Electrode polarization impedance in weak NaCl aqueous solutions

In this paper, we characterize the polarization impedance behavior of several common metals in diluted NaCl solution operated at low current densities. The objective was to provide a useful reference for those wishing to calculate the electrode polarization impedance in diluted NaCl solutions. Serial equivalent resistance (R) and capacitance (C) for silver, aluminum, gold, platinum, and medical stainless-steel were measured as a function of frequency (10(-2)-10(3) Hz) and NaCl concentration (2.4-77.0 mmol/L). The ratio of electrode polarization impedance with respect to the bulk resistance was calculated and plotted against concentration for each metal. Such a ratio shows the effect of the electrode polarization contribution as a function of electrolyte concentration when the bulk resistance of the solution changes. All metals showed a decrease of serial resistance Rp and capacitance Cp as a function of frequency. The medical stainless-steel electrode showed largest impedance values at lower frequencies compared to the other electrodes, and was concentration independent at all frequencies. Aluminum had smallest polarization impedance at low frequencies. Pure gold and platinum behaved similar with the exception that the serial resistance for gold showed a lower value at higher frequencies.     

脉冲电镀添加剂和氯离子对铜电极过程作用的电化学研究

文章采用正交实验以及在不同条件下电极的极化曲线、循环伏安曲线和电化学交流阻抗谱等电化学暂态技术,研究了酸性脉冲电镀专用添加剂S3、S4以及氯离子对铜电极的阴极极化和阳极行为的影响。     

A comparison of two- and four-electrode techniques to characterize blood impedance for the frequency range of 100 Hz to 100 MHz

Measurement setups that characterize the impedance of suspensions of blood over the wide frequency range of 100 Hz to 100 MHz are presented in this paper. The performance of the two- and four-electrode techniques have been compared and evaluated. By applying a combination of the two measurement techniques the best result is achieved when taking into account the main nonidealities, such as electrode polarization impedance and parasitic capacitances. It has been found that the conventional three-element model for the impedance of blood can be used for frequencies up to 1 MHz. For frequencies exceeding 1 MHz, an extended model is introduced where a constant phase angle element is used for modeling the cell membrane and a capacitor C(liq) is added for modeling the electrical capacitance of water in blood.     

Pt/YSZ电极结构形貌的表征

根据YSZ型氧传感器中O在电极表面的吸附、扩散以及Pt/YSZ界面O(Pt电极中)/O2(YSZ中)的传递的机理,提出了一种对Pt /YSZ电极界面进行定量表征的模型。用此模型对不同烧结温度下的电极形貌Pt/空气/ YSZ三相界面长度进行了定量表征,同时,采用复阻抗测试技术和氧传感器响应测试技术对表征结果的合理性进行了验证。理论推算和试验结果都表明:采用1 000℃,1 h烧结的电极形貌具有最佳的电化学性能。     

Spatial Resolution of Four Electrode Array

The in vivo measurement of specific impedance in brain tissue involves several technical aspects. The most stringent difficulties relate to electrode polarization and spatial resolution of the measuring system. The polarization is solved by usinga four electrode arrangement with a very high impedance preamplifier on the potential electrodes. This paper discusses the relative effectiveness of the various possible linear configurations of four electrodes in terms of spatial resolution. The accuracy of computed spatial resolution with respect to corresponding experimental ones is specified.     

Human Body Impedance for Electromagnetic Hazard Analysis in the VLF to MF Band

A knowledge of the average electrical impedance of the human body is essential for the analysis of electromagnetic hazards in the VLF to MF band. The purpose of our measurements was to determine the average body impedance of several human subjects as a function of frequency. Measurements were carried out with the subjects standing barefoot on a ground plane and touching various metal electrodes with the hand or index finger. The measured impedance includes the electrode polarization and skin impedances, spread impedance near the electrode, body impedance, stray capacitance between the body surface and ground, and inductance due to the body and grounding strap. These components are separated and simplifed equivalent circuits are presented for body impedance of humans exposed to free-space electromagnetic waves as well as in contact with large ungrounded metaltic objects therein.     

Adsorption and Direct Electron Transfer from Hemoglobin into a Three‐Dimensionally Ordered Macroporous Gold Film

Application of protein‐based, direct electron communication in bioelectronic devices, biosensors, or biofuel cells usually requires high stability and function density of the immobilized proteins or enzymes. Traditional methods have been used to increase the function density using multilayer immobilization techniques at the expense of losing stability and electron‐communication rate, that is, generally only protein molecules near the electrode surface are electroactive. In order to overcome the above problems, a three‐dimensional, ordered, macroporous gold film electrode is synthesized electrochemically by an inverted colloidal crystal template technique. The uniform, three‐dimensional macroporous gold provides superior conductivity, high stability, and large surface area. Its interconnected macroporous structure, containing gold nanoparticles, significantly enhances the amount of adsorbed hemoglobin (Hb) molecules at the monolayer level and also provides a good microenvironment for retaining the biological activity of the adsorbed protein, as confirmed by electrochemical and attenuated total reflection Fourier‐transform infrared spectroscopy. Therefore, direct electron transfer between the adsorbed Hb and the electrode is achieved. Adsorption of Hb on the macroporous gold film electrode is monitored using electrochemical impedance spectroscopy. The saturated adsorption amount, Γ, of the Hb is determined to be 6.55×10^–10 mol cm^–2 with a surface coverage of 88.1 %. The electrochemical behavior and the adsorption mechanism of Hb on the macroporous gold film electrode are discussed on the basis of the experimental results.     

一种透射型线-圆极化转换超表面的设计及应用

提出了一种单对角线开缝的方形单元构成的透射型极化旋转超表面,并将其应用于宽带圆极化微带缝隙天线的设计中。采用等效电路法分析了超表面实现线-圆极化转换的工作机制,并对天线圆极化带宽的影响因素进行了参数扫描。仿真结果表明:加载超表面使线极化微带缝隙天线产生了圆极化辐射;同时,扩展了天线的阻抗带宽。天线相对阻抗带宽达到了33.2%,3 dB轴比带宽达到了19.5%,在阻抗带宽内天线增益均高于6.8 dBi,证实了新型超表面结构具有良好的极化旋转特性。     

Hybrid Electrodes Used in Polymer Electro-Optic Modulator with Ultra-Broadband

Hybrid electrode combined coplanar waveguide (CPW) and microstrip lines in ultra-broadband electro-optic modulators. The characteristics of the modulators with hybrid electrode is like that of the modulator with the microstrip lines, in which the microstrip electrode is loaded above only one arm of Mach-Zehnder (M-Z) optical waveguide, besides the problem of microstrip line to coaxial transition and corona polarization in polymer modulators have been best solved at the same time. By using finite element method (FEM), the characteristic parameters such as half-wave voltage, modulation bandwidth characteristic impedance, effective microwave refractive index of polymer modulators with microstrip line and hybrid electrode are analysed and compared in this paper. The results present that velocity match, impendence match and lower microwave propagating loss is easily realized in modulators with hybrid electrode.     

CdZnTe晶体缺陷的交流阻抗谱研究

宽禁带II-VI族半导体化合物碲锌镉(CdZnTe)晶体是制备室温X和γ射线探测器的理想半导体材料,但其晶体缺陷特性对探测器性能有重要的影响,一直是人们研究的热点与难点。文中采用垂直布里奇曼法生长了CdZnTe晶锭,XRD测试表明晶片呈现(111)取向。通过测试样品不同温度下的交流阻抗谱,研究了晶体缺陷的阻抗特性。结果表明,制备的CdZnTe单晶具有负温度系数效应,化学法制备的Au电极与晶片之间形成了欧姆接触,没有出现电极界面和晶界对阻抗谱曲线影响,晶粒导电机制占主导。利用Arrhenius方程拟合曲线获得晶体缺陷的激活能为0.48 eV,表明晶体缺陷以Cd空位为主。     

一种新颖开槽切角圆极化微带天线单元的设计

为了简化方形切角圆极化微带天线单元的设计流程,提出了一种新颖的开槽切角圆极化微带天线单元形式。利用在微带天线单元上开矩形槽的方法,避免了调试切角圆极化单元的谐振频点和轴比时的反复迭代过程,缩短了调试时间。分析了矩形槽的不同宽度和深度对阻抗和轴比的影响,并通过仿真设计出一款性能良好的微带天线单元。单层微带天线单元仿真的最终阻抗相对带宽(S11 <-10 dB)为2. 05% (1. 980 ~ 2. 021 GHz);仿真的最终轴比相对带宽(AR<3 dB)为0. 50%(1. 995 ~2. 005 GHz)。加工了天线单元实物并进行测试,实测的阻抗相对带宽(S11 <-10 dB)为2. 05%(1. 975 ~2. 016 GHz);实测的轴比相对带宽(AR<3 dB)为0. 50% (1. 990 ~ 2. 000 GHz)。实测结果与仿真结果具有良好的一致性,验证了设计的正确性。     

基于铂黑的微针电极阵列表面修饰方法

由于微针电极阵列尖端直径小,空间分辨率高,可以记录单个神经元的放电活动,已成为神经信号记录的首选.但商用微针电极阵列的阻抗较高,降低电极阻抗有利于提高信噪比,改善记录信号质量.采用超声电镀铂黑的方法对微针电极表面进行修饰.测试结果表明铂黑修饰后的微针电极电化学性能优异,1 kHz处阻抗约为2.5 kΩ,相比裸金电极降低...     

Novel dry polymer foam electrodes for long-term EEG measurement

A novel dry foam-based electrode for long-term EEG measurement was proposed in this study. In general, the conventional wet electrodes are most frequently used for EEG measurement. However, they require skin preparation and conduction gels to reduce the skin-electrode contact impedance. The aforementioned procedures when wet electrodes were used usually make trouble to users easily. In order to overcome the aforesaid issues, a novel dry foam electrode, fabricated by electrically conductive polymer foam covered by a conductive fabric, was proposed. By using conductive fabric, which provides partly polarizable electric characteristic, our dry foam electrode exhibits both polarization and conductivity, and can be used to measure biopotentials without skin preparation and conduction gel. In addition, the foam substrate of our dry electrode allows a high geometric conformity between the electrode and irregular scalp surface to maintain low skin-electrode interface impedance, even under motion. The experimental results presented that the dry foam electrode performs better for long-term EEG measurement, and is practicable for daily life applications.     

An integral equation model for intracardiac electrogram sensing

The electrogram sensed by an intracardiac electrode has long been characterized based on two approaches: (1) presuming that the electrode is very small and does not disturb the potential prior to applying the electrode; and (2) taking an average of the prior potential over the electrode surface. In fact, any intracardiac sensing electrode has a finite surface area where electrical charges are induced and disturb the external potential field, thus, the sensed potential is different from the potential prior to placing the electrode. In this paper, an integral equation model is proposed based on the current continuity equation in a homogeneous myocardial medium. The new model can accurately characterize the electrogram sensed by an electrode with a nonnegligible surface area and a load impedance. The new model can be solved numerically via the method of moments to obtain the potential induced on the electrode surface by an arbitrary dipole volume source. As an application of the proposed theory, several electrode configurations with different loads have been analyzed with an intent to show that a finite electrode surface will significantly reduce the electrogram peak amplitude and slope, and a load impedance lower than 20 kΩ will also degrade the electrogram sensitivity     

Nonlinearity of cardiac pacemaker electrodes

Nonlinear properties of electrodes immersed in saline were studied in the time domain and frequency domain. Three electrode materials were tested: platinum-iridium, Elgiloy, and stainless steel. For time domain measurements, current pulses of 1.0 to 2.0 ms duration and varying amplitudes were applied to the electrodes. Frequency domain measurements of polarization impedance were made with an impedance bridge, utilizing sinusoidal currents of varying amplitudes at frequencies between 0.1 and 10 kHz.     

A New Interdigital Electrode Transducer Geometry

A new interdigital electrode transducer geometry has been conceived and its theoretical performance verified experimentally. The transducer is composed of sets of electrodes which are connected in series through an offset or "dog-leg" electrode, thereby significantly increasing the electrical impedance of the transducer over that of a conventional one having the same aperture. This transducer radiates and receives a uniform straight-crested wavefront. The transducer is shown to have unique impedance properties suited for wide-aperture surface-wave devices or those requiring some form of wave-amplitude weighting. Experiments have been conducted on YZ LiNbO/sub 3/ which verify that the terminal impedance of the transducer is proportional to the square of the number of equal-aperture constant-amplitude sections.     

Ultrasensitive Detection of Mitochondrial DNA Mutation by Graphene Oxide/DNA Hydrogel Electrode

Ultrasensitive detection of nucleic acid has attracted considerable attention recently in academic research and clinic diagnostics. Current approaches for DNA analysis involve complicated or expensive processes for labeling and often yield a high detection limit. In this study, a hydrogel electrode prepared from graphene oxide and fish sperm DNA is used for label?free mitochondrial DNA detection by impedimetric approach. The hydrogel has a bionic structure containing rich water and natural biomolecule fish sperm DNA that would benefit the adsorption and hybridization of DNA. Graphene oxide is a semiconductor and its conductivity can be improved by doping negatively charged DNA molecules. The result shows that the conductivity and impedance change of hydrogel electrode could be tuned by its length and component. The linear range for DNA detection by the optimized hydrogel is from 1.0 × 10^?9 to 1.0 × 10^?20 M with a detection limit of 1.0 × 10^?20 M. The result is ascribed to the bionic structure and tunable conductivity of hydrogel electrode. The hydrogel electrode has been used to detect the real DNA samples from patients of ovarian cancer with satisfactory results.     

Numerical computation of impedances of a human tooth for estimation of the root canal length

Alternative current (ac) current conduction through a human tooth has been investigated through numerical simulation. Numerical calculation of impedance between the file (electrode) inserted in the root canal of the tooth and the outer electrode enables investigation of the impedance method used in dentistry for evaluation of the root canal length. Simulations confirm the improved sensitivity of the impedance method using the results of multiple frequency measurements.     

Simulation of a phased-array antenna in waveguide

A method has been developed for simulating a large planar phased-array antenna in order to determine the performance of its radiating elements. By simple measurements of a few elements inside of waveguides, their performance in the antenna array as a function of frequency, scan angle, and polarization may be determined. The number of elements that need to be constructed is small, and the method is well-suited to economical, empirical design of an element for an array having a very large number of elements. For this purpose, such an array is well represented by the infinite array which results from imaging by the waveguide walls. Five waveguide simulators, sampling five significant combinations of scan angle and polarization, have been developed for a particular array comprising circular elements in a square arrangement. The array impedance has been measured in the simulators, and from these measurements the reflection loss of the array has been calculated. An equivalent circuit for the element in the array has been obtained from two simple waveguide-impedance measurements, and the active impedance of the elements has been determined therefrom. Finally, these results have been employed to determine the behavior of the elements when the array is excited for circular polarization; the departure from circularity of the radiated polarization, as well as the reflection in both senses of circular polarization, have been obtained.     

Dielectric,Impedance and Conduction Behavior of Double Perovskite Pr<Subscript>2</Subscript>CuTiO<Subscript>6</Subscript> Ceramics

Polycrystalline Pr₂CuTiO₆ (PCT) ceramics exhibits dielectric, impedance and modulus characteristics as a possible material for microelectronic devices. PCT was synthesized through the standard solid-state reaction method. The dielectric permittivity, impedance and electric modulus of PCT have been studied in a wide frequency (100 Hz–1 MHz) and temperature (303–593 K) range. Structural analysis of the compound revealed a monoclinic phase at room temperature. Complex impedance Cole–Cole plots are used to interpret the relaxation mechanism, and grain boundary contributions towards conductivity have been estimated. From electrical modulus formalism polarization and conductivity relaxation behavior in PCT have been discussed. Normalization of the imaginary part of impedance (Z″) and the normalized imaginary part of modulus (M″) indicates contributions from both long-range and localized relaxation effects. The grain boundary resistance along with their relaxation frequencies are plotted in the form of an Arrhenius plot with activation energy 0.45 eV and 0.46 eV, respectively. The ac conductivity mechanism has been discussed.