Equivalent Current Density Research Articles

Effect of reactor configuration on the kinetics and nitrogen byproduct selectivity of urea electrolysis using a boron doped diamond electrode

Electrochemical systems have emerged as an advantageous approach for decentralized management of source-separated urine with the possibility of recovering or removing nutrients and generating energy. In this study, the kinetics and byproduct selectivity of the electrolytic removal of urea were investigated using a boron doped diamond working electrode under varied operational conditions with a primary focus on comparing undivided and divided reactors. The urea removal rate in the undivided and divided reactors was similar, but the divided reactor had an increased required cell voltage needed to maintain the equivalent current density. The current efficiency was similar for 0.1, 0.25, and 0.5 A (33.3, 83.3, 167 mA/cm2), suggesting no interference from competing reactions at higher potentials. In a divided reactor, increasing the anolyte pH reduced the urea removal rate presumably from hydroxyl radical scavenging by hydroxide. Further, for all divided reactor experiments, the final pH was less than 1, suggesting that the transport of protons across the ion exchange membrane to the cathode was slower than the oxidation reactions producing protons. The nitrogen byproduct selectivity was markedly different in the undivided and divided reactors. In both reactors, nitrate (NO3−) formed as the main byproduct at the anode, but in the undivided reactor it was reduced at the stainless steel cathode to ammonia. In the presence of 1 M chloride, the urea removal kinetics improved from the generation of reactive chlorine species, and the byproduct selectivity was shifted away from NO3− to presumably chloramines and N2. Overall, these results indicate that the electrochemical reactor configuration should be carefully considered depending on the desired outcome of treating source-separated urine (e.g., nitrogen recovery, H2 generation).

Output Signal Prediction of an Eddy-Current Probe When Scanning Arbitrary-Shape Surface Cracks in Metals

This article proposes an efficient modeling technique to predict the output signal of an eddy-current (EC) probe when scanning arbitrary-shape surface cracks in metals. The probe is excited by an arbitrary-shape wire carrying an ac current of arbitrary frequency with no restriction on the crack depth profile or magnetic permeability of the metal. In the proposed technique, the equivalence principle is adopted to replace the crack with the equivalent electric and magnetic current densities, and the governing volume integral equations (VIEs) are derived using appropriate Green’s functions. The VIEs are solved by the method of moments (MoM) for the unknown electric and magnetic fields inside the crack. This is done by expanding the electric and magnetic fields in terms of basis functions compatible with the problem. To support the validity of the proposed modeling technique, we compare the predicted output signals of various EC probes with their experimental counterparts and those available in the literature.

Additive Transport, Adsorption, and Inclusion in Electroless Deposition of Copper

Not requiring an external current source, electroless deposition provides unique capability in laying down thin metallic layers on top of non-conductive substrates. This is particularly advantageous for the semiconductor industry, enabling the metallization of electrically isolated features and narrower, future generation, interconnects. The latter are currently electroplated with copper, using special additives mixtures that provide the essential bottom-up fill. While electroplating additives have been extensively studied and their interactions in the electroplating process have been well-characterized and quantitatively modeled1,2, no similar characterization is available for electroless plating. The absence of appropriate electroless plating additives and the non-availability of a model for their function impose a barrier on the technological adaptation of electroless plating to hi-tech precision applications. The research described here addresses these limitations by providing a quantitative model for the deposit thickness distribution in a general, additives-containing electroless process. The model quantifies the effects of additives in an electroless plating system, accounting for additives transport, adsorption, and incorporation within the deposit. The model builds on and extends a previously presented model for prediction of electroless plating rate in an additives-free system, accounting for reactant concentration, pH, and transport3. The model presented here includes an important extension: a prediction of the average plating rate based on the fractional surface coverage of the additive. This model is compared to experimental data obtained in an electroless plating system consisting of copper and glyoxylic acid, with mercaptopropane sulfonic acid (MPS) as the additive. An additive mass balance model, similar to that developed by Roha and Landau4, is used to estimate the concentration of the additive on the electrode surface. [1] Adsorption: NA=kACS,Add(Γsat-Γ) [2] Desorption: N-A=k-AΓ [3] Inclusion: NI=kIiΓ Here, N is the additive flux, k is its adsorption rate constant, and CS,Add is the additive concentration in solution adjacent to the surface. Γ and Γsat are the surface concentration of the adsorbed additive and its saturation concentration, respectively. i is the current density, or the equivalent current density associated with the deposit build-up. The subscripts A, -A, and I refer to the adsorption, desorption, and inclusion processes, respectively. Langmuir-type adsorption is assumed. While equations 1-3 are general, additional assumptions were made for the specific system studied here: (i) plating is completely inhibited at sites occupied by the additive, and (ii) the additive desorption flux is negligible as compared to adsorption and inclusion. At steady-state, the rate of adsorption and inclusion are therefore equal, leading to the following equation for the fractional additive surface coverage as a function of known or measurable parameters: [4]: (kACb,Add[1-θ])/(1+[δkAΓsat(1-θ)]/D)=kIiθ Here, Cb,Add is the bulk additive concentration, θ is its fractional surface coverage, δ is the additive diffusion boundary layer thickness, and D is its diffusion coefficient. As the plating does not occur on sites with adsorbed additive, we can relate the surface coverage to current density (and to an equivalent plating rate): [5]: i=iNo Add(1-θ) As shown in Fig. 1, the model matches the experimental data well. Of particular importance, the model captures the trend of increasing plating rate with rotation speed (and higher transport rates) to a maximum of around 100 rpm before dropping to almost zero at high rotation speeds. Additional analysis and further experimental details are provided in the presentation. Acknowledgements Atotech GMBH is acknowledged for funding this study and for providing helpful input. References R. Akolkar and U. Landau, "A time-dependent transport-kinetics model for additive interactions in copper interconnect metallization", J. Electrochem. Soc., 151, C702 (2004).R. Akolkar and U. Landau, “Mechanistic analysis of the "bottom-up" fill in copper interconnect metallization”, J. Electrochem. Soc., 156, D351 (2009).R. A. Zeszut Jr., and U. Landau, “Transport and reactants concentration effects in electroless deposition of copper”, Metallization of Flexible Electronics Symposium, 231st Electrochemical Society Meeting, (2017).D. Roha, U. Landau, “Mass transport of leveling agents in plating: steady-state model for blocking additives,” J. Electrochem. Soc., 137, 824 (1990).R. A. Zeszut Jr., “Effect of transport and additives on electroless copper plating”, PhD Dissertation, Department of Chemical and Biomolecular Engineering, Case Western Reserve University, (2017). Figure 1

Fictitious electric conductivity modelling of eddy current evaluation of magnetic materials

ABSTRACTThis paper presents a new modeling approach of eddy current nondestructive evaluation systems containing magnetic materials. Originally, the proposed model is based on coupled circuits principle and the notion of equivalent current density. In order to make the model homogenous, we consider the current density as a state variable since this density is compatible with the representation of the magnetisation by equivalent currents. By introducing the fictitious electric conductivity approach, the sensor impedance is expressed according to magnetic tube or plate characteristics such as electric conductivity and magnetic permeability. An excellent concordance is achieved by comparing the calculated results to those of analytical ones. Regarding the mesh simplicity and the fast calculation, this method is very adapted for the resolution of the inverse problems for real time evaluation of the properties of magnetic materials.

Spatially resolved oxygen reaction, water, and temperature distribution: Experimental results as a function of flow field and implications for polymer electrolyte fuel cell operation

In situ and ex situ spatially-resolved techniques are employed to investigate reactant distribution and its impacts in a polymer electrolyte fuel cell. Temperature distribution data provides further evidence for secondary flows inferred from reactant imaging data, highlighting the contribution of convection in heat as well as reactant distribution. Water build-up from neutron tomography is linked to component degradation, matching the pattern seen in the reactant distribution and thus suggesting that high, non-uniform local current densities shape degradation patterns in fuel cells. The correlations shown between different techniques confirm the use of the versatile reactant imaging technique, which is used to compare commonly used flow field designs. Among serpentine-type designs, the single serpentine is superior in both equivalent current density and reactant distribution, showing large contributions from convective flow. On the other hand, the interdigitated design is shown to produce larger equivalent current densities, while showing a somewhat poorer reactant distribution. Considering the correlations drawn between the techniques, this suggests that the interdigitated design compromises durability in favour of power output. The results highlight how established techniques provide a robust background for the use of a new and flexible imaging technique toward designing advanced flow fields for practical fuel cell applications.

A Macromodeling Approach to Efficiently Compute Scattering from Large Arrays of Complex Scatterers

Full-wave electromagnetic simulations of electrically large arrays of complex antennas and scatterers are challenging, as they consume large amount of memory and require long CPU times. This paper presents a new reduced-order modeling technique to compute scattering and radiation from large arrays of complex scatterers and antennas. In the proposed technique, each element of the array is replaced by an equivalent electric current distribution on a fictitious closed surface enclosing the element. This equivalent electric current density is derived using the equivalence theorem and it is related to the surface currents on the scatterer by the Stratton-Chu formulation. With the proposed approach, instead of directly solving for the unknown surface current density on the scatterers, we only need to solve for the unknowns on the equivalent surface. This approach leads to a reduction in the number of unknowns and better conditioning when it is applied to problems involving complex scatterers with multiscale features. Furthermore, the proposed approach is accelerated with the adaptive integral equation method to solve large problems. As illustrated in several practical examples, the proposed method yields speed up of up to 20 times and consumes up to 12 times less memory than the standard method of moments accelerated with the adaptive integral method.

226 nm AlGaN/AlN UV LEDs using p-type Si for hole injection and UV reflection

Deep ultraviolet (UV) light-emitting diodes (LEDs) at a wavelength of 226 nm based on AlGaN/AlN multiple quantum wells using p-type Si as both the hole supplier and the reflective layer are demonstrated. In addition to the description of the hole transport mechanism that allows hole injection from p-type Si into the wide bandgap device, the details of the LED structure which take advantage of the p-type Si layer as a reflective layer to enhance light extraction efficiency (LEE) are elaborated. Fabricated LEDs were characterized both electrically and optically. Owing to the efficient hole injection and enhanced LEE using the p-type Si nanomembranes (NMs), an optical output power of 225 μW was observed at 20 mA continuous current operation (equivalent current density of 15 A/cm2) without external thermal management. The corresponding external quantum efficiency is 0.2%, higher than any UV LEDs with emission wavelength below 230 nm in the continuous current drive mode. The study demonstrates that adopting p-type Si NMs as both the hole injector and the reflective mirror can enable high-performance UV LEDs with emission wavelengths, output power levels, and efficiencies that were previously inaccessible using conventional p-i-n structures.

Measurement and Torque Calculation of Magnetic Spur Gear Based on Quasi 3-D Analytical Method

This paper presents the torque characteristics analysis and torque measurement of a magnetic spur gear with a three-segment Halbach array based on the Quasi Three-Dimension (3-D) Analytical Method. It analyzes a magnetic spur gear that uses a Halbach array by employing an analytical method for torque calculation. In the analytical method, from the magnetic vector potential and a coordinate system conversion, analytical solutions are obtained for magnetic fields produced by source magnets. By using the derived magnetic field solutions, an analytical solution is obtained for the external magnetic flux density. The drive magnet is next reduced to the equivalent current densities, and the torque is computed from these currents in the external magnetic field, which is obtained from the second process. Finally, the leakage flux in the z-direction occurring in the magnetic gear is considered using the 3-D analytical method. Thus, an analytical result can be obtained. These results are validated by comparison with the finite element method.

Zeroth-Order-Mode Circular Microstrip Antenna With Patch-Like Radiation Pattern

A zeroth-order-mode circular microstrip patch antenna is presented, consisting of two axial symmetrical semicirculars and pins, which are in essential two composite right/left-handed metamaterial unit cells. The patch-like radiation pattern was achieved for the zeroth-order mode by modifying the equivalent magnetic current densities along the perimeter of the proposed antenna. The variations of the resonant frequency affected by the locations of the pins were also investigated. The dispersion diagrams revealed the phase variation on one period, thus validating the existence of the zeroth-order mode. A prototype of the antenna, operative at 5.83 GHz, was designed on a substrate of ${\text{72 mm }}\times \,{\text{50 mm }}\times \,{\text{1.5 mm}}$ . Simulations and measurements were made to prove the theory and design concept.

Identification of Manganese Distribution Using Very Low Frequency (VLF) Method at Karangsari Village, Pengasih Sub-District, Kulonprogo Regency, DIY

Research of manganese distribution was conducted in the village of Karangsari, Pengasih sub-district, Kulonprogo Regency, DIY which is the former area exploration and exploitation of manganese. The purpose of the research is known the value of relative conductivity and the distribution of manganese. The method used very low frequency tilt mode. The tools used 2 set of T-VLF BRGM (sensor and monitor) and the data processing software are Ms. Excel and KHFILT. T-VLF operated with 2 frequencies that are 19800 Hz from Australia and 22.200 Hz from Elbino Japan. The total lines are 6 lines with 75 m space. Distance between measured points is 15 m, whereas line length is 300 m. The parameters measured from VLF method are tilt (%) and ellipticity (%). The raw data VLF is processed by Ms Excel to obtain a tilt, ellipse, fraser graph vs distance and the RAE from Karous Hjelt filter. While the results of processed by KHFILT software is the equivalent current density contour map. Relative conductivity of area research are line 1 (-10 to 10) mho/m, line 2 (-40 to 30) mho/m, line 3 (-20 to 20) mho/m, line 4 (-30 to 10) mho/m, line 5 (-40 to 30) mho/m and line 6 (-30 to 40) mho/m. The spread of manganese were in the high conductivity, toward west and east of research area with depth up to 45 m.

Multi-Temperature in Situ Magnetic Resonance Imaging of Polarization and Salt Precipitation in Li-Ion Battery Electrolytes

The parameterization and validation of robust electrochemical models for lithium-ion batteries in automotive applications, which are intended to address both the state of charge (SOC) and state of health (SOH) estimation problems, is an important milestone in their widespread deployment. Much effort has been focused on the mass transport characteristics of the electrode domains, but a significant fraction of overall polarization stems from concentration gradients that form in the electrolyte domain and their attendant effect on the mass transport parameters, which have recently been shown by in situ MRI to be quite significant, even within modest operational regimes.1 The effect of temperature on these concentration gradients remains to be explored by in situ MRI. The mass transport in the electrolyte domain is typically modelled as being governed by material balance of a binary salt in a concentrated solution, which can be realized by modifying the Nernst-Planck equation to have non-constant, concentration-dependent coefficients (Equation 1).2 This system has a steady-state concentration gradient (Equation 2) when migration flux driven by the potential and diffusion flux against the concentration gradient are in equilibrium (see Figure 1A). Using in situ MRI, the evolution of this gradient toward the steady-state upon constant-current charging can be monitored (Figure 1B). A surprising outcome of these studies was that at 10°C, an equal parts (v/v) mixture of EC/DEC with 1.00 M LiPF6 exhibited anomalous concentration gradient formation (Figure 2) with a current density corresponding to 6 A·m-2 (or ~C/4), whereas the same mixture and cell construction could be polarized without difficulty at room temperature. On comparing raw MR images from before the polarization and after the relaxation of the disrupted concentration gradient, it is clear that the overall signal intensity is lower whilst the shape of the profile is retained, which is a direct indicator that salt precipitation has occurred. There are two routes by which this salt precipitation phenomenon can be avoided: lowering the salt concentration, so that the absolute concentration at the upper portion of the gradient is decreased proportionately for an equivalent current density, and the selection of an electrolyte with better low-temperature solvation characteristics. Successful polarization and visualization of the electrolyte domain in situ was achieved with a 0.85 M variant of the equal-parts EC/DEC mixture utilized above, at a series of temperatures. This constitutes a means of avoiding the critical concentration at the low temperature where the 1.00 M variant exhibited precipitation, but it would come with a trade-off of reduced ionic conductivity. More significantly, a ‘full-strength’ 1.00 M LiPF6 in EC/PC/DMC, 5:2:3 (v/v) mixture was also successfully polarized at low, room, and elevated temperatures, with the same 6 A·m-2 applied current density. Previous ex situ experiments using the pulsed-field gradient NMR technique, in conjunction with conductivity measurements, had revealed that ion pairing at low temperature was significantly reduced in electrolyte mixtures where the fraction of high-dielectric solvent was maximized.3 A quantitative comparison of the steady-state concentration gradients at a series of inter-electrode distances and temperatures was also conducted with this electrolyte formulation, to assess how the magnitudes of the gradients varied with temperature, and to test the hypothesis inherent in Equation 2 that the inter-electrode spacing does not play a role in determining the magnitude of the steady-state gradient. Within 3σ confidence intervals, the inter-electrode spacing was not found to affect the inter-electrode spacing, which directly confirms that the in situ MRI technique can generate steady-state mass transport parameters which are relevant to real battery modelling efforts. A significant effect of the temperature on the magnitude of the steady-state concentration gradient is also illustrated in these multi-temperature imaging experiments, demonstrating the importance of characterizing the spatial variation and temperature-dependence of electrolyte mass transport characteristics for electrochemical model parameterization and validation. References (1) Krachkovskiy, S. A.; Bazak, J. D.; Werhun, P.; Balcom, B. J.; Halalay, I. C.; Goward, G. R. Visualization of Steady-State Ionic Concentration Profiles Formed in Electrolytes during Li-Ion Battery Operation and Determination of Mass-Transport Properties by in Situ Magnetic Resonance Imaging. J. Am. Chem. Soc. 2016, 138 (25), 7992–7999. (2) Sethurajan, A. K.; Krachkovskiy, S. A.; Halalay, I. C.; Goward, G. R.; Protas, B. Accurate Characterization of Ion Transport Properties in Binary Symmetric Electrolytes Using In Situ NMR Imaging and Inverse Modeling. J. Phys. Chem. B 2015, 119 (37), 12238–12248. (3) Krachkovskiy, S. A.; Bazak, J. D.; Fraser, S.; Halalay, I. C.; Goward, G. R. Determination of Mass Transfer Parameters and Ionic Association of LiPF 6 : Organic Carbonates Solutions. J. Electrochem. Soc. 2017, 164 (4), A912–A916. Figure 1

A 3-D Differential Surface Admittance Operator for Lossy Dipole Antenna Analysis

This letter presents a novel approach to simulate materials with arbitrary properties, in particular good conductors, in a boundary integral equation context. The advocated differential surface admittance operator permits the replacement of the material by the background medium through the introduction of an equivalent surface current density. A formulation based on the eigenfunctions of the volume is constructed and successfully demonstrated through scattering at a conducting cylinder and through the analysis of a lossy dipole antenna.

Metal Salt Solutions as a Simulant for the Chemistry in Crevices of Nickel Alloy 625

The development of a critical crevice solution plays an important role in crevice corrosion propagation in nickel alloy 625. In this investigation, the polarization response of alloy 625 in a set of simulated crevice chemistries using metal chloride salts has been studied. Specifically, solutions were made from NiCl2, CrCl3, FeCl2, MoCl3, and NbCl5 in the same stoichiometric ratio as they appear in the alloy and ranging in concentration from 3.0 to 5.0 molal (m). It was found that Mo and Nb contributed to lower open circuit potentials (OCP) and increased critical peak current densities (i.e. activation). Solutions that substituted NiCl2 for MoCl3 and NbCl5, such that the chloride content was equivalent to that of the NiCrFeMoNb solution, presented high OCP values and passive behavior. To better understand the polarization data, solution speciation and pH were calculated using a commercially available software package. It was found that for concentrations ranging from 3.0 to 5.0 m, the pH values were on the order of −1.0. In addition, the active to passive transition appeared to correlate with an increase of Mo3+ concentration in solution. For comparison, the polarization response of alloy 625 in HCl-based solutions was investigated. Over the range of HCl concentrations studied, the critical peak current densities were typically lower than the metal salt solutions at equivalent calculated pH. In addition, an equation for preparing HCl solutions at the needed pH to obtain an equivalent critical peak current density as observed in the NiCrFeMoNb solutions is presented.

Membrane-less hybrid flow battery based on low-cost elements

The capital cost of conventional redox flow batteries is relatively high (>USD$ 200/kWh) due to the use of expensive active materials and ion-exchange membranes. This paper presents a membrane-less hybrid organic-inorganic flow battery based on the low-cost elements zinc (<USD$ 3 Kg−1) and para-benzoquinone (<USD$ 8 Kg−1). Redox potential and voltammetric studies show that the open-circuit voltage of the battery is 1.17–1.59 V over a wide range of pH. Half-cell charge-discharge and dissolution experiments indicate that the negative electrode reaction is limiting due to the presence of chemical side reactions on the electrode surface. The positive electrode redox reactions are not affected and exhibit (half-cell) coulombic efficiencies of >92.7% with the use of carbon felt electrodes. In the presence of a fully oxidized active species close to its solubility limit, dissolution of the deposited anode is relatively slow (<2.37 g h−1 cm−2) with an equivalent corrosion current density of <1.9 mA cm−2. In a parallel plate flow configuration, the resulting battery was charge-discharge cycled at 30 mA cm−2 with average coulombic and energy efficiencies of c.a. 71.8 and c.a. 42.0% over 20 cycles, respectively.

New Single-Source Surface Integral Equation for Magneto-Quasi-Static Characterization of Transmission Lines Situated in Multilayered Media

We recently proposed a novel single-source integral equation (SSIE) for accurate broadband resistance and inductance extraction and current flow modeling in 2-D conductors. The new surface integral equation is advantageous compared with the traditional volume electric field integral equation (V-EFIE) used for the inductance extraction, since the unknown function is defined on the surface of conductors as opposed to the volumetric unknown current density in V-EFIE. The new SSIE is also more suitable for the solution of inductance extraction problems than the traditional surface integral equation formulations, as it features only a single unknown surface function as opposed to having the unknown equivalent electric and magnetic surface current densities. The new equation also features only the electric field Green’s functions unlike the previously known SSIE formulations. The latter property makes the new SSIE equation particularly suitable to the inclusion of the multilayered substrate effect into the inductance extraction model. This paper describes the generalization of the new SSIE formulation to the case of transmission line models embedded into the multilayered lossy substrates. This paper also shows how the matrix sparsity in the method of moments discretization of the novel integral equation can be exploited to accelerate its numerical solution and reduce associated memory use. This sparsity arises due to the skin-effect-based attenuation of the fields in conductors’ cross sections leading to vanishing levels of the matrix elements corresponding to the distant interactions. Typical examples of inductance extraction in complex interconnects situated in lossy substrate are considered to validate the proposed techniques against traditional approaches.

A Novel Single-Source Surface Integral Method to Compute Scattering From Dielectric Objects

Using the traditional surface integral methods, the computation of scattering from a dielectric object requires two equivalent current densities on the boundary of the dielectric. In this paper, we present an approach that requires only a single current density. Our method is based on a surface admittance operator and is applicable to dielectric bodies of arbitrary shape. The formulation results in four times lower memory consumption and up to eight times lower time to solve the linear system than the traditional PMCHWT formulation. Numerical results demonstrate that the proposed technique is as accurate as the PMCHWT formulation.

Noninvasive Imaging of Human Atrial Activation during Atrial Flutter and Normal Rhythm from Body Surface Potential Maps.

BackgroundKnowledge of atrial electrophysiological properties is crucial for clinical intervention of atrial arrhythmias and the investigation of the underlying mechanism. This study aims to evaluate the feasibility of a novel noninvasive cardiac electrical imaging technique in imaging bi-atrial activation sequences from body surface potential maps (BSPMs).MethodsThe study includes 7 subjects, with 3 atrial flutter patients, and 4 healthy subjects with normal atrial activations. The subject-specific heart-torso geometries were obtained from MRI/CT images. The equivalent current densities were reconstructed from 208-channel BSPMs by solving the inverse problem using individual heart-torso geometry models. The activation times were estimated from the time instant corresponding to the highest peak in the time course of the equivalent current densities. To evaluate the performance, a total of 32 cycles of atrial flutter were analyzed. The imaged activation maps obtained from single beats were compared with the average maps and the activation maps measured from CARTO, by using correlation coefficient (CC) and relative error (RE).ResultsThe cardiac electrical imaging technique is capable of imaging both focal and reentrant activations. The imaged activation maps for normal atrial activations are consistent with findings from isolated human hearts. Activation maps for isthmus-dependent counterclockwise reentry were reconstructed on three patients with typical atrial flutter. The method was capable of imaging macro counterclockwise reentrant loop in the right atrium and showed inter-atria electrical conduction through coronary sinus. The imaged activation sequences obtained from single beats showed good correlation with both the average activation maps (CC = 0.91±0.03, RE = 0.29±0.05) and the clinical endocardial findings using CARTO (CC = 0.70±0.04, RE = 0.42±0.05).ConclusionsThe noninvasive cardiac electrical imaging technique is able to reconstruct complex atrial reentrant activations and focal activation patterns in good consistency with clinical electrophysiological mapping. It offers the potential to assist in radio-frequency ablation of atrial arrhythmia and help defining the underlying arrhythmic mechanism.

PEMFC Reactant Mass Transfer Coefficient Measurement and Separation – Method Extension to the Mixed Kinetic and Mass Transfer Control Regime

Additional cost reductions are needed for proton exchange membrane fuel cells (PEMFC) to effectively compete with internal combustion engine powered vehicles. Recent trends have focused on the use of a high current density and a lower Pt catalyst loading to reduce the quantity of expensive materials. However, such strategies have led to higher mass transfer overpotentials (1). These performance losses are advantageously characterized by the mass transfer coefficient. Its separation into fundamental contributions will focus research efforts to improve cell performance. A separation method previously proposed (2) was extended, which provides information for a wider cell voltage range of relevance to duty cycling operation. The extended model yields a closed form and implicit current distribution expression (Eq. 1) where X represents the dimensionless Cartesian coordinate along the flow field channel, ie the inlet oxygen flow rate equivalent current density, ik the kinetic current density, iL ,0 the inlet limiting current density and i the current density. Experimental data obtained with a segmented single cell of 100 cm2 active area (Gore catalyst coated membrane, 18 μm thick membrane, 0.2 and 0.1 mg Pt cm- 2 catalyst loading, segmented and unsegmented Sigracet 25BC gas diffusion layer for the cathode and anode, respectively) validated Eq. 1 (Fig. 1a) and led to overall oxygen mass transfer coefficients k (derived from iL ,0 and operating conditions). A plot of 1/k versus M, the diluent molecular weight, yields a linear relation (Eq. 2) enabling the separation of the overall mass transfer coefficient into 2 contributions where ke +K represents the oxygen mass transfer coefficient in the electrolyte and the gas phase (Knudsen diffusion), km the oxygen mass transfer coefficient in the gas phase (molecular diffusion) for the specified diluent (subscript He for helium, N for N2, CF for C3F8) and b a parameter. The molecular diffusion mass transfer coefficient km is larger with a lighter diluent (Fig. 1b). Each mass transfer coefficient increases as the cell voltage is decreased. However, the increase in the mass transfer coefficient in the electrolyte and the gas phase (Knudsen diffusion) ke +K is more substantial than for the other contribution. As a result, the k/ke +K ratio decreases for lower cell voltages. Specifically for N2, the mass transfer rate limiting step is associated with the electrolyte and the gas phase (Knudsen diffusion), which suggests a focus on the micro-porous and catalyst layers to increase performance. Two reasons are proposed to explain the cell voltage dependency observed in Fig. 1b. First, the local change in gas phase composition promotes convection. This effect is particularly important before reaching the mass transfer control regime, in the mixed kinetic and mass transfer control region, as the interfacial oxygen concentration changes from its bulk flow field channel value to near 0 in the 0.75 to 0.6 V cell potential range creating a diluent enriched layer. Second, the local temperature in the gas diffusion electrode (through plane direction) is also higher at a lower cell voltage owing to additional heat production. The larger local temperatures in turn promote larger diffusion coefficients in the gas phase (molecular and Knudsen) and permeabilities in the ionomer phase. A comparison with other mass transfer coefficient values derived from impedance data (3) and the model limits of validity will also be discussed. Acknowledgments We gratefully acknowledge funding from the Army Research Office (W911NF-15-1-0188). The authors are grateful to the Hawaiian Electric Company for their ongoing support of the operations of the Hawaii Sustainable Energy Research Facility.

Transient analysis of electromagnetic wave interactions on plasmonic nanostructures using a surface integral equation solver.

Transient electromagnetic interactions on plasmonic nanostructures are analyzed by solving the Poggio-Miller-Chan-Harrington-Wu-Tsai (PMCHWT) surface integral equation (SIE). Equivalent (unknown) electric and magnetic current densities, which are introduced on the surfaces of the nanostructures, are expanded using Rao-Wilton-Glisson and polynomial basis functions in space and time, respectively. Inserting this expansion into the PMCHWT-SIE and Galerkin testing the resulting equation at discrete times yield a system of equations that is solved for the current expansion coefficients by a marching on-in-time (MOT) scheme. The resulting MOT-PMCHWT-SIE solver calls for computation of additional convolutions between the temporal basis function and the plasmonic medium's permittivity and Green function. This computation is carried out with almost no additional cost and without changing the computational complexity of the solver. Time-domain samples of the permittivity and the Green function required by these convolutions are obtained from their frequency-domain samples using a fast relaxed vector fitting algorithm. Numerical results demonstrate the accuracy and applicability of the proposed MOT-PMCHWT solver.

High-Gm differential regulated cascode transimpedance amplifier

A differential cross-coupled regulated cascode(RGC)transimpedance amplifier(TIA)is proposed. The theory of multi-stage common-source (CS) configuration as an auxiliary amplifier to enhance the bandwidth and output impedance of RGC topology is analyzed. Additionally, negative Miller capacitance and shunt active inductor compensation are exploited to further expand the bandwidth. The proposed RGC TIA is simulated based on UMC 0.18 µm standard CMOS process. The simulation results demonstrate that the proposed TIA has a high transimpedance of 60.5 dBΩ, and a -3 dB bandwidth of 5.4 GHz is achieved for 0.5 pF input capacitance. The average equivalent input noise current spectral density is about 20 pA/Hz1/2 in the interested frequency, and the TIA consumes 20 mW DC power under 1.8 V supply voltage. The voltage swing is 460 mVpp, and the saturation input current is 500 µA.