This work introduces a groundbreaking Open-Ended Hollow Coaxial Cable Resonator (OE-HCCR) CO2 sensor and the OE-HCCR as a chemical sensing platform technology. This OE-HCCR chemical sensing platform has a displacement detection limit of 0.01nm, interpreted as less than one ppb change in sensing material permittivity values. The OE-HCCR sensor is employed for high-performance CO2 monitoring by integrating novel CO2-sensitive composite materials with the developed platform, marking the first instance of this application worldwide. This sensor has the potential to revolutionize CO2 monitoring in challenging industrial environments, which would contribute to global decarbonization efforts and assist with environmental preservation activities.
This work presents a distributed optical fiber specklegram sensor (FSS) specifically designed for the detection and localization of water leaks. The sensor analyzes specklegram images generated by a No-Core Fiber (NCF) under different water leak conditions, employing a low-cost CCD camera as an interrogation unit. To enhance the accuracy of leak detection, a convolutional neural network (CNN) model is employed to post-process the specklegram images for monitoring the different water leak conditions. The sensor demonstrates high sensitivity, accurately detecting water volumes as small as 0.1 mL. In the initial series of experiments, the sensor achieved a remarkable 100% accuracy in predicting the location of leak spots situated 1 cm apart. However, in subsequent rounds of the experiment, a slight reduction in accuracy was observed (87.5%) due to the issue of water droplet overflow across the Kapton tape used to mark the various test leak spots after multiple cycles of water addition and removal. Therefore, employing an impermeable material for the demarcation will mitigate the water droplet overflow problem. In summary, the proposed sensor offers an efficient approach for water leak detection through the application of machine learning-based specklegram analysis. The findings of this research underscore the potential of FSS as a low-cost, easily implementable, and real-time monitoring system for the detection and localization of water leaks.
This research demonstrates femtosecond (FS) laser-written distributed fiber Bragg gratings (FBGs) sensors within sapphire crystalline fiber, tailored for steelmaking applications. The study precisely assesses sensor stability during a 72-hour exposure to severe conditions, including temperatures reaching 1600°C. The FBGs exhibit excellent signal strength and a maintained high signal-to-noise ratio (SNR) by averting external surface reactions with the sapphire fiber. Extensive annealing at 1600°C purifies the sheathing material. By utilizing an extended 1-meter sapphire fiber, this work surmounts the challenges of cascading FBGs in highly multimode waveguides, enabling FBG signal capture in demanding applications. This research enhances our comprehension of FBG performance in high-temperature environments and paves the way for robust optical fiber systems in steelmaking applications, including tundish probes and submerge entry nozzles (SEN) for molten metal casting. Additionally, the exceptional efficiency and precision of sapphire FBG sensors, in contrast to conventional thermocouples, offer the potential to boost productivity, lower energy consumption, and reduce the carbon footprint in the steel industry.
This study presents a pioneering technique for fabricating highly cascaded first-order fiber Bragg gratings (FBGs) using a femtosecond laser-assisted point-by-point inscription method in highly multimode optical fibers, specifically Sapphire crystalline fiber, and pure silica coreless fiber. Notably, it marks the first successful demonstration of a distributed array comprising 10 FBGs within highly multimode fibers. This achievement is facilitated by a high-power laser technique that yields larger reflectors characterized by a Gaussian intensity profile. These first-order FBGs offer various advantages, including enhanced reflectivity, reduced fabrication time, and simplified spectral characteristics, enhancing their accessibility for interpretation when contrasted with higher-order FBGs. In addition to that it encompasses a comprehensive analysis of the robustness and efficacy of these FBGs, with particular emphasis on their ability to endure extreme temperatures. These FBGs demonstrate an advantageous capability for localized multi-point temperature monitoring, reaching temperatures up to 1500°C with sapphire crystalline fiber and 1100°C with pure silica coreless fiber. This resilience makes them suitable for deployment in harsh environmental conditions. This innovative approach substantially broadens the potential applications of highly multimode optical fibers, particularly in the arena of sensing and communication, where challenges related to thermal gradients and harsh environments prevail. These groundbreaking first-order FBGs signify a substantial advancement in the realm of distributed temperature sensing, offering supreme capabilities for temperature monitoring and signal stability. As such, our work holds the promise of a substantial impact on industries and applications that demand unwavering reliability under extreme conditions.
This study presents an advancement in high-temperature Raman spectroscopy, specifically for analyzing molten materials. It introduces an approach by integrating a fiber-optic Raman probe with a copper block protection system designed to endure extreme thermal conditions. The copper block features an open port designed to accommodate an external telescope with a 3cm focal length, enabling Raman spectra collection in challenging high-temperature environments. A built-in gas channel ensures a continuous flow of argon gas to prevent flux intrusion. The robust copper block acts as a reliable shield, safeguarding the fiber-optic Raman probe within molten materials. This enhancement maintains the probe's integrity and significantly improves its resilience, making it ideal for rigorous investigations of molten substances. This advancement is particularly relevant in metallurgy, where flux materials impact production quality and efficiency. The ability to acquire Raman signals under elevated thermal conditions offers opportunities for studying molecular dynamics, compositional changes, and chemical interactions within molten substances. This introduced direct immersion probing technique has implications, benefiting both scientific and industrial fields. It holds promise for advancing research and exploration in various contexts, from fundamental scientific inquiries to practical applications in metallurgical processes, where flux materials are critical for optimizing production quality and efficiency. This approach enhances the capabilities of high-temperature Raman spectroscopy, making it a valuable tool for investigating molten materials and their properties in diverse settings.
This study focuses on the critical aspect of interfacial heat transfer during the solidification process in metal casting, aiming to optimize these manufacturing processes. Fiber-optic sensors were employed to provide continuous real-time monitoring of mold gaps and temperature profiles during the solidification of A356 aluminum in a permanent mold-casting environment. A specially designed mold system, constructed from unheated, uncoated tool steel, facilitated the seamless integration of these advanced fiber-optic sensors. One key technique used was the Extrinsic Fabry-Perot interferometric (EFPI) sensor, which uniquely utilized molten metal as the second reflection interface for measuring mold gaps. This method yielded impressively accurate results, with a maximum error of just 2μm compared to physical measurements. Additionally, using the Rayleigh backscattering (RBS) technique, a stainless steel-encased fiber provided real-time temperature measurements with an impressive spatial resolution of 0.65mm. The study demonstrates that combining high-resolution temperature profiles with gap evolution measurements significantly enhances our understanding of heat transfer dynamics at the mold-metal interface, proving particularly beneficial for optimizing complex-shaped castings and continuous casting processes. Furthermore, the capability to monitor the shape of the casting in real-time as it exits a continuous casting mold introduces a novel tool for quality control and process safety improvement by early detection of conditions that might lead to slab cracking and breakouts, ultimately enhancing overall process efficiency and reliability.
This study presents an assembly-free ball lens structure at the tip of tapered multimode optical fiber to enhance the light collection efficiency for pH measurements. A 35 µm diameter ball lens was fabricated at the sensor tip. In addition, a thin layer of fluorescence dye was mixed with sol-gel that formed at the fiber tip for pH sensing. The simulation result demonstrates the light propagation on the ball lens tip. The experiment results reveal that the proposed sensor has a rapid response time (< 3 seconds), high sensitivity, and pinpoint accuracy (±1.0%) in the pH range of 6.0-8.0.
Hydration reactions of cement-based materials are of great significance to their properties and durability. Various technologies have been investigated to study the hydration processes regarding reaction heat, chemical changes, or microstructures. As a non-destructive chemical analysis technique, Raman spectroscopy provides detailed information about chemical structures, which takes advantage of tracking and monitoring the chemical change during the hydration reaction. In this study, a novel in situ fiber optic Raman probe was utilized to continuously monitor the long-term hydration process of cement clinker stages, from early to late hydration stages and from fresh to hardened state of paste samples. With the remarkable capability of this technique for dry or moist, crystalline or amorphous samples, the hydration process of tricalcium silicate (C3S) pastes with different water-to-solid (w/s) ratios can be monitored from the beginning of the hydration reaction. The main hydration products, especially C-S-H and silicate (CH), have been successfully identified, and there in situ quantitative changes have been continuously monitored. The effect of the w/s ratio on the hydration process of C3S slurries is also discussed. Moreover, the X-Ray Powder Refraction (XRD) results strongly correlate with the Raman spectra of the hydration products, demonstrating the technique's reliability. By comparing with the existing in situ fiber optic Raman spectroscopy technique, the proposed sensor performs a significantly better signal-to-noise ratio (SNR), providing essential aid for future use in the construction field for monitoring and assessing the health and performance of concrete structures.
This study presents a novel in situ high-temperature fiber optic Raman probe that enables the study of the physical properties and structure of molten samples at temperatures up to 1400 °C. To demonstrate the functionality of the high-temperature fiber optic Raman probe, different composition mold fluxes were evaluated in this report. The Raman spectra at flux molten temperature were successfully collected and analyzed. A deconvolution algorithm was employed to identify peaks in the spectra associated with the molecular structure of the components in each sample. The experimental results demonstrate that the composition-dependent Raman signal shift can be detected at high temperatures, indicating that molten materials analysis using a high-temperature Raman system shows significant promise. 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.
Food quality and safety have been critical issues in the world. There is an urgent need for a fast, simple, selective, and inexpensive food detection method for the identification of the degree of food spoilage. As a molecular analysis tool, Raman spectroscopy has the advantages of high selectivity, accurate analysis, simple operation, and low sample consumption. This paper reports a novel remote fiber optic Raman sensor for real-time application in food spoilage detection. Eight volatile organic compounds (VOC) liquids that typically generated by corrupted food were under-tested. The proposed sensor successfully captures the back-scattered Raman spectra for all testing samples with various dilution levels. Multiple machine learning algorithms are also applied to further analyze the correlation between Raman spectra and molecules in spoiled foods by diluting chemical samples. As a result of combining with Raman spectroscopy and machine learning algorithm, the remote fiber optic Raman probe allows qualitative measurements of VOC samples at 100-fold dilution. In comparison with surface-enhanced Raman scattering (SERS), the remote fiber optic Raman sensor allows for direct Raman spectroscopy detection without sample and SERS substrate preparation, which opens a new chapter on the nondestructive and sensitive detection of food analytes.
This paper reports a novel Extrinsic Fabry-Pérot Interferometer (EFPI) sensor platform based on ~50 μm-diameter porous silica microspheres attached to the ends of single-mode optical fibers. The glass spheres, with 45% internal void volumes, act as geometrically well-defined Fabry-Pérot (FP) cavities that produce interferograms that only depend on the index of refraction of guest molecule types and loadings. The primary advantage of the sensor is that the silica micropores inside the glass spheres present inherent surface hydroxyl groups, which can be chemically modified using a wide selection of silanization reactions. Silanized silica microspheres provide a novel and broad sensor platform where myriad silane coupling agents act as bridges connecting organic and inorganic materials. Commercially available silanization reagents are diverse and afford silica pores with selectivity for sensing chemicals and biochemicals. When guest molecules are adsorbed in the pores of the microspheres, a proportional change in the light path length can be calculated and measured. A gas sample generator consisting of vapor generators, analyte permeation tubes, and flow controllers were configured to characterize the sensor response to various volatile organic compounds. An optical interrogator with a 1 Hz scan frequency and 80 nm wavelength range was employed for full spectral scanning and data acquisition. Experimental results demonstrate shifts of the interferogram when an EFPI glass microsphere is exposed to different vapors and vapor concentrations. Future work will compare EFPI results of guest molecule adsorptions by unaltered versus silanized porous glass microspheres.
A miniaturized fiber-optic Raman probe for Raman spectroscopy, which can eliminate the high backscattering Raman signal from the long-fused silica fiber that is used for the biochemical application, is presented. Its main purpose is to provide a technique for the detection of very small substances and separate Raman backscattering signal of optical fiber. After a brief introduction of the traditional fiber Raman technology, the experimental operation of the design optimization of the miniaturized fiber-optic Raman probe was discussed. We successfully used the home build fiber taper device to combine seven multi-mode fibers as one fiber taper with approximately 30µm as the probe diameter for Raman spectral analysis. By comparing the traditional fiber-optic Raman sensor and the miniaturized fiber-optic Raman probe with experiments on a variety of materials, the correlation of the Raman signal has been demonstrated. We observed that the miniaturized fiber-optic Raman probe not only effectively removes the backscattering Raman signal of the fiber itself, but also provides a comparable signal-noise ratio, which provides an argument for this research.
The continuous casting process for steel production utilizes specially designed oxyfluoride glasses (mold fluxes) to lubricate the mold and control the steel solidification process. The composition of the flux controls important properties, such as viscosity, basicity, and crystallization rate, which in turn influences the quality of the as-cast product. However, these fluxes also interact with the steel during casting, causing chemistry shifts that must be anticipated in the design of the flux.
Today, the in-service chemistry of the flux must be determined by taking flux samples from the mold during casting and then processing the samples off-line to determine chemistry and other physical properties, such as viscosity. Raman spectroscopy provides an alternative method for flux analysis, with the possibility of performing direct on-line analysis during casting. Raman spectroscopy has the unique ability to identify specific molecules through well-resolved vibrational bands that provide fingerprint signatures of the structure of the molecules. Specific peaks in the Raman spectra can be correlated with flux chemistry and viscosity.
The work reported here aims to assess the structure and chemical composition of flux samples at high temperatures using fiber-optic Raman spectroscopy. Results from Raman spectral analyses captured the 1300 °C for a range of flux chemistries are presented. The experimental results demonstrate that the composition-dependent Raman signal shift can be detected at high temperatures and that on-line flux analysis using a high-temperature Raman system shows significant promise.
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