Influence displacement currents

Fig. 28. (a) Sketch of current lines of the dielectric displacement current between a contact needle and a counter-electrode indicating the influence of the stray capacitance, (b) Equivalent circuit (including the stray capacitance) representing microelectrode measurements on single crystals and the two simplified subcases for ohmic and non-ohmic microelectrodes. 

Equations of set (A) are valid for constant fields, but there will be additional effects to consider for alternating fields. In other words, when time-varying electromagnetic fields are considered, there is another source for the magnetic field in addition to the conduction currents. However, for the so-called quasistationary field, the influence of the second source of the magnetic field (displacement currents) is negligible as this is the case in induction logging, and equations of set (A) can be applied. 

Let us notice that eq. 4.149 is valid not only for a quasistationary field but also in a more general case when the influence of displacement currents is significant. This fact is of great practical interest for the realization of dielectric logging. 

The last stage corresponds to the quasistationary field when the influence of displacement currents is absent. This feature of the alternating field is inherent for a conducting medium, regardless of how small its conductivity, but the moment of transition to the quasistationary field starts earlier with an increase of conductivity. 

In a general case, when the influence of displacement currents is essential, the transversal resistivity depends on frequency. It is explained by the fact that surface charges are a function of dielectric constant and frequency. 

We can assume that if the electric field is not uniform and changes along the layer, the longitudinal conductance is also a function of a frequency. Curves, presented in Fig. 11.3 characterize the influence of displacement currents on coefficient on anisotropy. 

Figure 22 illustrates the various influences/current components the transistor experiences as the time duration for the application of the pulse voltage is extended. On application of the pulse voltage the displacement current starts to flow and decays quickly. Then there is a time duration for which no current flows through the drain. This is followed by the appearance of the conduction current which causes charges... 

As follows from numerical analysis, in this case five angular harmonics describe the field with high accuracy for all considered values of a//ii where h is the skin depth in the borehole. It is appropriate to notice that the influence of displacement on inphase and quadrature component of the field increases with an increase of frequency. At the same time within this range of frequencies the inphase component is less sensitive to displacement than is the quadrature component. For example, even if a/h = 1.6 we have In/iJ(e = 0.5)/In/i (e = 0) = 1.04, while Q/i (e = 0.5)/Qh e = 0) = 1.51. It is explained by the fact that within a wide range of frequencies the density of charges arising at the interface between the borehole and the formation is shifted in phase by 90° with respect to the current in the transmitter. Correspondingly, we can expect that the quadrature component of the field for a two-coil probe will be mainly subjected to the influence of eccentricity. 

We currently do not have any measurement concerning shear stiffness of the discontinuities of Coaraze. Measurements of shear displacement will be undertaken and analyzed in order to characterize the shear in situ behaviour of discontinuities and to quantify its influence on hydraulic conductivity of fracture network. 

The nature of current distribution influences the shape generation. The recession takes place in the direction of current density and the amount of recession depends on the magnitude of current density which can be explained by Eqn (3.5). Current distribution is calculated for a given time step by numerical solution of Laplace equation with nonlinear boundary conditions. Finite element method and boundary element method have been used for simulation of shape evolution during EMM. The new shape is obtained from the immediate previous shape by displacing the boundary proportional to the magnitude and in the direction of current density. The results of these simulation techniques agreed with the experimental results [6]. 

First, let us consider the measurement of CVR When the density of the particles Pp differs from that of the medium Pjjj, the particles move relative to the medium under the influence of an acoustic wave. This motion causes a displacement of the internal and external parts of the double layer (DL). The phenomenon is usually referred to as a polarization of the DL (6). This displacement of opposite charges gives rise to a dipole moment. The superposition of the electric fields of these induced dipole moments over the collection of particles gives rise to a macroscopical electric field which is referred to as the colloid vibration potential (CVP). Thus, the fourth mechanism of particles interaction with sound leads to the transformation of part of the acoustic energy to electrical energy. This electrical energy may then be dissipated if die opportunity for electric current flow exists. 

Provided buffer concentrations are sufficiently low, parameters of permittivity and viscosity can be taken to be the same as for pure water [10]. After obtaining the current-time curve, the experiment is run again in the reverse direction. This complete process should be repeated at least once, which provides a total of four separate curves for each data point. Having repeatable results helps minimize the influence of inability to precisely evaluate the start and end points of the displacement cxuwe. 

Field measurements of clearance between the east-west skips and the pressure over the surfaces of the east skip during the travels were carried out for a production shaft of a potash mine in August 2010. The acceleration, velocity and displacement of the east skip were captured with a three-dimensional motion sensor. The measured displacements of the skips at current 3300 fpm (16.76 m/s) velocity were the resultant movements under the combined influences of airflow, Coriolis effect and guide rope vibration. 

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