Detectability of Intermediate conductive and resistive layers by time‐domain electromagnetic sounding

Geophysics ◽  
1979 ◽  
Vol 44 (11) ◽  
pp. 1862-1878 ◽  
Author(s):  
Rajni K. Verma ◽  
Kumarendra Mallick
Keyword(s):  
Time Domain ◽  
Intermediate Layer ◽  
Mutual Coupling ◽  
Pulse Excitation ◽  
Layered Earth ◽  
Layer Sequence ◽  
Wide Range ◽  
Earth Models ◽  
Element System ◽  
The Time Domain

An analysis in the time domain has been made of the detectability of an intermediate layer in a three‐layer earth model by the horizontal coplanar loops (system I) and loop‐wire element (system V) electromagnetic (EM) sounding systems for a train of half‐sinusoidal and square waveforms of alternating polarity. The studies involve conversion into the time domain by a Fourier series summation of the matched complex mutual coupling ratios, computed by the digital linear filter method, of the layered‐earth models. The three‐layer earth models considered here have the following resistivity distribution: [Formula: see text], [Formula: see text] for the conductive case, and [Formula: see text], [Formula: see text] for the resistive case (subscripts 1, 2, and 3 represent the first, second, and third layer in the three‐layer sequence; ρ is the resistivity). The intermediate‐layer thickness varies over a wide range. The responses of the three‐layer earth models have been compared with that of a homogeneous earth with the resistivity of the top layer in the three‐layer sequence. The measurement error is assumed to be of the order of 3 percent, and an rms difference of 10 percent between the responses for the three‐layer and the homogenous earth is defined as the detectability level. On the basis of this definition, it is observed that the horizontal coplanar loops system (system I) is better than the loop‐wire element system (system V) in detecting the thin intermediate layer, which may be either conductive or resistive. For a transmitter‐receiver separation (R) of 1000 m by square‐pulse excitation, a conductive intermediate layer as thin as 1/14 of the top layer can be detected by system I and as thin as 1/6 by system V. For the resistive intermediate layer, the corresponding thickness ratios are 0.6 for system I and 1.25 for system V. The detectability is lower in the case of half‐sinusoidal pulse excitation. Instead of normalizing the mutual coupling of the layered earth to the free‐space coupling, the detectability is enhanced markedly if the normalization is done to the coupling over a homogeneous ground. For system V, it is observed that an intermediate layer as thin as 1/100 in the conductive case and 1/4 in the resistive case of the top layer can be detected easily by this approach. Some direct comparisons between the time‐domain and the frequency‐domain results also are given.

Electromagnetic modeling of 3-D sources over 2-D inhomogeneities in the time domain

Geophysics ◽  
1992 ◽  
Vol 57 (8) ◽  
pp. 994-1003 ◽  
Author(s):  
Michael Leppin
Keyword(s):  
Differential Equations ◽  
Diffusion Equation ◽  
Time Domain ◽  
Magnetic Induction ◽  
Host Rock ◽  
Vertical Component ◽  
Wavenumber Domain ◽  
Transient Electromagnetic ◽  
Wide Range ◽  
The Time Domain

A numerical method is presented by which the transient electromagnetic response of a two‐dimensional (2-D) conductor, embedded in a conductive host rock and excited by a rectangular current loop, can be modeled. This 2.5-D modeling problem has been formulated in the time domain in terms of a vector diffusion equation for the scattered magnetic induction, which is Fourier transformed into the spatial wavenumber domain in the strike direction of the conductor. To confine the region of solution of the diffusion equation to the conductive earth, boundary values for the components of the magnetic induction on the ground surface have been calculated by means of an integral transform of the vertical component of the magnetic induction at the air‐earth interface. The system of parabolic differential equations for the three magnetic components has been integrated for 9 to 15 discrete spatial wavenumbers ranging from [Formula: see text] to [Formula: see text] using an implicit homogeneous finite‐difference scheme. The discretization of the differential equations on a grid representing a cross‐section of the conductive earth results in a large, sparse system of linear equations, which is solved by the successive overrelaxation method. The three‐dimensional (3-D) response has been computed by an inverse Fourier transformation of the cubic spline interpolated scattered magnetic induction in the wavenumber domain using a digital filtering technique. To test the algorithm, responses have been computed for a two‐layered half‐space and a vertical prism embedded in a conductive host rock. These examples were then compared with results obtained analytically or numerically using frequency‐domain finite‐element and time‐domain integral equation methods. The new numerical procedure gives satisfactory results for a wide range of 2-D conductivity distributions with conductivity ratios exceeding 1:100, provided the grid is sufficiently refined at the corners of the conductivity anomalies.

scholarly journals Innovative Multi-Site Photoplethysmography Analysis for Quantifying Pulse Amplitude and Timing Variability Characteristics in Peripheral Arterial Disease

2018 ◽  
Author(s):  
Michael Bentham ◽  
Gerard Stansby ◽  
John Allen
Keyword(s):  
Peripheral Arterial Disease ◽  
Frequency Domain ◽  
Time Domain ◽  
Domain Analysis ◽  
Arterial Disease ◽  
Timing Variability ◽  
Wide Range ◽  
Healthy Control ◽  
The Time Domain ◽  
Peripheral Arterial

Photoplethysmography (PPG) is a simple-to-perform vascular optics measurement technique that can detect changes in blood volume in the microvascular tissue bed. Beat-to-beat analysis of the PPG waveform enables the study of the variability of pulse features such as amplitude and pulse arrival time (PAT), and when quantified in the time and frequency domains, has considerable potential to shed light on perfusion changes associated with peripheral arterial disease (PAD). In this pilot study innovative multi-site bilateral finger and toe PPG recordings from 43 healthy control subjects and 31 PAD subjects were compared (recordings each at least 5 minutes, collected in a warm temperature-controlled room). Beat-to-beat normalized amplitude and PAT variability was then quantified in the time-domain using SD and IQR measures and in the frequency-domain bilaterally using Magnitude Squared Coherence (MSC). Significantly reduced normalized amplitude variability (healthy control 0.0384 (IQR 0.0217-0.0744) vs PAD 0.0160 (0.0080-0.0338) (p<0.001) and significantly increased PAT variability (healthy control 0.0063 (0.0052-0.0086) vs PAD 0.0093 (0.0078-0.0144) (p<0.001) was demonstrated in PAD using the time-domain analysis. Frequency-domain analysis demonstrated significantly lower MSC values across a range of frequency bands for PAD patients. These changes suggest a loss of right-to-left body side coherence and cardiovascular control in PAD. This study has also demonstrated the feasibility of using these measurement and analysis methods in studies investigating multi-site PPG variability for a wide range of cardiac and vascular patient groups.

scholarly journals Application of L1 Trend Filtering Technology on the Current Time Domain Spectroscopy of Dielectrics

Electronics ◽  
2019 ◽  
Vol 8 (9) ◽  
pp. 1046
Author(s):  
Changyou Suo ◽  
Zhonghua Li ◽  
Yunlong Sun ◽  
Yongsen Han
Keyword(s):  
Time Series ◽  
Time Domain ◽  
Time Complexity ◽  
Time Range ◽  
Test Results ◽  
Current Time ◽  
Time Domain Spectroscopy ◽  
Filtering Algorithms ◽  
Wide Range ◽  
The Time Domain

The current time domain spectroscopy of dielectrics provides important information for the analysis of dielectric properties and mechanisms. However, there is always interference during the testing process, which seriously affects the analysis of the test results. Therefore, the effective filtering of current time domain spectroscopy is particularly necessary. L1 trend filtering can estimate the trend items exactly in a set of time series. It has been widely used in the fields of economics and sociology. Therefore, this paper attempts to apply L1 trend filtering to the current time domain spectroscopy. Firstly, polarization and depolarization currents are measured in the laboratory. Then the test results are filtered by L1 trend filtering and the filtering effects are compared with several common filtering algorithms, such as a sliding mean filter and Savitzky–Golay smoothing filter. Finally, the robustness and time complexity of L1 trend filtering are analyzed. The filtering results show that because the polarization currents vary in a wide range of the time domain (about 2–3 orders of magnitude), smooth and undistorted curves in the whole test time range can hardly be obtained through common filtering algorithms, while they can be obtained by L1 trend filtering. The results of robustness analysis and time complexity analysis show that L1 trend filtering can extract the trend items accurately in the time series under given different noise levels, and the execution time is also lower than 176.67 s when the number of tested points is no more than 20,000. Those results show that L1 trend filtering can be applied to the time domain current spectroscopy of dielectrics.

scholarly journals Time domain solution of electromagnetic radiation model of the grounding system excited by pulse current

2020 ◽  
Vol 35 (1) ◽  
pp. 74-81
Author(s):  
Nedis Dautbasic ◽  
Adnan Mujezinovic
Keyword(s):  
Differential Equation ◽  
Electromagnetic Radiation ◽  
Time Domain ◽  
Gauge Condition ◽  
Pulse Excitation ◽  
Solution Technique ◽  
Grounding System ◽  
Integro Differential Equation ◽  
Transient Voltage ◽  
The Time Domain

This paper deals with an advanced electromagnetic radiation approach for analyzing the time-domain performance of grounding systems under pulse excitation currents. The model of the grounding systems presented within this paper is based on the homogeneous Pocklington integro-differential equation for the calculation of the current distribution on the grounding system and Lorentz gauge condition which is used for the grounding system transient voltage calculation. For the solution of the Pocklington integro-differential equation, the indirect boundary element method and marching on-in time method are used. Fur- thermore, the solution technique for the calculation of the grounding system transient voltage is presented. The numerical model for the calculation of the grounding system transients was verified by comparing it with onsite measurement results.

scholarly journals A Computationally Efficient Algorithm for Feedforward Active Noise Control Systems

Electronics ◽  
2020 ◽  
Vol 9 (9) ◽  
pp. 1504 ◽  
Author(s):  
Stefano Gaiotto ◽  
Antonino Laudani ◽  
Gabriele Maria Lozito ◽  
Francesco Riganti Fulginei
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Noise Control ◽  
Active Noise Control ◽  
Parameter Tuning ◽  
Processing Load ◽  
Block Basis ◽  
Active Noise ◽  
Wide Range ◽  
The Time Domain

In this paper, a novel algorithm with high computational efficiency is proposed for the filter adaptation in a feedforward active noise control system. The proposed algorithm Zero Forcing Block Adaptive Filter (ZF-BAF) performs filter adaptation on a block-by-block basis in the frequency domain. Filtering is performed in the time domain on a sample-by-sample basis. Working in the frequency domain permits us to get sub-linear complexity, whereas filtering in the time domain minimizes the latency. Furthermore, computational burden is tunable to meet specific requirements about adaptation speed and processing load. No other parameter tuning according to the working condition is required. Computer simulations, performed in different realistic cases against other high-performing time and frequency-domain algorithms, show that achievable performances are comparable, or even better, with those of the algorithms perfectly tuned for each specific case. Robustness exhibited in the tests suggests that performances are expected to be even better in a wide range of real cases where it is impossible to know a priori how to tune the algorithms.

Time Domain Response of Electrical Ceramics Micro to Megaseconds

1997 ◽  
Vol 500 ◽  
Author(s):  
F. A. Modine
Keyword(s):  
Electrical Properties ◽  
Power Law ◽  
Time Domain ◽  
Polarization Current ◽  
Electrical Measurements ◽  
Dispersive Transport ◽  
Electron Traps ◽  
Source Impedance ◽  
Wide Range ◽  
The Time Domain

ABSTRACTThe electrical properties of ceramics can be measured in either the time domain or in the frequency domain. But for electrically nonlinear ceramics such as varistors, time-domain measurements provide insights that are different and more relevant to material performance as well as being more physically incisive. This article focuses specifically on the electrical properties of ZnO varistors, but much of it is of relevance for other materials, in particular those materials with grain-boundary barriers and disordered ceramics or glasses. The interpretation of electrical measurements in the time domain is profoundly influenced by such practical matters as source impedance and waveform characteristics. Experimental results are presented for both high and low source impedance relative to that of a test varistor, and the difference in experimental difficulty and ease of interpretation is described. Time-domain measurements of capacitance and of the inductive response of varistors to large, fast electrical pulses are presented and their implications for varistor theory are given. Experimental evidence is given of short- and long-term memory in varistors. These memory phenomena are ascribed respectively to the life time of holes that become trapped in barriers and to polarization currents originating from deep electron traps. Polarization current measurements are presented for a wide range of time and temperature. The power-law time dependence and “universal” behavior of these currents is discussed. The exponent that describes the power law behavior is seen to change with temperature, and the change is interpreted as a double transition from diffusive to dispersive transport that originates with current from two different electron traps.

scholarly journals Comparison of observed borehole temperatures in Antarctica with simulations using a forward model driven by climate model outputs covering the past millennium

2020 ◽  
Vol 16 (4) ◽  
pp. 1411-1428
Author(s):  
Zhiqiang Lyu ◽  
Anais J. Orsi ◽  
Hugues Goosse
Keyword(s):  
Surface Temperature ◽  
Antarctic Peninsula ◽  
Time Domain ◽  
Climate Model ◽  
Forward Model ◽  
Model Data ◽  
West Antarctica ◽  
Data Comparison ◽  
Wide Range ◽  
The Time Domain

Abstract. The reconstructed surface-temperature time series from boreholes in Antarctica have significantly contributed to our understanding of multidecadal and centennial temperature changes and thus provide a good way to evaluate the ability of climate models to reproduce low-frequency climate variability. However, up to now, there has not been any systematic model–data comparison based on temperature from boreholes at a regional or local scale in Antarctica. Here, we discuss two different ways to perform such a comparison using borehole measurements and the corresponding reconstructions of surface temperature at the West Antarctic Ice Sheet (WAIS) Divide, Larissa, Mill Island, and Styx Glacier in Antarctica. The standard approach is to compare the surface temperature simulated by the climate model at the grid cell closest to each site with the reconstructions in the time domain derived from the borehole temperature observations. Although some characteristics of the reconstructions, for instance the nonuniform smoothing, limit to some extent the model–data comparison, several robust features can be evaluated. In addition, a more direct model–data comparison based on the temperature measured in the boreholes is conducted using a forward model that simulates explicitly the subsurface temperature profiles when driven with climate model outputs. This comparison in the depth domain is not only generally consistent with observations made in the time domain but also provides information that cannot easily be inferred from the comparison in the time domain. The major results from these comparisons are used to derive metrics that can be applied for future model–data comparison. We also describe the spatial representativity of the sites chosen for the metrics. The long-term cooling trend in West Antarctica from 1000 to 1600 CE (−1.0 ∘C) is generally reproduced by the models but often with a weaker amplitude. The 19th century cooling in the Antarctic Peninsula (−0.94 ∘C) is not reproduced by any of the models, which tend to show warming instead. The trend over the last 50 years is generally well reproduced in West Antarctica and at Larissa (Antarctic Peninsula) but overestimated at other sites. The wide range of simulated trends indicates the importance of internal variability in the observed trends and shows the value of model–data comparison to investigate the response to forcings.

scholarly journals Innovative Multi-Site Photoplethysmography Analysis for Quantifying Pulse Amplitude and Timing Variability Characteristics in Peripheral Arterial Disease

Diseases ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 81 ◽  
Author(s):  
Michael Bentham ◽  
Gerard Stansby ◽  
John Allen
Keyword(s):  
Peripheral Arterial Disease ◽  
Frequency Domain ◽  
Time Domain ◽  
Domain Analysis ◽  
Arterial Disease ◽  
Amplitude Variability ◽  
Wide Range ◽  
Healthy Control ◽  
The Time Domain ◽  
Peripheral Arterial

Photoplethysmography (PPG) is a simple-to-perform vascular optics measurement technique that can detect blood volume changes in the microvascular bed of tissue. Beat-to-beat analysis of the PPG waveform enables the study of the variability of pulse features, such as the amplitude and the pulse arrival time (PAT), and when quantified in the time and frequency domains, has considerable potential to shed light on perfusion changes associated with peripheral arterial disease (PAD). In this pilot study, innovative multi-site bilateral finger and toe PPG recordings from 43 healthy control subjects and 31 PAD subjects were compared (recordings each at least five minutes, collected in a warm temperature-controlled room). Beat-to-beat normalized amplitude variability and PAT variability were then quantified in the time-domain using two simple statistical measures and in the frequency-domain bilaterally using magnitude squared coherence (MSC). Significantly reduced normalized amplitude variability (healthy control 0.0384 (interquartile range 0.0217–0.0744) vs. PAD 0.0160 (0.0080–0.0338) (p < 0.0001)) and significantly increased PAT variability (healthy control 0.0063 (0.0052–0.0086) vs. PAD 0.0093 (0.0078–0.0144) (p < 0.0001)) was demonstrated for the toe site in PAD using the time-domain analysis. Frequency-domain analysis demonstrated significantly lower MSC values across a range of frequency bands for PAD patients. These changes suggest a loss of right-to-left body side coherence and cardiovascular control in PAD. This study has also demonstrated the feasibility of using these measurement and analysis methods in studies investigating multi-site PPG variability for a wide range of cardiac and vascular patient groups.

scholarly journals The time-domain magnetotelluric response over three-layer earth models

1995 ◽  
Vol 123 (1) ◽  
pp. 125-130
Author(s):  
R. P. Singh ◽  
Y. Kant ◽  
U. K. Singh
Keyword(s):  
Time Domain ◽  
Earth Models ◽  
The Time Domain
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