A time‐domain EM system measuring the step response of the ground

Geophysics ◽  
1984 ◽  
Vol 49 (7) ◽  
pp. 1010-1026 ◽  
Author(s):  
G. F. West ◽  
J. C. Macnae ◽  
Y. Lamontagne
Keyword(s):  
Magnetic Fields ◽  
Impulse Response ◽  
Electric Fields ◽  
Time Domain ◽  
Wide Band ◽  
Step Response ◽  
System Function ◽  
Response Measurement ◽  
Resistivity Method ◽  
Electric And Magnetic Fields

A wide‐band time‐domain EM system, known as UTEM, which uses a large fixed transmitter and a moving receiver has been developed and used extensively in a variety of geologic environments. The essential characteristics that distinguish it from other systems are that its system function closely approximates a stepfunction response measurement and that it can measure both electric and magnetic fields. Measurement of step rather than impulse response simplifies interpretation of data amplitudes, and improves the detection of good conductors in the presence of poorer ones. Measurement of electric fields provides information about lateral conductivity contrasts somewhat similar to that obtained by the gradient array resistivity method.

The quantitative advantages of using B-field sensors in time-domain EM measurement for mineral exploration and unexploded ordnance search

Geophysics ◽  
2012 ◽  
Vol 77 (4) ◽  
pp. WB137-WB148 ◽  
Author(s):  
Michael W. Asten ◽  
Andrew C. Duncan
Keyword(s):  
Impulse Response ◽  
Time Constant ◽  
Exponential Decay ◽  
Time Domain ◽  
Step Response ◽  
Late Time ◽  
Additional Parameter ◽  
Unexploded Ordnance ◽  
Response Measurement ◽  
Response Systems

The use of simple models for decay of conductive targets under conductive overburden and for the decay of magnetically permeable conductive steel objects allows quantitative consideration of the advantages of the use of magnetic-field detectors in time-domain electromagnetic (TEM) measurements, or more generally, the advantage of step response over impulse response TEM systems. We identified eight advantages of the step response versus impulse-response systems. The first two advantages relate to the inductive limit (early time) decay behavior, in which a target response amplitude is largely dependent on geometrical rather than conductivity parameters. Five further advantages occur when measuring response of a target in a conductive host or under conductive overburden; the maximum target-to-overburden response occurs 25%–30% earlier in time, the earliest target detection time occurs a factor 2–4 earlier, and the amplitude advantage of target-to-overburden response is a factor in the range of 1–10 for the step versus impulse-response systems, respectively. These advantages agree quantitatively with field observations on a chalcopyrite orebody under conductive cover. We used a model response for a conductive permeable sphere to derive mathematically consistent approximations for the power-law and exponential decay behaviors for step and impulse responses of metal objects, from which the onset of late-time exponential decay of EM responses of unexploded ordnance occurs about a factor of two earlier in time for the step response. This earlier-time transition together with the higher signal-to-noise ratio available from the step-response measurement makes measurement of the fundamental time-constant of unexploded ordnance (UXO) possible for medium and large UXO where the time constant is in the range of tens of milliseconds. This time-constant thus becomes accessible as an additional parameter for UXO characterization and discrimination.

scholarly journals Wide-band modelling of tower-footing grounding systems based on the impulse response measurement

2019 ◽  
Vol 29 (29) ◽  
pp. 1-11
Author(s):  
Ranko Jasika ◽  
Jovan Mrvić ◽  
Stefan Obradović ◽  
Ninoslav Simić
Keyword(s):  
Impulse Response ◽  
Wide Band ◽  
Response Measurement

Radiation in Materials

2019 ◽  
pp. 303-365
Author(s):  
Richard Freeman ◽  
James King ◽  
Gregory Lafyatis
Keyword(s):  
Magnetic Fields ◽  
Time Domain ◽  
Measurement Techniques ◽  
Group Versus ◽  
Index Of Refraction ◽  
The Real ◽  
Versus Phase ◽  
Fundamental Relationship ◽  
Electric And Magnetic Fields ◽  
The Time Domain

The interaction of electromagnetic radiation and matter is examined, specifically electric and magnetic fields in materials with real and imaginary responses: under certain conditions the fields move through the material as a wave and under others they diffuse. The movement of a pulse of radiation in dispersive materials is described in which there are two wave velocities: group versus phase. The reflection of light from a sharp interface is analyzed and the Fresnel reflection/transmission equations derived. The response of materials to applied electric and magnetic fields in the time domain are correlated to their frequency response of the material’s polarization. The generalized Kramers–Kronig equations are derived and their applicability as a fundamental relationship between the real and imaginary parts of any material’s polarizability is discussed in detail. Finally, practical measurement techniques for extracting the real and imaginary components of a material’s index of refraction are introduced.

Hall Currents and the Ejection of Prominences by Sunspots

1949 ◽  
Vol 2 (1) ◽  
pp. 39
Author(s):  
RG Giovanelli
Keyword(s):  
Magnetic Fields ◽  
Electric Fields ◽  
Magnetic Force ◽  
Large Space ◽  
Space Charges ◽  
Surrounding Atmosphere ◽  
Electric And Magnetic Fields ◽  
Order Of Magnitude ◽  
General Movement ◽  
Set Up

During the growth of sunspots induced electric fields may be expected to be set up in the surrounding atmosphere. It is shown that, because of the comparatively low conductivity perpendicular to lines of magnetic force, there are localized regions where large space charges occur, resulting in large electric fields perpendicular to the lines of magnetic force. Consequently both positive and negative charges drift in the same sense in a direction which is at right angles to the electric and magnetic fields, giving rise to a general movement of the gas. The drift velocities are difficult to estimate, but appear to be of the order of magnitude of those found in eruptive prominences.

Elastic Constants of Nematic Liquid Crystals

1972 ◽  
Vol 27 (6) ◽  
pp. 966-976 ◽  
Author(s):  
Hans Gruler ◽  
Terry J. Scheffer ◽  
Gerhard Meier
Keyword(s):  
Magnetic Fields ◽  
Electric Fields ◽  
Detailed Comparison ◽  
Theoretical Treatment ◽  
Electrical Capacitance ◽  
Normal Deformation ◽  
Electric And Magnetic Fields ◽  
The Magnetic Field ◽  
Dynamic Phenomena ◽  
Good Agreement

Abstract We present a theoretical treatment and give experimental observations of the deformation that occurs in a nematic liquid crystal when electric or magnetic fields are applied. We consider only normal deformations in the nematic material where fluid flow and other dynamic phenomena play no role. Three important sample geometries are considered in the magnetic field, and the experimentally observed deformations are in good agreement with theory. The normal deformation induced by electric fields is of interest from a device standpoint, and we give a solution for the deformation that is valid even for large dielectric anisotropics. This solution has been experimentally verified. We give a detailed comparison of the distortions produced by electric and magnetic fields and show that the deformations are of a similar form even though the field is nonuniform in the electric case. The change in birefringence and electrical capacitance as a function of distortion is discussed as a means of observing the deformation.

scholarly journals Влияние магнитных и электрических полей на динамику образования плазмоидов в гатчинском разряде

2022 ◽  
Vol 92 (3) ◽  
pp. 366
Author(s):  
Shixin Zhao ◽  
Chengxun Yuan ◽  
А.А. Кудрявцев ◽  
Jingfeng Yao ◽  
Г.Д. Шабанов
Keyword(s):  
Magnetic Fields ◽  
Electric Fields ◽  
Electric Charge ◽  
Active Phase ◽  
Ball Lightning ◽  
Electric And Magnetic Fields ◽  
Direction Of Movement

The behavior in magnetic and electric fields of the Gatchina discharge, which is used mainly to create an analog of ball lightning in the laboratory in a normal atmosphere, is analyzed. Shown that in these studies it is possible to determine the sign of an uncompensated electric charge as in the active phase of the discharge, and in the forming long-lived luminous formations. Also shown that electric and magnetic fields can change the direction of movement of the forming luminous formation and even completely block its formation. The type and mechanism of existence firework ball lightning are considered, photos of which are presented in widely known monographs on the ball lightning.

Reply to J. R. Wait by D. Rankin and R. P. Singh

Geophysics ◽  
1984 ◽  
Vol 49 (8) ◽  
pp. 1388-1388
Author(s):  
D. Rankin ◽  
R. P. Singh
Keyword(s):  
Magnetic Fields ◽  
Electric Fields ◽  
Horizontal Surface ◽  
Electric And Magnetic Fields ◽  
Surface Measurements

There is no real dispute between the magnetotellurist (Cagniard school) and the radio physicist (Norton school) in surface measurements of VLF and ULF fields. Each defines a mutually exclusive quantity which requires a different mode of measurement. The magnetotellurist measures the horizontal surface electric and magnetic fields, whereas, as Wait correctly points out, the radio physicist measures the horizontal and vertical electric fields.

Subtraction of powerline harmonics from geophysical records

Geophysics ◽  
1993 ◽  
Vol 58 (6) ◽  
pp. 898-903 ◽  
Author(s):  
Karl E. Butler ◽  
R. Don Russell
Keyword(s):  
North America ◽  
Magnetic Fields ◽  
Fundamental Frequency ◽  
Time Domain ◽  
Seismic Data ◽  
Power Transmission ◽  
Power Lines ◽  
Electric And Magnetic Fields ◽  
Harmonic Noise

Harmonic noise generated by power lines and electric railways has plagued geophysicists for decades. The noise occurs as electric and magnetic fields at the fundamental frequency of power transmission (typically 60 Hz in North America) and its harmonics. It may be recorded directly during time‐domain measurements of electric and magnetic felds, or indirectly, by geophone cables during the acquisition of seismic data.

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