Determination of Thickness of Silver Coatings on Brass by Measuring the Impedance of a Thin Elliptic Coil

To measure the impedance of a thin elliptically shaped coil, in presence of a flat plate with a coat of metal, can be an instrument for determination of the cladding thickness. An electromagnetic field from the coil is then forced to the object, producing eddy currents inside the object. These are influenced by the characteristics of the object and the coil and give rise to an impedance change, which can be detected and correlated to the thickness of the coating. An electromagnetic model accounting for the impedance of the elliptic coil with different values on the numerical eccentricity and the coating thickness is described. The model is based on a dyadic Green function formulation of the problem from which the electric field and hence the impedance is evaluated by utilizing the method of scattering super position. Numerical calculations based on the model and experimental measurements have been taken. An example shows how the model can be used to model a brass surface with a coat of silver to find expected impedance as function of the coating thickness     

Coupling-of-modes analysis and modeling of polymer-coated surface acoustic wave resonators for chemical sensors

The analysis and modeling of SAW resonator devices based on the coupling-of-modes (COM) theory are described, integrating the effect of polymer coating so that the sensor effects can be accounted for in the device transfer function. Based on the perturbation method, the effects of film coating are included in determining the parameters for the model. The COM parameters are, therefore, modified and its simple analytical approaches are presented. The model is validated using the experimental data of a two-port SAW resonator device fabricated on ST-X quartz substrate. The experimental results for a device coated with Parylene C are compared with the simulation results of the proposed model. The comparative results of the electrical characteristics and the frequency sensitivity to film thickness show a good agreement which proves the validity of the model. This analysis and model will provide insight into the influence of the device design parameters on the sensor performance and help in practical design and optimization of SAW-based chemical sensor systems.     

NOSER: An algorithm for solving the inverse conductivity problem

The inverse conductivity problem is the mathematical problem that must be solved in order for electrical impedance tomography systems to be able to make images. Here we show how this inverse conductivity problem is related to a number of other inverse problem. We then explain the workings of an algorithm that we have used to make images from electrical impedance data measured on the boundary of a circle in two dimensions. This algorithm is based on the method of least squares. It takes one step of a Newton's method, using a constant conductivity as an initial guess. Most of the calculations can therefore be done analytically. The resulting code is named NOSER, for Newton's One-Step Error Reconstructor. It provides a reconstruction with 496 degrees of freedom. The code does not reproduce the conductivity accurately (unless it differs very little from a constant), but it yields useful images. This is illustrated by images reconstructed from numerical and experimental data, including data from a human chest.     

Scaling Analysis of Conductivity-Related Quantities of YBCO Using Ac Loss Peak Temperature as Scaling Parameter

The ac response of polycrystalline YBCO sample in the frequency range 10–2500 kHz has been measured by using a contactless method. For this purpose, two parameters S(ω,T) and S′(ω,T) have been derived from the measured impedance of the system. The parameters S(ω,T) and S′(ω,T) are related to the real and imaginary parts of ac conductivity, respectively. Both the real and the imaginary parts of ac conductivity show frequency-dependent nature. All the observed features have been interpreted by considering the flux flow losses. Due to the flux penetration, S(ω,T) exhibits a peak below the transition temperature (T _C ), which could be explained on the basis of Anderson’s thermally activated flux creep model. Finally, we have applied a model-independent scaling technique to scale all the measured data and obtained the scaling functions by curve fitting method. The same scaling analysis has been found to be also useful for ac susceptibility data.     

Impacts of atomistic coating on thermal conductivity of germanium nanowires

By using nonequilibrium molecular dynamics simulations, we demonstrated that thermal conductivity of germanium nanowires can be reduced more than 25% at room temperature by atomistic coating. There is a critical coating thickness beyond which thermal conductivity of the coated nanowire is larger than that of the host nanowire. The diameter-dependent critical coating thickness and minimum thermal conductivity are explored. Moreover, we found that interface roughness can induce further reduction of thermal conductivity in coated nanowires. From the vibrational eigenmode analysis, it is found that coating induces localization for low-frequency phonons, while interface roughness localizes the high-frequency phonons. Our results provide an available approach to tune thermal conductivity of nanowires by atomic layer coating.     

Eddy current nondestructive testing by a perturbation method

This paper presents an analytical solution for the change in impedance due to a flaw of rectangular cross-section in the case when the conductivity of the flaw is sufficiently close to the conductivity of the surrounding medium. The solution, which is found by the small perturbation method, is used to compute the impedance change as a function of the parameters of the flaw. An eddy current nondestructive method based on this consideration can detect the presence of such flaws and, in some cases, determine their size.     

Effect of coatings on the distribution of heat in bar-disk tribosystems

We develop an analytic method for the evaluation of the surface temperature and the coefficient of distribution of heat in a tribosystem formed by an immobile bar and a rapidly rotating disk with coating. The analysis of numerical results demonstrates that surface temperature increases with the thickness of the coatings if the thermal conductivity of the coating is lower than the thermal conductivity of the disk. For coatings of fixed thickness, surface temperature decreases as the angular velocity increases. We also study the dependences of the coefficient of distribution of heat between the bodies on their geometric parameters and thermal properties. Franko L'viv University, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 3, pp. 43–49, May–June, 1997.     

Estimation of the average residual reflectance of broadband antireflection coatings

We deal with optimal two-material antireflection (AR) coatings for the visible and adjacent spectral regions. It has been shown before that, for a given set of input parameters (refractive indices of the substrate, ambient medium and high- and low-index coating materials, and for a given spectral width of the AR coating), such designs consist of one or more clusters of layers of approximately constant optical thickness and number of layers. We show that, through the analysis of many different optimal coatings, it is possible to derive two parameters for a simple empirical expression that relates the residual average reflectance in the AR region to the number of clusters. These parameters are given for all possible combinations of relative spectral bandwidth equal to 2, 3, and 4; low-index to ambient-medium index ratio equal to 1.38 and 1.45; and high-to-low index ratio equal to 1.4, 1.5, and 1.7. The agreement between the numerically and the empirically calculated values of residual average reflectance is excellent. From the information presented the optical thin-film designer can quickly calculate the required number of layers and the overall optical thickness of an AR coating having the desired achievable residual average reflectance.     

基于EIS研究镁水泥混凝土中涂层钢筋的耐腐蚀性

通过模拟室内自然状态、氯化镁溶液和水三种工作环境,采用CS350电化学工作站,结合理论与试验分析,对镁水泥混凝土涂层钢筋的交流阻抗谱进行研究。结果表明:通过对交流阻抗谱和涂层电阻的表征分析得出该涂层可以很好地保护镁水泥混凝土中的钢筋免受腐蚀。不同的混凝土保护层厚度对同时期的涂层电阻有一定的影响,涂层电阻的大小随保护层厚度增加而增加。从而得出该涂层对镁水泥钢筋混凝土中的钢筋起到很好的保护作用,进而解决镁水泥钢筋混凝土在盐渍土地区应用易受侵蚀的问题。     

吸波材料优化匹配的理论分析

为了研究电磁参数和涂层的厚度对单/双层吸波材料的吸收性能的影响,以期制备出具有良好的电磁匹配特征的吸波材料,利用通过单/双层吸波涂层内电磁波传播的理论机制,计算机模拟技术,分析了涂层厚度、电磁参数及频率变化对材料的电磁波吸收性能影响的规律.同时提出了双层吸波材料设计中厚度匹配和阻抗匹配等基本原则.结果显示,随着厚度的增加,吸波材料对电磁波的吸收峰向低频移动,并且相继出现多个吸收峰.当电磁匹配常数M=0.25时,涂层材料展现了很好的吸波性能.对于双层吸波材料,阻抗渐变原则和厚度匹配规律直接影响到其吸收性能.     

Life Prediction of Thin Organic Films by a Combination of Digital Shearography and Electrochemical Impedance Spectroscopy

A critical (steady state) value of the conductivity of different organic coatings was determined by a combination of digital shearography and electrochemical impedance spectroscopy (EIS). The behavior of organic coatings, i.e., ACE premium-gray enamel, white enamel, beige enamel (spray coatings), a yellow acrylic lacquer, and a gold nail polish on a metallic alloy, i.e., a carbon steel, was investigated over a temperature range of 20–60 °C. The value of the conductivity of coatings was determined by correlating the in-plan displacement of the coating (by shearography over a temperature range 20–60 °C) and the value of the alternating current impedance of the coating by EIS in 3% NaCl solution. The integrity of the coatings with respect to time was assessed by comparing the measured value of conductivity to the critical (steady state) or asymptotic value of conductivity. In other words, by shearography, measurement of coating properties could be performed independent of parameters such as UV exposure, humidity, presence of chemical species, and other parameters which may normally interfere with conventional methods of the assessing of the integrity of coatings. Therefore, one may measure the conductivity of coatings, regardless of the history of the coating, in order to assess the integrity of coatings. Also, the obtained shearography data were found to be in a reasonable trend with the data of EIS in 3% NaCl solution.     

石墨烯涂层对直升机旋翼防/除冰组件传热的影响

采用水性和油性石墨烯涂层对复合材料防/除冰组件进行测温及防/除冰实验.针对直升机旋翼对结冰的敏感等特点,提出了旋翼防/除冰组件包铁表面涂覆石墨烯涂层改性传热性能的方法,从而提高旋翼防/除冰组件除冰效率.为验证石墨烯涂层对防/除冰组件传热效率具有显著的提高作用,采用搭建的除冰实验平台并对涂覆的旋翼防/除冰组件进行传热实验...     

Analytical solutions in eddy current testing of layered metals withcontinuous conductivity profiles

In this paper exact analytical expressions for the impedance of a cylindrical air-core coil above a layered metal structure whose conductivity varies continuously with depth are presented. Although the model is general, attention is focused on three conductivity profiles: the linear, the quadratic and the exponential. The derived expressions for the impedance change for each profile could provide a useful tool for the solution of the inverse problem: that of determining the conductivity from variable frequency measurements of the impedance. Furthermore, the obtained final formulas contain elegant mathematical functions and show a substantially higher computational efficiency with respect to existing methods     

Estimation of mixing parameters for cancellation of discretized eddy current signals using time and frequency domain techniques

In this paper, we present two methods for estimating the mixing parameters used in scaling, rotating, and time shifting discrete time eddy current impedance plane trajectories in order to suppress unwanted support plate signals. One method operates directly on the time signals. The other method operates on the frequency domain representation of these signals and consequently is computationally more involved. Both methods require the minimization of a functional which measures the energy difference between the horizontal and vertical components of the high and low frequency data. Three illustrative examples are presented, and it is shown that the use of the frequency domain method is justified if the data are corrupted with random noise as well as with unknown multisample time shifts.     

Independent electromagnetic optimization of the two coating thicknesses of a dielectric layer on the facets of an echelle grating in Littrow mount

Abstract

Electromagnetic investigations using the integral equation system method with parametrization (IESMP) show that the two-coating thicknesses of a dielectric layer on the facets of an echelle grating in a Littrow mount have to be independently optimized. While the optimal coating thickness on the blaze facet is the same for maximal efficiency and minimal absorption in both polarizations, this is not the case for the anti-blaze facet. Therefore, it is only possible to optimize the two-coating thicknesses for one of the purposes. On the blaze facet, a simple formula based on thin-film optical considerations describes the optimal thickness very well. Additionally, we found that resonance anomalies can significantly reduce efficiency if the wrong coating thickness is used on the anti-blaze facet. The coating thickness creating the resonance anomaly can be deduced by investigating the poles of the reflection coefficient of a dielectric coated metallic mirror in grazing incidence. This value can be used to optimize the layer for maximal efficiency. Consequently, we are generally able to describe the optimal coating thicknesses for minimal absorption as well as for maximum efficiency in both, TE- and TM-polarization, using only thin-film optical considerations without any further rigorous calculation.     

等离子喷涂-物理气相沉积制备7YSZ热障涂层及其热导率研究

通过等离子喷涂-物理气相沉积(PS-PVD)技术在3种不同工艺参数下制备7YSZ热障涂层。采用XRD和SEM分析涂层的相结构和微观组织,利用激光脉冲法测量涂层不同温度下的热导率。结果表明:通过调整工艺参数中电流的大小和等离子气体成分,可以制备截面呈柱状、致密层状和柱-颗粒状混合组织结构,表面呈"菜花"状或起伏的多峰状的YSZ热障涂层。涂层的相结构由粉末的单斜相氧化锆(m-ZrO_2)转变为涂层中的四方相氧化锆(t-ZrO_2),并保留至室温。在700~1100℃时,YSZ涂层的热导率随着温度的升高而增大。柱状晶结构涂层因具有较大的孔隙率,可以有效降低涂层的热导率,其热导率为1.0~1.2W·m~(-1)·K~(-1);而层状结构涂层由于比较致密,其热导率相对较高。     

Influence of synthesis methodology on the ionic transport properties of BaSnF4

The high performance fluoride ion conductor BaSnF₄ has been prepared by a simple precipitation in addition to both solid state reaction and mechanochemical synthesis techniques. XRD results indicate that the material BaSnF₄ obtained by all the methods crystallizes with the same tetragonal structure (P₄/nmm). The crystallite size and morphology of the BaSnF₄ particles determined by XRD and FE-SEM show a variation with respect to different methods of preparation. The transport properties of BaSnF₄ have been investigated by impedance spectroscopy and the results show that the conductivity values are closely related to the crystallite size and micro-strain. The transport number measurement and NMR studies further confirm that the increase in conductivity is due to fluoride ions. The scaling result of complex impedance plots shows that the dynamical process occurring at various frequencies are independent of temperature.     

Spin-current-driven thermoelectric coating

Energy harvesting technologies, which generate electricity from environmental energy, have been attracting great interest because of their potential to power ubiquitously deployed sensor networks and mobile electronics. Of these technologies, thermoelectric (TE) conversion is a particularly promising candidate, because it can directly generate electricity from the thermal energy that is available in various places. Here we show a novel TE concept based on the spin Seebeck effect, called 'spin-thermoelectric (STE) coating', which is characterized by a simple film structure, convenient scaling capability, and easy fabrication. The STE coating, with a 60-nm-thick bismuth-substituted yttrium iron garnet (Bi:YIG) film, is applied by means of a highly efficient process on a non-magnetic substrate. Notably, spin-current-driven TE conversion is successfully demonstrated under a temperature gradient perpendicular to such an ultrathin STE-coating layer (amounting to only 0.01% of the total sample thickness). We also show that the STE coating is applicable even on glass surfaces with amorphous structures. Such a versatile implementation of the TE function may pave the way for novel applications making full use of omnipresent heat.     

Solving the Inverse Heat Conduction Problem in Using Long Square Pulse Thermography to Estimate Coating Thickness by Using SVR Models Based on Restored Pseudo Heat Flux (RPHF) In-Plane Profile

This research develops a method to estimate opaque coating thickness based on time-and-space-resolved thermography. Thermography is a viable technique for measuring coating thickness. However, time-resolved thermography becomes unreliable when uncontrolled constant thermal stimulation amplitude appears. Therefore, a time- and space-resolved thermography technique for coating thickness measurement called restored pseudo heat flux (RPHF) has been developed by using Fourier–Hankel transform. A non-dimensional analysis was conducted and the results show RPHF curves with different coating thicknesses converging as the thermal diffusivity ratio or thermal conductivity ratio goes to one. For large thermal conductivity ratio values, the RPHF curves have two inflection points along the non-dimensional radius. Fifty-nine samples were tested using the proposed method. Support vector regression (SVR) models were constructed with the in-plane distribution of RPHF and the temporal distribution of the measured surface temperature as inputs. To avoid overfitting, cross validation was applied to all the models. Later, another twenty-eight samples were tested to validate the SVR models. The results suggest that a support vector regression model with in-plane profiles of RPHF handles uncontrolled heat flux variation better and yields a better performance in coating thickness measurement than the temporal profile does. With in-plane RPHF profile as input, the SVR model can evaluate coating thickness with a relative root mean square error at 25.3% even when heat amplitude varies 50%.     

The Reflected Impedance of a Circular Coil in the Proximity of a Semi-Infinite Medium

Most analyses on a circular coil when used in the eddy current method for nondestructive testing are empirical. Theories based on simple models are often inadequate to account for some experimental observations when the spacing between the coil and the material became small. In the present paper this problem is formulated as a boundary value problem. Wave equations of the magnetic vector potential are solved. The change in the coil impedance, when placed above a semi-infinite medium, is obtained by means of the induced voltage method, which is shown to depend only on the ? component of the magnetic vector potential. This change in impedance is found to be dependent on a number of factors: the shape and size of the coil; the spacing between the coil and the metal; the thickness, conductivity, and composition of the material, etc. Numerical computations are discussed for a few selected materials in connection with experimental results obtained elsewhere. The comparison made lent support to the present analysis. Extension of this method to the case of a stratified media is included.