Amplitude Of Current Oscillations Research Articles

Analytical workload dependence of self-heating effect for SOI MOSFETs considering two-stage heating process

Dynamic self-heating effect (SHE) of silicon-on-insulator (SOI) MOSFET is comprehensively evaluated by ultrafast pulsed I–V measurement in this work. It is found for the first time that the SHE complete heating response and cooling response of SOI MOSFETs are conjugated, with two-stage curves shown. We establish the effective thermal transient response model with stage superposition corresponding to the heating process. The systematic study of SHE dependence on workload shows that frequency and duty cycle have more significant effect on SHE in first-stage heating process than in the second stage. In the first-stage heating process, the peak lattice temperature and current oscillation amplitude decrease by more than 25 K and 4% with frequency increasing to 10 MHz, and when duty cycle is reduced to 25%, the peak lattice temperature drops to 306 K and current oscillation amplitude decreases to 0.77%. Finally, the investigation of two-stage (heating and cooling) process provides a guideline for the unified optimization of dynamic SHE in terms of workload. As the operating frequency is raised to GHz, the peak temperature depends on duty cycle, and self-heating oscillation is completely suppressed.

Quasi-pyroelectricity in the TGS crystal

ABSTRACTIt has been shown that a side electrode perpendicular to the measurement ones can significantly enhance the transverse electric current in TGS. Such a current, measured in a zero external electric field, resembles the classic longitudinal one. However, the amplitude of the transverse current oscillation, observed while cooling and heating the sample, rises much more slowly with the time of the transverse electric field preliminary application. Such exposure to the transverse field is required prior to the measurements for the transverse current to be observed, in a similar way to a longitudinal field that is applied in order to achieve a single domain state before longitudinal pyroelectric current measurements. A huge difference in the time of reaction to the electric fields preliminarily applied in order to achieve the maximum amplitude of the current oscillations in both cases is the evidence that the transverse current cannot be considered to be originated just for geometrical reasons.

Nonlinear series resonance and standing waves in dual-frequency capacitive discharges

It is well-known that the nonlinear series resonance in a high frequency capacitive discharge enhances the electron power deposition and also creates standing waves which produce radially center-high rf voltage profiles. In this work, the dynamics of series resonance and wave effects are examined in a dual-frequency driven discharge, using an asymmetric radial transmission line model incorporating a Child law sheath. We consider a cylindrical argon discharge with a conducting electrode radius of 15 cm, gap length of 3 cm, with a base case having a 60 MHz high frequency voltage of 250 V and a 10 MHz low frequency voltage of 1000 V, with a high frequency phase shift between the two frequencies. For this phase shift there is only one sheath collapse, and the time-averaged spectral peaks of the normalized current density at the center are mainly centered on harmonic numbers 30 and 50 of the low frequency, corresponding to the first standing wave resonance frequency and the series resonance frequency, respectively. The effects of the waves on the series resonance dynamics near the discharge center give rise to significant enhancements in the electron power deposition, compared to that near the discharge edge. Adjusting the phase shift from π to 0, or decreasing the low frequency from 10 to 2 MHz, results in two or more sheath collapses, respectively, making the dynamics more complex. The sudden excitation of the perturbed series resonance current after the sheath collapse results in a current oscillation amplitude that is estimated from analytical and numerical calculations. Self-consistently determining the dc bias and including the conduction current is found to be important. The subsequent slow time variation of the high frequency oscillation is analyzed using an adiabatic theory.

Interference effects of multi-head operation of anode layer Side by side (SBS) system

For near-future large-scale space programs, high-power Hall thruster cluster systems are required. At Gifu University, based on the prior studies of magnetic-layer thruster discharge characteristics, a study to investigate interference effects on discharge characteristics for the cluster system was initiated. To characterize cluster operations, a side-by-side (SBS) system comprising two anode layer heads and a hollow cathode was developed. In this study, discharge characteristics for a two-head anode layer thruster system (SBS operation) and a single thruster system (single operation) were compared to investigate interference effects of multi-head operation. The discharge currents in SBS operation increased relative to those in single operation. The discharge current oscillation amplitudes in SBS operation at coil currents increased substantially relative to those in single operation. Increases in the discharge current and ionization oscillation amplitude were likely caused by plume interference of the two heads. The differences in the discharge current and ionization oscillation amplitude between same-direction and opposite-direction applied magnetic fields were small.

Mode Transitions in Hall-Effect Thrusters Induced by Variable Magnetic Field Strength

Mode transitions in a 6 kW laboratory Hall-effect thruster were induced by varying the magnetic field intensity while holding all other operating parameters constant. Ultrafast imaging, discharge current, and thrust measurements were used to characterize the change in discharge channel current density and thruster performance through mode transitions. The modes are described here as global oscillation mode and local oscillation mode. In global mode, the entire discharge channel is oscillating in unison and spokes are either absent or negligible with discharge current oscillation amplitude (root mean square) greater than 10% of the mean value and can even be as high as 100%. In local oscillation mode, perturbations in the discharge current density are seen to propagate in the direction. Spokes are localized oscillations that are typically 10–20% of the mean discharge current density value. The discharge current oscillation amplitude and mean values are significantly lower than global mode. The mode transitions changed with operating conditions, where the transition between global mode and local mode occurred at higher relative magnetic field strengths for higher mass flow rate or higher discharge voltage. The thrust was approximately constant through the mode transition, but the thrust-to-power ratio and anode efficiency decreased significantly in global mode. The peaks in thrust to power and anode efficiency typically occur near the transition point. Thruster performance maps should include variation in discharge current, discharge voltage, and magnetic field, known as maps, at different flow rates to identify transition regions throughout the life of a thruster. These results are used to calculate a transition surface for use by operators to keep the thruster operating in an optimal mode.

Effect of interminiband tunneling on the generation of current in a semiconducting superlattice

The effect of the bandgap width between the first and second energy minibands on the charge transport in a semiconducting superlattice to which electric and tilted magnetic fields are applied is studied theoretically. The time dependences of the current passing through the superlattice are calculated, and the dependences of the amplitude and frequency of electric current oscillations on the applied voltage are constructed. It is found that the interminiband electron tunneling facilitates a decrease in the amplitude of current oscillations, but simultaneously increases their frequency.

Computer modeling of ion current pulsations in track-containing foils

A phenomenological model for description of ion current pulsations in track-containing foils is proposed. Such structures belong to artificial porous materials having diverse applications. Typically pulsations of the ion current are observed in experiments in which the track-containing polymer foils are embedded in electrolytes, and AC voltage is applied. The proposed model is designed on the base of classical molecular dynamics. The interacting currents in tracks are simulated by two-dimensional system of oscillating model particles located in the nodes of a plane lattice. In the model external discontinuous forces are introduced to simulate an application of AC voltage. Interaction between model particles is varied to clarify its influence on pulsation effect. It is assumed that the average amplitude of oscillations of model particles is proportional to the average amplitude of current oscillations in real track structure. The model describes adequately the main features of the pulsation effect that were found experimentally. The obtained results can be useful for creation and improvement of sensors and other devices of track electronics.

Theoretical formalism for collective electromagnetic response of discrete metamaterial systems

We develop a general formalism to describe the propagation of a near-resonant electromagnetic field in a medium composed of magnetodielectric resonators. As the size and the spatial separation of nanofabricated resonators in a metamaterial array is frequently less than the wavelength, we describe them as discrete scatterers, supporting a single mode of current oscillation represented by a single dynamic variable. We derive a Lagrangian and Hamiltonian formalism for the coupled electromagnetic fields and oscillating currents in the length gauge, obtained by the Power-Zienau-Woolley transformation. The response of each resonator to electromagnetic field is then described by polarization and magnetization densities that, to the lowest order in a multipole expansion, generate electric and magnetic dipole excitations. We derive a closed set of equations for the coherently scattered field and normal mode amplitudes of current oscillations of each resonator both within the rotating wave approximation, in which case the radiative decay rate is much smaller than the resonance frequency, and without such an assumption. The set of equations includes the radiative couplings between a discrete set of resonators mediated by the electromagnetic field, fully incorporating recurrent scattering processes to all orders. By considering an example of a two-dimensional split ring resonator metamaterial array, we show that the system responds cooperatively to near-resonant field, exhibiting collective eigenmodes, resonance frequencies, and radiative linewidths that result from strong radiative interactions between closely-spaced resonators.

The Nonlinear Theory of GUNN's Effect

A nonlinear theory of the Gunn effect in GaAs-type semiconductors with negative differential conductivity has been devoleped. The amplitude and the frequency of current oscillations in the second approximation have been found by the method of Bogoliubov-Mitropolski. The dependence of the amplitude of current oscillations on electric field strength has been investigated. The amplitude and frequency of current oscillations on the in here and elsewhere have been calculated in a typical experiment. Subject Index: 341, 356

Investigation of Acceleration Channel Processes in Hall Thrusters by Particles Simulations

In a previous work based on numerical analyses and experiments, the effects of anode orifice configuration on the 20 kHz-range discharge current oscillation amplitude and the thrust performance have been analyzed. In the present work, for the purpose of more detail investigation of the influence of the orifice parameters on the current oscillation and the thrust performance, the ionization and acceleration process in the acceleration channel for various orifice positions were analyzed using a hybrid-PIC code. The results show that the amplitude of the oscillation, the ion loss to the channel walls, and the electron current has the largest value for the orifice set in the middle radial position.

Nature of damped current oscillations in the formation of a static acoustoelectric domain in a n-InGaAs/GaAs quantum-well heterostructure

It is shown experimentally that reflection of the acoustic flux from the sample borders under the conditions of formation of a static acoustoelectric domain in a n-InGaAs/GaAs quantum-well heterostructure in a lateral electric field substantially affects the duration of the incubation period of domain formation and the shape and amplitude of current oscillations.

B201 粒子シミュレーションによるホールスラスタ内プラズマの可視化

Hall thruster is an electric propulsion device in which high thrust efficiency is achieved in the middle specific impulse. In previous works based on experiments and numerical analyses, the dependency of the 20 kHz-range discharge current oscillation amplitude on anode orifice configuration has been analyzed. Using the results of neutral direct-simulations, the influence of the neutral distribution on the amplitude has been investigated. In the present work, for the purpose of more detail investigation of the influence of the neutral distribution, the ionization and acceleration process in the acceleration channel for various orifice diameters were analyzed using a hybrid-PIC code. The results of visualizations of the ionization rate distribution, which influences the oscillation amplitude, show that the smaller orifice causes the ionization concentration.

Hysteresis curves and self-field alternating-current losses in superconducting tapes with transport current: Edge barrier effect

The combined influence of both bulk pinning and edge barrier on zero-field transport properties and alternating-current (ac) losses in superconducting tapes and films is considered. The equilibrium distributions of the magnetic flux density n(y) and of the sheet current density i(y) are found analytically for the tapes with an oscillating transport current. The critical current is calculated taking into account both bulk and edge pinning of the magnetic flux, and the dependence of the dissipation loss power upon the ac amplitude I0 is found. The crossover from barrier- to pinning-controlled ac losses is predicted with the increase of current oscillation amplitude I0.

Amplitude of current oscillations in an ADC based on a bispin device

The amplitude, shape, and length of the output pulses must be known when the new device BISPIN, which converts incident light flux into a regular current pulse train, is used as an amplitude-to-digital converter. The factors that determine the amplitude of the pulses generated are considered.

Periodic orbit theory for resonant tunneling diodes: Comparison with quantum and experimental results

We investigate whether the quantal and experimental amplitudes of current oscillations of resonant tunneling diodes in tilted fields are obtainable from periodic orbit (PO) theories by considering recently proposed PO approaches. We show that accurate amplitude and frequency shifts for the current oscillations (typically to within a few %) can be obtained from a simple analytical formula both in the stable (torus-quantization) limit and the unstable regimes of the experiments that are dominated by isolated PO's. But we find that the PO approach does not describe quantitatively the dynamically interesting intermediate experimental regimes that appear to be dominated by contributions from complex orbits and multiple nonisolated PO's. We conclude that these regimes will not easily be described by the usual PO approach, even with simple normal forms.

Study of Self Oscillatory Belousov-Zhabotinsky Systems Under the Perturbation of External EMF

An examination of the current and potential oscillations in the self oscillatory Belousov-Zhabotinsky system under the application of external EMF is presented for the first time. The system involves Mn(II) as the metal ion catalyst and malic acid/citric acid/malonic acid as the substrate. External EMF shifts the oscillatory profile to the higher potential range by the magnitude of applied EMF. The amplitude of current oscillations increases with the magnitude of external EMF. The behaviour of the system with and without a complexing agent (tetrasodium pyrophosphate) is rationalised in terms of individual steps involved in the overall reaction.

Electrochemical oscillatory behavior under a scanning electrochemical microscopic configuration

Diffusion coupled oscillatory behavior of the Au|HCI system was investigated in the presence of substrate “feedback” of the scanning electrochemical microscopic (SECM) system. It is shown that the amplitude of current oscillation can be increased significantly with a slight decrease in the oscillation frequency when the Pt substrate is positioned close to the small Au oscillating electrode. Such a “feedback” effect of the substrate may also become the driving force to induce current oscillation at the potential where normally electrodissolution occurs. The use of SECM to distinguish the types of oscillation mechanism of chosen systems is demonstrated by further fulfillment of a similar experiment on the surface process controlled potential oscillation system of Pt|HCHO. For this purpose, a special home-made galvanostat-potentiostat was employed which is generally necessary for studies of surface process controlled oscillation and may also be useful for studies of diffusion coupled oscillation under current control. It is shown that such an investigation under SECM configuration may provide insight into the oscillatory behavior from a new point of view.

超電導変圧器の雷サージに対する応答特性の理論的評価 ＩＩＩ． 単調増加電流によるクエンチ

Induced current by lightning surge increases monotonically with time, while small oscillating components are superposed on it as shown in the previous papers. In this paper, it is shown that a quench occurs when the induced current exceeds the critical current of superconducting cable, even if amplitude of current oscillation is too small to induce quench by ac losses. Firstly a simplified equivalent circuit and basic equations which can describe the quench due to excess current are proposed. Its applicability is confirmed by the fact that obtained analytic results show good agreement with numerically calculated results by full equivalent circuit and basic equations shown in the previous paper. The dependence of peak value of induced current on wave tail duration of lightning surge is estimated for various voltage-level superconducting transformers by taking account of line surge impedance at secondary side and for the number of simultaneous penetration phase. It is shown that the current peak becomes large in case of underground line at the secondary side and a small % impedance. With the aid of the obtained results, methods to evade the quench are discussed in connection to lightning impulse withstand level and the ratio of transportable current of superconducting cable to the rated current.

Wettability Effect on the Corrosion Kinetics of Iron Anodes in Sulfuric Acid Solutions

The interdependence of electrode wetting and electrode corrosion rate was studied for the iron anode in aqueous sulfuric acid solutions. The effects of acid solution concentration and surface‐active agents on the corrosion rate and passive‐active transition current oscillation amplitude were measured. The results show that both are dependent on the electrode wetting. The electrode wettability is shown to change as a function of time which results in convective liquid displacement around the electrode and on variable corrosion rates.