Double Clamping Current Inverter with Adjustable Turn-off Time for Bucking Coil Helicopter Transient Electromagnetic Surveying

2020 ◽  
pp. 1-1
Author(s):  
Lihua Liu ◽  
Jutao Li ◽  
Ling Huang ◽  
Xiaojun Liu ◽  
Guangyou Fang
Keyword(s):  
Transient Electromagnetic ◽  
Current Inverter ◽  
Off Time

scholarly journals Double Trapezoidal Wave Transmitting System with Controllable Turn-Off Edge

2020 ◽  
Vol 10 (21) ◽  
pp. 7932
Author(s):  
Yuan Jiang ◽  
Yanju Ji ◽  
Yibing Yu ◽  
Shipeng Wang ◽  
Yuan Wang
Keyword(s):  
Polarization Effect ◽  
Induced Polarization ◽  
Emission Current ◽  
Wire Loop ◽  
Transient Electromagnetic ◽  
Charging Time ◽  
The Earth ◽  
Electromagnetic Measurement ◽  
Induced Polarization Effect ◽  
Off Time

For time domain transient electromagnetic measurement, the negative sign often appears in the polarization region, which contains the induced polarization information. It is considered that the polarization effect is caused by the capacitance charge of the earth. Extending the turn-off time of the emission current means increasing the charging time, and reducing the charging voltage, which makes the polarization effect easier to observe. Therefore, a double trapezoidal wave transmitting system with a controllable turn-off edge is designed in this paper. In the process of current transmitting, the turn-off time can be controlled by changing the clamping voltage depending on the passive clamping technology. By cutting into the absorption resistance, the current oscillation can be eliminated under the condition of ensuring linearity. To verify the effectiveness of the system, we designed a polarized wire loop based on the filament model simulating the polarized earth. Comparing the response of the wire loop, the emission current with short and long turn-off times contributes to inducing the induction and polarization fields respectively. The double trapezoidal wave transmitting system with a controllable turn-off edge is suitable for measuring the induced polarization effect.

scholarly journals Effects of full transmitting-current waveforms on transient electromagnetics: Insights from modeling the Albany graphite deposit

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. E255-E268 ◽  
Author(s):  
Sihong Zeng ◽  
Xiangyun Hu ◽  
Jianhui Li ◽  
Colin G. Farquharson ◽  
Peter C. Wood ◽  
...  
Keyword(s):  
Real Data ◽  
Forward Modeling ◽  
Northern Ontario ◽  
Data Set ◽  
Rock Types ◽  
Full Waveform ◽  
Transient Electromagnetic ◽  
Steady Stage ◽  
Geologic Model ◽  
Off Time

In transient electromagnetic (TEM) methods, the full transmitting-current waveform, not just the abrupt turn-off, can have effects on the measured responses. A 3D finite-element time-domain forward-modeling solver was used to investigate these effects. This was motivated by an attempt to match, via forward-modeling, real data from the Albany graphite deposit in northern Ontario, Canada. Initial modeling results for homogeneous half-spaces illustrate the effects that a full waveform can have on TEM responses, especially the durations of the steady stage and turn-off time. For the Albany data set, a geophysical conductivity model was developed from a geologic model that itself had been constructed predominantly from drillhole information. The conductivities of the various geologic units in the model were first estimated based on typical conductivity values for the respective rock types, then adjusted to fit the measured TEM data as closely as possible. We found that the TEM responses differed significantly from the pure step-off response and that incorporating the effects of the full waveform (particularly the linear ramp turn-off) greatly improved the match between observed and computed responses, especially for the early measurement times. In addition, this Albany example illustrates the presence of sign changes in TEM data caused primarily by localized conductivity targets.

Study of transient electromagnetic method measurements using a superconducting quantum interference device as B sensor receiver in polarizable survey area

Geophysics ◽  
2018 ◽  
Vol 83 (2) ◽  
pp. E111-E116 ◽  
Author(s):  
Shangyu Du ◽  
Yi Zhang ◽  
Yifeng Pei ◽  
Kun Jiang ◽  
Liangliang Rong ◽  
...  
Keyword(s):  
Quantum Interference ◽  
Electromagnetic Method ◽  
Transient Electromagnetic Method ◽  
Primary Field ◽  
Survey Area ◽  
Superconducting Quantum Interference Device ◽  
Sign Reversal ◽  
Wire Loop ◽  
Transient Electromagnetic ◽  
Off Time

Time-domain transient electromagnetic method (TEM) measurements sometimes exhibit a sign reversal in the secondary field during the off-time, which is usually attributed to the induced-polarization (IP) effect. In contrast with the conventional IP method, which uses a current source, TEM with an ungrounded transmitting loop operates using a pure voltage source, which is induced by the primary field switching on and off. We performed TEM measurements in a resistive survey area showing an IP effect, and we used a low-temperature superconducting quantum interference device (LT-SQUID) with sensitivity of [Formula: see text] as a magnetic field sensor. A sign reversal in all of our measurements was observed; furthermore, the negative amplitude reached [Formula: see text]. In-depth analysis with an extended version of a wire-filament circuit reveals that the large negative signal may be due to discharging of in-ground capacitance, an IP effect. The conduction response of the ground can be restored by subtracting the fitted discharging response (negative valued) from the observed data. To verify this operation, we compared TEM measurements with and without wire-loop targets, which can induce a conduction field with a known decay time constant during the off-time. The extracted conduction responses of the wire-loop targets match the expected ones well. This research reveals that the primary field switch-off must always be included when interpreting TEM data with sign reversal and an LT-SQUID may be a good alternative sensor for studying the IP effect in TEM.

Transient electromagnetic smoke rings in a halfspace during active transmitter excitation

Geophysics ◽  
2021 ◽  
pp. 1-38
Author(s):  
Adam Smiarowski ◽  
Greg Hodges
Keyword(s):  
Current Distribution ◽  
Current System ◽  
Primary Field ◽  
Depth Of Penetration ◽  
Near Surface ◽  
Surface Sensitivity ◽  
Field Coupling ◽  
Transient Electromagnetic ◽  
Smoke Ring ◽  
Off Time

The smoke ring concept is a useful device for understanding how the electromagnetic fields induced in a 1-D earth propagate and diffuse through a medium. Aside from facilitating a physical understanding of field propagation, the smoke ring concept has been used to interpret behavior of vertical and radial magnetic fields at the surface and used to estimate depth of penetration for conductivity-depth transforms. Past studies have focused on the current distribution during the off-time. We calculate and illustrate the current in a halfspace from a half-sine excitation (which provides a continuous induction). In comparison, the current pattern from a continuously excited waveform is more densely distributed near-surface than the off-time current system, suggesting that measurements during a continuously excited on-time are more sensitive to shallow targets. For airborne applications, where the primary field coupling changes and is an important noise source, a primary field-stripping algorithm impacts the current distribution but does not deleteriously affect near-surface sensitivity.

Excitation process under the ramp-step waveform of inductive source-induced polarization method

Geophysics ◽  
2020 ◽  
Vol 85 (2) ◽  
pp. E57-E65
Author(s):  
Yanju Ji ◽  
Yanqi Wu ◽  
Yuheng Wu ◽  
Yi Zhang
Keyword(s):  
Debye Model ◽  
Induced Polarization ◽  
Frozen Soil ◽  
Polarization Field ◽  
High Resistivity ◽  
Excitation Process ◽  
Transient Electromagnetic ◽  
Source Contributions ◽  
Polarizable Body ◽  
Off Time

Most previous studies explain the induced polarization (IP) effects in transient electromagnetic (TEM) data using an idealized but unrealizable step-waveform transmitter current. However, the ramp-step waveform, which is commonly applied in TEM measurement, has been given less attention. To explore the effects of the switch-off time, we have compared the IP responses induced by two waveforms: the step and the ramp step. We apply a wire-filament circuit composed of a Debye model and an inductor to identify the differences in the aspect of the energy transfer process. Furthermore, we extend the analysis to illustrate the IP effects in a frozen-soil zone, metallic sulfide ore, and graphite ore and to analyze the relationship between the switch-off time, IP effects, and the polarization parameters. The results indicate that the primary and secondary fields act as excitation sources of the polarization field. In the step waveform case, the excitation source of the polarization field is the secondary field. As the switch-off time increases, the contribution rate of the primary field gradually increases, especially in the high-resistivity media. The finding provides a new understanding of the excitation process of the IP effects and indicates that source contributions are variable in different situations. Moreover, a longer switch-off time weakens the IP effects severely, and in the high-resistivity, high-polarizable media, the IP effects are more sensitive to the switch-off time. Therefore, a suitable switch-off time should be chosen based on the properties of the polarizable media, such as resistivity and time constant. To detect a relatively high-resistivity, high-polarizable body, the switch-off time should be as short as possible. Nevertheless, to detect a relatively low-resistivity polarizable body, the IP effects are fairly insensitive to the switch-off time, so the transmitter waveform can easily meet the requirements.

Design of Transient Electromagnetic Transmitter Based on FPGA

2014 ◽  
Vol 496-500 ◽  
pp. 630-633 ◽  
Author(s):  
Lei Zhang ◽  
Qing Ming Duan ◽  
Hao Sun ◽  
Ting Zhe Huang ◽  
Jun Wei Shi ◽  
...  
Keyword(s):  
High Power ◽  
Detection System ◽  
High Reliability ◽  
Field Application ◽  
Constant Voltage ◽  
Transient Electromagnetic ◽  
Electromagnetic Detection ◽  
Voltage Clamping ◽  
Electromagnetic Transmitter ◽  
Off Time

Transient electromagnetic transmitter is a part of the transient electromagnetic detection system. In the aspect of short turn-off time for high-power current, there are still many problems to be solved urgently. This paper put forward a design scheme of transient electromagnetic transmitter, amplified the control signal with triode, and put forward a kind of passive constant voltage clamping absorbing circuit, which made the turn-off time shorter and the linearity of the emission currents lagging edge higher. This transient electromagnetic transmitter system is portable and easy to operate. Through experiments we can prove that the transmitter has the characteristic of short turn-off time and high reliability, and it has reached the requirements of field application.

scholarly journals 3D full-time anisotropic TEM modelling using a mixed BDF2/SAI method

2021 ◽  
Vol 18 (6) ◽  
pp. 995-1006
Author(s):  
Kui Huang ◽  
Kailiang Lu ◽  
Jianmei Zhou ◽  
Xiu Li ◽  
Lifei Meng
Keyword(s):  
Krylov Subspace ◽  
Coefficient Matrix ◽  
Time Response ◽  
Full Time ◽  
Anisotropic Model ◽  
Require Time ◽  
Transient Electromagnetic ◽  
Time Period ◽  
Spatial Discretisation ◽  
Off Time

Abstract Transient electromagnetic (TEM) data are affected by resistivity anisotropy, which should be considered in 3D modelling. The influence of anisotropy on full-time response is the main focus of this research. For spatial discretisation of an anisotropic model, the mimetic finite volume approach was applied. The accuracy of the shift-and-invert (SAI) Krylov subspace approach and the two-step backward differentiation formula (BDF2) for modelling 3D full-time electromagnetic data has been demonstrated. However, both algorithms require time-consuming calculations. The SAI technique requires a number of projection subspace constructions, whereas the BDF2 algorithm necessitates numerous coefficient matrix decompositions. We proposed a novel mixed BDF2/SAI algorithm in this paper, which combines the advantages of the two algorithms. The on-time response is computed using BDF2, while the off-time response is computed using the SAI-Krylov subspace method. The forward results of a 1D model with a half-sine waveform demonstrated that the new algorithm is accurate and faster than both the BDF2 algorithm and the SAI algorithm. During the full-time period, the forward results of a 3D anisotropic model with half-sine waveform show that abnormal responses can be induced. It was shown that the relative abnormal of ${{{\bf b}}_{\boldsymbol{z}}}$ is higher during the on-time period, while the relative abnormal of $\partial {{{\bf b}}_{\boldsymbol{z}}}/\partial t$ is higher during the off-time period. Furthermore, the change in relative anomaly is more obvious as the anisotropic block rotates around the x-axis. And the larger the rotation angle, the larger the relative anomaly.

Robust estimation of the band‐limited inductive‐limit response from impulse‐response TEM measurements taken during the transmitter switch‐off and the transmitter off‐time: Theory and an example from Voisey’s Bay, Labrador, Canada

Geophysics ◽  
2000 ◽  
Vol 65 (2) ◽  
pp. 476-481 ◽  
Author(s):  
Richard S. Smith ◽  
S. J. Balch
Keyword(s):  
Inductive Limit ◽  
Massive Sulfide ◽  
Drill Hole ◽  
Primary Response ◽  
Diagnostic Feature ◽  
Primary Field ◽  
Transient Electromagnetic ◽  
Ore Bodies ◽  
Band Limited ◽  
Off Time

Modern transient electromagnetic systems are able to take measurements in the transmitter on‐time. Integrating measurements taken during the transmitter switch‐off and those collected in the transmitter off‐time yield an estimate of the primary field plus the secondary inductive‐limit response. If the transmitter loop position is known and the position and orientation of the receiver dipoles are known, it is possible to calculate the primary field. When the theoretical primary field is subtracted from the measured inductive‐limit‐plus‐primary response, the inductive‐limit response can be isolated. An anomalous inductive‐limit response is a diagnostic feature of highly conductive ore bodies. On‐ and off‐time PROTEM data collected in a drill hole proximal to the Reid Brook Zone (one of the Voisey’s Bay deposits in Labrador, Canada) shows a strong inductive‐limit anomaly corresponding to an off‐hole conductor. A drill hole targeted to test this conductor intersected 20.4 m of mineralization, including 8.25 m of massive sulfide.

Effekte von L-Dopa auf die Speicherung und den Abruf verbaler Informationen bei Schlaganfallpatienten

2004 ◽  
Vol 15 (4) ◽  
pp. 275-286 ◽  
Author(s):  
D. Golz ◽  
E. Erdfelder
Keyword(s):  
Off Time

Zusammenfassung: In einer Doppel-Blind-Studie wurde geprüft, ob das katecholaminerg stimulierende Medikament L-Dopa die Gedächtnisleistungen von Schlaganfallpatienten steigern kann. 37 Patienten wurden zur On-Time und Off-Time des Medikaments einer neuropsychologischen Untersuchung unterzogen. Mittels Varianzanalysen konnte gezeigt werden, dass L-Dopa die verbalen episodischen Gedächtnisleistungen verbessern kann, und zwar offenbar speziell die Reproduktion und weniger die Rekognition von Informationen. Analysen auf der Grundlage des Speicherungs-Abruf-Modells von Batchelder und Riefer (1980 , 1986 ) demonstrierten darüber hinaus, dass eher die itemspezifische als die semantisch-relationale Verarbeitung von Itemgruppen profitiert. Eine Steigerung der Aufmerksamkeitsleistung im Sinne der “Alertness” konnte nicht ausgemacht werden, ebenso wenig ein bedeutsamer Zusammenhang von Aufmerksamkeits- und Gedächtnisleistungen. Die Ergebnisse können zusammenfassend dahingehend interpretiert werden, dass insbesondere der Abruf itemspezifischer Informationen durch L-Dopa selektiv gefördert werden kann. Die mögliche vermittelnde Rolle des Neurotransmitters Noradrenalin wird diskutiert.

Sign in / Sign up

Export Citation Format

Share Document