Pulse Of Opposite Polarity Research Articles

Spoke-Type Structures in an Ion Diode with Magnetic Insulation of Electrons

The article presents the results concerning the cross-sectional energy density distribution of a pulsed ion beam for two types of diodes with electron open drift: with external magnetic insulation (250 kV, 80 ns, 0.6 T) and with self-magnetic insulation of electrons (250–300 kV, 120 ns, 0.8 T). Anode plasma is formed using a breakdown along the surface of the anode dielectric coating (single-pulse mode) or explosive electron emission (with double opposite-polarity pulses). It was found that, when the energy density of the ion beam exceeds ≈0.4 J/cm2, periodic spoke-type structures with a step of 3–6 cm in the beam cross section are formed. The processes of formation of such a structure—nonuniform density of anode plasma and self-organization of anode and/or cathode plasma in crossed electric and magnetic fields—are analyzed. It is shown that the formation of local plasma regions in the anode–cathode gap of an ion diode can cause the formation of a periodic structure of the cross-sectional energy density distribution.

Theoretico-experimental analysis of bistability in the oscillatory response of a TaOx ReRAM to pulse train stimuli

Fading memory is the capability of a physical system to approach a unique asymptotic behaviour, irrespective of the initial conditions, when stimulated by an input from a certain class. Standard stimuli from the AC periodic class typically induce fading memory effects in non-volatile memristors, as uncovered for the first time back in 2016. Very recently, a deep investigation of resistance switching phenomena in a TaOx resistive random access memory cell revealed the capability of the nano-device to exhibit one of two possible oscillatory behaviours, depending upon the initial condition, when subject to a particular periodic excitation. This interesting finding was, however, left unexplained. Bistability is the simplest form of local fading memory. In a system, endowed with local fading memory under a given stimulus, the initial condition does not affect the long-term behaviour of the state as long as it is drawn from the basin of attraction of either of the distinct coexisting state-space attractors (two limit cycles for the periodically forced memristor acting as a bistable oscillator). Here, the history of the system, encoded in the initial condition, is, thus, erasable only locally through ad hoc stimulation. Motivated by the discovery of local history erase effects in our resistive random access memory cell, this study applies a powerful system-theoretic tool, enabling the analysis of the response of first-order systems to square pulse train-based periodic stimuli, known as the time-average state dynamic route, to an accurate physics-based mathematical model, earlier fitted to the nano-device, to determine a strategy for specifying the parameters of an excitation signal, consisting of the sequence of two square pulses of opposite polarity per period so as to induce various forms of monostability or multistability in the non-volatile memristor. In particular, as an absolute novelty in the literature, experimental measurements validate the theoretical prediction on the capability of the device to operate as one of two distinct oscillators, depending upon the initial condition, under a specific pulse train excitation signal. The coexistence of multiple oscillatory operating modes in the periodically forced resistive random access memory cell, an example par excellence of their unique non-linear dynamics, may inspire the development and circuit implementation of novel sensing and mem-computing paradigms.

An analytical approach to engineer multistability in the oscillatory response of a pulse-driven ReRAM

A nonlinear system, exhibiting a unique asymptotic behaviour, while being continuously subject to a stimulus from a certain class, is said to suffer from fading memory. This interesting phenomenon was first uncovered in a non-volatile tantalum oxide-based memristor from Hewlett Packard Labs back in 2016 out of a deep numerical investigation of a predictive mathematical description, known as the Strachan model, later corroborated by experimental validation. It was then found out that fading memory is ubiquitous in non-volatile resistance switching memories. A nonlinear system may however also exhibit a local form of fading memory, in case, under an excitation from a given family, it may approach one of a number of distinct attractors, depending upon the initial condition. A recent bifurcation study of the Strachan model revealed how, under specific train stimuli, composed of two square pulses of opposite polarity per cycle, the simplest form of local fading memory affects the transient dynamics of the aforementioned Resistive Random Access Memory cell, which, would asymptotically act as a bistable oscillator. In this manuscript we propose an analytical methodology, based on the application of analysis tools from Nonlinear System Theory to the Strachan model, to craft the properties of a generalised pulse train stimulus in such a way to induce the emergence of complex local fading memory effects in the nano-device, which would consequently display an interesting tuneable multistable oscillatory response, around desired resistance states. The last part of the manuscript discusses a case study, shedding light on a potential application of the local history erase effects, induced in the device via pulse train stimulation, for compensating the unwanted yet unavoidable drifts in its resistance state under power off conditions.

Генератор пар импульсов противоположной полярности с повышенной мощностью с применением сумматора на нерегулярно-включенных полосковых линиях

A pulse pair generator with a subnanosecond front is considered, in which pulses of opposite polarity are created by separate generators, and then supplied to the bridge combiner of the original design (on suspended striplines). For the first time in devices of this type, an output power of 18 watts was achieved. A distinctive feature of this structure is that a half of the power of the generators is dissipated on the ballast resistor (due to the alternating appearance of pulses at the inputs of the combiner). To partially compensate for this effect, a half-standard (25 ohms) input resistance of the adder is selected. In the current circuit of generators it leads to an increase in power takeoff from them. The generators themselves are made on step recovery diodes (SRD) according to a scheme close to the traditional one, but differ by a diode circuit at the output, which eliminates penetration of parasitic lobes of a pulse of opposite polarity to the output and protects the SRD from the action of the pulse of the neighboring generator. The shaper is used in experiments to study nonlinear scattering.

Resistive Memory Based on the Spin-Density-Wave Transition of Antiferromagnetic Chromium

Spin density waves (SDWs) are antiferromagnetic ground states characterized by real-space spin modulation. When an electronic system undergoes a paramagnetic-SDW transition, the translational symmetry is spontaneously broken and energy gaps are developed near the Fermi level, which offers potential for constructing various SDW components. Here we report a prototype resistive memory device based on a prototypical SDW metal, antiferromagnetic chromium. Transport and magnetic measurements show that the paramagnetic-SDW transition, i.e., the SDW antiferromagnetism, can be effectively suppressed by the electric-field-generated piezoelectric strain in epitaxial $\mathrm{Cr}/0.7\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}$--$0.3{\mathrm{Pb}\mathrm{Ti}\mathrm{O}}_{3}$ (PMN-PT) heterostructures. This enables a large electroresistance effect for metallic systems as the SDW band gaps can be intentionally controlled to vanish or develop. Combining this electroresistance effect with the different remanent piezoelectric strain of PMN-PT after poling by electric-field pulses of opposite polarity, we obtain two nonvolatile resistance states differing by about 1.8% and stable against a magnetic field of 3 T at room temperature. Our work unveils the electric-field controllability of the SDW transitions in thin films and the consequent wide application prospects of SDW materials.

Design and Development of a High-Power Pulse Transmitter for Underground Environmental Perception

This article represents a design for a high-power pulse transmitter for high-depth imaging applications. The pulse transmitter consists of an avalanche transistor-based pulse-shaping network, an improved step recovery diode (SRD)-based configuration, and a pulse-shifting circuit with a broadband combiner to generate a first derivative Gaussian pulse for high-power applications. The output pulse of the transistor-based circuit is fed to a balun, which produces two opposite polarity pulses and then feeds two parallel SRD pulse-shaping circuits that produce ultrashort pulses. The SRD-based part of the circuit was developed to have a high amplitude output pulse. Moreover, using a technique based on pulse shifting, a higher power monopulse was achieved without using a balun and a differentiator. This design achieved a monopulse of 169-ps pulsewidth with a peak power of <inline-formula> <tex-math notation="LaTeX">$P =5.78$ </tex-math></inline-formula> W. In order to check the validity of the transmitter for imaging applications, several experiments for buried objects in the sand are conducted, including metal objects, water pipe, rock, and copper veins. All reconstructed 3-D images clearly represent the target shape and dimension, confirming the functionality of the designed transmitter for sensing and imaging applications.

Application of the Wavelet Transform on the Unusual Lightning Flashes of the Himalayan Region, Nepal.

The unusual lightning events are characterized by a pronounced opposite-polarity pulse prior to the main electric field waveform. These electric fields are pertinent to the unusual lightning events recorded in the Himalayan region, at the height of about 1300 m above the sea level, during the premonsoon period of 2015. For the case of unusual events, a downward positive leader approaches the ground, and there is an increase in the downward-directed electric field due to which negative leaders move upwards and will try to intercept. Continuous wavelet transform has been used to understand the features of different events of lightning frequency. The wavelet transform of different events of unusual signals in the present study reveals that the unusual flashes radiate in the spectral range of 1–412.5 kHz in the initial stage and 0.9375–337.5 kHz in the overshoot which conclude that they radiate in very low frequency to very high frequency indicating that they are composed of many microdischarges and low frequencies indicating that they are composed of very long discharges. It is believed that this research work will be useful to design engineers for installing appropriate protective measures on the appliances in the Himalayan regions.

Measuring the reversible heat of lithium-ion cells via current pulses for modeling of temperature dynamics

This article introduces a novel calorimetric measurement method, namely the ‘Double Pulse Method’, to measure reversible heat in lithium-ion battery cells. In Li-ion cells, reversible heat has a material-dependent characteristic as it is closely related to both entropy change and the temperature dependence of the open circuit voltage. The proposed method measures reversible heat as a highly resolved function of the cell’s state of charge. The determination of reversible heat is based on the evaluation of the temperature difference generated by two current pulses of opposite polarity. Unlike established potentiometric methods, the Double Pulse Method is simple to set up, fast, and cost-effective. The accuracy of the Double Pulse Method is demonstrated for an automotive lithium iron phosphate (LFP) cell, and the entropy changes are compared with measurements of the same cell using the established potentiometric method. Simulation results indicate that the cell temperature is more accurate when determined by the reversible heat measurement obtained by the Double Pulse Method than from the potentiometric method.

Terahertz pulse emission from photoexcited bulk crystals of transition metal dichalcogenides

Multilayer MoS2, MoSe2, and WSe2 crystals were excited with femtosecond optical pulses of various wavelengths. The emitted terahertz (THz) radiation pulses were found to be the most intense at photon energies coinciding with the direct energy gap at the K points of the Brillouin zone of corresponding materials. It was shown that the transition metal dichalcogenides of different dopant type emit THz pulses of opposite polarity, suggesting that the surface field plays a role in THz emission. Nevertheless, the optical pump–THz probe experiments contradicted THz emission observations, demonstrating a decrease in photoconductivity at higher energy quanta. The proposed THz pulse generation mechanism, therefore, assumes the accumulation of excitonic electric dipoles during optical pulse absorption and a fast build-up of the internal electric field inside the samples. This assumption was supported by double optical pulse investigations.

Unique lightning signatures observed from sub-tropical, mountainous country, Nepal

Unique lightning signatures have been observed from sub-tropical, mountainous country, Nepal. These signatures were observed by measuring the electric field using a simple circuit and antenna system. The unique unusual signatures analysed are assumed to be positive ground flashes. These lightning signatures were each characterised by a relatively slow, negative electric field events preceded by a pronounced opposite-polarity pulse. The average durations of the main waveform was 523.84 μs and the average duration of preceding opposite-polarity pulses was 37.99 μs.

Unique lightning signatures observed from sub-tropical, mountainous country, Nepal

Unique lightning signatures have been observed from sub-tropical, mountainous country, Nepal. These signatures were observed by measuring the electric field using a simple circuit and antenna system. The unique unusual signatures analysed are assumed to be positive ground flashes. These lightning signatures were each characterised by a relatively slow, negative electric field events preceded by a pronounced opposite-polarity pulse. The average durations of the main waveform was 523.84 μs and the average duration of preceding opposite-polarity pulses was 37.99 μs.

Cancellation effect is present in high-frequency reversible and irreversible electroporation

It was recently suggested that applying high-frequency short biphasic pulses (HF-IRE) reduces pain and muscle contractions in electrochemotherapy and irreversible ablation treatments; however, higher amplitudes with HF-IRE pulses are required to achieve a similar effect as with monophasic pulses. HF-IRE pulses are in the range of a microseconds, thus, the so-called cancellation effect could be responsible for the need to apply pulses of higher amplitudes. In cancellation effect, the effect of first pulse is reduced by the second pulse of opposite polarity. We evaluated cancellation effect with high-frequency biphasic pulses on CHO-K1 in different electroporation buffers. We applied eight bursts of 1–10 µs long pulses with inter-phase delays of 0.5 µs – 10 ms and evaluated membrane permeability and cell survival. In permeability experiments, cancellation effect was not observed in low-conductivity buffer. Cancellation effect was, however, observed in treatments with high-frequency biphasic pulses looking at survival in all of the tested electroporation buffers. In general, cancellation effect depended on inter-phase delay as well as on pulse duration, i.e. longer pulses and longer interphase delay cause less pronounced cancellation effect. Cancellation effect could be partially explained by the assisted discharge and not by the hyperpolarization by the chloride channels.

Stimulation or Cancellation of Ca2+ Influx by Bipolar Nanosecond Pulsed Electric Fields in Adrenal Chromaffin Cells Can Be Achieved by Tuning Pulse Waveform

Exposing adrenal chromaffin cells to single 150 to 400 ns electric pulses triggers a rise in intracellular Ca2+ ([Ca2+]i) that is due to Ca2+ influx through voltage-gated Ca2+ channels (VGCC) and plasma membrane electropores. Immediate delivery of a second pulse of the opposite polarity in which the duration and amplitude were the same as the first pulse (a symmetrical bipolar pulse) or greater than the first pulse (an asymmetrical bipolar pulse) had a stimulatory effect, evoking larger Ca2+ responses than the corresponding unipolar pulse. Progressively decreasing the amplitude of the opposite polarity pulse while also increasing its duration converted stimulation to attenuation, which reached a maximum of 43% when the positive phase was 150 ns at 3.1 kV/cm, and the negative phase was 800 ns at 0.2 kV/cm. When VGCCs were blocked, Ca2+ responses evoked by asymmetrical and even symmetrical bipolar pulses were significantly reduced relative to those evoked by the corresponding unipolar pulse under the same conditions, indicating that attenuation involved mainly the portion of Ca2+ influx attributable to membrane electropermeabilization. Thus, by tuning the shape of the bipolar pulse, Ca2+ entry into chromaffin cells through electropores could be attenuated while preserving Ca2+ influx through VGCCs.

Multi-Level Capacitive Memory Effect in Metal/Oxide/Floating-Schottky Junction

We experimentally demonstrate that metal/oxide/floating-Schottky junction has multiple effective capacitances depending on the amount of electrons stored in the floating metal electrode. The oxide thin film covering the Schottky junction is used to trap electrons in the floating metal. The electron flow into and out of the floating metal is controlled by applying voltage pulses of opposite polarities onto the semiconductor substrate. With the amount of excess charges in the floating metal, the depletion capacitance of Schottky junction varies synchronously, which dominantly affects the effective capacitance of the whole junction. Interestingly, the capacitance of metal/oxide/floating-Schottky junction measured as a function of applied voltage pulse shows a hysteretic behavior, which supports its capacitive memory effect. It is expected that our metal/oxide/floating-Schottky junction can work as a memcapacitor capable of recording multiple switchable capacitance values and it can be readily fabricated with the current Si CMOS technology.

Modulation of biological responses to 2 ns electrical stimuli by field reversal

Nanosecond bipolar pulse cancellation, a recently discovered phenomenon, is modulation of the effects of a unipolar electric pulse exposure by a second pulse of opposite polarity. This attenuation of biological response by reversal of the electric field direction has been reported with pulse durations from 60 ns to 900 ns for a wide range of endpoints, and it is not observed with conventional electroporation pulses of much longer duration (>100 μs) where pulses are additive regardless of polarity. The most plausible proposed mechanisms involve the field-driven migration of ions to and from the membrane interface (accelerated membrane discharge). Here we report 2 ns bipolar pulse cancellation, extending the scale of previously published results down to the time required to construct the permeabilizing lipid electropores observed in molecular simulations. We add new cancellation endpoints, and we describe new bipolar pulse effects that are distinct from cancellation. This new data, which includes transport of cationic and anionic permeability indicators, fluorescence of membrane labels, and patterns of entry into permeabilized cells, is not readily explained by the accelerated discharge mechanism. We suggest that multi-step processes that involve first charged species movement and then responses of cellular homeostasis and repair mechanisms are more likely to explain the broad range of reported results.

Effects of the relative timing of opposite-polarity pulses on loudness for cochlear implant listeners.

The symmetric biphasic pulses used in contemporary cochlear implants (CIs) consist of both cathodic and anodic currents, which may stimulate different sites on spiral ganglion neurons and, potentially, interact with each other. The effect on the order of anodic and cathodic stimulation on loudness at short inter-pulse intervals (IPIs; 0-800 μs) is investigated. Pairs of opposite-polarity pseudomonophasic (PS) pulses were used and the amplitude of each pulse was manipulated independently. In experiment 1 the two PS pulses differed in their current level in order to elicit the same loudness when presented separately. Six users of the Advanced Bionics CI (Valencia, CA) loudness-ranked trains of the pulse pairs using a midpoint-comparison procedure. Stimuli with anodic-leading polarity were louder than those with cathodic-leading polarity for IPIs shorter than 400 μs. This effect was small-about 0.3 dB-but consistent across listeners. When the same procedure was repeated with both PS pulses having the same current level (experiment 2), anodic-leading stimuli were still louder than cathodic-leading stimuli at very short intervals. However, when using symmetric biphasic pulses (experiment 3) the effect disappeared at short intervals and reversed at long intervals. Possible peripheral sources of such polarity interactions are discussed.

Electric field distribution in a surface plasma flow actuator powered by ns discharge pulse trains

Electric field vector components in a nanosecond pulse, surface dialectric barrier discharge plasma actuator are measured by picosecond second harmonic generation, for positive, negative, and alternating polarity pulse trains. Plasma images show that in the same polarity train, the positive polarity discharge develops as two consecutive surface ionization waves, while the negative polarity discharge propagates as a single diffuse ionization wave. In the alternating polarity train, both positive and negative polarity discharge plasmas become strongly filamentary. In all pulse trains, the measurement results demonstrate a significant electric field offset before the discharge pulse, due to the surface charge accumulation during previous discharges pulses. This demonstrates that charge accumulation is a significant factor affecting the electric field in the discharge, even at very low pulse repetition rates. Peak electric field measured in the alternating polarity pulse train is lower compared to that in same polarity trains. However, the coupled pulse energy in the alternating polarity train is much higher, by a factor of 3–4, most likely due to the neutralization of the surface charge accumulated on the dielectric during the previous, opposite polarity pulses. This suggests that plasma surface actuators powered by alternating polarity pulse trains may generate higher amplitude thermal perturbations, producing a stronger effect on the flow field. The present results show that the time scale for the electric field reduction in the plasma after breakdown is fairly long, several tens of ns, including the conditions when the discharge develops as a diffuse ionization wave. This suggests that a considerable fraction of the energy is coupled to the plasma at a relatively low reduced electric field, several tens of Townsend. At these conditions, the discharge energy fraction thermalized as rapid heating would remain fairly low, thus limiting the effect on the flow caused by the high-amplitude localized thermal perturbations.

Magnetic angular position sensor enabled by spin-orbit torque

We propose a simple scheme for magnetic angular position sensor based on current-induced spin-orbit torque effect. A full range detection of 360° is realized with a pair of Hall crosses made of heavy metal/ferromagnet heterostructures. The current axes of the two Hall crosses are aligned orthogonal to each other, such that when both devices are subject to a rotational in-plane magnetic field, the differential Hall voltage due to current pulses of opposite polarity exhibits a sine and cosine angular dependence on the field direction, respectively. The field rotational angle is then calculated from the sine and cosine output signals via the arctan2 function. A linear correspondence between the calculated and actual field angle is obtained in the field range of 500–2000 Oe, with an average angle error of 0.38°–0.65°.

A Highly Stable Source of Current Pulses with an Adjustable Amplitude of up to 350 A for a Nonlinear Complex Load

The application of high-power semiconductor lasers for creating a population inversion in active gaseous media is an integral part of studies that are aimed at the achievement of a sufficient level of laser-radiation energy to initiate a thermonuclear reaction. The stability of the laser radiation and, thus, the repeatability of experimental results, depend on the stability of the parameters of current pulses for pumping laser-diode arrays with a pulse amplitude of up to several hundred amperes. The flow of current pulses with such an amplitude through a cable that connects the load to the output of the current-pulse source must not lead to the formation of voltage pulses of opposite polarity across the load, which can damage it. This can be prevented by correcting the current pulse edges. It is proposed to develop a source of current pulses with a high amplitude on the basis of several modules of fast linear current amplifiers with individual control loops, whose outputs are connected in parallel. It is established that a compensation-type current sensor on the basis of the Hall effect is operable at high frequencies and can be used in these modules, but it has pronounced resonance properties, which must be canceled. It is shown that analog driving pulses of each module can be formed using aperiodic chains with parameters that eliminate oscillatory processes in the load circuit. A dynamic model of a module of the linear current amplifier and the calculation relationships for the parameters of its components, which follow from this model, are presented. The experimental results that confirm stability of the parameters of the formed current pulses are presented.

Unusual lightning electric field waveforms observed in Kathmandu, Nepal, and Uppsala, Sweden

Unusual lightning events have been observed in Uppsala, Sweden, and Kathmandu, Nepal, using essentially the same electric field measuring system developed at Uppsala University. They occurred in the storms that also generated “normal” lightning events. The unusual events recorded in Uppsala occurred on one thunderstorm day. Similar events were observed in Kathmandu on multiple thunderstorm days. The unusual events were analyzed in this study assuming them to be positive ground flashes (+CGs), although we cannot rule out the possibility that some or most of them were actually cloud discharges (ICs). The unusual events were each characterized by a relatively slow, negative (atmospheric electricity sign convention) electric field waveform preceded by a pronounced opposite-polarity pulse whose duration was some tens of microseconds. To the best of our knowledge, such unusual events have not been reported in the literature. The average amplitudes of the opposite-polarity pulses with respect to those of the following main waveform were found to be about 33% in Uppsala (N = 31) and about 38% in Kathmandu (N = 327). The average durations of the main waveform and the preceding opposite-polarity pulse in Uppsala were 8.24 ms and 57.1 μs, respectively, and their counterparts in Kathmandu were 421 μs and 39.7 μs. Electric field waveforms characteristic of negative ground flashes (-CGs) were also observed, and none of them exhibited an opposite-polarity pulse prior to the main waveform. Possible origins of the unusual field waveforms are discussed.