Electrode Topologies Research Articles

Effect of Traps on the UV Sensitivity of Gallium Oxide-Based Structures

Resistive metal/β-Ga2O3/metal structures with different interelectrode distances and electrode topologies were investigated. The oxide films were deposited by radio-frequency magnetron sputtering of a Ga2O3 (99.999%) target onto an unheated sapphire c-plane substrate (0001) in an Ar/O2 gas mixture. The films are sensitive to ultraviolet radiation with wavelength λ = 254. Structures with interdigital electrode topology have pronounced persistent conductivity. It is shown that the magnitude of responsivity, response time τr, and recovery time τd are determined by the concentration of free holes p involved in recombination processes. For the first time, it is proposed to consider hole trapping both by surface states Nts at the metal/Ga2O3 interface and by traps in the bulk of the film.

Local enhancement of electron heating and neutral species generation in radio-frequency micro-atmospheric pressure plasma jets: the effects of structured electrode topologies

The effects of structured electrode topologies on He/O2 radio frequency micro-atmospheric pressure plasma jets driven at 13.56 MHz are investigated by a combination of 2D fluid simulations and experiments. Good qualitative agreement is found between the computational and experimental results for the 2D spatio-temporally resolved dynamics of energetic electrons measured by phase resolved optical emission spectroscopy, 2D spatially resolved helium metastable densities measured by tunable diode laser absorption spectroscopy and 2D spatially resolved atomic oxygen densities measured by two photon absorption laser induced fluorescence. The presence of rectangular trenches of specific dimensions inside the electrodes is found to cause a local increase of the electron power absorption inside and above/below these surface structures. This method of controlling the electron energy distribution function via tailored surface topologies leads to a local increase of the metastable and atomic oxygen densities. A linear combination of trenches along the direction of the gas flow is found to result in an increase of the atomic oxygen density in the effluent, depending linearly on the number of trenches. These findings are explained by an enhanced Ohmic electric field inside each trench, originating from (a) the low electron density, and, consequently, the low plasma conductivity inside the trenches, and (b) the presence of a current focusing effect as a result of the electrode topology.

Pulsed Electric Field Inactivation of Microorganism Using Chambers With Different Electrode Topologies

The effects of electrode topology on pulsed electric field (PEF) inactivation of microorganisms was investigated in the present study. Three PEF treatment chambers with different electrode topologies, which were parallel-plane, coaxial, and co-field respectively, were designed and built. PEF inactivation of yeast Saccharomyces cerevisiae suspension was conducted using these chambers with different electric field strength and a number of impulses. The performance of PEF inactivation was assessed by comparison of the population density of treated and untreated yeast samples. The results showed that the sterilization rate, as a function of the specific energy density, followed the same tendency regardless of the electrode topology, electric field strength, or the number of impulses. This strong correlation suggested that the specific energy density (energy per unit mass) could play a dominant role in the PEF inactivation of microorganisms once the threshold field strength was reached.

Customized Woven Carbon Fiber Electrodes for Bioelectrochemical Systems—A Study of Structural Parameters

Commercial carbon fiber (CF) fabrics are popular electrode materials for bioelectrochemical systems (BES), but are usually not optimized for the specific application. This study investigates BES-relevant material characteristics on fabric level, such as weave types and weave parameters. The two contrasting weave types plain and leno weave were characterized with respect to their envisaged application types: 1) BES with mainly advective flow regimes and 2) stirred systems, which could benefit from fluid flow through a fabric electrode. Experiments with batch and continuously fed pure cultures of Geobacter sulfurreducens PCA and Shewanella oneidensis MR-1 reveal that µm-scale electrode topologies are of limited use for the thick biofilms of G. sulfurreducens, but can boost S. oneidensis’ current generation especially in batch and fed-batch reactors. For advective flow regimes, deeper layers of biofilm inside microporous electrodes are often mass transport limited, even with thin biofilms of S. oneidensis. Therefore, low porosity plain weave electrodes for advective flow operation as in wastewater treating BES should be thin and flat. A trade-off between maximized current density and electrode material utilization exists, which is optimized exemplarily for an advective flow operation. For stirred BES of biotechnological applications, a flow-through of electrolyte is desired. For this, leno weave fabrics with pores at cm-scale are produced from 100% CF for the first time. In a preliminary evaluation, they outperform plain weave fabrics. Mass transfer investigations in stirred BES demonstrate that the large pores enable efficient electrode utilization at lower power input in terms of stirring speed.

Gas-Sensing Properties of a Carbyne-Enriched Nanocoating Deposited onto Surface Acoustic Wave Composite Substrates with Various Electrode Topologies

The application of carbyne-enriched nanomaterials opens unique possibilities for enhancing the functional properties of several nanomaterials and unlocking their full potential for practical applications in high-end devices. We studied the ethanol-vapor-sensing performance of a carbyne-enriched nanocoating deposited onto surface acoustic wave (SAW) composite substrates with various electrode topologies. The carbyne-enriched nanocoating was grown using the ion-assisted pulse-plasma deposition technique. Such carbon nanostructured metamaterials were named 2D-ordered linear-chain carbon, where they represented a two-dimensionally packed hexagonal array of carbon chains held by the van der Waals forces, with the interchain spacing approximately being between 4.8 and 5.03 Å. The main characteristics of the sensing device, such as dynamic range, linearity, sensitivity, and response and recovery times, were measured as a function of the ethanol concentration. To the authors’ knowledge, this was the first time demonstration of the detection ability of carbyne-enriched material to ethanol vapors. The results may pave the path for optimization of these sensor architectures for the precise detection of volatile organic compounds, with applications in the fields of medicine, healthcare, and air composition monitoring.

Perspectives for next generation lithium-ion battery cathode materials

Transitioning to electrified transport requires improvements in sustainability, energy density, power density, lifetime, and approved the cost of lithium-ion batteries, with significant opportunities remaining in the development of next-generation cathodes. This presents a highly complex, multiparameter optimization challenge, where developments in cathode chemical design and discovery, theoretical and experimental understanding, structural and morphological control, synthetic approaches, and cost reduction strategies can deliver performance enhancements required in the near- and longer-term. This multifaceted challenge requires an interdisciplinary approach to solve, which has seen the establishment of numerous academic and industrial consortia around the world to focus on cathode development. One such example is the Next Generation Lithium-ion Cathode Materials project, FutureCat, established by the UK’s Faraday Institution for electrochemical energy storage research in 2019, aimed at developing our understanding of existing and newly discovered cathode chemistries. Here, we present our perspective on persistent fundamental challenges, including protective coatings and additives to extend lifetime and improve interfacial ion transport, the design of existing and the discovery of new cathode materials where cation and cation-plus-anion redox-activity can be exploited to increase energy density, the application of earth-abundant elements that could ultimately reduce costs, and the delivery of new electrode topologies resistant to fracture which can extend battery lifetime.

Modeling the Impact of Sensitivity Distribution Variations of Tetrapolar Impedance Configurations in Microfluidic Analytical Devices

Goal: The purpose of this work is to investigate the effects of electrode topology and electrode configuration of tetrapole electrical impedance measurement (TEIM) systems used in microfluidic devices. Methods: Two different electrode topologies with fixed dimensions, selected based on reported applications, are investigated. Three dimensional sensitivity maps, generated using finite element modelling (FEM), show fundamental differences in sensitivity distribution between six different injecting and measuring electrode configurations. Transfer impedance values generated for different band sizes and migrating band trains were compared to show the influence of sensitivity distribution on the performance of TEIM used in electrophoresis or cellomics. Results: Fundamental differences of sensitivity distribution between different electrode configurations were detected, with “Inline Dipole” and “Square Across” configurations exhibiting areas of negative sensitivity in the tetrapole centre. This causes baseline impedance differences of up to one order of magnitude and effecting the performance when measuring heterogeneous fluids. Conclusion: The results suggest that certain electrode configurations should be avoided for applications relying on high spatial resolution. Significance: This work demonstrates the significance of impedimetric sensor geometry design in ultimately enabling the miniaturisation of electrophoretic systems towards increasingly portable devices.

Design of Bio-Impedance Electrode Topologies for Specific Depth Sensing in Skin Layer.

Bio-impedance analysis provides non-invasive estimation of body composition. Recently, applications based on bio-impedance measurement in skin tissue such as skin cancer diagnosis and skin composition monitoring have been studied. For scanning the electrical properties along the skin depth, the relationship between the electrode topologies and the depth sensitivity should be clarified. This work reports a systematic analysis on designing line electrode topologies to measure the bio-impedance of the skin layer at specific depth using a finite element method (FEM). Four electrodes consisting of two outer current electrodes and two inner voltage electrodes in the form of Wenner-Schlumberger array were employed on the top of a collagen layer as a skin model. The numerical results demonstrate a change in the effective depth of measurement depending on the electrode topologies, which also have a good agreement with an analytic solution. This study suggests a decision guideline for designing the electrode topologies to achieve target depth sensitivity in bio-impedance measurement of skin tissue.Clinical Relevance-This establishes the effect of electrode topologies on depth sensitivity in bio-impedance measurements in skin layer.

Advanced Porous Electrode Modelling Framework Based on More Consistent Virtual Representation of the Electrode Topology

The paper proposes an advanced continuum level modelling framework characterized by a more consistent virtual representation of electrode topology to enhance prediction capability and generality of porous electrode theory based models. The proposed modelling framework, therefore, establishes the missing link between the mesoscopic scale with a detailed 3D representation of electrode topology and the continuum single cell scale, where interrelation to the real electrode topology was missing. This link is established by elaborating a unified approach for modelling materials with significantly different topologies of active material by virtually creating agglomerates, representing secondary particles, from primary particles. Proposed approach relies on multi-particle size distribution of primary particles and particle-to-particle connectivity. Generality of the proposed modelling framework is demonstrated by simulating LFP and NMC materials featuring significantly different electrode topologies by the same modelling framework while adapting only virtual representation of electrode topologies and intrinsic material properties. Credibility of the proposed modelling framework is confirmed through good agreement with experimental results for various discharge tests. Insightful simulation results also reveal background of the topologically driven low Li utilization at high current densities of the LFP material and topologically driven voltage response difference during the memory effect of different LFP materials.

Signal Processing for Capacitive Ice Sensing: Electrode Topology and Algorithm Design

Atmospheric ice accretion is considered a severe safety issue for technical systems such as communication infrastructure, power lines, blades of wind turbines, and so on in cold climate regions. Among different sensing systems to detect and provide reliable information about the state of ice, capacitive sensing has been reported as a suitable technique. In capacitive sensing, measured capacitances are influenced due to ice accretion. Signal processing for ice sensors requires to estimate parameters for the state of ice from the data. In this paper, we present a model-based estimation approach for capacitive ice sensors. We analyze different electrode topologies for ice sensing and provide a statistical analysis of the sensor behavior. We hereby consider the random nature of natural ice accretion. From simulations, we show how a statistical model for the measurement process can be derived and demonstrate the construction of estimation algorithms within the Bayesian framework. We will demonstrate the capability of our approach for automated ice detection by means of long-term field data showing the ability to estimate ice layers with a precision better than 1 mm.

Smart Test Strips: Next-Generation Inkjet-Printed Wireless Comprehensive Liquid Sensing Platforms

By combining radio-frequency identification (RFID) and paper-microfluidics technologies, a low-cost first-of-its-kind platform for comprehensive liquid sensing, i.e., the “smart test strip,” is presented, which enables portable wireless real-time liquid sensing with handhold devices (e.g., cell phones), and integration of various multifunctional electrical and chemical sensors, for numerous Lab-on-Chip applications, including manufacturing control, environmental monitoring, and point-of-care medical diagnostics. The fabrication of RFID tags and two types of microfluidics are accomplished by a single inkjet-printing process in a cost-effective environmental-friendly additive manufacturing approach, which makes possible the production of disposable, lightweight, and flexible sensing platforms. Taking advantage of the proposed smart test strips platforms, we demonstrate two proof-of-concept high-performance electrical sensors based on interdigitated electrode topologies: a resistivity-based sensor with a 1782 $\Omega$ /( $\Omega$ *m) sensitivity; nevertheless, the proposed permittivity-based sensor with a 15%/ $\epsilon _r$ sensitivity, but the proposed integrated wireless platform, can facilitate the integration of even more chemical and electrical sensors. In addition, two on-strip antenna prototypes have been designed, optimized, and tested to work at 2.4 GHz and 13.56 MHz, respectively. Furthermore, the wireless interrogation of a complete proof-of-concept smart test strip is presented, which shows an excellent sensing resolution of 1.33 $\Omega$ over the range of 0–1371 $\Omega$ .

High on/off capacitance ratio RF MEMS capacitive switches

In this paper, high on/off capacitance ratio radio frequency micro-electro-mechanical-systems (RF MEMS) switches are designed, fabricated, measured and analyzed. Two types of RF MEMS switches, a shunt switch with a contact point and an inline switch without a contact point, are presented. Metal–insulator–metal (MIM) fixed capacitors are used in the MEMS switches. The electrode topologies of RF MEMS switches are analyzed. The parameter λ is defined to describe the relationship between the capacitance ratio, the height of the beam and the actuation voltage. The measured results indicate that, for MEMS switch #1 with a contact point and gap of 1 µm, the insertion loss is better than 0.64 dB up to 40 GHz, and the isolation is more than 20 dB from 11.28 to 30.38 GHz with an actuation voltage of 42 V. For the inline MEMS with a displacement of 1.5 µm, the insertion loss is better than 0.56 dB up to 40 GHz, and the isolation is more than 20 dB from 4.45 to 30.48 GHz with an actuation voltage of 36 V. Circuit models and measured results of the proposed MEMS switches show good agreement. From the fitted results, the on/off capacitance ratio is ~227 for the MEMS switch #1 and ~313 for the MEMS switch #2, respectively. Compared with traditional MEMS capacitive switches with dielectric material Si3N4 and a relatively lower gap (1.5 µm), the proposed MEMS switches exhibit high on/off capacitance ratios.

SU-8 microchannels for live cell dielectrophoresis improvements

In this work a novel SU-8 fabrication technology is employed to construct microfluidic devices for sensitive dielectrophoretic (DEP) manipulation of budding yeast cells. Identical devices were produced with standard soft-lithography processes. In comparison to standard PDMS based soft-lithography, an SU-8 layer was used to construct the microchannel walls sealed by a flat sheet of PDMS to obtain the microfluidic channels. Direct bonding of PDMS to SU-8 surface was achieved by efficient wet chemical silanization combined with oxygen plasma treatment of the contact surface. The presented fabrication process significantly improved the alignment of the microstructures. In addition, PDMS delamination above electrode topologies was significantly decreased over standard soft-lithography devices. The fabrication time and costs of the proposed methodology were found to be roughly the same. Sensitivity of the devices was tested by discriminating Saccharomyces cerevisiae cells in the G1 phase from cells in the S/G2/M phase using dielectrophoresis. This level of sensitivity necessitated high precision electrode structure that was designed using an FEM model based approach. Attaining such high precision using standard soft-lithography can be difficult due to additional requirements of an alignment stage and its associated tight timing limits.

Polarity effects on breakdown of short gaps in a point-plane topology in air

Electrical breakdown in air in a point-plane topology involves complex processes that are still not fully understood. Unlike uniform-field topologies, the highly-divergent fields produced by point-plane topologies create pre-breakdown corona with volumetric space charge. It is known that space charges developed by corona discharge have significant impacts on the breakdown voltage in non-uniform electrode topologies. With large inter-electrode gaps (>cm) the breakdown voltage for a HV point cathode in air at atmospheric pressure is noticeably larger than a HV point anode. However, this paper shows that in shorter point-plane gaps in air (less than ~10 mm), in the air pressure range 0.1-0.35 MPa, an HV point anode has a similar breakdown voltage which eventually is surpassed by the HV point cathode as the inter-electrode gap is increased. The inter-electrode gap at which the HV cathode has a higher hold-off voltage is found to be dependent on the gas pressure and radius of the point electrode.

Investigation of the Traveling-Wave Oscillations of Piezoelectric Cylinder

Piezoelectric actuators are widely used for the nano/micro positioning and adjustment systems. In the paper, the investigation on the oscillations of contacting surfaces of the piezoelectric thick-walled cylinder is presented. Piezoelectric cylinder is the main component of piezomechanical system named as piezo-screw and is used to turn the screw. This investigated piezomechanical system can be used for the precise positioning with a high resolution (less than 50 nanometers). Piezoelectric cylinder has radial polarization. Traveling-wave oscillations of the second circumferential modal shape (n = 2, m = 1) are excited. Three different electrode topologies are used to drive the screw. Electrodes are grouped into upper and low groups in both topology cases. Each group consists of six electrodes where positions of corresponding electrodes in upper and lower group are shifted by π/6. Numerical investigation of the traveling wave oscillation is performed and dependencies oscillation trajectories of contact surfaces on excitation schemes are determined when three different electrode topologies are used. Dependency of oscillations of contacting points upon length of the actuator is analyzed as well. Advantages and disadvantages of each excitation case are discussed.

Effect of structured electrodes on heating and plasma uniformity in capacitive discharges

The effect of various structured (non-planar) electrode topologies, e.g. rectangular, rounded and triangular trenches, on the electron heating dynamics and ion density profile in capacitively coupled radio frequency plasmas is investigated experimentally and by an analytical model. The measurements are carried out in neon. 2D Phase resolved optical emission spectroscopy is utilized to study the dynamics of energetic electrons inside and outside these structures at the kinetic level. In the presence of structured electrodes, non-planar RF sheaths form and affect the electron heating dynamics. We observe a local agglomeration of energetic electrons above the structures. These electrons originate from sheath expansion heating. Inside the structures, opposite vertical sheaths cause a temporal confinement of electrons. Non-planar sheaths at the trench orifice cause convergent fluxes of energetic electrons. Also, the ionization and, as a consequence, the plasma density are modified by these effects. This is characterized by radially resolved Langmuir probe measurements and described by a diffusion model with localized sources. Subsequently, the control of the radial plasma density profile is demonstrated. Via customized electrode topologies, high plasma uniformity at specific pressures and heights above the electrode is achieved with the additional benefit of strong enhancement of the plasma density.

The Triggered Behavior of a Controlled Corona Stabilized Cascade Switch

Corona stabilized switches have been shown to have advantages in pulse power switching applications due to their high repetition rates and low jitter. Work performed in recent years by the High Voltage Technologies Group within the Department of Electronic and Electrical Engineering at the University of Strathclyde has shown that the operating voltage range of such switches can be extended by using a multigap cascade configuration. One particular multigap topology, filled with pressurized atmospheric air, was shown to operate at 80 kV with a switching jitter of ~ 2 ns. It has since been shown that, by modifying the topology of the corona sources on the electrodes, it is possible to control the grading of the voltage distribution across the gaps in the cascade. The voltages across each gap and the self-break behavior of the cascade were found to be in close agreement with the values predicted from the corona emission characteristics for the tested electrode topologies. This paper reports on a further examination of the behavior of the corona controlled switching topology, where the triggered operation of the switch has been investigated for different voltage distributions across the cascade gaps.

Gas Phase Electrodeposition: A Programmable Localized Deposition Method for Rapid Combinatorial Investigation of Nanostuctured Devices and 3D Bulk Heterojunction Photovoltaic Cells

ABSTRACTThis article applies a recently discovered gas phase nanocluster electrodeposition process to the formation and combinatorial improvement of 3D bulk heterojunction photovoltaic cells. The gas phase deposition process used here is a single reactor system that forms charged nanoclusters (gold, silver, tungsten, and platinum) at atmospheric pressure. The clusters deposit onto selected surface areas with sub 100 nm lateral resolution using a programmable concept similar to liquid phase electrodeposition such that biased electrodes turn ON or OFF deposition in selected areas. Continued deposition of the nanoparticles results in a tower array with different lengths and density on a single substrate which is used as contacts to the active organic layer of 3D bulk heterojunction photovoltaic cells. Applying a combinatorial approach identifies in a massively parallel way electrode designs and topologies that improve light scattering, absorption, and minority carrier extraction. We report photovoltaic cells with higher and denser nanocluster tower arrays that improve the power conversion efficiency of bulk heterojunction photovoltaic cells by approximately 47.7%.

(Invited) Perspectives on SiC and III-N Based Devices for Power Electronics

SiC devices for power electronics are a reality. A first generation of reliable SiC rectifier devices outperforming all silicon devices has been released on the market with up to 1500V voltage handling capability. At best, GaN based rectifiers, with similar electrical performance and production cost, may reach the market by year 2015. For the same voltage range, prototypes of switching triode SiC devices with control electrode, using JFET and BJT topologies, are also under market evaluation. It seems nobody knows yet whether SiC MOS will finally get reliable enough for voltage over 200 V. III-N based HEMT hetero-junction devices may become superior alternative to the existing SiC switching triode devices. Still, a lot of work will be needed for reaching good enough reliability. On the long term, due to expectable Gallium shortage, SiC based heterojunction devices would offer sustainable solution, although the ideal hetero-structure has not been demonstrated yet.

Transcranial direct current stimulation (tDCS) in a realistic head model

Distributions of current produced by transcranial direct current stimulation (tDCS) in humans were predicted by a finite-element model representing several individual and collective refinements over prior efforts. A model of the entire human head and brain was made using a finely meshed (1.1×1.1×1.4mm3 voxel) tissue dataset derived from the MRI data set of a normal human brain. The conductivities of ten tissues were simulated (bone, scalp, blood, CSF, muscle, white matter, gray matter, sclera, fat, and cartilage). We then modeled the effect of placing a “stimulating” electrode with a saline-like conductivity over F3, and a similar “reference” electrode over a right supraorbital (RS) location, as well as the complements of these locations, to compare expectations derived from the simulation with experimental data also using these locations in terms of the presence or absence of subjective and objective effects. The sensitivity of the results to changes in conductivity values were examined by varying white matter conductivity over a factor of ten. Our simulations established that high current densities were found directly under the stimulating and reference electrodes, but values of the same order of magnitude occurred in other structures, and many areas of the brain that might be behaviorally active were also subjected to what may be substantial amounts of current. The modeling also suggests that more targeted stimulations might be achieved by different electrode topologies.