Amplitude Of Voltage Oscillations Research Articles

Use of an accelerated testing method to characterize inner front pole cover erosion in a high power Hall thruster

Erosion characteristics on the cover of the inner front pole in a 12.5 kW Hall thruster were measured over a wide range of operating conditions in tests of 6–14 h duration using an accelerated test method and a very sensitive, radioactive tracer-based erosion diagnostic. The operating points included the nominal 300–600 V conditions on a constant 20.8 A throttle curve and conditions at other currents spanning the throttling envelope and with varying magnetic field strength, facility pressure, and discharge voltage oscillation amplitude. Surprisingly, the results show that the highest wear rates occur at the lowest voltages and currents. The wear rates were insensitive to discharge voltage ripple but increased monotonically with magnetic field strength, particularly near the inner radius of the pole cover. The inner region was also sensitive to facility pressure, showing lower rates at a higher pressure level. Separate experiments in which the energy distributions of ions generated by the hollow cathode were measured suggest that the cathode plume may be a source of energetic ions responsible for some of the erosion trends, in addition to ions originating in the thruster plume.

Zero‐voltage‐switching full‐bridge converter with low filter requirement and voltage oscillation amplitude

This article presents a new full-bridge converter with three-winding coupled inductor. The proposed converter can solve the drawbacks of traditional full-bridge converter, such as narrow zero-voltage-switching range, serious voltage oscillation, and large primary circulating current. By introducing a coupled inductor into the full-bridge converter, the currents of leading-leg and lagging-leg are optimised and a wide zero-voltage-switching range can be achieved. In the proposed converter, the secondary voltage oscillation occurs only when the rectified voltage is low. Thus, the amplitude of voltage oscillation and the voltage stress of rectified diodes are well suppressed. Furthermore, the primary power can be continually transferred to the output side during the whole switching period, resulting in reduced circulating current and low filter requirement. Finally, the theoretical analysis is verified on a laboratory prototype. Experimental results show the effectiveness of the proposed converter.

Electrochemical Oscillation in Li-Ion Batteries

Summary Two-phase reactions are prevalent in Li-ion batteries, whereas the underlying dynamics of phase separation in a real electrode still remain elusive, since numerous electrode particles constitute a formidably complex system for existing experimental techniques. Here we present an intriguing oscillatory phenomenon in the typical phase-separating electrode material Li 4 Ti 5 O 12 . During galvanostatic processes, the voltage oscillates due to the discrete nature of multi-particle phase-separating reactions, and the subtle oscillatory signals allow us to evaluate the fraction of actively phase-separating particles in real time. Through the analysis of oscillatory phenomena, we unveil the dependence of the active fraction on the depth of charge/discharge, cycling current, and working temperature, considerably deepening our understanding of the multi-particle phase-separation reaction. Moreover, it is the first time that electrochemical oscillations have been identified in rechargeable battery systems, opening up a new frontier for both theoretical and experimental researchers.

Simulation of Si and GaAs submicron TRAPATT diodes

Plasma formation and extraction processes in submicron silicon N + NP + , GaAs N + NP + , and GaAs NM Schottky TRAPATT (TRApped Plasma Avalanche Triggered Transit) diodes were simulated. The simulation of GaAs TRAPATT diodes was done for the first time. The quasi-hydrodynamic model was chosen for the simulation of the processes. The Synopsys TCAD Sentaurus Software Package was used. The carrier mobility dependence on phonon scattering, impurity scattering, carrier-carrier scattering, intervalley scattering (for GaAs), and mobility saturation in a high electric field was taken into account. Several generation-recombination mechanisms were included: impact ionization, Shockley–Read–Hall recombination (SRH) with doping-dependent lifetimes, trap-assisted tunnelling, band-to-band tunnelling, Auger recombination, and radiative recombination (for GaAs). We show that the so-called critical current density for plasma formation in the submicron diodes increases with the active layer thickness decrease and almost does not depend on the doping density in the active layer. The critical current density for silicon diodes is about two times lower than for the GaAs diodes. The intensive minority carrier storage in the N + and P + regions has a high influence on the voltage oscillation amplitude and frequency after the first plasma formation and extraction period. Oscillation damping takes place in the N + NP + GaAs diode with the active layer thickness of less than 0.3 µm.

Ac Josephson effect induced by spin injection

Pure spin currents can be injected and detected in conductors via ferromagnetic contacts. We consider the case when the conductors become superconducting. A DC pure spin current flowing in one superconducting wire towards another superconductor via a ferromagnet contact induces AC voltage oscillations caused by Josephson tunneling of condensate electrons. Quasiparticles simultaneously counterflow resulting in zero total electric current through the contact. The Josephson oscillations can be accompanied by Carlson-Goldman collective modes leading to a resonance in the voltage oscillation amplitude.

Persistent Sodium Current Contributes to Induced Voltage Oscillations in Locomotor-Related Hb9 Interneurons in the Mouse Spinal Cord

Neurochemically induced membrane voltage oscillations and firing episodes in spinal excitatory interneurons expressing the HB9 protein (Hb9 INs) are synchronous with locomotor-like rhythmic motor outputs, suggesting that they contribute to the excitatory drive of motoneurons during locomotion. Similar to central pattern generator neurons in other systems, Hb9 INs are interconnected via electrical coupling, and their rhythmic activity does not depend on fast glutamatergic synaptic transmission. The primary objective of this study was to determine the contribution of fast excitatory and inhibitory synaptic transmission and subthreshold voltage-dependent currents to the induced membrane oscillations in Hb9 INs in the postnatal mouse spinal cord. The non-N-methyl-D-aspartate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) reduced the amplitude of voltage oscillations but did not alter their frequency. CNQX suppressed rhythmic motor activity. Blocking glycine and GABAA receptor-mediated inhibitory synapses as well as cholinergic transmission did not change the properties of CNQX-resistant membrane oscillations. However, disinhibition triggered new episodes of slow motor bursting that were not correlated with induced locomotor-like rhythms in Hb9 INs. Our observations indicated that fast excitatory and inhibitory synaptic inputs did not control the frequency of induced rhythmic activity in Hb9 INs. We next examined the contribution of persistent sodium current (INaP) to subthreshold membrane oscillations in the absence of primary glutamatergic, GABAergic and glycinergic synaptic drive to Hb9 INs. Low concentrations of riluzole that blocked the slow-inactivating component of sodium current gradually suppressed the amplitude and reduced the frequency of voltage oscillations. Our finding that INaP regulates locomotor-related rhythmic activity in Hb9 INs independently of primary synaptic transmission supports the concept that these neurons constitute an integral component of the rhythmogenic locomotor network in the mouse spinal cord.

Potential and Impedance Imaging of Polycrystalline BiFeO3 Ceramics

Electrostatic‐force‐sensitive scanning probe microscopy (SPM) is used to investigate grain boundary behavior in polycrystalline BiFeO3 ceramics. Scanning surface potential microscopy (SSPM) of a laterally biased sample exhibits potential drops due to resistive barriers at the grain boundaries. In this technique, the tips acts as a moving voltage probe detecting local variations of potential associated with the ohmic losses within the grains and at the grain boundaries. An approach for the quantification of grain boundary, grain interior, and contact resistivity from SSPM data is developed. Scanning impedance microscopy (SIM) is used to visualize capacitive barriers at the grain boundaries. In SIM, a dc‐biased tip detects the variations of local potential induced by the lateral ac voltage applied to the sample. Unlike the traditional dc and ac transport measurement, both of these techniques are sensitive to the variation of local potential (SSPM) or local voltage oscillation amplitude and phase (SIM), rather than to current. Therefore, special attention is paid to the relationship between SSPM and SIM images and data obtained from traditional impedance spectroscopy and dc transport measurements. For BiFeO3 ceramics excellent agreement between the local SIM measurements and impedance spectroscopy data are demonstrated.

Numerical Investigation and Model Approximation for the Hysteretic Current-Voltage Characteristics of Josephson Junctions with Nonlinear Quasiparticle Resistance

We present a model analysis for the current-voltage (I-V) characteristics of Josephson junctions having superconductor-insulator-superconductor (SIS) structure. The numerical result for the V m value, which is the product of the maximum supercurrent and the observed subgap resistance, shows a marked decrease with increasing junction critical current density (J c). The marked decrease is independent of leak current. Increasing J c reduces the junction capacitance C J and enlarges the amplitude of the junction voltage oscillation. Nonlinearity of the quasiparticle resistance restricts the voltage oscillation amplitude to the gap voltage, which results in the rapid decrease of the V m value. In this paper, we introduce a sinusoidal oscillation model for the junction voltage, and derive the approximated expressions for the V m value. The model approximation results agree well with the numerical results.

A distributed carbon cathodic vacuum arc

We report here on a new form of steady state vacuum arc whereby an anomalous emission is observed from a thermally insulated carbon cathode. The arc is distributed over a diffuse area instead of being confined to cathodic spots. It occurs when the power per unit area is sufficient for the active region cathode surface to reach a critical temperature. At ignition the discharge evolves mainly as microscopic spots over the surface of the initially cold cathode. The rise in the cathode temperature, required for the carbon plasma around the cathode surface to be sufficient for the formation of a distributed arc, is caused by the reverse ion bombardment and Joule heating of the thermally insulated cathode. Note-worthy features of such an arc are its significantly lower current density, marginally higher arc voltage than that of the cathodic spot arc and reduced amplitude of voltage oscillations. The macroparticle content of its associated plasma is also lower than in the case of the cathodic spot arc. In order to achieve an understanding of the emission mechanism of such an arc, the emanating plasma stream is characterized by its electron density, temperature and the energy distribution of the ions. The spatial temperature profile of the cathode surface is also monitored during deposition. Since stable arcs of the above-mentioned type have also been observed on other materials such as undoped Si, the prospect of using such arcs as a source of ions for deposition of thin films is encouranging.

Phase Vortices And Charge Density Wave Conduction Noise

Abstract Carrier conversion from the charge-density-wave (CDW) condensate to quasi particles should occur at the interface between moving and stationary CDW regions. This conversion is effected by moving phase vortices transverse to the advancing CDW. The present model predicts both the local origin of the narrow band noise and the amplitude of voltage oscillation. The effect of a thermal gradient on the noise frequency also provides support for this model.

Transistorized Oscillator as a Magnetic Fluxmeter

Effect of magnetic field on the amplitude of voltage oscillation of a transistorized oscillator is studied. A magnetic fluxmeter based on this effect has been designed. Effect of ambient temperature variations on the sensitivity of such a fluxmeter has been investigated and a suitable circuit is designed to eliminate this. Important practical applications of the study are given.