group of methods, which are based on calculating the parameters related to the spectrum differences between the local average values in the range of occurrence of the cladding modes. The basic parameter used in this group of methods is the mean absolute deviation from the local mean, which is characterized by the best linearity among the considered group of methods. The calculated parameters, in their cumulative form, can also be used to determine the cut-off wavelength, which can also indirectly indicate the refractive index value. The proposed approaches were compared, in terms of measurement resolution, to the most commonly used methods, such as the cladding modes’ envelope area and the spectral contour lengths.
Liquid level measurement (LLM) systems are extensively used in industry. Although most liquid measurement systems are based on indirect measurement, flow‐based monitoring is the most used secondary measuring technique for LLM. A comprehensive review of the existing LLM techniques including optical, image‐based, capacitive, and float sensors is presented in this article. Here, we describe the classification of sensors based on their sensing principle, methods, and types. The article aims to study the effect of physical parameters on existing LLM techniques for various characteristics, such as temperature, sensitivity, measurement range, response time, and errors. The comparative analysis presented in this paper serves as a valuable resource for researchers, engineers, and practitioners seeking to understand the strengths and weaknesses of different liquid‐level sensing techniques and make informed decisions in selecting the most suitable sensor for specific applications. Further, the paper also presents the results of research work carried out to calculate the liquid level using a pressure sensor for different liquid parameters such as temperature, density, and liquid inlet velocity. This article reports the performance of a differential pressure‐based instrument (specifically an orifice sensor) used to attain reliable and accurate liquid‐level detection. Computational fluid dynamics (CFD) is used to model, design, and analyze the performance of the liquid‐level process.
In this paper, we develop a novel fiber-optic sensor based on a hollow-core Bragg fiber (HCBF) for high-precision detection of liquid level. The intensity responses of anti-resonance reflecting optical waveguide are theoretically analyzed in terms of level and refractive index (RI) of liquid. Simultaneous measurements are conducted and the obvious intensity variations as the changed liquid level are exhibited, with near-zero RI crosstalk. The average liquid level sensitivity reaches −11.24 dB/cm in the range of 0 ~ 4 cm, with high linearity. Additionally, high repeatability and low temperature intensity drift guarantee the measurement error can be constrained within 0.03 mm.
This paper proposes an intensity-modulated liquid level sensor based on cascaded long-period fiber grating (LPFG) and fiber Bragg grating (FBG) structure with temperature compensation. Its unique structure converts the wavelength shift of the LPFG transmission peak caused by the liquid level change into a variable in the intensity of the FBG reflection peak. By inducing the combined action of LPFG and FBG, a new coupling peak is generated in the reflection spectrum for temperature compensation, reducing the interference of environmental temperature on liquid level measurement. A rigorous theoretical model was established, simulations were conducted, and experiments were performed to verify the results. In the experiment, the intensity variation of the FBG peak and the wavelength variation of the LPFG-FBG interaction peak in the reflection spectrum were used to measure the two parameters. The results show that when the liquid level changes within 15 mm, the intensity sensitivity of the corresponding FBG peak is -0.488 dB/mm. The wavelength of the LPFG-FBG interaction peak remains essentially unchanged. Within the temperature range of 30-60 °C, the intensity sensitivity of the corresponding FBG peak is 0.0374 dB/°C, and the wavelength sensitivity of the LPFG-FBG interaction peak is 8.78 pm/°C. Using a 2×2 matrix, simultaneous measurement of liquid level and temperature can be achieved, realizing temperature compensation. This sensor features high sensitivity, simple structure, high linearity, and low detection cost, promising a good application prospect in the field of liquid level sensing.
Fiber optic-based precise measurements of liquid level and temperature are crucial for remote controlling in pharmaceutics, chemistry, and bromatology. Thus, it is essential to monitor liquid level and temperature simultaneously. In this paper, we propose all-fiber intermodal interferometers for highly sensitive liquid level and temperature measurements. We fabricated two different structures of single mode fiber-no core fiber-single mode fiber (SMF-NCF-SMF). One of them was used to measure the liquid level when the liquid soaked the NCF, and the other one was further coated with polydimethylsiloxane(PDMS) thermal-optic material and utilised to detect temperature. The measurement sensitivity of liquid level was 580 pm/mm within the range of 0–20 mm, while that of temperature was 1 nm/°C within the range of 28 °C–51 °C. A matrix was finally obtained by demodulating the measurements of liquid level and temperature. The proposed liquid level and temperature sensors, exhibiting the merits of high sensitivity, easy fabrication, and low cost, could be a candidate for precise and remote monitoring of liquid levels.
The refractive index of seawater is one of the essential parameters in ocean observation, so it is necessary to achieve high-precision seawater refractive index measurements. In this paper, we propose a method for measuring the refractive index of seawater, based on a position-sensitive detector (PSD). A theoretical model was established to depict the correlation between laser spot displacement and refractive index change, utilizing a combination of a position-sensitive detector and laser beam deflection principles. Based on this optical measurement method, a seawater refractive index measurement system was established. To effectively enhance the sensitivity of refractive index detection, a focusing lens was incorporated into the optical path of the measuring system, and simulations were conducted to investigate the impact of focal length on refractive index sensitivity. The calibration experiment of the measuring system was performed based on the relationship between the refractive index of seawater and underwater pressure (depth). By measuring laser spot displacement at different depths, changes in displacement, with respect to both refractive index and depth, were determined. The experimental results demonstrate that the system exhibits a sensitivity of 9.93×10−9 RIU (refractive index unit), and the refractive index deviation due to stability is calculated as ±7.54×10−9 RIU. Therefore, the feasibility of this highly sensitive measurement of seawater refractive index is verified. Since the sensitivity of the refractive index measurement of this measurement system is higher than the refractive index change caused by the wake of underwater vehicles, it can also be used in various applications for underwater vehicle wake measurement, as well as seawater refractive index measurement, such as the motion state monitoring of underwater navigation targets such as AUVs and ROVs.
The battery technology progress has been a contradictory process in which performance improvement and hidden risks coexist. Now the battery is still a “black box”, thus requiring a deep understanding of its internal state. The battery should “sense its internal physical/chemical conditions”, which puts strict requirements on embedded sensing parts. This paper summarizes the application of advanced optical fiber sensors in lithium-ion batteries and energy storage technologies that may be mass deployed, focuses on the insights of advanced optical fiber sensors into the processes of one-dimensional nano–micro-level battery material structural phase transition, electrolyte degradation, electrode–electrolyte interface dynamics to three-dimensional macro-safety evolution. The paper contributes to understanding how to use optical fiber sensors to achieve “real” and “embedded” monitoring. Through the inherent advantages of the advanced optical fiber sensor, it helps clarify the battery internal state and reaction mechanism, aiding in the establishment of more detailed models. These advancements can promote the development of smart batteries, with significant importance lying in essentially promoting the improvement of system consistency. Furthermore, with the help of smart batteries in the future, the importance of consistency can be weakened or even eliminated. The application of advanced optical fiber sensors helps comprehensively improve the battery quality, reliability, and life.
Temperature sensing is extremely important factor for many biomedical applications toward a prompt and accurate medical control and examination. The purpose of this work is to investigate theoretically the design of novel single mode tapered fiber Bragg gratings (TFBGs) with maximum temperature sensitivity to be used in biomedical field. The parameters which govern the functionality of TFBGs were studied in order to optimize the temperature sensitivity. Coupled mode theory (CMT) and transfer matrix method were applied to analyze TFBG structure. A numerical analysis was performed to investigate the mechanical properties of TFBGs and the cladding diameter on temperature sensitivity. Herein, the TFBGs are assumed to a reflection Bragg wavelength around 1550 nm and are inscribed in single mode fiber (Corning SMF-28). The results show that the temperature sensitivity of TFBGs at optimized parameters could reach, which is superior to those of conventional fiber Bragg gratings with the same parameters (). Moreover, the effect of taper ratio on sensitivity was investigated in this study. The findings also demonstrate that the sensor sensitivity can be adjusted with variation to the taper ratio. From the results, it is confirmed that the sensitivity of TFBGs was improved by reducing linearly the fiber diameter up to 15 μm compared to uniform FBGs ones, achieving the highest temperature sensitivity.
Commercial fiber Bragg grating (FBG) sensors typically rely on require plastics, acrylates or glues for encapsulation and adhesion, making them susceptible to aging, creep, and high-temperature intolerance. To overcome these issues, this study introduces an electrochemical deposition process aimed at creating adhesive-free sensors by embedding FBGs into metal structures. This approach enhances the operational range and lifespan of the sensor. The embedding method facilitates the detection of bending strains by the FBG. Consequently, a temperature-insensitive inclination sensor is designed and fabricated. Two FBGs are embedded on either side of a metal strip, precisely aligned with its central axis, to measure bending strain. When bending stress is applied to the metal steel, the two FBGs experience opposite strains, causing their central wavelengths to drift in opposite directions. Analyzing the wavelength shift difference between the two FBGs yields a sensor with higher inclination sensitivity and temperature insensitivity. The experimental results indicate that the designed sensor has a high sensitivity of 42.76 pm/°, resolution of 0.0023°, and linearity of 0.9994. Temperature-response tests demonstrate the excellent temperature insensitivity of the fabricated sensor, allowing for reliable operation in high-temperature conditions. Furthermore, this metal encapsulation method exhibits significant potential for expanding the applications of FBGs.
A new method of demodulation of salinity and temperature (ST) two-parameter sensor based on tilted fiber Bragg grating (TFBG) and Fabry-Perot structure using a double-branch convolutional neural network (CNN) with dense connected blocks is proposed. A total of 4344 spectral samples were collected when the sensor was immersed in sodium chloride solution with different salinities and temperatures, in an attempt to train and test the CNN model. Experimental results showed that the well-trained CNN model could realize real-time and high-precision demodulation of the ST dual-parameter sensor. The mean absolute errors (MAE) of salinity and temperature are 0.207‰ and 0.11 °C respectively, and the determination coefficients are 85.51% and 99.96%, respectively. The predicted ST value of sodium chloride solution by the proposed characterization approach is consistent with the truth value, which shows great potential applications of such a sensor for high-precision double-parameter measurement.
New energy storage devices such as batteries and supercapacitors are widely used in various fields because of their
irreplaceable excellent characteristics. Because there are relatively few monitoring parameters and limited understanding of their operation, they present problems in accurately predicting their state and controlling operation, such as state of charge, state of health, and early failure indicators. Poor monitoring can seriously affect the performance of energy storage devices. Therefore, to maximize the effciency of new energy storage devices without damaging the equipment, it is important to make full use of sensing systems to accurately monitor important parameters such as voltage, current, temperature, and strain. These are highly related to their states. Hence, this paper reviews the sensing
methods and divides them into two categories: embedded and non-embedded sensors. A variety of measurement methods used to measure the above parameters of various new energy storage devices such as batteries and supercapacitors are systematically summarized. The methods with different innovative points are listed, their advantages and disadvantages are summarized, and the application of optical fiber sensors is emphasized. Finally, the challenges and prospects for these studies are described. The intent is to encourage researchers in relevant fields to study the
early warning of safety accidents from the root causes.
We propose and demonstrate a new method for fabricating a Fabry-Perot interferometer sensor. This work uses photopolymerizable materials to construct Fabry-Perot interference structures, making the fabrication process more straightforward and less expensive than other methods. We put a 532 nm laser into the single-mode fiber (SMF) to fabricate photopolymer probes on the face of the fiber. The end face of the probe and the end face of the SMF will form a Fabry-Perot interferometer (FPI). At the same time, to demonstrate its ability to be easily fabricated for sensing various parameters, we incorporated PDMS into the photopolymer material and conducted temperature sensing experiments. The relationship between the concentration of the PDMS and the temperature sensitivity is studied. The experimental results show that the higher the concentration of PDMS, the higher the temperature sensitivity. In the case of ensuring other capabilities, the sensitivity has reached -1.18 nm/°C in the temperature range of 20 °C to 110°C.
A corrugated surface long period grating (LPG) imprinted on a plastic optical fiber (POF) was proposed as a liquid level sensor. The LPG was fabricated by a simple mechanical die-press-print method. The operation principle of the sensor was analyzed by the method of geometrical optics. The liquid-level sensing performances of the sensor with different structural parameters were evaluated. The results showed that the diameter of POF and the structure parameters of LPG would affect the liquid level sensing performance. When the LPG with a period of 300μm, a groove depth of 75μm, and a tilted angle of 30° was fabricated on a POF with a diameter of 0.25 mm, the highest sensitivity of -0.4381 dB/mm was obtained in the water-level range of 20 mm. The calculated results nearly coincided with the measured results. The hysteresis of the proposed sensor performed well and the sensitivity of the sensor was increased when the liquid RI was increased. Moreover, the water absorption would influence the liquid level sensing performance when the LPG was immersed in the water for a long time.
A three-parameter sensor based on a point-by-point fiber Bragg grating (PBP-FBG) is proposed. The fabricated sensor is 40 mm long. The spectrum loss at 1336.15 nm is selected to measure the surrounding liquid level. The sensitivity for liquid level sensing is 0.046 dB/mm. The temperature is measured using the Bragg dip shifts with sensitivity of 10.06 pm/C. The cut-off mode shift is used to measure the surrounding refractive index with sensitivity of 535.14 nm/RIU. As a benefit of femtosecond laser direct inscription fabrication, the grating length is controllable and the liquid level sensing range is expandable. This sensor provides a simple, reliable method for accurate liquid level, temperature and refractive index measurements in hazardous environments.
A compact optical fiber sensor (OFS) based on an inline Mach-Zehnder interferometer for simultaneous measurement of liquid level and the temperature is proposed and demonstrated experimentally. The proposed sensor is formed by fusion splicing a thin core fiber (TCF) with an ultra-thin fiber (UTF) with core offset, then TCF and UTF are sandwiched between two standards of single mode fibers (SMFs). The liquid level or temperature change will lead to the dips shifts in the interference spectrum, and the liquid level and temperature sensitivities can be measured independently by monitoring the resonance dips shifts. Then the simultaneous measurement of liquid level and temperature can be obtained through the demodulation matrix. Four sensors with different UTF length are fabricated based on numerical simulation. The experimental results show that the proposed sensor with a UTF length of 8 mm has the optimal liquid level and temperature sensitivities of −231.67 pm/mm and 77.86 pm/°C, respectively. The measuring liquid level and temperature ranges are 0–8 mm and 30–60 °C. The proposed sensing configuration has practical application potential in various industries due to the advantages of high sensitivity, simple fabrication and low cost.
In this paper, a novel in-fiber modal interferometer for liquid level sensing is proposed and experimentally demonstrated based on the cascaded quasi-microfiber and double-cladding fiber (QM-DCF) structure. The QM is utilized to monitor the change of liquid level with intensity modulation and the part of DCF is always immersed into the liquid and serves to sense the variation of ambient temperature. Then the comprehensive tests are performed and the experimental results show that, due to the massive loss of evanescent field in the area of taper waist, a competitive liquid-level response up to −0.972 dB/mm with high linearity is gained and the calculated detection limit reaches
. Moreover, this cascaded structure is almost immune to the varied refractive index (RI) of liquid especially in the range of 1.33-1.357 RIU and its temperature sensitivity is 0.164 nm/°C but with a fluctuation of < 0.1 dB. Thus, high intensity-sensitive liquid-level measurement is achieved with near-zero crosstalk in terms of RI and temperature. Besides our sensor with the merits of practicality, low-cost, ease of fabrication is very promising and potential for simultaneous high-discrimination measurement of multi-parameter.
Carbon fiber reinforced plastics (CFRP) have many mechanical properties that are superior to those of conventional structural materials and are becoming more and more widely used. Monitoring the curing process used to produce such composite material is important to ensure the quality of the process, especially for the characterization of residual strains after the material has been manufactured. In this study, we present a tilted fiber Bragg grating (TFBG) sensor used to monitor the curing of CFRP composite materials. The TFBG sensor was embedded into the layers of CFRP laminates to study the curing residual strain of the laminates. The experimental results showed that the curing residual stress was about −22.25 MPa, the axial residual strain was −281.351 με, and lateral residual strain of 89.91 με. The TFBG sensor was found to be sensitive to the curing residual strain of the CFRP, meaning that it has potential for use in applications involving composite curing processes. Moreover, it is indeed possible to improve the properties of composite materials via the optimization and monitoring of their curing parameters.
Fiber Bragg grating has embraced the area of fiber optics since the early days of its discovery, and most fiber optic sensor systems today make use of fiber Bragg grating technology. Researchers have gained enormous attention in the field of fiber Bragg grating (FBG)-based sensing due to its inherent advantages, such as small size, fast response, distributed sensing, and immunity to the electromagnetic field. Fiber Bragg grating technology is popularly used in measurements of various physical parameters, such as pressure, temperature, and strain for civil engineering, industrial engineering, military, maritime, and aerospace applications. Nowadays, strong emphasis is given to structure health monitoring of various engineering and civil structures, which can be easily achieved with FBG-based sensors. Depending on the type of grating, FBG can be uniform, long, chirped, tilted or phase shifted having periodic perturbation of refractive index inside core of the optical fiber. Basic fundamentals of FBG and recent progress of fiber Bragg grating-based sensors used in various applications for temperature, pressure, liquid level, strain, and refractive index sensing have been reviewed. A major problem of temperature cross sensitivity that occurs in FBG-based sensing requires temperature compensation technique that has also been discussed in this paper. © 2020 Society of Photo-Optical Instrumentation Engineers (SPIE).
There are several issues that present in conventional sensor including its accuracy, safety, durability and RF effect. These issues could be minimized with the implementation of fiber optic sensor. This project is to design and implement optical sensor using FBG for various temperature and liquid density sensing. The FBG sensor was submerged in liquid substances to determine the sensing conditions. The available pigtail was connected to the circulator, 1550nm laser source and optical spectrum analyzer (OSA). The data regarding temperature and density sensing captured from OSA were observed and analyzed. It is found that the relationship between the change in temperature and the change in wavelength is virtually linear in both environments making FBG a good candidate for sensing temperature.
A diaphragm-based hydrostatic level transducer with the use of a single Fibre Bragg grating (FBG) is presented for simultaneous measurement of water level and temperature. In order to distinguish the mismatch between water level and temperature sensitivity, a bandwidth modulation and centre wavelength shift measurement technique was introduced. The change in bandwidth is sensitive towards water level variations with a sensitivity of 0.0015 nm/cm. Meanwhile, the change of centre wavelength is sensitive towards water level and temperature variations, with sensitivities of 0.0008 nm/cm and 0.0365 nm/°C, respectively. By expressing the obtained sensitivities in a matrix equation approach, simultaneous water level and temperature measurement can be predicted accurately.
To save the cost of the fiber grating sensing technology demodulation equipment and broaden the range of its detection application, one heterogeneous fiber grating spectrum separation (HFGPS) method based on transfer matrix and the adaptive algorithm is proposed. First, a theoretical mode of the HFGPS method is introduced. Second, simulation experiment on linearly chirped fiber Bragg grating (LCFBG) and fiber Bragg grating (FBG) is carried out to obtain the separation effect. After simulation experiment data analyses, relative errors between the separated spectrum signal and the heterogeneous original signal are no >5.29 %, which occurs at spectrum fringe region of FBG and LCFBG, and the separation algorithm can achieve single wavelength or multiwavelength mixing heterogeneous spectrum efficient separation with high precision. Lastly, the temperature calibration experiment is carried out on FBG temperature sensor and LCFBG to further verify the effect of the HFGPS method. After the temperature experiment data analyses, the result shows that sensitivity relative error of FBG between original and heterogeneous separated is 0.4%, and the HFGPS method can achieve heterogeneous spectrum efficient separation and has small influence on the detection performance of the FBG sensor. All these experiment data confirm that the HFGPS method can achieve effective heterogeneous spectrum separation with high precision and has certain practical application value. © 2019 Society of Photo-Optical Instrumentation Engineers (SPIE).
A novel and highly sensitive liquid level sensor based on a polymer optical fiber Bragg grating (POFBG) is experimentally demonstrated. Two different configurations are studied and both configurations show the potential to interrogate liquid level by measuring the strain induced in a POFBG embedded in a silicone rubber diaphragm, which deforms due to hydrostatic pressure variations. The sensor exhibits a highly linear response over the sensing range and a good repeatability. For comparison, a similar sensor using a FBG inscribed in silica fiber is fabricated, which displays a sensitivity that is a factor of 5 smaller than the POFBG. The temperature sensitivity is studied and a novel multi-sensor arrangement proposed which has the potential to provide level readings independent of temperature and the liquid density.
A simple and compact reflective liquid level sensor based on modes conversion in the thin-core fiber incorporating one tilted fiber Bragg grating (TFBG) is proposed and experimentally demonstrated. A piece of thin-core fiber containing one TFBG ensures the modes conversion between the core mode and cladding modes. The external liquid can induce the cladding modes covert to the radiation modes and lead to the decrement of the collected cladding modes power, then the liquid level can be measured from the collected cladding modes power. The modes conversion in the proposed structure is theoretically analyzed. The experimental results show the high liquid level sensitivity and temperature immunity of the proposed sensor, and its significant advantage is that the measurement range is not limited to the length of the TFBG itself.
In this paper the comparative study of spectral transmission characteristics of tilted Bragg gratings made using uniform phase mask and chirped phase mask are presented. Results are focused on low tilt angles with special interest on cladding modes behavior. The spectral characteristic shape for simultaneously tilted and chirped Bragg gratings point out its potential applications as amplitude discriminator in fiber sensing applications and gain flattening element for EDFA.
We investigate the changes in the transmission spectrum
of long period fibre gratings and tilted short-period fibre Bragg gratings
versus the refractive index of the surrounding medium. The
metrological characteristics of tilted short-period fibre Bragg gratings and
an analytical method enabling their potential use in accurate refractometry
are discussed.
We demonstrate a liquid level sensor based on the surrounding medium refractive index (SRI) sensing using of an excessively tilted fibre Bragg grating (ETFBG). The sensor has low thermal cross sensitivity and high SRI responsivity.
We review the recent developments in the area of optical fiber
grating sensors, including quasi-distributed strain sensing using Bragg
gratings, systems based on chirped gratings, intragrating sensing
concepts, long period-based grating sensors, fiber grating laser-based
systems, and interferometric sensor systems based on grating reflectors
The design and packaging of simple, small, and low cost sensor heads, used for continuous liquid level measurement using uniformly thinned (etched) optical fiber Bragg grating (FBG) are proposed. The sensor system consists of only an FBG and a simple detection system. The sensitivity of sensor is found to be 23 pm/cm of water column pressure. A linear optical fiber edge filter is designed and developed for the conversion of Bragg wavelength shift to its equivalent intensity. The result shows that relative power measured by a photo detector is linearly proportional to the liquid level. The obtained sensitivity of the sensor is nearly -15 mV/cm. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)
A dual-parameter optical fiber sensor is proposed and demonstrated. It is based on an intermodal interferometer (IMI) with an inline embedded fiber Bragg grating (FBG). The IMI is formed by cascading a taper structure and a spherical-shaped structure through a segment of a single-mode fiber. Due to the different wavelength shifts of the IMI and FBG to temperature and liquid level, simultaneous measurement can be achieved. Experimental results indicate a good linear relation between the wavelength shift and external parameters (temperature and liquid level). The sensitivities of 0.066 nm/°C and-0.133 nm/mm are achieved experimentally for temperature and liquid level, respectively. The interesting properties of the sensor include good operation linearity, compact size, and high sensitivity.
A fiber laser sensor for simultaneous measurement of liquid level and temperature is proposed and demonstrated experimentally. The sensor is based on two taper structures and a fiber Bragg grating (FBG). The two taper structures form a novel fiber interferometer, which is fabricated by cascading two tapers in a section of single-mode fiber (SMF). The FBG and the interferometer serve as the filters of the laser cavity. Corresponding to the two filters, the laser outputs are stable dual-wavelength outputs, which have different characteristics to the liquid level and the temperature. The wavelength produced by the FBG is not sensitive to the liquid level. The temperature sensitivity of the wavelength produced by the FBG is 0.0123 nm/°C. The wavelength produced by the interferometer is sensitive to the liquid level and the sensitivity is up to 0.2294 nm/mm. The temperature sensitivity of the wavelength produced by the interferometer is 0.0648 nm/°C. According to the different spectral responses of the liquid level and the temperature, simultaneous measurement can be realized. Furthermore, the proposed sensor has the advantages of less detection limit (DL), higher resolution and higher sensitivity compared to other optical fiber sensors.
In this work half the length of the single FBG is chemically etched and the un-etched half is glued on a cantilever. The response of the grating is investigated as a function for buoyancy force on the cantilever due to liquid level and temperature. Simultaneous measurement of liquid level and temperature is achieved from the coefficients of liquid level and temperature sensitivities obtained from the experimental results.
We present and experimentally analyze the applications of tilted fiber Bragg grating (TFBG) for the measurement of
liquid parameters, including the concentration (or refractive index), liquid-level and dynamic concentration change. On
the basis of analyzing the measurement principle of refractive index using TFBG, its spectral variations with the glycerol
concentration and liquid-level are obtained. Meanwhile, a fast demodulation technique monitoring the small variation of
TFBG transmission power in a strong background is employed to measure dynamic change in the liquid concentration.
The results show that the method is easy to achieve fast, cost-effective measurement of the change process of liquid
concentration.
A fiber sensor based on core-offset singlemode–multimode–singlemode (SMS) interferometer for simultaneous measurement of temperature and liquid level is proposed. The sensor is fabricated by a SMS interferometer spliced with a single mode fiber (SMF) in core-offset way. Since the cladding mode of SMF is excited in the core-offset SMS, two different kinds of interference dips which are formed by the SMF and the SMS interferometer respectively are obtained. Using the difference sensitivities to the two parameters of the selected dips, temperature and liquid level can be measured simultaneously. The chosen interference dips are at 1529.632 nm and 1553.18 nm. Experiments indicate that the dip at 1529.626 nm is insensitive to liquid level, the temperature sensitivity is 0.064 nm/°C. The temperature sensitivity of the dip at 1553.18 nm is 0.082 nm/°C. The temperature measurement precision is 0.001 nm/°C. When the liquid is water (n=1.33), the sensitivity of the liquid level is 0.140 nm/mm. When the liquid is sodium chloride solution (n=1.38), the sensitivity of the liquid level is 0.290 nm/mm. The liquid level measurement precision is 0.001 nm/mm. The interferometer also can be applied in other sensing fields.
An optic-fiber liquid-level sensor based on tapered chirped grating was proposed and demonstrated experimentally. With a properly designed column buoy hung to chain wheel, the liquid-level variation was converted to axial strain, which made the reflection spectrum of the tapered chirped grating narrowed or broadened correspondingly. And a high-sensitive liquid-level sensor was obtained by monitoring the bandwidth variation of the tapered chirped grating. Compared with traditional absolute wavelength or power detection, this special monitoring technique based on bandwidth modulation makes the liquid-level sensor insensitive to spatially uniform temperature variations and power fluctuations from down-lead or light source.
We report a liquid-level variation sensor based on a fiber Bragg grating (FBG) inscribed in a 6.5-mumdiameter microfiber. The proposed microfiber Bragg grating (MFBG) in air has two separated reflection peaks, which are caused by the fundamental mode reflection and the higher-order mode reflection. Each of the two peaks will split into another two adjacent peaks when a fraction of the MFBG sensor immerses into liquid. By measuring the reflectivity difference between the two original peaks and their respective adjacent liquid-induced peaks, the liquid-level variation can be determined.
In this paper, we present a novel fiber optic sensor for the simultaneous measurement of liquid level and surrounding refractive index based on tilted fiber Bragg grating (TFBG). The transmission loss and the bandwidth of cladding modes are two measures of the liquid level, while their resonance wavelengths are employed to determine the surrounding refractive index. A liquid level sensitivity of over 0.6dB/mm is achieved with good linearity. Temperature independent surrounding refractive index sensing is possible using the Bragg mode of TFBG as a temperature reference. What is more, a scheme is proposed to realize a large measurement range of liquid level by connecting a certain number of TFBGs in series or parallel. The scheme is verified by an experiment in which three TFBGs are connected in parallel.
A liquid-level sensor based on a side-polished fiber Bragg grating (FBG) is proposed and experimentally demonstrated. The sensor can detect height variation of liquids of arbitrary refractive index (RI). For liquids with RI lower than that of fiber core, liquid-level variation can be monitored by the peak power difference of the grating segments surrounded by the liquid and air. For liquids with RI higher than that of fiber core, liquid-level information can be obtained from the influence of the shortening of the effective length of the immersed grating segment upon the reflection spectrum.
In this paper, we propose and demonstrate a novel scheme for simultaneous measurement of liquid level and temperature based on a simple uniform fiber Bragg grating (FBG) by monitoring both the short-wavelength-loss peaks and its Bragg resonance. The liquid level can be measured from the amplitude changes of the short-wavelength-loss peaks, while temperature can be measured from the wavelength shift of the Bragg resonance. Both theoretical simulation results and experimental results are presented. Such a scheme has some advantages including robustness, simplicity, flexibility in choosing sensitivity and simultaneous temperature measurement capability.
Contenido: Introducción al control de proceso; Enlaces de control de proceso; Fundamentos eléctricos y electrónicos; Fundamentos de sistemas digitales; Medida de la presión; Control y medida del nivel; Medida de la temperatura; Control y medidas analíticas; Medida del flujo; Elementos del control final; Computadoras en el control de proceso; Apéndices.
A highly sensitive liquid-level sensor based on etched fiber Bragg grating is proposed and demonstrated. The fiber Bragg grating is etched to enhance the sensitivity to the refractive index of liquid, when a portion of etched fiber Bragg grating is immersed in the liquid, the original single transmission dip splits into two transmission dips because of the fiber Bragg grating spectrum is affected by the fraction of the length of the etched fiber Bragg grating that is surrounded by the liquid. By measuring the transmission dips variations, the liquid level can be measured. The experiments show that for a liquid level variation of 24mm, the transmission dip difference changes about 32dB. Also in the linear region, a high liquid level sensitivity of 2.56dB/mm is achieved.
A temperature insensitive fiber Bragg grating (FBG) liquid level sensor based on bending cantilever beam (BCB) is proposed and demonstrated. The BCB induces axial strain gradient along the sensing FBG, resulting in a Bragg bandwidth modulation. The broadening of FBG spectrum bandwidth and the reflection optical power change with the liquid level and they are insensitive to spatially uniform temperature variations. For a liquid level variation of 500 mm and a temperature range from 0°C to 80°C, the measured liquid level fluctuates less than 2% without any temperature compensation. By optical power detection via a pin photodiode, the liquid-level sensor avoids complex demodulation process and potentially costs low.