Capacitive Decay Research Articles

ID: 210792 Stimulation Capacitive Artifact and Electromyogram Bleed-through in Recorded Evoked Neural Spinal Recordings

Recently, evoked compound action potentials (ECAPs) has gained attention as both a research tool and to deliver closed-loop targeted spinal cord stimulation (SCS). Historically, neural components of ECAPs are very prone to misinterpretation outside of tightly controlled experimental settings, due to confounding variables such as motion artifact, extended capacitive decay of the stimulation artifact, filter ringing, and activated muscles causing electromyographic (EMG) bleed-through. In this study, we characterized how the relative position of the recording and stimulating electrodes with respect to the root and rootlets entering the spinal cord, impacts direct and indirect efferent activation of the back muscles and capacitive decay of the stimulation artifact, distorting the calculation of the ECAP components in spinal recordings.

Integrated Electrode‐Electrolyte Optimization to Manufacture a Real‐Life Applicable Aqueous Supercapacitor with Record‐Breaking Lifespan

Aqueous supercapacitors (SCs) have been regarded as a promising candidate for commercial energy storage device due to their superior safety, low cost, and environmental benignity. Unfortunately, an age‐old challenge of achieving both long electrode lifespan and qualified energy‐storage property blocks their practical application. Herein, we develop an electrode‐electrolyte integrated optimization strategy to fulfill the real‐life device requirements. Electrode optimization simultaneously regulates the nanomorphology and surface chemistry of the tungsten oxide anode, resulting in superior electrochemical performance given by an ideal “bird‐nest” structure with optimal oxygen vacancy status; the anodes interact with and are protected from dissolution and structural collapse by the rationally designed hybrid electrolyte with optimized pH and facilitated cation desorption behavior. Collaboratively, a record‐breaking durability of no capacitive decay after 250 000 cycles is achieved. On the basis of this integrated optimization, the first aqueous pouch SCs with real‐life practicability were manufactured by a soft‐package encapsulation technique, which can steadily power commercial 3 C products such as tablets and smartphones and maintain safely working against extreme conditions. This work demonstrates the possibility of using aqueous energy storage devices with enhanced safety and lower cost to replace the commercial organic counterparts for wide range of daily applications.

Redox-etching induced porous carbon cloth with pseudocapacitive oxygenic groups for flexible symmetric supercapacitor

Constructing high-performance electrodes with both wide potential window (e.g. ≥ 2 V in aqueous electrolyte) and excellent mechanical flexibility represents a great challenge for supercapacitors. Because of the outstanding conductivity and flexibility, carbon cloth (CC) has shown unlimited prospects for constructing flexible electrodes, but is rarely used directly as electrode material due to its electrochemical inertness and small specific surface area. To tackle these two critical limitations, we design a novel redox-etching strategy to synthesize CC-based electrode with 3D interconnecting pore structure. The sponge-like highly porous CC was further activated by strong oxidant to form abundant oxygenic groups, which occupy the interior and surface of current collector to render substantial pseudocapacitance. The as-synthesized CC electrode yielded an impressive capacitance of 4035 mF cm−2 at 3 mA cm−2 and satisfying cycling durability in a wide potential range of −1 – 1 V vs. SCE, which surpass the majority of reported CC-based electrodes. A symmetric supercapacitor with stable voltage of 2 V is assembled and delivers remarkable energy density of 6.57 mWh cm−3. Significantly, the device demonstrates an unparalleled flexibility with no capacitive decay after 100 bending cycles. This facile chemical etching and post-treatment processes are designed for large-scale manufacturing of the CC electrodes by providing high surface area and abundant electrochemically active sites, promising for industry application. The innovative synthetic strategy opens up new opportunities for high-performance flexible energy storage.

An electro-activated bimetallic zinc-nickel hydroxide cathode for supercapacitor with super-long 140,000 cycle durability

Inorganic double hydroxides are promising battery-type cathode materials for supercapacitors. Currently, the main limitation for the practical application of double hydroxides is their poor cyclic stability, which is originating from the relatively low electrical conductivity and irreversible phase transition. Herein, bimetallic zinc-nickel double hydroxide nanosheet arrays (ZNDH NSAs) are designed and assembled into an asymmetric supercapacitor with ultralong cyclic stability, demonstrating enormous potential as a high-performance cathode in practical applications. This bimetallic hydroxide is first spontaneously crystallized into two-dimensional nanosheets with thickness of ~10 nm, which ensure highly active sites for surface reactions. Then the as-prepared materials are further modified over an electro-activation process, which, as demonstrated by combining experimental evidence and computational simulation, leads to more defective oxygen, enlarged lattice, and reduced Ni valence, synergistically improving the charge transfer kinetics. Moreover, the introduction of Zn effectively suppresses phase transformation during ultralong cyclic stability tests and leads to improved conductivity of Zn-Ni hydroxide system. Therefore, the electro-activated ZNDH NSAs electrode exhibits an excellent capacitance of 6834 mF cm −2 at 3 mA cm −2 , and superior rate capability. The assembled supercapacitor delivers a record high cycling stability with zero capacitive loss after 140,000 cycles. To our knowledge, it is the best cycling performance for asymmetric supercapacitors. We demonstrate for the first time a novel “electro-activation” strategy that can substantially enhance the durability (no capacitive decay in 140,000 cycles) and charge storage performance of Zinc-Nickel double hydroxide electrode through controlled variation of activated upper potential. • An “electro-activation” strategy is demonstrated that enhance the charge storage performance of Zn-Ni hydroxide. • Electro-activation leads to more defective oxygen, reduced Ni valence, and loose porous network. • The Zn-Ni hydroxide-based supercapacitor shows zero capacitive loss after 140,000 cycles.

Electrical and Structural Dual Function of Oxygen Vacancies for Promoting Electrochemical Capacitance in Tungsten Oxide.

Intrinsic defects, including oxygen vacancies, can efficiently modify the electrochemical performance of metal oxides. There is, however, a limited understanding of how vacancies influence charge storage properties. Here, using tungsten oxide as a model system, an extensive study of the effects of structure, electrical properties, and charge storage properties of oxygen vacancies is carried out using both experimental and computational techniques. The results provide direct evidence that oxygen vacancies increase the interlayer spacing in the oxide, which suppress the structural pulverization of the material during electrolyte ion insertion and removal in prolonged stability tests. Specifically, no capacitive decay is detected after 30000 cycles. The medium states and charge storage mechanism of oxygen-deficient tungsten oxide throughout electrochemical charging/discharging processes is studied. The enhanced rate capability of the oxygen-deficient WO3- x is attributed to improved charge storage kinetics in the bulk material. The WO3- x electrode exhibits the highest capacitance in reported tungsten-oxide based electrodes with comparable mass loadings. The capability to improve electrochemical capacitance performance of redox-active materials is expected to open up new opportunities for ultrafast supercapacitive electrodes.

Pulse-height loss in the signal readout circuit of compound semiconductor detectors

Compound semiconductor detectors such as CdTe, CdZnTe, HgI2 and TlBr are known to exhibit large variations in their charge collection times. This paper considers the effect of such variations on the measurement of induced charge pulses by using resistive feedback charge-sensitive preamplifiers. It is shown that, due to the finite decay-time constant of the preamplifiers, the capacitive decay during the signal readout leads to a variable deficit in the measurement of ballistic signals and a digital pulse processing method is employed to correct for it. The method is experimentally examined by using sampled pulses from a TlBr detector coupled to a charge-sensitive preamplifier with 150 μs of decay-time constant and 20 % improvement in the energy resolution of the detector at 662 keV is achieved. The implications of the capacitive decay on the correction of charge-trapping effect by using depth-sensing technique are also considered.

Waterproof, Ultrahigh Areal-Capacitance, Wearable Supercapacitor Fabrics.

High-performance supercapacitors (SCs) are promising energy storage devices to meet the pressing demand for future wearable applications. Because the surface area of a human body is limited to 2 m2 , the key challenge in this field is how to realize a high areal capacitance for SCs, while achieving rapid charging, good capacitive retention, flexibility, and waterproofing. To address this challenge, low-cost materials are used including multiwall carbon nanotube (MWCNT), reduced graphene oxide (RGO), and metallic textiles to fabricate composite fabric electrodes, in which MWCNT and RGO are alternatively vacuum-filtrated directly onto Ni-coated cotton fabrics. The composite fabric electrodes display typical electrical double layer capacitor behavior, and reach an ultrahigh areal capacitance up to 6.2 F cm-2 at a high areal current density of 20 mA cm-2 . All-solid-state fabric-type SC devices made with the composite fabric electrodes and water-repellent treatment can reach record-breaking performance of 2.7 F cm-2 at 20 mA cm-2 at the first charge-discharge cycle, 3.2 F cm-2 after 10 000 charge-discharge cycles, zero capacitive decay after 10 000 bending tests, and 10 h continuous underwater operation. The SC devices are easy to assemble into tandem structures and integrate into garments by simple sewing.

Amorphous Mixed-Valence Vanadium Oxide/Exfoliated Carbon Cloth Structure Shows a Record High Cycling Stability.

Previous studies show that vanadium oxides suffer from severe capacity loss during cycling in the liquid electrolyte, which has hindered their applications in electrochemical energy storage. The electrochemical instability is mainly due to chemical dissolution and structural pulverization of vanadium oxides during charge/discharge cyclings. In this study the authors demonstrate that amorphous mixed-valence vanadium oxide deposited on exfoliated carbon cloth (CC) can address these two limitations simultaneously. The results suggest that tuning the V4+ /V5+ ratio of vanadium oxide can efficiently suppress the dissolution of the active materials. The oxygen-functionalized carbon shell on exfoliated CC can bind strongly with VO x via the formation of COV bonding, which retains the electrode integrity and suppresses the structural degradation of the oxide during charging/discharging. The uptake of structural water during charging and discharging processes also plays an important role in activating the electrode material. The amorphous mixed-valence vanadium oxide without any protective coating exhibits record-high cycling stability in the aqueous electrolyte with no capacitive decay in 100 000 cycles. This work provides new insights on stabilizing vanadium oxide, which is critical for the development of vanadium oxide based energy storage devices.

Optical, dielectric and visco-elastic properties of a few hockey stick-shaped liquid crystals with a lateral methyl group

Measurements of birefringence (Δn), dielectric permittivity (ε‖, ε⊥), elastic moduli (K11, K33) and rotational viscosity (γ1) have been carried out on the nematic (N) phase of a few hockey stick-shaped compounds 4-(3-n-alkyloxy-2-methyl-phenyliminomethyl)phenyl 4-n-alkyloxycinnamates with a lateral methyl group inserted between the m-alkyloxy chain and the azomethine connecting group. Interestingly, a dual characteristic (i.e. partially calamitic like and partially bent-core like) is revealed in the N phase of these compounds. The SmCa–N transition is found to be of first order in nature while the SmCs–N transition is either second order or weakly first order. All the mesogens exhibit a temperature dependent inversion in the static dielectric anisotropy (Δε = ε‖ − ε⊥) from positive to negative values on entering the SmCa phase. Remarkably in the entire nematic range, the bend elastic modulus (K33) is substantially lower than the corresponding splay modulus (K11). The rotational viscosity coefficient (γ1) as obtained by extracting the relaxation time (τ0) values from two precise, independent probing methods, viz. the capacitive decay technique and the optical phase-decay-time measurement method, are slightly higher than those of many known calamitic systems. Moreover, the activation energy (Ea) calculated from the viscosity data is found to be considerably higher in the nematic phase than those obtained for conventional calamitics. The observed behaviours are accounted for by considering the intriguing shape-determined inter-molecular interactions and molecular associations appearing in the mesophase.

Corrigenda

CorrigendaCorrigendaPublished Online:01 Feb 2007https://doi.org/10.1152/jn.z9k-8066-corr.2007Original articlesIntrinsic and Synaptic Mechanisms Determining the Timing of Neuron Population Activity During Hippocampal Theta OscillationRole for the Subthreshold Currents ILeak and IH in the Homeostatic Control of Excitability in Neocortical Somatostatin-Positive Inhibitory NeuronsMoreSectionsPDF (19 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Volume 96, July 2006 Pages 420–432: Gibson JR, Bartley AF, and Huber KM. “Role for the Subthreshold Currents ILeak and IH in the Homeostatic Control of Excitability in Neocortical Somatostatin-Positive Inhibitory Neurons” (doi:10.1152/jn.01203.2005; http://jn.physiology.org/cgi/content/full/96/1/420). The following sentence in the 2nd paragraph in methods (9th sentence under heading Electrophysiology) is in error:The capacitance was obtained by multiplying the series resistance by the fastest time constant of a double-exponential decay calculated fitted to the first 20 ms of the capacitive transient decay induced by a voltage step.The sentence should read:The capacitance was calculated by first obtaining the decay time constant of a current transient induced by a voltage step (the faster time constant of a double-exponential decay fitted to the first 20 ms) and then dividing this by the series resistance. Volume 96, December 2006 Pages 2889–2904: Orbán G, Kiss T, and Érdi P. “Intrinsic and Synaptic Mechanisms Determining the Timing of Neuron Population Activity During Hippocampal Theta Oscillation” (doi:10.1152/jn.01233.2005; http://jn.physiology.org/cgi/content/full/96/6/2889). In the methods section, under the heading Neuron types, in the first sentence, Warman et al. (1994) is erroneously cited; the correct reference is Varona et al. (2000), which was not included in the reference list. Therefore, the sentence should read: “The multicompartmental pyramidal cell model was an extended version of the 256 compartmental model of Varona et al. (2000).” The full citation information is as follows: Varona P, Ibarz JM, Lopez-Aguado L, Herreras O. Macroscopic and subcellular factors shaping population spikes. J Neurophysiol 83: 2192-2208, 2000.This article has no references to display. Download PDF Previous Back to Top FiguresReferencesRelatedInformationRelated ArticlesIntrinsic and Synaptic Mechanisms Determining the Timing of Neuron Population Activity During Hippocampal Theta Oscillation 01 Dec 2006Journal of NeurophysiologyRole for the Subthreshold Currents ILeak and IH in the Homeostatic Control of Excitability in Neocortical Somatostatin-Positive Inhibitory Neurons 01 Jul 2006Journal of Neurophysiology More from this issue > Volume 97Issue 2February 2007Pages 1869-1869 Copyright & PermissionsCopyright © 2007 by the American Physiological Societyhttps://doi.org/10.1152/jn.z9k-8066-corr.2007History Published online 1 February 2007 Published in print 1 February 2007 Metrics

Some studies on the pulse-height loss due to capacitive decay in the detector-circuit of parallel plate ionization chambers

Pulse-type ionization chambers are invariably operated in the electron-sensitive mode where the capacitive decay in the detector-circuit during the electron collection produces loss in the pulse-height. In order to understand and appreciate the effect of this capacitive decay on the detector response, we have carried out Monte Carlo simulations of the response of two-electrode parallel plate ionization chambers with and without the capacitive decay keeping shaping time so large that the ballistic deficit is negligibly small. These simulations have been carried out incorporating the physical processes, namely, emission of charged particles from a point radioactive source, the generation of charge carriers in the active volume, separation and acceleration of the charge carriers, transport of the charge carriers, induction of charges on the electrodes, pulse processing by preamplifier-amplifier network, etc. These simulations have shown that the concerned capacitive decay produces appreciable loss in the pulse-height, if the detector-circuit time constant is of the order of maximum electron collection time. We have also carried out measurements on the pulse-height loss due to the capacitive decay in the detector-circuit during the electron collection for a two-electrode parallel plate ionization chamber. The experimental data on the pulse-height loss match reasonably well with the theoretical predictions.

Integrated Description of Electrode/Electrolyte Interfaces Based on Equivalent Circuits and Its Verification Using Impedance Measurements

An integrated theory describing both faradaic and nonfaradaic currents obtained upon potential step at an electrified electrode/electrolyte interface has been developed based on equivalent circuits that had been used to explain electrochemical reactions and experimentally verified. The faradaic current is shown to consist of the mass transport-dependent and -independent parts, which is in general agreement with the expression previously derived from the diffusion equations. The decay of the capacitive current is determined by the time constant represented by the product of the resistance obtained from the parallel connection of the solution and polarization resistances and the double layer capacitance; this is not consistent with the current understanding of the capacitive current decay, which takes into account the double layer capacitance and the solution resistance only. Many insights into the electron-transfer reactions are discussed based on the interpretation of impedance representation of the system, which would not have been possible without the present theory.

Parameter-extraction of a two-compartment model for whole-cell data analysis

Neuronal modeling of patch-clamp data is based on approximations which are valid under specific assumptions regarding cell properties and morphology. Certain cells, which show a biexponential capacitance transient decay, can be modeled with a two-compartment model. However, for parameter-extraction in such a model, approximations are required regarding the relative sizes of the various model parameters. These approximations apply to certain cell types or experimental conditions and are not valid in the general case. In this paper, we present a general method for the extraction of the parameters in a two-compartment model without assumptions regarding the relative size of the parameters. All the passive electrical parameters of the two-compartment model are derived in terms of the available experimental data. The experimental data is obtained from a DC measurement (where the command potential is a hyperpolarizing DC voltage) and an AC measurement (where the command potential is a sinusoidal stimulus on a hyperpolarized DC potential) performed on the cell under test. Computer simulations are performed with a circuit simulator, XSPICE, to observe the effects of varying the two-compartment model parameters on the capacitive transients of the current response. Our general solution for the parameter-estimation of a two-compartment model may be used to model any neuron, which has a biexponential capacitive current decay. In addition, our model avoids the need for simplifying and perhaps erroneous approximations. Our equations may be easily implemented in hardware/software compensation schemes to correct the recorded currents for any series resistance or capacitive transient errors. Our general solution reduces to the results of previous researchers under their approximations.

Tolerance to analog hardware of on-chip learning in backpropagation networks

In this paper we present results of simulations performed assuming both forward and backward computation are done on-chip using analog components. Aspects of analog hardware studied are component variability, limited voltage ranges, components (multipliers) that only approximate the computations in the backpropagation algorithm, and capacitive weight decay. It is shown that backpropagation networks can learn to compensate for all these shortcomings of analog circuits except for zero offsets, and the latter are correctable with minor circuit complications. Variability in multiplier gains is not a problem, and learning is still possible despite limited voltage ranges and function approximations. Fixed component variation from fabrication is shown to be less detrimental to learning than component variation due to noise. Weight decay is tolerable provided it is sufficiently small, which implies frequent refreshing by rehearsal on the training data or modest cooling of the circuits. The former approach allows for learning nonstationary problem sets.