Electric fields in dielectric structures with nonuniformly distributed surface charges

1999 ◽  
Vol 44 (8) ◽  
pp. 995-997
Author(s):  
A. S. Yastrebov
Keyword(s):  
Electric Fields ◽  
Surface Charges ◽  
Dielectric Structures

scholarly journals Surface Tracking of MgO/Epoxy Nanocomposites: Effect of Surface Hydrophobicity

2019 ◽  
Vol 9 (3) ◽  
pp. 413 ◽  
Author(s):  
Zhaoliang Xing ◽  
Chong Zhang ◽  
Xiangnan Hu ◽  
Panhui Guo ◽  
Jingyuan Zhang ◽  
...  
Keyword(s):  
Contact Angle ◽  
Electric Fields ◽  
Surface Hydrophobicity ◽  
Surface Charges ◽  
Surface Tracking ◽  
Surface Contact ◽  
Surface Contact Angle ◽  
Tracking Behavior ◽  
Composite Samples ◽  
Reduced Surface

Surface tracking has been one of the challenges for outdoor organic insulations, in electronic and electrical devices. In this paper, surface tracking behavior of nano-MgO/epoxy composite samples were measured according to the standard IEC 60112. Improved tracking resistance was obtained in nanocomposites with an 18.75% uplift in the comparative tracking index, and a decrease of 58.20% in the surface ablation area at a fixed 425 V. It was observed that the tracking resistance and surface hydrophobicity shared the same tendency—both, the comparative tracking index and surface contact angle increased with an increase of the nanofiller content. Samples with better hydrophobicity exhibited a higher tracking resistance. It could be the case that the conductive pathway of contamination was harder to form, as a result there were fewer discharging processes. With the development of surface tracking, the surface contact angle abruptly decreased, at first, and tended to be constant, which was also accomplished with the failure of samples. In addition, reduced surface resistivity was also found in the nanocomposites, which was beneficial for releasing surface charges and inhibiting distortions in the electric fields.

Surface displacements and surface charges on Ba2CuWO6 and Ba2Cu0.5Zn0.5WO6 ceramics induced by local electric fields investigated with scanning-probe microscopy

2007 ◽  
Vol 22 (1) ◽  
pp. 193-200
Author(s):  
Ralf-Peter Herber ◽  
Gerold A. Schneider
Keyword(s):  
Electric Fields ◽  
Ferroelectric Properties ◽  
Piezoresponse Force Microscopy ◽  
Ferroelectric Material ◽  
Relaxor Ferroelectrics ◽  
Surface Charges ◽  
Kelvin Probe ◽  
Force Microscopy ◽  
Atomic Force ◽  
Surface Displacements

Ba2CuWO6 (BCW) was first synthesized in the mid 1960s, and it was predicted to be a ferroelectric material with a very high Curie temperature of 1200 °C [N. Venevtsev and A.G. Kapyshev: New ferroelectrics. Proc. Int. Meet. Ferroelectr.1, 261 (1966)]. Since then, crystallographic studies were performed on the compound with the result that its crystal structure is centrosymmetric. Thus for principal reason, BCW cannot be ferroelectric. That obvious contradiction was examined in this study. Disk-shaped ceramic samples of BCW and Ba2Cu0.5Zn0.5WO6 (BCZW) were prepared. Because of the low electrical resistivity of the ceramics, it was not possible to perform a typical polariszation hysteresis loop for characterization of ferroelectric properties. Scanning electron microscopy investigations strongly suggest that the reason for the conductivity is found in the impurities/precipitations within the microstructure of the samples. With atomic force microscopy (AFM) in piezoresponse force microscopy (PFM) mode, it is possible to characterize local piezoelectricity by imaging the ferroelectric domains. Neither BCW nor BCZW showed any domain structure. Nevertheless, when local electric fields were applied to the surfaces of the ceramics topographic displacements, imaged with AFM, and surface charges, imaged with Kelvin probe force microscopy (KFM) and PFM, were measured and remained stable on the surface for the time of the experiment. Therefore BCW and BCZW are considered to be electrets and possibly relaxor ferroelectrics.

Electrohydrodynamic Kelvin-Helmholtz Instability of Two Rotating Dielectric Fluids

1998 ◽  
Vol 53 (1-2) ◽  
pp. 17-26
Author(s):  
Mohamed Fahmy El-Sayed
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Applied Electric Field ◽  
Rotation Frequency ◽  
Short Wave ◽  
Surface Charges ◽  
Rotation Surface ◽  
Dielectric Fluids ◽  
Fluid Velocities ◽  
Conditions Of Stability

Abstract A linear stability analysis of a novel electrohydrodynamic Kelvin-Helmholtz system consisting of the superposition of two uniformly rotating dielectric media is presented. The characteristic equation for such an arrangement is derived, which in turn yields a stability criterion for velocity differences of disturbances at a given rotation frequency. The conditions of stability for long and short wave perturbations are obtained, and their dependence on rotation, surface tension and applied electric field is discussed. Limiting cases for vanishing fluid velocities, rotation frequency, and applied electric field are also discussed. Under suitable limits, results of previous works are recovered. A detailed analysis for tangential and normal applied electric fields, in the presence and absence of surface charges, is carried out.

scholarly journals Lifting of Tribocharged Grains by Martian Winds

2021 ◽  
Vol 2 (6) ◽  
pp. 238
Author(s):  
Maximilian Kruss ◽  
Tim Salzmann ◽  
Eric Parteli ◽  
Felix Jungmann ◽  
Jens Teiser ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Electric Fields ◽  
Wind Shear ◽  
Particle Surface ◽  
Shear Velocity ◽  
Sand Transport ◽  
Particle Collisions ◽  
Surface Charges ◽  
Martian Soil ◽  
Open Question

Abstract It is a long-standing open question whether electrification of wind-blown sand due to tribocharging—the generation of electric charges on the surface of sand grains by particle–particle collisions—could affect rates of sand transport occurrence on Mars substantially. While previous wind tunnel experiments and numerical simulations addressed how particle trajectories may be affected by external electric fields, the effect of sand electrification remains uncertain. Here we show, by means of wind tunnel simulations under air pressure of 20 mbar, that the presence of electric charges on the particle surface can reduce the minimal threshold wind shear velocity for the initiation of sand transport, u *ft, significantly. In our experiments, we considered different samples, a model system of glass beads as well as a Martian soil analog, and different scenarios of triboelectrification. Furthermore, we present a model to explain the values of u *ft obtained in the wind tunnel that is based on inhomogeneously distributed surface charges. Our results imply that particle transport that subsides, once the wind shear velocity has fallen below the threshold for sustained transport, can more easily be restarted on Mars than previously thought.

scholarly journals RESEARCH OF AIR IONIZATION OF AIR IN PREMISES ON OPERATION OF COMPUTER EQUIPMENT

2021 ◽  
Vol 4 (164) ◽  
pp. 215-219
Author(s):  
O. Panova ◽  
L. Levchenko ◽  
I. Teslytsky
Keyword(s):  
Electric Fields ◽  
Ionic Composition ◽  
Critical Distance ◽  
Personal Computers ◽  
Surface Charges ◽  
Laptop Computer ◽  
Air Ions ◽  
Field Source ◽  
Computer Equipment ◽  
Ultrasonic Humidifier

All known studies on the effect of computer equipment on the concentration of air ions of both signs have been used for rooms where desktop computers are operated. The expediency of conducting research using a laptop computer is substantiated. Therefore, the urgent task is to study the dynamics of the air ionic composition of the air from the operation of personal computers and identify ways to maintain this indicator at the regulatory level. It is shown that the switched on computer deionizes air, and mainly on one polarity. It is established that this is a consequence of electrification of polymer surfaces. The cause of electrification is triboelectric phenomena, including the directional movement of dry air from the CPU cooling fan. Additional electrification (and consequently - deionization of air) gives the presence of the user. Confirmation of the cause of deionization is the slow recovery of the concentration of air ions after turning on the computer to a certain neutralization of surface charges. The dependences of the change of air ion concentrations on the distance from the electric field source are established. At its intensity of about 5 kV/m with dimensions of 1.0×1.0 m, the critical distance is 1.2-1.3 m. It is recommended to carry out wet absorption for an unambiguous workplace, which provides insignificant electric fields for 1.5 hours. During the operation of many personal computers, it is advisable to neutralize surface charges with an ultrasonic humidifier-ionizer. It is emphasized that the conducted research has a separate character. This is due to the presence of specific synthetic materials It is advisable to conduct research in standard rooms for the operation of computer equipment to obtain information that can be summarized and used to develop sanitary standards for the operation of computer equipment.

scholarly journals The problem of the electrical discharge in an internally wired capacitor

2016 ◽  
Vol 38 (3) ◽  
Author(s):  
F. B. Rizzato
Keyword(s):  
Solid State ◽  
Electric Fields ◽  
Electrical Discharge ◽  
Critical Value ◽  
Surface Charges ◽  
Electrical Discharges ◽  
Solid State Devices ◽  
Conducting Wire ◽  
The Wire ◽  
Rc Circuit

The present work investigates the dynamics of electrical discharges in a capacitor where both plates are internally connected by a conducting wire. A simplifying assumption used to solve the problem is to consider a uniform distribution of the surface charges on the plates. This implies uniform electric fields as well, and allows to calculate the current in the wire as if it were flowing along a simple RC circuit. We show that although the assumption is good if the conductivity of the wire is small, it fails if the conductivity becomes larger than a critical value. The device's behavior beyond this critical value is then analyzed and discussed. The relevance of the problem is discussed in connection to solid-state devices, as well as in problem solving contexts.

Back to Basic, Optical Evaluation of Motion in Electric Fields for Specific Surface Charge Determinations

2019 ◽  
Author(s):  
Julio Bastos Arrieta ◽  
Linlin Wang ◽  
Aidee Garcia-Zintzun ◽  
Juliane Simmchen
Keyword(s):  
Surface Charge ◽  
Electric Fields ◽  
Spherical Shape ◽  
Complex Surface ◽  
Light Sources ◽  
Hard Sphere Model ◽  
Surface Charges ◽  
Bacterial Surface ◽  
Commercial Device

<p>Dynamic Light Scattering (DLS) is a widely used tool for the measurement of Zeta Potential, taking benefit of automated detection to achieve fast measurements. However, the mathematical criteria on which the calculations in DLS devices are based, assume a very narrow set of conditions. One of them is a perfect spherical shape, since a hard sphere model is assumed for calculating scattering patterns and therefore the analysis of different shapes could result in significant deviations. One frequent example where the determination of the surface charge in rod shaped colloids is required is the characterization of bacterial surface charges, which is complicated by complex surface properties. To test whether the commercial device gives a reasonable approximation, we constructed a homemade optical device and tested inorganic spherical and rod-shape SiO<sub>2</sub> particles and compared them to a model bacterium. A different case is the determination of surface potentials of light sensitive materials under illumination. Commercial devices often do not allow the additional implementation of light sources other than the laser, but our setup flexibly enables us to plug in different illuminations.</p>

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