Liquid Level Sensitivity Research Articles

A liquid lever sensor based on an abrupt taper and micro‐arc Michelson interferometer in single‐mode fiber

AbstractA novel two‐parameter sensor is proposed based on the abrupt taper and micro‐arc Michelson interferometer (MI) in single‐mode fiber. When there is a regular change in the liquid level or temperature, the phase difference changes, and the spectral intensity or wavelength of the interfering valleys of this sensor is directionally shifted. This study enriches the construction of MI and provides a new perspective on liquid level measurement. We experimentally explored the sensor's sensing performance over temperature and liquid level: this sensor's temperature sensitivity and liquid level sensitivity were up to 62.9 pm/°C and 0.2896 dB/mm, respectively. In addition, this sensor is characterized by compactness, simplicity, low cost, and high reliability, and it is suitable for measurement of liquid level and temperature, expanding the application field of MI.

Simultaneous measurement of temperature, liquid level and axial strain based on torsional taper Mach-Zehnder interferometer with Vernier effect

A novel and simple highly-sensitive temperature, liquid level and axial strain sensor based on a torsional taper Mach-Zehnder interferometer (MZI) with Vernier effect is proposed. An interesting finding, which is the linear relationships between the wavelength shifts of resonance peaks (envelopes) and temperature, liquid level and axial strain surrounding the sensing fiber, is demonstrated experimentally. Another interesting feature is that the sensor with Vernier effect magnifies the temperature, liquid level and axial strain sensitivities by 11.3, 11.2 and 12.6 times, respectively. In the proposed method, the sensor is fabricated by cascading one polarization mode interferometer (PMI) as reference interferometer and one torsional taper MZI as sensing interferometer. The PMI is composed of polarization maintaining fiber (PMF), and cascaded MZI is composed of thin-core photosensitive fiber (TPSF). Combined with the characteristic of high sensitivity, the sensor can be widely used in the field of environmental and structural safety monitoring.

Liquid‐level sensor based on Michelson interferometer with double hook structure

AbstractA new type of Michelson interferometer (MI) based on a double hook structure is proposed for measurement of liquid level and temperature. The optical fiber MI based on the double‐hook structure is fabricated using a hydroxide flame heating device. Furthermore, the angle and sensing length of the double‐hook structure can be controlled by a rotating platform. The sensor is fixed on a ruler, which is set vertically on the iron support stand employing a beaker clamp, and the position of the beaker clamp is adjusted so that the double hook structure of the sensor overflows the water surface in the beaker. The temperature and liquid level sensitivities of the sensor are 129.8 pm/°C and −186.2 pm/mm, respectively. The novel optical fiber MI based on the double‐hook structure has the advantages of high sensitivity, low cost and easy fabrication, which has a great market prospect in production and life.

Design of anti-temperature interference liquid level sensor based on π-phase-shifted LPFG near phase-matched turning points

A new, to the best of our knowledge, type of liquid level sensor with π-phase-shifted long-period fiber grating operating near the phase-matched turning point is proposed. The sensor introduces a π-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 −1.316dB/mm 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 −0.139nm/∘C 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.

High-sensitivity liquid level sensor based on single mode-coreless-seven core-coreless-single mode fiber structure

A liquid level sensor based on single mode-coreless-seven core-coreless-single mode fiber structure is proposed, in which two short sections of coreless fibers are utilized as fiber couplers, so as to improve the coupling efficiency between the single mode fiber and the seven core fiber, thus enhance the mode interference perception of external liquid level. Experimental results reveal that the liquid level sensitivities of the sensors with seven core fiber length of 16 mm, 18 mm and 20 mm, are −0. 3163 nm/mm, −0.2687 nm/mm and −0.2471 nm/mm in the liquid level ranges of 16 mm, 18 mm and 20 mm, respectively. In addition, stability test is performed and the maximum instability is 0.04 nm with a standard error of 0.16 mm. The sensor possesses advantages of robustness, low fabrication cost, high sensitivity and good stability, indicating it has a prospective potential in petrochemical and biological applications for liquid level sensing.

Multi-Parameter Sensors Based on Optical Reflective Coupler Probe

We propose and demonst rate multi-parameter sensors based on optical reflective coupler probe (ORCP), for detection of liquid level, temperature, and refractive index (RI). Single-mode fiber ORCP (S-ORCP), few-mode fiber ORCP (F-ORCP) and multi-mode fiber ORCP (M-ORCP) are fabricated by adiabatically tapering and weak fusion technology. The highest liquid level sensitivity is 363.64 nm/mm, achieved by the M-ORCP, with detection limit of as low as 0.06 μm. In addition, multi-parameter measurement of liquid level, temperature and RI can be achieved by the M-ORCP, with temperature and RI sensitivities of −0.327 nm/°C and 7859.27 nm/RIU, respectively. With the merits of high sensitivity, stability, and compact half-coupler probe structure, the proposed ORCP sensors of ∼ cm length can measure the liquid level range of ∼3 mm, which have broad application prospects in the fields of fuel storage and chemical liquid level measurement, especially for chemical reagents, biological tissue liquids and flammable and explosive liquids.

Liquid Level Sensor With High Sensitivity Based on Hetero Core Structure

In this paper, a novel liquid level sensor with high sensitivity is proposed. The proposed sensor is configured by multimode fiber-No-core fiber-multimode fiber (MMF-NCF-MMF) hetero core structure (MNM-HCS). The sensor is composed of two MMF structures spliced on both ends of NCF, in which NCF is used as a sensing unit, and the MMF at both ends excites higher cladding modes to improve the sensitivity of the sensor to the external environment. Interference occurs when light is transmitted from MMF to NCF. Experimental results show that the compact sensor with a length of 12.2 mm has a high liquid level sensitivity of 1034 pm/mm in the water level (RI <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$=$ </tex-math></inline-formula> 1.333) range of 0-10 mm. The temperature sensitivity is 20 pm/°C in the range of 35- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$95^{\circ }\text{C}$ </tex-math></inline-formula> . The temperature-liquid level cross sensitivity of the proposed sensor is 0.019 mm/°C. Due to the advantages of high sensitivity, good linearity and stable performance, MNM-HCS has potential application potential application prospects in the field of high sensitivity liquid level measurement.

In-line reflected fiber sensor for simultaneous measurement of temperature and liquid level based on tapered few-mode fiber.

An in-line reflective dual-parameters fiber-optic sensor is proposed in this work, whereas it is experimentally verified by measuring both the liquid level and the local temperature distribution simultaneously. The proposed sensor configuration comprises a single-mode fiber (SMF), a tapered few-mode fiber (TFMF), as well as a silver-coated capillary tube. The extracted experimental results indicate that the liquid level only affects the power of the resonant dips, while having little impact on the wavelength. On the other hand, both the wavelength and the power of the resonant dips vary with the temperature change. Therefore, the simultaneous measurement of the liquid level and temperature can be realized according to the different responses of the resonant dips to the liquid level and temperature. The obtained liquid level and temperature sensitivities can reach the values of 0.106 dB/mm and 0.029 dB/°C, 35 pm/°C, respectively. The sensor exhibits the advantages of high stability and low cost, the demodulation relates on only one wavelength which can shorten the scanning wavelength range during measurement. The proposed sensor can be potentially applied where accurate and simultaneous measurements of both temperature and liquid level are required.

An Intensity-Modulated In-Fiber Liquid Lever Sensor Based on Intermodal Michelson Interferssometer

A compact in-fiber Michelson interferometer (MI) for liquid level measurement is proposed and demonstrated. The interferometer is fabricated by simply splicing a section of multimode fiber (MMF) with a standard singlemode fiber (SMF). The reflection spectrum of the MI is dependent on the portion of the length of the MMF which is immersed in liquid. The sensing characteristics of the liquid level and temperature are theoretically and experimentally investigated. The experimental results show that the liquid level sensitivity is −1.20 dB/mm when the liquid is water, and the liquid level measurement error induced by temperature is 0.004 mm/°C. The advantages of temperature-immune, cost-effective and reflective intensity demodulation offer the prospective application in chemical and petroleum industrial sensing.

An inline Mach-Zehnder interferometer for simultaneously measuring liquid level and temperature

A compact optical fiber sensor (OFS) based on an inline Mach-Zehnder interferometer for simultaneousmeasurement of liquid level and the temperature isproposedanddemonstrated 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.

Simultaneous Measurement of Liquid Level and Temperature Using In-Fiber Grating-Based Mach-Zehnder Interferometer and Faraday Rotator Mirror.

Here we propose an optical fiber sensor capable of simultaneous measurement of liquid level and temperature by utilizing cascaded long-period fiber gratings (LPFGs) inscribed on high-birefringence fiber (HBF) and a Faraday rotator mirror (FRM). Due to the in-fiber Mach-Zehnder interference and birefringence of the HBF, these cascaded LPFGs have polarization-dependent discrete interference spectra, each of which is created within one of the two different attenuation bands obtained in the two orthogonal input polarization states, e.g., linear horizontal polarization (LHP) and linear vertical polarization (LVP). The minimum transmittance dip was selected as a sensor indicator for each interference spectrum obtained for LHP or LVP input signal. To monitor these indicator dips associated with LHP and LVP, referred to as the IDH and IDV, respectively, with one spectral scanning, an FRM was connected to the end of the cascaded LPFGs. Both the IDH and IDV spectrally shifted according to liquid-level or temperature changes and showed very linear responses to them with adjusted R₂ values greater than 0.997. The liquid-level sensitivities of the IDH and IDV were measured as approximately -37.29 and -121.08 pm/mm in a liquid-level range of 0 to 55 mm, respectively. The temperature sensitivities of the IDH and IDV were measured as ˜28.79 and ˜218.21 pm/°C in a temperature range of 30 to 60 °C, respectively. Owing to their linear and independent responses to liquid level and temperature, our sensor can perform temperature-independent liquid-level measurement using their pre-determined liquid-level and temperature sensitivities, even if both liquid level and temperature change simultaneously.

Simultaneous measurement of liquid-level and density by detecting buoyancy and hydraulic pressure.

In this Letter, we propose and experimentally demonstrate a method for simultaneous and complete discriminative measurement of liquid-level and density for the first time, to the best of our knowledge. The principle is to measure the responses of optical fiber sensing units caused by buoyancy and hydraulic pressure. By utilizing a designed steel diamond structure, the sensor sensitivity is significantly improved. The theoretical models and experimental methods are analyzed in detail. For large-range liquid-level measurement, a high sensitivity of 77.3 pm/cm with resolution of 0.129 mm (accuracy of 0.149‰) is achieved. As a trade-off between density measurement and sensor capability, a dual-parameter sensing is demonstrated experimentally, which features liquid-level sensitivity of 34.7 pm/cm and density sensitivity varying from 1 to 3.44nm/g/cm3. Taking advantage of the compact size, easy fabrication, and low cost, this method has great potential in real-time intelligent monitoring of reserves and quality for industrial storage of fuels and chemicals.

고복굴절 광섬유 장주기 격자 기반 광섬유 내 마하 젠더 간섭계를 이용한 수위 및 온도 분리 측정 광섬유 센서에 관한 연구

Here, we propose an optical fiber sensor capable of discriminating liquid level and temperature using an in-fiber Mach-Zehnder interferometer (MZI) composed of cascaded long-period fiber gratings (LPFGs) written on high-birefringence fiber (HBF). A 5.0-cm-long grating-free fiber region between the two LPFGs written on HBF, referred to as HB-LPFGs, serves as an active area of the sensor head. If the external refractive index of the active area changes due to an increase in the water level along the longitudinal direction of the sensor head, an additional phase shift of the recoupled cladding mode occurs due to the difference in the refractive index between water and air. This additional phase shift causes a wavelength shift in the interference spectrum generated by the in-fiber MZI. Due to the birefringence of HBF, the in-fiber MZI shows interference spectra with significantly different wavelengths for two orthogonal input polarization states. Its liquid level sensitivities were measured as -0.384 and -1.295nm/cm for x- and y-polarization in a water level range of 0∼5.0cm, respectively. its temperature sensitivities were also measured as ∼31.57 and ∼217.29pm/℃ for x- and y-polarization in a temperature range of 30∼60℃, respectively.

Thin fiber-based Mach-Zehnder interferometric sensor for measurement of liquid level, refractive index, temperature, and axial strain.

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 $ - {131.7092}\;{\rm nm/RIU}$-131.7092nm/RIU and $ - {120.7}\;{\rm pm/mm}$-120.7pm/mm 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 $-4.84×10-4nm/µε, respectively. In addition, the sensor shows superiority in measuring multiple parameters simultaneously.

Michelson liquid-level sensor based on cascaded no-core fiber and single-mode fiber structure

A novel Michelson sensor is proposed and applied to detect the liquid level. The sensor was fabricated by a section of no-core optical fiber (NCF) which is sandwiched between two single-mode fibers (SMFs). One single-mode fiber (SMF1) acts as light guide, and the tip of the other single mode fiber (SMF2) is coated with silver film as mirror. The high-order modes are excited when light travels from SMF1 to NCF and couple into the SMF2 at the NCF-SMF2 interface. The core and the cladding modes are reflected by the silver film of SMF2 and then couple twice at the NCF-SMF2 interface to form Michelson interference. Through simulation optimization and experimental verification, the optimized lengths of 15 mm and 30 mm are determined for NCF and SMF2, respectively. Interestingly, the NCF and SMF2 have the similar sensing responsivity in the liquid level sensing measurement. In the range of 15−90 °C, the sensor exhibits a temperature-insensitive characteristic. In the 0–44 mm liquid level range, the sensitivities of the deionized water, 5 % NaCl, 10 % NaCl and 15 % NaCl aqueous solutions are 216.16, 232.22, 253.41 and 276.87 pm/mm, respectively, and the refractive index sensitivity is 2223.5658 pm/mm/RIU. The sensor has clear interference fringes, simple structure, high liquid level sensitivity, good linearity and temperature insensitivity. It has the potential application in the field of small-scale liquid level monitoring.

Optical fiber liquid level sensor realized by cascading two spherical-shape structures

An optical fiber sensor for liquid level measurement of NaCl soultion based on Mach-Zehnder interferometer (MZI) is proposed and demonstrated. The MZI consists of two spherical-shape structures. The simulations of the light propagation of the spherical-shape structure with different diameters are performed, and it shows that the spherical-shape structure with diameter values of 200 μm can couple 50% energy of the core-mode into the cladding mode, and it is helpful to obtain best interference contrast. The liquid level sensitivity is -1.172 nm/cm for pure water, and -1.401 nm/cm for NaCl solution(n = 1.382). The sensor has advantages of easy fabrication, good robustness, and low hysteresis.

Liquid-level sensing based on a hollow core Bragg fiber.

A novel optical fiber liquid level sensor based on a hollow core Bragg fiber (HCBF) was proposed and demonstrated. The HCBF was first designed and successfully fabricated with periodic transmission band in the spectrum and a transmission loss of ~3.48 dB/cm. An inline optical fiber liquid-level sensor was fabricated by simply sandwiching a piece of HCBF between two single mode fibers. The sensing performance was experimentally tested. A linear liquid-level sensitivity of ~1.1 dB/mm, and fast response time less than 3s was obtained by the intensity demodulation measurement. The temperature and refractive index cross-sensitivities were also investigated. The experimental results indicate that our proposed structure has tiny temperature and RI dependence, which makes it a promising liquid level sensing platform for different liquids.

High sensitivity optical fiber liquid level sensor based on a compact MMF-HCF-FBG structure

An ultra-high sensitivity fiber liquid level sensor based on wavelength demodulation is proposed and demonstrated. The sensor is composed of a segment of multimode fiber and a large aperture hollow-core fiber assisted by a fiber Bragg grating (FBG). Interference occurs due to core mismatching and different modes with different effective refractive indices. The experimental results show that the liquid level sensitivity of the sensor is 1.145 nm mm−1, and the linearity is up to 0.996. The dynamic temperature compensation of the sensor can be achieved by cascading an FBG. Considering the high sensitivity and compact structure of the sensor, it can be used for real-time intelligent monitoring of tiny changes in liquid level.

Temperature Insensitive Liquid Level Sensor Based on Antiresonant Reflecting Guidance in Silica Tube

We propose and demonstrate an optical fiber sensor based on a section of silica tube fusion spliced between single mode fibers. When light is conducted into the hollow core of the silica tube, anti-resonant reflecting guidance occurs, which leads to the periodic attenuation dips in the transmission spectra of the structure. The transmission intensity of the attenuation dips can be influenced by the surrounding medium, which gives rise to the application for liquid level sensing. A liquid level sensitivity of 0.4 dB/mm is achieved by immersing the sensor head vertically into water. Experimental results also prove that such a sensor is insensitive to temperature, eliminating the requirement for temperature compensation.

Dual-parameter optical fiber sensor based on concatenated down-taper and multimode fiber

A novel dual-parameter optical fiber sensor based on a single-mode fiber (SMF) down-taper and multimode fiber (MMF) is proposed and demonstrated. The sensor structure is formed by cascading a down-taper and MMF through a segment of SMF. The transmission spectrum exhibits response of the interference between core and different cladding modes. Two interference dips can be observed within a certain range of detection. Due to the different wavelength shifts of the selected two dips, simultaneous measurement of temperature and liquid level can be achieved. Experiment results indicate a good linear relation between the wavelength shift and external parameters (temperature and liquid level). The measured temperature sensitivities are 0.02nm/°C and 0.031nm/°C, and liquid level sensitivities are 0.022nm/mm and 0.07nm/mm, respectively. In addition, the fiber sensor has the advantages of compact size, simple fabrication and cost-effective.