Refractive Index Of Fluid Research Articles

Flow Characterisation Using Fibre Bragg Gratings and Their Potential Use in Nuclear Thermal Hydraulics Experiments

With the ever-increasing role that nuclear power is playing to meet the aim of net zero carbon emissions, there is an intensified demand for understanding the thermal hydraulic phenomena at the heart of current and future reactor concepts. In response to this demand, the development of high-resolution flow analysis instrumentation is of increased importance. One such under-utilised and under-researched instrumentation technology, in the context of fluid flow analysis, is fibre Bragg grating (FBG)-based sensors. This technology allows for the construction of simple, minimally invasive instruments that are resistant to high temperatures, high pressures and corrosion, while being adaptable to measure a wide range of fluid properties, including temperature, pressure, refractive index, chemical concentration, flow rate and void fraction—even in opaque media. Furthermore, concertinaing FBG arrays have been developed capable of reconstructing 3D images of large phase structures, such as bubbles in slug flow, that interact with the array. Currently a significantly under-explored application, FBG-based instrumentation thus shows great potential for utilisation in experimental thermal hydraulics; expanding the available flow characterisation and imaging technologies. Therefore, this paper will present an overview of current FBG-based flow characterisation technologies, alongside a systematic review of how these techniques have been utilised in nuclear thermal hydraulics experiments. Finally, a discussion will be presented regarding how these techniques can be further developed and used in nuclear research.

Design and Analysis of the Low Bend Losses 2D Photonic Crystal Fiber-based Rhombic Ring Resonator for Magnetic Field Sensor

We designed and analyzed a magnetic field sensor with low bend losses 2D photonic crystal fiber based on a rhombic ring resonator. The proposed design consists of silicon rods with a diameter of 200 nm in the X and Z directions, which are 61 × 61 silicon rods. The Refractive Index (RI) of silicon is n = 3.48 at λ = 1.55 mm and the number of air holes along the direction is 33 × 33. It was found that the photonic crystal fibers used the photonic band gap phenomenon to guide light but rather an area of the fiber core with a lower refractive index of 0.9 nm. It is important to note that there are low bend losses in 2D photonic crystal fibers, enabling response to small changes in the magnetic fluid viscosity, refractive index, and other physical parameters. The flow of electromagnetic energy, indicated by the Poynting vector (s), indicates that the magnitude of the power carrier per unit area in the direction of S is approximately 1.23 W/m2.

Optical Identification of Parenteral Nutrition Solutions Exploiting Refractive Index Sensing

Parenteral artificial nutrition (PAN) is a lifesaving treatment for a large population of patients affected by different diseases, and it consists of intravenous injection of nutritive fluids by means of infusion pumps. Wrong PAN solutions are, unfortunately, often administered, thus threatening the patients’ well-being. Here, we report an optofluidic label-free sensor that can distinguish PAN solutions on the basis of their volumetric refractive index (RI). In our system, a monochromatic light beam, generated by a laser diode, travels obliquely through a transparent, square-section polystyrene channel, is then back-reflected by a mirror, and finally exits the channel in a position that depends on the filling fluid RI. The displacement of the output light spot ΔXexperim is easily detected with a linear, 1-D position sensitive detector (PSD). We initially calibrated the sensor with water-glucose solutions demonstrating a sensitivity S = ΔXexperim/Δn = 13,960 µm/RIU. We then clearly distinguished six commercial PAN solutions, commonly administered to patients. To the best of our knowledge, this is the first reported healthcare sensing platform for remote contactless recognition of PAN fluids, which could be inserted into infusion pumps to improve treatment safety, by checking the compliance to the prescription of the fluid actually delivered to the patient.

Miniaturized FPI-FBG integrated sensor for parallel monitoring of magnetic field and magnetic fluid refractive index

In this paper, a sensor combining Fabry–Perot interferometer (FPI) with fiber Bragg grating (FBG) is designed, fabricated, and experimentally demonstrated as an excellent alternative to traditional sensors to detect the magnetic field and refractive index (RI), simultaneously. The sensor comprises a magnetostrictive Ni-Fe alloy coated on partially-unclad FBG, connecting the two reflecting surfaces of the micro-FPI cavity. The magnetostrictive analysis shows that magnetostriction reaches the maximum value at 59.3% Ni concentration. The sensor performance test was conducted on the RI of magnetic fluid and external magnetic field changes. The probe sensitivity was found to be as high as 625.38 nm/RIU and 7.71 nm mT−1, respectively. A matrix for simultaneous measurement of the magnetic field and RI was constructed using these sensitivity values. The stability of the sensor system over more than 300 h is at a satisfactory level. Considering the accurate FBG modulation and particular design of the experiment proposed by this method, the resolution of 1.69 × 10−4 RIU and 0.016 mT for magnetic fluid and magnetic field could be achieved, respectively, which can meet the sensing demand for a wide range of applications.

Silicon Nanodisk Huygens Metasurfaces for Portable and Low-Cost Refractive Index and Biomarker Sensing.

Biomarker detection and bulk refractive index sensing are important across multiple industries ranging from early medical diagnosis to chemical process quality control. The bulky size, high cost, and complex architecture of existing refractive index and biomarker sensing technologies limit their use to highly skilled environments like hospitals, large food processing plants, and research labs. Here, we demonstrate a compact and inexpensive refractive index sensor based on resonant dielectric photonic nanoantenna arrays or metasurfaces. These dielectric resonances support Mie dipole and asymmetric resonances that shift with changes in their external environment. A single-wavelength transmission measurement in a portable (<250 in.3), low-cost (<$4000) sensor shows sensitivity to 1.9 × 10–6 change in the fluid refractive index without the use of a spectrometer or other complex optics. Our sensor assembly allows for measurements using multiple metasurfaces with identical resonances or varying resonance types for enhanced diagnostics on the same chip. Furthermore, a 10 kDa culture filtrate peptide CFP-10, a marker for human tuberculosis, is detected with our sensor with 10 pM resolution. This system has the potential to enable facile, fast, and highly sensitive measurements with adequate limits of detection for personalized biomedical diagnoses.

Case Study: Sound-Speed Measurement: Unique Measurement Across All Fluids for In-Situ Properties

Fluid samples collected using either wireline or logging-while-drilling (LWD) formation-testing technology for reservoir fluid characterization have long been accepted as the most representative of reservoir fluid. This, though, comes with a caveat that the collected sample is clean and devoid of any mud-filtrate contamination. With both techniques performed soon after drilling a well, there is always a risk of contaminating the collected fluid with mud filtrate. Toward the goal of reducing this risk, since the early 2000s, technologies have been brought forth to help identify the fluid down hole. There have been multiple developments with sensors for absorbance spectroscopy, fluorescence, fluid resistivity, fluid refractive index, and so on. Each sensor development was targeted toward a specific fluid interaction with the mud filtrate, thereby helping to differentiate the reservoir fluid from the mud filtrate. Downhole sampling conditions can be classified into two broad groups: one case where the reservoir fluid is miscible with the mud filtrate and the other where the reservoir fluid is not miscible with the mud filtrate. The immiscible cases are generally straightforward, since sensors such as absorbance spectroscopy can easily differentiate among oil, water, and gas. In addition, the technique can be used to determine the fractional portion of each phase in the flow. Complications arise when the reservoir fluids happen to be miscible with the mud filtrate system; for example, while sampling reservoir water in the presence of water-based mud filtrate, absorbance spectroscopy by itself is unable to differentiate among the fluids. Table 1 provides generic information about different fluid systems as well as the sensors used to differentiate the fluids. While there are other sources of correlation-based fluid-property information, the basic sensors mentioned are the ones used for correlations. As mentioned, each sensor provides detailed information for specific cases, but only sound speed provides a single-sensor solution for the conditions expected. Sound-Speed (SS) Measurement While acoustic data have long been used for reservoir characterization, data have been used for fluid characterization during downhole sampling for only a decade. Experience has shown that this measurement is sensitive enough to not only differentiate injection water or formation water but also to track and quantify small changes in oil compressibility—an important step in focused sampling. The measurement uses a pulse-echo technique based on the principle that an acoustic signal propagates approximately as a plane wave, and that the speed of sound is based on the distance the pulse travels divided by the time it took to traverse the distance. (SPWLA-2013-FFF). The 10-MHz piezoelectric transducer is mounted onto a machined flat surface on the flowline of RCX (the wireline formation testing tool reservoir characterization instrument) as schematically shown in Fig. 1. The travel path length is the distance between the two internal surfaces of the flowline. The result was a bulk measurement of the speed of sound across all the fluid flowing though the flowline. The only calibration needed is for this path length, which can differ due to slight machining variations. A calibrated sensor was able to differentiate fluids which exhibited sound-speed differences as small as 4.7 m/sec (0.5 msec/ft of sound-speed slowness).

Optical fiber SPR magnetic field sensor based on photonic crystal fiber with the magnetic fluid as cladding

In this paper, a novel optical fiber surface plasmon resonance (SPR) magnetic field sensor is proposed and experimentally demonstrated. The structure is fabricated by splicing a section of photonic crystal fiber between two multimode fibers. After the structure is coated with 10 nm Cr and 50 nm Au, the high refractive index (RI) sensitivity, from 1973.72 nm RIU−1 to 3223.32 nm RIU−1 in the range of 1.3326–1.3680, verifies the SPR sensor, which is higher than the structure based on single mode fiber with the same coating. In addition, the microscopic mechanism of the tunable characteristics of magnetic fluid RI with the ambient magnetic field is simulated by the molecular dynamics method. To measure the external magnetic field, the sensing region of the SPR sensor is fully inserted in a capillary tube, which is filled with magnetic fluid and sealed with UV glue. A maximum sensitivity of 4.42 nm mT−1 is achieved in the range of 0–24 mT, experimentally. Due to high sensitivity, simple manufacturing and compact size, the proposed sensor possesses attractive application prospects in environmental monitoring, power transmission and biomedical applications.

Magnetic field sensor with truncated honeycomb photonic crystal fiber: analysis under the variations in magnetic fluid composition and temperature for high performance in near infrared

A photonic crystal fiber (PCF)-based magnetic field sensor is simulated and analyzed by using a honeycomb fiber without the first ring of air holes where the core air hole is filled with a magnetic fluid which is surrounded by a gold layer. The variation of the refractive index with the magnetic field at a fixed wavelength (1557 nm) is considered for the study. The sensor is based on variation of the transmission loss of optical power with the magnetic field. The real part of the effective index increases with the magnetic field. The simulation and analysis is carried out at (i) three different temperatures (t = 24.3 °C, 40 °C, and 60 °C) and, (ii) for different values of the volume fractions (c = 1.21%, 1.48%, 1.52%, and 1.93%) of Fe3O4 particles in a magnetic fluid solution. All the concerned values of magnetic fluid refractive index are adapted from the previously-reported experimental work. The detailed analysis of the simulation results indicates that the proposed PCF sensor has the capability of providing high sensitivity, ultrafine resolution, and low thermal sensitivity. The variation of Fe3O4 provides another crucial degree of freedom to further enhance the sensitivity of the magnetic field detection. The sensor can provide a sensitivity of 4.3763 dB/Oe and magnetic field resolution of 2.2850 × 10–3 Oe for a large enough range (∆H = 163.87 Oe) of magnetic field (28.58 Oe ≤ H ≤ 192.45 Oe).

Spectral Phase Shift Interferometry for Refractive Index Monitoring in Micro-Capillaries.

In this work, we demonstrate spectral phase-shift interferometry operating in the near-infrared wavelength range for refractive index (RI) monitoring of fluidic samples in micro-capillaries. A detailed theoretical model was developed to calculate the phase-sensitive spectral reflectivity when low-cost rectangular glass micro-capillaries, filled with samples with different refractive indices, are placed at the end of the measurment arm of a Michelson interferometer. From the phase-sensitive spectral reflectivity, we recovered the cosine-shaped interferometric signal as a function of the wavelength, as well as its dependence on the sample RI. Using the readout radiation provided by a 40-nm wideband light source with a flat emission spectrum centered at 1.55 µm and a 2 × 1 fiberoptic coupler on the common input-output optical path, experimental results were found to be in good agreement with the expected theoretical behavior. The shift of the micro-capillary optical resonances, induced by RI variations in the filling fluids (comparing saline solution with respect to distilled water, and isopropanol with respect to ethanol) were clearly detected by monitoring the positions of steep phase jumps in the cosine-shaped interferometric signal recorded as a function of the wavelength. By adding a few optical components to the instrumental configuration previously demonstrated for the spectral amplitude detection of resonances, we achieved phase-sensitive detection of the wavelength positions of the resonances as a function of the filling fluid RI. The main advantage consists of recovering RI variations by detecting the wavelength shift of “sharp peaks”, with any amplitude above a threshold in the interferometric signal derivative, instead of “wide minima” in the reflected power spectra, which are more easily affected by uncertainties due to amplitude fluctuations.

Transparent high-pressure nozzles for visualization of nozzle internal and external flow phenomena.

A new design for transparent high-pressure nozzles is presented in this work. This new design enables using the innovative Selective Laser Etching (SLE) method to manufacture transparent nozzles with outstanding accuracy. Therefore, not only the simultaneous visualization of the flow mechanics inside and outside the nozzle is enabled, but the manufacturing method applied also allows for the realization of individual nozzle geometries. Thus, nozzle internal flow phenomena (e.g., cavitation, swirl, and air inlet) and their influence on primary breakup can be analyzed with realistic nozzle geometries, e.g., for automotive applications. In addition, targeted three dimensional nozzle geometric parameters can be designed and manufactured in order to get specific tailor-made spray characteristics (e.g., droplet size distribution, spray angle, and penetration length). The basis for the transparent nozzle design is a two-parted nozzle, consisting of a re-machined original serial nozzle body and a transparent nozzle tip. The innovative SLE is used to produce the geometry of the transparent nozzle tip in fused silica, and laser polishing is utilized to achieve a maximum optical quality of nozzle surfaces for visualization. Bonding of both nozzle parts is achieved by a specially designed adhesive method. For a first feasibility study, a transparent nozzle with a simplified nozzle geometry is manufactured and used for a first study. In this study, simultaneous investigation of nozzle internal flow phenomena and their impact on spray breakup are visualized. First microscopic images of the nozzle internal flow show the formation of cavitation, its effect on nozzle internal temperature (apparent by differences in the fluid refractive index), and also the corresponding impact on spray breakup during injection. The penetration of ambient gas into the nozzle is verified at the end of injection as well as the influence of this air on the spray formation during the start of injection.

Design and Optimization of an Opened Suspended Core Fiber-Based SPR Sensor with Gold Cylinder Structures

In this study, an opened three-hole suspended core fiber surface plasmon resonance sensor structure based on the combination of photonic crystal fiber and surface plasmon resonance (SPR) mechanism was proposed and analyzed. One hole in the clad layer was exposed to the outside, and a lay of gold cylinders with the same size and gap was placed along the inside of the opened hole. The existence of the gold cylinders could stimulate the SPR effect and selecting the suitable gaps between the cylinders could enhance the SPR effect and increase its sensitivity. Then COMSOL software was used to simulate how the cylinder diameter, the gaps between the cylinders, and the fluid refractive index variation affect the sensor’s transmission loss spectrum, field enhancement effect, and the sensitivity. The optimized results show that the sensitivity of this proposed SPR sensor could be high, up to 1 × 10−5 RIU/nm, and it was much higher than the sensitivity of the existing photonic crystal fiber SPR sensor (1 × 10−4 RIU/nm), which was an order of magnitude improvement. This study could provide a reliable theoretical basis for future research and design of real-time and high-sensitivity opened fiber SPR sensors.

Help from a Hindrance: Using Astigmatism in Round Capillaries To Study Contact Angles and Wetting Layers.

Round glass capillaries are a basic tool in soft-matter science, but often are shunned due to the astigmatism they introduce in micrographs. Here, we show how refraction in a capillary can be a help instead of a hindrance to obtain precise and sensitive information on two important interfacial properties: the contact angle of two immiscible fluids and the presence of thin films on the capillary wall. Understanding optical cusps due to refraction allows direct mesurement of the inner diameter of a capillary at the meniscus, which, with the height of the meniscus cap, determines the contact angle. The meniscus can thus be measured without intrusive additives to enhance visibility, such as dyes or calibrated particles, in uniform, curved, or even tapered capillaries or under demanding conditions not accessible by conventional methods, such as small volumes (μL), high temperatures, or high pressures. We further elicit the conditions for strong internal reflection on the inner capillary wall, involving the wall and fluid refractive indices and the wall thickness, and show how to choose the capillary section to detect thin (submicron) layers on the wall, by the contribution of total internal reflection to the cusps. As examples, we report the following: (i) CO2-water or -brine contact angles at glass interfaces, measured at temperatures and pressures up to 200 °C and 600 bar, revealing an effect apparently so far unreported-the decrease in the water-wet character of glass, due to dissolved salts in brine, is strongly reduced at high temperatures, where contact angles converge toward the values in pure water; (ii) A tenuous gas hydrate layer growing from the water-guest contact line on glass, invisible in transmission microscopy but prominent in the cusps due to total internal reflection.

An ancient technique in the endoscopic era of otologic surgery: The Role of Refractive Index of Fluids

An ancient technique in the endoscopic era of otologic surgery: The Role of Refractive Index of Fluids

Rigorous analysis of optical forces between two dielectric planar waveguides immersed in dielectric fluid media

This work presents a rigorous analysis of optical forces between planar waveguides immersed in an arbitrary background medium. This approach exploits the Minkowski stress tensor formulation, which is compared with a normalized version of the dispersion relation method, showing excellent results agreement for different dielectric fluid media. Due to slot‐waveguide effect, optical forces from TM modes are more sensitive to changes in the fluid refractive index than the TE counterparts. Furthermore, the repulsive optical force from the antisymmetric TM1 mode becomes stronger for higher refractive indexes, whereas the attractive force of the symmetric TM0 mode becomes weaker. The methodology and results presented in this work provide a rigorous analysis of nano‐optomechanical devices actuated by optical forces in a broad range of materials and applications. Therefore, this study may impact areas of light‐induced interactions presenting novel optofluidic and optomechanical functionalities, thus finding applications in nanoscale transport, sensing and manipulation. image

Laser doppler velocimetry and confined flows

Finding the mode, in which two component laser Doppler velocimetry can be applied to flows confined in cylindrical tubes or vessels, was the aim of this study. We have identified principle issues that influence the propagation of laser beams in laser Doppler velocimetry system, applied to flow confined in cylindrical tube. Among them, the most important are influences of fluid and wall refractive indices, wall thickness and internal radius ratio and beam intersection angle. In analysis of the degrees of these influences, we have applied mathematical model, based on geometrical optics. The separation of measurement volumes, that measure different velocity components, has been recognized as the main drawback. To overcome this, we propose a lens with dual focal length ? primary focal length for the measurement of one velocity component and secondary focal length for the measurement of the other velocity component. We present here the procedure for calculating the optimal value of secondary focal length, depending on experimental set-up parameters. The mathematical simulation of the application of the dual focal length lens, for chosen cases presented here, confirmed the accuracy of the proposed procedure.

Refractive Index Sensing in Rectangular Glass Micro-Capillaries by Spectral Reflectivity Measurements

We report the application of rectangular glass micro-capillaries with cross-section of 20 μm × 200 μm and 50 μm × 500 μm as capillary-driven liquid-core optical cavities for fluid refractive index sensing. Reflected power spectra in two wavelength bands (around 1.3 μm and 1.55 μm) are detected with readout broadband radiation crossing the capillary in orthogonal direction with respect to the flat sides. Using a fiberoptic scheme for remote, non-contact measurements and inserting glucose or bovine serum albumin solutions in water at different concentrations as test fluids, we have revealed the shift of the wavelength position of the reflectivity minima due to refractive index variations. The combination of these low-cost devices with a spectral readout method allows achieving sensitivities higher than 250 nm/RIU and limits of detection better than 1.3 × 10−3 RIU.

Analysis of Surface Plasmon Resonance Curves with a Novel Sigmoid-Asymmetric Fitting Algorithm.

The present study introduces a novel curve-fitting algorithm for surface plasmon resonance (SPR) curves using a self-constructed, wedge-shaped beam type angular interrogation SPR spectroscopy technique. Previous fitting approaches such as asymmetric and polynomial equations are still unsatisfactory for analyzing full SPR curves and their use is limited to determining the resonance angle. In the present study, we developed a sigmoid-asymmetric equation that provides excellent curve-fitting for the whole SPR curve over a range of incident angles, including regions of the critical angle and resonance angle. Regardless of the bulk fluid type (i.e., water and air), the present sigmoid-asymmetric fitting exhibited nearly perfect matching with a full SPR curve, whereas the asymmetric and polynomial curve fitting methods did not. Because the present curve-fitting sigmoid-asymmetric equation can determine the critical angle as well as the resonance angle, the undesired effect caused by the bulk fluid refractive index was excluded by subtracting the critical angle from the resonance angle in real time. In conclusion, the proposed sigmoid-asymmetric curve-fitting algorithm for SPR curves is widely applicable to various SPR measurements, while excluding the effect of bulk fluids on the sensing layer.

Beyond Interferometers Based on Silicon-Air Bragg Reflectors: Toward On-Chip Optical Microinstruments—A Review

In this paper, we review recent advances in optical microinstruments based on distributed Bragg reflectors (DBR) focusing mainly on two application areas: spectrometry and profilometry. For spectrometry applications, we consider state-of-the-art architectures. Among these are novel architectures of high-Q Fabry-Perot resonators based on cylindrical surfaces. In addition, we consider a microelectromechanical Michelson interferometer based on a robust (silicon-air) beam splitting interface. Its measurement principle relies on recording the spatial interferogram using movable mirror followed by inverse Fast Fourier transform (iFFT) to deduce the spectral content of the tested sample. For profilometry applications instead, an elaborated Michelson interferometer based on planar DBR is deployed for profile measurements using the technique of wavelength sweep and FFT to extract the dimensional characteristics. In the last section, we revisit the applications of DBR structures in optofluidics wherein a curved FP cavity has been deployed for optical trapping and binding of microparticles. Besides, a Michelson-based optofluidic probe has been deployed for off-chip measurements of fluid refractive index and absorbance. Globally, DBR based microinstruments demonstrate a strong potential in the targeted application areas.

Theoretical analysis of a Mach–Zehnder interferometer with a porous-film waveguide

Here we present a comprehensive theoretical study of a porous-film sensor of fluid in Mach–Zehnder configuration. It is found that the penetration of a fluid into the film pores causes amplitude and phase modulation of the interferometer output signal, maximizing the sensitivity at a certain value of the fluid refractive index. We define the Fisher information for this interferometer and show that it is a good measure of its sensitivity, hence suitable as an evaluation function in sensor optimization. We propose the sensor structure and design thin films that maximize its sensitivity to water, alcohol solutions and oils. The estimated sensitivity of the order of to the fluid refractive index and of to the changes in the film thickness indicate the potential of this sensor for applications in biomedicine, chemistry and environmental protection, and as a tool for the film characterization.

Photonic crystal‐based fluid sensors: Toward practical application

We present an uncomplicated and inexpensive system for refractive index measurements of fluids based on the optical properties of photonic crystals (PhCs). The photonic band gap of inverse opals depends on the refractive index contrast between the crystal and the pore fluid. A change of refractive index of the pore fluid causes variations in the photonic band gap which can be observed as change in the wavelength of reflected light of the crystal (color change). Based on this principle a measurement cell for continuous fluid measurements was build (see figure) and used for identification of water/ethanol mixtures. Based on photonic band structure simulations general rules/recommendations for the design of this sensor type are given, for example, periodicity of the inverse opal, choice of material (refractive index), or measurement mode. For the proof of concept tungsten oxide (WO3) inverse opal structure was utilized as sensing layer. However, depending on the application other metal oxides or even polymers can be used. With the presented method a limit of detection (LoD) of 0.001 refractive index unit (RIU) was achieved.The figure shows the cross section of the custom built measurement cell: the reflectivity of the WO3 inverse opal (round image, left) is measured by a spectrometer in dependence of the fluid in contact to the crystal. Different refractive indices of the fluids cause spectral shifts of the reflection peak (right graph).