Voltage Stimuli Research Articles

Nanoscale light- and voltage-induced lattice strain in perovskite thin films.

We report on localized nonlinear lattice deformation and nanoscale structural rearrangement in methylammonium lead triiodide films triggered by the combined action of light and voltage. These effects, revealed by second harmonic piezoresponse force microscopy, are connected with organic cation motion, implicating localized cation migration as a key contributor to perovskite optoelectronic device instability under operating conditions.

Effects of sodium metavanadate on the electrical stimulation of sciatic nerve of toads (Bufo regularis)

Introduction: Vanadium and its compounds have been documented to exert toxic effects on almost all systems in living organisms including cardiovascular, reproductive and nervous systems. In the nervous system however, toxicity assays have been on the brain and its structures with little information on its effects on peripheral nerves. This study was therefore conducted to examine the toxicity of vanadium in the peripheral nervous system. Methods: Vanadium as sodium metavanadate was used in the study. Fifteen toads (Bufo regularis) were randomly distributed into 3 groups (A-C); A served as control and was administered distilled water during the experiment, B were intraperitoneally (i.p.) administered with sodium metavanadate at 3 mg/kg while C were administered with sodium metavanadate at 5 mg/kg i.p. for 7 consecutive days. Nerve conduction was studied in isolated toad sciatic nerve-gastrocnemius muscle preparation following electrical stimulation. The recordings were obtained on a kymograph for each group. Results: The results showed significant (p<0.05) reduction in the peak amplitude of the action potential and an increase in the latency of the onset of the action potential at 5 mg/kg sodium metavanadate. Furthermore, an increased threshold stimulus voltage was also observed in group administered with 5 mg/kg sodium metavanadate. The values of these parameters in the 3 mg/kg sodium metavanadate group were not statistically different from the control group. Significance: The findings of this preliminary study suggest that vanadium at 5 mg/kg may result in decrease speed of impulse conduction which may be as a result of demyelination in the sciatic nerve.

Electrets: A Remedy for Partial Discharge Caused by Power Electronics Switching

In this article, a novel approach that mitigates partial discharge (PD) by neutralizing local electric fields with the incorporation of electrets is presented. The surface charge density requirement of electret films that enable electric field neutralization is derived and numerical analysis is performed to validate them. The fabrication process of electrets is introduced, and we experimentally demonstrate the electret films reducing PD caused by the high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> of power electronics switching voltage stimuli for the first time. The PD measurements of an uncharged polyvinylidene fluoride (PVDF) film and a charged PVDF (electret) film are compared as a function of the rise time of square voltage stimuli. In addition, we compare the PD inception voltage of the two films while maintaining <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> at a constant value to regulate the impact of capacitive current pulses falsely being detected as PD. The results show great promise in the electret-based approach and suggest that further development of the technology may be able to completely solve PD that has been both chronic and emerging issues in the power industry.

Roles of TRP Channels in Neurological Diseases.

Transient receptor potential (TRP) proteins consist of a superfamily of cation channels that have been involved in diverse physiological processes in the brain as well as in the pathogenesis of neurological disease. TRP channels are widely expressed in the brain, including neurons and glial cells, as well as in the cerebral vascular endothelium and smooth muscle. Members of this channel superfamily show a wide variety of mechanisms ranging from ligand binding to voltage, physical, and chemical stimuli, implying the promising therapeutic potential of TRP in neurological diseases. In this review, we focus on the physiological functions of TRP channels in the brain and the pathological roles in neurological disorders to explore future potential neuroprotective strategies.

Aggregation-induced emission enhancement -active triarylamine-based polyamides containing fused ring groups towards electrochromic smart window and sensor for HCl and TNP

A series of new polyamides (PAs) were designed and synthesized based on two novel triarylamines (TAA) with fused ring groups via phenyl bridge through the Suzuki coupling reaction. These novel PAs have amorphous structure and excellent thermal stability, with a carbon residue rate of up to 70% at 800 °C in nitrogen atmosphere. In the process of electrochemical oxidation, there is no obvious recessionary in current and transmittance over 1000s with a cycle time of 10s, which showing high contrast and excellent cycle stability. And the electrofluorochromic (EFC) performance can also be adjusted by being applied voltage. 1NAT-CA and 9AAT-CA have solvatochromic effect in absorption, fluorescence (PL) in solvents, 1NAT-6F and 1NAT-BA have aggregation-induced emission enhancement (AIEE) properties in solid state. The kind of multifunctional integrated PAs show characteristics of responding to voltage, explosive and hazardous gas stimuli and the stimuli-responsive mechanisms are investigated, which have the prospect of application in photoelectric sensors, explosive detectors and high-contrast displays.

Study of Real-Time Spatial and Temporal Behavior of Bacterial Biofilms Using 2-D Impedance Spectroscopy.

The purpose of this paper is to demonstrate the use of 2-D impedance spectroscopy to identify areas of biofilm growth on a CMOS biosensor microelectrode-array. This paper presents the design and use of a novel multichannel impedance spectroscopy instrument to allow 2-D spatial and temporal evaluation of biofilm growth. The custom-designed circuits can provide a wide range of frequencies (1Hz-100kHz) to allow customization of impedance measurements, as the frequency of interest varies based on the type and state of biofilm under measurement. The device is capable of taking measurements as fast as once per second on the entire set of impedance sensors, allowing real-time observation. It also supports adjustable stimulus voltages. The distance between neighboring sensors is 220 micrometers which provides reasonable spatial resolution for biofilm study. Biofilm was grown on the surface of the chip, occupancy was measured using the new tool, and the results were validated optically using fluorescent staining. The results show that the developed tool can be used to determine the bacterial biofilm presence at a given location. This paper confirms that 2-D impedance spectroscopy can be used to measure biofilm occupancy. The new tool developed to perform the measurements was able to display real-time results, and determine biofilm coverage of the array electrodes. The system presented in this report is the first fully integrated 2-D EIS measurement system with full software support for capturing biofilm growth dynamics in real-time. Due to its ability to nondestructively monitor biofilms over time, 2-D impedance spectroscopy using a microelectrode-array is a useful tool for studying biofilms.

Comprehensive model for the electronic transport in Pt/SrTiO3 analog memristive devices

The presented study considers the electronic conduction across a $\mathrm{SrTi}{\mathrm{O}}_{3}\text{/}\mathrm{Pt}$ Schottky electrode in a resistive switching cell. It is generally accepted that the resistive switching effect is based on the migration of oxygen vacancies, which can be understood as mobile donors. In the experimental approach, a $\mathrm{Nb}:\mathrm{SrTi}{\mathrm{O}}_{3}\text{/}\mathrm{SrTi}{\mathrm{O}}_{3}\text{/}\mathrm{Pt}$ resistive switching cell is fabricated and tested for its electronic and resistive switching characteristics. Using different voltage stimuli, several analog resistance states are realized. Afterwards, the electrical transport properties under different applied voltages and temperatures are measured for each analog resistive state. To gain physical insight into the analog resistive switching a numerical simulation model is developed. The electronic conduction is calculated based on the single band transport theory and a phonon scattering theory accounting for polar material systems. The simulation model allows testing of the conduction in these resistive switching cells by using different doping (oxygen vacancy) concentrations. Combining the simulation model and the experiment, it delivers a comprehensive physical description for the conduction. By means of simulation, the energy resolved current transport across the Schottky barrier is analyzed. It forms a peaklike distribution, originating from the limited thermal excitation and tunneling probability across the $\mathrm{SrTi}{\mathrm{O}}_{3}\text{/}\mathrm{Pt}$ Schottky barrier. Thus, the conduction processes in all states are identified as a balance between a thermally assisted tunneling effect and a phonon dominated bulk transport. Applying this understanding, the resistive switching effect is reduced to a modification of the Schottky tunnel barrier, based on the rearrangement of oxygen vacancies. Thus a low vacancy concentration leads to a high and wide tunneling barrier, which is reduced and shortened for higher concentrations. All resistance states in between are understood as an adjustment of intermediate tunneling barriers. The physical insights leading to the realization of analog resistance states is mandatory to realize new types of neuromorphic computing circuits based on resistive switching devices. Furthermore, the obtained results could be easily transferred to other systems where a static doping concentration applies. This makes the results highly interesting to other applications in the field of electronic oxides and Schottky barrier dominated systems.

Reverse-engineering and modeling the 3D passive and active responses of skeletal muscle using a data-driven, non-parametric, spline-based procedure

In this work we present a non-parametric data-driven approach to reverse-engineer and model the 3D passive and active responses of skeletal muscle, applied to tibialis anterior muscle of Wistar rats. We assume a Hill-type additive relation for the stored energy into passive and active contributions. The terms of the stored energy have no upfront assumed shape, nor material parameters. These terms are determined directly from experimental data in spline form solving numerically the functional equations of the tests from which experimental data is available. To characterize typical longitudinal-to-transverse behavior in rodent's muscle, experiments from Morrow et al. (J. Mech. Beh. Biomed. Mater. 2010; 3: 124–129) are employed. Then, the passive and active behaviors of Wistar rats are determined from the experiments of Calvo et al. (J. Bomech. 2010; 43:318–325) and Ramirez et al. (J. Theor. Biol. 2010; 267:546–553). The twitch shape is not assumed, but reverse-engineered from experimental data. The influence of the strain and the stimulus voltage and frequency in the active response, are also modeled. A convenient stimulus power-related variable is proposed to comprise both voltage and frequency dependencies in the active response. Then, the behavior of the resulting muscle model depends only on the muscle strain maintained during isometric tests in the muscle and the stimulus power variable, along the time from initiation of the tetanus state.

Accumulative effect of partial discharges at impulse voltage wave tail

This study describes a technique for evaluating partial discharges at fast impulse voltages. Fast transient voltages are increasingly present in power equipment and industrial environments due to the ubiquitous application of power electronics switching devices. Special attention should be paid to the dangers caused by the accumulative effect of repetitive impulse voltages on electrical insulation. This study describes a method of analysing partial discharges occurring during impulse voltage stimuli. A repetitive train of pulses is applied to a dielectric specimen and the accumulated PD pattern is obtained. This study focuses on the reverse discharges which occur during the tail part of the impulse voltage waveform acquired in time-resolved mode. Investigations of the partial discharges in the wave tail can potentially lead to greater degradation of the insulation due to the formation of longer, repetitive sequence occurring along the decaying impulse voltage tail. Experiments were performed which investigated the influence of rise time, fall time and peak voltage on discharge pattern reshaping, intensity and time to inception on the tail. In the future, such an approach might be further developed for diagnostic applications and for extended factory tests.

Design of Dual-Mode Stimulus Chip With Built-In High Voltage Generator for Biomedical Applications.

In this work, a dual-mode stimulus chip with a built-in high voltage generator was proposed to offer a broad-range current or voltage stimulus patterns for biomedical applications. With an on-chip and built-in high voltage generator, this stimulus chip could generate the required high voltage supply without additional supply voltage. With a nearly 20 V operating voltage, the overstress and reliability issues of the stimulus circuits were thoroughly considered and carefully addressed in this work. This stimulus system only requires an area of 0.22 mm2 per single channel and is fully on-chip implemented without any additional external components. The dual-mode stimulus chip was fabricated in a 0.25-μm 2.5V/5V/12V CMOS (complementary metal-oxide-semiconductor) process, which can generate the biphasic current or voltage stimulus pulses. The current level of stimulus is up to 5 mA, and the voltage level of stimulus can be up to 10 V. Moreover, this chip has been successfully applied to stimulate a guinea pig in an animal experiment. The proposed dual-mode stimulus system has been verified in electrical tests and also demonstrated its stimulation function in animal experiments.

Long-range temporal correlations in scale-free neuromorphic networks.

Biological neuronal networks are the computing engines of the mammalian brain. These networks exhibit structural characteristics such as hierarchical architectures, small-world attributes, and scale-free topologies, providing the basis for the emergence of rich temporal characteristics such as scale-free dynamics and long-range temporal correlations. Devices that have both the topological and the temporal features of a neuronal network would be a significant step toward constructing a neuromorphic system that can emulate the computational ability and energy efficiency of the human brain. Here we use numerical simulations to show that percolating networks of nanoparticles exhibit structural properties that are reminiscent of biological neuronal networks, and then show experimentally that stimulation of percolating networks by an external voltage stimulus produces temporal dynamics that are self-similar, follow power-law scaling, and exhibit long-range temporal correlations. These results are expected to have important implications for the development of neuromorphic devices, especially for those based on the concept of reservoir computing.

2D Resistive Switching Based on Amorphous Zinc–Tin Oxide Schottky Diodes

AbstractA room‐temperature‐processed resistive switching Schottky diode that can be operated in two distinct modes, depending solely on the choice of device initialization mode, is presented. Electroforming in the diode's reverse polarity leads to an abrupt filamentary switching with inherently long data retention at the expense of rectification. After this electroforming process, the devices may work in either a bipolar or unipolar manner with a resistance window of at least two orders of magnitude. Device initialization in the forward direction shows a smooth area‐dependent switching over two orders of magnitude, which conserves the current rectification and allows for analog control over the resistance states (dependence of device history and applied voltage stimuli). This secondary mechanism involves ion exchange or charge trapping at the Schottky interface without a contribution from the bulk (hence, it is termed 2D), which is reported for the first time for an amorphous oxide semiconductor switching matrix.

Voltage dependent conduction abnormalities in His bundle pacing in patients without His Purkinje system disease

BackgroundDuring His bundle (HB) pacing, the active fixation of HB lead may cause disruption of the enclosed conduction fibers and cause conduction delay. His Purkinje conduction delays have been shown to revert to normal with higher voltage pacing. ObjectiveTo determine if conduction delays seen with penetrative HB pacing are voltage dependent and can resolve with higher stimulus voltage. MethodsIn 17 patients undergoing HBP, the effect of voltage on a composite His Purkinje system-ventricular activation time (hVAT) as well as electrocardiographic (ECG) evidence of conduction delay, was systematically evaluated. ResultsThere was highly significant prolongation of hVAT indicative of conduction delay in 13/17 patients. ECG changes of rightward delay were also seen in 9/13 patients. Both types of delays we manifest at lower voltages and we uniquely resolved by higher stimulation voltage.A pre-excitation like abnormality was also seen in 15/17 patients. This conduction abnormality was manifest at higher voltage without prolongation of hVAT. In 6/15 patients the pre-excitation like abnormality ceased at lower voltage. ConclusionHB pacing is associated with evidence of significant conduction delay noted at low voltage, which resolves with higher stimulation voltage. The more common pre-excitation like abnormality appears to occur at high voltage and, in of itself, does not appear to prolong hVAT.

Ferroelectret nanogenerators for loudspeaker applications: A comprehensive study

A ferroelectret nanogenerator (FENG) was recently developed as a flexible energy harvesting device with bi-directional capability between electrical and mechanical energy domains, and its use as a loudspeaker/microphone was demonstrated. Dependencies of Sound Pressure Levels (SPLs) generated by FENG due to an AC voltage stimulus, surface area, geometric shape, and addition of layers are presented here. Also, the relation between the sound output to the electrical input is studied and shown to be linear, which demonstrates that these flexible loudspeakers have low distortion within the human audible range of 20 Hz to 20 kHz. A study for ultrasonic frequencies up to 40 kHz is also presented. A theoretical model relating the electrical and acoustical domain of the FENG is developed based on the experimental observations made and using Boundary Element Methods (BEM) to accurately mimic the testing environment for simulation purposes. The comparison between this model and the actual behavior is presented under several cases and observed to be closely correlated.

A Neuromorphic Device Implemented on a Salmon-DNA Electrolyte and its Application to Artificial Neural Networks.

A bioinspired neuromorphic device operating as synapse and neuron simultaneously, which is fabricated on an electrolyte based on Cu2+‐doped salmon deoxyribonucleic acid (S‐DNA) is reported. Owing to the slow Cu2+ diffusion through the base pairing sites in the S‐DNA electrolyte, the synaptic operation of the S‐DNA device features special long‐term plasticity with negative and positive nonlinearity values for potentiation and depression (αp and αd), respectively, which consequently improves the learning/recognition efficiency of S‐DNA‐based neural networks. Furthermore, the representative neuronal operation, “integrate‐and‐fire,” is successfully emulated in this device by adjusting the duration time of the input voltage stimulus. In particular, by applying a Cu2+ doping technique to the S‐DNA neuromorphic device, the characteristics for synaptic weight updating are enhanced (|αp|: 31→20, |αd|: 11→18, weight update margin: 33→287 nS) and also the threshold conditions for neuronal firing (amplitude and number of stimulus pulses) are modulated. The improved synaptic characteristics consequently increase the Modified National Institute of Standards and Technology (MNIST) pattern recognition rate from 38% to 44% (single‐layer perceptron model) and from 89.42% to 91.61% (multilayer perceptron model). This neuromorphic device technology based on S‐DNA is expected to contribute to the successful implementation of a future neuromorphic system that simultaneously satisfies high integration density and remarkable recognition accuracy.

Elaboration and Characterization of Conductive Polymer Nanocomposites with Potential Use as Electrically Driven Membranes.

In this work, a general, facile, and relatively low-cost method to produce electrically driven non-porous membranes by revalorization of recycled polyolefins is proposed. The polymer matrices are poly(propylene) (PP) and poly(ethylene) (PE) and their corresponding recycled samples, which are respectively mixed with carbon nanotubes (CNT). The performances of the elaborated nanocomposites are studied by morphological, rheological, and electrical conductivity tests. The Joule heating effect is evaluated by applying an electric field and recording the corresponding temperature rise. An increase of 90 °C is obtained in certain cases, which represents the highest temperature enhancement reached so far by the Joule effect in thermoplastics, to our knowledge. The work shows a route to develop stimulus (voltage)-response (temperature) materials with low cost and with potential applications in many fields. As an example, the increase of the permeability with temperature of membranes made of the indicated nanocomposites, is analyzed.

Transient Simulation of Current and Electrophosphorescence in Organic Light-Emitting Diodes Using the Master Equation

Lack of consistent and efficient analyses on electrical excitation, charge carrier, and exciton dynamics has inspired us to perform transient simulations on current and electroluminescence characteristics of a phosphorescent organic light-emitting diode (OLED). The backward Euler scheme is utilized to discretize the time-dependent master equation (ME) for charge carriers and excitons, and a Newton–Raphson approach ensures quadratic convergence in both potential and triplet occupancy. The OLEDs doped with various emitter profiles of Ir(ppy)3 in the emission layer (EML) are investigated under step and pulse voltage stimuli. Results suggest that, under a high step voltage, a broadening recombination zone in sufficiently doped devices contributes to enhancement in turn-on electrophosphorescence. On the other hand, after a pulse stimulus is switched off, the decay in turn-off phosphorescence slows down with a longer pulse duration resulting from the temporary recombination of residual charge carriers within the EML. Nevertheless, provided that further spreading of charge carriers in the EML is inhibited, strengthening in the triplet quenching effects under highly growing triplet accumulation will lead to a faster phosphorescence decay.

Dynamics of set and reset processes on resistive switching memories

In this work, we have characterized hafnium oxide based bipolar resistive switching memories (RRAM) by measuring the small-signal conductance. The samples under study exhibit a continuum of intermediate states which can be accurately controlled by means of adequate sequence of the applied stimulus. The experimental results are analyzed to obtain information on the dynamics of the set and reset processes. This study reveals that ON-to-OFF (reset) and OFF-to-ON (set) processes are not symmetrical. Set transition is gradual and depends on the voltage stimulus according to an Erlang function which consists of a sum of k independent and identically distributed mechanisms, each having an exponential distribution. In contrast, reset process is more abrupt and can be described by a sigmoidal law. Time dependencies of set and reset process at fixed voltage values are explored as well. Set process is gradual at any positive voltage, whereas reset process is characterized by a time constant which depends on the applied voltage. Experimental results are explained in terms of the formation of interfacial barrier between the top electrode and the conductive filament.

Arbitrary waveform constant current stimulator for long-term wearable applications

Subsensory electrical noise stimulation has been shown to improve sensory perception in humans. However, the majority of this work has been limited to the laboratory due to unavailability of portable body-worn stimulators. In this paper, we present a robust and reliable stimulator, engineered for wearable applications and designed to extend modulation of human sensory perception outside the physiology laboratory.The stimulator provides an arbitrary waveform constant current stimulation, offering continuous current stimulation up to ±5 mA with a voltage compliance of ±25 V (expandable up to 70 V). A graphical user interface allows setting of stimulus parameters within fixed ranges via a USB connected computer. The interface is very simple using a single power switch and a single multi-coloured LED for device feedback. The applied stimulus voltage and current are continually monitored and used to detect short circuit, high impedance conditions. These conditions, and other errors e.g. low battery state, put the device in a safe state with the user disconnected via a relay. All captured data, including accelerometer data, is logged to a removable SD card. Powered by an interchangeable, Li-Ion battery pack >4 h stimulation is achievable. The full circuit, system software and bench tests performed are presented.

The Missed Role of Cytoskeletal Filaments in Information Processing

Recently, substantial experimental evidence on Cytoskeleton filaments have demonstrated that the concurrent propagation of both electrical signals along cytoskeleton filaments and electrochemical currents along the axonal membrane are highly possible. This discovery opened an unexplored frontier in understanding brain information processing, neural plasticity and changes in the cytoskeleton. However, the molecular mechanisms governing the bionanowire properties in cytoskeleton filaments under physiological and pathological conditions are still poorly understood. In this presentation, we introduce an innovative multi-scale approach able to account for the atomistic details of a protein molecular structure, its biological environment, and their impact on electrical impulses propagating along wild type Actin filaments. Our results for in-vitro and intracellular conditions show a significant influence of the voltage stimulus and biological environment on the electrical impulse shape, attenuation and propagation velocity. The filament is shown to sustain the ionic wave propagation at almost constant velocity for the in-vitro condition, whereas the intracellular condition displays a remarkable deceleration. As a unique feature, this multi-scale theory is able to account for molecular structure conformation (mutation) and biological environment changes (pH and ionic concentrations) often present in pathological conditions. Thus, it may be potentially useful in providing a molecular understanding for how and why age and inheritance conditions induce dysfunction and malformation in cytoskeleton filaments associated with a variety of neurological diseases. It is also applicable to other conducting biopolymers with relevance in biomedicine and biophysics and their potential nanotechnological applications.