The theoretical basis of a hypothetical spherical electrode detector was investigated in our previous work. It was found that the proposed detector has very good electrical characteristics, such as ...greatly reduced full depletion voltage, small capacitance and ultra-fast collection time. However, due to the limitations of current technology, spherical electrode detectors cannot be made. Therefore, in order to use existing CMOS technology to realize the fabrication of the detector, a hemispherical electrode detector is proposed. In this work, 3D modeling and simulation including potential and electric field distribution and hole concentration distribution are carried out using the TCAD simulation tools. In addition, the electrical characteristics, such as I-V, C-V, induced current and charge collection efficiency (CCE) with different radiation fluences, are studied to predict the radiation hardness property of the device. Furthermore, a customized manufacturing method is proposed and simulated with the TCAD-SPROCESS simulation tool. The key is to reasonably set the aspect ratio of the deep trench in the multi-step repetitive process and optimize parameters such as the angle, energy, and dose of ion implantation to realize the connection of the heavily doped region of the near-hemispherical electrode. Finally, the electrical characteristics of the process simulation are compared with the device simulation results to verify its feasibility.
This work addresses the steady-state boundary layer developed close to a rotating iron hemispherical electrode in an electrochemical cell. Dissolution of the electrode in the electrolyte directly ...related to the current passage gives rise to a concentration boundary layer, much thinner than the hydrodynamic one, due to a Schmidt number Sc=2000. This boundary layer, caused by the potential applied to the electrode, leads to an increase in the fluid viscosity close to the electrode, and to a decrease in the diffusion coefficient of the medium, coupling the hydrodynamic and chemical species fields. A phenomenological law is assumed, relating the fluid viscosity to the concentration of the chemical species. A parameter appearing in this law, previously evaluated on the basis of experimental electrochemical data (Mangiavacchi et al., 2007) is assumed. The steady-state solution of the governing equations is then obtained in terms of a power series of the polar angle. The radial velocity profiles are quantitatively close to the ones developed by constant viscosity electrolytes, except at a short distance from the electrode surface corresponding to the aforementioned boundary layer, thus modifying the torque, the mass flux, and therefore, the transport-limited current with respect to a constant properties solution.
•Steady-state boundary layer of electrolytes dissolving iron RHSE electrochemical cells.•Coupled hydrodynamics and concentration due to variable viscosity and diffusivity.•Experimental law relating fluid viscosity/diffusivity to species concentration.•Numerical solutions obtained by power series of the polar angle and FEM.•Variable properties increase torque and decrease average mass flux and limiting current.
High-voltage pulse discharge in water is a promising technology to enhance the permeability of coal seam and rock mass by generating fractures within them. With the aim of improving the stability and ...efficiency of this technology, a high voltage electric pulse experiment system was constructed. The discharge electrodes in the experiment was hemispherical. The positive and negative electrodes were arranged on the same axis with adjustable spacing. Five sets of experiments were undertaken with the electrode spacing of 1mm, 2mm, 3mm, 4mm, and 5mm, respectively. In the experiments, an oscilloscope was used to analyze the voltage, current, and pressure wave signals. The experimental results of two typical voltage-current curves indicate that the peak pressure of plasma shock wave follows a parabolic trend with the electrode spacing, and there is an optimal electrode spacing for a given discharge voltage. The peak pressure of plasma shock wave tends to increase linearly with the increase of discharge voltage. The greater the electrode spacing, the greater the sensitivity of shock wave peak pressure to the discharge voltage. The shock wave peak pressure sensitivity of 5 mm discharge spacing is 4.7 times that of 1 mm discharge spacing. The experimental results for the voltages of 9 kV, 12 kV, and 24 kV with the optimal electrode spacing show that a power function is the best fit for the attenuation of the peak pressure of shock wave with its propagation distance.
Metallic electrodes are widely used in many applications, the analysis of their frequency-domain behavior is an important subject, particularly in applications related to earthing/grounding systems, ...from dc up into the MHz range. In this paper, a numerical evaluation of the frequency-dependent complex impedance of the hemispherical ground electrode is implemented. A closed-form solution for non-zero frequencies is still a difficult task to achieve as evidenced in a previous paper dedicated to the subject and, therefore, numerical approaches should be an alternative option. The aim of this article is to present a solution based on a numerical method using finite element analysis. In typical commercial FE tools, electric currents exhibit azimuthal orientation and, as such, the magnetic field has a null azimuthal component but non-null axial and radial components. On the contrary, a dual problem is considered in this work, with a purely azimuthal magnetic field. To overcome the difficulty of directly using a commercial FE tool, a novel formulation is developed. An innovative 2D formulation, the ι-form, is developed as a modification of the H-formulation applied to axisymmetric magnetic field problems. The results are validated using a classical 3D H-formulation; comparisons showed very good agreement. The electrode complex impedance is analyzed considering two different cases. Firstly, the grounding system is constituted by a hemispherical electrode surrounded by a remote concentric electrode; in the second case, the grounding system is constituted by two identical thin hemispherical electrodes. Computed results are presented and discussed, showing how the grounding impedance depends on the frequency and, also, on the radius of the remote concentric electrode (first case) or on the distance between the two hemispherical electrodes (second case).
The hemispherical ground electrode is a basic electrode whose analysis appears in many textbooks on electromagnetics in chapters dedicated to steady currents. Considering a soil with a given ...resistivity and an electrode with a given perimeter, the electrode DC resistance is simply calculated from the ratio resistivity/perimeter. Strangely, the generalization of this result to AC regimes is missing. The issue of the frequency-domain impedance of the hemispherical ground electrode has been avoided in the literature despite its trivial geometry. But the problem is indeed not easy; electromagnetic field calculation involves Legendre and Bessel functions; the application of boundary conditions involves an infinite set of points, and some integrals involved need to be calculated recursively. We analyzed the math and physics of the problem but failed to find a closed-form solution. This article with “negative results” can, however, be useful; on one hand it may prevent researchers from wasting their time following the same steps, and, on the other hand, it may attract the interest of new researchers to the subject, ultimately, accelerating its analytical solution (if the solution exists).
Ultramicroelectrodes (UMEs) have led to unprecedented advances in electrochemical studies since their introduction to electroanalytical chemistry about twenty five years ago. During this time, ...several UME geometries have been reported of which disk, ring, ring‐disk, hemispherical, spherical, and etched (finite cone) UMEs are the most commonly used. In this review, the design and fabrication procedures for each are described. Issues related to UME electrode surface treatment and characterization are also addressed.
Nano-precision gap measurement in the sub-micron range presents its own unique engineering challenge. The popular capacitive sensor platform, for example, is susceptible to the erroneous effect of ...electrode tilting and high noise floor, both of which are exacerbated by the small form factor required of a nano-precision gap sensor. In this paper, a capacitive gap sensor with a hemispherical electrode, used in combination with a SAW filter is presented. The proposed system outperforms the existing ones on two fronts. First, the system is virtually immune to the effect of electrode tilting due to the improved capacitor geometry. Second, it benefits from the outstanding signal conditioning capability of the SAW filter. Construction and characterization of a SAW-based capacitive gap sensor having resolution as fine as 10
nm are described.
To investigate the effect of aging on surface discharge of the pressboard on the shielding electrode at the end of bushing, a thermal aging preparation methods of different aging degrees of ...pressboard samples, surface defect model, and the associated hemisphere are designed and the step-up method is used for subsequent experimental work. Finally, the partial discharges (PDs) under different degrees of aging are compared and combined with Fourier Transform Infrared spectra and electric field simulation. Results show that the pre-discharge occurs mainly in the oil gap between the hemispherical electrode edge and the pressboard. The aging of the pressboard exerts no obvious effect on the discharge characteristics in the initial stage of PD; with the development of the discharge, the development of aging of pressboard leads to a higher electric field intensity acting over a greater area, the more intense the discharge, the faster the relative discharge increases and the larger its amplitude. This discharge will cause decomposition of the oil in the pores of the aging pressboard thus generating gas bubbles which will move as discharge develops. When the bubbles reach the surface of the pressboard, the local electric field intensity will increase and the discharge will become more intense.
Dielectric elastomers are widely investigated as soft electromechanically active polymers (EAPs) for actuators, stretch/force sensors, and mechanical energy harvesters to generate electricity. ...Although the performance of such devices is limited by the dielectric strength of the constitutive material, the electrical breakdown of soft elastomers for electromechanical transduction is still scarcely studied. Here, we describe a custom-made setup to measure electrical breakdown of soft EAPs, and we present data for a widely studied acrylic elastomer (VHB 4905 from 3M). The elastomer was electrically stimulated via a planar and a hemispherical metal electrode. The breakdown was characterized under different conditions to investigate the effects of the radius of curvature and applied force of the hemispherical electrode. With a given radius of curvature, the breakdown field increased by about 50% for a nearly 10-fold increase of the applied mechanical stress, while with a given mechanical stress the breakdown field increased by about 20% for an approximately twofold increase of the radius of curvature. These results indicate that the breakdown field is highly dependent on the boundary conditions, suggesting the need for reporting breakdown data always in close association with the measurement conditions. These findings might help future investigations in elucidating the ultimate breakdown mechanism/s of soft elastomers.
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