Four-electrode Probe Research Articles

A simple control and high accuracy measurement method of open-cell four-electrode conductivity electrode

The paper presents a simple control and high-accuracy measurement method for a four-electrode conductivity probe based on the principle of the bi-directional voltage pulse. The two-way differential AC (alternating current) pulse voltage signal for the reference resistance and solution resistance is modulated into the single DC stationary voltage response signal to drop the demand for software and hardware and effectively eliminate the influence of excitation voltage pulse amplitude on measurement accuracy, and then the synchronous rectification DC measurement is proposed without any control timing. Meanwhile, the mathematical expression between the single output DC voltage signal and the solution conductivity is given. The test results in the laboratory and in the field indicate that the relative error of the conductivity measurement is within 2.5% in a conductance range of 10 uS/cm to 200 mS/cm, and the proposed measurement method has a good application prospect in application.

Relationship Between the Conductivity of Human Blood and Blood Counts

Achieving a better characterization of human blood conductivity is of high relevance for medical applications. In this study we measured the complex impedance of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> = 10 human whole blood samples (from <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> = 10 oncology patients) at room temperature ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> = 22.6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm\; 0.8\;^\circ \mathrm{C}$</tex-math></inline-formula> ) and at body temperature ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> = 36.6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm\; 0.4\;^\circ \mathrm{C}$</tex-math></inline-formula> ). The complex impedance was measured using the measurement setup consisting of a custom made four-electrode probe and a commercially available galvanostat. The measured complex impedance data were used to calculate the conductivity of whole blood over the 631 Hz–100 kHz frequency range. The calculated conductivity data is presented and was compared with the literature data. The data from our study is in good agreement with the data available in the literature. Additionally, full blood counts were provided for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> = 8 samples and Pearson correlation coefficient was calculated between the conductivity and blood counts at different frequencies. The three blood count parameters with the highest correlation coefficient are haematocrit (Hct), haemoglobin (Hgb) and red cell count (RBC). The correlation coefficient was shown to decrease as the frequency increases and was the highest at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> = 631 Hz, which is the lowest reported frequency. To our knowledge this is the first study to measure low-frequency (i.e. below 1 MHz) conductivity of whole human blood at body temperature using the four-electrode technique. The results of this study represent an important contribution to the literature, which is currently limited in this area and will help further medical device design.

Four-electrode probe for plasma studies in the GOL-NB multiple-mirror trap

A system of four-electrode Langmuir probes developed for the GOL-NB multiple-mirror trap is discussed. The system is used for studies of a low-temperature start plasma (1019–1020 m-3, 5 eV) that fills the device during the initial phase of the experiment. The probe allows simultaneous measurements of plasma density, electron temperature and radial electric field. The accuracy of the probe measurements is also discussed.

Performance Evaluation of Multiple Electrodes Based Electrical Impedance Spectroscopic Probe for Screening of Cervical Intraepithelial Neoplasia

As regular cervical cancer screening becomes more common, the detection of cervical intraepithelial neoplasia (CIN) is increasing. We proposed a noninvasive and low-cost multi-channel electrical impedance spectroscopy (EIS) and probe with multiple active electrodes for screening CIN. Compared with four-electrode probes for impedance spectroscopy, the multiple active electrodes facilitated more flexible combination of current injection and voltage measurement, which allowed well-designed measurement protocols for focused sensitivity underneath the large size of the probe. Furthermore, the multiple active electrodes reduced the negative effects of the cabling between the system and probe inserted into the cervix. After presenting the basic performance, the EIS probe was tested by three different experimental phantoms using four different materials of electrical properties. The corresponding experimental results were presented to prove the functionality of the EIS probe and characterize the electrical properties at a wide range of frequencies from 0.625 to 100 kHz. It had high sensitivity underneath the surface of the probe and a rapidly decreased outer. Furthermore, we verified the frequency-dependent impedance changes using the giant vesicle phantoms with different amounts of extra- and intra-fluids separated by the insulating membranes. This study facilitates the feasibility into clinical practice for identifying CIN in the future.

Autonomous Electrolyte Discovery for Batteries with Experimentally Informed Bayesian Optimization

An autonomous battery electrolyte experimental platform capable of mixing multi-component electrolyte systems and characterizing the transport and electrochemical properties in a high-throughput manner is disclosed. A Bayesian optimization software package found novel electrolyte compositions through optimization of the high-dimensional electrolyte design space over key design objectives like electrochemical stability and conductivity.Electrolyte optimization is difficult because 1) electrolyte evaluation is expensive and takes time, and 2) the space of possible electrolytes is expansive, formed by many possible choices for solvents (often in ternary blends), salts (often in binary mixtures), and trace additives. Bayesian optimization methods are well suited for the optimization of high-dimensional functions with costly evaluations, often producing an efficient design-of-experiments to converge on multi-objective optimal formulations in few experiments. To expedite the optimization over the expansive design space, theoretical predictions of electrolyte properties via the Advanced Electrolyte Model were utilized as “priors” in the statistical model.Implementation of the novel experimental platform was carried out by two novel test stands developed to automate the mixing and characterization of electrolytes: Otto (for aqueous systems) and Clio (for aprotic/organic systems). The test stands characterized the ionic conductivity and electrochemical stability of electrolyte systems, featuring a four-electrode conductivity probe, pH meter, and a flow-through three-electrode cell and potentiostat. Clio also integrated electrochemically active electrodes for optimization of electrolyte/electrode systems. The active electrode systems used were common functional ceramic metal oxides.A software orchestration and data layer linked the test-stands to human experimenters and machine-learning packages through a web-services architecture; all experiment data and meta-data is saved in a database. Additional out-of-the-loop characterization was conducted on cathodic systems to validate composition, structure, and oxidation state.The aqueous design space consisted of aqueous blends of lithium and sodium salts, including nitrates, sulfates, and other commonly-used battery salts. High-concentration aqueous electrolyte candidates were discovered by optimizing of electrochemical voltage stability and conductivity, including low-cost, high-performing alternatives to known but costly aqueous electrolytes (e.g. LiTFSI). Clio’s design space includes blends of both aprotic organic solvents and solutes in additional to various compositions of electrochemically active electrodes. The test-stands are demonstrated to be significantly faster than common human experimentation techniques, converging on novel, optimized electrolyte mixtures in mere hours or days of experimentation.

Using a physical model to determine the hydrodynamic dispersion coefficient of a solution through a horizontal sand column

Miscible displacement can be understood as a physical process in a porous medium whereby two or more fluids fully dissolve into each other when a fluid mixes and goes into the pore space occupied by other fluids without the existence of an interface. A physical model was made in Can Tho University, which included an electrical current system connecting nine groups of four-electrode probes for measuring the electrical conductivity of a potassium chloride solution flowing through a horizontal sand column placed in a firm frame. The experiments were performed with different volumetric flow rates and three types of sand (fine, medium and coarse). The breakthrough curves were analysed, and then the hydrodynamic dispersion coefficients were calculated. The hydrodynamic dispersion coefficient was one of the hydraulic and solute transport parameters used to design a constructed subsurface flow wetland. The research proves that the flows were laminar, and that mechanical dispersions dominated over molecular diffusions and that the dispersions were large enough to cause combined mixing and flowing processes.

EIS Study on Detection of Corrosion Site of Reinforced Concrete By Two Sensing Electrodes

A reinforced concrete has been used for the civil engineering and construction in the whole world. In order to obtain the real-time information of reinforced concrete, Dawson et al. 1) attempted to investigate the electrochemical behavior of reinforced concrete by an electrochemical impedance spectroscopy (EIS). John et al. 2) proposed the equivalent circuit to interpret the impedance spectrum of reinforced concrete. Though these methods can be applied to the investigation of conditions of reinforced concrete, an electrical connection of reinforced concrete to the measurement device is required. Keddam et al. 3) proposed the concept of floating electrode for contact-less electrochemical measurement of reinforced concrete. In this method, a four-electrode probe was set on the reinforcement, and the capacitive loop related to the double-layer capacitance at the cement-rebar interface was measured 3). In the present study, a new method to detect the corrosion site of reinforced concrete was proposed by using two sensing electrodes. The sensing electrodes were placed on the surface of reinforced concrete as working and counter electrodes. The electrochemical impedance measurement was performed in this setup. The impedance related to the corrosion site of steel rebar in concrete with different cover thickness is measured by proposed method. In addition, the current and voltage distributions between sensing electrodes set on the concrete surface were discussed by a finite element method. Reference: 1. J. L. Dawson, L. M. Callow, K. Hladky and J. A. Richardson, Corrossion/78, No-125(1978). 2. D. G. John, P. C. Searson, J. L. Dawson, Br Corros J, 16, 102-106 (1981). 3. M. Keddam, X. R. Nòvoa, V. Vivier, Corros. Sci., 51, 1795-1801 (2009).

Laboratory modeling and measurement of the electrical resistivity of hydrate-bearing sand samples

In this paper, we describe a setup for modeling hydrate-bearing rock samples and measuring their electrical resistivity at different pressures and temperatures using an AMNB cylindrical four-electrode probe. Methods for modeling hydrate-bearing rock samples and measuring their resistivity are considered. The setup was used in a series of experiments to measure the resistivity of sand samples containing water, ice or tetrahydrofuran (THF) hydrate. It is shown that when the rock pores contain hydrates and a partially unfrozen aqueous solution of NaCl and THF, the electrical resistivity is determined by the high resistivity of the solution and increases with the formation of hydrate. The presence of THF hydrate in the experimental samples increased their resistivity by 180-320 Ohm·m at a temperature of about 0 °C. After the formation of hydrate and freezing of residual water, the resistivity of the sample is stabilized at 70-80 Ohm·m at a temperature of -15 °C.

Single ZnO Nanowire-Based Gas Sensors to Detect Low Concentrations of Hydrogen.

Low concentrations of hazardous gases are difficult to detect with common gas sensors. Using semiconductor nanostructures as a sensor element is an alternative. Single ZnO nanowire gas sensor devices were fabricated by manipulation and connection of a single nanowire into a four-electrode aluminum probe in situ in a dual-beam scanning electron microscope-focused ion beam with a manipulator and a gas injection system in/column. The electrical response of the manufactured devices shows response times up to 29 s for a 121 ppm of H2 pulse, with a variation in the nanowire resistance appreciable at room temperature and at 373.15 K of approximately 8% and 14% respectively, showing that ZnO nanowires are good candidates to detect low concentrations of H2.

Ex vivo electrical impedance measurements on excised hepatic tissue from human patients with metastatic colorectal cancer

Point-wise ex vivo electrical impedance spectroscopy measurements were conducted on excised hepatic tissue from human patients with metastatic colorectal cancer using a linear four-electrode impedance probe. This study of 132 measurements from 10 colorectal cancer patients, the largest to date, reports that the equivalent electrical conductivity for tumor tissue is significantly higher than normal tissue (p < 0.01), ranging from 2–5 times greater over the measured frequency range of 100 Hz–1 MHz. Difference in tissue electrical permittivity is also found to be statistically significant across most frequencies. Furthermore, the complex impedance is also reported for both normal and tumor tissue. Consistent with trends for tissue electrical conductivity, normal tissue has a significantly higher impedance than tumor tissue (p < 0.01), as well as a higher net capacitive phase shift (33° for normal liver tissue in contrast to 10° for tumor tissue).

Monitoring of breast tissue thermo-ablation by means of impedance measurements

A usefulness of a developed probe combining power delivery to ablated breast tumour and simultaneous impedance measurements is discussed in the paper. It consists of a cylindrical electrode used for applying ablation current and four rings electrodes. They are located, in pairs, at both ends of the ablation electrode. The probe properties were examined using a simulation studies – Laplace and bio-heat equations were solved. An associated distribution of power absorbed by tissue was calculated. Temperature dependence of tissues' conductivity was assumed. This dependence involved an iteration procedure for solving the considered problem. The four-electrode probe enabled monitoring the insertion and the ablation process.

Calibration and Simultaneous Monitoring of Soil Water Content and Salinity with Capacitance and Four-electrode Probes

Non-destructive monitoring of soil water content (W) and the electrical conductivity of the soil solution (ECw) has been desired for environmental evaluation and sustainable agriculture. Dielectric probes and four-electrode probes are widely used for the non-destructive determination of W and the soil bulk electrical conductivity (ECb), respectively. Since the output of dielectric probes is affected by soil salinity, the calibration for the effect is indispensable for accurate determination of W. Meanwhile, four-electrode probes require the W value for determination of ECw from ECb. We present an empirical calibration method for the salinity dependence of commercial capacitance moisture probes. A four-electrode probe was also calibrated to investigate the possibility of simultaneous monitoring of W and ECw by combining each calibration equation for capacitance and four-electrode probes. A laboratory experiment was conducted using a sandy soil to obtain probe outputs at various W (air-dry-near-saturation) and ECw (0-31.9 dS m-1). The output of the capacitance probe exhibited strong, nonlinear dependence on ECw. The root mean square error (RMSE) between actual W and calculated W using the linear functions provided by the manufacturer was at a maximum of 0.162 m3 m-3. A calibration equation, describing the probe output as a function of W and ECw, was developed using curve fitting approach. The RMSE between the actual and calibrated W by this equation was at a maximum of 0.011 m3 m-3. The output of the four-electrode probe (ECb) was also expressed as a function of W and ECw. The calibration equations for each probe were combined and solved for W and ECw. Although both W and ECw were determined with acceptable accuracy, the combined calibration equation had multiple solutions for W. Development of the method to select optimal solutions will be needed for the practical application of this probe combination.

Possible Four-Electrode Configurations for Measuring Cardiac Tissue Fiber Rotation

A number of electrode configurations, based on the usual four-electrode probe, are analysed in relation to the effect that changes in cardiac fiber rotation have on the potentials measured. Simulations are carried out using a mathematical model and a new solution technique, based on Fourier series followed by a simple one-dimensional finite difference scheme. This electrode analysis leads to the proposal of an in-principle method for determining cardiac fiber rotation.

Comparison of electrical conductivity data obtained by four-electrode and four-point probe methods for graphite-based polymer composites

A comparison of the volume conductivity measured by standard four-electrode (FE) and four-point probe (FPP) methods for graphite-based powdery polypropylene (PP) and poly(vinylidene fluoride) (PVDF) composite bar specimens was made in this study. Significant difference in the conductivity data obtained by standard FE and FPP methods was found for highly conductive PP and PVDF composites which were molded from hybrid carbon/polymer powders dry-blended in a high-speed mixer and jar ball mill. However, it was found that the conductivity values were approximately equal for moderately conductive PVDF/graphite and PP/graphite composites. It was also shown that polishing the specimens to remove 100–150 μm of the surface layer and decrease surface roughness did not bring about significant changes in conductivity values. Consequently, bulk non-uniformity and inhomogeneity of graphite-based polymer material were considered to be the most probable sources of the difference in the volume conductivity values measured by the FE and FPP methods.

A Probe for Organ Impedance Measurement

In this paper, we describe the theory and practical implementation of an electrical impedance probe for making in vivo measurements of the electrical admittance of living tissue. The probe uses concentric annular electrodes and is shown to sample a more localized, yet greater, volume of tissue than the standard four-electrode probe. We have developed a mathematical model for the conduction of current between the probe electrodes assuming that we are investigating a uniform, isotropic, semi-infinite region and taking into account the contact impedance between the electrodes and the organ. The electric fields produced by the probe have been calculated by solving a weakly singular Fredholm integral equation of the second kind. The size and position of the probe electrodes have been optimized to maximize both the accuracy in the admittance measurement and insensitivity to contact impedance. A probe and driving hardware have been constructed and experimental results are provided showing the accuracy of admittance measurements at 50 and 640 KHz.

TDR estimation of electrical conductivity and saline solute concentration in a volcanic soil

Relative to montmorillonitic or kaolinitic soils, volcanic soils have atypical dielectric characteristics that interfere with the applicability of the Time Domain Reflectometry (TDR) technique for soil moisture ( θ) determination when common, empirical calibration equations are used. This particular dielectric response affects estimation of salinity in volcanic soils. Six TDR-based methods to estimate bulk electrical conductivity ( σ a) on a range of KCl saline reference solutions were compared, with Nadler's method giving the best results ( R 1:1 2=0.988). Three models (linear, non-linear and empirical) for predicting soil solution electrical conductivity ( σ w) based on σ a and θ, were experimentally tested on 24 hand-packed soil columns varying in salinity (Br −) from 0.2 to 4.0 dS m −1, each in four θ levels (36–58%). Rhoades' linear model performed better, especially for large water contents, than the other two ( R 1:1 2=0.986 vs. 0.976 and 0.983, respectively). An interpretation in terms of mobile vs. immobile volumetric fractions of water present in volcanic soils is suggested as a possible explanation for these results. The empirical model resulted over-parameterized and an alternative equation with fewer non-correlated parameters, σ a=( aθ 2+ bθ) σ w+ cθ 2, is proposed and tested with good results in volcanic soils from the Canary Islands and New Zealand. The equation encompasses both the relative dielectric dominance of the mobile water fraction at high water content typical of volcanic soils, and of the immobile fraction at low water contents. Simultaneous measurements made with a standard four-electrode probe and TDR gave good correlation ( R 2=0.964). A good linear correlation was also found between tracer concentration in the soil solution and σ w ( R 2=0.960). Nadler's and the new empirical model also tested with good results under dynamic (flow) conditions during a miscible displacement experiment in a large monolith using bromide as a tracer. The method reveals itself as a robust tool for solute transport studies under controlled salinity conditions in a volcanic soil.

Pre-treatment with the Na+/H+ exchange inhibitor cariporide delays cell-to-cell electrical uncoupling during myocardial ischemia.

Inhibition of Na(+)-H(+) exchange (NHE) delays the onset of myocardial rigor contracture during ischemia. The aim of this study was to analyse the effects of NHE inhibition on cell-to-cell electrical uncoupling during myocardial ischemia/reperfusion. Twenty-six isolated rat hearts and 23 in situ porcine hearts were submitted to no-flow ischemia followed by reperfusion, with or without pre-treatment with cariporide (7 microM in rats and 3 mg/kg in pigs). Ischemic rigor and hypercontracture, conduction velocity and myocardial electrical impedance were monitored. Pre-treatment with cariporide delayed ATP depletion (luminescence assay in rat myocardium) and onset of rigor contracture (tension recordings or ultrasonic crystals) during ischemia both in rat and pig hearts (P<0.05). In addition, cariporide delayed the onset of sharp changes in tissue resistivity and phase angle in impedance recordings (four-electrode probes) from 10+/-1 to 13+/-1 min (P<0.001) in rat hearts, and from 22+/-1 to 38+/-2 min (P<0.001) in pigs. Blockade of impulse propagation (transmembrane action potentials in rat hearts) was also markedly delayed by cariporide (from 14+/-1 to 20+/-1 min, P<0.001). Reperfusion-induced LDH release in rat hearts and infarct size in pigs were markedly reduced by pre-treatment with cariporide. Inhibition of NHE with cariporide slows the progression of ischemic injury during myocardial ischemia, and delays the onset of cell-to-cell electrical uncoupling.

Hydrodynamic Dispersion in an Unsaturated Dune Sand

Solutes spread relative to the mean displacement position during water flow in soils as a result of meandering through the (partially) saturated pore complex. Spreading is characterized by the hydrodynamic dispersion coefficient in the convection-dispersion equation (CDE). This coefficient has been extensively studied for saturated soils. In this study hydrodynamic dispersion coefficients for nonaggregated dune sand were determined as a function of volumetric water contents, θ, ranging from saturation to 0.08 cm3cm−3 in columns of 5-cm diam. and 25- to 40-cm length. Unit-gradient flow experiments were conducted to measure solute breakthrough curves (BTCs) using four-electrode salinity probes at several column depths. Transport parameters for the CDE and the mobile-immobile model (MIM) were determined by optimizing analytical solutions to observed BTCs. A maximum dispersivity, λ, of 0.97 cm was found at θ = 0.13, whereas for saturated flow λ ≈ 0.1 cm irrespective of pore-water velocity ranging from 208 to 5878 cm d−1 For the MIM, the mobile water fraction, θm/θ, gradually deceased from almost unity at saturation to a minimum of 0.85 at θ = 0.15 followed by a slight increase with further desaturation. The exchange time between the mobile and immobile phases, 1/α, was 0.1 to 0.2 d for θ > 0.15 presumably because of the relatively homogeneous flow with convective solute mixing. For lower θ, the exchange became much slower since flow predominantly occurs in water films enveloping sand particles. The Peclet number for molecular diffusion, Pe, decreases as the role of transverse diffusion increases at lower θ because of smaller v and thinner water films while the resistance increases for solute exchange between mobile and immobile phases. These combined effects lead to a maximum dispersivity value at intermediate water contents in the case of the nonaggregated dune sand.

Simple sensors to achieve fine spatial resolution in continuous measurements of soil moisture and salinity

Abstract. It is increasingly necessary to be able to measure, simultaneously, continuously and at fine spatial resolution, the salinity and water content of soil. This paper reports the design, construction, calibration and laboratory testing of two simple but robust instruments that enable this to be achieved. Salinity in solution was measured reliably, at 10-mm spacing, by multi-electrode resistivity probes up to saturation with NaCl (c. 6 mol l–1), though these probes required individual calibration and were unable to detect precipitated salt. Volumetric water content was measured with great sensitivity over a wide range, from air-dryness (0.06 m3m–3) to saturation (0.55 m3m–3) in a sandy loam, using thermal-conductivity probes that used a common calibration and were unaffected by the salinity of the soil solution, by temperature and by ageing. Keywords: soil moisture, soil salinity, thermal-conductivity moisture probe, four-electrode salinity probe

Effects of electrical stimulation and seminal plasma on the motility of mouse sperm.

The effects of electric current (in vivo and in vitro) and seminal plasma on epididymal and ejaculated sperm obtained from C57BL x CBA and C57BL/6J mice were investigated by studying motility parameters, fertilization and embryo development. Electroejaculates were obtained by applying a series of computer-generated sinusoidal alternating currents (0.25-3.0 V at 50 Hz) delivered for 1, 2 and 3 s with 1-s rest periods using a four-electrode rectal probe for 4 min. Epididymal sperm obtained from the same mice were either subjected to electric current in vitro in a Plexiglass chamber or incubated in a medium containing seminal plasma for 2 h. In vitro electric current application and incubation in a medium containing seminal plasma significantly (P < 0.01) decreased sperm motility. Neither electroejaculates nor epididymal spermatozoa incubated with seminal plasma could fertilize oocytes by conventional IVF (P < 0.001), whereas sperm subjected to in vitro electric current had lost little of their ability to fertilize oocytes. Following transfer of embryos generated by intracytoplasmic sperm injection (ICSI), the number of live pups obtained from electroejaculated sperm (10.2%; 6/59) was significantly (P < 0.01) lower than from epididymal sperm (50.0%; 22/42). Electroejaculation using a rectal probe had little effect on motility and fertilization capacity of mouse epididymal sperm, whereas the presence of seminal plasma decreased motility and prevented fertilization.