Fiber Optic Probe Research Articles

Impact of shear-coaxial injector hydrodynamics on high-frequency combustion instabilities in a representative cryogenic rocket engine

The excitation mechanism of a thermoacoustic instability in a 42-element research rocket thrust chamber with representative operating conditions with respect to European cryogenic rocket engines is investigated in detail. From previous research it was known that the chamber 1T mode can be excited by persistent heat release rate oscillations which are modulated by the resonant modes of the liquid oxygen injectors. The excitation source of the longitudinal injector eigenmodes is investigated in this study. Fibre-optical probes measuring the OH* dynamics from the recess volume of two injectors showed additional frequency content which could neither be explained by the chamber acoustics, nor the acoustics of the injection system. Instead, the temporal evolution of these frequencies correlate with the oxidizer flow velocity. In this work we show that the additional flame modulation originates from a hydrodynamic effect in the injection system. Even though the exact process cannot be precisely identified, an effect designated orifice whistling at the injector inlet orifice seems to be a likely candidate. Combining the new results with previous publications about this combustor, it is now possible to explain past and present observations in terms of the hydrodynamic and thermoacoustic conditions which are necessary for the combustion instability to appear. The conditions, which lead to an injection-driven excitation of the 1T mode are matching frequencies of the 2L mode of the injectors and the chamber 1T mode as well as a Strouhal number between 0.2 and 0.4 based on the length and flow velocity of the injector inlet orifice.

Effects of the nozzle contraction angle on particle flow behaviors in a gas-particle two-phase jet

The particle dynamics of a conical jet with different contraction angles (the cone angle of the contraction wall, α = 20°, 40°, 60°, 80°) were investigated using particle image velocimetry (PIV) and optical fiber probes. The axial and radial distributions of particle-phase velocity and concentration were measured within a confined chamber at the mass loading ratio mp = 0.3–3.3 and jet Reynolds number Re = 11,843–104,497. Due to the nozzle contraction effect, the particle dynamics of conical jet are significant differences from the pipe jet and the smooth contraction jet. In the axial direction, there is a strong slip velocity between two phases near the nozzle exit (x/D = 0–6), which leads to the occurrence of particle acceleration. In the radial direction, the particles preferentially converge towards the centerline, forming the particle contraction, which intensifies the momentum transfer from the axial to radial direction and thus increases the particle dispersion. The particle acceleration and contraction are more pronounced with the increase of contraction angle. Furthermore, the order of the velocity decay rate and the spreading rate for different contraction angles are 40° > 80° > 60° > 20°. The nozzle contraction angle of 40° shows the best entrainment and mixing characteristics. In addition, the particles contraction near the nozzle exit as well as the particles accumulation in the wall region (r/R = 0.83–1.00) increase the non-uniformity of particle concentration.

On-Line Monitoring of the Tobacco Leaf Composition during Flue-Curing by Near-Infrared Spectroscopy and Deep Transfer Learning

The yield, quality, and output value of tobacco leaves are strongly affected by the flue-curing conditions. To effectively control the flue-curing and guarantee quality, it is necessary to quantify the chemical composition of tobacco leaves and provide timely feedback during this process. Therefore, the practicability of on-line monitoring of moisture, starch, protein, and soluble sugars for tobacco leaves by near-infrared (NIR) spectroscopy and deep transfer learning was explored. The results showed that the use of an NIR spectrometer equipped with a fiber-optic probe with a deep learning algorithm accurately predicted the content of these components during the curing process. The convolutional neural networks model showed greater potential for on-line monitoring than partial least squares and support vector machines. Furthermore, a network-based deep transfer learning strategy was crafted to include seasonal and temperature variability to accurately predict samples from a new harvest season in a curing barn. The overall studies indicated the efficacy of NIR diffuse reflectance spectroscopy as a rapid and nondestructive method for on-line and simultaneous determination of moisture, starch, protein, and soluble sugars in the flue-curing process to assist in making decisions.

Shock wave diagnostics with an ultra-short optical fiber probe

We report a highly localized, rapid-response pressure measurement of a shock wave front in a solid by utilizing a miniature fiber-optic-based probe. The probe used was a 100 μm-long fiber Bragg grating (FBG) inscribed on a standard silica communication fiber, 125 μm in diameter. The optical fiber was embedded within a ceramic zirconia ferrule and was shocked axially by a polycarbonate impactor fired from a gas gun. In a second ferrule, included in the same experiment, a 1 mm long FBG was embedded for comparison. Both FBGs were positioned at the front face of their respective ferrules, in order to sense the region where the shock wave is pristine, with no release waves, and where the stress conditions were expected to be constant for a few hundreds of nanoseconds. A simulation has been performed using LS-DYNA software describing the temporal dependence of the axial stress operating on the zirconia target and the embedded fiber gratings. The reflected spectra of both fiber grating probes were interrogated by an array of wavelength division demultiplexers and 200 MHz InGaAs detectors. Both probes exhibited a wavelength shift that corresponded to the pressure profile of the shock wave that traveled through the fiber, agreeing quite well with the predictions of the simulation. The wavelength blueshift was about 3.5 nm under a calculated shock pressure in the silica of 320 MPa, induced by a shock pressure of 700 MPa in the host zirconia target. Overall, the 100 μm probe demonstrated superior measurement capabilities to the 1 mm probe, both in time response and localization, as well as better agreement with the simulation. Multiple probes can be applied to provide high resolution mapping of shock phenomena in space and time, thus assisting in establishing the dynamic properties of materials under impact loading.

In vivo Raman spectroscopy monitors cervical change during labor

Biochemical cervical change during labor is not well understood, in part, because of a dearth of technologies capable of safely probing the pregnant cervix invivo. The need for such a technology is 2-fold: (1) to gain a mechanistic understanding of the cervical ripening and dilation process and (2) to provide an objective method for evaluating the cervical state to guide clinical decision-making. Raman spectroscopy demonstrates the potential to meet this need, as it is a noninvasive optical technique that can sensitively detect alterations in tissue components, such as extracellular matrix proteins, lipids, nucleic acids, and blood, which have been previously established to change during the cervical remodeling process. We sought to demonstrate that Raman spectroscopy can longitudinally monitor biochemical changes in the laboring cervix to identify spectral markers of impending parturition. Overall, 30 pregnant participants undergoing either spontaneous or induced labor were recruited. The Raman spectra were acquired invivo at 4-hour intervals throughout labor until rupture of membranes using a Raman system with a fiber-optic probe. Linear mixed-effects models were used to determine significant (P<.05) changes in peak intensities or peak ratios as a function of time to delivery in the study population. A nonnegative least-squares biochemical model was used to extract the changing contributions of specific molecule classes over time. We detected multiple biochemical changes during labor, including (1) significant decreases in Raman spectral features associated with collagen and other extracellular matrix proteins (P=.0054) attributed to collagen dispersion, (2) an increase in spectral features associated with blood (P=.0372), and (3) an increase in features indicative of lipid-based molecules (P=.0273). The nonnegative least-squares model revealed a decrease in collagen contribution with time to delivery, an increase in blood contribution, and a change in lipid contribution. Our findings have demonstrated that invivo Raman spectroscopy is sensitive to multiple biochemical remodeling changes in the cervix during labor. Furthermore, invivo Raman spectroscopy may be a valuable noninvasive tool for objectively evaluating the cervix to potentially guide clinical management of labor.

In vivo PS-OCT needle probe scan of human skeletal muscle.

Polarization-sensitive optical coherence tomography (PS-OCT) derived birefringence values effectively identify skeletal muscle structural disruption due to muscular dystrophy and exercise-related muscle damage in animal models in ex vivo tissue. The purpose of this investigation was to determine if a PS-OCT needle probe inserted into the leg of a human subject could accurately identify various anatomical structures with implications for use as a diagnostic tool for the determination of skeletal muscle pathology. A healthy middle-aged subject participated in this study. A custom-built PS-OCT system was interfaced with a side-viewing fiber-optic needle probe inserted into the subject's vastus lateralis muscle via a motorized stage for 3D data acquisition via rotation and stepwise pullback. The deepest recorded PS-OCT images correspond to a depth of 6 mm beneath the dermis with structural images showing uniform, striated muscle tissue. Multiple highly birefringent band-like structures with definite orientation representing connective tissue of the superficial aponeurosis appeared as the depth of the needle decreased. Superficial to these structures the dominating appearance was that of adipose tissue and low birefringent but homogeneous scattering tissue. The data indicate that a PS-OCT needle probe can be inserted into live human skeletal muscle for the identification of relevant anatomical structures that could be utilized to diagnose significant skeletal muscle pathology.

A Dual-angle fiber dynamic light scattering system integrated with microfluidic chip for particle size measurement

Dynamic light scattering (DLS) is an effective tool for measuring the distribution of the size of particles. In this work, we design a novel integrated dual-angle DLS prototype which incorporates microfluidic chip and fiber optic probes to achieve measurement at high concentration and a small amount of sample consumption(30 μl). The experimental results show that for the suspension with concentrations up to 14 mg/ml, the instrument can achieve high accuracy (relative error less than 6%). Particle size prediction at a series of concentration is calibrated using linear regression model in machine learning. Furthermore, we firstly implement dual angle on-line measurement in the fiber DLS system with microfluidic chip. The experiment results show improved repeatability of dual-angle DLS when compared with single-angle DLS measurement.

Double-Clad Fiber-Based Multifunctional Biosensors and Multimodal Bioimaging Systems: Technology and Applications.

Optical fibers have been used to probe various tissue properties such as temperature, pH, absorption, and scattering. Combining different sensing and imaging modalities within a single fiber allows for increased sensitivity without compromising the compactness of an optical fiber probe. A double-clad fiber (DCF) can sustain concurrent propagation modes (single-mode, through its core, and multimode, through an inner cladding), making DCFs ideally suited for multimodal approaches. This study provides a technological review of how DCFs are used to combine multiple sensing functionalities and imaging modalities. Specifically, we discuss the working principles of DCF-based sensors and relevant instrumentation as well as fiber probe designs and functionalization schemes. Secondly, we review different applications using a DCF-based probe to perform multifunctional sensing and multimodal bioimaging.

In-situ monitoring of cyclic olefin ring-opening metathesis polymerization by Raman spectroscopy: An effective tool for functional polymer and copolymer design

Kinetics of ring opening metathesis polymerization (ROMP) of cyclic olefins and their functional derivatives using Grubbs catalysts have been effectively monitored via Raman spectroscopy. By attaching detection optic fiber probe of the Raman spectrometer onto transparent reactor, the real-time concentration of monomers can be rapidly determined by the Raman intensity ratio between monomer characteristic bands and internal reference bands. Raman was shown to be an effective and straightforward tool to monitor and understand the ROMP process of homo-polymerization, and also could provide quantitative prediction of the functional group (–OH) incorporation ratio as well as the molecular weight distribution in copolymerization of cyclooctene and 5-norbornene-2-methanol. This analytical method enable an in-situ measurement of monomer and polymer composition during the reaction, and provide fundamental understanding for novel polymer/copolymers design.

Reflective SFT-FBG Hybrid Micro-Probe for Simultaneous Measurement of Relative Humidity and Temperature

An optical fiber probe composed of a fiber Bragg grating (FBG) and a reflective S fiber taper (SFT) with graphene oxide (GO) film, for simultaneous relative humidity (RH) and temperature measurement, was proposed and experimentally demonstrated in this paper. The SFT is made into reflection type by depositing silver mirror at the fiber end face, which is highly sensitive to surrounding refractive index (RI). The GO nanosheets, as a two-dimensional hydrophilic nano material, is coated on the fiber surface, acting as a RH-to-RI converter. The simultaneous RH and temperature measurements are realized by monitoring the characteristic wavelength shifts of the SFT and FBG in the reflection spectrum. Experimental results show that the RH sensitivity of the probe is 161.1 pm/%RH during the range of 30%RH∼90%RH, and the temperature sensitivity is 14.1 pm/°C during the range of 10 °C∼50 °C. The proposed probe is compact, flexible, and easy to be fabricated, which has potential application for precise localized measurement in medical and biochemical fields.

Random trilobe packing using rigid body approach and local Gas-Liquid hydrodynamics simulation through CFD with experimental validation

It is quite difficult to measure the local information of the gas/liquid flow inside random packed extrudate catalyst beds in a large scale. Obtaining the local information through computational fluid dynamic (CFD) simulations in such system is also difficult due to the complexity of random particle packing and two-phase flow simulation. An efficient packing scheme was implemented to randomly pack 2917 trilobe particles (10 cm in height) in a 2-inch column to represent the trickle bed reactor (TBR) based on the rigid body approach. The generated geometry was used to define the computational domain for the two-phase hydrodynamics simulation based on the volume of fluids (VOF) approach. This hydrodynamics modelling study is paired with an experimental study using our in-house developed advanced measurement techniques based on optical fiber probes, which allowed to determine local liquid velocity and saturation profiles. The experimental measurements were used for local validation of the implemented model.

Fabrication of a three-dimensional (3D) SERS fiber probe and application of in situ detection.

Surface-enhanced Raman scattering (SERS) fiber probes are useful for remote and online detection of harmful molecules using the SERS effect. In this study, a 3-dimensional (3D) SERS optical fiber probe is proposed. The formation of the 3D optical fiber probe mainly included three steps: construction of monolayer polystyrene (PS) spheres as a mask on the end face of the fiber, reactive ion etching (RIE) for PS spheres and fibers, and metal sputtering deposition. Compared with flat surface fiber probes, these 3D SERS fiber probes are composed of ordered nanocolumn arrays, which have the advantages of a simple manufacturing process, low cost, high sensitivity, and good stability. The structures of the 3D SERS fiber probe can be well controlled by changing the size of the PS sphere and etching time. The formation of the nanocolumn was studied using time evolution experiments. The obtained fiber SERS probe has good stability and high sensitivity for the in situ detection of 4-aminothiophenol (4-ATP) in solution. Therefore, these 3D SERS fiber probes have potential applications in harmful molecules for real-time detection.

Liquid Resin Infusion Process Validation through Fiber Optic Sensor Technology.

In the proposed work, a fiber-optic-based sensor network was employed for the monitoring of the liquid resin infusion process. The item under test was a panel composed by a skin and four stringers, sensorized in such a way that both the temperature and the resin arrival could be monitored. The network was arranged with 18 Fiber Bragg Gratings (FBGs) working as temperature sensors and 22 fiber optic probes with a modified front-end in order to detect the resin presence. After an in-depth study to find a better solution to install the sensors without affecting the measurements, the system was investigated using a commercial Micron Optics at 0.5 Hz, with a passive split-box connected in order to be able to sense all the sensors simultaneously. The obtained results in terms of resin arrival detection at different locations and the relative temperature trend allowed us to validate an infusion process numerical model, giving us better understanding of what the actual resin flow was and the time needed to dry preform filling during the infusion process.

Hybrid structure design, preparation of Ag-GO SERS optical fiber probe and its chemical, electromagnetic enhancement mechanism

Incorporating Ag-graphene oxide hybrid material (Ag-GO) on optical fiber offers a novel approach for flexible ultrasensitive detection in biomedical and environmental areas. In this work, Ag-GO surface-enhanced Raman scattering (SERS) optical fiber probe was synthesized by a SnCl2-sensitized solvothermal method and modified Hummer’s method. After optimizing SERS test parameters, SERS performance of the fiber probes synthesized by different synthetic procedures of GO, Ag-GO hybrid structures and GO concentration are compared. The obtained GO shows superior ability to quench fluorescence by reducing the photobleaching of dyes. GO with high oxidation degree is preferred. Compared to Ag and hybrid structures including GO/Ag and GO/Ag/GO, Ag/GO fiber probe exhibits strongest enhancement due to π-π stacking and charge transfer process from lone pair of electrons on GO to the molecules. Ag/GO fiber probe with 5 mg/mL GO displays strongest SERS enhancement. Apart from chemical enhancement, it is worthwhile to note that GO is also found to selectively enhance specific vibrations regarding π bond or lone pair of electrons. The fiber probe shows high sensitivity (10−9 M R6G), good reproducibility (RSD of 3.5%) and good stability. Moreover, the enhanced area of Ag-GO fiber probe occurs in core area and cladding edge. The enhancement mechanism of Ag-GO fiber probe is that, as GO provides an additional route for excited dyes to decay through its Fermi level, photobleaching of dyes is reduced by charge transfer process. The enhancement is a synergic effect of chemical enhancement of GO, electromagnetic enhancement of silver and waveguide propagation of optical fiber.

Mid-IR fiber-optic sensors based on especially pure Ge20Se80 and Ga10Ge15Te73I2 glasses

Optical fibers on the base of especially pure Ge20Se80 and Ga10Ge15Te73I2 glasses are prepared and applied as the material of sensing elements. To connect the sensing element to the attachment of an IR Fourier spectrometer, flexible fibers based on polycrystalline silver halides and As-Se glasses are used. The prepared multimode As38Se62/As35Se65 fiber has a minimum optical loss of 40 dB/km at 3 µm that is a record low value among core-clad selenide fibers. Fiber-optic probes with various combinations of the material of flexible fibers and sensing elements are manufactured and tested for FEWS analysis of different model organic mixtures. The promising version of a fiber-optic probe is shown to be a device with polycrystalline silver halide flexible fibers and the chalcogenide fiber sensing element. The Ga10Ge15Te73I2 fiber tips allow analysis in the 5–15 µm spectral range. The U-shaped Ge20Se80 sensing elements with a taper show the highest sensitivity.

Gas-liquid phase-detection and liquid film thickness measurement on a sprayed surface with a two-fluid jet using a fiber-optic probe and laser displacement sensor

The two-fluid jet method, which impacted droplets accelerated by a high-speed air stream, is widely used in cleaning the semiconductor manufacturing process. A wafer must always be covered with a liquid film during the cleaning process because local drying may cause some defects. However, the liquid film thickness formed by the high-speed airflow and droplets and whether a liquid film exists on the impingement surface have not been investigated. In this study, we tried to measure the liquid film thickness using an optical fiber probe and a laser displacement meter. We discuss the return light signal from the optical fiber probe installed on the surface irradiating the two-fluid jet.

光ファイバーを用いた圧力測定におけるプローブ先端形状の検討

Fiber-optic probes have advantages such as high time resolution on the order of GHz, high spatial resolution on the order of hundreds of microns, corrosion resistance, heat resistance, and pressure resistance. Due to these advantages, application to fluid pressure measurement has been studied. This is useful in the medical field for the development of ultrasonic therapy equipment. However, the signal change of the fiber-optic probe is small concerning the pressure change of the liquid, and it is difficult to measure with high sensitivity. Here, we focused on the tip shape of the fiber-optic probe and investigated the effect on the sensitivity. This study prepared the types of cleave, convex sphere, cone, and truncated cone. We experimented on each shape by immersing it in 6 different concentrations of glycerin-water solutions. We found that the cleave and the convex spherical surface polished with a roughness of 0.02 μm have good sensitivity. Moreover, the cone showed a sensitivity exceeding the theoretical line. From there, the surface roughness and shape of the probe should be selected correctly in pressure measurement.

Design of a fiber-optic composite probe for engine intake total temperature and pressure (invited)

Design of a fiber-optic composite probe for engine intake total temperature and pressure (invited)

Simultaneous High-Speed Observation in Two Directions and Impulsive Pressure Measurement for Bubble Collapse near a Rigid Wall

Simultaneous high-speed observations in two-directions and pressure measurements using a Fiber Optic Probe Hydrophone (FOPH) are conducted to investigate the collapse of a laser-induced bubble near a rigid wall and the corresponding impulsive pressure distribution. It is shown that the measured pressure distributions next to the wall and the observations of top and side views reveal a strong correlation with the pitting damage due to the bubble collapse by Philipp and Lauterborn (1998). The results also show that asymmetric bubble collapse is observed at the second collapse.

Применение индивидуального позиционера, спроектированного методом CAD, для световодного зонда при лазерной диагностике микроциркуляции пародонта

Objective: To perform laser Doppler flowmetry (LDF) periodontal microcirculation assessment using custom-made, computer-aided-designed probe holders manufactured by stereolithography (SLA). Methods: 66 young people aged 21-23 years old with clinically healthy periodontium were examined. The first group consisted of subjects where a custom-made probe holder was fabricated using a silicone impression mould technique. The second group consisted of subjects where a custom-made computer-aided-design probe holder made of a photopolymer by SLA was used. The basic microcirculation parameters were analysed to evaluate periodontal microcirculation by the LDF method: the PM – average perfusion value in periodontal tissues; δ – the average square deviation of the amplitude of blood flow fluctuations from the arithmetic mean value, Kv – coefficient of variation (%). Statistical processing of the results was carried out using the software package Statistica 13.0 (StatSoft Inc, USA). Results: Statistical analysis results indicated that the functional characteristics of the periodontal microcirculation using various custom-made fibre optic probe holders used in capillary blood flow monitoring had significant differences p&lt;0.05. The value of the median PM when using a silicone holder in group I was 1.6 times lower than when using a photopolymer holder in group II. The median value of the σ index when using a silicone holder in group I was 2.3 times higher than when using a photopolymer holder in group II. The median value of the Kv when using a silicone holder in group I was 2.5 times higher than when using a photopolymer holder in group II. Conclusion: A photopolymer probe holder, unlike a silicone one, provides a constant fixed distance between the periodontal tissues and the LDF probe, prevents movement or probe displacement, and makes it possible to avoid pressure on the gingival tissue, ensuring high accuracy of laser diagnostics Keywords: Functional diagnostics, LDF, microcirculation, periodontium, CAD, stereolithography.