Discrete Electrodes Research Articles

Directed Networks as a Novel Way to Describe and Analyze Cardiac Excitation: Directed Graph Mapping.

Networks provide a powerful methodology with applications in a variety of biological, technological and social systems such as analysis of brain data, social networks, internet search engine algorithms, etc. To date, directed networks have not yet been applied to characterize the excitation of the human heart. In clinical practice, cardiac excitation is recorded by multiple discrete electrodes. During (normal) sinus rhythm or during cardiac arrhythmias, successive excitation connects neighboring electrodes, resulting in their own unique directed network. This in theory makes it a perfect fit for directed network analysis. In this study, we applied directed networks to the heart in order to describe and characterize cardiac arrhythmias. Proof-of-principle was established using in-silico and clinical data. We demonstrated that tools used in network theory analysis allow determination of the mechanism and location of certain cardiac arrhythmias. We show that the robustness of this approach can potentially exceed the existing state-of-the art methodology used in clinics. Furthermore, implementation of these techniques in daily practice can improve the accuracy and speed of cardiac arrhythmia analysis. It may also provide novel insights in arrhythmias that are still incompletely understood.

Monolithic Integration of Silicon Nanowire Networks as a Soft Wafer for Highly Stretchable and Transparent Electronics.

Assembling nanoscale building blocks into an orderly network with a programmable layout and channel designs represents a critical capability to enable a wide range of stretchable electronics. Here, we demonstrate the growth-in-place integration of silicon nanowire (SiNW) springs into highly stretchable, transparent, and quasicontinuous functional networks with a close to unity interconnection among the discrete electrode joints because of a unique double-lane/double-step guiding edge design. The SiNW networks can be reliably transferred to a soft elastomer substrate, conformally attached to highly curved surfaces, or deployed as self-supporting/movable membranes suspended over voids. A high stretchability of >40% is achieved for the SiNW network on an elastomer, which can be employed as a transparent and semiconducting thin-film material endowed with a high carrier mobility of >50 cm2/(V s), Ion/Ioff ratio >104, and a tunable transmission of >80% over a wide spectrum range. Reversibly stretchable and bendable sensors based on the SiNW network have been successfully demonstrated, where the local strain distribution within the spring network can be directly observed and analyzed by finite element simulations. This SiNW network has a unique potential to eventually establish a new generically purposed waferlike platform for constructing soft electronics with Si-based hard performances.

Multifrequency Induced-Charge Electroosmosis.

We present herein a unique concept of multifrequency induced-charge electroosmosis (MICEO) actuated directly on driving electrode arrays, for highly-efficient simultaneous transport and convective mixing of fluidic samples in microscale ducts. MICEO delicately combines transversal AC electroosmotic vortex flow, and axial traveling-wave electroosmotic pump motion under external dual-Fourier-mode AC electric fields. The synthetic flow field associated with MICEO is mathematically analyzed under thin layer limit, and the particle tracing experiment with a special powering technique validates the effectiveness of this physical phenomenon. Meanwhile, the simulation results with a full-scale 3D computation model demonstrate its robust dual-functionality in inducing fully-automated analyte transport and chaotic stirring in a straight fluidic channel embedding double-sided quarter-phase discrete electrode arrays. Our physical demonstration with multifrequency signal control on nonlinear electroosmosis provides invaluable references for innovative designs of multifunctional on-chip analytical platforms in modern microfluidic systems.

Activating the levator to elevate the eyelid

To demonstrate in an animal model the feasibility of elevating the eyelid in a functionally useful manner by chronically stimulating the levator palpebrae superioris (LPS) muscle with an implanted electrode. Five rabbits were implanted with electrodes designed to stimulate the nerve innervating the LPS near its entry to the muscle. Bipolar platinum electrodes in a silicone rubber envelope with silicone-sleeved, PTFE-coated platinum lead wires were used to provide long-term stimulation with bipolar square-wave pulse trains of 0.18-0.80mA and 200Hz at a duty cycle of 8seconds on and 2seconds off. Explanted electrodes were examined for damage, and stimulated tissues were evaluated for abnormalities by light microscopy. We achieved mean lid elevation of 1.6mm, approaching the diameter of the light-adapted pupil, with 0.5mA stimulus. Stimulus currents below 1.0mA produced no signs of discomfort. Three animals with which we attempted daily stimulation, averaged 16.1hours per week. Experiments lasted 22weeks on average. Lid lifting with a well-implanted platinum electrodes was stable, with no apparent tissue or electrode damage after as long as 29.1weeks. Stable, functionally useful eyelid lifting was achieved with stimulation currents that caused no apparent discomfort or damage to muscles or nerves. A simple, discrete bipolar electrode was effective and survivable.

A Lumped Mass Model for Circular Micro-Resonators in Coriolis Vibratory Gyroscopes.

Coriolis vibratory gyroscopes (CVGs) with circular micro-resonators, such as hemispherical, ring, and disk resonators, exhibit excellent performances and have extraordinary potential. This paper discusses a generalized lumped mass model for both 3D and planar circular micro-resonators, establishing the relationship between the modal effective mass, the modal equivalent force, and the point displacement of the resonator. The point displacement description of a continuous circular resonator’s motion is defined from the view of capacitance measurement. The modal effective mass is, consequently, determined by the kinetic and the potential energy of the structure and is computed with numerical simulations. Moreover, the modal equivalent force, which can be theoretically calculated for any configuration of discrete electrodes, is deduced by using the concept of force density and the force distribution function. By utilizing the lumped mass model in this paper, the stiffness softening, the mode tuning, and the quadrature correction of the micro-resonators are investigated in detail. The theoretical model is verified by both the finite element method (FEM) and the experiments.

Active vibration control of a smart functionally graded piezoelectric material plate using an adaptive fuzzy controller strategy

In this article, the active vibration control of a smart structure made out of a single functionally graded piezoelectric material layer, equipped with a network of discrete electrodes, is studied. The material properties vary continuously across the direction of thickness, so that top and bottom surfaces consist of pure PZT4 and the mid surface is composed of pure aluminium. The percolation phenomenon is taken into account. A functionally graded piezoelectric material plate finite element based on the first-order shear deformation theory hypothesis and layer-wise approximation for electric potential is implemented. An optimization procedure is considered to define the relevant electrodes for actuators and sensors, based on controllable and observable criteria. An adaptative fuzzy controller system is used, activating with relevance the actuators according to the most excited eigenmodes. Simulations show the effectiveness of this kind of concept.

Dielectrophoretic separation of microalgae cells in ballast water in a microfluidic chip.

The composition of the ship's ballast water is complex and contains a large number of microalgae cells, bacteria, microplastics, and other microparticles. To increase the accuracy and efficiency of detection of the microalgae cells in ballast water, a new microfluidic chip for continuous separation of microalgae cells based on alternating current dielectrophoresis was proposed. In this microfluidic chip, one piece of 3-dimensional electrode is embedded on one side and eight discrete electrodes are arranged on the other side of the microchannel. An insulated triangular structure between electrodes is designed for increasing the inhomogeneity of the electric field distribution and enhancing the dielectrophoresis (DEP) force. A sheath flow is designed to focus the microparticles near the electrode, so as to increase the suffered DEP force and improve separation efficiency. To demonstrate the performance of the microfluidic separation chip, we developed two species of microalgae cells (Platymonas and Closterium) and a kind of microplastics to be used as test samples. Analyses of the related parameters and separation experiments by our designed microfluidic chip were then conducted. The results show that the presented method can separate the microalgae cells from the mixture efficiently, and this is the first time to separate two or more species of microalgae cells in a microfluidic chip by using negative and positive DEP force simultaneously, and moreover it has some advantages including simple operation, high efficiency, low cost, and small size and has great potential in on-site pretreatment of ballast water.

Multi-channel aerosol dielectric electrical discharge machining ablation based on discrete electrode

The electrical discharge machining (EDM) ablation processing energy comes from the chemical energy released by metal combustion, which is much higher than in conventional EDM. In singular pulse voltage, only one discharge channel induces and activates metal substrate. Thus, the processing energy is concentrated, which impedes the improvement of material removal efficiency and workpiece surface quality. Multi-channel EDM ablation in aerosol dielectric is proposed in this study. Multi-channel discharge induces multi-spot ablation, which not only expands the scope of the ablation region and improves the machining efficiency of EDM ablation, but also disperses the discharge energy and enhances the surface quality of EDM ablation. The discrete electrode in which the method is based contained multiple copper tube electrodes. Each electrode was electrically insulated and connected to the pulse generator through a resistance. It generated multi-channel discharge in singular pulse voltage. In this study, the mechanism of multi-channel discharge was elucidated, and the machining characteristics of multi-channel aerosol dielectric EDM ablation were evaluated. On the basis of the results of the experiment by using Cr12 die steel as the workpiece, it was concluded that relative to that in aerosol dielectric EDM ablation, the material removal rate in multi-channel aerosol dielectric EDM ablation was improved by 92%. This rate was 3.12 times higher than that obtained in multi-channel inner jetted EDM and nearly 10 times higher than that in inner jetted EDM. The surface quality was improved as well.

Fuel Cell Electrodes Based on Functional Meso-Structured Arrays

State-of-the-art fuel cell catalyst layers consist of a random mixture of functional components (catalyst, ionomer, and pore) that are formed in an uncontrolled ink deposition process. The random nature of these structures makes it difficult to optimize the functional domains and hence causes severe mass transport limitations during high-power operation, resulting in a loss in performance and requiring that the fuel cell be oversized to maintain an acceptable level of performance. The ionomer binder adds an additional transport resistance and becomes significant at lower Pt loadings [1]. Decreasing this transport resistance would remove the main barrier to low-cost, ultra-high power density fuel cells. Rational design of the electrode structure in PEFCs could improve performance and reduce cost. By separating the different electrode functions into discrete electrode elements, each element can be optimized for specific functions. Arranging these optimized discrete elements in a controlled, low-tortuosity array configuration enables transport limitations to be reduced or eliminated. We have demonstrated this approach through fabrication of freestanding arrays of vertically-oriented ionomer channels with different aspect ratios, and incorporation of these channels into fuel cell electrodes where they serve as non-tortuous proton-transport highways (Figure 1). Providing effective proton transport through these low-tortuosity percolating highways allows the catalyst domain to have a lower ionomer/catalyst ratio, reducing transport resistance. Proof of concept was demonstrated by achieving a 15% increase in performance with channels with an aspect ratio of 8. Further work is underway to increase channel aspect ratio and improve integration of channels with surrounding catalyst layer, leading to further transport improvements and increases in performance. Fig. 1. Left: freestanding array of ionomer channels. Right: catalyst layer incorporating ionomer channels. References N. Nonoyama, S. Okazaki, A. Z. Weber, Y. Ikogi, and T. Yoshida, J. Electrochem. Soc., 158, B416 (2011). Acknowledgments This research is supported by DOE Fuel Cell Technologies Office, through the Fuel Cell Performance and Durability (FC-PAD) Consortium. Figure 1

Long term electroencephalography in preterm neonates: Safety and quality of electrode types

ObjectivesThe objective of this study was to compare gold cup and hydrogel electrodes for frequency of electrode replacement, longevity of the original electrodes after initial placement, recording quality, and skin safety issues in long-term EEG studies in preterm neonates. MethodsWe performed a prospective trial with newborns born at ≥23 weeks and ≤30 weeks of gestational age (GA). Two mirror image EEG electrode arrays were utilized on consecutive subjects, where gold cup electrodes alternated with hydrogel electrodes. ResultsOur sample included 50 neonates with mean GA of 27 (±1) weeks. The mean recording time was 84 (±15) hours. No difference was present in the frequency of replacement of either type across the total recording time (p = 0.8). We collected the time at which electrodes were first replaced, and found that hydrogel electrodes showed a longer uninterrupted recording time of 28(±2) hours vs. 20(±2) hours for gold cup electrodes (p = 0.01). Recording quality was similar in either type (p = 0.2). None of the patients experienced significant skin irritation from a discrete electrode. ConclusionLong-term EEG studies can be performed with either gold cup or hydrogel electrodes, validating the safety and quality of both electrode types. SignificanceHydrogel electrodes are a reasonable alternative for use in long-term EEG studies in preterm neonates.

Droplet Translation Actuated by Photoelectrowetting.

In traditional electrowetting-on-dielectric (EWOD) devices, droplets are moved about a substrate using electric fields produced by an array of discrete electrodes. In this study, we show that a drop can be driven across a substrate with a localized light beam by exploiting the photoelectrowetting (PEW) effect, a light-activated variant of EWOD. Droplet transport actuated by PEW eliminates the need for electrode arrays and the complexities entailed in their fabrication and control, and offers a new approach for designing lab-on-a-chip applications. We report measurements of the maximum droplet speed as a function of frequency and magnitude of the applied bias, intensity of illumination, volume of the droplet, and viscosity and also introduce a model that reproduces these data.

A novel capacitive absolute positioning sensor based on time grating with nanometer resolution

The present work proposes a novel capacitive absolute positioning sensor based on time grating. The sensor includes a fine incremental-displacement measurement component combined with a coarse absolute-position measurement component to obtain high-resolution absolute positioning measurements. A single row type sensor was proposed to achieve fine displacement measurement, which combines the two electrode rows of a previously proposed double-row type capacitive displacement sensor based on time grating into a single row. To achieve absolute positioning measurement, the coarse measurement component is designed as a single-row type displacement sensor employing a single spatial period over the entire measurement range. In addition, this component employs a rectangular induction electrode and four groups of orthogonal discrete excitation electrodes with half-sinusoidal envelope shapes, which were formed by alternately extending the rectangular electrodes of the fine measurement component. The fine and coarse measurement components are tightly integrated to form a compact absolute positioning sensor. A prototype sensor was manufactured using printed circuit board technology for testing and optimization of the design in conjunction with simulations. Experimental results show that the prototype sensor achieves a ±300 nm measurement accuracy with a 1 nm resolution over a displacement range of 200 mm when employing error compensation. The proposed sensor is an excellent alternative to presently available long-range absolute nanometrology sensors owing to its low cost, simple structure, and ease of manufacturing.

Simulation analysis of rectifying microfluidic mixing with field-effect-tunable electrothermal induced flow.

We report herein field-effect control on in-phase electrothermal streaming from a theoretical point of view, a phenomenon termed "alternating-current electrothermal-flow field effect transistor" (ACET-FFET), in the context of a new technology for handing analytes in microfluidics. Field-effect control through a gate terminal endows ACET-FFET the ability to generate arbitrary symmetry breaking in the transverse vortex flow pattern, which makes it attractive for mixing microfluidic samples. A computational model is developed to study the feasibility of this new microfluidic device design for micromixing. The influence of various parameters on developing an efficient mixer is investigated, and an integrated layout of discrete electrode array is suggested for achieving high-throughput mixing. Our physical demonstration with field-effect electrothermal flow control using a simple electrode structure proves invaluable for designing active micromixers for modern micro total analytical system.

Bipolar Electrode Array Embedded in a Polymer Light-Emitting Electrochemical Cell.

A linear array of aluminum discs is deposited between the driving electrodes of an extremely large planar polymer light-emitting electrochemical cell (PLEC). The planar PLEC is then operated at a constant bias voltage of 100 V. This promotes in situ electrochemical doping of the luminescent polymer from both the driving electrodes and the aluminum discs. These aluminum discs function as discrete bipolar electrodes (BPEs) that can drive redox reactions at their extremities. Time-lapse fluorescence imaging reveals that p- and n-doping that originated from neighboring BPEs can interact to form multiple light-emitting p-n junctions in series. This provides direct evidence of the working principle of bulk homojunction PLECs. The propagation of p-doping is faster from the BPEs than from the positive driving electrode due to electric field enhancement at the extremities of BPEs. The effect of field enhancement and the fact that the doping fronts only need to travel the distance between the neighboring BPEs to form a light-emitting junction greatly reduce the response time for electroluminescence in the region containing the BPE array. The near simultaneous formation of multiple light-emitting p-n junctions in series causes a measurable increase in cell current. This indicates that the region containing a BPE is much more conductive than the rest of the planar cell despite the latter's greater width. The p- and n-doping originating from the BPEs is initially highly confined. Significant expansion and divergence of doping occurred when the region containing the BPE array became more conductive. The shape and direction of expanded doping strongly suggest that the multiple light-emitting p-n junctions, formed between and connected by the array of metal BPEs, have functioned as a single rod-shaped BPE. This represents a new type of BPE that is formed in situ and as a combination of metal, doped polymers, and forward-biased p-n junctions connected in series.

Meso-Structured Array Electrode for Polymer Electrolyte Fuel Cells

Current state-of-the-art fuel cell cathodes rely on high loading of platinum (Pt) or Pt-alloy on high surface area carbon supports mixed with Nafion. The cost of the high Pt loading is still a hindrance to the commercialization of polymer electrolyte fuel cells (PEFCs) 1. The electrode structure consists of a random aggregation of the functional components (catalyst, ionomer, and pore space) that are formed in an uncontrolled ink deposition process. The random nature of these structures makes it difficult to optimize the functional domains and hence causes severe mass transport limitations during high-power operation, resulting in a loss in performance and requiring a higher loading and active area of Pt to maintain an acceptable level of performance. The ionomer binder adds an additional transport resistance and becomes significant at lower Pt loadings2. Decreasing this transport resistance would remove a significant barrier to low-cost, ultra-high power density fuel cells. Rational design of the electrode structure in PEFCs could improve performance and reduce cost. However, in current state-of-the-art fuel cells, each unit volume of electrode contains a random mix of components that must simultaneously provide catalytic activity, water transport, O2transport, electronic conductivity, and protonic conductivity. Since each unit must provide all functions, units cannot be optimized for individual functions. By separating the different electrode functions into discrete electrode elements, each element can be optimized for specific functions as shown in Figure 1a. Arranging these optimized discrete elements in a controlled, low-tortuosity configuration enables transport limitations to be reduced or eliminated. In previous work, Middlemen et al. showed under optimal conditions oriented catalyst layer structure can be fabricated but didn’t present any electrochemical evaluation 3. Komini Babu et al. fabricated vertically oriented Nafion nanofibers and deposited Pt via vapor deposition 4. The Nafion nanofiber electrode showed increase in performance compared to Pt sputtered on Nafion 115 electrode but lower in performance to Pt/C based electrode. In this work, we propose an alternate electrode structure to enable good transport behavior and high cell performance through controlled deposition of electrode components in an optimized, organized structural configuration. Figure 1b shows the SEM image of Nafion nanofibers for proton transport, fabricated by solution casting on a porous template. Providing effective proton transport through these low-tortuosity percolating highways allows the catalyst domain to have a lower ionomer/catalyst ratio, reducing transport resistance. Acknowledgments This research is supported by DOE Fuel Cell Technologies Office, through the Fuel Cell Performance and Durability (FC-PAD) Consortium; Fuel Cells program manager: Dimitrios Papageorgopoulos.

А two-electrode multichannel analyzer of charged particles with discrete outer cylindrical and flat end electrodes

Using computer simulation, I have determined the parameters of a multichannel analyzer of charged particles of a simple design that I have proposed having the form of a cylindrical capacitor with a discrete outer cylinder and closed ends in a wide range of simultaneously recorded energies (E max/E min = 100). When introducing an additional cylindrical electrode of small dimensions near the front end of the system, it is possible to improve the resolution by more than an order of magnitude in the low-energy region. At the same time, the energy resolution of the analyzer in all the above energy range is ρ = (4–6) × 10–3.

Increasing productivity in assembling z-folded electrode-separator-composites for lithium-ion batteries

Lithium-ion batteries (LIB) are key components of electromobility and a major cost factor of electric-vehicles. With a rising demand, affordable LIB become a success-factor for electromobility. LIB have different electrode-separator-composite-designs. Assembling a z-folded composite is currently characterized through time-consuming sequential pick-and-place operations for handling discrete electrodes and folding uncoiled-strip separators, causing high manufacturing costs. To avoid time-consuming sequential handling tasks, a novel process featuring a continuous separator feeding-speed and a high-speed synchronous handling of discrete electrodes has been developed, hereby enabling for a significant decrease of cycle-times and thus reducing manufacturing costs.

Effects of discrete-electrode arrangement on traveling-wave electroosmotic pumping

Traveling-wave electroosmotic (TWEO) pumping arises from the action of an imposed traveling-wave (TW) electric field on its own induced charge in the diffuse double layer, which is formed on top of an electrode array immersed in electrolyte solutions. Such a traveling field can be merely realized in practice by a discrete electrode array upon which the corresponding voltages of correct phase are imposed. By employing the theory of linear and weakly nonlinear double-layer charging dynamics, a physical model incorporating both the nonlinear surface capacitance of diffuse layer and Faradaic current injection is developed herein in order to quantify the changes in TWEO pumping performance from a single-mode TW to discrete electrode configuration. Benefiting from the linear analysis, we investigate the influence of using discrete electrode array to create the TW signal on the resulting fluid motion, and several approaches are suggested to improve the pumping performance. In the nonlinear regime, our full numerical analysis considering the intervening isolation spacing indicates that a practical four-phase discrete electrode configuration of equal electrode and gap width exhibits stronger nonlinearity than expected from the idealized pump applied with a single-mode TW in terms of voltage-dependence of the ideal pumping frequency and peak flow rate, though it has a much lower pumping performance. For model validation, pumping of electrolytes by TWEO is achieved over a confocal spiral four-phase electrode array covered by an insulating microchannel; measurement of flow velocity indicates the modified nonlinear theory considering moderate Faradaic conductance is indeed a more accurate physical description of TWEO. These results offer useful guidelines for designing high-performance TWEO microfluidic pumps with discrete electrode array.

An orbital shear platform for real-time, in vitro endothelium characterization.

Electrical impedance techniques have been used to characterize endothelium morphology, permeability, and motility in vitro. However, these impedance platforms have been limited to either static endothelium studies and/or induced laminar fluid flow at a constant, single shear stress value. In this work, we present a microfabricated impedance sensor for real-time, in vitro characterization of human umbilical vein endothelial cells (HUVECs) undergoing oscillatory hydrodynamic shear. Oscillatory shear was applied with an orbital shaker and the electrical impedance was measured by a microfabricated impedance chip with discrete electrodes positioned at radial locations of 0, 2.5, 5.0, 7.5, 10.0, and 12.5 mm from the center of the chip. Depending on their radial position within the circular orbital platform, HUVECs were exposed to shear values ranging between 0.6 and 6.71 dyne/cm(2) (according to numerical simulations) for 22 h. Impedance spectra were fit to an equivalent circuit model and the trans-endothelial resistance and monolayer's capacitance were extracted. Results demonstrated that, compared to measurements acquired before the onset of shear, cells at the center of the platform that experienced low steady shear stress (∼2.2 dyne/cm(2) ) had an average change in trans-endothelial resistance of 6.99 ± 4.06% and 1.78 ± 2.40% change in cell capacitance after 22 hours of shear exposure; cells near the periphery of the well (r = 12.5 mm) experienced transient shears (2.5-6.7 dyne/cm(2) ) and exhibited a greater change in trans-endothelial resistance (24.2 ± 10.8%) and cell capacitance (4.57 ± 5.39%). This study, demonstrates that the orbital shear platform provides a simple system that can capture and quantify the real-time cellular morphology as a result of induced shear stress. The orbital shear platform presented in this work, compared to traditional laminar platforms, subjects cells to more physiologically relevant oscillatory shear as well as exposes the sample to several shear values simultaneously. Biotechnol. Bioeng. 2016;113: 1336-1344. © 2015 Wiley Periodicals, Inc.

PZT based tunable Interdigital Transducer for Lamb waves based NDT and SHM

In this paper a novel concept of a tunable transducer for generation and sensing of the Lamb waves is presented. The proposed transducer is developed based on a commonly applied Interdigital Transducer (IDT). In the proposed design, further referred to as the Tunable IDT (T-IDT), the conventional comb electrodes with fixed pitch are replaced by a series of densely distributed discrete electrode strips. These electrodes can be easily interconnected in different configurations to match the required wavelength without a need of applying physical changes to the electrode layout. In order to verify the properties of the T-IDT, numerical simulations and experimental tests were performed and their results were compared to the ones obtained for the IDT. The outcomes from both the numerical and experimental analyses proved that the beampatterns generated by the T-IDT are similar to those determined for the conventional transducer. Moreover, the changes in electrode connections lead to the changes of phase-amplitude characteristics.