Fiber Optic Sensor Research Articles

Metal–semiconductor sulfide bilayer based SPR fiber optic sensors for the detection of methanol adulteration of ethanol using machine learning algorithms: an investigative study

Metal–semiconductor sulfide bilayer based SPR fiber optic sensors for the detection of methanol adulteration of ethanol using machine learning algorithms: an investigative study

(Invited) Development of Fiber-Optic Hydrogen Sensor Using Platinum-Supported Tungsten Trioxide-Silica Composite Film

A fiber-optic hydrogen gas sensor using a platinum-supported tungsten oxide-silica composite film was fabricated. This sensor utilizes the absorption of the evanescent field interaction in the hydrogen sensitive clad which was composed of WO3 and SiO2, coated on a silica core with sol-gel process. As a first step, transmission spectra of sensing film itself were measured. The transmittance of the sensitive film decreased in the range of wavelengths above about 500 nm after exposure to pure hydrogen, and the change in transmittance at 1300 nm was greater than that at 850 nm. Then, fiber optic sensor device was fabricated, and the amount of propagating light was measured. In the case of using the light source with a wavelength of 1300 nm, the sensitivity with respect to the hydrogen response was nearly twice and the response speed was faster, compared with those at 850 nm.

The Application of Distributed Fiber-Optic Sensing Technology in Monitoring the Loose Zone in the Floor of Stoping Roadway

The Application of Distributed Fiber-Optic Sensing Technology in Monitoring the Loose Zone in the Floor of Stoping Roadway

Experimental Study of Fiber-Optic Temperature Sensor Based on Dual FSIs

To improve the sensitivity measurement of temperature sensors, a fiber optic temperature sensor structure based on the harmonic Vernier effect with two parallel fiber Sagnac interferometers (FSIs) is designed, and theoretical analysis and experimental testing are conducted. The FSI consisting of two polarization maintaining fibers (PMFs) with lengths of 13.62 m and 15.05 m respectively is used to achieve the basic Vernier effect. Then by changing the length of one PMF to approximately i times that of the others, the FSI composed of two PMFs of 7.1 m and 15.05 m is used to achieve the first-order harmonic Vernier effect. Afterward, temperature sensing tests are conducted to observe the wavelength drift during temperature changes and ultimately achieve high sensitivity. The experimental results show that the temperature sensitivity of the sensor based on the first-order harmonic Vernier effect is −28.89 nm/°C, which is 17.09 times that of a single FSI structure (−1.69 nm/°C) and 1.84 times that of the sensitivity generated by the structure based on the basic Vernier effect (−15.69 nm/°C). The experimental results are consistent with the theoretical analysis. The structure proposed in this paper achieves drift measurement of 0.1 °C variation based on 1 °C drift, making the fiber optic temperature sensor applicable to related fields that require high precision temperature. The proposed temperature sensor has the simple structure, low production cost, high sensitivity, and broad application prospects.

Strain measurement of CFRP-Steel bonded joints using distributed optical fibre sensors

ABSTRACT Externally bonded carbon fibre reinforced polymer (CFRP) is widely employed for strengthening steel structures. The CFRP-steel bond behaviour is typically conducted using the single-lap joint (SLJ) and double-lap joint (DLJ) shear tests. This study utilizes advanced distributed optical fibre sensors (DOFS) to measure strains in CFRP-steel SLJs and DLJs, with a specific focus on examining the bending effect. An experimental investigation was conducted to verify the appropriate adhesive and fibre coating materials, achieving synergistic deformation between optical fibre sensors and adherends. The strain results reveal that PI-coated fibres bonded with epoxy resin enhance deformation compatibility. The CFRP strain distributions within the joints are accurately measured by DOFS, enabling the calculation of bending strain to assess joint bending effects. The observed strain aligns well with the finite element (FE) predictions. A more significant bending effect is observed in SLJs compared to DLJs, predominantly concentrated at the loaded end. It can be inferred that the SLJs are subjected to mixed-mode I/II loading in shear tests, and the DLJs appears to be mainly influenced by mode II loading. Additionally, the verified FE model demonstrates that the shear strain across the thickness of the adhesive layer exhibits significant variation at the bond ends.

In-line fiber optic optofluidic sensor based on a fully open Fabry-Perot interferometer

In-line fiber optic optofluidic sensor based on a fully open Fabry-Perot interferometer

Sensitivity-enhanced optical fiber sensor based on the Vernier effect for detection of ammonia in water

A sensitivity-enhanced optical fiber sensor for the detection of dissolved ammonia in water based on the Vernier effect is proposed and demonstrated. The sensor comprises a sensing Fabry-Perot interferometer (S-FPI) and a reference Fabry-Perot interferometer (R-FPI) in parallel. The S-FPI is an open cavity fabricated by the dislocation welding of single-mode fiber(SMF), which is filled with a mixture of ultraviolet-curable resin NOA 170 and Oxazine 170 perchlorate (O17). The R-FPI is a sealed cavity, which is constructed by fusion splicing of SMF and hollow core fiber (HCF). The proposed sensor is based on the chemical reaction between the dissolved ammonia and O17. This chemical reaction alters the refractive index (RI) of the S-FPI, resulting in a wavelength shift of the reflected spectrum. The two interferometers exhibit a nearly identical free spectral range (FSR), thereby enabling the generation of the Vernier effect, which markedly enhances the ammonia sensitivity of the sensor. Experimental results indicate that the sensor sensitivity is 0.34 nm/ppm in the dissolved ammonia range of 5-40 ppm, which is approximately 9.1 times that of the single S-FPI. The proposed sensor exhibits both good repeatability and a short response time, in addition to selectivity for the detection of ammonia.

Fiber optic magnetic field sensor based on a magnetic-fluid-induced phase-shift FLRD

A magnetic field sensing system based on a phase-shift fiber loop ring-down (FLRD) technique and multi-mode interferometer (MI) coated with magnetic fluid (MF) is proposed and demonstrated. The MI is constructed by splicing a segment of no-core fiber between two sections of single-mode fibers, which is then immersed in MF to serve as a sensing head with the advantages of simple fabrication and specific magnetic sensitivity. Due to the magnetic refractive index tunable properties of the MF, the magnetic-field-dependent loss will be introduced in the fiber loop by the sensing head. Such magnetic-induced loss would be accumulated during the round trip of the optical carrier and reflected on the phase information of the modulated signal. The phase-shift changes with the applied magnetic field strength, enabling magnetic field sensing through phase-shift measurements. The sensing system is experimentally demonstrated and a sensitivity of 0.704×10−3deg/Gs in the linear region is achieved. Moreover, the stability and repeatability of the system are verified, leading to a promising method for magnetic field measurements.

Damage detection of Kevlar woven fabric using optical fiber multimode interferometer

Kevlar woven fabric is crucial for the lightweight design of aerospace structures due to its unique advantages. However, it is susceptible to damage during operation, making effective damage detection essential for ensuring structural reliability. Nevertheless, conventional sensors used for damage detection have limitations such as complex manufacturing processes and weight. To address this issue, this paper proposed a simple singlemode-multimode-singlemode (SMS) optical fiber sensor to collect vibration signals and construct a damage recognition model based on natural frequency in order to identify the size of damages in Kevlar woven fabrics. To achieve a highly linear and accurate sensor, a length determination criterion for multimode optical fiber segments based on quasi-image, notch, and transmission spectrum loss was proposed. An optical sensor was fabricated based on this criterion. The feasibility and sensitivity of the sensor for vibration signal measurement were verified by constructing a vibration signal measurement device. An experimental study was conducted to detect damage in Kevlar tapes, where the natural frequency changes measured by the SMS sensor were integrated with an optimized multi-variable gray model for damage size detection. The experimental results indicate that the estimated error in damage size is 0.71%. The damage identification system proposed in this paper offers a simple and cost-effective solution for measuring damage in flexible structures using fiber optic sensors.

A Study on Sensitivity Improvement of the Fiber Optic Acoustic Sensing System Based on Sagnac Interference.

A new pickup structure was introduced and modified to improve the resolution of the linear Sagnac optical fiber acoustic sensing system. The maximum strains corresponding to the material, diameter, wall thickness, and height of the pickups were analyzed by simulation. An aluminum cylinder with a diameter of 110 mm, a wall thickness of 3 mm, and a height of 120 mm was chosen as the basic pickup. A four-groove pickup with a vertical width of 80 mm and a horizontal width of 20 mm was introduced to improve the sensitivity of the system. The experiments showed that the average peak-to-peak sensitivity of the four-groove pickup increased by 215.54% to 106.806 mV/Pa. The improved pickup can be applied in areas to monitor the situation of invasion of the Sagnac optical fiber acoustic sensing system.

Application of acrylic plates as load cell for detecting strain and force in structures

This study presents the use of two superimposed transparent acrylic plates as a load cell for strain and force measurement. The gap between the plates behaves like an interferometer. When a monochromatic light beam is incident upon the gap, it interacts with the two air-acrylic interfaces, causing constructive and destructive interference. This phenomenon results in the formation of an interference pattern. Interferometers are devices used for high-precision measurements. In this work, the strain and force applied to an aluminum bar were precisely measured using two acrylic plates fixed to the bar. The experiments showed that the proposed method has a measurement range of 0–60[Formula: see text] and a resolution of 0.27[Formula: see text]. It is demonstrated that the proposed method offers a low-cost strain measurement technique with a wider measurement range compared to fiber optic sensors

Detection of tendon breaks in prestressed concrete structures using coda wave interferometry

AbstractTendon breaks significantly threaten the safety of prestressed concrete structures. Failure of embedded tendons does not necessarily indicate as surface cracks, demonstrating the need for early detection methods. This paper presents a novel ultrasound‐based approach for detecting and localizing tendon breaks using coda wave interferometry. Already few embedded ultrasonic transducers form a robust monitoring network able to detect subtle changes in the structure. To demonstrate the feasibility of detecting tendon breaks, a post‐tensioned concrete beam was fabricated at Ruhr University Bochum, Germany. A break of a centric and eccentric tendon was artificially created by drilling from the outside. Both were successfully detected and localized through characteristic changes in the ultrasound results without any evidence of damage on the concrete surface. Measurements with fiber optic sensors validate the ultrasonic findings and provide insights into the re‐anchoring behavior after tendon failure.

Comparison of PMMA layers doped with methyl red and CdSe quantum dots for application in fibre optic

The paper presents a study of the luminescence properties in the visible spectral range of poly(methyl methacrylate) (PMMA) doped with organic dye-methyl red and CdSe quantum dots. The emission spectra of polymer-doped composite structures were investigated and compared with pure PMMA. Optical characterisation was carried out, focused on the measurement and analysis of excitation and luminescence spectra. Comparison of the spectroscopic characteristics of the developed materials allowed comparing the effect of doping on the luminescence properties of the obtained materials and considering their potential application as luminescent materials in fibre optic sensors.

Investigation of the Robust Integration of Distributed Fibre Optic Sensors in Structural Concrete Components.

In recent times, the value of data has grown. This tendency is also observeable in the construction industry, where research and digitalisation are increasingly oriented towards the collection, processing and analysis of different types of data. In addition to planning data, measurement data is a main focus. fibre optic measurements offer a highly precise and comprehensive approach to data collection. It is, however, important to note that this technology is still in research regarding concrete structures. This paper presents two methods of integrating filigree sensors into concrete structures. The first approach entails wrapping a fibre around a tendon duct and analysing the installation and associated measurements. The second method involves bonding polyimide and acrylate-coated fibres with 2K epoxy and cyanoacrylate in the grooves of rebars, exposing them to chemical environments. The resulting measurement data is evaluated qualitatively and quantitatively to ascertain its resilience to environmental factors. These developed criteria are consolidated in a decision matrix. Fibre-adhesive combinations necessitate protection from chemical and mechanical influences. The limitations of the solutions are pointed out, and alternative options are proposed.

Revealing the Impact of Composition on Oil Monitoring Performance of Ni-Ti-Cu Coated Optical Fiber

Shape Memory Alloy-coated optical fiber provides an economical, Smart, and real-time monitoring technological solution for Industry 4.0. In this work, the compositional influence of Ni-Ti-Cu coating on optical signal actuation has been studied. Morphological studies showed improvement in the grain size, surface roughness, and a better shape memory effect. Thermal characteristics revealed an increase in the phase transformation temperature of NiTiCu with higher copper content. Experimental analysis of optical fiber sensors in Mineral Oil resulted in a gradual shift in the actuation temperature range. A sensitivity of ∼52 mV/°C was recorded in the actuation window, showcasing the improved response time for copper-rich composition. A comparison of coated-uncoated optical fiber performance in oil has also been presented, and delamination studies were conducted by continuously exposing the samples to hot oil. The work can be referred for requirement-based composition selection for real-time and smart monitoring capability in the Oil industries.

An optical fiber high sensitivity temperature sensor with MZI and FPI parallel connection

Accurate detection of temperature is of great significance in the field of medical research. The focal point of this article centers around an optical fiber sensor that integrates Fabry Perot interferometer (FPI) filled with polydimethylsiloxane (PDMS) and Mach Zehnder interferometer (MZI), leveraging the principle of the vernier effect. By introducing the vernier effect principle, the sensitivity is 31.09 nm/°C in the detection range of 36 ∼ 40°C, and the maximum temperature measurement error is about 0.55 %. In addition, good linear response and longtime stability make it suitable for application in various scenarios where accurate temperature measurement is required.

Single mode optical fiber sensor based on surface plasmon resonance for the detection of the Lactic acid for the chemical sensor

Single mode optical fiber sensor based on surface plasmon resonance for the detection of the Lactic acid for the chemical sensor

Investigation of near infrared and Raman fibre optic process sensors for protein determination in milk protein concentrate

This study investigated the potential of two fibre optic process sensors based on near infrared (NIR) or Raman spectroscopic technology for protein measurement in milk protein concentrate (MPC). Partial least squares (PLS) models were developed using NIR, Raman, and fusion of NIR and Raman spectra data. Calibration models developed were optimized by selecting different spectral pre-treatment methods and spectral regions. Overall, the three optimal models (NIR, Raman, fused NIR and Raman) yielded R2p values >0.9 and RMSEP values in the range of 0.168–0.185 %. The optimised fusion model outperformed all Raman models and had a similar protein prediction accuracy (R2p = 0.911 and RMSEP = 0.178 %) compared to the optimised NIR model (R2p = 0.917 and RMSEP =0.168 %). Results of the study demonstrated that both NIR and Raman process probes can be used as process analytical technology (PAT) tools for inline protein measurements of MPC post membrane filtration.

Distributed salinity sensor based on optical frequency domain reflectometry with polyimide coated single mode fiber

A distributed optical fiber sensor for salinity sensing is proposed and analyzed. The sensor uses a single mode fiber coated with polyimide and is based on optical frequency domain reflectometry. By applying the polyimide solution to the surface of the fiber, a layer of polyimide film is formed by heating. As the polyimide coating is very sensitive to changes in the salinity of the external solution, the polyimide film will expand or shrink as the external concentration changes. This converts the value of salt concentration into the frequency shift in the spectrum through cross-correlation. To characterize the sensor, four polyimide-coated sensors with different average coating thicknesses of 126 µm, 170 µm, 192 µm and 249 µm were fabricated. The sensitivities of -21.71 GHz/(mol/L), -28.55 GHz/(mol/L), -29.97 GHz/(mol/L) and -42.78 GHz/(mol/L) were achieved when the salinity was measured from 0 mol/L to 3.09 mol/L, respectively. The sensitivity and response time of polyimide fibers with different diameters were measured. The minimum salinity measurement uncertainty of the sensor is 0.05 mol/L. The sensor has high sensitivity and has promising applications in observing ocean parameters and ion chemical sensing.

A fiber optic refractive index sensor with temperature compensation based on cascaded Mach-Zehnder interference and Intermodal interference

Optical fiber refractive index (RI) sensor with temperature (T) compensation has important application values in biomedicine and environmental monitoring. In order to solve the problem that the detection accuracy of liquid RI is affected by T in practical applications, a T-compensated RI fiber sensor based on cascaded Mach-Zehnder interference (MZI) and multimode interference (IMI) is proposed in this paper. Experimental results showed the proposed sensor achieved a sensitivity of 797.41 nm/RIU for the measurement of RI in the range of 1.3333–1.3640, and a sensitivity of 0.120 nm/°C for the measurement of T in the range of 0–60 °C. The resolution (R) of RI and T measurements reached 2.5 × 10−5 RIU and 0.167 °C, respectively. The detection limits (DL) of RI and T measurements are 3.135 × 10−8 RIU and 1.392 °C, respectively. A matrix is obtained to demodulate the cross-sensitivity in RI and T measurements. The proposed sensor shows the advantages of simple structure, low hysteresis, and good stability.