Rectangular Voltage Pulses Research Articles

Microfluidic Optical Shutter Flexibly x-y Actuated via Electrowetting-on-Dielectrics with <20 ms Response Time

Tunable microoptics deals with devices of which the optical properties can be changed during operation without mechanically moving solid parts. Often a droplet is actuated instead, and thus tunable microoptics is closely related to microfluidics. One such device/module/cell type is an optical shutter, which is moved in or out of the path of the light. In our case the transmitting part comprises a moving transparent and electrically conductive water droplet, embedded in a nonconductive blackened oil, that is, an opaque emulsion with attenuation of 30 dB at 570 nm wavelength over the 250 μm long light path inside the fluid (15 dB averaged over the visible spectral range). The insertion loss of the cell is 1.5 dB in the “open shutter” state. The actuation is achieved via electrowetting-on-dielectrics (EWOD) with rectangular AC voltage pulses of 2·90 V peak-to-peak at 1 kHz. To flexibly allow for horizontal, vertical, and diagonal droplet movement in the upright x-y plane, the contact structures are prepared such that four possible stationary droplet positions exist. The cell is configured as two capacitors in series (along the z axis), such that EWOD forces act symmetrically in the front and back of the 60 nl droplet with a response time of <20 ms.

P1087New method for determination of tubular membrane capacity in intact cardiomyocytes

Introduction: Transverse tubular system (TTS) plays a key role in the fast transmission of action potential from the cell surface to the depth of cardiomyocytes, thus, near to calcium stores and contractile machinery. The function of TTS is highly dependent on the presence of transport proteins whose distribution considerably differs in TTS and surface cell membrane. Knowledge of TTS capacity is required for the proper analysis of TTS function. Determination of TTS capacity and its contribution to the total cell capacity may be done by measurement of the membrane capacity before and after the so called detubulation, i.e. detachment of TTS caused by osmotic shock. However, this method is irreversible and, moreover, may result in wrong data due to incomplete TTS detachment. Purpose: The aim of this work was to suggest an alternative method for determination of TTS capacity that preserves the measured cardiomyocyte intact and, thus, enables repetitive measurements in the same cell. Method: It is impossible to distinguish TTS capacity and surface membrane capacity during measurement of the cell membrane capacity in normal conditions because both membrane systems are connected closely one to another. The newly developed method is based on the alternative electrical cell circuit with two membrane systems separated by electrical resistance of TTS. Transient application of isotonic sucrose solution (ISS) on the measured cell causes a significant increase of TTS resistance and, therefore, electrical separation of the two systems. Analysis of current responses to the imposed rectangular voltage pulses (by a new quantitative model) then enables to reveal capacity of the surface membrane and TTS separately. In this work, the membrane capacities were determined on enzymatically isolated rat ventricular myocytes. Results: After ISS application, a transitory phenomenon was observed. It was registered by changes of the membrane current at the imposed constant voltage. The analysed parameters gradually changed, first only the surface membrane parameters and, with a delay, also TTS parameters. It enabled to visualize the process of solution diffusion into TTS by a newly suggested quantitative model. Capacities of TTS and surface membranes (CTTS = 68.0±4.8 pF a CS = 99.8±3.9 pF, respectively; n = 16) were determined in the steady-state from approximation of the responses to rectangular pulses by the sum of two exponential waveforms. Ratio of both surfaces was determined as SS/STTS = 0.40±0.02, assuming the same specific capacity. Conclusion: The newly suggested method leaves the measured cell intact and allows repetitive measurements. Determined value of the tubular capacity fraction (Ct/Cm = 0.43) falls into the range of published data obtained by various methods (0.21-0.64). Recent estimates are based on the model of cell membrane with concentrated parameters. Further improvement of this method may be achieved after implementation of TTS description as a system with distributed parameters.

The Spatial Extent of Epiretinal Electrical Stimulation in the Healthy Mouse Retina

Background/Aims: Retinal prostheses use electrical stimulation to restore functional vision to patients blinded by retinitis pigmentosa. A key detail is the spatial pattern of ganglion cells activated by stimulation. Therefore, we characterized the spatial extent of network-mediated electrical activation of retinal ganglion cells (RGCs) in the epiretinal monopolar electrode configuration. Methods: Healthy mouse RGC activities were recorded with a micro-electrode array (MEA). The stimuli consisted of monophasic rectangular cathodic voltage pulses and cycling full-field light flashes. Results: Voltage tuning curves exhibited significant hysteresis, reflecting adaptation to electrical stimulation on the time scale of seconds. Responses decreased from 0 to 300 µm, and were also dependent on the strength of stimulation. Applying the Rayleigh criterion to the half-width at half-maximum of the electrical point spread function suggests a visual acuity limit of no better than 20/946. Threshold voltage showed only a modest increase across these distances. Conclusion: The existence of significant hysteresis requires that future investigations of electrical retinal stimulation control for such long-memory adaptation. The spread of electrical activation beyond 200 µm suggests that neighbouring electrodes in epiretinal implants based on indirect stimulation of RGCs may be indiscriminable at interelectrode spacings as large as 400 µm.

Improved spatial resolution for spot sampling in thermal desorption atomic force microscopy - mass spectrometry via rapid heating functions.

The key to advancing materials is to understand and control their structure and chemistry. However, thorough chemical characterization is challenging since existing techniques characterize only a few properties of the specimen, thereby necessitating multiple measurement platforms to acquire the necessary information. The multimodal combination of atomic force microscopy (AFM) and mass spectrometry (MS) transcends existing analytical capabilities for nanometer scale spatially resolved correlation of the chemical and physical properties of a sample surface. One such hybrid system employs heated AFM cantilevers for thermal desorption (TD) sampling of molecules from a surface and subsequent gas phase ionization and detection of the liberated species by MS. Herein, we report on the use of voltage pulse trains to tailor cantilever heating such that spot sampling size was reduced and mass spectral signal was improved compared to constant voltage, static heating of the cantilever. Desorption efficiency (DE), defined as the quotient of the mass spectral signal intensity and the volume of the desorption crater, was used to judge the effectiveness of a particular tailored heating function. To guide the development and optimization of the heating functions and aid in interpreting experimental results, a 1D finite element model was developed that predicted the cantilever response to different heating functions. Three tailored heating functions that used different combinations, magnitudes, and durations of rectangular voltage pulses, were used for surface spot sampling. The resultant sampling spot size and DE were compared to the same metrics obtained with the conventional method that uses a single voltage pulse. Using a model system composed of a thin film of ink containing pigment yellow 74 as a model system, desorption craters shrunk from 2 μm, using the conventional approach, to 310 nm using the optimum tailored heating function. This same pulsed heating function produced a 381× improvement in the DE and an 8× improvement in spatial resolution compared to the conventional heating approach showing that signal/amount of material sampled was improved significantly by this new cantilever heating strategy.

Design and Sensorless Control of a Novel Axial-Flux Permanent Magnet Machine for In-Wheel Applications

This paper proposes an axial-flux-modulation permanent magnet (PM) machine and its sensorless control strategy for in-wheel application in electrical vehicles. A Vernier structure is integrated with the axial-flux PM machine to include the magnetic gear effect and improve output torque. The sensorless control strategy of the proposed machine, including initial rotor position estimation and rotating position estimation, is proposed for flux-modulation motors in this paper. The initial rotor position estimation is based on the technique of rectangular pulse voltage injection and the rotating rotor position estimation is based on the sliding mode observer (SMO). The saturation effect on inductances, which is the theoretical basis of the rectangular pulse voltage injection, makes the stator parameter variation in different loads and affects the SMO estimation. To overcome this problem, a novel online parameter self-adjustment procedure for the SMO is introduced. The machine design and its sensorless control performance are verified by simulation and prototype experiments.

The effect of surface conductivity and adhesivity on the electrostatic manipulation condition for dielectric microparticles using a single probe

By clarifying the effect of surface conductivity and adhesivity on the electrostatic manipulation condition, a dielectric particle made of any material can be manipulated with surface conductivity. The manipulation system consists of three elements: a conductive probe as a manipulator, a conductive plate as a substrate, and a dielectric particle as the target object for manipulation. The particle can be successfully picked up/placed if a rectangular pulse voltage is applied between the probe and the plate. Four kinds of particle materials are used in the experiment: silica, soda-lime glass, polymethyl methacrylate coated by conductive polymer, and polystyrene coated by surfactant. The radius of each particle is 15 μm. A first-order resistor-capacitor (RC) circuit model is adopted to describe the effect of surface conductivity and adhesivity on the manipulation condition. The manipulation system is modeled as a series circuit consisting of a resistor and a capacitor by considering the surface conductivity. A detachment voltage is defined as the capacitance voltage to detach the particle adhered to the plate or probe. Parameters of the RC model, surface resistance, surface capacitance and detachment voltage are identified by a simulation and measurements. To verify the RC model, the particle’s behavior is observed by a high-speed camera, and the electrical current is measured by an electrometer. A manipulation experiment is demonstrated to show the effectiveness of the model. The particle reaction is observed for each duration and magnitude of the pulse voltage for the manipulation. The optimum pulse voltage for successful manipulation is determined by the parameters of the RC model as the standard. This knowledge is expected to expand the possibility of micro-fabrication technology.

Sensorless Speed Control with Initial Rotor Position Estimation for Surface Mounted Permanent Magnet Synchronous Motor Drive in Electric Vehicles

The accurate information of the initial rotor position is very critical for successful starting of the Surface-mounted Permanent Magnet Synchronous Motor (SPMSM). In order to solve the problems of low accuracy and unreliability in the conventional estimation strategy, in this paper, an improved initial rotor position estimation strategy without any position sensor for SPMSM at standstill is proposed based on rectangular pulse voltage injection. In the work, when the second series of pulse voltages were applied. By the ways of strengthening the effect of weakening or strengthening magnetic fields and increasing the difference between each current of the vector. The improved strategy enhanced reliability and raised the initial position estimation accuracy from 7.5° to 1.875°. The improved strategy does not need any additional hardware. Experimental results demonstrate the validity and usefulness of the improved strategy.

Pulse voltage determination for electrostatic micro manipulation considering surface conductivity and adhesion of glass particle

A model with surface conductivity and adhesional force is proposed to investigate the mechanism for electrostatic micro manipulation of a dielectric object using a single probe. The manipulation system consists of three elements: a conductive probe as a manipulator, a conductive plate as a substrate, and a dielectric particle as the target object for manipulation. The particle can be successfully picked up/placed if a rectangular pulse voltage is applied between the probe and the plate. The reliability of the picking up/placing operation is improved by applying a pulse voltage that is determined by a theoretical model considering surface conductivity and adhesion. To verify the theoretical prediction, manipulation experiment is conducted using soda-lime glass particles with radii of 20 μm and 40 μm.

Measurements of the Capacitance of a Biological Cell by a Pulse Method

We propose a method for measuring the electrical capacitance of a biological cell using a previously developed pulse conductimetry apparatus. The method is based on using an RC circuit to differentiate a rectangular voltage pulse applied to the cell with microelectrodes.

Spectroscopy of Single Vacuum Arc Cathode Spots With Improved Sensitivity

Recently, we reported on the optical emission of vacuum arc discharges with a single cathode spot. The discharges were initiated by rectangular voltage pulses of 100-ns length produced by a cable generator. In combination with the application of a liquid Ga-In alloy cathode and ultrahigh vacuum conditions, a high reproducibility was obtained. An improvement of the sensitivity and the signal-to-noise ratio was achieved by the replacement of the streak camera by an intensified charge-coupled device camera. Thus, the accumulation of calibrated spectra with high temporal, spatial, and wavelength resolution was possible. Distinct differences in the temporal development of the atomic and ionic line intensities were found depending on the spatial position, that is, comparing the spot core and the spot surrounding.

Smart Structural Health Monitoring Based on Detecting Picometer-Scale Wavelength Shift of Fiber Bragg Grating

The real-time monitoring technologies of smart civil structure based on detecting picometer-scale wavelength shift of fiber Bragg grating (FBG), including the wavelength demodulation technology of FBG, are researched extensively at home and abroad. In the paper, using the technologies of wavelength division multiplex (WDM) and time division multiplex (TDM), fiber Bragg grating (FBG) sensor network was built for monitoring smart structure health condition. Based on SOPC (System on Programmable Chip) technology and fiber comb filter, a high-speed and high-precision wavelength demodulation scheme of FBG sensor network was proposed. The optical system and hardware circuit for demodulation system were designed specifically. To improve the accuracy of demodulation system of FBG, a constant temperature channel of the demodulation system connected with a fiber comb filter, which offered reference points to calibrate the Bragg grating center wavelength. Based on 32-bit soft-core processor NoisⅡ, the embedded system collected and processed the photoelectric signal voltage transformed to rectangular voltage pulse. The upper computer displayed dynamically the FBG wavelength demodulation process and calibrated the Bragg grating center wavelength. The experiments of FBG wavelength demodulation and health monitoring of smart structural embedded fiber Bragg gratings were done. Experimental results show that, the FBG wavelength demodulation method can be used to demodulate the FBG wavelength with high speed and high precision (± 2 pm), which can be used extensively in large-scale multipoint monitor engineering, and the strains of the smart structure can be measured accurately.

Spike-Timing-Dependent Plasticity Using Biologically Realistic Action Potentials and Low-Temperature Materials

Spike-timing-dependent plasticity (STDP) is a fundamental learning rule observed in biological synapses that is desirable to replicate in neuromorphic electronic systems. Nanocrystalline-silicon thin film transistors (TFTs) and memristors can be fabricated at low temperatures, and are suitable for use in such systems because of their potential for high density, 3-D integration. In this paper, a compact and robust learning circuit that implements STDP using biologically realistic nonmodulated rectangular voltage pulses is demonstrated. This is accomplished through the use of a novel nanoparticle memory-TFT with short retention time at the output of the neuron circuit that drives memristive synapses. Similarities to biological measurements are examined with single and repeating spike pairs or different timing intervals and frequencies, as well as with spike triplets.

Solar Power Conditioners Using Bidirectional Chopper Circuits Connected in Series

AbstractThis paper proposes a new high‐efficiency grid‐connection inverter suitable for the interface with thin‐film solar cells, which is composed of two bidirectional buck converters and an H‐bridge PWM converter connected in series. The switching frequencies of the first bidirectional buck converters are equal to the grid frequency, while the second is operated at twice the grid frequency. The combination of these two converters synthesizes an AC rectangular voltage pulse train from the DC input power. The H‐bridge PWM converter is operated at 20 kHz with a low DC capacitor voltage to compensate for the harmonic voltage included in the rectangular voltage pulse train. As a result, the proposed grid‐connection inverter makes it possible to reduce both switching loss and common mode voltage. Experimental results obtained by a 1‐kW single‐phase inverter demonstrate a high efficiency of 98% without any common mode voltage. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(2): 51–60, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22379

Einzel lens chopper and behavior of the chopped beam in the KEK digital accelerator

The KEK digital accelerator (KEK-DA), which is a small-scale rapid-cycle induction synchrotron (IS), has commenced operation. A permanent magnet $x$-band electron cyclotron resonance ion source serves as the KEK-DA ion source and delivers various ions. A new Einzel lens beam chopper has been developed to provide the necessary pulse width of a few microseconds. The chopper is implemented by applying a rectangular pulse voltage generated by a solid-state Marx generator to the middle electrode of the Einzel lens. Momentum modulation at the bunch head and tail resulting from chopping in longitudinal direction has been observed. This intrinsic property of the chopped pulse has been clearly observed in a long drift (a free run in the circular ring) in KEK-DA.

Transport and ionization of sputtered atoms in high-power impulse magnetron sputtering discharges

We use a non-stationary two-zone model to verify predictions of a steady-state phenomenological model (Vlček and Burcalová) under the conditions in typical high-power impulse magnetron sputtering discharges (copper target of 50 mm diameter, argon pressure of 1 Pa, rectangular voltage pulses of 200 µs length with amplitudes from 400 to 1000 V and repetition frequency of 100 Hz). It is shown that the steady-state phenomenological model provides a reliable description of fundamental deposition parameters characterizing efficiency of magnetron sputtering and the transfer of target material ions to the substrate in these discharges with relatively long steady-state discharge regimes established during pulses. Based on the results, we recommend to lower the magnetic field strength in a magnetron system at a fixed average target power density in a pulse and thereby use a higher magnetron voltage in order to enhance the deposition rate and keep or even increase the ionized fraction of sputtered target material atoms in the flux onto the substrate.

EFFICACY OF A NEW CHARGE-BALANCED BIPHASIC ELECTRICAL STIMULUS IN THE ISOLATED SCIATIC NERVE AND THE HIPPOCAMPAL SLICE

Most deep brain stimulators apply rectangular monophasic voltage pulses. By modifying the stimulus shape, it is possible to optimize stimulus efficacy and find the best compromise between clinical effect, minimal side effects and power consumption of the stimulus generator. In this study, we compared the efficacy of three types of charge-balanced biphasic pulses (CBBPs, nominal duration 100 μs) in isolated sciatic nerves and in in vitro hippocampal brain slices of the rat. Using these two models, we tested the efficacy of several stimulus shapes exclusively on axons (in the sciatic nerve) and compared the effect with that of stimuli in the more complex neuronal network of the hippocampal slice by considering the stimulus-response relation. We showed that (i) adding an interphase gap (IPG, range 100-500 μs) to the CBBP enhances stimulus efficacy in the rat sciatic nerve and (ii) that this type of stimuli (CBBP with IPG) is also more effective in hippocampal slices. This benefit was similar for both models of voltage and current stimulation. In our two models, asymmetric CBBPs were less beneficial. Therefore, CBBPs with IPG appear to be well suited for application to DBS, since they enhance efficacy, extend battery life and potentially reduce harmful side effects.

Improving gas identification accuracy of a temperature-modulated gas sensor using an ensemble of classifiers

Data processing methods commonly used in conjunction with the array- and quasi-array-based gas identification systems generally include a dimension reduction followed by categorization using a classifier. Here, we have applied an ensemble of classifiers, directly to the high dimensional feature vectors and fused their verdicts by majority voting. The quasi-array investigated is a metal oxide sensor temperature-modulated with different rectangular heating voltage pulses. The experimental database was developed by recording the temporal responses obtained at different conditions to methanol, ethanol and 1-butanol vapors. Features related to each response were extracted by wavelet transform. The classification rates achieved with traditional methods were compared to that obtained using an ensemble of classifiers. The classification rate was improved by majority voting among the classifiers, each trained on different feature subsets, for the classification verdict.

Influence of helium mole fraction distribution on the properties of cold atmospheric pressure helium plasma jets

The influence of helium mole fraction distribution in air on the cold atmospheric plasma jets excited by 1.5 kHz rectangular high voltage pulse is studied in this work. Computational fluid dynamics (CFD) with incorporation of large eddy simulation (LES) model is used to simulate the helium mole fraction distribution in air under the helium flow from laminar to turbulent regime with increasing helium outlet velocity. Numerical simulation results are combined with experimental results in order to determine the influence of helium distribution on the cold plasma jets. It reveals that the structure of the helium distribution caused by diffusion or by turbulent mixing in turbulent regime determines the characteristics of the cold plasma jets. On the other hand, the curves of plasma jet length (L) versus helium outlet velocity (V) at different jet diameters (D) are unified in a map of jet Reynolds number (Re = ρHe·V·D/μHe, where μHe is the helium viscosity constant) versus dimensionless plasma jet length (l = L/D). The map is allowed to predict the flow pattern of helium jet in order to estimate and control the plasma jet length at different jet diameters.

Note: Compact helical pulse forming line for the generation of longer duration rectangular pulse

The helical pulsed forming line (PFL) can generate longer duration rectangular pulse in a smaller length. A compact PFL using helical water line is designed and experimentally investigated. The impedance of the helical PFL is 22 [ohm sign]. The compactness is achieved in terms of reduction in length of the PFL by a factor of 5.5 using helical water PFL as compared to coaxial water PFL of same length. The helical PFL was pulsed charged to 200 kV using a high voltage pulse transformer in 4.5 μs and discharged into the matched 22 Ω resistive load through a self-breakdown pressurized spark gap switch. The rectangular voltage pulse of 100 kV, 260 ns (FWHM) is measured across the load. The effect of reduction in water temperature on the pulse width is also studied experimentally. The increase in pulse width up to 7% more is observed by reducing the temperature of the deionized water to 5 °C. It will further reduce the length of the PFL and make the system small for compact pulsed power drivers.

Profile of the Late Sodium Current during Cardiac Action Potential in Guinea Pig Ventricular Cardiomyocytes

The late sodium current [INa,late] can play an important role in generating arrhythmogenic afterdepolarisations in cardiac myocytes. However the profile of INa,late during the action potential [AP] has not yet been directly measured. The goal of the present study was to directly record and describe the profile of INa,late as it could be observed in situ (in a physiological milieu, during AP, with undisturbed cellular calcium homeostasis).METHODS: Our newly developed ‘Onion-Peeling’ technique (a variant of action potential voltage-clamp) was utilised to dissect out INa,late during AP by using tetrodotoxin. The experiments were done on isolated guinea pig ventricular myocytes at 36 °C. In one set of experiments no exogenous calcium buffer was used in the internal solution, which enabled intracellular calcium cycling during AP. In the other set of recordings intracellular calcium concentration was clamped with BAPTA. The intracellular calcium concentration was measured by using Fura-2.RESULTS: The tetrodotoxin-sensitive current first displayed a large peak during the AP upstroke attributable to the fast sodium current, and then showed a sustained current throughout the AP due to INa,late. With cycling calcium, INa,late showed a gradual increase during the AP plateau phase and then peaked during the fast repolarising phase. When the intracellular calcium was clamped, INa,late showed larger current density throughout the AP time course but the overall current profile remained similar.CONCLUSION: The INa,late profile directly recorded in situ by using the ‘Onion-Peeling’ method is different from what previously predicted by model simulations based on the data obtained using conventional voltage-clamp under simplified conditions (ion substitution, calcium buffering, rectangular voltage pulses). The observed high INa,late density during the AP repolarising phase underlies the arrhythmogenic role of the current.