scholarly journals High resolution electromagnetic methods and low frequency dispersion of rock conductivity

1999 ◽  
Vol 42 (4) ◽  
Author(s):  
B. S. Svetov ◽  
V. V. Ageev
Keyword(s):  
High Resolution ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Electromagnetic Methods ◽  
Near Zone ◽  
Vertical Magnetic Dipole ◽  
Time Domains ◽  
Debye Formula ◽  
Wave Phenomena ◽  
Depth Of Investigation

The influence of frequency dispersion of conductivity (induced polarization) of rocks on the results of electromagnetic (EM) sounding was studied on the basis of calculation of electric field of vertical magnetic dipole above horizontally layered polarizable sections. Frequency dispersion was approximated by the Debye formula. Polarizable homogeneous halfspace, two, three and multilayered sections were analyzed in frequency and time domains. The calculations for different values of chargeability and time constants of polarization were performed. In the far zone of a source, the IP of rocks led to quasi-wave phenomena. They produced rapid fluctuations of frequency and transient sounding curves (interference phenomena, multireflections in polarizable layers). In the case of transient sounding in the near zone of a source quasistatic distortions prevailed, caused by the counter electromotive force arising in polarizable layers which may lead to strong changes in transient curves. In some cases quasiwave and quasistatic phenomena made EM sounding curves non-interpretable in the class of quasistationary curves over non-dispersive sections. On the other hand, they could increase the resolution and depth of investigation of EM sounding. This was confirmed by an experience of "high-resolution" electroprospecting in Russia. The problem of interpretation of EM sounding data in polarizable sections is nonunique. To achieve uniqueness it is probably necessary to complement them by soundings of other type.

scholarly journals Quasi-Static Solution for ELF/SLF near-Zone Field of a Vertical Magnetic Dipole near the Surface of a Lossy Half-Space

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Lina He ◽  
Tong He ◽  
Kai Li
Keyword(s):  
Magnetic Dipole ◽  
Numerical Solutions ◽  
Low Frequency ◽  
Analytical Techniques ◽  
Static Solution ◽  
Static Approximation ◽  
Near Zone ◽  
Vertical Magnetic Dipole ◽  
Validity Limit ◽  
Zone Field

Dipole antennas over the boundary between two different media have been widely used in the fields of geophysics exploration, oceanography, and submerged communication. In this paper, an analytical method is proposed to analyse the near-zone field at the extremely low frequency (ELF)/super low frequency (SLF) range due to a vertical magnetic dipole (VMD). For the lack of feasible analytical techniques to derive the components exactly, two reasonable assumptions are introduced depending on the quasi-static definition and the equivalent infinitesimal theory. Final expressions of the electromagnetic field components are in terms of exponential functions. By comparisons with direct numerical solutions and exact results in a special case, the correctness and effectiveness of the proposed quasi-static approximation are demonstrated. Simulations show that the smallest validity limit always occurs for component H2z, and the value of k2ρ should be no greater than 0.6 in order to keep a good consistency.

scholarly journals Development Of High-Resolution Mechanical Spectroscopy, HRMS: Status And Perspectives. HRMS Coupled With A Laser Dilatometer

2015 ◽  
Vol 60 (3) ◽  
pp. 2069-2076 ◽  
Author(s):  
L.B. Magalas
Keyword(s):  
High Resolution ◽  
Materials Science ◽  
Low Frequency ◽  
Research Area ◽  
Computing Methods ◽  
Stress And Strain ◽  
Loss Angle ◽  
Mechanical Spectroscopy ◽  
Mechanical Loss ◽  
Time Domains

Abstract Recent achievements in the development of low-frequency high-resolution mechanical spectroscopy (HRMS) are briefly reported. It is demonstrated that extremely low values of the loss angle, ϕ, (tanϕb = 1×10−5) can be measured as a function of frequency, and the precision in estimation of the dynamic modulus is better than 1×10−5 in arbitrary units. Three conditions must be fulfilled to obtain high resolution in subresonant and resonant mechanical loss measurements: (1) noise in stress and elastic strain signals must be lower than 70 dB, (2) high quality of stress and strain signals must be tested both in the frequency- and time-domains, and (3) the estimation of the mechanical loss and modulus must be verified by at least two different computing methods operating in the frequency- and time-domains. It is concluded that phase measurements in the subresonant domain are no longer determined by precision in estimation of the loss angle. Recent developments in high-resolution resonant mechanical loss measurements stem from the application of advanced nonparametric and parametric computing methods and algorithms to estimate the logarithmic decrement and the elastic modulus from exponentially damped free decaying oscillations embedded in experimental noise. It is emphasized that HRMS takes into account the presence of noise in the stress and strain signals, which has not yet been addressed in the literature. The coupling of a low-frequency mechanical spectrometer with an in-situ laser dilatometer is suggested as a new perspective research area in Materials Science.

Numerical evaluation of active source magnetics as a method for imaging high-resolution near-surface magnetic heterogeneity

Geophysics ◽  
2017 ◽  
Vol 82 (5) ◽  
pp. J27-J38 ◽  
Author(s):  
Kyubo Noh ◽  
Ki Ha Lee ◽  
Seokmin Oh ◽  
Soon Jee Seol ◽  
Joongmoo Byun
Keyword(s):  
High Resolution ◽  
Frequency Domain ◽  
Remanent Magnetization ◽  
Low Frequency ◽  
Magnetic Response ◽  
Near Surface ◽  
Magnetic Interpretation ◽  
Active Source ◽  
Em Induction ◽  
Depth Of Investigation

We have evaluated a geophysical method that uses a low-frequency magnetic source to image subsurface magnetic heterogeneity. This active source approach can be used to image magnetic features at higher resolutions than the conventional passive geomagnetic method. Importantly, this frequency-domain active source approach is independent of the effects of remanent magnetization, which complicates the interpretation of geomagnetic data. We carried out forward modeling of frequency-domain electromagnetic (EM) data and we found that, at frequencies of a few hertz, the magnetostatic response due to the induced magnetization dominates the EM induction response. The result suggests that it is possible to make magnetic interpretation of low-frequency EM data without having to consider the conductivity structure and the corresponding EM induction effect. We compare the anomalous magnetic responses with magnetic noise components and find that the proposed active source magnetic (ASM) method has a depth of investigation of approximately 300 m. Free-space field and inductive noise are considered as the most important issues affecting the depth of investigation. We also determine the potential for linear interpretation of magnetic heterogeneity under 0.1 SI by showing that the low-frequency magnetic response can be approximated by a linear magnetic response. In our synthetic experiments, inversion of the ASM data shows a marked enhancement in resolution, with no effect of the remanent magnetization, in contrast to geomagnetic inversion. These results show that the ASM method is a useful geophysical tool, especially when high-resolution imaging of magnetic susceptibility is required or where strong remanent magnetization complicates the magnetic interpretation.

Practical High Resolution Microscopy

1968 ◽  
Vol 26 ◽  
pp. 302-303
Author(s):  
P. A. Marsh ◽  
T. Mullens ◽  
D. Price
Keyword(s):  
High Resolution ◽  
Magnetic Fields ◽  
Low Frequency ◽  
Resolving Power ◽  
Careful Attention ◽  
Electron Microscopes ◽  
The Relationship ◽  
High Resolution Microscopy ◽  
New Facilities

It is possible to exceed the guaranteed resolution on most electron microscopes by careful attention to microscope parameters essential for high resolution work. While our experience is related to a Philips EM-200, we hope that some of these comments will apply to all electron microscopes.The first considerations are vibration and magnetic fields. These are usually measured at the pre-installation survey and must be within specifications. It has been our experience, however, that these factors can be greatly influenced by the new facilities and therefore must be rechecked after the installation is completed. The relationship between the resolving power of an EM-200 and the maximum tolerable low frequency interference fields in milli-Oerstedt is 10 Å - 1.9, 8 Å - 1.4, 6 Å - 0.8.

Magnetic Permeability and Relaxation Frequency in High Frequency Magnetic Materials.

2001 ◽  
Vol 674 ◽  
Author(s):  
M.I. Rosales ◽  
H. Montiel ◽  
R. Valenzuela
Keyword(s):  
High Frequency ◽  
Domain Walls ◽  
Magnetocrystalline Anisotropy ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Anisotropy Constant ◽  
Relaxation Frequency ◽  
Resonance Relaxation ◽  
Frequency Behavior

ABSTRACTAn investigation of the frequency behavior of polycrystalline ferrites is presented. It is shown that the low frequency dispersion (f < 10 MHz) of permeability is associated with the bulging of pinned domain walls, and has a mixed resonance-relaxation character, closer to the latter. It is also shown that there is a linear relationship between the magnetocrystalline anisotropy constant, K1, and the relaxation frequency. The slope of this correlation depends on the grain size. Such a relationship could allow the determination of this basic parameter from polycrystalline samples.

scholarly journals Low frequency (74 MHz) radio continuum observations of the inner 13° × 7° of the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 464-466
Author(s):  
M. Rickert ◽  
F. Yusef-Zadeh ◽  
C. Brogan
Keyword(s):  
High Resolution ◽  
Molecular Cloud ◽  
Supernova Remnant ◽  
Galactic Center ◽  
Low Frequency ◽  
Radio Continuum ◽  
Large Array ◽  
Very Large Array ◽  
Image Displays ◽  
Western Side

AbstractWe analyze a high resolution (114″ × 60″) 74 MHz image of the Galactic center taken with the Very Large Array (VLA). We have identified several absorption and emission features in this region, and we discuss preliminary results of two Galactic center sources: the Sgr D complex (G1.1–0.1) and the Galactic center lobe (GCL).The 74 MHz image displays the thermal and nonthermal components of Sgr D and we argue the Sgr D supernova remnant (SNR) is consistent with an interaction with a nearby molecular cloud and the location of the Sgr D Hii region on the near side of the Galactic center. The image also suggests that the emission from the eastern side of the GCL contains a mixture of both thermal and nonthermal sources, whereas the western side is primarily thermal.

High-resolution and wideband optical vector analysis using fixed low-frequency detection

2021 ◽  
Author(s):  
Ting Qing ◽  
Shupeng Li ◽  
Lihan Wang ◽  
Xiaohu Tang ◽  
Ping Li ◽  
...  
Keyword(s):  
High Resolution ◽  
Low Frequency ◽  
Vector Analysis ◽  
Frequency Detection

COMPARATIVE ANALYSIS OF SPECTRA OF THE 2000-YEAR NORTHERN HEMISPHERE AVERAGE SURFACE AIR TEMPERATURE RECONSTRUCTIONS

2021 ◽  
pp. 5-13
Author(s):  
N. M. DATSENKO ◽  
◽  
D. M. SONECHKIN ◽  
B. YANG ◽  
J.-J. LIU ◽  
...  
Keyword(s):  
High Resolution ◽  
Northern Hemisphere ◽  
Air Temperature ◽  
Wavelet Transforms ◽  
Spectral Composition ◽  
Low Frequency ◽  
Surface Air Temperature ◽  
Temporal Variations ◽  
Continuous Wavelet Transforms ◽  
Stable Estimation

The spectral composition of temporal variations in the Northern Hemisphere mean surface air temperature is estimated and compared in 2000-year paleoclimatic reconstructions. Continuous wavelet transforms of these reconstructions are used for the stable estimation of energy spectra. It is found that low-frequency parts of the spectra (the periods of temperature variations of more than 100 years) based on such high-resolution paleoclimatic indicators as tree rings, corals, etc., are similar to the spectrum of white noise, that is never observed in nature. This seems unrealistic. The famous reconstruction called “Hockey Stick” is among such unrealistic reconstructions. Reconstructions based not only on high-resolution but also on low-resolution indicators seem to be more realistic, since the low-frequency parts of their spectra have the pattern of red noise. They include the “Boomerang” reconstruction showing that some warm periods close to the present-day one were observed in the past.

Revealing Hidden Information: High-Resolution Logging-While-Drilling Slowness Measurements and Imaging Using Advanced Dual Ultrasonic Technology

2021 ◽  
Vol 62 (1) ◽  
pp. 89-108
Author(s):  
Matthew Blyth ◽  
◽  
Naoki Sakiyama ◽  
Hiroshi Hori ◽  
Hiroaki Yamamoto ◽  
...  
Keyword(s):  
High Resolution ◽  
Elastic Wave ◽  
Horizontal Wells ◽  
Wellbore Stability ◽  
Frequency Range ◽  
Ultrasonic Technology ◽  
Logging While Drilling ◽  
Pulse Echo ◽  
Depth Of Investigation ◽  
Wave Properties

A new logging-while-drilling (LWD) acoustic tool has been developed with novel ultrasonic pitch-catch and pulse-echo technologies. The tool enables both high-resolution slowness and reflectivity images, which cannot be addressed with conventional acoustic logging. Measuring formation elastic-wave properties in complex, finely layered formations is routinely attempted with sonic tools that measure slowness over a receiver array with a length of 2 ft or more depending upon the tool design. These apertures lead to processing results with similar vertical resolutions, obscuring the true slowness of any layering occurring at a finer scale. If any of these layers present significantly different elastic-wave properties than the surrounding rock, then they can play a major role in both wellbore stability and hydraulic fracturing but can be absent from geomechanical models built on routine sonic measurements. Conventional sonic tools operate in the 0.1- to 20-kHz frequency range and can deliver slowness information with approximately 1 ft or more depth of investigation. This is sufficient to investigate the far-field slowness values but makes it very challenging to evaluate the near-wellbore region where tectonic stress redistribution causes pronounced azimuthal slowness variation. This stress-induced slowness variation is important because it is also a key driver of wellbore geomechanics. Moreover, in the presence of highly laminated formations, there can be a significant azimuthal variation of slowness due to layering that is often beyond the resolution of conventional sonic tools due to their operating frequency. Finally, in horizontal wells, multiple layer slownesses are being measured simultaneously because of the depth of investigation of conventional sonic tools. This can cause significant interpretational challenges. To address these challenges, an entirely new design approach was needed. The novel pitch-catch technology operates over a wide frequency range centered at 250 kHz and contains an array of receivers having a 2-in. receiver aperture. The use of dual ultrasonic technology allows the measurement of high-resolution slowness data azimuthally as well as reflectivity and caliper images. The new LWD tool was run in both vertical and horizontal wells and directly compared with both wireline sonic and imaging tools. The inch-scale slownesses obtained show characteristic features that clearly correlate to the formation lithology and structure indicated by the images. These features are completely absent from the conventional sonic data due to its comparatively lower vertical resolution. Slowness images from the tool reflect the formation elastic-wave properties at a fine scale and show dips and lithological variations that are complementary to the data from the pulse-echo images. The physics of the measurement are discussed, along with its ability to measure near-wellbore slowness, elastic-wave properties, and stress variations. Additionally, the effect of the stress-induced, near-wellbore features seen in the slowness images and the pulse-echo images is discussed with the wireline dipole shear anisotropy processing.

Volume low-frequency dispersion in a semi-insulating system

1988 ◽  
Vol 23 (2) ◽  
pp. 209-213 ◽  
Author(s):  
A.K. Jonscher ◽  
L. Levesque
Keyword(s):  
Low Frequency ◽  
Frequency Dispersion
Sign in / Sign up

Export Citation Format

Share Document