Current Density Profiles of Surface Mounted and Recessed Electrodes for Neural Prostheses

A Green's function approach has been used to solve Lapalce's equation for the quasi-static fields of a recessed, disk electrode. The resulting integral equation was solved numerically using the moment method. An analysis of the error in the approximate solution shows that it must be less than 7 percent for the cases studied. The calculations indicate that a recessed electrode has a more uniform current density profile than a surface mounted electrode. This is true both at the electrode surface, and at the electrode carrier?tissue junction. The significance of this finding is discussed as is its application to electrochemical, histopathological, and physiological studies of neural prostheses. The clinical use of recessed electrodes in cochlear implants is recommended.     

A minimum profile uniform current density electrode

Present methods of determining the safe injected charge levels for disk-type electrodes are given in terms of an average charge density, although the charge density is higher near the periphery of the electrode. This paper describes an electrode that produces an injected charge density that is uniform over the surface of the electrode and thus permits maximum utilization of the surface. Charge density is the time integral of current density, and the alteration of the current density is obtained by adding curvature to the electrode and recessing it within a cylindrical insulating well. A novel numerical method is used to determine the recession and curvature, and this numerical method is also presented. The benefit of this technique is that it permits a reduction in the electrode size while maintaining the maximum safe injected charge level of a disk-type electrode. A minimum profile uniform current density electrode and the algorithms used in its design are presented in this paper. Finally, a flat electrode that is recessed by as little as 1/10 of its diameter is shown to have an injected current density on the electrode surface that is superior to that of a flat surface mounted electrode.     

Three-dimensional finite element analysis of current density andtemperature distributions during radio-frequency ablation

This study analyzed the influence of electrode geometry, tissue-electrode angle, and blood flow on current density and temperature distribution, lesion size, and power requirements during radio-frequency ablation. The authors used validated three-dimensional finite element models to perform these analyses. They found that the use of an electrically insulating layer over the junction between electrode and catheter body reduced the chances of charring and coagulation. The use of a thermistor at the tip of the ablation electrodes did not affect the current density distribution. For longer electrodes, the lateral current density decreased more slowly with distance from the electrode surface. The authors analyzed the effects of three tissue-electrode angles: 0, 45, and 90°. More power was needed to reach a maximal tissue temperature of 95°C after 120 s when the electrode-tissue angle was 45°. Consequently, the lesions were larger and deeper for a tissue-electrode angle of 45° than for 0 and 90°. The lesion depth, volume, and required power increased with blood flow rate regardless of the tissue-electrode angle. The significant changes in power with the tissue-electrode angle suggest that it is safer and more efficient to ablate using temperature-controlled RF generators. The maximal temperature was reached at locations within the tissue, a fraction of a millimeter away from the electrode surface. These locations did not always coincide with the local current density maxima. The locations of these hottest spots and the difference between their temperature and the temperature read by a sensor placed at the electrode tip changed with blood flow rate and tissue-electrode angle     

Optimal Electrode Configurations for External Cardiac Pacing and Defibrillation: An Inhomogeneous Study

We have developed an inhomogeneous two-dimensional finite element computer model of the human torso, and have used it to study electrode performance in defibrillation and external cardiac pacing. Gross individual organ effects were assessed first for different electrode configurations by creating models which included one organ at a time, and comparing the results to those obtained with a homogeneous body. Electrode placement on the body was varied in order to determine, within the limitations of the model, optimal electrode configurations for external cardiac pacing and defibrillation. Finally, the electrical and geometric parameters of a previously proposed plate electrode design were optimized for the selected external pacing position. It was found that organs of extreme resistivity, close to the body surface, and within the direct current path between two electrodes, tended to have dominant effects on the surface current density distributions. The optimum pacing position is to place the driven electrode directly over the heart and the receiving electrode on the left lateral chest wall. For defibrillation, the driven electrode is moved to the right of the sternum.     

Proposal of a new method for narrowing and moving the stimulated region of cochlear implants: animal experiment and numerical analysis

We have proposed the tripolar electrode stimulation method (TESM) for narrowing the stimulation region and continuously moving the stimulation site for cochlear implants. The TESM stimulates the auditory nerve array using three adjacent electrodes which are selected among the electrodes of an electrode array within the lymphatic fluid. Current is emitted from each of the two lateral electrodes and received by the central electrode. The current received by the central electrode is made equal to the sum of the currents emitted from the lateral electrodes. In this paper, we evaluate whether or not TESM works according to a theory which is based on numerical analysis using an electrical equivalent circuit model of the auditory nerve fibers. In this simulation, the sums of the excited model fibers are compared to the compound action potentials (CAP's) which we obtained through animal experiments. To identify the main parameter while maintaining the amplitude of the CAP (the sum of the fired fibers), we assumed the presence of some parameters from the radial current density profile. In the case of the width value among the parameters being kept constant, the amplitude of the CAP was almost constant; thus, the number of the fired fibers was also almost constant. The width value equals the distance between the points at which the profile of the radial current density of the electrode array and the line of the radial threshold current density of the electrode array intersect. It is possible to determine the measure of the stimulation region or site by controlling the width value and the ratios of the currents emitted from the lateral electrodes. As a result, we succeeded in narrowing the stimulation region by controlling the sum of the currents emitted from the two lateral electrodes. Also we succeeded in continuously moving the stimulation site by modifying the currents emitted from the two lateral electrodes.     

Three-dimensional computer model of electric fields in internaldefibrillation

The automatic internal defibrillator delivers a low-energy shock directly to the heart. Optimal strategies for these shock deliveries are determined by studying a three-dimensional computer model of the electric fields produced by initial defibillation electrodes. A finite-element analysis technique is used to calculate energy and current density distributions in three commonly used electrode configurations: (1) patch-patch (PP), (2) catheter-patch (CP), and (3) catheter-catheter (CC). analysis of these simulations indicates that : (1) the PP and CP configurations are more effective at channeling energy to the myocardium than the CC configuration; (2) small electrodes and the edges of the electrodes give rise to high local current densities which might cause damage to the myocardium: (3) energy delivered to the myocardium is not significantly altered for different electrode placements tested; (4) electrode size influences current density distribution, especially near the electrodes; and (5) energy distribution is sensitive to the relative conductances of the myocardial tissue and blood     

电镀法制备汇流电极的研究

汇流电极是等离子体显示板(PDP)中的必要结构。本文首次提出了制备汇流电极的电镀法,分析了电极电位、电流密度以及电流在阴极上的分布对电镀过程的影响,研究了汇流电极的电镀工艺,包括基板的预处理、电镀液的选择与配制和汇流电极的电镀。本文用电镀法实际制备了汇流电极,测试了它的导电性和均匀性。实验结果证明,本文研究的制备技术能够制备汇流电极,并因此技术的设备低廉、生产效率高而为降低PDP的成本开辟了一条新途径。     

基于石墨毡生长的镍钴基化合物电极的双功能电催化性能

以先水热后硫化的方法制备出基于石墨毡基底的镍钴基化合物(NiCo2O4/GF和NiCo2 S4/GF)电极,探究不同水热温度对电极的催化特性的影响.通过扫描电子显微镜(SEM)、能量色散X射线光谱仪(EDS)、X射线衍射仪(XRD)和X射线光电子能谱仪(XPS)对样品表面形貌、结构、晶向及元素分布进行分析.通过循环伏安...     

The effect of bonding wires on longitudinal temperature profiles oflaser diodes

The thermal effect of bonding wires in laser diodes is analyzed using the analytical temperature solution for a five-layer structure and an iteration technique. Finite element method is used to confirm the results. Due to the bonding wire, the longitudinal temperature profile of laser diodes exhibits significant reduction at the foot of the wire even with uniform longitudinal heat distribution. For lasers designed with uniform longitudinal current density, heat increases toward the laser facets because of nonradiative recombination of carriers through surface quantum states on the facets. This leads to local temperature concentration on and near the facets. The conduction of heat through the bonding wire at the top center of laser chips further enhances this temperature concentration. In use, the stripe electrode of laser diodes is at uniform voltage. Under this operation condition, the current density would increase in the higher temperature regions due to bandgap decrease, causing higher heat flux. And consequently even higher temperature. Accordingly, the location of bonding wire and the shape of stripe electrode require careful consideration in the design phase to achieve uniform longitudinal temperature profile     

Finite element analyses of uniform current density electrodes for radio-frequency cardiac ablation

The high current density at the edge of a metal electrode causes hot spots, which can lead to charring or blood coagulation formation during radio-frequency (RF) cardiac ablation. We used finite element analysis to predict the current density distribution created by several electrode designs for RF ablation. The numerical results demonstrated that there were hot spots at the edge of the conventional tip electrode and the insulating catheter. By modifying the shape of the edge of the 5-mm tip electrode, we could significantly reduce the high current density at the electrode-insulator interface. We also studied the current density distribution produced by a cylindrically shaped electrode. We modified the shape of a cylindrical electrode by recessing the edge and filled in a coating material so that the overall structure was still cylindrical. We analyzed the effects of depth of recess and the electrical conductivity of the added material. The results show that more uniform current density can be accomplished by recessing the electrode, adding a curvature to the electrode, and by coating the electrode with a resistive material.     

Design Strategies toward High-Performance Hybrid Carbon Bilayer Anode for Improved Ion Transport and Reaction Stability

Compositing carbon-based materials with different properties can significantly improve the energy density of lithium-ion batteries for applications that require high power, such as electric vehicles, owing to their effective current distribution. Nevertheless, the chemical reaction is not uniform throughout the entire depth of conventionally blended electrodes. This study proposes a hybrid patterned bilayer anode that comprises a blended layer of spherical crystalline graphite (SCG) and soft carbon and a single layer of SCG alone, which maintains a stable ionic reaction at the electrode surface and improves ion transport. This bilayer anode has a smaller, more uniform solid electrolyte interphase layer that is more evenly distributed throughout the electrode compared with the blended electrode. The electrode pattern interfaces, which are optimized by controlling the pattern size, ensure excellent mechanical adhesion and low internal resistance. Consequently, the patterned bilayer half-cell achieves a high-capacity retention of 85.9% after 500 charge–discharge cycles at 1 C. The full cell also attains an energy density of 178.7 Wh kg⁻¹ with fast discharging at 10 C, which is 2.3 times higher than that of the single-layer SCG electrode.     

An electrostatically suspended contactless platform

Electrostatic suspension of a silicon disk with explicit control of the lateral translational degrees-of-freedom is reported. The transduction subsystem configures electrode pairs to exert electrostatic forces on the disk and to also measure differential capacitances related to the disk position. Disk sidewall forcing electrodes are not necessary to control the disk’s lateral position because tilting the disk relative to the plane of the electrodes exerts lateral forces on the disk. Despite the fact that the disk’s lateral and angular degrees-of-freedom are strongly coupled, the system is not strongly stabilizable using only the disk’s vertical position and tilt estimates derived from electrode–disk gap measurements. Nevertheless, a stabilizing controller is proposed and lateral position measurements are added for regulating the disk’s in-plane position. Extensive experimental results corroborate the model and analysis.     

Theoretical determination of the current density distributions inhuman vertebral bodies during electrical stimulation

Electrical stimulation with a 60 kHz sinewave input signal, supplied via external plate electrodes on the skin surface, is presently being studied as a treatment for human systemic osteoporosis. In this paper, Maxwell's equations were solved for voltage and current density values at nodal points in a three-dimensional, anatomically-based, finite element grid model of the human trunk constructed from T5 to L5. Based on the dose response results from Luessenhop's castrated Sprague Dawley breeder rat experiment and our theoretical determination, the magnitude of the input current to the electrodes necessary to induce a response in the human vertebral body was determined. Four different electrode systems in current clinical use were evaluated, and the optimal input current determined. In addition, the effect of subcutaneous fat was studied.     

The Characterization of Transcutaneous Stimulating Electrodes

A simple mathematical model of a transcutaneous stimulating electrode molded from conductive elastomer is used to predict the current density pattern produced by such electrodes. A general method has been developed to determine experimentally the current distribution produced by this class of electrodes. Preliminary experimental results are qualitatively in agreement with predictions made from the model. The experimental method for the determination of current spread yields a valid assessment of electrode performance independent of the accuracy of the mathematical model.     

The potential distribution generated by surface electrodes ininhomogeneous volume conductors of arbitrary shape

The use of the boundary element technique in the computation of the potential distribution within isotropic inhomogeneous volume conductors of arbitrary shape set up by current injected through surface electrodes is presented. The derived algorithm is validated by comparing its solution to analytical solutions in the case of a concentric bipolar electrode configuration on a homogeneous, spherical volume conductor. This problem is essentially a mixed boundary value problem. It is shown that approximations by treating this problem as a Neumann problem, which have recently appeared in the literature, are valid for remote field points only. Applications to the modeling of the field of cardiac defibrillation electrodes are presented.     

Modeling current density distributions during transcutaneouscardiac pacing

The authors developed a two-dimensional finite element model of a cross-section of the human thorax to study the current density distribution during transcutaneous cardiac pacing. The model comprises 964 nodes and 1,842 elements and accounted for the electrical properties of eight different tissues or organs and also simulated the anisotropies of the intercostal muscles. The finite element software employed was a version for electrokinetics problems of Finite Element for Heat Transfer (FEHT) and the authors assessed the effects upon the efficacy of transcutaneous cardiac pacing of several electrode placements and sizes. To minimize pain in the chest wall and still be able to capture the heart, the authors minimized the ratio, R, between the current density in the thoracic wall (which causes pain) and the current density in the heart wall (which captures the heart). The best placement of the negative electrode was over the cardiac apex. The best placement of the positive electrode was under the right scapula, although other placements mere nearly as good. The efficiency of pacing increased as electrode size increased up to 70 cm and showed little improvement for larger areas. Between different configurations of the precordial electrodes V1, V2, ···, V6 the most efficient configuration to pace with was V1 and V2 positive and V5 and V6 negative. A more efficient configuration uses an auxiliary electrode located at the right subscapular region     

Control of specific absorption rate distribution using capacitiveelectrodes and inductive aperture-type applicators: implications forradiofrequency hyperthermia

A method of controlling the specific absorption rate (SAR) distribution in radiofrequency hyperthermia is proposed. The superposition of the current density associated with capacitively coupled electrodes and that associated with H-field coupled inductive aperture-type applicators modifies the actual current distribution in the heating material. Using a two-dimensional finite element method, we have shown that "focusing" is possible such that the SAR at the center of a phantom can be adjusted to be approximately twice that in superficial regions, even though the wavelength is considerably greater than the dimensions of the phantom.     

Selective activation of distant nerve by surface electrode array

Neural prostheses for restoring lost functions can benefit from selective activation of nerves with limited number and density of electrodes. Here, we show by simulations and animal experiments that multipoint simultaneous stimulation with a surface electrode array can selectively activate nerves in a bundle at a desired location in between the array or at a desired depth, which are referred to as lateral or depth-wise gating stimulation, respectively. The stimulation broadly generates action potentials with cathodic source electrodes, and simultaneously blocks unnecessary propagation with downstream anodic gate electrodes. In general, stimulation with a small diameter electrode can affect a nearly hemispherical region, while a large electrode is effective at a more vertically compressed region, i.e., a surface of nerve bundle. The gating stimulation takes advantage of the size effects by utilizing an asymmetrical electrode array. The array of the lateral gating stimulation is designed to have four electrodes; a pair of large source electrodes and a pair of small gate electrodes. The depth-wise gating stimulation array consists of two electrodes; a large gate and small source electrodes. The simulation first demonstrated that appropriate combination of currents at the source and gate electrodes can change recruitment patterns of nerves with lateral or depth-wise selectivity as desired. We then applied the lateral gating stimulation on the rat spinal cords and obtained a preliminary support for the feasibility.     

Errors due to measuring voltage on current-carrying electrodes inelectric current computed tomography

Electric current computed tomography is a process for determining the distribution of electrical conductivity inside a body based upon measurements of voltage or current made at the body's surface. Most such systems use different electrodes for the application of current and the measurement of voltage. This paper shows that when a multiplicity of electrodes are attached to a body's surface, the voltage data are most sensitive to changes in resistivity in the body's interior when voltages are measured from all electrodes, including those carrying current. This assertion is true despite the presence of significant levels of skin impedance at the electrodes. This conclusion is supported both theoretically and by experiment. Data were first taken using all electrodes for current and voltage. Then current was applied only at a pair of electrodes, with voltages measured on all other electrodes. We then constructed the second data set by calculation from the first. Targets could be detected with better signal-to-noise ratio by using the reconstructed data than by using the directly measured voltages on noncurrent-carrying electrodes. Images made from voltage data using only noncurrent-carrying electrodes had higher noise levels and were less able to accurately locate targets. We conclude that in multiple electrode systems for electric current computed tomography, current should be applied and voltage should be measured from all available electrodes.     

Electrical behavior of defibrillation and pacing electrodes

This article discusses the electrodes and their interfaces for internal and external defibrillation and external pacing applications. Of primary concern is the nature of the current delivery and distribution at the electrode-tissue interface and the techniques that may be used to generate a uniform distribution of current density in order to minimize pain and burning. The cost of achieving a uniform current distribution is tolerable for external pacing applications, but questionable for defibrillation applications. In the process of examining the nature of the electrode interface, we also discuss various models of its behavior, including analytic, equivalent circuit, numerical, and empirical models