Threshold Electric Field Research Articles

Electric field induced buckling of inversion walls in lens-shape liquid crystal droplets

Lens-shaped liquid crystal samples have the potential for their use in tunable multifocal optical lenses. In previous observations (Phys. Rev. Research, 2, 023261 (2020) and J. Mol. Liq., 334, 116085 (2021)) plano-convex spherical lens-shaped liquid crystal sessile droplets were studied either in magnetic or AC electric fields, and the formation of an inversion wall (a one-dimensional soliton) moving toward the periphery was observed and explained.Here we present experimental observations of the structure of plano-convex lens-shaped nematic liquid crystal droplets subjected to simultaneous competing magnetic and electric fields. It is found that above a threshold electric field the initially straight defect wall buckles to form a zig-zag shape. This phenomenon is compared to those observed in sandwich cells with uniform thickness and the differences in their theoretical description are discussed.

Comparative study of pulsed breakdown processes and mechanisms in self-triggered four-electrode pre-ionized switches

This work investigates the pulsed breakdown processes and mechanisms of self-triggered pre-ionized switches with a four-electrode structure in nitrogen through intensified charge coupled device photographs. The diameter of the trigger plane hole mainly determines the switch’s electric field distribution. Two configurations with minimum and maximum trigger plane holes are adopted for comparison. In the switch with a minimum trigger plane hole, the maximum electric field distributes at the surfaces of the main electrodes. Although charged particles in the triggering spark channel cannot drift out, homogeneous discharges can be stimulated from both the cathode and anode surfaces through ultraviolet illumination. Two sub-gaps are likely to break down simultaneously. In the switch with a maximum trigger plane hole, the maximum electric field locates near the trigger electrodes. Discharges in both sub-gaps initiate from the trigger electrodes in the form of a positive or negative streamer. Due to the lower breakdown voltage and electric field threshold for discharge initiation, the cathode side sub-gap breaks down first. The analysis of two extreme examples can be referenced in the future design and improvement of self-triggered four-electrode switches with different trigger electrode structures.

Sub-MHz bursts of nanosecond pulses excite neurons at paradoxically low electric field thresholds without membrane damage

Neuromodulation applications of nanosecond electric pulses (nsEP) are hindered by their low potency to elicit action potentials in neurons. Excitation by a single nsEP requires a strong electric field which injures neurons by electroporation. We bypassed the high electric field requirement by replacing single nsEP stimuli with high-frequency brief nsEP bursts. In hippocampal neurons, excitation thresholds progressively decreased at nsEP frequencies above 20–200 kHz, with up to 20–30-fold reduction at sub-MHz and MHz rates. For a fixed burst duration, thresholds were determined by the duty cycle, irrespective of the specific nsEP duration, rate, or number of pulses per burst. For 100-μs bursts of 100-, 400-, or 800-ns pulses, the threshold decreased as a power function when the duty cycle exceeded 3–5 %. nsEP bursts were compared with single “long” pulses whose duration and amplitude matched the duration and the time-average amplitude of the burst. Such pulses deliver the same electric charge as bursts, within the same time interval. High-frequency nsEP bursts excited neurons at the time-average electric field 2–3 times below the threshold for a single long pulse. For example, the excitation threshold of 139 ± 14 V/cm for a single 100-μs pulse decreased to 57 ± 8 V/cm for a 100-μs burst of 100-ns, 0.25-MHz pulses (p < 0.001). Applying nsEP in bursts reduced or prevented the loss of excitability in multiple stimulation attempts. Stimulation by high-frequency nsEP bursts is a powerful novel approach to excite neurons at paradoxically low electric charge while also avoiding the electroporative membrane damage.

Pulsewidth Control of Nonlinear GaAs Photoconductive Semiconductor Switch

The nonlinear gallium arsenide photoconductivity semiconductor switch (GaAs PCSS) can generate high-voltage and strong current electrical pulses with low light triggering at the order of microjoule. Due to the lock-on effect of the GaAs PCSS, the output pulsewidth is usually on the order of hundreds of nanoseconds or even tens of microseconds. This severely limits the application of nonlinear GaAs PCSS. This article presents the output pulsewidth modulation of nonlinear GaAs PCSS through the dual regulation of energy-storage capacitance and current-limiting resistance. When triggered by a pulse laser with a width of 10 ns and a single pulse energy of 200 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{J}$ </tex-math></inline-formula> , the switch can output the minimum pulsewidth of 6.3 ns and the maximum pulsewidth of 196 ns. In the meantime, combined with the theoretical analysis of photon-activated charge domain (PACD), the electric field intensity of nonlinear GaAs PCSS is less than the threshold electric field of PACD, and the switch will be turned off quickly so that different pulsewidths can be output. The experimental results indicate that adding different current-limiting resistances and energy-storage capacitance in the circuit can control the electric field intensity so that different pulsewidths can be output.

Charging and Discharging Current Characteristics of Polypropylene Film under Varied Electric Fields

Charging and discharging current behavior under high DC electric field in polypropylene (PP) film is closely related to the charge transport and accumulation process, which has an important effect on the electrical insulating properties of PP. In this paper, the dependence of the charging and discharging current of polypropylene films on time and electric field has been comprehensively studied. The results showed that the transient and steady current values of the charging and discharging process increase with the increase of electric field. Dependence of the charging current on the electric field conformed well to the space charge limited current (SCLC) theory with a transition electric field of 270 kV/mm, at which the charge transport changed from ohmic conduction to SCLC conduction. The carrier mobility derived from the discharging current became significantly smaller with increase of the charging electric field. The charge accumulation after discharging was derived from the integration of the difference of the charging and discharging current and it showed an increase with the electric field and increased sharply above a certain threshold electric field (the same as the transition electric field in SCLC theory). It was proved that the conduction current and charge accumulation evolution and dependence on the electric field were mainly determined by the balance between the electrode charge injection process and the bulk conduction process.

Optical readout of moisture in sand employing bipolar electrochemistry

The fast and wireless estimation of moisture in sand and other bulk materials usually requires high-tech instrumentation and computation. To overcome the complexity of such systems, we have employed bipolar electrochemistry as a fast, straightforward, and cost-effective method to wirelessly produce an optical signal. An electric field generated across moist sand is used to polarize an immersed light-emitting diode (LED), triggering an electrochemical reaction and causing a current to flow. Therefore, the bipolar activation of the LED by a threshold electric field creates an optically readable moisture sensor. The light emission intensity depends on two factors: the amount of moisture and the salt concentration. As two stimuli control the light emission, the signal can be considered as an AND logic gate, which is expected to open possibilities in wireless and user-friendly moisture sensors.

The role of catechin in electroporation of pancreatic cancer cells – Effects on pore formation and multidrug resistance proteins

Catechin is a bioflavonoid known for its anti-cancer properties. In the present study, we combined theoretical and experimental approaches to reveal the potential of catechin application in the electroporation (EP) or electrochemotherapy (ECT) of pancreatic cancer cells. The molecular dynamics simulations were implemented to examine the interactions of catechin with a model of a membrane, its influence on the membrane’s thickness, and the impact of the catechin-membrane interaction on the pore formation. The data were confronted with experimental measurement of the threshold electric field required for permeabilization of pancreatic cancer cells to a fluorescent dye YO-PRO-1. Further, we examined the influence of catechin on cell viability following electroporation with cisplatin or calcium ions. Finally, we investigated the catechin impact on four proteins associated with multidrug resistance: P-glycoprotein, MRP1, BCRP, and LRP. We demonstrated that catechin may boost the effects of electroporation through various mechanisms: i) increasing the cell permeability prior to electroporation ii) increasing the electroporation threshold iii) sensitization of cells to chemotherapeutic compounds. We showed that catechin incubation influences mRNA levels and mitigates the immunoreactivity of Pgp, MRP1, BCRP, and LRP but these changes did not translate to the efficacy of electrochemotherapy.

Electric Switching Behaviors and Dielectric Relaxation Properties in Ferroelectric, Antiferroelectric, and Paraelectric Smectic Phases of Bent-Shaped Dimeric Molecules.

This study reports the electric switching behaviors and dielectric properties of the ferroelectric smectic-A (SmAPF), anti-ferroelectric smectic-A (SmAPA), anti-ferroelectric SmCAPA, and smectic-A (SmA) phases formed by mixing the bent-shaped dimeric molecules, α,ω-bis(4-alkoxyanilinebenzylidene-4'-carbonyloxy)pentanes. These four phases each show characteristic features. The SmAPF shows a low threshold electric field for ferroelectric switching and a large dielectric strength due to the collective fluctuation mode of dipoles at around 500 Hz. Both the threshold electric field and dielectric strength are strongly dependent on the cell thickness. The threshold field decreases to 0.1 V μm-1, and the dielectric strength increases up to a huge value of 10,000 as the cell thickness increases up to 80 μm. The SmAPA also shows a similar collective mode at around 2 kHz with a relatively small dielectric strength (around 200), which may be induced by the anti-phase rotation of dipoles in adjacent layers. In these collective modes, the dielectric strength is found to be inversely proportional to the switching threshold field. On the other hand, another anti-ferroelectric SmCAPA as well as the paraelectric SmA show only the non-collective mode (i.e., rotational relaxation of individual molecules around their short axes) at a high frequency of around 100 kHz.

The degradation of silicone rubber composites with ZnO microvaristors under impulse voltage

In this study, the degradation behavior of silicone rubber (SiR) composites with ZnO microvaristors under impulse voltage was investigated. Typical impulse voltages with different amplitudes were applied to the samples, and the degraded threshold electric field (E b) and nonlinear coefficient (α) of the samples were obtained by conductivity test after every impulse was applied. Scanning electron microscope and energy dispersive spectroscopy were used to characterize the micro performance of the samples. The failure of the SiR composites was found to be attributed to the aging behavior in the microstructure of ZnO microvaristors, which was divided into four stages caused by the precipitation of Bi2O3 and the dissipation of the honeycomb grain-boundary structure. The mechanism of degradation was internal local heat accumulation and damage of the microelement caused by the thermal stress, generated by impulse voltage. This work is helpful to develop smart compositematerials with self-adaptive capability to control high electrical field and increasethe stability and durability of power apparatus and electronic devices.

Tunable optical bistability based on Bloch surface waves in one-dimensional photonic crystal with graphene

Graphene possesses large nonlinear conductivity in terahertz region, which makes it a very promising material for nonlinear bistable devices. In this paper, we theoretically study the optical bistability (OB) of reflected beam in a multilayer structure with graphene embedded between the truncated layer and the substrate. The Bloch surface wave excited by the one-dimensional photonic crystal (1D PC) coupling structure significantly enhances the local electric field near the nonlinear graphene, which provides a positive condition for the realization of low-threshold OB. Through parameter optimization, we obtain a threshold electric field with an incident electric field of 105 V/m levels. Furthermore, the influences of graphene’s Fermi energy and relaxation time, as well as those of the incidence angle, on the hysteretic behavior and the threshold of OB are clarified. This approach may provide a feasible scheme for the nonlinear optical bistable devices.

Pseudo-polar order in the tilted smectic phases of bent-core hockey stick shaped molecules

ABSTRACT We discuss the liquid crystal phases of a compound consisting of bent-core hockey-stick-shaped molecules. The compound exhibits two smectic phases with an in-plane pseudo-polar order in addition to the tilt order in the layers. The transverse shape anisotropy and dissimilar arm lengths of these bent-core molecules stabilise these pseudo-polar tilted smectic phases. The higher temperature smectic phase has an anti-clinic organisation of the molecules in successive layers. An intermediate organisation between the synclinic and anti-clinic structures is found in the lower temperature smectic phase. We have developed a simple phenomenological model to account for these phases. In the higher temperature smectic phase, a field-induced Freedericksz type transition is observed beyond a threshold electric field. We also account for this field-induced transition using our theoretical model.

Low threshold optical bistability based on topological edge state in photonic crystal heterostructure with Dirac semimetal.

The special band structure of three-dimensional Dirac semimetal (3D DSM) makes it show strong nonlinear optical characteristics in the terahertz region, which provides a new way to develop terahertz nonlinear devices with low threshold. In this paper, we theoretically study the optical bistability (OB) of transmitted light in a multilayer structure with 3D DSM embedded in two one-dimensional photonic crystals (1D PhC). The topological edge state (TES) excited by the 1D PhC heterostructure significantly enhances the local electric field near the nonlinear 3D DSM, which provides a positive condition for the realization of low threshold OB. Through parameter optimization, we obtain a threshold electric field with an incident electric field of 106 V/m levels. Furthermore, the influences of the Fermi energy and thickness of 3D DSM and the angle of the incident light on the hysteretic behavior as well as the threshold of OB are clarified. 3D DSM-based optical devices with intrinsic OB provide a building block for future integrated optical and all-optical networks.

Lethal Electric Field Thresholds for Cerebral Cells With Irreversible Electroporation and H-FIRE Protocols: An In Vitro Three-Dimensional Cell Model Study

The lethal electric field (LEF) thresholds for three typical cerebral cells, including a malignant glioblastoma (GBM) cell line and two cell lines from the healthy blood-brain barrier (BBB), treated by irreversible electroporation (IRE) or high-frequency irreversible electroporation (H-FIRE) protocols were investigated in an in vitro three-dimensional (3D) cell model. A conventional IRE protocol (90 pulses, 1 Hz, and 100-μs pulse duration) and three novel H-FIRE protocols (1-3-1, 0.5-1-0.5, and 1-1-1) were used to treat the cerebral cells in both 3D single-cell and two-cell models. The electrical conductivity of the 3D cell model under different electric field strengths were characterized with the method of electrochemical impedance spectroscopy (EIS). Based on EIS, a numerical electrothermal model of electroporation was built for the determination of the LEF threshold with different protocols and temperature monitoring. Cell viability was assessed by fluorescence staining 6 h after the treatment. The results showed no thermal lethal effect on cells when these protocols were used. The LEF threshold for GBM cells was significantly lower than that of the healthy BBB cells. These results suggest the possibility of selective ablation of human cerebral GBM by IRE and H-FIRE treatments with no injury or reversible injury to healthy cells, and the potential use of IRE or H-FIRE for transient disruption of the BBB to allow chemotherapy to reach the tumor.

Numerical and Experimental Investigation of the Effects of Dimensional Parameters on Carbon-Nanotube-Coated Copper Plasma Limiter

The plasma limiter (PL) is a suitable method to protect electronic devices from high-power electromagnetic pulses. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> -band PL has target specifications of 100 kW of power handling capability, < 100 ns of response time, and < 0.5 dB of insertion loss. Carbon nanotube (CNT) can be used to reduce power losses and instrument corrosion under frequent electromagnetic attacks. This article used CNT-coated copper needles in a PL to increase the electric field for the rapid breakdown process. Furthermore, the impact of dimensional parameters (needle’s length, needle’s radius, and axial displacement of the needles) were investigated. The experiment was conducted at 1800 W of peak power and 25 ns of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> -band (2.45 GHz) microwave duration. In this case, the height of 19 mm and diameter of 1 mm were found to be the optimal needle parameters, in which the fastest breakdown of the electric field is available. The finite-element method was used by CST software to verify the experiment results. The transmission losses were < 5% in the normal state. The breakdown electric field threshold was ~431 kV/m near the atmospheric pressures. There was an error of < 1.28 in the case with the lowest compatibility.

Numerical mesoscale tissue model of electrochemotherapy in liver based on histological findings

Electrochemotherapy (ECT) and irreversible electroporation (IRE) are being investigated for treatment of hepatic tumours. The liver is a highly heterogeneous organ, permeated with a network of macro- and microvasculature, biliary tracts and connective tissue. The success of ECT and IRE depends on sufficient electric field established in whole target tissue; therefore, tissue heterogeneity may affect the treatment outcome. In this study, we investigate electroporation in the liver using a numerical mesoscale tissue model. We numerically reconstructed four ECT experiments in healthy porcine liver and computed the electric field distribution using our treatment planning framework. We compared the computed results with histopathological changes identified on microscopic images after treatment. The mean electric field threshold that best fitted the zone of coagulation necrosis was 1225 V/cm, while the mean threshold that best fitted the zone of partially damaged liver parenchyma attributed to IRE was 805 V/cm. We evaluated how the liver macro- and microstructures affect the electric field distribution. Our results show that the liver microstructure does not significantly affect the electric field distribution on the level needed for treatment planning. However, major hepatic vessels and portal spaces significantly affect the electric field distribution, and should be considered when planning treatments.

Thickness effect on threshold electric field of ZnO microvaristors/silicone rubber composite with nonlinear conductivity

As a functional material, ZnO microvaristors/silicone rubber composite, with nonlinear conductivity, will be manufactured to different thicknesses for different applications. However, few study focuses on the thickness effect of the composite. In this paper, ZnO/SiR composites with thickness from 50 μm to 2800 μm were prepared. The conductivity results show that the threshold electric field (Eb) of the composites increases from 40 V/mm to a stable value (more than 1000 V/mm) as the thickness increases. A simulation model based on the Voronoi network was carried out to explore the mechanism. For the thickness close to the diameter of fillers, the key element determining Eb is the microstructural nonuniformity of electrical characteristics of microvaristors. As the sample becomes thick, the increasingly tortuous conduction path is considered to trigger off the increase of Eb. The thickness effect discussed in this paper will be helpful in designing electrostatic discharge elements in electronic devices.

Modeling Methods for Treatment Planning in Overlapping Electroporation Treatments.

Irreversible electroporation (IRE) is a non-thermal tissue ablation therapy which is induced by applying high voltage waveforms across electrode pairs. When multiple electrode pairs are sequentially used, the treatment volume (TV) is typically computed as the geometric union of the TVs of individual pairs. However, this method neglects that some regions are exposed to overlapping treatments. Recently, a model describing cell survival probability was introduced which effectively predicted TV with overlapping fields in vivo. However, treatment overlap has yet to be quantified. This study characterizes TV overlap in a controlled in vitro setup with the two existing methods which are compared to an adapted logistic model proposed here. CHO cells were immobilized in agarose gel. Initially, we characterized the electric field threshold and the cell survival probability for overlapping treatments. Subsequently, we created a 2D setup where we compared and validated the accuracy of the different methods in predicting the TV. Overlap can reduce the electric field threshold required to induce cell death, particularly for treatments with low pulse number. However, it does not have a major impact on TV in the models assayed here, and all the studied methods predict TV with similar accuracy. Treatment overlap has a minor influence in the TV for typical protocols found in IRE therapies. This study provides evidence that the modeling method used in most pre-clinical and clinical studies seems adequate.

Microwave breakdown of sub-atmospheric argon gas in the vicinity of a microgap

The microwave electric field at breakdown for argon gas in a microgap (generally, gap size &amp;lt;1 mm) over a wide range of pressures and gap sizes was found to exhibit two behavioral pressure regimes. A high microwave electric field was established in the gap of a re-entrant mode resonator. By slowly raising the microwave electric field level, a breakdown level is reached where impact ionization induces low pressure argon gas to breakdown preferentially outside of the gap. At high pressure, breakdown is found to occur preferentially inside the gap, but only after the pressure is high enough for impact ionization to produce breakdown there. Impact ionization has a lower threshold electric field than the boundary-controlled processes, such as secondary electron emission, that would eventually produce breakdown inside the microgap if impact ionization did not occur first. Thus, the lower pressure regime is characterized by breakdown outside of the gap, while in the high-pressure regime, breakdown occurs inside the gap, in both cases by impact ionization. The transition pressure PT between these two pressure regimes depends on the gap size dgap, roughly as PT ∝ dgap−2. Consistent with the model developed here, this corresponds to the full-amplitude of electron oscillation in the gap field being commensurate with the gap size.

MoS2 nanosheet arrays grown on Mo foils for high-performance field emission

Free-standing molybdenum disulfide (MoS2) nanosheets with different morphologies on molybdenum (Mo) foil were synthesized through hydrothermal method using thiourea as the sulphur source and Mo foil as the Mo source. The effect of the concentration of thiourea in the reaction solution on the morphology and field emission (FE) properties of MoS2 nanosheets were investigated. The vertically aligned MoS2 nanosheets exhibit a low turn-on (∼1.90 V/μm) and threshold electric field (∼2.51 V/μm), along with good emission stability. The results are attributed to the high geometrical field enhancement factor (∼1979) and the sturdy structure of the MoS2 grown on highly conductive Mo substrate.

Estimating the Switching phenomenon for Se98Te2 and Se96Te2X2 (X=Zn or Cd) Chalcogenide glasses.

The switching behavior was investigated for Se98Te2 and Se96Te2X2 (X= Zn or Cd) Chalcogenide glasses in thin film form. The thermal evaporation process was used for the preparation of the film samples. I−V curves were investigated in the thickness range (200-670 nm) and temperature range (293-318 K). The I−V curves show a memory switch. The values of threshold voltage (Vth) found to decrease with the addition of Zn and Cd to Se98Te2 respectively. Also, the threshold voltage (Vth) values decrease exponentially with increasing temperature and increase with thickness. The ratio between the threshold voltage activation energy Δεth and dc electrical activation energy ΔEσ for the studied compositions suggests the explanation of the switching process by the electrothermal model. The threshold electric field Eth values were obtained and show an inverse relation with temperature for our studied system. The effect of Cd and Zn addition to Se98Te2 on the obtained parameters was also explained.