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There is an important difference between piezoelectric polymer films and solid crystals for the application of piezoelectric generators. In the case of polymers, the optimal piezoelectric response imposes a large bending regime. Starting from the linear Curie's constitutive equations, we develop an analytical model under the assumption of the large bending regime resulting from bulge testing configuration. This model shows a specific non-linear piezoelectric response, which follows a power of 2 / 3 of the mechanical excitation. The piezoelectric voltage and the corresponding power are then studied experimentally as a function of the angular frequency ω of the mechanical excitation, the load resistance R , and the thickness of the film ℓ. The experimental results carried out on piezoelectric polyvinylidene fluoride (PVDF) films validate the model. [ABSTRACT FROM AUTHOR]

Based on experimental data, we propose a model to evaluate the energy dissipated during quantum tunneling processes in solid-state junctions. This model incorporates a nonlinear friction force expressed in the general form f (x) = γ v (x) α , where γ is the frictional coefficient, which is fitted to data. We study this by applying voltages just below the barrier height up to near breakdown voltages. Furthermore, by lowering the temperature and adjusting the applied voltage to the junction, the effect on dissipation caused by the variation in barrier height is examined. We underline that the crucial dependency of dissipation on the fraction of particle energy lost is modulated by two primary mechanisms: the application of voltage and the variation of temperature. The fraction of energy dissipated decreases, in general, for increasing energies of the tunneling particles at a given temperature. However, for a given energy of the tunneling particle, the present work demonstrates a turning point at a temperature of 137 K, after which the dissipated energy starts increasing for higher temperatures. The latter can possibly be due to the increase of electron–phonon interactions, which become predominant over barrier height reduction at higher temperatures, and hence, we identify T = 137 K as a critical temperature for a change in the dissipative characteristics of the solid-state junction under consideration. Notably, the study also identifies significant changes in dissipation parameters, γ and α, above 137 K, exhibiting a linear decline and underscoring the importance of further research at higher temperatures. [ABSTRACT FROM AUTHOR]

We exhaustively investigate the temporal correlations between the ultrahigh-frequency (of the order of 1–6 GHz), very high-frequency (of the order of 10–100 MHz), and x-ray (photons with energies from 5 keV to 1 MeV) emissions together with the optical emissions in the near-infrared (within 700–1100 nm) and near-ultraviolet (within 300–400 nm) wavelength regions. The emissions are produced by a laboratory atmospheric discharge developing in an 55 cm air gap at voltages up to 1 MV. When registering various electromagnetic emissions, the discharge current and voltage are measured, as well as nanosecond imaging of the discharge evolution in its own glow is performed. The spatiotemporal localization of the discharge regions associated with the x-ray generation is carried out by employing the group of fast scintillation detectors, and the evolution of plasma structures during the x-ray generation is traced. A chronological map is constructed providing an in-depth understanding of the temporal character and correlations of various electromagnetic emissions. The map allows one to analyze fast ionization processes occurring in the gas-discharge medium and triggering the generation of the corresponding emissions. The generation mechanisms of the considered emissions in an extended high-voltage discharge are discussed. The findings can be helpful in revealing the sources of various electromagnetic emissions accompanying the formation of laboratory and atmospheric discharges. [ABSTRACT FROM AUTHOR]

Ferroelectric thin-film transistors (Fe-TFTs) have promising potential for flexible electronics, memory, and neuromorphic computing applications. Here, we report on a physics-based efficient device model for Fe-TFTs that effectively describes memory switching and device I–V characteristics. This model combines a stochastic multi-domain description of FE switching dynamics with a virtual source treatment of TFT device characteristics. It demonstrates that the memory window of Fe-TFTs depends on the amplitude and duration of the applied voltage pulses, thus suggesting quantitative means of programming and control. Additionally, we introduce a machine-learning-enabled method to automatically generate optimal voltage pulses for accurately programming multiple intermediate FE states, which is crucial for multi-bit memory and neuromorphic computing applications. To showcase the model's applications, we simulate a 4 × 4 crossbar array circuit based on Fe-TFTs, highlighting its utility in performing multiply-accumulate computing operations. This small array can achieve a high speed of ∼ 1.28 tera operations per second (OPS) and a power efficiency of ∼ 0.43 W/PetaOPS. The model developed here is valuable for exploring the capabilities of Fe-TFTs in future flexible memory and computing technologies. [ABSTRACT FROM AUTHOR]

Results of experimental research and two-dimensional hydrodynamical simulations of close to critically damped microsecond timescale underwater electrical explosions of butterfly-shaped foils for six different materials are presented. Using current and voltage waveforms along with multi-frame shadow images of the shocks generated in water, the values of the specific action integral, h, were determined. It is shown that values of h can be calculated based on the average current density and that its value (within error bars) does not change in the range of current densities (0.5–1) × 108 A/cm2. The values of h were found to be consistent with those obtained for sub-microsecond underwater electrical explosions of wires made of the same material but differ from those obtained in earlier research with explosion of wires in vacuum. [ABSTRACT FROM AUTHOR]

To mimic the intricate and adaptive functionalities of biological ion channels, electrohydrodynamic ion transport has been studied extensively, albeit mostly, across uniformly charged nanochannels. Here, we analyze the ion transport under coupled electric field and pressure across heterogeneously charged nanopores with oppositely charged sections on their lateral surface. We only consider such pores with symmetric hourglass-like and cylindrical shapes to focus on the effects of the non-uniform surface charge distribution. Finite-element simulations of a continuum model demonstrate that a pressure applied in either direction of the pore-axis equally suppresses or amplifies the ionic conductance, depending on the electric field polarity, by distorting the quasi-static distribution of ions in the pore. The resulting anomalous mechanical deactivation and activation of ionic current under opposite voltage biases exhibit the functional modularity of our setup, while their intensities are highly tunable, substantially greater than those of analogous behaviors in other nanochannels, and fundamentally correlated to ionic current rectification (ICR) in our pores. A detailed study of ICR subsequently reveals its counterintuitive non-monotonous variations, in the pores, with the magnitude of applied voltage and the pore length, that can help optimize their diode-like behavior. We further illustrate that while the hourglass-shaped nanopores yield the more efficient mechanical suppressors of ion transport, their cylindrical analogs are the superior rectifiers and mechanical amplifiers of ion conduction. Therefore, this article provides a blueprint for the strategic design of nanofluidic circuits to attain a robust, modular, and tunable control of ion transport under external electrical and mechanical stimuli. [ABSTRACT FROM AUTHOR]

The possibility observation of the electric field controlled multicaloric response through quasi-isostatic compression as a result of the converse piezoelectric effect was demonstrated on the cylindrical type magnetoelectric composite MnAs/PZT. It was shown that an electric voltage of 100 V corresponding to an electric field of E ∼0.3 kV/mm applied to the walls of the piezoelectric component PZT of the MnAs/PZT composite contributes to an increase in the maximum adiabatic temperature change by 0.2 K in the temperature range of the magnetostructural phase transition of MnAs ∼317 K at a magnetic field change of 1.8 T. Numerical analysis using the finite element method has shown that an electric field voltage of 100 V is capable of creating a quasi-isostatic mechanical stress in the region inside a cylindrical PZT tube of ∼3 MPa. Moreover, in the region of weak pressures up to 10 MPa, the contribution to the total adiabatic temperature change from piezo-mechanical compression linearly depends on the electrical voltage that can be used for control by magnetic and caloric properties of multicaloric materials. [ABSTRACT FROM AUTHOR]

Surface flashover that occurs on the surface of epoxy resin (EP) is one of the main causes of insulation failure in the power system. The newly emerging polar groups on the surface are highly desirable for enhancing the surface flashover performance of EP. Here, we present a facile ultraviolet (UV) irradiation method to enable the controlled introduction of C–OH and C = O groups on the EP surface. The resultant UV-irradiated EPs (UV-EPs) are highly uniform with little variation in surface roughness while exhibiting tunable polar content with the irradiation time. We also present the first systematic investigation into the effect of UV irradiation time on the surface flashover voltage of UV-EPs, with a maximum increase of 23.07% compared to the pristine EP. Mechanistic studies suggest that the enhancement of the surface flashover voltage is mainly dominated by the density of the deep trap, which is strongly dependent on the UV-induced C–OH and C = O groups on the surface. Besides that, the UV-EPs also display long-term stability due to the stable presence of polar groups, which further demonstrates the feasibility of this method for the development of EP with excellent properties. [ABSTRACT FROM AUTHOR]

Alternating current (AC) loss measurement is crucial for the theoretical evaluation and optimization in the fabrication of superconducting AC devices. Lock-in amplifier based on the lock-in phase is commonly adopted and inevitably involves with phase error. In this work, a novel approach for measuring transport AC loss by determining the minimum compensated voltage (MCV) was developed, in which the lock-in amplifier was removed. Since it just uses the voltage signal from an AC voltmeter, it is phase-error immune. Experimental results demonstrated that when using the lock-in amplifier, there existed a system error as the initial phase difference between the sampled (reference) and real current phases, which required careful compensation. In contrast, the phase error no longer needed to be considered by the MCV method, and the AC loss results were obtained much more conveniently with the relative error between the theoretical and the experimental of less than 5%. Finally, the AC loss of a coated conductor spiral wound on an epoxy bar was obtained using the presented approach, demonstrating its low cost, ease of operation, and high accuracy. [ABSTRACT FROM AUTHOR]

The failure of polymeric solid insulation under transient voltages is closely associated with space charge. In this study, DC and AC field dependent conduction characteristics of epoxy resin were investigated using the space charge limited current and high voltage broadband dielectric spectrum methods. The breakdown voltages (BDVs) were examined over a wide range of DC voltage ramp rates. The results reveal a threshold effect of AC conduction loss below 600 Hz with respect to the electric field. By analyzing charge migration laws, a mobility distribution was deduced, with an upper limit of 10 − 9 m 2 V − 1 s − 1 , which is much higher than the measured DC mobility of 10 − 14 m 2 V − 1 s − 1 . A multi-mobility bipolar charge transport model was proposed by introducing the obtained mobility distribution. Compared to the single-mobility model, high-mobility carriers induce larger unblocked space charge currents for high dv/dt voltages, leading to lower values of BDV, which is consistent with experiment results. As the voltage ramp rate decreases, both simulation and experiment demonstrate higher BDVs due to the field shielding effect of homocharges. [ABSTRACT FROM AUTHOR]

Due to the erratic switching phenomenon of the Si avalanche bipolar junction transistor (ABJT) in the Marx bank circuit (MBC), an explanation of the leakage current trigger mode in the overvoltage state with a lack of displacement current is proposed. There are random switching properties (i.e., switching or non-switching) in the ABJT with emitter–base shorted, triggered by a voltage ramp to the overvoltage state temporarily with dV/dt rate close to 0 V/ns. The experimental conditions and characteristics of erratic behaviors are summarized. The optical visualization of the current channel in an erratic switching state is obtained, and the corresponding physical model of the leakage current trigger mode is established. It shows that the switching event occurs with the change in the position of the conductive channel. The process of emitter electron injection is caused by the leakage current in the overvoltage state instead of the displacement current. Meanwhile, the intensity of this trigger mode is weak, and the instability of the leakage current may cause the failure of switching. The study of erratic switching is of great significance for the working reliability of MBCs and failure analysis of ABJTs. The proposed explanation is validated by the agreement between the simulation results and the experimental observations. [ABSTRACT FROM AUTHOR]

The study of insulation degradation processes is crucial for the reliable operation of power equipment and electronic devices. The phase field method has been widely used in recent years to simulate the degradation process of insulation materials. However, the effect of space charge was ignored. In this paper, a novel phase field method based on the bipolar carrier transfer model is suggested. This model can simulate degradation under different temperatures and DC or combined AC/DC voltage. The cases under AC and combined AC/DC voltage at different temperatures are simulated by COMSOL. Methods to ensure model convergence are proposed. The results show that the field strength distribution under a combined AC/DC field is more uniform, especially for negative polarity. For the same voltage form, temperature and breakdown time show an exponential relationship. The results are consistent with those of previous experimental studies, proving the usability of the model. In addition, the processes of initiation, growth, and breakdown stage of the dielectric degradation process, as well as the stagnation period, are explored theoretically. The stagnation time at low temperatures under combined AC/negative DC voltage is long. The research in this paper is useful for insulation optimization design, condition assessment, and longevity prediction. [ABSTRACT FROM AUTHOR]

As we known waves contain important information, however, to realizing high-precision quantification for ocean exploitation and utilization is challenging. In this paper, we proposed a neural network for wave height detection by training the voltage waveform of a triboelectric nanogenerator (TENG). First, we analyzed the voltage signal obtained using a TENG. Second, we proposed a lightweight artificial neural network model that achieves a minimal monitoring error of 0.049% at low amplitudes and yields better monitoring results than the linear model. The findings presented in this paper enable the measurement of water surface waves and eliminate the influence of external factors on sensor performance. Wave parameters can be obtained using neural networks, and this work provides a new strategy for computational and intelligent applications by using wave data. [ABSTRACT FROM AUTHOR]

Vector inversion generators or spiral generators are compact, high voltage pulse generators consisting of a pair of conducting foils wound in a spiral and a switch. We developed an improved analytical model predicting the time evolution of the output voltage of such spiral generators. Our model (i) takes into account that the current in the switch results from the current on active and passive waveguides and (ii) takes into account the losses of the conductor in equations describing the propagation of voltage and current pulses in both waveguides. The model is compared to experimental results involving different input switches and at different temperatures to investigate the influence of resistive losses on the output voltage. The model is further developed to obtain the time evolution of the current in the switch. Our model is then used to predict the amplitude of the first two peaks of the oscillatory response of spiral generators as a function of a set of dimensionless parameters. [ABSTRACT FROM AUTHOR]

In this work, we investigate the device-to-device variations in the remanent polarization of metal–ferroelectric–insulator–metal stacks based on ferroelectric hafnium–zirconium–oxide (HZO). Our study employs a 3D dynamic multi-grain phase-field model to consider the effects of the polycrystalline nature of HZO in conjunction with the multi-domain polarization switching. We explore the dependence of variations on various design factors, such as the ferroelectric thickness and voltage stimuli (set voltage, pulse amplitude, and width), and correlate the trends to the underlying polarization switching mechanisms. Our analysis reveals a non-monotonic dependence of variations on the set voltage due to the coupled effect of the underlying polycrystalline structure variations and the voltage dependence of polarization switching mechanisms. We further report that collapsing of oppositely polarized domains at higher set voltages can lead to an increase in variations, while ferroelectric thickness scaling lowers the overall device-to-device variations. Considering the dynamics of polarization switching, we highlight the key role of voltage and temporal dependence of domain nucleation in dictating the trends in variations. Finally, we show that using a lower amplitude pulse for longer duration to reach a target mean polarization state results in lower variations compared to using a higher amplitude pulse for shorter duration. [ABSTRACT FROM AUTHOR]

A model predicting the number of emission sites and total current from a porous conical electrospray emitter as functions of voltage is derived. A pressure balance between capillary and electric forces is used to determine an onset criterion for individual menisci, and an ionic emission scaling law is invoked to predict the current each meniscus emits. These submodels are integrated over a phenomenological meniscus size distribution and the area of the emitter to yield a model for emitter performance as a function of five free parameters, two for the ionic emission submodel and three for the meniscus size distribution. Bayesian inference is applied to determine these model parameters from an existing dataset [Dressler et al., J. Propul. Power 38, 809 (2022)]. The model predictions after training are compared to the experimental data, and it is found that the majority of the data are within a 90% credible interval. The ability of the model to capture key trends in the experimental data is attributed to the interplay of two effects: the distribution over meniscus size on the emitter and the position-dependent electric field. The calibrated model results also suggest that the emitter surface is wetted by a series of large but sparsely distributed pools of propellant. The performance and extensibility of the model are examined within the context of model-based design for porous electrospray array thrusters. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) is one of the key factors leading to premature insulation failure of film capacitors used in pulse power devices. To study the effect of frequency on the PD characteristics of biaxially oriented polypropylene (BOPP) film, a sphere-plate electrode was used to simulate defects of the air gap between the film layers. PD experiments of the BOPP film were carried out under 1, 10, 100, 500 Hz, and 1 kHz with a rising edge of 65 ns and a pulse width of 300 ns. The results show that the repetitive partial discharge inception voltage (RPDIV), the number of discharges, the rising stage discharge (RSD) amplitude, and the falling stage discharge (FSD) time-lag, all show an increase and then decrease with increasing pulse frequencies and reach a maximum value at a pulse frequency of 100 Hz. Moreover, the FSD discharge amplitude and the RSD discharge time-lag increase with an increasing pulse frequency. From the perspective of initial electron generation, the quantitative mathematical relationship between PD characteristics (RPDIV, PD amplitude, PD number, and PD time-lag) and frequency was established based on the Fowler–Nordheim field emission effect for the first time, which can reflect the influence of frequency on the memory effect and the development process of PD. The results can provide an experimental basis and a mechanistic explanation for the evaluation of PD characteristics for film capacitors under nanosecond pulse voltage. [ABSTRACT FROM AUTHOR]

To study the initiation and development of interfacial electrical damage in multi-layer dielectrics, an aging test of 3-layer polyimide films was conducted under pulsed voltage with a repetitive frequency of 500 Hz and a maximal amplitude of 30 kV. The variation in the damage morphology with the number of applied pulses was analyzed by a statistical method. The circuit current and partial discharge at different aging stages was measured, and the Fourier transform infrared spectrum analysis results of the aged and unaged sample regions were compared. The results demonstrate that the partial discharge in the dielectric interface gap, which is unavoidable in manufacturing, is the main cause of damage. It initiates from the interface and grows into the interior of the dielectric with the application of pulses. When there are no macroscopic defects on dielectric films, damage presents a punctiform morphology. The damage process can be divided into the following three stages: surface roughening damage, steady growth stage of damage points, and pre-breakdown stage. Differing from dielectrics without macroscopic defects, dielectrics with original void defects present transverse dendritic damage channels that initiate from the edge of the defect. [ABSTRACT FROM AUTHOR]

ZnO varistors are widely employed for overvoltage protections and surge absorptions due to their excellent nonlinear current–voltage characteristics originating from double Schottky barriers (DSBs). In most cases, they are operating under moderate ac voltages, while calculating the transient current responses of DSBs remains a challenge, impeding the development of condition assessments. In this paper, a transient conducting model for the DSB is proposed by quantifying the charge trapping processes of the interface states. The DSB is found to quickly reach a quasi-steady state, where the interfacial charge stabilizes with only small modulations at a relatively high level above the dc equilibrium value, even though the applied ac voltage varies in time and polarity. This is the result of efficient charge trapping and slow de-trapping by grain boundary interface states. For charge compensation under the time-varying voltage, the width of the two depletion regions of the DSB shows periodic changes. The proposed model is validated by a satisfying agreement between experimentally measured current responses and simulation results of ZnO varistors. The findings of this study provide a perspective on investigating the time-varying conducting systems and open avenues for condition assessments of nonlinear conducting devices. [ABSTRACT FROM AUTHOR]

The development of neuromorphic computing is expected to enable the computer to realize the integration of storage and computation. The development of memristors provides hardware support possibilities for the development of neuromorphic computing. In this work, we have prepared a (La0.67, Sr0.33)MnO3/BaTiO3-based memristor with good forward and reverse memristor function and multilevel resistive tunability, including an increased resistance state at forward voltage and a decreased resistance state at reverse voltage. This is mainly due to the barriers of the ferroelectric dielectric layer and its ferroelectric polarization under the electric field, and the migration of oxygen vacancy under the electric field. The devices also successfully implement the synaptic simulations of short-term plasticity, long-term plasticity, excitatory postsynaptic current, paired-pulse facilitation, spike-rate-dependent plasticity, and spike-timing-dependent plasticity and reimplement these synaptic simulations by varying the amplitude and pulse width of the applied voltage. We have also achieved a classification accuracy of 96.7% for the given handwritten digit data by an artificial neural network with supervised learning. The high classification accuracy is attributed to the good nonlinearity of the device in terms of continuous conductance decreased (0.91) and increased (0.58). Our results are expected to provide a good reference value for neural devices. [ABSTRACT FROM AUTHOR]

The results of experimental research on the acoustic and electrical characteristics of underwater spark discharges facilitated by a preliminary discharge are presented. The latter was produced through the application of a short duration high-voltage pulse formed by a Marx generator. The application of this pulse lead to the formation of a low-density region in the form of a streamer which transformed to an oscillating vapor cavity. It was shown that this method provided a breakdown of a significantly increased interelectrode gap for the same charging voltage of the main capacitor and allowed the generation of stronger shocks. The temporal development of transient discharges in a long gap and the relationships between the hydrodynamic and electrical parameters of such discharges are reported and analyzed. [ABSTRACT FROM AUTHOR]

This experimental study aims to better understand the electrical and optical properties of a positive DC corona discharge and to highlight the influence of applied voltage and electrode gap on the discharge regime. When the high voltage is increased, three successive regimes have been observed, including one that has never been reported in the literature to the best of our knowledge. This is certainly due to the fact that the tungsten needle used in these experiments is a commercial needle, with a tip of perfect surface finish. In fact, after the ignition voltage, the mean current slowly increases, and it perfectly follows the theoretical Townsend's law; this is the glow regime. When the voltage reaches a first threshold, a few small current pulses appear. However, this is not the breakdown streamer regime because photographs and intensified camera visualizations highlight that the propagation of streamers toward the grounded plate is limited to half of the gap. In this regime, the time-averaged current becomes higher than that of Townsend's law. Each current pulse is composed of only one bump, and the pulse frequency is higher (approximately 20 kHz) than that of the breakdown streamers. When the voltage reaches a second threshold, the magnitude of current pulses suddenly increases, but their frequency decreases (a few kHz); this is the transition toward the breakdown streamer regime. In this regime, each current pulse is composed of two bumps: the first one corresponds to the arrival of a primary streamer at the plate and the second one corresponds to a secondary streamer. Finally, we investigated the effects of the electrode gap. The magnitude and frequency of the current pulses increase when the gap decreases. Consequently, the offset between Townsend's curve and the experimental I–V characteristics increases when the gap decreases, because the pulse component of the total discharge current increases. [ABSTRACT FROM AUTHOR]

More than a decade of active electrocaloric (EC) material research has produced several EC materials that exhibit a giant electrocaloric effect (ECE) at high electric fields, which is assured by direct measurement. These EC materials have enabled the demonstration of EC cooling devices, which exhibit temperature lifts of more than 10 K. These research and development efforts have revealed the critical importance of electrical breakdown, which is common in all electric and dielectric materials and devices under high voltages and electric fields. In general, the electric field for reliable device operation of dielectrics has to be less than 25% of the typical electric breakdown strength. To realize EC cooling devices with competitive performance requires advanced EC materials that generate large ECE (ΔT > 5 K) under these low electric fields. Double-bond (DB) defect modified P(VDF-TrFE-CFE) relaxor polymers, as reported recently, generate large ECE under low electric fields without any fatigue effects even after 1 × 106 field cycles. These relaxor ferroelectrics promise to meet the application challenge. A closely coupled experimental and theoretical study of EC materials will undoubtedly lead to advanced EC materials that generate large ECE at low electric fields beyond the DB modified relaxor polymers. This will result in practical and high-performance EC coolers, which are environmentally benign, compressor-free, and highly efficient. [ABSTRACT FROM AUTHOR]

The motion of an ion in a radiofrequency (rf) Paul trap is described by the Mathieu equation and the associated stability parameters that are proportional to the rf and dc electric field gradients. Here, a higher-order, iterative method to accurately solve the stability parameters from measured secular frequencies is presented. It is then used to characterize an endcap trap by showing that the trap's radial asymmetry is dominated by the dc field gradients and by measuring the relation between the applied voltages and the gradients. The results are shown to be in good agreement with an electrostatic finite-element-method simulation of the trap. Furthermore, a method to determine the direction of the radial trap axes using a "tickler" voltage is presented, and the temperature dependence of the rf voltage is discussed. As an application for optical ion clocks, the method is used to predict and minimize the electric quadrupole shift (EQS) using the applied dc voltages. Finally, a lower limit of 1070 for the cancellation factor of the Zeeman-averaging EQS cancellation method is determined in an interleaved low-/high-EQS clock measurement. This reduces the EQS uncertainty of our 88 Sr + optical clock to ≲ 1 × 10 − 19 in fractional frequency units. [ABSTRACT FROM AUTHOR]

A novel dielectric barrier discharge (DBD) plasma-actuator module with an exposed electrode and two covered electrodes was developed to enhance electrohydrodynamic force generation based on the concept that it separates the ionization and acceleration processes. The conventional three-electrode configuration of the DBD plasma actuator suffers from unexpected spark discharge between the exposed electrodes, thereby failing to strengthen the electric field intensity for accelerating charged particles or generating a stable ionic wind. In this study, a third electrode was embedded in the dielectric layer to prevent spark discharge. Furthermore, an alternating current (AC) waveform was employed as the bias voltage, which was applied to the third electrode, instead of the direct current (DC) voltage used in a conventional DBD plasma actuator. Induced flow visualization using particle image velocimetry technique revealed that the DC bias voltage forms a weak ionic wind in the proposed DBD plasma actuator owing to the electric field screening effect, and the ionic wind periodically appears when the polarity of the voltage is reversed by applying an AC-bias voltage. The velocity of the ionic wind increases with increasing frequency and the AC bias voltage amplitude. Also, decreasing the distance between the second and third electrodes results in ionic wind enhancement. The results obtained in this study provide insights into the drastic improvement in the performance of DBD plasma actuators with the enhancement of the electric field intensity for charged particle acceleration. [ABSTRACT FROM AUTHOR]

The importance of gas discharges for numerous applications with increasingly small device size motivates a more fundamental understanding of breakdown mechanisms. Gas breakdown theories for these gap sizes unify field emission with the Townsend avalanche, which depends on Townsend's first ionization coefficient α ; however, the ratio of the electric field E to gas pressure p for microscale gas breakdown exceeds the range of validity for the typical empirical equation. While some studies have used particle-in-cell simulations to assess α in this range, they only examined a narrow range of experimental conditions. This work extends this approach to characterize ionization in microscale gaps for N2, Ar, Ne, and He for a broader range of pressure, gap distance d, and applied voltage V. We calculated α at steady state for 0.75 ≤ d ≤ 10 μ m and p = 190, 380, and 760 Torr. As expected, α / p is not a function of reduced electric field E / p for microscale gaps, where the electron mean free path is comparable to d and E / p is high at breakdown. For d < 2 μ m , α / p scales with V and is independent of p. For d > --> 10 μ m , α / p approaches the standard empirical relationship for E / p ≲ 1000 V Tor r − 1 c m − 1 and deviates at higher levels because the ionization cross section decreases. We develop a more rigorous semiempirical model for α , albeit not as universal or simple, for a wider range of d and p for different gas species that may be incorporated into field emission-driven breakdown theories to improve their predictive capability. [ABSTRACT FROM AUTHOR]

In this work, we consider MEMS devices made of mechanically coupled microbeams under electric actuation. We conduct an experimental study to identify the occurrence of veering and then investigate its dynamic response for different electric actuations. A slight change in the DC voltage bias from the veering point is observed to affect significantly the frequency response. Indeed, jump to large orbits occurred when perturbing the applied DC voltage while operating near the cyclic-fold bifurcation point. We also develop and validate a mathematical model to simulate the response of the device. The model showed similarities in the softening effect of the DC voltage bias and an added mass when matching their induced shift in the natural frequency. As such, one can discern the inherent nonlinear effects of DC voltage bias on coupled resonators and exploit them for mass sensing applications without going over the hassle of mass deposition, which requires the deployment of complex processes. We also investigate different mass detection mechanisms. We show the potential of mode localization and the significant and abrupt jumps in the deflection of the coupled microbeams due to mass perturbation to enhance the sensitivity of MEMS mass sensors. [ABSTRACT FROM AUTHOR]

Experiments were conducted at the University of Illinois at Urbana Champaign Electric Propulsion Laboratory to study the ion-induced secondary charge emission from surfaces bombarded by an [Emim][BF4] electrospray plume. The surfaces were unpolished and had oxide and hydrocarbon layers typical of as-received materials used in electrospray experiments. The effect of changing the bias from −85 to +85 V on the target collecting current from the electrospray plume was measured. These data are used to calculate the yield of positive and negative charged species emission from the target due to bombarding cations and anions. The yields of positive charges per incident cation (γ c a t i o n +) , negative charges per incident cation (γ c a t i o n −) , positive charges per incident anion (γ a n i o n +) , and negative charges per incident anion (γ a n i o n −) are measured for eight different industrial materials commonly used in electrospray diagnostics or thruster and spacecraft construction. These yields range from 0 to 1.3 charges per incident ion over a range of emitter voltages from 1.5 to 2.9 kV and largely display linearly increasing trends with increasing emitter voltage. Over this emitter voltage range, γ c a t i o n + ranges from 0 to 0.55, γ c a t i o n − ranges from 0 to 0.75, γ a n i o n + ranges from 0 to 0.4, and γ a n i o n − ranges from 0.3 to 1.3. The data show for the first time positive and negative charges being emitted due to both cation and anion bombardment and suggest that secondary ions sputtered from the surface are important to the secondary charge emission behavior in electrospray plumes. [ABSTRACT FROM AUTHOR]

Nano- and micro-electromechanical systems (N/MEMSs) are traditionally based on electrostatic or piezoelectric coupling, which couples electrical and mechanical energy through acoustic resonator structures. Most recently, N/MEMS devices based on magnetoelectrics are gaining much attention. Unlike electrostatic or piezoelectric N/MEMS that rely on an AC electric field or voltage excitation, magnetoelecric N/MEMS rely on the electromechanical resonance of a magnetostrictive/piezoelectric bilayer heterostructure exhibiting a strong strain-mediated magnetoelectric coupling under the excitation of a magnetic field and/or electric field. As a consequence, magnetoelectric N/MEMS enable unprecedented new applications, ranging from magnetoelectric sensors, ultra-compact magnetoelectric antennas, etc. This Tutorial will first outline the fundamental principles of piezoelectric materials, resonator design, specifically different acoustic modes, and piezoelectric-based N/MEMS applications, i.e., radio frequency front end filters and infrared radiation sensors. We will then provide an overview of magnetoelectric materials and N/MEMS focusing on the governing physics of the magnetoelectric effect, magnetic material properties for achieving high magnetoelectric coupling, state-of-the-art magnetoelectric N/MEMS devices, and their respective applications. [ABSTRACT FROM AUTHOR]

The transient processes in the electric conduction of fine disperse 2D-MoS2 powder samples, occurring at changing voltages applied to the sample under the conditions of uniaxial compression, have been studied. The long-term transient changes in conduction occurring both after switching on and off the applied voltage were observed. The current–voltage characteristics have a hysteresis of branches corresponding to increasing and decreasing voltages. The observed results are explained within the frame of the migration (interlayer) polarization model. [ABSTRACT FROM AUTHOR]

The backward discharge induced by residual charge has attracted considerable attention, but the complex mechanism requires further investigation. This article analyzes the surface discharge and the residual surface charge accumulation characteristics in atmospheric air under a positive impulse. The photographic figure method, the dust figure method, and the electrostatic probe method are employed, allowing the residual charge distribution to be quantitatively determined. One main forward discharge is observed at the impulse front and several subsequent backward discharges are observed at the impulse tail. The propagation length of the forward streamer is closely related to the voltage at the moment of discharge. A model illustrating the evolution process of surface forward and backward discharges as well as the corresponding residual charge accumulation characteristics is established. The residual surface charge plays a significant role in the development of the streamer discharge. The backward discharge is incurred by the positive charge that is deposited by the previous forward discharge. [ABSTRACT FROM AUTHOR]

A 2D axisymmetric study of the atmospheric pressure plasma jets driven by a trapezoidal pulse voltage with different polarities is performed in this work. The basic properties of the plasma jet in three stages, including the first discharge, the secondary discharge, and the afterglow of the plasma jet, are studied, with emphasis on the influence of voltage polarity on the secondary discharge and the afterglow. For the positive pulse voltage, the plasma jet propagates in the form of a bullet during the first stage. At the falling edge of the pulse, a new ionization wave resulting from the secondary discharge is formed and propagates forward along the preceding jet path in a continuous mode, resulting in a mixing jet propagation mode with the primary bullet and the luminous channel coexist. The plasma jet is finally converted to the continuous mode at the afterglow stage. Meanwhile, the first bullet almost stops propagating after the secondary discharge is ignited due to the rapid reduction of the electric field in the bullet head. In contrast, in the case of negative pulse voltage, a diffusive arrow-like plasma plume is observed during the first stage. The secondary discharge ignition does not completely change the direction of the electric field in the first ionization head and inhibits the propagation of the primary plasma jet. The dominant physics mechanisms associated with these observations are analyzed and discussed. In addition, the dependence of the reactive species on the secondary discharge under different pulse polarities is also compared. [ABSTRACT FROM AUTHOR]

We report on a novel scissor-like electromechanical metamaterial (SEMM) with enhanced and tunable damping properties, stemming from its electromechanical resonant effects. The displacement amplification mechanism of the scissor-like structure in SEMM is exploited to amplify the damping ratio for stronger vibration mitigation through the enhanced electrical dissipation of the amplified voltage of the piezoelectric element. The relative dissipation performance, termed as metadamping, is quantified based on complex band structures, which allow frequencies to be complex valued. Using different shunting circuits, the overall damping performance of SEMM is demonstrated to be higher than a statically equivalent traditional systems, such as acoustic metamaterials and monatomic lattices. The dissipation performance of SEMM is numerically verified via finite structure analysis and found to be in an excellent agreement with Bloch's wave analysis. Furthermore, the electromechanical nature of the piezoelectric material in SEMM provides a convenient way to tune the metadamping by adjusting the piezoelectric shunting circuit. [ABSTRACT FROM AUTHOR]

CuCr1−xMgxO2 (x = 0 and 0.02) epitaxial thin films were prepared on 5°/10° vicinal cut α-Al2O3 (000l) substrates using pulsed laser deposition. The laser-induced thermoelectric voltage (LITV) effect in these inclined delafossite thin films was observed for the first time. The thin films were characterized by resistivity temperature measurement and atomic force microscopy. Because of the enhanced resistivity anisotropy and high carrier concentration in the ab-plane owing to Mg doping, the 10°-tilted CuCr0.98Mg0.02O2 film exhibits an evident LITV signal with a maximum transverse thermoelectric voltage of 156 mV. Thermal conductivity results indicate that CuCr1−xMgxO2 (x = 0 and 0.02) films have a dominant phonon thermal conductivity, which may contribute to a long decay time for the LITV signal. These results indicate potential for future transverse thermoelectric applications based on transparent conductive oxides. [ABSTRACT FROM AUTHOR]

Numerous investigations on plasma–liquid interaction have been published in the literature using various reactor geometries. However, our understanding of the basic configuration of a pin-to-plane dielectric barrier discharge (DBD) in contact with water is still incomplete. We, therefore, performed the electrical diagnostics of such a discharge, operated in an AC regime with sinusoidal high voltage, focusing mainly on the power injected into the plasma in relation with several experimental parameters. It was found that the injected power increased linearly with the amplitude of the applied voltage, while without water, the evolution followed a second-order polynomial. In both cases, the discharge power was proportional approximately with the frequency. For the DBD above water, the power was about three times greater than that without water for the same air gap. It was observed that changing the discharge gap from 1 to 5 mm led to a slight increase in power by only 15%. The water conductivity also influenced the power injected into the plasma only to a small extent. Thus, the variation in water conductivity over four orders of magnitude determined a fluctuation in discharge power of ±20%. [ABSTRACT FROM AUTHOR]

A two-step photon upconversion (TPU) solar cell is a single-junction solar cell with a suitably designed heterointerface in the intrinsic layer. At this interface, upconversion can take place by absorbing infrared light, which excites carriers to energies above the heterojunction barrier, and then an electric field extracts these upconverted carriers to the barrier material. In this work, we study this photoabsorption process in a TPU solar cell with a modulation-doped structure. The modulation doping technique enables us to control the electric field at the heterointerface, and we demonstrate that the efficiency of the TPU process strongly depends on the electric field at the heterointerface. While we show that the TPU process induced by infrared light leads to a significant increase in the external quantum efficiency, we also note that this TPU process is an adiabatic process. It is shown that the adiabatic intraband photoexcitation at the heterointerface is able to increase the open-circuit voltage even above the open-circuit voltage that we predict from the diode equation and the actual current increase. We demonstrate obvious voltage boost effects and elucidate the relationship between the current and voltage. [ABSTRACT FROM AUTHOR]

Harnessing detachment of an aqueous droplet via electrowetting on a flat surface has been of considerable interest for potential practical applications, ranging from self-cleaning to novel optical and digital microfluidic devices, due to the wettability of the droplet on a solid substrate enhanced by applying an electric voltage between the droplet and the insulated substrate. However, a quantitative understanding of the detachment process and an accurate prediction on the thresholds of applied voltage for droplet detachment on curved surfaces are still lacking. In this paper, based on energy conservation, we derive a critical condition theoretically for electrowetting-induced droplet detachment from a hydrophobic curved surface. Furthermore, phase diagrams are constructed in terms of droplet volume, viscosity, the Ohnesorge number, friction coefficient at contact line, surface curvature, surface wettability, and electrowetting number. The deduced critical condition offers a general and quantitative prediction on when the detachment occurs, a criterion enabling us to gain more insights into how to accurately manipulate the electrowetting-induced detachment of an aqueous droplet on a curved surface. The results obtained in this paper also imply that the detachable regimes of the phase diagrams can be enlarged through increasing droplet volume and surface curvature and reducing liquid viscosity, friction coefficient, the Ohnesorge number, and wettability of substrates. [ABSTRACT FROM AUTHOR]

Avalanche multiplication characteristics in a reverse-biased homoepitaxial GaN p–n junction diode are experimentally investigated at 223–373 K by novel photomultiplication measurements utilizing above- and below-bandgap illumination. The device has a non-punch-through one-side abrupt p–-n+ junction structure, in which the depletion layer mainly extends to the p-type region. For above-bandgap illumination, the light is absorbed at the surface p+-layer, and the generated electrons diffuse and reach the depletion layer, resulting in an electron-injected photocurrent. On the other hand, for below-bandgap illumination, the light penetrates a GaN layer and is absorbed owing to the Franz–Keldysh effect in the high electric field region (near the p–n junction interface), resulting in a hole-induced photocurrent. The theoretical (non-multiplicated) photocurrents are calculated elaborately, and the electron- and hole-initiated multiplication factors are extracted as ratios of the experimental data to the calculated values. Through the mathematical analyses of the multiplication factors, the temperature dependences of the impact ionization coefficients of electrons and holes in GaN are extracted and formulated by the Okuto–Crowell model. The ideal breakdown voltage and the critical electric field for GaN p–n junctions of varying doping concentration are simulated using the obtained impact ionization coefficients, and their temperature dependence and conduction-type dependence were discussed. The simulated breakdown characteristics show good agreement with data reported previously, suggesting the high accuracy of the impact ionization coefficients obtained in this study. [ABSTRACT FROM AUTHOR]

The recent developments in nanosecond pulsed power supplies facilitate the emission of high density electron bursts but their safe operation demands avoiding breakdowns. Using the theoretical and numerical modeling of the electron emission phenomena from a tip (micro-protrusion), the breakdown threshold (pre-breakdown) is analyzed considering it as the highest value of the voltage preserving the system out of the thermo-emission instability regime. However, the space charge that builds up in front of the tip limits the performance of these electron sources by decreasing the local electric field and consequently the thermo-field emission as well as the temperature of the emissive surface. Hence, it is found that the system can safely hold higher voltages (without breakdown) in the presence of dense space charge. In direct current, for a titanium elliptic tip, the highest operation voltage increases by about 15%, whereas for a tungsten hyperbolic tip, it increases by 70%. Remarkably, the emitted current close to the pre-breakdown voltage stays unchanged with or without taking into account the space charge. Surprisingly, when very short pulses (3 ns) are applied to a tungsten hyperbolic tip, the pre-breakdown voltage additionally increases by 30%, and the Coulomb screening, very effective in front of the tip apex, enlarges the electron emission area by 60%, releasing about 1.3 times more electrons compared to vacuum emission (without the space charge). Moreover, the ring effect, experimentally discovered by Dyke and Trolan [Phys. Rev. 89, 799 (1953)] on the radial electron density distribution, can be microscopically observed and understood with your model. [ABSTRACT FROM AUTHOR]

Despite the very different underlying physics of organic photovoltaics (OPVs), inorganic p-n junction's Shockley's diode equation is often applied to describe current density–voltage (JV) curves of OPVs. The model parameters, including the diode saturation current, diode ideality factor, series, and parallel resistances, are usually extracted and treated as constants in JV curve analyses. In this work, we develop a drift-diffusion bilayer interface (DD-BI) model for bilayer OPVs, which treats the donor–acceptor (D–A) heterojunction using the detailed balance between densities of polaron pairs, free electrons, and free holes. From the DD-BI model, we derive a diode equation, which is of Shockley's equation form, but each parameter is explicitly written in terms of the D–A interface properties. We call this model the self-consistent diode (SCD) model as it is consistent with the DD-BI results provided that the key parameters are from the simulation data. By studying the effects of light intensity and carrier mobility, we find that the Shockley SCD parameters are voltage dependent because of space charge accumulation around the D–A heterojunction. Our models are successful in explaining the common discrepancies in OPV JV curve analyses, such as the validity of fitting for series resistance, deviation of ideality factor from the theoretical values, and different resistance values under light and dark conditions. The results provide a better understanding of OPVs with a D–A heterojunction and how we can capture its physics using the SCD equation. [ABSTRACT FROM AUTHOR]

This paper deals with the investigation of the discharge in the solution of 0.9% NaCl in water for the conditions, when the voltage at the gap is in a vicinity of the so-called critical voltage at which the discharge in a thin vapor layer at the surface of active electrode appears. In the experiments, the critical voltage is at a level of (180–200) V. Most of the data correspond to powering the discharge by the bipolar voltage pulses of 5 s duration. The main attention is centered on the nonsteady (transient) processes and on the forms of the discharge operation. For the voltage pulses of negative polarity, when the metal electrode is the cathode, the discharge is sustained in the glow regime with the occasional glow-to-spark transitions. At the positive polarity of the voltage, the surface of liquid inside the vapor layer plays a role of cathode in the gas-discharge gap. In these conditions, the process of the glow-to-spark transition is suppressed and the discharge is sustained in the glow regime. [ABSTRACT FROM AUTHOR]

Besides the resonance frequency, the resonance strength is another key optical characteristic for metamaterials. In the present work, a theoretical model for the resonance strength is proposed, which has been numerically and experimentally verified by the fundamental and high-order resonances of metamaterials. Results show that the resonance strength is determined by the electric potential difference induced by incident waves and could be efficiently tuned by changing the polarized state of incident waves or the shape of resonant units. Interestingly, the fundamental resonance could be completely suppressed, and the maximum magnitude of the high-order resonance strength for a metamaterial also can be predicted with the model. Further simulated results indicated that, among different-shaped metamaterials, I-shaped metamaterials as a simpler structure can have a stronger resonance strength in both of the low-order and high-order resonances. It may inspire the design of metasurfaces based high-order resonances and may offer a powerful strategy for further optimizations of the performance of metamaterial-based devices. [ABSTRACT FROM AUTHOR]

In this paper, we developed a new dip-pen nanolithography (DPN) method. Using this method, we fabricated conductive nanowires with diameters of 30-50 nm on silicon substrates. To accomplish this, indium was transferred from an atomic force microscopy tip to the surface by applying a potential difference between the tip and substrate. The fabricated indium nanowires were several micrometers in length. Unlike thermal DPN, our DPN method hardly oxidized the indium, producing nanowires with conductivities from 5.7×10-3 to 4×10-2 Ω cm. [ABSTRACT FROM AUTHOR]

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