High-intensity Electric Fields Research Articles

Metal whisker growth induced by localized, high-intensity DC electric fields

ABSTRACTIn this work, a very high, locally applied electric field was used to induce whisker nucleation on an Sn film. The field was generated by using a conductive AFM tip and applying a voltage bias between the sample and the conductive cantilever. The tip-sample separation distance was thus controllable, and any dielectric breakdown could be avoided. At locations where the AFM tip was positioned for an extended period, minuscule whiskers were observed, whose growth direction matched vertical orientation of the field.

Gallium Phosphide-on-Silicon Dioxide Photonic Devices

The development of integrated photonic circuits utilizing gallium phosphide requires a robust, scalable process for fabrication of GaP-on-insulator devices. Here, we present the first GaP photonic devices on SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The process exploits direct wafer bonding of a GaP/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> P/GaP heterostructure onto a SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -on-Si wafer followed by the removal of the GaP substrate and the Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> P stop layer. Photonic devices such as grating couplers, waveguides, and ring resonators are patterned by inductively coupled-plasma reactive-ion etching in the top GaP device layer. The peak coupling efficiency of the fabricated grating couplers is as high as -4.8 dB. Optical quality factors of 20 000 as well as second- and third-harmonic generation are observed with the ring resonators. Because the large bandgap of GaP provides for low two-photon absorption at telecommunication wavelengths, the high-yield fabrication of GaP-on-insulator photonic devices enabled by this work is especially interesting for applications in nanophotonics, where high quality factors or low mode volumes can produce high electric field intensities. The large bandgap also enables integrated photonic devices operating at visible wavelengths.

Ultrafast Pulse Generation in an Organic Nanoparticle-Array Laser.

Nanoscale coherent light sources offer potentially ultrafast modulation speeds, which could be utilized for novel sensors and optical switches. Plasmonic periodic structures combined with organic gain materials have emerged as promising candidates for such nanolasers. Their plasmonic component provides high intensity and ultrafast nanoscale-confined electric fields, while organic gain materials offer fabrication flexibility and a low acquisition cost. Despite reports on lasing in plasmonic arrays, lasing dynamics in these structures have not been experimentally studied yet. Here we demonstrate, for the first time, an organic dye nanoparticle-array laser with more than a 100 GHz modulation bandwidth. We show that the lasing modulation speed can be tuned by the array parameters. Accelerated dynamics is observed for plasmonic lasing modes at the blue side of the dye emission.

Laser damage resistance of polystyrene opal photonic crystals

The laser damage behavior of three-dimensional photonic crystals (3D-PCs) with an opal structure is investigated using both experimental and simulation methods. Polystyrene (PS) colloidal crystals films with a reflection peak at 1064 nm are used as the model material. Disordered films (DF) are fabricated with PS microspheres as contrast samples. The laser-induced damage threshold (LIDT) of 3D-PCs is tested, which is as 2.35 times high as the LIDT of DF. All laser damages are derived from defects in 3D-PCs, implying that the LIDT of ideal 3D-PCs will be significantly increased. The simulation results show that the electric field is contained in the pores of 3D-PCs while it is reduced in the PS microspheres, which may decrease the absorption of laser energy by 3D-PCs. In contrast, the electric field distribution is irregular in DF. Enhanced electric field areas are located in both the pores and microspheres of DF. Considering higher electric field intensity causes more energy absorption and higher temperature, the DF have a lower LIDT. The 3D-PCs structure uses ordered vacancy to contain and strike back laser energy and can increase the LIDT without changing the chemical composition of materials.

Simultaneous Detection of Two Chemicals Using a TE20-Mode Substrate-Integrated Waveguide Resonator.

Microwave resonators working as sensors can detect only a single analyte at a time. To address this issue, a TE20-mode substrate-integrated waveguide (SIW) resonator is exploited, owing to its two distinct regions of high-intensity electric fields, which can be manipulated by loading two chemicals. Two microfluidic channels with unequal fluid-carrying capacities, engraved in a polydimethylsiloxane (PDMS) sheet, can perturb the symmetric electric fields even if loaded with the two extreme cases of dielectric [ethanol (E), deionized water (DI)] and [deionized water, ethanol]. The four layers of the sandwiched structure considered in this study consisted of a top conductive pattern and a bottom ground, both realized on a Rogers RT/Duroid 5880. PDMS-based channels attached with an adhesive serve as the middle layers. The TE20-mode SIW with empty channels resonates at 8.26 GHz and exhibits a −25 dB return loss with an unloaded quality factor of Q ≈ 28. We simultaneously load E and DI and demonstrate the detection of the four possible combinations: [E, DI], [DI, E], [E, E], and [DI, DI]. The performance of our proposed method showed increases in sensitivity (MHz/εr) of 7.5%, 216%, and 1170% compared with three previously existing multichannel microwave chemical sensors.

Magnetic Dipole Resonance and Coupling Effects Directly Enhance the Raman Signals of As-Grown Graphene on Copper Foil by over One Hundredfold

Large-area graphene is commonly prepared through chemical vapor deposition (CVD); in situ and nondestructive methods for its characterization are desirable. In this paper, we demonstrate a practical method—exploiting magnetic dipole resonance and coupling effects—with which the Raman signals of graphene on copper (Cu) foil can be directly, faithfully, and greatly enhanced. The magnetic dipole resonance of a silicon nanoparticle (SiNP) can effectively couple its electromagnetic field with the Cu foil to induce an enormous electric field located solely at the position of the SiNP on the graphene. The coupled electromagnetic field can lead to hot spots of high electric field intensity (E2/E02 = 123.2) within the graphene. Even when we positioned only a few SiNPs upon the graphene/Cu foil, we obtained a Raman signal enhancement (ca. 206 times) much greater than that of graphene transferred onto a 300 nm oxide film (ca. 12 times). From a series of experiments comparing the Raman signals of graphene before and ...

Heat transport in electrically aligned multiwalled carbon nanotubes dispersed in water

A modified Ångström method was used to determine the thermal diffusivity and thermal conductivity of aqueous dispersions of multiwalled carbon nanotubes as a function of their weight fraction concentration and in the presence of an externally applied electric field. Measurements were performed in planar samples, with a fixed thickness of 3.18 mm applying an AC voltage in the range from 0 to and for concentrations of carbon nanotubes from 0 to 2 wf%. It is shown that this field induces the formation of clusters followed by their alignment along the electric field, which can favor heat transfer in that direction. Heat transfer measurements show two regimes, in the first one under 0.5 wf%, voltages lower than are not strong enough to induce the adequate order of the carbon nanostructures, and as a consequence, thermal diffusivity of the dispersion remains close to the thermal diffusivity of water. In contrast for higher concentrations (above 1.5 wf%), are enough to get a good alignment. Above such thresholds of concentrations and voltages, thermal diffusivity and conductivity increase, when the electric field is increased, in such a way that for an applied voltage of and for a concentration of 1.5 wf%, an increase of 49% of the thermal conductivity was obtained. It is also shown that this approach exhibits limits, due to the fact that the electric-field induced structure, can act as a heating element at high electric field intensities and carbon nanotubes concentrations, which can induce convection and evaporation of the liquid matrix.

Electric field numerical simulation of disc type electrostatic spinning spinneret

Electrospinning is a new type of free-end spinning built on electric field. Different from traditional single needle spinneret, in this study, a new disc type free surface spinneret is used to produce multiple jets, this will greatly improve production efficiency of nanofiber. The electric-field distribution of spinneret is the crux of the formation and trajectory of jets. In order to probe the electric field intensity of the disc type spinneret, computational software of Ansoft Maxwell 12 is adopted for a precise and intuitive analysis. The results showed that the whole round cambered surface of the spinning solution at edge of each layer of the spinneret with the maximum curvature has the highest electric field intensity, and through the simulation of the electric field distribution of different spinneret parameters such as layer, the height and radius of the spinneret. Influences of various parameters on the electrostatic spinning are obtained.

Immunogenic and structural properties of ovalbumin treated by pulsed electric fields

ABSTRACTIn this study, the immunogenic and structural properties of ovalbumin (OVA) induced by pulsed electric fields (PEF) treatment were investigated. The immunogenic properties were estimated by the IgG and IgE binding abilities, which were determined by enzyme-linked immunosorbent assay (ELISA) using rabbit polyclonal antibodies and egg-allergy patients’ sera, respectively. The structural changes were monitored by circular dichroism (CD), ultraviolet absorption, and fluorescence spectroscopy. When the OVA samples were treated at low electric field intensity (below 25 kV/cm, for 180 μs) or for short time (less than 60 μs, at 35 kV/cm), the IgG and IgE binding capacities gradually increased due to the partial unfolding of OVA. This was reflected in the increase in free SH content, surface hydrophobicity, and UV absorption. However, when the OVA samples were treated at high electric field intensity (exceeding 25 kV/cm, for 180 μs) or for long time (more than 60 μs, at 35 kV/cm), the IgG and IgE binding abilities significantly reduced due to the aggregation of OVA. This was also reflected in the decrease in free SH content, surface hydrophobicity, and UV absorption. Moreover, high-intensity PEF treatment caused a loss of the α-helix structure. The results showed that the largest decrease in the immunogenic properties was observed at 35 kV/cm for 180 μs. Therefore, PEF processing has the potential for utilization as a method for egg desensitization.

Controlled chaos: Heterogeneous catalysis

A technique for controlling the catalytic process using the impact on heterogeneous catalyst capable of staying in at least two conformational states has been described. The distinctive feature of conformers is their topological difference in the region of space of no less than 1 nm3. Binding of ligands or the presence of high intensity electric field makes it possible to change in a specified way the catalyst affinity to reaction’s substrates/products.

Numerical study on the effect of EHD flow on mass transfer of gas mixtures

PurposeThe paper aims to discuss the mass transfer of gas mixtures under the influence of electrohydrodynamic (EHD) flow induced by direct current (DC) corona discharge of wire-to-plane electrode, using a coupled numerical model.Design/methodology/approachA coupled numerical method is developed in this paper. Lattice Boltzmann model of binary gas mixtures coupled with the Coulomb force as an external force is introduced to predict the gas flow and species transport affected by EHD flow. Meanwhile, the distributions of electric field and space charge density during DC corona discharge are obtained using the finite difference method and the method of characteristics.FindingsThe numerical results of mass transfer effected by EHD flow reveal that the high electric field intensity is observed near the surface of corona wire, which causes the higher Coulomb force to form the EHD flow pattern of anticlockwise vortex. The EHD vortex flow plays a considerable role in the mass transport enhancement of gas species emit from the plane electrode, and the significant difference of the local Sherwood number is presented along the direction parallel to plane electrode. In addition, the enhance effectiveness with the different applied voltage is assessed, and the influencing mechanism of enhancement is investigated in this work.Originality/valueThe proposed numerical model will be useful in the study of mass transfer and fluid flow effected by EHD.

The use of optical coherence tomography for the evaluation of textural changes of grapes exposed to pulsed electric field

Application of pulsed electric fields (PEF) to food is a nonthermal technology of food processing. The short pulses of high intensity electric field can modify the internal structures of fruits and vegetables by affecting the cell permeability. In the presented study three popular grape wine cultivars – Johanniter, Hibernal and Marechal Foch were exposed to PEF at electric field strengths of 3.3kV/cm and 5kV/cm. The significant textural changes of near peel grape layers influenced by electric field were observed in optical coherence tomography (OCT) images, using infrared light of 1300nm. These changes were expressed by the variation of entropy, standard deviation or lacunarity features and evaluated in a dedicated software tool developed by the authors in Matlab environment. The OCT is a non-destructive technique in which no sample preparation is needed and grapes still remain intact (undamaged) during imaging. The OCT cross-sections revealed the progressive process of expanding zone with strong echo in sub-peel layers what may indicate cell permeabilization or even loosing parenchyma cells integrity. Also grape surface deformations under PEF were quantified. It has been shown that the values of considered textural features in near peel grape tissue were related to the intensity of electric field. Marechal Foch cultivar appeared to be more resistant to PEF than two other grape varieties.

Continuous-frequency measurements of high-intensity microwave electric fields with atomic vapor cells

We demonstrate continuous-frequency electric field measurements of high-intensity microwaves via optical spectroscopy in a small atomic vapor cell. The spectroscopic response of a room-temperature rubidium atomic vapor in a glass cell is investigated and employed for absolute measurements of Ka-band microwave electric fields from ∼200 V/m to &amp;gt;1 kV/m over a continuous frequency range of ±1 GHz (15% band coverage). It is established that in strong microwave fields, frequency-specific spectral features allow for electric field measurements over a large continuous frequency range.

Study on antenna radiation electric field and coupling of microwave heating asphalt mixtures

ABSTRACTA single-antenna radiation electric field model and a radiation coupling electric field model between antennas are established to study the impacts of coupling on antenna radiation electric field during the microwave heating of asphalt mixtures. Radiation electric and temperature fields are simulated. Results show that the electric and temperature fields are not uniformly distributed when asphalt mixtures are heated with a single antenna. Two symmetrical regions with fairly high electric field intensities exist on the surface of the asphalt mixture. The temperature field of the asphalt mixture follows an elliptical distribution, with the temperature reaching maximum value at the centre and decreases away from the centre. The electric and temperature fields are large at the separatrix of the antennas when the asphalt mixture is heated with the coupling antennas with no gap between the antennas. Moreover, the electric and temperature fields of the asphalt mixtures have poor distribution uniformity. Maintaining certain antenna spacing can improve the uniformity of field distribution.

Microwave fluidized bed for biomass pyrolysis. Part I: Process design

AbstractThe production of bio‐oils from microwave pyrolysis has received increasing attention from bioenergy researchers, but no studies reported to date have proposed reliable solutions to avoid thermal runaway. The motivation of this paper is to develop and demonstrate a systematic methodology to exploit the benefits of microwave heating for biomass pyrolysis, and to overcome previously reported challenges of heating heterogeneity and thermal runaway. The multidisciplinary design methodology for a microwave fluidized bed system is presented, which is based on processing raw biomass without the need for added microwave susceptors. The design process considers the minimum fluidizing velocity of biomass particles, a heat‐transfer model to establish the power density requirements, and electromagnetic simulations to determine the optimal dimensions. It was found that a minimum power density of 54 MW m−3 was necessary to reach temperatures of 400 °C for particles with an average size of 600 µm at the minimum fluidization velocity (0.38 m s−1). Higher gas velocities required higher power levels; however, the energy efficiency of the process could be improved when using a high power at low gas velocities, with 1.07 kJ g−1 attainable at power densities in excess of 100 MW m−3. A microwave fluidized bed system was subsequently designed, and shown to be effective in enabling pyrolysis whilst limiting heterogeneity and thermal runaway effects. Thermal runaway could be controlled by ensuring an appropriate fluidization regime to prevent liquid condensation and solid deposition within areas of high electric field intensity. The developed design opens opportunities for large‐scale production of bio‐oil using microwaves. © 2017 Society of Chemical Industry and John Wiley &amp; Sons, Ltd

Factors that increase the electric field of the dielectric barrier ozone generators

The dielectric barrier discharge cell (DBDC), also called ozone cell, is the main component of the ozone generators widely used. When the cell is powered with a high voltage value (> 5 kV) in the dielectric gas, arises a high intensity electric field that influences ozone generation processes by silent discharge also called dielectric barrier discharge. The intensity of the electric field depends by a number of factors such as the constructive form of the cell, the cell sizes, the value and the waveform of the supply voltage, the type of insulators used as dielectric barrier. The insulators which constituting the dielectric barrier, influence the intensity of the electric field through the dielectric constant of the liquid or solid shows the values of intensity electrical fields from ozone cells, with plane electrodes and ozone cells with cylindrical electrodes. The paper presents a graphic variation of the electric field from the gap and the dielectric barrier of cells with plane electrodes and cylindrical collinear electrodes. Experimental research highlights current-voltage characteristic for several types of dielectrics. Distilled water was highlighted as dielectric with the best results.

Effects of Ohmic Heating, Including Electric Field Intensity and Frequency, on Thermal Inactivation of Bacillus subtilis Spores

Methods for microbial inactivation are important in the food industry; however, conventional external heating (CH) reduces food quality. Accordingly, the nonthermal effects of ohmic heating (OH) on Bacillus subtilis spores in a sodium chloride aqueous solution at 101°C (i.e., the boiling point), as well as the effects of electric field intensity and frequency during OH, were investigated. Survival kinetics were compared between OH and external CH. The inactivation effect on B. subtilis was greater for all electric field conditions (5, 10, and 20 V/cm) than for CH. In particular, 20 V/cm showed a significantly higher inactivation effect (P < 0.05) on B. subtilis than those of CH at 8, 10, 12, 14, and 16 min. The survival data were fitted to various primary kinetic models. In the Weibull model and the log-linear model, there were significant differences (P < 0.05) in the rate parameters δ and kmax between OH at 20 V/cm and CH. However, there were no significant differences (P > 0.05) in survival kinetics between 20, 40, and 60 kHz; B. subtilis spores were inactivated more efficiently as the frequency increased. B. subtilis spores were almost completely inactivated at 14 to 16 min for the 60-kHz treatment, but spores were still alive at 20 and 40 kHz for the same treatment times. These results demonstrated that OH inactivates B. subtilis spores more effectively than CH. OH conditions with high electric field intensities and high frequencies resulted in efficient B. subtilis spore inactivation.

An assessment of potential applications with pulsed electric field in wines

Pulsed electric fields (PEF) is a non-thermal processing technology that uses instantaneous, pulses of high voltage for a short period in the range of milliseconds to microseconds; the application of high intensity electric field on toasted wood chips leads to a quick diffusion of extractable molecules. Currently most PEF studies, in the field of oenology, have been focusing on the application of PEF as a pretreatment of grape musts by examining the microbial inactivation and the enhancement of polyphenol extraction. In this study a post-treatment of wine is introduced as method to enhance the wood flavor in the wine with a green noninvasive technology. Major phenolic aldehydes that have been identified as the characteristic compounds of oak volatile compounds were selected as markers and were analyzed instrumentally to compare the influence of PEF processing to non-treated samples. PEF treated samples brought about higher concentrations of the examined oak compounds in the samples treated with PEF, which may explain the advantages of its application. The modulation of the intensity of the electric field and the period of pulses influenced the concentrations of the volatile phenols that were leached out. Differences found between the assayed treatments indicate that PEF application could be a potential practice for a rapid extraction of volatile compounds from oak.

Differentiating the roles of shrimp and aquatic insects in leaf processing in a Neotropical stream

There is interest in the relationships between macroconsumers (e.g. shrimp) and aquatic insects, as well as their role in ecological processes, including leaf breakdown, in tropical freshwater environments. Many studies have shown that shrimp have the capacity to reduce the abundance of aquatic insects (by predation and behavioural inhibition) and promote leaf breakdown as shredders. To discriminate between these effects, we used fresh leaves of Erythroxylum pulchrum and manipulated the presence of shrimp and insects by electric exclusion at high and low intensities of electric field. In the control treatment (no electric exclusion) shrimp (the brushing collector Potimirim brasiliana and the shredding omnivore Macrobrachium olfersii) and aquatic insects (including shredders) were present. The low-intensity electric field excluded only shrimp, whereas the high-intensity electric field excluded both shrimp and medium- and large-sized aquatic insects (&gt;2mm). Leaf processing was approximately twice as fast in the absence of shrimp and in the presence of insects than when both or neither were present. This implied a trophic cascade of shrimp acting as potential predators of insect shredders, but not acting as shredders themselves. We postulate that increased leaf processing was caused by a behavioural response of the putative shredders to the absence of shrimp; abundant leptophlebiid ephemeropterans were the most likely shredders.

Concentrated high intensity electric field (CHIEF) system for non-thermal pasteurization of liquid foods: Modeling and simulation of fluid mechanics, electric analysis, and heat transfer

Abstract This study develops an integrated, multi-scale model of the pilot concentrated high intensity electric field (CHIEF) system using the finite element method (FEM). The CHIEF system is a novel non-thermal pasteurization technology that uses medium to low voltage (≤10 kV) frequency AC (60 Hz) power supply, and offers satisfactory pasteurization results for liquid food such as juice and milk. The model in this study provides accurate predictions for the fluid behavior, electric field distribution and temperature profile and is validated using experimental results. Results from the model shows that the CHIEF system can provide electric field up to 4000 kV/m with a power supply of 10 kV, enabling a 6-log reduction of bacteria kill. Furthermore, recommendations and optimizations are made based on the modeling results, which would benefit for the process scale-up and design.