A transient electric dipole‐dipole method for mapping the conductivity of the sea floor

Geophysics ◽  
1986 ◽  
Vol 51 (4) ◽  
pp. 984-987 ◽  
Author(s):  
R. N. Edwards ◽  
A. D. Chave
Keyword(s):  
Electrical Conductivity ◽  
Half Space ◽  
Electric Dipole ◽  
Sea Water ◽  
Early Time ◽  
Electrical Measurements ◽  
Transient Responses ◽  
Electromagnetic System ◽  
Sea Floor ◽  
Conductivity Contrast

The electrical conductivity of the sea floor is usually much less than that of sea water, and not all electrical measurements made on the sea floor are particularly sensitive to the electrical conductivity value. The analytic impulse and step‐on transient responses of two conductive, adjoining half‐spaces (with a large conductivity contrast) to an in‐line electric dipole‐dipole electromagnetic system located on the interface are derived. The shape of the transient at relatively early time is seen to be independent of the conductivity of the more conductive half‐space and is indicative of the conductivity of the less conductive haft‐space. Based on this observation, a simple, practical system can be designed to measure sea floor conductivity.

Two‐dimensional modeling of a towed in‐line electric dipole‐dipole sea‐floor electromagnetic system: The optimum time delay or frequency for target resolution

Geophysics ◽  
1988 ◽  
Vol 53 (6) ◽  
pp. 846-853 ◽  
Author(s):  
R. N. Edwards
Keyword(s):  
Time Delay ◽  
Half Space ◽  
Electric Dipole ◽  
Late Time ◽  
Crustal Material ◽  
Two Dimensional ◽  
Optimum Time ◽  
Electromagnetic System ◽  
Sea Floor ◽  
Dipole System

Towed in‐line transient electric dipole‐dipole systems are being used to map the electrical conductivity of the sea floor. The characteristic response of a double half‐space model representing conductive seawater and less conductive crustal material to a dipole‐dipole system located at the interface consists of two distinct parts. As time in the transient measurements progresses, two changes in field strength are observed. The first change is caused by the diffusion of the electromagnetic field through the resistive sea floor; the second is caused by diffusion through the seawater. The characteristic times at which the two events occur are measures of sea‐floor and seawater conductivity, respectively. Entirely equivalent responses are observed in a frequency‐domain measurement as frequency is swept from high to low. The simple double half‐space response is modified when the towed array crosses over a conductivity anomaly. I evaluate the magnitude of the anomalous response as a function of delay time and frequency using a two‐dimensional theory and a vertical, plate‐like target. If the ratio of the conductivity of the seawater to that of the sea floor is greater than unity, then an optimum time delay or frequency can be found which maximizes the response. For large conductivity contrasts, the optimum response is greater than the response at late time or zero frequency by a factor of the order of the conductivity ratio.

The transient EM step response of a dipping plate in a conductive half‐space

Geophysics ◽  
1992 ◽  
Vol 57 (9) ◽  
pp. 1116-1126 ◽  
Author(s):  
James E. Hanneson
Keyword(s):  
Half Space ◽  
Free Space ◽  
Early Time ◽  
Step Response ◽  
Current Loop ◽  
Late Time ◽  
Electromagnetic System ◽  
University Of Toronto ◽  
Transient Electromagnetic ◽  
Induction Process

An algorithm for computing the transient electromagnetic (TEM) response of a dipping plate in a conductive half‐space has been developed. For a stationary [Formula: see text] current loop source, calculated profiles simulate the response of the University of Toronto electromagnetic system (UTEM) over a plate in a 1000 Ω ⋅ m half‐space. The objective is to add to knowledge of the galvanic process (causing poloidal plate currents) and the local induction process (causing toroidal currents) by studying host and plate currents with respect to surface profiles. Both processes can occur during TEM surveys. Plates are all [Formula: see text] thick with various depths, dips, and conductances. Calculated host and plate currents provide quantitative examples of several effects. For sufficiently conductive plates, the late time currents are toroidal as for a free‐space host. At earlier times, or at all times for poorly conducting plates, the plate currents are poloidal, and the transitions to toroidal currents, if they occur, are gradual. At very late times, poloidal currents again dominate any toroidal currents but this effect is rarely observed. Stripped, point‐normalized profiles, which reflect secondary fields caused by the anomalous plate currents, illustrate effects such as early time blanking (caused by noninstantaneous diffusion of fields into the target), mid‐time anomaly enhancement (caused by galvanic currents), and late time plate‐in‐free‐space asymptotic behavior.

Effect of MCl (M = Na, K) addition on microstructure and electrical conductivity of forsterite

2020 ◽  
Vol 92 (1) ◽  
pp. 10901
Author(s):  
Saloua El Asri ◽  
Hamid Ahamdane ◽  
Lahoucine Hajji ◽  
Mohamed El Hadri ◽  
Moulay Ahmed El Idrissi Raghni ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Electrical Conductivity ◽  
Single Phase ◽  
Sol Gel ◽  
Complex Impedance ◽  
Transmission Spectra ◽  
Electrical Measurements ◽  
Cation Type ◽  
Edx Analyses ◽  
The Fourier Transform

Forsterite single phase powder Mg2SiO4 was synthesized by sol–gel method alongside with heat treatment, using two different cation alkaline salts MCl as mineralizers (M = Na, K) with various mass percentages (2.5, 5, 7.5, and 10 wt.%). In this work, we report on the effect of the cation type and the added amount of used mineralizer on microstructure and electrical conductivity of Mg2SiO4. The formation of forsterite started at 680–740  °C and at 630–700  °C with KCl and NaCl respectively, as shown by TG-DTA and confirmed by XRD. Furthermore, the Fourier transform infrared (FTIR) transmission spectra indicated bands corresponding to vibrations of forsterite structure. The morphology and elemental composition of sintered ceramics were examined by SEM-EDX analyses, while their densities, which were measured by Archimedes method, increased with addition of both alkaline salts. The electrical measurements were performed by Complex Impedance Spectroscopy. The results showed that electrical conductivity increased with the addition of both mineralizers, which was higher for samples prepared with NaCl than those prepared with KCl.

Radio and Electrical Measurements on Glacial Streams

1987 ◽  
Vol 33 (114) ◽  
pp. 239-242
Author(s):  
M. E. R. Walford
Keyword(s):  
Electrical Conductivity ◽  
Water Channel ◽  
Water System ◽  
Low Frequency ◽  
Water Channels ◽  
Radiative Loss ◽  
Radio Waves ◽  
Electrical Measurements ◽  
Water Conductivity ◽  
Glacier Surface

AbstractWe discuss the suggestion that small underwater transmitters might be used to illuminate the interior of major englacial water channels with radio waves. Once launched, the radio waves would naturally tend to be guided along the channels until attenuated by absorption and by radiative loss. Receivers placed within the channels or at the glacier surface could be used to detect the signals. They would provide valuable information about the connectivity of the water system. The electrical conductivity of the water is of crucial importance. A surface stream on Storglaciären, in Sweden, was found, using a low-frequency technique, to have a conductivity of approximately 4 × 10−4 S m−1. Although this is several hundred times higher than the conductivity of the surrounding glacier ice, the contrast is not sufficient to permit us simply to use electrical conductivity measurements to establish the connectivity of englacial water channels. However, the water conductivity is sufficiently small that, under favourable circumstances, radio signals should be detectable after travelling as much as a few hundred metres along an englacial water channel. In a preliminary field experiment, we demonstrated semi quantitatively that radio waves do indeed propagate as expected, at least in surface streams. We conclude that under-water radio transmitters could be of real practical value in the study of the englacial water system, provided that sufficiently robust devices can be constructed. In a subglacial channel, however, we expect the radio range would be much smaller, the environment much harsher, and the technique of less practical value.

scholarly journals Simultaneous Desalination of Sea water and Electricity Production with New Membrane Technology, Air-Cathode Microbial Desalination Cells

2015 ◽  
Vol 10 (1) ◽  
pp. 115-120 ◽  
Author(s):  
Mahdi Asadi-Ghalhari ◽  
Nasser Mehrdadi ◽  
Gholamreza Nabi-Bidhendi
Keyword(s):  
Electrical Conductivity ◽  
Sea Water ◽  
Low Energy ◽  
Electricity Production ◽  
Synthetic Wastewater ◽  
Air Cathode ◽  
Middle Chamber ◽  
Microbial Desalination Cell ◽  
Voltage Generation ◽  
Maximum Voltage

Water and energy shortages, has increased the need for methods that can provide low energy for desalination of sea water. Microbial desalination cell is one of the most important of these methods. In this study we use air cathode MDC for desalination of seawater. The maximum voltage, power and current density was 607mV, 521mW/m2 and 858mA/m2 (25mM PBS) and 701mV, 695mW/m2 and 992mA/m2 (50mM PBS) respectively. During the period of the voltage generation in 50mM PBS was about 1.5 times of 25mM PBS. Under this situation, EC of seawater with initial electrical conductivity declined by 48.31±3% (25mM PBS) and 46.71±2.73% (50mM PBS). As well as decrease of salt from sea water in the middle chamber, EC in synthetic wastewater and catholyte slightly increased. So that Change percent of EC in synthetic wastewater was 44.20 ± 11.94(25mM PBS) and 27.94 ± 3 (50 mM PBS) and in catholyte was 211.66 ± 22.41(25mM PBS) and 119.24 ± 11.25 (50 mM PBS) respectively. These results show that the MDC can also be used as a pretreatment to reverse osmosis; simultaneously the energy required in this process is also partly meet.

Vetem - A Very Early Time Electromagnetic System - The First Year

1995 ◽  
Author(s):  
Louise Pellerin ◽  
Victor F. Labson ◽  
M. Cathy Pfeifer
Keyword(s):  
Early Time ◽  
First Year ◽  
Electromagnetic System
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