Electrode Length Research Articles

Effects of electrodes length and insulation for transcranial electric stimulation.

Background:The aim of this study is to investigate the effects of length and insulation of the corkscrew electrodes for transcranial motor evoked potential (tMEP) monitoring.Methods:We used the finite element method to visualize the electric field in the brain, which was generated by electrodes of different lengths (4, 7, and 12 mm). Two types of head models were generated: A model that included a subcutaneous fat layer and another without a fat layer. Two insulated needle types of conductive tip (5 and 2 mm) were studied. The stimulation threshold levels of hand tMEP were measured in a clinical setting to compare normal corkscrew and insulated 7-mm depth corkscrew.Results:The electric field in the brain depended on the electrode depths in the no fat layer model. The deeper the electrodes reached, the stronger the electric fields generated. Electrode insulation made a difference in the fat layer models. The threshold level recordings of tMEP revealed that the 7-mm insulated electrodes showed a lower threshold than the normal electrodes by one-side replacement in each patient: 33.6 ± 9.6 mA and 36.3 ± 11.0 mA (n =16, P < 0.001), respectively. The 7-mm insulated electrodes also showed a lower threshold than the normal electrodes when both sides, electrodes were replaced: 34.4 ± 8.6 mA and 37.5 ± 9.2 mA (n =10, P = 0.003), respectively.Conclusions:The electrodes depth reached enough to skull is considered to be efficient. Insulation of the electrodes with a conductive tip is efficient when there is subcutaneous fat layer.

Comparison of geometric and drive-induced nonlinearities in doubly clamped,thermoelastic nanoelectromechanical systems

The performance of resonant sensors based on nanoelectromechanical systems depends critically on the maximum amplitude of oscillation reached in the linear regime. The maximum linear amplitude is determined by nonlinear mechanisms that can originate from the material, geometric and transduction mechanism related factors. Here we compare the two competing effects, the geometric and drive-induced nonlinearities, for a commonly used device family, the thermoelastically driven, doubly clamped beams. We find that the geometric nonlinearity dominates for most of the device designs used in the literature, however the drive-induced nonlinearity becomes the determining factor for thicker beams with small electrode lengths.

The Effect of Cochlear Size on Cochlear Implantation Outcomes.

Objectives To determine if cochlear duct length and cochlear basal diameter, measured using routinely available radiology software, affect hearing outcomes after cochlear implantation with two different length electrodes. Methods55 patients who received a Med-El Flex electrode were retrospectively reviewed. 34 patients received the Flex 31 electrode (31mm) and 21 patients received the Flex 28 electrode (28mm). Preoperative high-resolution CT scans of the temporal bone were reformatted in the axial and coronal plane. The basal diameter of the cochlear (A-value) and the outer-wall lengths of the cochlear duct were measured using readily available imaging software. Postoperative plane X-rays were used to determine the degree of electrode insertion and the number of electrodes within the cochlea and speech discrimination scores at 6 months were evaluated. Results The cochlear metrics obtained were comparable with those previously published in the literature. There was no significant difference in the degree of insertion or speech outcomes between the two electrode lengths. However, when the group who had received the shorter electrode were analysed, there was an association seen between both cochlear duct length and cochlear diameter and speech outcomes. ConclusionsCochlear size may be a factor in determining speech outcomes that cannot be explained solely by insertion depth or degrees of insertion. Further studies are required to determine if cochlear duct length is an independent predictor of speech outcomes.

The Effect of Cochlear Coverage on Auditory and Speech Performance in Cochlear Implant Patients.

To determine the effect of cochlear coverage on audiological and speech parameters in patients with cochlear implants. Previous work has investigated the effect of tailoring electrode size to a cochlear implant recipient's individual cochlear duct length (CDL). However, no clear relationship has been found between speech development and the extent of electrode insertion, and the benefits of apical stimulation are not yet clear. In this retrospective study, we assessed the effect of cochlear coverage on audiological and speech performance. Participants were prelingually deaf children who received cochlear implants between June 2013 and December 2014 under the care of a single cochlear implant surgeon. Cochlear coverage was estimated for each ear according to electrode type, depth of insertion, and the number of active electrodes. Electrode type and length were determined by the individual's CDL, measured by computed tomography (CT), and full insertion was documented intraoperatively. The number of active electrodes was recorded using intraoperative audiological response telemetry. Audiological assessments were obtained 6 months and 1 year postoperatively. Results of the categories of auditory performance-II and speech intelligibility rating scales were obtained after 3 years. Patients were divided into two groups based on their cochlear coverage and their audiological and speech outcomes were compared. Of the 97 children recruited, 47 were girls. Temporal bone CT scans showed the right and left mean CDLs among girls were 27.7 and 27.9 mm, respectively, and 29.2 mm for both ears in boys. For each sex, the right and left CDLs did not differ significantly (p = 0.07). Twenty patients were lost to follow-up, leaving 77 patients (120 ears), which were divided into groups according to cochlear coverage (complete vs. incomplete). Significant between-group differences were not found in assessments of audiology, categories of auditory performances, or speech intelligibility ratings after 3 years. Audiological parameters do not differ according to the degree of cochlear coverage, specifically for low-frequency tones. Speech parameters are also comparable. Therefore, complete cochlear coverage does not appear to provide significant benefit over incomplete coverage for prelingually deaf cochlear implant recipients.

Drafting a Surgical Procedure Using a Computational Anatomy Driven Approach for Precise, Robust, and Safe Vestibular Neuroprosthesis Placement-When One Size Does Not Fit All.

To design and evaluate a new vestibular implant and surgical procedure that should reach correct electrode placement in 95% of patients in silico. Computational anatomy driven implant and surgery design study. Tertiary referral center. The population comprised 81 patients that had undergone a CT scan of the Mastoid region in the Maastricht University Medical Center. The population was subdivided in a vestibular implant eligible group (28) and a control group (53) without known vestibular loss. Canal lengths and relationships between landmarks were calculated for every patient. The relationships in group-anatomy were used to model a fenestration site on all three semicircular canals. Each patient's simulated individual distance from the fenestration site to the ampulla was calculated and compared with the populations average to determine if placement would be successful. Lengths of the semicircular canals, distances from fenestration site to ampulla (intralabyrinthine electrode length), and rate of successful electrode placement (robustness). The canal lengths for the lateral, posterior, and superior canal were respectively 12.1 mm ± 1.07, 18.8 mm ± 1.62, and 17.5 mm ± 1.23, the distances from electrode fenestration site to the ampulla were respectively 3.73 mm ± 0.53, 9.02 mm ± 0.90, and 5.31 mm ± 0.73 and electrode insertions were successful for each respective semicircular canal in 92.6%, 66.7%, and 86.4% of insertions in silico. The implant electrode was subsequently revised to include two more electrodes per lead, resulting in a robustness of 100%. The computational anatomy approach can be used to design and test surgical procedures. With small changes in electrode design, the proposed surgical procedure's target robustness was reached.

Establishment of a Numerical Model to Design an Electro-Stimulating System for a Porcine Mandibular Critical Size Defect

Electrical stimulation is a promising therapeutic approach for the regeneration of large bone defects. Innovative electrically stimulating implants for critical size defects in the lower jaw are under development and need to be optimized in silico and tested in vivo prior to application. In this context, numerical modelling and simulation are useful tools in the design process. In this study, a numerical model of an electrically stimulated minipig mandible was established to find optimal stimulation parameters that allow for a maximum area of beneficially stimulated tissue. Finite-element simulations were performed to determine the stimulation impact of the proposed implant design and to optimize the electric field distribution resulting from sinusoidal low-frequency ( f = 20 Hz ) electric stimulation. Optimal stimulation parameters of the electrode length h el = 25 m m and the stimulation potential φ stim = 0.5 V were determined. These parameter sets shall be applied in future in vivo validation studies. Furthermore, our results suggest that changing tissue properties during the course of the healing process might make a feedback-controlled stimulation system necessary.

AC plasma retarded flame spread over thin solid fuels in a simulated microgravity environment

The flame spread over thin solid fuels in a narrow channel by the action of AC plasma was first proposed and reported to show a trade-off between the flame instability produced by ionic wind and the kinetic enhancement stimulated by energetic and chemically active species. The 6 mm height narrow channel apparatus has been demonstrated the ability to suppress buoyant flow in horizontally spreading flames, and can successfully simulate a microgravity environment. Plasma acted on flame spread over thin solid fuels led to a confined behavior not typically seen in previous researches, which was investigated by integrated studies of experiment and supporting analysis using BOLSIG+. Four primary variables including flow velocity, reduced electric field, oxygen concentration and electrode length were considered. Among them, the reduced electric field and the oxygen concentration were found the crucial factors affecting the flame spread and further the flammability limit. The experimental results showed the affected field of the flame spread matched the field acted by AC discharge, which suggested a one-to-one correspondence between AC plasma action and flame slowing down or extinguishing. The results also showed that the narrow channel apparatus could capture the essential features of the flame spread in a simulated microgravity, for example the flame-lets phenomenon. The dependence of ionic wind on the reduced electric field was additionally investigated by solving the electron energy deposition into different excited channels and the electron energy distribution function (EEDF), which was essentially in agreement with the experimental observations. This study would develop a new and successful tool with rapid control of spacecraft fire and response to future exploration vehicles.

Flexible graphene-based micro-capacitors using ultrafast laser ablation

This study investigated the sensor performance and durability of flexible graphene-based micro-capacitor using ultrafast laser ablation with picosecond (PS) pulses. Micro-patterns were fabricated under varying electrode widths, lengths, and gaps on the flexible polyethylene terephthalate (PET) substrates for optimal capacitive performance. The experimental results showed that the untouched capacitance of the micro-capacitors had an approximately linear relationship with electrode widths and lengths. Increasing the electrode width can effectively enhance capacitance of the micro-capacitor, especially under small electrode gap. Micro-capacitors exhibited stable relative resistance change and excellent capacitance retention when bending angle θ ≤ 30° after 1000 times bending test. The decreasing rates of capacitance retention substantially increased with bending angles from 30° to 180°. Touched capacitances increased sharply as pressure rose from 0 to 6 kPa. These experimental results can be considered in designs of durable and high sensitivity flexible graphene-based touch sensors.

A novel design approach of charge plasma tunnel FET for radio frequency applications

In this paper, the impact of extra electron source (EES) and dual metal gate engineering on conventional charge plasma TFET (CP-TFET) have been done for improving DC and analog/RF parameters. CP-TFET structure is upgraded to double source CP-TFET (DS-CP-TFET) by placing an EES below the source/channel junction for enhancing the device performance in terms of driving current and RF figures of merit (FOMs). But, in spite of these pros, the approach is having cons of higher leakage current similar to MOSFET and negative conductance (inherent nature of TFET). Both the issues have been resolved in the double source dual gate CP-TFET (DS-DG-CP-TFET) by gate workfunction engineering and drain underlapping respectively. Additionally, for getting the optimum performance of DS-DG-CP-TFET, the device sensitivity has been investigated in terms of position of EES, length of drain electrode and workfunction of gate electrode 1 (GE1).

(Invited) The Role of Advanced Characterisation in Understanding the Initiation and Propagation of Failure in Li-Ion Batteries

Recent years have witnessed a number of high profile failures of Li-ion batteries; from cell-phones to aircraft, it is essential to improve understanding of failure mechanisms in order to design solutions to effectively mitigate the risks of cell thermal runaway. The increasingly diverse and demanding range of applications for Li-ion batteries necessitates a redoubling of efforts to tackle safety issues. Here, we apply a suite of in-situ and operando characterisation tools to understand safety and failure criteria over a range of time and length scales. At the electrode length scale, we utilise high resolution X-ray computed tomography to examine the complex, heterogeneous microstructures characteristic of Li-ion batteries. These can be effectively combined with imaged based modelling tools to explore the local electrochemical and physical behaviour, which can be correlated with electrochemical and thermal measurements. We can extend these investigations into the fourth dimension to explore the change in electrode morphology with time, to evaluate the role of microstructure evolution on cell degradation and failure. At the cell length scale, we utilise a combination of high-speed X-ray imaging, thermal imaging, calorimetry and acoustic spectroscopy, to understand the nucleation and propagation of failure in devices. In concert, these tools provide unique insight into degradation and failure process from the particle to the cell scale, from sub-second thermal runaway, to long term in-situ degradation studies. Increasingly we are equipped to evaluate new innovations in Li-ion battery technology, and moreover to effectively design and optimise next generation battery chemistries.

Alkaline Water Electrolysis at 20 a cm-2 with a Microfibrous, Flow-through Electrolyzer

Improving both the efficiency and productivity of water electrolysis is necessary for making the electrochemical generation of hydrogen economically competitive. Flow-through electrodes are widely used to improve the efficiency and productivity of electrochemical processes, but studies of their use in alkaline water electrolysis are relatively rare. This work aimed to (1) test the hypothesis that the use of a flow-through electrode could enhance the rate of bubble removal from the electrode surface, thereby improving productivity, and (2) determine what length scale of electrode would maximize the surface area available for electrolysis without hindering bubble removal. To determine how the efficiency and productivity of the flow-through electrode depends on the electrode length scale, the performance of the oxygen evolution reaction was compared with flow-through electrodes consisting of a Ni foam, Ni microfibers (Ni MFs, d = 1.2 mm), and Ni-coated Cu nanowires (NiCu NWs, d = 350 nm). Although the turnover frequency (TOF) for the Ni foam was 2.4 times higher than the Ni MF electrode and 42 times higher than the NiCu NW electrode, its surface area was more than 90 times lower than the other electrodes, resulting in the lowest overall current density. Although the NiCu NW electrode had a higher surface area than the Ni MF electrode, it had a lower overall current density because of its low TOF. We attribute the high performance of the Ni MF electrode to the fact that the mean pore size of the Ni MF electrode (5-10 mm) is on the order of the mean bubble size (20 mm) that was measured by examining the bubbles generated from a mesh electrode. The performance of the Ni MF electrode was further improved by coating it with a Ni-Fe layered double hydroxide (LDH) catalyst, resulting in an OER overpotential of 247 mV at 0.1 A cm-2 and a Tafel slope of 26 mV dec-1. These values are among the lowest reported for Ni-Fe LDH catalysts. A Ni MF anode was paired with a Pt-coated Ni MF cathode to measure the overall productivity for water splitting. The maximum current density for water splitting was 20 A cm-2 at 3.9 V in 30% KOH, which is 20 times greater than the highest current densities previously reported for alkaline water electrolysis. This current density and voltage could be sustained for at least 8 hours with no signs of degradation. This high current density was attributed to the ability of the flowing fluid to promote bubble removal and keep the hot electrode surface from boiling water. This work demonstrates that flow-through microfibrous electrodes can improve the efficiency and productivity of alkaline water electrolysis. Figure 1

A computational model to investigate the influence of electrode lengths on the single probe bipolar radiofrequency ablation of the liver

Background and objectives: Recently, there have been calls for RFA to be implemented in the bipolar mode for cancer treatment due to the benefits it offers over the monopolar mode. These include the ability to prevent skin burns at the grounding pad and to avoid tumour track seeding. The usage of bipolar RFA in clinical practice remains uncommon however, as not many research studies have been carried out on bipolar RFA. As such, there is still uncertainty in understanding the effects of the different RF probe configurations on the treatment outcome of RFA. This paper demonstrates that the electrode lengths have a strong influence on the mechanics of bipolar RFA. The information obtained here may lead to further optimization of the system for subsequent uses in the hospitals.Methods: A 2D model in the axisymmetric coordinates was developed to simulate the electro-thermophysiological responses of the tissue during a single probe bipolar RFA. Two different probe configurations were considered, namely the configuration where the active electrode is longer than the ground and the configuration where the ground electrode is longer than the active. The mathematical model was first verified with an existing experimental study found in the literature.Results: Results from the simulations showed that heating is confined only to the region around the shorter electrode, regardless of whether the shorter electrode is the active or the ground. Consequently, thermal coagulation also occurs in the region surrounding the shorter electrode. This opened up the possibility for a better customized treatment through the development of RF probes with adjustable electrode lengths.Conclusions: The electrode length was found to play a significant role on the outcome of single probe bipolar RFA. In particular, the length of the shorter electrode becomes the limiting factor that influences the mechanics of single probe bipolar RFA. Results from this study can be used to further develop and optimize bipolar RFA as an effective and reliable cancer treatment technique.

Properties of a cylindrical Penning trap with conical endcap openings

We describe the results of analytical calculations and numerical simulations of the confinement properties of a mechanically compensated cylindrical Penning trap which has conical endcap openings for large-solid-angle access for example with highly focused laser beams. While the analytical calculations show that under the common geometrical conditions the harmonicity of the confining fields near the centre of the trap does not change when a conical shape of the endcap electrodes is introduced, numerical simulations show significant changes when the opening angle of the cone exceeds a certain critical angle. We also show that these sharp features are due to the fringe-field effects above the critical angle, which are not described by the analytical calculations. These effects are also observed in a cylindrical Penning trap when the length of the endcap electrodes is reduced below a certain critical value.

Electrochemical measurement of the size of microband electrodes: A theoretical study

A theoretical proof-of-concept study demonstrating the use of an electrochemical method to measure the width and length of a band electrode of unknown dimensions is presented. It is found that by using a fully irreversible redox couple it is possible to characterise a band electrode without prior knowledge of the electron transfer rate constant or the formal potential. By using the peak-to-peak separation (Ep-p) and the magnitude of the ratio of backward peak current to forward peak current (|Ibackward/Iforward|) as diagnostic parameters that characterise the shape and size of the resulting voltammetric wave, the band width can be estimated with an error of less than 4% compared to its true value and with an error in length of less than 1%.

Effects of pin and wire electrodes on flow boiling heat transfer enhancement in a vertical minichannel heat sink

In this paper, electrohydrodynamic (EHD) enhancement of flow boiling heat transfer in a vertical minichannel heat sink was investigated experimentally. The pin and wire electrodes are used to create different kinds of non-uniform electric fields. Flow boiling experiments of refrigerant R-141b under electric fields are conducted under various applied voltages. The results show that the application of pin and wire electrodes can promote the Onset of Nucleate Boiling (ONB) and effectively enhance heat transfer coefficient. For the pin and wire electrodes, the EHD enhancement effect increases with the increase of applied voltage. At the same heat flux, heat transfer enhancement for pin electrode is higher than that for wire electrode at low applied voltage (U ≤ 400 V), but is lower than that for wire electrode at high applied voltage (U ≥ 550 V). Moreover, the obtained maximum enhancement ratio for pin and wire electrodes could reach 1.72 and 1.80, respectively. The influence area of pin electrode is limited, whereas the influence area of wire electrode is the entire electrode length at U ≥ 400 V. Based on the simulation and experiment results, the enhancing mechanism of EHD on flow boiling heat transfer in minichannel was discussed.

A crack along a part of an interface electrode in a piezoelectric bimaterial under anti-plane mechanical and in-plane electric loadings

An electrically conducting crack along a part of an electrode in the interface of a piezoelectric bimaterial under the action of anti-plane mechanical and in-plane electric loadings is analyzed. The electrode is assumed to be much thinner than the piezoelectric material, and therefore, its mechanical properties are neglected. Using special representations of field variables via sectionally analytic functions, a combined Dirichlet–Riemann boundary value problem is formulated and solved analytically. Explicit expressions for the shear stress, the electric field and the crack faces’ sliding displacement are derived. These quantities are also presented graphically along the corresponding parts of the material interface. The intensity factors for stress and electric field are determined as well. The dependencies of the mentioned values on the magnitude of the external electric loading and different ratios of the crack and electrode lengths are presented.

Bipolar Voltage Mapping for the Evaluation of Atrial Substrate: Can We Overcome the Challenge of Directionality?

The relationship between atrial fibrosis and atrial fibrillation (AF) has been proven. Patient specific substrate ablation targeting fibrotic tissue estimated by bipolar voltage mapping has emerged as an alternative strategy for additional substrate modification beyond pulmonary vein isolation. The primary mechanism of a low-voltage electrogram has been suggested to be atrial fibrosis, however, no direct correlation between histological fibrosis and low-voltage zone has been confirmed. Furthermore, the definition of low-voltage zone is still controversial, and bipolar voltage amplitudes depend on multiple variables including electrodes orientation relative to direction of wavefront, electrode length, interelectrode spacing, and tissue contact. The aim of this article is to review the role and limitation of voltage mapping, and to share our initial experience of a newly released grid-pattern designed mapping catheter to make the voltage mapping more reliable to guide patient specific AF ablation.

(Invited) Multiscale Image-Based Control and Characterization of Lithium-Ion Batteries

Lithium-ion batteries (LIB) are today the main energy storage devices from portable electronics devices to electric vehicles. LIB have a high energy density, low self-discharge, and low memory effect allowing for large number of charging cycle without degrading storage capacity. Performance, cost and safety are the main factors driving research and different chemistry are investigated in order to achieve better performance at a lower cost and increase safety. Research, development and quality control of LIB can benefit much from X-ray Computed Tomography (CT) and Focused-Ion Beam – Scanning Electron Microscopy (FIB-SEM). MicroCT allows for complete non-destructive acquisition of a complete battery cell, allowing to control the production process and to monitor the changes occurring in the structure during multiple charging cycles. Different visualization techniques are proposed on a 7µm microCT acquisition of a Lithium Nickel Manganese Cobalt Oxide cell 18650 (NMC) which allow for a visual inspection of the internal structure of the cell, including techniques of unfolding to look at rolled electrodes and measurement such as electrode thickness, height, or length. Macroscopic properties of a battery, including mechanical, thermal and electrical, find their origins at a nano-scale. Using FIB-SEM, high resolution images can be acquired which can reveal the structure of the electrodes or the separator. Besides the volume fraction or surface areas of the different phases, the connectivity of pores and/or particles, their surface of contacts, path tortuosity or constrictivity, permeability or molecular diffusivity, become accessible. We will present simulation results on permeability and tortuosity on this sample. We will also present correlative experiment, performing first a microCT scan of a cathode foil sample on its aluminium collector, spotting sites of interest in it, and acquiring those volumes with FIB-SEM.

Research on Welding and Processing Behavior of Electrodes and Features of their Application in "Wet" Underwater Arc Welding

Three brands of special electrodes for underwater welding were analyzed: LKI-1P, EPS-AN, UW-EZ-2. Experimental data on welding and processing behavior of these types of electrodes in the conditions of underwater arc welding were obtained: melting factor, metal deposit factor and losses. Experiments have been performed to determine the value of the arc breaking length of electrodes when welding under water. A comparative analysis was made with UONII-13/55 electrodes when welding in air conditions.

Hearing Preservation in Cochlear Implant Surgery: A Meta-Analysis.

The aim of the present meta-analysis is to assess the effects of hearing preservation (HP) methods on residual hearing in patients undergoing cochlear implant (CI) surgery and to look at the effect of follow-up time on HP outcome. A systematic search was conducted in PubMed, Embase, and Cochrane Library. Only articles in English were included. Prospective studies published until January 2018 on hearing preservation methods were included. Studies were assessed on unaided pre- and postoperative hearing thresholds, follow up time, and methodological quality. A random-effects meta-regression was performed for the HP outcome in relation to surgical technique, electrode array design, inserted electrode length, insertion speed, and corticosteroid use for different follow up times (1 month, 6 months, and 12 months or more postoperatively). Hearing preservation in cochlear implant surgery is feasible. A statistically significant difference was found between the round window procedure and cochleostomy approach, in favor of the round window procedure at 6 months postoperatively (p = 0.001). A statistically significant difference was found between the straight and the perimodiolar electrode array at 1 month postoperatively in favor of the straight electrode array (p < 0.001). No statistically significant difference was found between the other HP methods. The round window approach with the straight electrode array might result in a better HP outcome at 1 month and 6 months postoperatively compared with the cochleostomy approach with the perimodiolar electrode array. A declining trend in HP outcome in both combinations was seen over time.