Electrode Profiles Research Articles

Simplification of Electrode Profiles for Piezoelectric Modal Sensors by Controlling Gap-Phase Length

This paper presents a method to optimize and simplify the electrode profile of a piezoelectric modal sensor. At the same time that the electrode profile is optimized to maximize the charge, a null-polarity phase is introduced. This gap-phase is modeled using the normalized norm of the spatial gradient of the polarity profile along with a two-step filtering and projection technique. High-order vibration modes generate a complex polarization profile that makes the manufacturing process difficult. The novelty of the proposed method is the addition of a constraint on the length of the interface in the topology optimization problem. This constraint simplifies the optimal designs and facilitates the fabrication process. Several examples show the simplified electrode profile that maximizes the electrical charge produced by a vibration mode, while reducing the number of different polarization regions by means of the gap-length constraint.

Effect of Electrode Profile and Polarity on Performance of Pressurized Sparkgap Switch

Sparkgap are most widely used closing switches in various high-voltage pulsed power systems and its reliable operation at desired voltage level is very essential. Conventionally by adjusting the filling gas pressure inside sparkgap switch, breakdown voltage level is altered but switching characteristics such as stability in hold-off voltage at various pressures, breakdown delay, plasma channel formation, and erosion rate are mainly dictated by adopted electrode profile and its dimensions, inter-electrode gap length and polarity. In this paper, experimental results obtained on breakdown characteristics of four different electrode geometries—Plane Parallel, Hemi-spherical, Bruce, and Rogowski and also a generalized criterion for fixing major dimensions of electrode and inter-gap length to ensure uniform electric field in the inter-electrode region are reported. All electrodes are of brass material and have common radius and thickness of 25 mm and 18 mm, respectively (surface finish <1 µm). Experiments performed on various electrode profiles in gap lengths of 2 mm to 5 mm range with pure nitrogen (N2) gas pressurization up to 50 psi reveal that among all profiles, Rogowski performs most reliably having stable hold-off voltage in wide operating range. Hold-off voltage magnitude and breakdown delay was commonly obtained higher for negative polarity in all trials. A comprehensive overview of experimental investigation reported herein compares suitability of various electrode profiles and polarity for reliable switching.

Calendar Vs. Cycle Aging of Lithium-Ion Cells with Silicon Anode

Silicon has been investigated for decades, as an alternative to the graphite used in lithium-ion battery anodes, because of its high theoretical capacity. However, the large volume change of Si during electrochemical cycling (cycle-aging) deteriorates the solid electrolyte interphase (SEI) layer on the particles, resulting in increased electrolyte reduction reactions and associated capacity decay. Capacity fade is also observed in cells that are not cycled but simply held at voltage for extended periods of time (calendar-aging). [1]Here we report the calendar and cycle-aging behavior of cells with a Si anode that is paired with a NMC532 cathode (Figure 1). The tests were conducted in coin cells and in cells with a reference electrode (prepared by in-situ lithiation of a 25 mm Cu wire). This reference electrode allowed us to determine changes in the individual electrode profiles during aging and to examine impedance changes that were monitored via hybrid pulse power characterization (HPPC) tests. [2]Our various experiments have revealed the following: (i) capacity-fade is greater during cycle-aging than during calendar-aging; (ii) the capacity fade is associated with shifts in both positive and negative electrode potentials; (iii) parasitic currents are observed during the calendar-life hold, which indicate ongoing electrolyte reduction reactions at the silicon electrode; (iv)both electrodes contribute to the significant impedance rise observed during cell aging.To further examine sources of the observed performance degradation we conducted experiments with cells with the Si paired with LiFePO4. These data, along with the probable mechanisms of cell aging, will also be discussed during the presentation.References Kalaga et al., Acta 2018, 280, 221-228. Klett et al., Electrochem. Soc. 163 (2016) p. A875. Acknowledgments: M.L. acknowledges the generous grants from the U.S. National Science Foundation with the award numbers of CMMI-1660572 and IIP-1918991 that enabled her research at Argonne National Laboratory. The electrodes and electrolytes used in this study are from Argonne’s Cell Analysis, Modeling and Prototyping (CAMP) Facility. We are grateful to Andrew Jansen, Bryant Polzin, and Steve Trask for their assistance during this study. Figure 1

Finite difference method for electric field optimization in high voltage power transformer bushings using engineering simulation and 3D design program

The electric field optimization minimizing the field strength on an electrode surface and providing its uniformity is important in designing high voltage power transformer bushings and other apparatus from the viewpoint of efficient utilization of the electric field space. The high voltage power transformer bushing with cylinder electrode system has been designed and tested in this investigation. It was found that the insulation method of the cylinder electrode was the most important factor to lower streamer initiation voltage. The optimized design uses both internal and external elements for electric stress grading at critical parts of the bushing. Applying optimization theory based on charge simulation method, the author developed a computation program for electric field automatic optimization in 3D dielectric axisymmetric field. The results of the computation realized some excellent electrode profiles with uniform electric field distribution. Moreover, the discrepancy from the electric field uniformity on 3D dimensional profile caused by applying it to an axisymmetric electrode was discussed. Then a new electrode with uniform field distribution was obtained by using the computation program for optimization.

Designing electrode profiles with the equipotential method

A good electrode design not only produces the goal electric fields, but also eliminates harmful high-field spots that can cause electrical breakdown. In this paper, we present the equipotential method to generate electrode profiles. It is a physical method. The desired field is constructed first by a set of virtual electrodes, and then the equipotential contours naturally become the electrode profiles. We will demonstrate the simple procedures to design uniform field electrodes and recessed electrodes to accommodate dielectric structures. It shows versatility and flexibility in designing electrodes of low symmetry or irregular shapes as well as in complex boundary conditions.

Generating multifunctional acoustic tweezers in Petri dishes for contactless, precise manipulation of bioparticles.

Acoustic tweezers are a promising technology for the biocompatible, precise manipulation of delicate bioparticles ranging from nanometer-sized exosomes to millimeter-sized zebrafish larva. However, their widespread usage is hindered by their low compatibility with the workflows in biological laboratories. Here, we present multifunctional acoustic tweezers that can manipulate bioparticles in a disposable Petri dish. Various functionalities including cell patterning, tissue engineering, concentrating particles, translating cells, stimulating cells, and cell lysis are demonstrated. Moreover, leaky surface acoustic wave-based holography is achieved by encoding required phases in electrode profiles of interdigitated transducers. This overcomes the frequency and resolution limits of previous holographic techniques to control three-dimensional acoustic beams in microscale. This study presents a favorable technique for noncontact and label-free manipulation of bioparticles in commonly used Petri dishes. It can be readily adopted by the biological and medical communities for cell studies, tissue generation, and regenerative medicine.

Effects of stepped cylindrical electrode in electrical discharge machining of blind holes

Electrical discharge machining (EDM) is a non-conventional machining process which has been widely used to machine difficult-to-cut materials. However, the efficiency of EDM hole making processes is low, and the quality of drilled holes is a concern especially when machining deep blind holes due to the poor removal of debris in the discharging gap. In this study, a new strategy based on shape modification of the electrode was developed to address this issue by indirectly changing the flow of dielectric. The electrodes of five different shapes with identical machining area were applied to improve the debris removal during the machining process. The effects of various electrode profiles on the machining performance were investigated. Machine time, material removal rate (MRR) and electrode wear rate (EWR) were used to evaluate the machining performance. The computational fluid dynamic (CFD) software Fluent was used to simulate the flow of dielectric caused by different electrode profiles. The results show that, compared with the straight electrode, the maximum effective cutting depth of curved electrodes and long-curved electrodes increased 13.793% and 132.184%, respectively, and the MRR of stepped electrodes was significantly higher after the machining depth reached 2 mm and 4 mm for electrodes with the working length of 2 mm and 4 mm, respectively. The surface roughness was identical for holes machined by all types of electrode. However, obvious carbon adhesion can be observed at lower cutting depth for straight electrode, followed by curved and long-curved electrodes.

Anomaly effect-driven optimization of direct-current geoelectric mapping surveys in large areas

In most hydrogeological, geotechnical, archaeological, and other geoscientific applications, we need to understand the lateral extent and connectivity of system-relevant subsurface features. Towards this end, direct-current electric resistivity tomography (ERT) with several 2-D profiles or 3-D grids provides a powerful tool for non-invasive resolution of electrical resistivity anomalies. On the downside, many hours of fieldwork to set up and break down long electrode profiles limit this method to study areas of few thousand square meters, as the workload multiplies with the number of profiles. In many projects, however, determining the extent and connectivity of subsurface anomalies and therefore their potential relevance to the system, may only require the target to be spatially traced instead of fully resolved. We therefore propose geoelectric mapping with a target-specific fixed electrode spacing as an efficient way to trace a resolved resistivity anomaly away from an initial ERT profile, which should be particularly valuable for large study areas. The target-specific electrode spacing is hereby determined by evaluating the effects of the targeted anomaly in the raw data of the preliminary ERT profile. We therefore introduce an anomaly effect applicable to measurements in environments with spatial trends in resistivity distribution. In synthetic simulations, we demonstrate that our approach can efficiently delineate lateral boundaries of resistivity anomalies in ERT data space and we visualize this in pseudosections of anomaly effects. We then apply this method to tracing a gravel-filled paleo-channel in the 8 km2 Ammer floodplain near Tübingen, Germany and determine a suitable electrode spacing for a subsequent mapping campaign from the ranges of anomaly effects. We traced the paleo-channel over several hundreds of meters away from an initial 550 m long ERT profile within 19 h, the same time needed to set up, measure, and dismantle the single initial ERT profile. The evaluation of anomaly effects proves to be an efficient tool to detect resistivity anomalies in geoelectric data and determine suitable electrode spacings for large-scale mapping campaigns. Once identified, anomalies and project-relevant subareas can be the target of more detailed investigations.

Topology optimization of piezo modal transducers considering electrode connectivity constraints

Piezo modal sensors/actuators are devices that utilize the piezoelectric effect to measure/excite a particular mode while remaining insensitive to the non-targeted modes. The design of such transducers is typically confined to determining the location of tailor-made electrodes of opposite polarity, meaning one seeks to determine which electrode areas have positive polarity (+1) and which areas are negative (-1). Surprisingly, these electrode profiles can be obtained as the solutions of a linear programming problem that elegantly models the design problem. Designs resulting from this process, however, typically exhibit isolated features of like-polarity, and this characteristic typically becomes more pronounced as additional modes are considered. These isolated features pose significant challenges from a manufacturing and operation point of view, as each feature must be connected to a current source, thereby resulting in complex or cumbersome wiring schemes. This work introduces a connectivity constraint on the electrode profiles to dramatically simplify electrode phase connectivity and therefore the required wiring schemes. The resulting design problem is solved using density-based topology optimization methods and numerical examples confirm that piezo modal transducers can be designed with simply-connected electrode phases, thereby providing efficient performance together with improved manufacturability.

The Test of a High-Power, Semi-Insulating, Linear-Mode, Vertical 6H-SiC PCSS

A high-power photoconductive semiconductor switch (PCSS) working in linear mode can be used for RF generation by modulating the illuminating light. Such a PCSS constructed of a semi-insulating 6H silicon carbide (6H-SiC) substrate and its characterization under a high electric field is presented. The PCSS is of a vertical structure, with one hollow/transparent electrode to let through the laser light and the other highly reflective to increase light absorption. First, to optimize the high-voltage withstanding, the factors affecting the field enhancement, such as substrate thickness, electrode profiles, and encapsulating materials, are discussed. Then, the PCSS is assembled and tested, and the 0.8-mm-thick 6H-SiC PCSS is able to work with electric fields up to 225 kV/cm and the power capacity up to 10.6 MW without failure when triggered by a Nd:YAG laser (532-nm, 17-ns full wavelength at half maximum). By varying the optical energy from 3 to 31.9 mJ, the minimum conducting resistance and the peak photocurrent of the PCSS are obtained. The PCSS fails with further increasing voltage, and the cause of the failure was identified to be a bulk breakdown. The result shows that the PCSS can work linearly and it is possible to be used in high-power compact RF generation.

Offset-electrode profile acquisition strategy for electrical resistivity tomography

We present an electrode layout strategy that allows electrical resistivity profiles to image the third dimension close to the profile plane. This “offset-electrode profile” approach involves laterally displacing electrodes away from the profile line in an alternating fashion and then inverting the resulting data using three-dimensional electrical resistivity tomography software. In our synthetic and field surveys, the offset-electrode method succeeds in revealing three-dimensional structures in the vicinity of the profile plane, which we could not achieve using three-dimensional inversions of linear profiles. We confirm and explain the limits of linear electrode profiles through a discussion of the three-dimensional sensitivity patterns: For a homogeneous starting model together with a linear electrode layout, all sensitivities remain symmetric with respect to the profile plane through each inversion step. This limitation can be overcome with offset-electrode layouts by breaking the symmetry pattern among the sensitivities. Thanks to freely available powerful three-dimensional resistivity tomography software and cheap modern computing power, the requirement for full three-dimensional calculations does not create a significant burden and renders the offset-electrode approach a cost-effective method. By offsetting the electrodes in an alternating pattern, as opposed to laying the profile out in a U-shape, we minimize shortening the profile length.

Improved performance of inkjet-printed Ag source/drain electrodes for organic thin-film transistors by overcoming the coffee ring effects

Inkjet printing is a promising technology for the scalable fabrication of organic electronics because of the material conservation and facile patterning as compared with other solution processing techniques. In this study, we have systematically investigated the cross-sectional profile control of silver (Ag) electrode via inkjet printing. A facile methodology for achieving inkjet-printed Ag source/drain with improved profiles is developed. It is demonstrated that the printing conditions such as substrate temperature, drop spacing and printing layers affect the magnitude of the droplet deposition and the rate of evaporation, which can be optimized to greatly reduce the coffee ring effects for improving the inkjet-printed electrode profiles. Ag source/drain electrodes with uniform profiles were successfully inkjet-printed and incorporated into organic thin-film transistors (OTFTs). The resulting devices showed superior electrical performance than those without special treatments. It is noted to mention that the strategy for modulating the inkjet-printed Ag electrodes in this work does not demand the ink formulation or complicated steps, which is beneficial for scaling up the printing techniques for potential large-area/mass manufacturing.

Procedure of creating three-dimensional solid models of tool electrodes for electrochemical pulse machining of gas turbine engine parts in CAD-systems with their parametric coupling with software module profiling

This work is dedicated to the creation of parametric solid models of tool electrodes based on the results of the calculation of the previously created software module. The developed technique will facilitate the solution of the problem of technological preparation of the operation of electrochemical machining (ECM) of a gas turbine emgine copressor. In this case, the solution could be obtained by simulations in several iterations and would completely preclude all machine work and mechanical hand-operated development of electrodes. The technique is based on a mathematical model of electrochemical shaping of a gas turbine engine airfoil using pulse current. In developing the model the electric comductivity and temperature were taken to be constant, the current output depended only on the current density, the anode and cathode overvoltage was determined by the polarization curves, the peculiarities of the anode process dynamics were considered by the current density and the parameters of the hydrodynamic conditions were taken to be optimal. A software module was developed in the course of developing the procedure. The module developed provides easy implementation of a mathematical model of profiling tool electrodes in ECM. Electronic models of electrode profiles that could be used in producing control software for machining electrode profiles on CNC machines are the end result of such simulation.

Design of piezoelectric modal filters by simultaneously optimizing the structure layout and the electrode profile

Modal transducers can be designed by optimizing the polarity of the electrode which covers the piezoelectric layers bonded to the host structure. This paper is intended as a continuation of our previous work (Donoso and Bellido J Appl Mech 57:434---441, 2009a) to make better the performance of such piezoelectric devices by simultaneously optimizing the structure layout and the electrode profile. As the host structure is not longer fixed, the typical drawbacks in eigenproblem optimization such as spurious modes, mode tracking and switching or repeated eigenvalues soon appear. Further, our model has the novel issue that both cost and constraints explicitly depend on mode shapes. Moreover, due to the physics of the problem, the appearance of large gray areas is another pitfall to be solved. Our proposed approach overcomes all these difficulties with success and let obtain nearly 0-1 designs that improve the existing optimal electrode profiles over a homogeneous plate.

Procedure of creating three-dimensional solid models of tool electrodes for electrochemical pulse machining of gas turbine engine parts in CAD-systems with their parametric coupling with software module profiling

This work is dedicated to the creation of parametric solid models of tool electrodes based on the results of the calculation of the previously created software module. The developed technique will facilitate the solution of the problem of technological preparation of the operation of electrochemical machining (ECM) of a gas turbine emgine copressor. In this case, the solution could be obtained by simulations in several iterations and would completely preclude all machine work and mechanical hand-operated development of electrodes. The technique is based on a mathematical model of electrochemical shaping of a gas turbine engine airfoil using pulse current. In developing the model the electric comductivity and temperature were taken to be constant, the current output depended only on the current density, the anode and cathode overvoltage was determined by the polarization curves, the peculiarities of the anode process dynamics were considered by the current density and the parameters of the hydrodynamic conditions were taken to be optimal. A software module was developed in the course of developing the procedure. The module developed provides easy implementation of a mathematical model of profiling tool electrodes in ECM. Electronic models of electrode profiles that could be used in producing control software for machining electrode profiles on CNC machines are the end result of such simulation.

Integrated circuits using fully solution-processed organic TFT devices with printed silver electrodes

We have demonstrated fully solution-processed inverter, NAND and NOR circuits using pseudo-CMOS logic and p-type organic TFT devices with printed electrodes that were fabricated using ink-jet printed silver nanoparticle inks at low temperatures. In order to optimize the gate electrode profiles, we thoroughly assessed the surface wettability of the silver nanoparticle inks. The pseudo-CMOS inverter circuit exhibited exceptional switching characteristics with a high signal gain of 34 at a supply voltage of 20V. The NAND and NOR circuits also exhibited excellent logic characteristics, whereby the switching voltage was approximately VDD/2 with a high noise margin and short delay time of 12.5ms.

Profile Control of Inkjet Printed Silver Electrodes and Their Application to Organic Transistors

We report on the cross-sectional profile control of printed electrodes fabricated from silver nanoparticle inks with water-based solvents by inkjet printing. Systematically varying the ambient conditions and time for the drying process corresponded to changes in electrode shape. In general, lower humidity levels resulted in concave electrode profiles due to the coffee-ring effect, while higher humidity levels resulted in convex profiles. Printed capacitors with trapezoidal-shaped lower electrodes showed much better electrical breakdown strength than those with concave-shaped lower electrodes. Solution-processed organic thin-film transistors with trapezoidal gate electrodes operated reproducibly and exhibited good electrical characteristics with very low gate-leakage currents. The methods can be utilized in the fabrication of printed electronic devices with stacked layers, such as thin-film capacitors and transistors.

Influence of Electrode Profiles on Electrical Discharge Machining of Titanium

Electric discharge machining (EDM) is an effective manufacturing technique that enables the production of parts made of hard materials with complicated geometry that are difficult to produce by conventional machining processes. EDM is a process of eroding material by transient action of electric sparks on electrically conductive materials, one being the workpiece the other being the electrode immersed in a dielectric fluid and separated by a spark gap. The EDM ability to control the process parameters to achieve the required dimensional accuracy and surface finish has placed this machining operation in a prominent position in industrial applications. This work reports on the different electrode profiles on the machinability factors of surface roughness (Ra) and material removal rate (MRR). The machining factors used in this study are the current (I), on-time and off-time. Based on the experimental results influence of the electrode profile on the responses were made and reported in this study.

A contoured gap coaxial plasma gun with injected plasma armature

A new coaxial plasma gun is described. The long term objective is to accelerate 100-200 microg of plasma with density above 10(17) cm(-3) to greater than 200 km/s with a Mach number above 10. Such high velocity dense plasma jets have a number of potential fusion applications, including plasma refueling, magnetized target fusion, injection of angular momentum into centrifugally confined mirrors, high energy density plasmas, and others. The approach uses symmetric injection of high density plasma into a coaxial electromagnetic accelerator having an annular gap geometry tailored to prevent formation of the blow-by instability. The injected plasma is generated by numerous (currently 32) radially oriented capillary discharges arranged uniformly around the circumference of the angled annular injection region of the accelerator. Magnetohydrodynamic modeling identified electrode profiles that can achieve the desired plasma jet parameters. The experimental hardware is described along with initial experimental results in which approximately 200 microg has been accelerated to 100 km/s in a half-scale prototype gun. Initial observations of 64 merging injector jets in a planar cylindrical testing array are presented. Density and velocity are presently limited by available peak current and injection sources. Steps to increase both the drive current and the injected plasma mass are described for next generation experiments.

Gas-Insulated Self-Breakdown Spark Gaps: Aspects on Low-Scattering and Long-Lifetime Switching

The influence of the electric field distribution between the electrodes and the seed electron generation rate on the scattering of the breakdown voltage of SF6-insulated spark gaps was investigated. The breakdown voltage scattering considerably can be reduced by applying large-gap-volume, uniform-field electrode profiles instead of spherical shaped electrodes. Moreover, uniform field electrode profiles exhibit an uniform discharge probability in the entire gap volume and following an almost uniform erosion of electrode material along the electrode’s surface. This preserves electrode shape and switching performance of the spark gap for a long maintenance-free lifetime. Breakdown voltage scattering further can be reduced by increasing the seed electron generation in the gap by an auxiliary corona discharge adjacent to the main gap. The experimental observations are discussed on the basis of the volume time law for discharge initiation.