Grid Electrode Research Articles

Stiffness Perception using Transcutaneous Electrical Stimulation during Active and Passive Prosthetic Control.

Haptic feedback allows an individual to identify various object properties. In this preliminary study, we determined the performance of stiffness recognition using transcutaneous nerve stimulation when a prosthetic hand was moved passively or was controlled actively by the subjects. Using a 2x8 electrode grid placed along the subject's upper arm, electrical stimulation was delivered to evoke somatotopic sensation along their index finger. Stimulation intensity, i.e. sensation strength, was modulated using the fingertip forces from a sensorized prosthetic hand. Object stiffness was encoded based on the rate of change of the evoked sensation as the prosthesis grasped one of three objects of different stiffness levels. During active control, sensation was modulated in real time as recorded forces were converted to stimulation amplitudes. During passive control, prerecorded force traces were randomly selected from a pool. Our results showed that the accuracy of object stiffness recognition was similar in both active and passive conditions. A slightly lower accuracy was observed during active control in one subject, which indicated that the sensorimotor integration processes could affect haptic perception for some users.

Evoking haptic sensations in the foot through high-density transcutaneous electrical nerve stimulations

Objective. Evoking haptic sensation on upper limb amputees via peripheral nerve stimulation has been investigated intensively in the past decade, but related studies involving lower limb amputees are limited. This study aimed to evaluate the feasibility of using non-invasive transcutaneous electrical nerve stimulation to evoke haptic sensation along the phantom limb of the amputated foot of transtibial amputees. Approach. A high-density electrode grid (4 × 4) was placed over the skin surface above the distal branching of the sciatic, tibial, and common peroneal nerves. We hypothesized that electrical stimulation delivered to distinct electrode pairs created unique electric fields, which can activate selective sets of sensory axons innervating different skin regions of the foot. Five transtibial amputee subjects (three unilateral and two bilateral) and one able-bodied subject were tested by scanning all possible electrode pair combinations. Main results. All subjects reported various haptic percepts at distinct regions along the foot with each corresponding to specific electrode pairs. These results demonstrated the capability of our non-invasive nerve stimulation method to evoke haptic sensations in the foot of transtibial amputees and the able-bodied subject. Significance. The outcomes contribute important knowledge and evidence regarding missing tactile sensation in the foot of lower limb amputees and might also facilitate future development of strategies to manage phantom pain and enhance embodiment of prosthetic legs in the future.

Active and Deformable Organic Electronic Devices based on Conductive Shape Memory Polyimide

Smart, deformable, and transparent electrodes are a significant part of flexible optoelectronic devices. In this work, a novel approach to making highly transparent, smooth, and conductive shape memory polyimide hybrids has been proposed. Colorless shape memory polyimide (CSMPI) with high optical transparency and high heat resistance is served as the substrate for flexible electronic devices for the first time. A hybrid (Au/Ag) metal grid electrode embedded in CSMPI (BMG/CSMPI) is first fabricated via self-cracking template and solution-coating, the advantages of which include ultrasmooth surface, superior mechanical flexibility and durability, strong surface adhesion, and excellent chemical stability due to the unique embedded hybrid structure. The resulting white polymer light emitting diodes (WPLEDs) based on BMG/CSMPI with shape memory effect are active and deformable, and are converted from 2D device into 3D devices depending on its variable stiffness characteristics. The deformed 3D devices could actively recover to the original shape upon heating. Furthermore, ultrathin and flexible 3D optoelectronic devices fabricated using shape memory polymers can promote the development of advanced optoelectronic applications in the future.

Adaptive Real-Time Identification of Motor Unit Discharges From Non-Stationary High-Density Surface Electromyographic Signals.

Estimation of the discharge pattern of motor units by electromyography (EMG) decomposition has been applied for neurophysiologic investigations, clinical diagnosis, and human-machine interfacing. However, most of the methods for EMG decomposition are currently applied offline. Here, we propose an approach for high-density surface EMG decomposition in real-time. A real-time decomposition scheme including two sessions, offline training and online decomposition, is proposed based on the convolutional kernel compensation algorithm. The estimation parameters, separation vectors and the thresholds for spike extraction, are first computed during offline training, and then they are directly applied to estimate motor unit spike trains (MUSTs) during the online decomposition. The estimation parameters are updated with the identification of new discharges to adapt to non-stationary conditions. The decomposition accuracy was validated on simulated EMG signals by convolving synthetic MUSTs with motor unit action potentials (MUAPs). Moreover, the accuracy of the online decomposition was assessed from experimental signals recorded from forearm muscles using a signal-based performance metrics (pulse-to-noise ratio, PNR). The proposed algorithm yielded a high decomposition accuracy and robustness to non-stationary conditions. The accuracy of MUSTs identified from simulated EMG signals was 80% for most conditions. From experimental EMG signals, on average, 12 ± 2 MUSTs were identified from each electrode grid with PNR of 25.0 ± 1.8dB, corresponding to an estimated decomposition accuracy 75%. These results indicate the feasibility of real-time identification of motor unit activities non-invasively during variable force contractions, extending the potential applications of high-density EMG as a neural interface.

FEMfuns: A Volume Conduction Modeling Pipeline that Includes Resistive, Capacitive or Dispersive Tissue and Electrodes

Applications such as brain computer interfaces require recordings of relevant neuronal population activity with high precision, for example, with electrocorticography (ECoG) grids. In order to achieve this, both the placement of the electrode grid on the cortex and the electrode properties, such as the electrode size and material, need to be optimized. For this purpose, it is essential to have a reliable tool that is able to simulate the extracellular potential, i.e., to solve the so-called ECoG forward problem, and to incorporate the properties of the electrodes explicitly in the model. In this study, this need is addressed by introducing the first open-source pipeline, FEMfuns (finite element method for useful neuroscience simulations), that allows neuroscientists to solve the forward problem in a variety of different geometrical domains, including different types of source models and electrode properties, such as resistive and capacitive materials. FEMfuns is based on the finite element method (FEM) implemented in FEniCS and includes the geometry tessellation, several electrode-electrolyte implementations and adaptive refinement options. The Python code of the pipeline is available under the GNU General Public License version 3 at https://github.com/meronvermaas/FEMfuns. We tested our pipeline with several geometries and source configurations such as a dipolar source in a multi-layer sphere model and a five-compartment realistically-shaped head model. Furthermore, we describe the main scripts in the pipeline, illustrating its flexible and versatile use. Provided with a sufficiently fine tessellation, the numerical solution of the forward problem approximates the analytical solution. Furthermore, we show dispersive material and interface effects in line with previous literature. Our results indicate substantial capacitive and dispersive effects due to the electrode-electrolyte interface when using stimulating electrodes. The results demonstrate that the pipeline presented in this paper is an accurate and flexible tool to simulate signals generated on electrode grids by the spatiotemporal electrical activity patterns produced by sources and thereby allows the user to optimize grids for brain computer interfaces including exploration of alternative electrode materials/properties.

Dependence of the Optimization of the Front Grid Design in Passivated Emitter and Rear Contact c-Si Solar Cells on the Finger Width and the Aspect Ratio

In this research, modeling was performed to optimize the grid of the front surface of a solar cell with the passivated emitter and rear contact (PERC) structure by considering the recombination characteristics. The front surface recombination velocity can be reduced in two main ways. The first method is to reduce the emitter Auger recombination by lowering the surface doping concentration during emitter formation, and the second method is to reduce the recombination that occurs at the surface when the electrode and the silicon are in contact, which is called metal-induced recombination and is represented by J0.metal. Because J0.metal increases in proportion to the area of the front electrode, minimizing the finger width and number by optimizing the electrode design is important. Therefore, the front electrode grid should be designed considering the emitter characteristics, J0.metal, according to the number of fingers and the resistance. In this research, the front grid of the solar cell was optimized via modeling using equations to calculate the number of fingers and the resistance. According to the finger width, the number of busbars, the sheet resistance, the aspect ratio, and the number of fingers corresponding to the maximum efficiency were identified. As a result, this modeling enabled us to optimize the front grid to the desired conditions, and we found that an increase in the number of busbars plays an important role in improving the efficiency of solar cells. In addition, the efficiency change with increasing number of busbars can be seen to be affected by the width of the finger and the resolution of the printed finger rather than the aspect ratio.

Optical and Electrical Properties of Multilayer Grid Electrodes for Highly Durable Transparent Conductive Electrodes

We report on the optical and electrical properties of MgZnO/Ag/MgZnO (MAM) grid electrodes grown at room temperature; these are proposed as an alternative to metal-based grid electrodes to meet the requirement for high stability in a harsh environment. The optical transmittance of Ag grid electrodes improved when the Ag grid layer was embedded in an MgZnO grid layer regardless of the fill factor. This improvement depends critically on the Ag grid layer thickness in the MAM grid electrodes. The Haack figure of merit for a MAM grid electrode with a 20 nm-thick Ag grid layer was approximately threefold higher than that of an Ag grid electrode. The electrode has an average transmittance of 85.8% at wavelengths range from 400 to 1100 nm and a sheet resistance of 26.9 Ω/sq. These results indicate that MAM grid electrodes can be an alternative to metal-based grid electrodes in optoelectronic devices that require stable wideband operation in a harsh environment and over a wide wavelength region.

A new method to determine conductivity distribution based on wire-mesh sensor by iteration

The wire-mesh sensor (WMS) is a kind of advanced instrument for gas-liquid two-phase flow measurements. In previous research, the sensitive volume was assumed to be uniformly distributed in the cross-section. The received current was assumed to represent the conductivity averaged over a uniform sensitive volume (USV), which is defined by symmetry considerations within the geometry of the electrode grids of the sensor. The void fraction within USV can be further determined based on the conductivity of USV. However, it is unphysical to determine the USV’s conductivity by the received current directly, since the true sensitive volume has an irregular shape due to the complexity of the potential field in the WMS. This study proposes an iterative method to determine the normalized conductivity averaged over each USV from the received current of WMS. The iterative method is based on potential field simulations within the electrode geometry of the WMS and an iterative process. To evaluate the performance of the iterative method, different normalized conductivity distributions were pre-defined. The maximum deviation between the pre-defined normalized conductivity and the normalized conductivity value determined by the new method was within 3%, instead of 30% for the conventional method. The performance of the new method for WMSs with different axial distance between transmitter and receiver grids La was also evaluated. For a larger La, more iterations need to be carried out to reach this accuracy. The limitation of this iterative method has been discussed. To reconstruct the sub-USV non-conductive phase distribution, the resolution of iterative method should be enhanced to describe the distribution of sub-USV non-conductive phase in future studies.

High-Density Surface EMG-Based Gesture Recognition Using a 3D Convolutional Neural Network.

High-density surface electromyography (HD-sEMG) and deep learning technology are becoming increasingly used in gesture recognition. Based on electrode grid data, information can be extracted in the form of images that are generated with instant values of multi-channel sEMG signals. In previous studies, image-based, two-dimensional convolutional neural networks (2D CNNs) have been applied in order to recognize patterns in the electrical activity of muscles from an instantaneous image. However, 2D CNNs with 2D kernels are unable to handle a sequence of images that carry information concerning how the instantaneous image evolves with time. This paper presents a 3D CNN with 3D kernels to capture both spatial and temporal structures from sequential sEMG images and investigates its performance on HD-sEMG-based gesture recognition in comparison to the 2D CNN. Extensive experiments were carried out on two benchmark datasets (i.e., CapgMyo DB-a and CSL-HDEMG). The results show that, where the same network architecture is used, 3D CNN can achieve a better performance than 2D CNN, especially for CSL-HDEMG, which contains the dynamic part of finger movement. For CapgMyo DB-a, the accuracy of 3D CNN was 1% higher than 2D CNN when the recognition window length was equal to 40 ms, and was 1.5% higher when equal to 150 ms. For CSL-HDEMG, the accuracies of 3D CNN were 15.3% and 18.6% higher than 2D CNN when the window length was equal to 40 ms and 150 ms, respectively. Furthermore, 3D CNN achieves a competitive performance in comparison to the baseline methods.

Contraction level, but not force direction or wrist position, affects the spatial distribution of motor unit recruitment in the biceps brachii muscle.

Different motor units (MUs) in the biceps brachii (BB) muscle have been shown to be preferentially recruited during either elbow flexion or supination. Whether these different units reside within different regions is an open issue. In this study, we tested wheter MUs recruited during submaximal isometric tasks of elbow flexion and supination for two contraction levels and with the wrist fixed at two different angles are spatially localized in different BB portions. The MUs' firing instants were extracted by decomposing high-density surface electromyograms (EMG), detected from the BB muscle of 12 subjects with a grid of electrodes (4 rows along the BB longitudinal axis, 16 columns medio-laterally). The firing instants were then used to trigger and average single-differential EMGs. The average rectified value was computed separately for each signal and the maximal value along each column in the grid was retained. The center of mass, defined as the weighted mean of the maximal, average rectified value across columns, was then consdiered to assess the medio-lateral changes in the MU surface representation between conditions. Contraction level, but neither wrist position nor force direction (flexion vs. supination), affected the spatial distribution of BB MUs. In particular, higher forces were associated with the recruitment of BB MUs whose action potentials were represented more medially. Although the action potentials of BB MUs were represented locally across the muscle medio-lateral region, dicrimination between elbow flexion or supination seems unlikely from the surface representation of MUs action potentials.

Flexible OPV modules for highly efficient indoor applications

The comparison of solution processed organic photovoltaics with two roll-to-roll coated electron transport layers (ETL), as well as printed grid or solid back electrodes provides insight into the future of R2R fabricated architectures. The variation in performance of the R2R slot-die coated zinc oxide (ZnO) versus the tin oxide (SnO2), showed a clear dependence on the spectrum of the illumination source. It was found that under indoor light conditions (200–1000 lux LED and fluorescent sources) the SnO2 outperformed the ZnO with highest efficiencies near 13% and 10% respectively. This is in contrast to results obtained under 1 Sun (AM 1.5) in which the cells fabricated with a ZnO ETL had a higher power conversion efficiency than those prepared with SnO2. The results also confirm the significance of the layout of the printed silver back contact; in which cells with the grid structure outperformed those with full coverage by approximately 35% for ZnO and just under 10% for SnO2 (all light conditions). The combination of a R2R coating and S2S printing process to prepare modules with 8 cells in series (PET/ITO/SnO2/PV2001:PCBM/PEDOT:PSS/silver grid) resulted in a PCE of 13.4% under indoor office light conditions.

Effect of sevoflurane on high-frequency brain electrical activity

Background. In 30 % of cases with epilepsy, it qualifies as medically intractable and requires surgical treatment. The need for improvement of epilepsy surgery effectiveness demands updating of the preoperative assessment protocols. Intraoperative wide-range electrocorticography is a novel technique for defining resection volume in focal structural epilepsy. Combined analysis of high-frequency and epileptiform activity provides additional information and allows prognosticating of surgery outcome. However, consistent evaluation of intraoperative monitoring results is only possible when general anesthetic effect on brain electrical activity is taken into account.Objective. This study was aimed at evaluation of anesthetic gas sevoflurane effect on high-frequency brain electrical activity, recorded directly from the cortex or deep brain structures.Design and methods. Eight patients were included in this study (2 females, 6 males), aged 19 to 47, with a long-term epilepsy (disease duration 15 to 38 years). Prolonged electrocorticographic monitoring was indicated to these patients, combined with eloquent zones mapping in some cases. Patients were implanted with grid electrodes on frontal and temporal cortex, and deep brain Spencer electrodes into the mesial temporal lobe. Wide-range electrocorticography was recorded during slow-wave sleep and intraoperatively under sevoflurane anesthesia. Pathological high-frequency oscillations (pHFOs) rate was counted.Results. In seven patients pHFOs were recorded extraoperatively. Pathological HFO rate varied between 13 and 30 % (mean — 19 %). Distribution of pHFO did not change due to anesthesia effects. Mean background noise amplitude was significantly decreased intraoperatively (z = 2.45; p = 0.014). This effect facilitated visual marking of pHFOs. There were no trends in comparison between extraoperative and intraoperative pHFO rate.Conclusion. Well-controlled levels of general anesthesia obtained with sevoflurane (0,9-1,1 MAC) showed minimal effect on high-frequency brain electrical activity. This allows thorough analysis of wide-range electrocorticogiaphy without waking the patient and provides more information about the extension of the epileptogenic zone and its resection rate intraoperatively.

Surface-enhanced resonance Raman spectroscopy of heme proteins on a gold grid electrode.

The combination of surface-enhanced resonance Raman spectroscopy (SERRS) and electrochemistry is an ideal tool to study the redox process of the heme proteins and is often performed on silver electrodes. In this manuscript, we present an approach using a microstructured gold surface that serves as the electrochemical working electrode, and at the same time, acts as SERS active substrate. The cell requires a micromolar concentration of sample at the electrode surface. Even if the performance of the gold grid as SERS substrate exhibited a smaller enhancement factor than expected for silver, oxidized and reduced spectra of proteins (Сyt c, Hb and Mb) monolayers could be obtained and the characteristic redox dependent shifts of the marker bands ν19, ν4 and ν10 were seen. The easy modification protocol and the higher stability of the gold electrode towards oxidative currents are the advantages of the present spectroeletrochemical cell. Finally, FDTD simulations confirm that the roughness of the gold grid has an effect on the Raman enhancement of the adsorbed proteins.

Synergistic Tandem Solar Electricity-Water Generators

Summary Energy and clean water are two intertwined fundamental elements for human civilization and sustainable development. Here, we devise a monolithic tandem solar electricity-water generator that synergistically produces electricity and clean water by utilizing the full spectrum of solar irradiance. The tandem generator has two components: a top infrared-transparent photovoltaic device using above-band-gap photons, and a bottom solar water purifier using the below-band-gap photons. More strikingly, a well-designed water-proof thermal interconnecting layer (WTIL) makes these two components work synergistically: the bottom purifier serves as an evaporative cooler of the top solar cell to increase its efficiency, whereas the thermalization energy of the top cell is reutilized by the bottom purifier for producing more clean water. We experimentally demonstrate that a prototype hybrid tandem solar device with WTIL can generate electricity with a power output of 204 W m−2 and purify water at a rate of 0.80 kg m−2 h−1 under 1-sun illumination.

The secondary drop formation of nanoparticle/surfactant-stabilized water droplets under non-uniform electric fields

Electrocoalescence is an energy-efficient and environmentally-friendly process for breaking water-in-oil emulsions. It has been used extensively in the oil and petroleum industries. In this study, the electrocoalescence process of nanoparticle/surfactant-stabilized water droplets with a planar interface in the presence of non-uniform electric fields was experimentally investigated. The effects of electric field patterns (i.e. uniform and non-uniform fields) and nanoparticles (i.e. concentrations) on the drop-interface electrocoalescence process were systematically examined, analyzed, and discussed. The results showed that the presence of Sodium Dodecyl Sulfate (SDS) significantly increased the volume of secondary droplets and led to the apex disintegration of the main secondary droplet because of the low surface tension. At high SiO2 concentrations, the liquid bridge between the droplet and interface was difficult to form, and the whipping filament regime, sheet breakup regime, and varicose jet breakup regime, were observed, which were determined by the accumulating surface charge. In addition, three types of non-uniform fields induced by different geometrical electrode configurations, i.e. grid electrodes, mesh electrodes, and coupled electrodes, were proposed and the electric field distributions were calculated in COMSOL Multiphysics. With increasing SiO2 concentrations, coupled electrodes produced much smaller detached droplet volumes than those of pairwise mesh and grid electrodes, which was helpful to complete the coalescence of the drop and interface. Furthermore, flat electrodes, which induced a uniform electric field, produced much larger secondary droplet volumes than those of the electrodes generating non-uniform electric fields. In summary, the utilization of coupled electrodes had a positive effect on drop-interface coalescence and increased the overall separation efficiency. The outcome of this work is potentially useful in the design of compact and efficient oil-water electro-dehydration devices.

Intracranial EEG monitoring methods

Resective surgery is considered to be the best option towards achieving seizure-free state in drug-resistant epilepsy. Intracranial EEG (iEEG) is necessary if the seizure-onset zone is localized near to an eloquent cortical area, or if the results of presurgical examinations are discordant, or if an extratemporal epilepsy patient is MRI-negative. Nowadays, 3 kinds of electrodes are used: (1) foramen ovale (FO) electrodes; (2) subdural strip or grid electrodes (SDG); (3) deep electrodes (stereo-electroencephalographia, SEEG). The usage of FO electrode is limited to bitemporal cases. SDG and SEEG have a distinct philosophical approach, different advantages and disadvantages. SDG is appropriate for localizing seizure-onset zones on hemispherial or interhemispherial surfaces; it is preferable if the seizure-onset zone is near to an eloquent cortical area. SEEG is excellent in exploration of deeper cortical structures (depths of cortical sulci, amygdala, hippocampus), although a very precise planning is required because of the low spatial sampling. The chance for seizure-freedom is relatively high performing both methods (SDG: 55%, SEEG: 64%), beside a tolerable rate of complications.

The sensitivity of network statistics to incomplete electrode sampling on intracranial EEG.

Network neuroscience applied to epilepsy holds promise to map pathological networks, localize seizure generators, and inform targeted interventions to control seizures. However, incomplete sampling of the epileptic brain because of sparse placement of intracranial electrodes may affect model results. In this study, we evaluate the sensitivity of several published network measures to incomplete spatial sampling and propose an algorithm using network subsampling to determine confidence in model results. We retrospectively evaluated intracranial EEG data from 28 patients implanted with grid, strip, and depth electrodes during evaluation for epilepsy surgery. We recalculated global and local network metrics after randomly and systematically removing subsets of intracranial EEG electrode contacts. We found that sensitivity to incomplete sampling varied significantly across network metrics. This sensitivity was largely independent of whether seizure onset zone contacts were targeted or spared from removal. We present an algorithm using random subsampling to compute patient-specific confidence intervals for network localizations. Our findings highlight the difference in robustness between commonly used network metrics and provide tools to assess confidence in intracranial network localization. We present these techniques as an important step toward translating personalized network models of seizures into rigorous, quantitative approaches to invasive therapy.

Minimally Invasive, Endoscopic-Assisted Device for Subdural Electrode Implantation in Epilepsy.

Subdural grids and strip electrodes provide wide coverage of the cerebral cortex, precise delineation of the extent of the seizure onset zone, and improved spatial sampling to perform functional mapping for eloquent cortex. To describe a novel device that allows for a minimally invasive approach to implantation of subdural grid and strip electrodes. A skull mounted device was created to allow for implantation of subdural electrodes through a keyhole craniotomy with direct visualization using the aid of a flexible neurovideoscope. The initial studies in preparation for grid development performed on cadaveric skulls were analyzed to determine the size of craniotomy required for deployment, maximal distance of strip electrode deployment from center of craniotomy, and visual inspection of the cortex was performed for any underlying damage. The device allowed for the placement of subdural electrodes through a 40-mm craniotomy. Subdural electrodes were deployed in multiple directions to a distance of a 70-mm radius from the center of the craniotomy. There was no visual damage to the underlying cortex after the procedures were completed. Large craniotomies are typically desired to provide direct visualization of the implantation of subdural electrodes, but can increase the risk of subdural hemorrhages and infections. This study describes a novel minimally invasive endoscopically assisted device for the implantation of subdural strip electrodes under direct visualization. With this device, we are able to limit the size of the craniotomy, avoid incision through the temporalis muscle, and implant subdural electrodes with visualization of the cortex.

Comment on “Sheath oscillations during directional motion of fire tube formation in expanding RF plasma” [Phys. Plasmas 26, 113502 (2019)

Measurements regarding the plasma-sheath instability have been described in a recent paper [Phys. Plasmas 26, 113502 (2019)] by the authors Paul and Chakraborty. They measured low frequency oscillations in a cylindrical, highly transparent grid electrode by using Langmuir probes and magnetic field sensors. This topic is very interesting for low temperature plasma physics, especially when it comes to the fundamental understanding of the stability of (multiple) double layers. However, it is questionable if the measured frequencies are originating from a plasma-sheath resonance instability as the observed oscillations are not consistent with the established theory of the plasma-sheath resonance instability.

Embedded-grid silver transparent electrodes fabricated by selective metal condensation

We report a new materials system for the fabrication of embedded silver grid electrodes with micron-sized linewidth >10 times narrower than can be achieved using the conventional printing techniques of screen, inject and flexographic printing.