Attenuation Of Electric Field Research Articles

Effect of desorbed gas on microwave breakdown on vacuum side of dielectric window

The gas desorbed from the dielectric surface has a great influence on the characteristics of microwave breakdown on the vacuum side of the dielectric window. In this paper, the dielectric surface breakdown is described by using the electromagnetic particle-in-cell-Monte Carlo collision (PIC-MCC) model. The process of desorption of gas and its influence on the breakdown characteristics are studied. The simulation results show that, due to the accumulation of desorbed gas, the pressure near the dielectric surface increases in time, and the breakdown mechanism transitions from secondary electron multipactor to collision ionization. More and more electrons generated by collision ionization drift to the dielectric surface, so that the amplitude of self-organized normal electric field increases in time and sometimes points to the dielectric surface. Nevertheless, the number of secondary electrons emitted in each microwave cycle is approximately equal to the number of primary electrons. In the early and middle stages of breakdown, the attenuation of the microwave electric field near the dielectric surface is very small. However, the collision ionization causes a sharp increase in the number density of electrons, and the microwave electric field decays rapidly in the later stage of breakdown. Compared with the electromagnetic PIC-MCC simulation results, the mean energy and number of electrons obtained by the electrostatic PIC-MCC model are overestimated in the later stage of breakdown because it does not take into account the attenuation of microwave electric field. The pressure of the desorbed gas predicted by the electromagnetic PIC-MCC model is close to the measured value, when the number of gas atoms desorbed by an incident electron is taken as 0.4.

Shielded Cone Coil Array for Non-Invasive Deep Brain Magnetic Stimulation.

Non-invasive deep brain stimulation using transcranial magnetic stimulation is a promising technique for treating several neurological disorders, such as Alzheimer's and Parkinson's diseases. However, the currently used coils do not demonstrate the required stimulation performance in deep regions of the brain, such as the hippocampus, due to the rapid decay of the field inside the head. This study proposes an array that uses the cone coil method for deep stimulation. This study investigates the impact of magnetic core and shielding on field strength, focality, decay rate, and safety. The coil's size and shape effects on the electric field distribution in deep brain areas are also examined. The finite element method is used to calculate the induced electric field in a realistic human head model. The simulation results indicate that the magnetic core and shielding increase the electric field intensity and enhance focality but do not improve the field decay rate. However, the decay rate can be reduced by increasing the coil size at the expense of focality. By adopting an optimum cone structure, the proposed five-coil array reduces the electric field attenuation rate to reach the stimulation threshold in deep regions while keeping all other regions within safety limits. In vitro and in vivo experimental results using a head phantom and a dead pig's head validate the simulated results and confirm that the proposed design is a reliable and efficient candidate for non-invasive deep brain magnetic stimulation.

Time-Domain Analysis of the Impact of Advanced Building Construction Materials on the Propagation of Lightning Electromagnetic Field and Its Mitigation Using Nanoforging

The comprehension of the propagation characteristics of lightning electromagnetic field (LEMF) is essential to inspect the impact of nearby lightning strike and its coupling effect on different systems and equipment. Undeniably, the presence of building structures alters LEMF reaching any point of installation of critical equipment. In this regard, this article attempts a complete time-domain analysis of the influence of building structures on LEMF propagation at near and far striking distance. The influence of aperture location on structures with respect to the direction of LEMF propagation is quantified first ever. The LEMF penetration capability of novel constructional materials, namely carbon nanotube (CNT)-forged concrete and glass fiber-reinforced gypsum, is compared to that of concrete, and surface charge estimation methodology is adopted for the first time to quantify the plausible LEMF shielding performance. It is observed that the presence of apertures influences the LEMF distribution, but their location has inconsequential effect. Among the materials, CNT-forged concrete offers nearly 2 dB of electric field attenuation and 10 dB in energy penetration due to LEMF, quantifying the field mitigation effect due to nanoforging. Experimental study confirms better shielding performance of nanocompounded concrete. For magnetic field, the presence of apertures and the type of construction material do not deliver a sizable effect.

Measurement of dc and ac Electric Fields inside an Atomic Vapor Cell with Wall-Integrated Electrodes

We present and characterize a Rb atomic vapor cell with silicon-ring electrodes embedded between borosilicate glass tubes. The ring electrodes can be externally connectorized for application of electric fields to the inside of the cell. An atom-based, all-optical, laser-spectroscopic field-sensing method is employed to measure electric fields in the cell. Here, the Stark effect of electric-field-sensitive rubidium Rydberg atoms is exploited to measure dc electric fields in the cell of approximately $5$ V/cm, with a relative uncertainty of 10%. Measurement results are compared with dc field calculations, allowing us to quantify electric field attenuation due to free surface charges inside the cell. We further measure the propagation of microwave fields into the cell, using Autler-Townes splitting of Rydberg levels as a field probe. Results are obtained for a range of microwave powers and polarization angles relative to the cell's ring electrodes. We compare the results with microwave-field calculations.

In situ, broadband measurement of the radio frequency attenuation length at Summit Station, Greenland

AbstractOver the last 25 years, radiowave detection of neutrino-generated signals, using cold polar ice as the neutrino target, has emerged as perhaps the most promising technique for detection of extragalactic ultra-high energy neutrinos (corresponding to neutrino energies in excess of 0.01 Joules, or 1017 electron volts). During the summer of 2021 and in tandem with the initial deployment of the Radio Neutrino Observatory in Greenland (RNO-G), we conducted radioglaciological measurements at Summit Station, Greenland to refine our understanding of the ice target. We report the result of one such measurement, the radio-frequency electric field attenuation length $L_\alpha$. We find an approximately linear dependence of $L_\alpha$ on frequency with the best fit of the average field attenuation for the upper 1500 m of ice: $\langle L_\alpha \rangle = ( ( 1154 \pm 121) - ( 0.81 \pm 0.14) \, ( \nu /{\rm MHz}) ) \,{\rm m}$ for frequencies ν ∈ [145 − 350] MHz.

Numerical simulation and optimization of the ceramic pigments production process using microwave heating

In this study, the continuous microwave production of (Pr, Zr)SiO2 and (Ti, Sb, Cr)O2 pigments was modelled. The mathematical model includes a two-way coupling between the Maxwell’s equations and the heat equation as well as the coupling between the thermal and the chemical interfaces. The COMSOL Multiphysics software was used together with a specially designed MATLAB controller developed to automatically manage the input power and the cavity impedance. A single-mode cavity operating at 2.45GHz, together with a rectangular waveguide, was used. A chemical model using experimental data was implemented using a model-fitting approach to predict the chemical conversion with time. Results show that the model-fitting method yields a good agreement with the experimental data. Attenuation occurs significantly within the material as the dielectric properties have high values. As such, prohibitive temperatures can be attained easily, although this was taken into account by the developed controller to manage the input power properly. The electromagnetic efficiency is highly dependent on the thermal field, making the boundary convection coefficient the parameter that affects the most the electromagnetic heating performance. A parametric study, that includes the variation of velocity and convection coefficient, was performed to access the impact of these variables in the efficiency of the process. The results show that increasing the velocity leads to a reduction of the maximum temperature, improving the electromagnetic efficiency. Moreover, the green-house gas specific emissions are lower when compared to the conventional process. The thermal conductivity is also a crucial parameter that can contribute to the electric field attenuation and the superficial heating.

Printed Electronic Sensor Array for Mapping Tire Tread Thickness Profiles

Tire tread wear is a significant vehicular safety concern; yet, monitoring tread depth (or thickness) still relies on manual detection, which is rarely done by consumers and is time-consuming for service lane technicians. In this paper, we present a fully printed, one-dimensional electrode array that is able to electrically measure the thickness profile of tread across the width of a tire. The sensor array consists of printed millimeter-sized electrodes composed of a hybrid silver nanoparticle-carbon nanotube (CNT) structure. The array is positioned directly against the outside of a tire (simulating a vehicle driving over the sensors). The thickness profile is then determined by applying an oscillating voltage between each of the electrode pairs in the array and measuring the associated electrical response. Correlation between the electrical response and tread depth across a tire is demonstrated for two distinct, measurable parameters: signal reflectance (S11) and impedance. A 2D electrostatic simulation is applied to explain the operation of the sensors and how the differentiation between grooves and tread blocks is possible based on differing electric field attenuation with distance. This printed sensor array shows promise for electrically monitoring tread profiles using relatively low-cost, readily implemented components.

Technical Note: Design of a handheld dipole antenna for a compact thermoacoustic imaging system.

Conventional antenna used in thermoacoustic imaging (TAI) is often bulky, making it difficult to translate TAI from the bench to the clinic. In this paper, we proposed a handheld dipole antenna which will be a good candidate for the construction of a compact TAI system. Here, we propose a TAI system based on a handheld dipole antenna with an aperture of 6cm and a weight of 230g. Compensation of the electric field attenuation for such a system was also investigated. Compared to the conventional open-ended waveguide and pyramidal horn antenna used in TAI, our results reveal that the electric field attenuation induced distortion is effectively reduced by using the attenuation factor 1/r2 for compensation and that the handheld dipole antenna provides the highest efficiency of microwave delivery. This study suggests that the handheld dipole antenna has the potential to be utilized for the construction of a compact TAI system, making TAI more suitable for preclinical and clinical applications.

The excess attenuation of electric field in the presence of deciduous trees

We present an approximation formula and numerical results for the excess attenuation of electric field of a wave propagating within deciduous forest. The formula is tuned to fit averaged attenuation obtained by full-wave simulations of stochastic 3D and 2D models of forests. The electric field was either vertically or horizontally polarized, at frequencies 30 MHz, 60 MHz and 100 MHz. The formula predicts the excess attenuation within several decibels, up to at least 100 MHz.

Transient electric field characteristics in oil-pressboard composite insulation under voltage polarity reversal

Polarity reversal generally enhances the electric field intensity in oil-pressboard composite insulation, leading to partial discharge and even insulation flashover or breakdown of the HVDC converter transformer. In an attempt to study the transient electric field in oil at polarity reversal, the present research adopted the Kerr electro-optic effect technique to conduct real-time measurement of the oil electric fields at the polarity reversal time of 10, 60 and 120 s respectively. Dielectric interface conditions were also adopted to capture the dynamic development of interface space charges. Research results indicate that (i) negative charges, under the absorption of insulation pressboard, are more likely to accumulate at the oil-pressboard interface. As a result, the development of electric field in oil at polarity reversal demonstrates prominent polarity effect, with faster electric field attenuation under negative voltage; (ii) the development of electric field in oil shows asymmetric features under double polarity reversals. The first reversal witnesses a high magnitude of electric field in oil that is about 1.47 times of the initial capacitive electric field, whilst the second reversal sees only 85% of the initial capacitive electric field. Such asymmetric development is mainly attributed to different accumulation performances of the positive and negative charges; iii) the shorter the polarity reversal time is, the higher the oil electric field strength will be. The maximum magnitudes of the field strength after polarity reversals with different time, however, are not much different from one another.

An in situ measurement of the radio-frequency attenuation in ice at Summit Station, Greenland

AbstractWe report an in situ measurement of the electric field attenuation length Lα at radio frequencies for the bulk ice at Summit Station, Greenland, made by broadcasting radio-frequency signals vertically through the ice and measuring the relative power in the return ground bounce signal. We find the depth-averaged field attenuation length to be at 75 MHz. While this measurement has clear radioglaciological applications, the radio clarity of the ice also has implications for the detection of ultra-high energy (UHE) astrophysical particles via their radio emission in dielectric media such as ice. Assuming a reliable extrapolation to higher frequencies, the measured attenuation length at Summit Station is comparable to previously measured radio-frequency attenuation lengths at candidate particle detector sites around the world, and strengthens the case for Summit Station as a promising northern site for UHE neutrino detection.

The Influence of L-Shaped Structure on Partial Discharge Radiated Electromagnetic Wave Propagation in GIS

To clarify the propagation process and improve the utilization of ultrahigh frequency (UHF) technique in partial discharge diagnosis, the propagation characteristics of electromagnetic wave in different directions in an L-shaped gas insulated switchgear tank are profoundly investigated in this paper. According to the property of electric field distribution and attenuation curves of the UHF signal, the influence of L-shaped structure is analyzed.

Coil design considerations for deep transcranial magnetic stimulation

ObjectivesTo explore the field characteristics and design tradeoffs of coils for deep transcranial magnetic stimulation (dTMS). MethodsWe simulated parametrically two dTMS coil designs on a spherical head model using the finite element method, and compare them with five commercial TMS coils, including two that are FDA approved for the treatment of depression (ferromagnetic-core figure-8 and H1 coil). ResultsSmaller coils have a focality advantage over larger coils; however, this advantage diminishes with increasing target depth. Smaller coils have the disadvantage of producing stronger field in the superficial cortex and requiring more energy. When the coil dimensions are large relative to the head size, the electric field decay in depth becomes linear, indicating that, at best, the electric field attenuation is directly proportional to the depth of the target. Ferromagnetic cores improve electrical efficiency for targeting superficial brain areas; however magnetic saturation reduces the effectiveness of the core for deeper targets, especially for highly focal coils. Distancing winding segments from the head, as in the H1 coil, increases the required stimulation energy. ConclusionsAmong standard commercial coils, the double cone coil offers high energy efficiency and balance between stimulated volume and superficial field strength. Direct TMS of targets at depths of ∼4cm or more results in superficial stimulation strength that exceeds the upper limit in current rTMS safety guidelines. Approaching depths of ∼6cm is almost certainly unsafe considering the excessive superficial stimulation strength and activated brain volume. SignificanceCoil design limitations and tradeoffs are important for rational and safe exploration of dTMS.

Electric field depth–focality tradeoff in transcranial magnetic stimulation: Simulation comparison of 50 coil designs

BackgroundVarious transcranial magnetic stimulation (TMS) coil designs are available or have been proposed. However, key coil characteristics such as electric field focality and attenuation in depth have not been adequately compared. Knowledge of the coil focality and depth characteristics can help TMS researchers and clinicians with coil selection and interpretation of TMS studies. ObjectiveTo quantify the electric field focality and depth of penetration of various TMS coils. MethodsThe electric field distributions induced by 50 TMS coils were simulated in a spherical human head model using the finite element method. For each coil design, we quantified the electric field penetration by the half-value depth, d1/2, and focality by the tangential spread, S1/2, defined as the half-value volume (V1/2) divided by the half-value depth, S1/2 = V1/2/d1/2. ResultsThe 50 TMS coils exhibit a wide range of electric field focality and depth, but all followed a depth–focality tradeoff: coils with larger half-value depth cannot be as focal as more superficial coils. The ranges of achievable d1/2 are similar between coils producing circular and figure-8 electric field patterns, ranging 1.0–3.5 cm and 0.9–3.4 cm, respectively. However, figure-8 field coils are more focal, having S1/2 as low as 5 cm2 compared to 34 cm2 for circular field coils. ConclusionsFor any coil design, the ability to directly stimulate deeper brain structures is obtained at the expense of inducing wider electrical field spread. Novel coil designs should be benchmarked against comparison coils with consistent metrics such as d1/2 and S1/2.

Ross Ice Shelf (Antarctica) in situ radio-frequency attenuation

AbstractWe have measured the in situ average electric field attenuation length, 〈Lα〉, for radio-frequency signals broadcast vertically through the Ross Ice Shelf, Antarctica. We chose a location, Moore Embayment, south of Minna Bluff, known for its high reflectivity at the ice–sea interface. We confirmed specular reflection and used the return pulses to measure the average attenuation length from 75–1250 MHz over the round-trip distance of 1155 m. We find 〈Lα〉 to vary from ∼500 m at 75 MHz to ∼300 m at 1250 MHz, with an experimental uncertainty of 55–15 m.

Polarization and Polarizability Assessed by Protein Amide Acidity

Hydroxide-catalyzed exchange rate constants were determined for those amides of FK506-binding protein (FKBP12), ubiquitin, and chymotrypsin inhibitor 2 (CI2) that are solvent-accessible in the high-resolution X-ray structures. When combined with previous hydrogen exchange results for the rubredoxin from Pyrococcus furiosus, the acidity of these amides was calculated by continuum dielectric methods as a function of the nonpolarizable electrostatic parameter set, internal dielectric, and the charge distribution of the peptide anion. The CHARMM22 parameter set with an internal dielectric value of 3 and an ab initio-derived anion charge distribution yielded an rmsd value of 7 for the 56 amide exchange rate constants ranging from 10(0.67) to 10(9.0) M(-1) s(-1). The OPLS-AA parameter set yielded comparably robust predictions, while that of PARSE, AMBER parm99, and AMBER ff03 performed more poorly. The small value for the optimal internal dielectric, combined with the brief lifetime of the peptide anion intermediate and the uniformity of the correlation between predicted and observed amide acidities, is consistent with electronic polarizability providing the dominant contribution to dielectric shielding. By construction, nonpolarizable force fields do not model electric field attenuation by electronic polarizability. Accurate prediction of the total electrostatic energy by such force fields necessitates the hyperpolarization of the atomic charge values in order to match the average electric field energy density (1/2)epsilon(tau)E(2)(tau) when epsilon(tau) is set to the in vacuo dielectric value of 1. The resulting predictions of the experimental hydrogen exchange data demonstrate the substantial systematic errors in the predicted electrostatic potential that can arise when dielectric shielding due to electronic polarizability is neglected.

South Polar in situ radio-frequency ice attenuation

AbstractWe have determined the in situ electric field attenuation length Lα (defined as the length over which the signal amplitude diminishes by a factor 1/e) for radio-frequency signals broadcast vertically through South Polar ice and reflected off the underlying bed. Conservatively assuming a bedrock field reflectivity for f = 380 MHz, and T = –50°C; the errors incorporate uncertainties in R. This value is consistent with previous estimates that the radiofrequency attenuation length exceeds the attenuation length at optical frequencies by an order of magnitude.

Guided electromagnetic waves in organic light emitting diode structures

A detailed analysis of the optical waveguide modes in organic light emitting diodes (OLEDs) is presented. The modes are compared with respect to their electric field profile, attenuation coefficient and optical confinement factor. The first transversal electric (TE) mode is best suited for an optimized energy transfer from emitting dipoles. The transversal magnetic (TM) modes are characterized by a large plasmon character with high absorption. The propagation constants of distinct modes have been measured in test devices by grating coupling.

Transmission and attenuation of vector modes in uniformly bent circular hollow waveguides for the infrared

Electric field distributions and attenuation constants of the eigenmodes in uniformly bent circular hollow waveguides have been evaluated based on a vector wave equation deduced from Maxwell's equations. A diagram representation of the parameter describing mode properties is introduced. It is numerically shown that vector modes gradually approach linearly polarized modes when the bending radius becomes small. A relation between attenuation constants in sharply bent circular and slab hollow waveguides is also discussed where the electric fields concentrate near the outer edge of the core. >

Transmission and attenuation of the dominant mode in uniformly bent circular hollow waveguides for the infrared: scalar analysis

A numerical evaluation is conducted of electric field distributions, phase constants, and attenuation constants of the lowest eigenmode in the general class of uniformly bent circular hollow waveguides. The analysis is based on a scalar equation, and numerical results are compared with those of existing approximate theories. Normalized forms of attenuation constants are presented for the parallel and perpendicular polarizations to the bending plane by using structural and material parameters. For sharply bent waveguides, useful and simple expressions are derived for the attenuation constants of the TE and TM modes in the corresponding slab geometry with suitable weighting parameters. >