A simple background elimination method for miniaturized fiber-optic Raman probe

Raman scattering is called a photonic - molecular interaction based on the kinetic model of the analytic. Due to the uniqueness of the Raman scattering technique, it can provide a unique fingerprint signal for molecular recognition. However, a serious challenge often encountered in Raman measurement comes from the requirements of fast, real-time remote sensing, background fluorescence suppression, and micro-environmental detection. A new Miniaturized Fiber-Optic Raman Probe (MFORP) for Raman spectroscopy, used especially for eliminating background fluorescence and enhancing sampling, is presented. Its main purpose is to provide an overview of excellent research on the detection of very small substances and to address the drawbacks of modern optical fiber Raman sensors that cannot be separated from background fluorescence interference. After a brief introduction of the traditional fiber Raman technology, the experimental operation of the design optimization of the new MFORP was discussed. We successfully combined several multi-mode fibers as one fiber taper for Raman spectral analysis by using the fiber tapering technique. The sensing principle and the fabrication of MFORP were discussed. In order to verify that MFORP is a better solution, we used traditional Fiber-Optic Raman sensor and MFORP to experiment on a variety of materials and compare the experimental results. We observed that MFORP not only effectively removes the background fluorescence of the fiber itself, but also improves the energy collection of the Raman spectrum, which provides an argument --Abstract, page iii

In Situ Monitoring Of The Hydration Of Calcium Silicate Minerals In Cement With A Remote Fiber-optic Raman Probe

This study utilized a novel in situ fiber-optic Raman probe to continuously monitor the hydration progress of tricalcium silicate (C3S) and dicalcium silicate (C2S) without the need for sampling, from early hydration stage to later stages, and from fresh to hardened states of paste samples. By virtue of the remarkable ability of this technique in characterizing either dry or wet and crystalline or amorphous samples, the hydration processes of C3S and C2S pastes with different water-to-solid (w/s) ratios could be monitored from the start of the hydration reaction. The main hydration products, calcium silicate hydrate (C–S–H) and portlandite/calcium hydroxide (CH), have been successfully identified and continuously monitored for variations in their respective amounts in situ. The effect of w/s ratio on the hydration processes of C3S and C2S pastes was also considered. Meanwhile, the x-ray diffraction (XRD) and thermogravimetric analysis (TGA) results showed a great correlation with the in situ Raman test results about hydration products, which demonstrated the reliability of this technology. Moreover, the signal-to-noise ratio (SNR) of this Raman probe is significantly superior to existing technologies for in situ fiber-optic Raman spectroscopy. This remote fiber-optic Raman probe enables the use of Raman spectroscopy in future construction projects for on-site monitoring and evaluation of health conditions and performance of concrete structures

Simultaneously Retrofit of Heat Exchanger Networks and Towers for a Natural Gas Purification Plant

As an essential part of Heat Integration, the heat exchanger network (HEN) plays a vital role in large-scale industrial fields. The optimisation of HEN can increase energy efficiency and considerably save the operating and investment cost of the project. This study presents a novel approach for simultaneous optimisation of plant operating variables and the HEN structure of an existing natural gas purification process. The objective function is the total energy consumption of the studied process. A two-stage method is developed for optimisation. In the first stage, a particle swarm optimisation (PSO) algorithm is developed to optimise variables including tower top pressure, tower bottom pressure, and reflux ratio on the HEN, thereby changing the initial temperatures of cold and hot streams in the HEN. In the second stage, a shifted retrofit thermodynamic grid diagram (SRTGD)-based model and the corresponding solving algorithm was applied to retrofit the HEN. The case study shows that the optimal operating conditions of towers and temperature spans of heat exchangers can be solved by the proposed method to reduce the total energy consumption. The case study shows that the total energy consumption is reduced by 41.5 %

Chemical Classification By Monitoring Liquid Evaporation Using Extrinsic Fabry-Perot Interferometer With Microwave Photonics

Identification of liquids is essential in chemical analysis, safety, environmental protection, quality control, and research. A novel liquid identification system based on Microwave Photonics (MWP) measured time transient evaporation signals is investigated. An extrinsic Fabry-Perot Interferometer (EFPI) based optical probe using single-mode fiber (SMF) is proposed to monitor evaporation of different liquids. The MWP system is used to measure the optical path changes during liquid evaporation due to its high sensitivity, selectivity, and Signal-to-Noise Ratio (SNR). The measured S21 continuous wave (CW) time Magnitude and Phase signals were processed to extract features such as histogram and Fast Fourier Transform (FFT) peaks. Using features extracted from droplet evaporation time transient events, machine learning classification accurately identified chemicals in each liquid with an accuracy rate of over 99%, employing three algorithms: Decision Trees, Support Vector Machine (SVM), and K-nearest neighbors (KNN). The classification results demonstrate accurate liquid identification based on evaporation measurements by the MWP system

Miniaturized fluorescence pH sensor with assembly free ball lens on a tapered multimode optical fiber

In biochemistry, the absence of a compact, assembly-free pH sensor with high sensitivity and signal-to-noise ratio has been a persistent hurdle in achieving accurate pH measurements in real time, particularly in complex liquid environments. This manuscript introduces what we believe to be a novel solution in the form of a miniaturized pH sensor utilizing an assembly-free ball lens on a tapered multimode optical fiber (TMMF), offering the potential to revolutionize pH sensing in biochemical applications. A multimode optical fiber (MMF) was subjected to tapering processes, leading to the creation of an ultra-thin needle-like structure with a cross-sectional diameter of about 12.5 µm and a taper length of 3 mm. Subsequently, a ball lens possessing a diameter of 20 µm was fabricated at the apex of the taper. The resultant structure was coated utilizing the dip-coating technique, involving a composite mixture of epoxy and pH-sensitive dye, 2’,7’-bis(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF), thereby ensconcing the tapered ball lens with dye molecules for pH sensing. This study encompassed the fabrication and evaluation of six distinct fiber structures, incorporating the cleaved endface, the convex lens, and the ball lens structures to compare light focal lengths and propagation intensities. Computational simulations and numerical analyses were conducted to elucidate the encompassing light focal distances across the full array of lens configurations. The efficacy of the proposed pH sensor was subsequently assessed through its deployment within a complex liquid medium spanning a pH spectrum ranging from 6 to 8. Real-time data acquisition was performed with a fast response time of 0.5 seconds. A comparative analysis with a pH sensor predicated upon a single TMMF embedded with the fluorescent dye underscored the substantial signal enhancement achieved by the proposed system twice the fluorescence signal magnitude. The proposed assembly-free miniaturized pH sensor not only substantiates enhanced signal collection efficiency but also decisively addresses the persistent challenges of poor signal-to-noise ratio encountered within contemporary miniaturized pH probes

Highly Sensitive Strain Sensor by Utilizing a Tunable Air Reflector and the Vernier Effect

A highly sensitive strain sensor based on tunable cascaded Fabry–Perot interferometers (FPIs) is proposed and experimentally demonstrated. Cascaded FPIs consist of a sensing FPI and a reference FPI, which effectively generate the Vernier effect (VE). The sensing FPI comprises a hollow core fiber (HCF) segment sandwiched between single-mode fibers (SMFs), and the reference FPI consists of a tunable air reflector, which is constituted by a computer-programable fiber holding block to adjust the desired cavity length. The simulation results predict the dispersion characteristics of modes carried by HCF. The sensor\u27s parameters are designed to correspond to a narrow bandwidth range, i.e., 1530 nm to 1610 nm. The experimental results demonstrate that the proposed sensor exhibits optimum strain sensitivity of 23.9 pm/με, 17.54 pm/με, and 14.11 pm/με cascaded with the reference FPI of 375 μm, 365 μm, and 355 μm in cavity length, which is 13.73, 10.08, and 8.10 times higher than the single sensing FPI with a strain sensitivity of 1.74 pm/με, respectively. The strain sensitivity of the sensor can be further enhanced by extending the source bandwidth. The proposed sensor exhibits ultra-low temperature sensitivity of 0.49 pm/°C for a temperature range of 25 °C to 135 °C, providing good isolation for eliminating temperature–strain cross-talk. The sensor is robust, cost-effective, easy to manufacture, repeatable, and shows a highly linear and stable response for strain sensing. Based on the sensor\u27s performance, it may be a good candidate for high-resolution strain sensing

In Situ High-Temperature Raman Spectroscopy Via a Remote Fiber-Optic Raman Probe

This Study Demonstrated for the First Time an in Situ High-Temperature Fiber-Optic Raman Probe to Study the Structure of Glass and Slag Samples at Temperatures Up to 1400 °C. a Customized External Telescope Was Integrated into a Portable Fiber-Optic Raman Probe to Extend the Optical Working Distance to Allow the Probe to Work in a High-Temperature Environment. Three Samples Were Evaluated to Demonstrate the Functionality of the High-Temperature Fiber-Optic Raman Probe. Room Temperature and High-Temperature Raman Spectra Were Successfully Collected and Analyzed. in Addition, a Deconvolution Algorithm Was Used to Identify Peaks in the Spectrum that Could Then Be Related to the Molecular Structure of Components in Each Sample. This Flexible and Reliable High-Temperature Raman Measurement Method Has Great Potential for Various Applications, Such as Materials Development, Composition, and Structure Monitoring during High-Temperature Processing, Chemical Identification, and Process Monitoring in Industrial Production

In Situ and Real-Time Mold Flux Analysis using a High-Temperature Fiber-Optic Raman Sensor for Steel Manufacturing Applications

Continuous Casting in Steel Production Uses Specially Developed Oxyfluoride Glasses (Mold Fluxes) to Lubricate a Mold and Control the Solidification of the Steel in the Mold. the Composition of the Flux Impacts Properties, Including Basicity, Viscosity, and Crystallization Rate, All of Which Affect the Stability of the Casting Process and the Quality of the Solidified Steel. However, Mold Fluxes Interact with Steel during the Casting Process, Resulting in Flux Chemistry Changes that Must Be Considered in the Flux Design. Currently, the Chemical Composition of Mold Flux Must Be Determined by Extracting Flux Samples from the Mold during Casting and Then Processing These Samples Offline to Estimate the Working Chemical Composition And, Therefore, the Expected Properties of the Flux. Raman Spectroscopy Offers an Alternative Method for Performing Flux Analysis with the Potential to Perform Measurements Online during the Casting Process. Raman Spectroscopy Uniquely Identifies Specific Chemical Bonds and Symmetries in the Glassy Flux by Revealing Peaks that Are a Fingerprint of the Vibration Modes of Molecules in the Flux. the Intensities of Specific Peaks in Raman Spectra Can Be Correlated with the Chemical Composition of the Melt and Associated Properties Such as Basicity and Viscosity. This Paper Reports on the First Use of a Portable Fiber-Optic Raman Sensor for in Situ Raman Spectroscopic Measurements of Molten Flux at 1400°C. the Work Demonstrates the Advantages of Fiber-Optic Raman Spectroscopy to Document the Structure and Chemical Composition of Flux Samples at Temperatures Typically Encountered in the Mold during Continuous Caster Operation. Experimental Results Demonstrate that the Composition-Dependent Raman Signal Shifts Can Be Detected at Caster Operating Temperatures, and the Use of High-Temperature Raman Analysis for In-Line Flux Monitoring Shows Significant Promise for the in Situ Detection of Changes in Flux Composition and Physical Properties during Casting