Analysis on the feasibility of optical tomography in measuring gas jet flow velocity

Enlightened by the wide application of optical computerized tomography (OCT) in various flow fields’ visualization and parameter measurement, the potential feasibility of it on measuring gas jet flow velocity is discussed in this paper. The dependence of flow velocity on flow field's refractive index and dynamic pressure is deduced initially. An argon gas jet flow is chosen as an example for experiment, and the refractive index measurement is achieved by moiré tomography, while the dynamic pressure is obtained by a pressure sensor. In a word, both the theoretical and experimental results prove that OCT could be feasible to obtain the flow velocity of gas jet flows.     

Flow field's temperature partition reconstruction based on its phase distribution

Aiming at the effect of species composition distribution on flow field's temperature reconstruction from the experimentally measured refractive index, a temperature partition reconstruction method based on flow field's phase distribution is proposed. Moiré deflection tomography is chosen to obtain the refractive index of a flame with probe wavelength of 808 nm. Enlightened by the visual characteristic of optical computerized tomography (OCT) for flow field and the practical structure of the flame, it is divided into three regions in radial direction based on its phase distribution. The essence is that the temperature is reconstructed with adopting different species composition for different regions. Finally, the rationality of the method is analyzed.     

Plasma polymerization of styrene with carbon dioxide under glow discharge conditions

Plasma polymerization gains increasing interest for the deposition of films with functional properties suitable for a wide range of modern applications on account of its advantageous features. In this study, carbon dioxide (CO₂) was chosen as carrier gas at flow rates of 30 and 60 sccm, respectively and styrene vapor was used as the monomer to prepare polystyrene films on glass substrates. The structure and composition of the plasma polymerized films were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and compared with the film prepared by conventional thermal polymerization. The morphology information of the films was provided by optical microscopy. XPS and FT-IR results reveal that chemical composition of the plasma polymerized films is different from that of the thermal polymerized film and that oxygen content in the plasma polymerized films increases with the flow rate of CO₂. Furthermore, the presence of oxygen-containing groups on the surface of plasma polymerized polystyrene films is confirmed. It is also found that the composition and morphology of the plasma polymerized films are controlled by the flow rate of CO₂.     

Theory and analysis of phase sensitivity-tunable optical sensor based on total internal reflection

This study presents a theory of a phase sensitivity-tunable optical sensor based on total-internal reflection (TIR). This investigation attempts to design a phase sensitivity-tunable optical sensor consisting of an isosceles right-angle prism, some quarter- and half-wave plates, and a Mach-Zehnder interferometer. When the azimuth angles of the quarter-wave plates are chosen properly, the final phase difference of the two interference signals are associated with the azimuth angle of the fast axis of the half-wave plates, thus creating the controllable phase sensitivity. Numerical analysis demonstrates that the high phase measuring sensitivity and the small measuring range, and the low phase measuring sensitivity and the wide measuring range can be performed by selecting the suitable azimuth angle of the half-wave plates. The feasibility of the measuring method was demonstrated by the experiment results. The sensor could be applied in various fields, such as chemical, biological, biochemical sensing, and precision machinery measurement.     

Integrating moiré and emission tomography to visualize and diagnose high-temperature flow fields

In this Letter, moiré and emission tomography are integrated to visualize and diagnose high-temperature flow fields, and a jet flame is chosen as a practical example for experiment. The refractive index and intensity distributions are simultaneously obtained by moiré and emission tomography, respectively. Based on the intensity distribution, the structure of the jet flame is well visualized, so that the spatial distribution of species composition can be considered in the temperature reconstruction process. Finally, the refractive index and intensity distributions are matched, and a partition model is adopted to reconstruct the temperature distribution of the jet flame.     

单极性带电粒子浓度测试方法的研究

提出一种新型球形传感器探测仪，在不同风速、不同激励场强以及不同测试点的情况下对大气压下电晕放电形式产生的带电粒子浓度进行了测量，并分析了等离子体的空间分布情况，同时与DLY型空气离子测量仪的测试结果进行比较. 实验结果表明，球形探测仪对带电粒子浓度的测试结果较为理想，同时，设备操作简单，占用空间小，便于局部定点测量，为研究等离子体的空间分布提供了条件. 关键词： 等离子体 带电粒子浓度 强电场电离放电 大气压     

Temperature's optical tomography diagnosis of arc plasma jet flowing into air

An argon arc jet plasma flowing into air is chosen as a practical example to study the multiple species jet plasma's optical computerized tomography (OCT) diagnosis. The refractive index models of the pure argon and the multiple species arc plasmas are supplied. On the basis of which, the temperature reconstruction model of the multiple species arc plasma is further derived. By theoretical calculation, the effect of mixed air on the refractive index is given. For the sake of better proving the effect of directly omitting the mixed air on flow field's temperature reconstruction from the refractive index, a simulated experiment is supplied. Finally, the condition, which can be adopted to estimate that whether the pure argon arc plasma refractive index model still can be used as the temperature reconstruction model of the argon arc plasma jet flowing into air, is proposed.     

Measurement of crater geometries after laser ablation of bone tissue with optical coherence tomography

The feasibility of measuring crater geometries by use of optical coherence tomography (OCT) is examined. Bovine shank bone on a motorized translation stage with a motion velocity of 3 mm/s is ablated with a pulsed CO2 laser in vitro. The laser pulse repetition rate is 60 Hz and the spot size on the tissue surface is 0.5 mm. Crater geometries are evaluated immediately by both OCT and histology methods after laser irradiation. The results reveal that OCT is capable of measuring crater geometries rapidly and noninvasively as compared to histology. There are good correlation and agreement between crater depth estimates obtained by two techniques, whereas there exists distinct difference between crater width estimates when the carbonization at the sides of craters is not removed.     

激光诱导击穿光谱技术在气体检测中的研究综述

随着工业技术的发展,气体检测领域对在线检测仪器及检测技术的要求越来越高,气体成分在气体流动时会发生复杂变化,通常的检测手段傅里叶变换红外光谱技术（FTIR）、光腔衰荡技术（CRDS）、电化学传感等往往不能满足检测要求或仅对局部区域检测。激光诱导击穿光谱（LIBS）作为一种新兴的原子发射光谱分析技术,得到光谱分析领域研究者的广泛重视与研究。LIBS技术具备多元素同时检测、非侵入式、实时在线以及无需样品特殊制备等技术优势,已应用于固体、液体和气体的检测。在环境恶劣、干扰较大的气体制造及检测领域LIBS技术能够实时准确地进行检测。介绍了LIBS技术基本原理并描述等离子体物理特性的两个参数等离子体温度及等离子体电子数密度,针对LIBS技术在气体检测领域中的应用,从通过原子谱线强度比分析燃料的当量比、燃料混合气燃烧产物的气体组分、工业制造中作为保护气的氮气及稀有气体、温室气体和新能源气体的检测,以及与之相关的LIBS实验装置及实验方法的改进与优化等6个方面介绍了LIBS技术应用于气体检测领域的近些年国内外进展。对气体检测领域激光诱导击穿光谱研究的前景进行了展望。     

Optical coherence tomography based particle image velocimetry (OCT-PIV) of polymer flows

The measurement of spatially resolved velocity distributions is crucial for modelling flow and for understanding properties of materials produced in extrusion processes. Traditional methods for flow visualization such as particle image velocimetry (PIV) rely on optically transparent media and cannot be applied to turbid polymer melts. Here we present optical coherence tomography as an imaging technique for PIV data processing that allows for measuring a sequence of time resolved images even in turbid media. Time-resolved OCT images of a glass-fibre polymer compound were acquired during an extrusion process in a slit die. The images are post-processed by ensemble cross-correlation to calculate spatially resolved velocity vector fields. The results compared well with velocity data obtained by Doppler-OCT. Overall, this new technique (OCT-PIV) represents an important extension of PIV to turbid materials by the use of OCT.     

Investigation of a nonstationary flow field generated by a dielectric barrier discharge

The search for ways of controlling a flow over flight vehicles is today an extremely topical issue, since the limiting capabilities of standard control methods are the bulk of the progress of space technology. A promising technique in this respect is the application of activators using a low-temperature plasma. Specifically, these electrogasdynamic devices can directly convert electrical energy to a mechanical action on the flow. An activator based on a dielectric barrier discharge is considered. The nonstationary behavior of the activator is studied by measuring the electrodynamic parameters of the discharge and also by measuring induced velocity fields with particle image velocimetry. The instantaneous and integral parameters of the gas acceleration stage are found, and the efficiency of the activator is determined.     

Intraluminal fiber-optic Doppler imaging catheter for structural and functional optical coherence tomography

We describe a miniature fiber-optic Doppler imaging catheter for integrated functional and structural optical coherence tomography (OCT) imaging. The Doppler catheter can map blood flow within a vessel as well as image vessel wall structures. A prototype Doppler catheter has been developed and demonstrated for measuring the intraluminal velocity profile in a vessel phantom (conduit). A simple mathematical model is demonstrated to estimate the total flow rate. This estimation technique also enables the spatial range of flow measurements to be extended by approximately two times the normal OCT image-penetration depth. The Doppler OCT catheter could be a powerful device for cardiovascular imaging.     

Small-size spectrometer for emission analysis of low-temperature plasma flows

Calculation data for characteristics of concave holographic arrays are reported, allowing development of low-size spectrometers with medium and high spectral resolution. The holographic arrays were fabricated around new subnanostructured films of chalcogenide semiconductors. A medium-resolution, small-size spectrometer was used to measure the distribution of temperature in the gas flow emanating from a DC plasmatorch with sectioned inter-electrode insert by the relative-intensity method. Presently available methods for measuring the temperature of non-uniform optically thin plasma were employed. A comparison of spectral and thermophysical methods for temperature measurements is given.     

Simulation of nanoparticle coagulation in radio-frequency capacitively coupled C_2H_2 discharges

A self-consistent fluid model is employed to investigate the coagulation stage of nanoparticle formation, growth,charging, and transport in a radio-frequency capacitively coupled parallel-plate acetylene(C2H2) discharge. In our simulation, the distribution of neutral species across the electrode gap is determined by mass continuity, momentum balance, and energy balance equations. Since a thermal gradient in the gas temperature induced by the flow of the neutral gas, a careful study of the thermophoretic force on the spatial distribution of the nanoparticle density profiles is indispensable. In the present paper, we mainly focus on the influences of the gas flow rate, voltage, and gas pressure on the spatial distribution of the nanoparticle density. It appears that the resulting density profile of the 10-nm particles experiences a significant shift towards the upper showerhead electrode once the neutral equations are applied, and a serious shift is observed when increasing the gas flow rate. Thus, the flow of neutral gas can strongly influence the spatial distribution of the particles in the plasma.     

Simple technique for measurement of energy spectra of ions from laser produced plasma

Old absorption technique is revived for measuring the energy spectra of ions arising from laser generated plasma. The technique suggested relies on implantation of produced ions into a light element target situated close to the ion production site. Then the ion energy spectra are reconstructed from the depth profile of the implanted ions measured by some of the common depth profiling techniques such as RBS or SIMS. Theoretical range vs. ion energy relations are used for this purpose. In this study the principles of the method are explained and its capabilities are assessed. The feasibility of the method is demonstrated on the energy spectra of Ta ions arising from the laser generated plasma.     

Investigations of Droplet‐Plasma Interaction using Multi‐Dimensional Coupled Model

Recently developed multi‐dimensional coupled fluid‐droplet model is used to investigate the behavior of complex interaction between the liquid precursor droplets and atmospheric pressure plasma (APP). The significance of this droplet‐plasma interaction is not well understood under diverse realm of working conditions in two‐phase flow. In this study, we explain the implication of vaporization of liquid droplets in APP which are subsequently responsible to control major characteristics of surface coating depositions. Coalescence of water droplets is more dominant than Hexamethyldisiloxane (HMDSO) droplets because of its sluggish rate of evaporation. A disparity in the performance of evaporation is identified in two independent mediums, such as gas mixture and discharge plasma using HMDSO precursor. The length of evaporation of droplets is amplified by an increment of gas flow rate indicating with a reduction in the gas temperature and electron mean energy. In particular, the spatio‐temporal density distributions of charged particles show a clear pattern in which the typical nitrogen impurity ions are primarily effective as compared to other helium ionic species along the pulse of droplets in APP. Finally, we contrast the behavior of discharge species in the pure helium and He‐N2 gas mixtures revealing the importance of stepwise and Penning ionization processes. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of Bubbly Flow by Ultrasonic Tomography

Computerized tomography (CT) means reconstruction of pictures from projections taken at different angles. This method is well known in fields such as medical diagnostics and nondestructive testing. The application of CT to gas/liquid flow measurement results in a non-intrusive method for measuring the spatial distribution of the gas phase in a cross-section of the flow. In our application the projection data are obtained from measurement of the extinction along a set of ultrasonic rays in this cross-section, using piezo-ceramic ultrasonic transducers. The transducers are arranged in a circular sensor array which is directly integrated in the pipe wall of the flow; instead of mechanical rotation, the sensors are sequentially switched.     

Zur Diagnostik der Ionenkomponente im Plasma der äußeren positiven Säule einer stromstarken,unmagnetisierten Argon-Hohlkatodenbogenentladung

This paper reviews two measuring methods of the ions and their results in low pressure plasmas, if spectroscopical methods are not applicable to this situation. The behaviour of ions in the positive column of a high current argon hollow cathode arc was studied in dependence of various plasma parameters with the help of a gridded probe and a quadrupole mass spectrometer. The obtained results were analysed with simple theoretical models and measured electron distribution functions.     

Numerical analysis of nitrogen-mixed argon plasma characteristicsand injected particle behavior in an ICP torch for ultrafine powdersynthesis

A numerical model is presented for the analysis of plasma characteristics of an ICP torch and gas mixing effects on the plasma when a nitrogen gas is added into the argon plasma as a carrier or sheath gas at the torch inlet, The fluid equations describing the plasma flow and temperature fields and the diffusions between two different gases are solved along with a magnetic vector potential equation for electromagnetic fields. The trajectory and the temperature change with time for a particle injected into the plasma are also investigated by a plasma-particle interaction model to find out optimum injection conditions for the synthesis of ultrafine nitride ceramic powders, It is found from the calculations that the nitrogen-mixed argon plasma with a nitrogen sheath gas is more favorable than the plasma with a nitrogen carrier gas for the reaction kinetics of nitride synthesis. It is also found that the radial injection through the holes of the tube wall Is preferable to the axial injection at the torch inlet for the complete evaporation of injected particle and the effective chemical reaction of reactant vapor with nitrogen. For the radial injection in an ICP torch of 20 cm in axial length, the optimum injection locations and initial velocities of 50 μm aluminum particles are found for synthesizing aluminum nitride are in the range of 6~12 cm apart from the torch inlet and over 15 m/s, respectively