Resistivity mapping using inductive sources

1989 ◽  
Vol 20 (2) ◽  
pp. 47 ◽  
Author(s):  
J. MacNae ◽  
P. McGowan ◽  
Y. Lamontagne
Keyword(s):  
Electric Field ◽  
Time Derivative ◽  
Constant Current ◽  
Magnetic Component ◽  
Late Time ◽  
Gold Mine ◽  
Practical Application ◽  
Electric Component ◽  
Resistive Zone

In electromagnetic (EM) exploration for conductive targets, measurements of the magnetic component or its time derivative have received more theoretical attention and practical application than have measurements of the electric component. However, the electric component can be shown to be particularly useful in the search for resistive zones not usually detected by the magnetic component. Normalized measurements of the surface voltage differences caused by the constant current induced at late time by the UTEM transmitter are called 'Inductive Source Resistivity' or ISR measurements.Data collected on a grid located just south of the Temora gold mine in N.S.W. clearly show the effectiveness of the ISR technique in detecting a resistive zone of silicification located unconformably under 10S of conductive cover. Due to the relatively slow falloff of the electric field from an inductive source, the technique is ideal for the rapid exploration of large areas.

The influence of a conductive host on two‐dimensional borehole transient electromagnetic responses

Geophysics ◽  
1984 ◽  
Vol 49 (7) ◽  
pp. 861-869 ◽  
Author(s):  
Perry A. Eaton ◽  
Gerald W. Hohmann
Keyword(s):  
Electric Field ◽  
Half Space ◽  
Time Window ◽  
Time Derivative ◽  
Finite Width ◽  
Late Time ◽  
Time Behavior ◽  
Two Dimensional ◽  
Peak Response ◽  
Transient Electromagnetic

We have computed transient borehole electromagnetic (EM) responses of two‐dimensional (2-D) models using a direct and explicit finite‐difference algorithm. The program computes the secondary electric field which is defined as the difference between the total field and the primary (half‐space) field. The time derivative of the vertical magnetic field in a borehole is computed by numerical differentiation of the total electric field. These models consist of a thin horizontal conductor with a finite width, embedded in a conductive half‐space. Dual line sources energized by a step‐function current lie on the surface of the half‐space and simulate the long sides of a large rectangular loop. Numerical results substantiate several important features of the transient impulse response of such models. The peak response of the target is attenuated as the resistivity of the host decreases. A sign reversal in the secondary electric field occurs later in time as the resistivity of the host decreases. The peak response and the onset of late‐time behavior are delayed in time as well. Secondary responses for models with different host resistivities (10–1000 Ω-m) are approximately the same at late time. If the target is less conductive, the effects of the host, i.e., the attenuation and time delay, are less. It is readily apparent that there exists a time window within which the target’s response is at a maximum relative to the half‐space response. At late time the shape of the borehole anomaly due to a thin conductive 2-D target appears to be independent of the conductivity of the host. The late‐time secondary decay of the target is neither exponential nor power law, and a time constant computed from the slope of a log‐linear decay curve at late time may be much larger than the actual value for the same target in free space.

INVESTIGATION OF THE INFLUENCE OF SPACE CHARGE ON THE ANODIC OXIDATION OF ALUMINUM, A TYPICAL VALVE METAL

1963 ◽  
Vol 41 (12) ◽  
pp. 3108-3117 ◽  
Author(s):  
M. J. Dignam ◽  
P. J. Ryan
Keyword(s):  
Field Strength ◽  
Oxide Film ◽  
Electric Field ◽  
Electric Field Strength ◽  
Anodic Oxidation ◽  
Ionic Conduction ◽  
Time Derivative ◽  
Ionic Current ◽  
Constant Current ◽  
Frenkel Defect

Measurements of the time derivative of the anodic overpotential of superpurity aluminum during anodic oxidation were made at various constant current densities. The data have been interpreted in terms of the variation of electric field strength with position in the oxide film. The analytic form of the profile of the electric field strength in the oxide film was deduced, assuming the high field Frenkel defect model. The data were found to be incompatible with the theoretical profile, providing, therefore, evidence against this model. The data are only consistent with a model for the transport process in which the concentration of ionic current carriers at a position in the oxide remote from the metal interface is independent of the field strength. A new model, proposed recently by Dignam to explain transient ionic conduction phenomena, is consistent with this conclusion.

Bi(Mg1/2Zr1/2)O3-PbZrO3-PbTiO3 relaxor ferroelectric ceramics with large and temperature-insensitive electric field induced strain response

2021 ◽  
Author(s):  
Hongrui Jia ◽  
Zhigang Liang ◽  
Zhen Li ◽  
Fei Li ◽  
Linghang Wang
Keyword(s):  
Electric Field ◽  
Ceramic Materials ◽  
Ferroelectric Ceramic ◽  
Relaxor Ferroelectric ◽  
Ferroelectric Ceramics ◽  
Harsh Environment ◽  
Strain Response ◽  
Practical Application ◽  
Electric Field Induced Strain ◽  
Relaxor Ferroelectric Ceramics

Ferroelectric ceramic materials with large and temperature-insensitive strain response are highly desired for the practical application of actuator in harsh environment conditions. In this work, a novel xBi(Mg1/2Zr1/2)O3-(0.55-x)PbZrO3-0.45PbTiO3 (xBMZ-PZ-0.45PT) ternary...

scholarly journals A parallel finite‐difference approach for 3D transient electromagnetic modeling with galvanic sources

Geophysics ◽  
2004 ◽  
Vol 69 (5) ◽  
pp. 1192-1202 ◽  
Author(s):  
Michael Commer ◽  
Gregory Newman
Keyword(s):  
Magnetic Field ◽  
Finite Difference ◽  
Electric Field ◽  
Electric Fields ◽  
Time Derivative ◽  
Stable Solution ◽  
Parallel Computer ◽  
Staggered Grid ◽  
Electromagnetic Modeling ◽  
Transient Electromagnetic

A parallel finite‐difference algorithm for the solution of diffusive, three‐dimensional (3D) transient electromagnetic field simulations is presented. The purpose of the scheme is the simulation of both electric fields and the time derivative of magnetic fields generated by galvanic sources (grounded wires) over arbitrarily complicated distributions of conductivity and magnetic permeability. Using a staggered grid and a modified DuFort‐Frankel method, the scheme steps Maxwell's equations in time. Electric field initialization is done by a conjugate‐gradient solution of a 3D Poisson problem, as is common in 3D resistivity modeling. Instead of calculating the initial magnetic field directly, its time derivative and curl are employed in order to advance the electric field in time. A divergence‐free condition is enforced for both the magnetic‐field time derivative and the total conduction‐current density, providing accurate results at late times. In order to simulate large realistic earth models, the algorithm has been designed to run on parallel computer platforms. The upward continuation boundary condition for a stable solution in the infinitely resistive air layer involves a two‐dimensional parallel fast Fourier transform. Example simulations are compared with analytical, integral‐equation and spectral Lanczos decomposition solutions and demonstrate the accuracy of the scheme.

Dependence of Reliability of Ultrathin Mos Gate Oxides on the Fermi Level Positions at Gate and Substrate

1997 ◽  
Vol 473 ◽  
Author(s):  
Tien-Chun Yang ◽  
Navakanta Bhat ◽  
Krishna C. Saraswat
Keyword(s):  
Electric Field ◽  
Fermi Level ◽  
Breakdown Strength ◽  
Gate Oxide ◽  
High Energy ◽  
Constant Current ◽  
Oxide Breakdown ◽  
Mos Devices ◽  
High Energy Electrons ◽  
Substrate Doping

ABSTRACTWe demonstrate that the reliability of ultrathin (< 10 nm) gate oxide in MOS devices depends on the Fermi level position at the gate, and not on the position at the substrate for constant current gate injection (Vg-). The oxide breakdown strength (Qbd) is less for p+ poly-Si gate than for n+ poly-Si gate, but, it is independent of the substrate doping type. The degradation of oxides is closely related to the electric field across the gate oxide, which is influenced by the cathode Fermi level. P+ poly-Si gate has higher barrier height for tunneled electrons, therefore, the cathode electric field must be higher to give the same injection current density. A higher electric field gives more high energy electrons at the anode, and therefore the damage is more at the substrate interface. Different substrate types cause no effect on the oxide electric field, and as a result, they do not influence the degradation.

scholarly journals Modeling Compact Intracloud Discharge (CID) as a Streamer Burst

Atmosphere ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 549
Author(s):  
Vernon Cooray ◽  
Gerald Cooray ◽  
Marcos Rubinstein ◽  
Farhad Rachidi
Keyword(s):  
Electric Field ◽  
Electrical Activity ◽  
Radiation Field ◽  
Time Derivative ◽  
Vertical Direction ◽  
Maximum Growth ◽  
Nanosecond Duration ◽  
Peak Current ◽  
Radiation Fields ◽  
Large Current

Narrow Bipolar Pulses are generated by bursts of electrical activity in the cloud and these are referred to as Compact Intracloud Discharges (CID) or Narrow Bipolar Events in the current literature. These discharges usually occur in isolation without much electrical activity before or after the event, but sometimes they are observed to initiate lightning flashes. In this paper, we have studied the features of CIDs assuming that they consist of streamer bursts without any conducting channels. A typical CID may contain about 109 streamer heads during the time of its maximum growth. A CID consists of a current front of several nanosecond duration that travels forward with the speed of the streamers. The amplitude of this current front increases initially during the streamer growth and decays subsequently as the streamer burst continues to propagate. Depending on the conductivity of the streamer channels, there could be a low-level current flow behind this current front which transports negative charge towards the streamer origin. The features of the current associated with the CID are very different from those of the radiation field that it generates. The duration of the radiation field of a CID is about 10–20 μs, whereas the duration of the propagating current pulse associated with the CID is no more than a few nanoseconds in duration. The peak current of a CID is the result of a multitude of small currents associated with a large number of streamers and, if all the forward moving streamer heads are located on a single horizontal plane, the cumulative current that radiates at its peak value could be about 108 A. On the other hand, the current associated with an individual streamer is no more than a few hundreds of mA. However, if the location of the forward moving streamer heads are spread in a vertical direction, the peak current can be reduced considerably. Moreover, this large current is spread over an area of several tens to several hundreds of square meters. The study shows that the streamer model of the CID could explain the fine structure of the radiation fields present both in the electric field and electric field time derivative.

scholarly journals Time evolution of electric fields and currents and the generalized Ohm's law

2005 ◽  
Vol 23 (4) ◽  
pp. 1347-1354 ◽  
Author(s):  
V. M. Vasyliūnas
Keyword(s):  
Electric Field ◽  
Electric Current ◽  
Time Evolution ◽  
Time Scales ◽  
Current Density ◽  
Time Derivative ◽  
Electron Plasma ◽  
Displacement Current ◽  
Ohm’S Law ◽  
Ohm's Law

Abstract. Fundamentally, the time derivative of the electric field is given by the displacement-current term in Maxwell's generalization of Ampère's law, and the time derivative of the electric current density is given by the generalized Ohm's law. The latter is derived by summing the accelerations of all the plasma particles and can be written exactly, with no approximations, in a (relatively simple) primitive form containing no other time derivatives. When one is dealing with time scales long compared to the inverse of the electron plasma frequency and spatial scales large compared to the electron inertial length, however, the time derivative of the current density becomes negligible in comparison to the other terms in the generalized Ohm's law, which then becomes the equation that determines the electric field itself. Thus, on all scales larger than those of electron plasma oscillations, neither the time evolution of J nor that of E can be calculated directly. Instead, J is determined by B through Ampère's law and E by plasma dynamics through the generalized Ohm's law. The displacement current may still be non-negligible if the Alfvén speed is comparable to or larger than the speed of light, but it no longer determines the time evolution of E, acting instead to modify J. For theories of substorms, this implies that, on time scales appropriate to substorm expansion, there is no equation from which the time evolution of the current could be calculated, independently of ∇xB. Statements about change (disruption, diversion, wedge formation, etc.) of the electric current are merely descriptions of change in the magnetic field and are not explanations.

Electro-Mechanical Properties of PbZrO3-PbTiO3 -Pb(Mn1/3Sb2/3)O3 Ceramics Under Vibration-Level Change

1994 ◽  
Vol 360 ◽  
Author(s):  
Sadayuki Takahashi ◽  
Yasuhiro Sasaki ◽  
Seiji Hirose ◽  
Kenji Uchino
Keyword(s):  
Mechanical Properties ◽  
Solid Solution ◽  
Electric Field ◽  
Heat Generation ◽  
Constant Current ◽  
Vibration Velocity ◽  
Ternary Solid Solution ◽  
Vibration Level ◽  
Low Field ◽  
Solid Solution System

AbstractElectro-mechanical properties in the pseudo-ternary solid solution system of PbZrO3-PbTiO3- Pb(Mn1/3Sb2/3)O3 piezoelectric ceramics were studied by changing the vibration- level using a constant current / velocity driving method. The vibration velocity is proportional to the driving electric field under a relatively low field. The velocity, however, deviates from a linear relationship as electric field increases and converges on a certain value.The increase of the vibration-level is accompanied by a large amount of heat generation as well, and this heat generation sets a practical upper limit of the vibration-level. The heat generation is caused by a dissipated-vibration-energy which is represented as a function of vibration velocity and the constants depending on the materials and transducers.In these pseudo-ternary solid solution ceramics, the compositional ratio which shows excellent electro-mechanical properties under a relatively low vibration-level does not necessarily coincide with the compositional ratio which is excellent under a relatively high vibration-level.

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