Quantifying background magnetic-field inhomogeneity for improved interpretation of free induction decay measurements

Geophysics ◽  
2014 ◽  
Vol 79 (1) ◽  
pp. E11-E21 ◽  
Author(s):  
Denys Grombacher ◽  
Jan O. Walbrecker ◽  
Rosemary Knight
Keyword(s):  
Magnetic Field ◽  
Free Induction Decay ◽  
Pulse Sequences ◽  
Relaxation Times ◽  
Statistical Distribution ◽  
Pore Scale ◽  
Background Magnetic Field ◽  
Free Induction ◽  
Scale Properties ◽  
The Impact

Nuclear magnetic resonance measurements provide useful insight into pore-scale properties of porous media. One influence affecting the measurement is inhomogeneity in the static background magnetic field ([Formula: see text]). This inhomogeneity can significantly alter the relaxation signal and potentially obscure pore-scale information. To improve the understanding of this effect on the free-induction decay (FID), a measurement still commonly used in practice, a novel methodology is developed to estimate the statistical distribution of [Formula: see text]. A suite of preparatory pulse sequences is developed to encode information about the [Formula: see text] field in the initial amplitude and phase of the FID following each sequence and an inversion is employed to predict the statistical distribution of [Formula: see text]. Knowledge of the [Formula: see text] distribution is then used to correct for the impact of [Formula: see text] inhomogeneity on the FID measurement; this is essential for improving the usefulness of FID measurements for the estimation of pore-scale properties. Results are presented for both numerical and laboratory studies verifying the feasibility of the developed methodology in a controlled laboratory environment, and demonstrating that knowledge of the statistical distribution of [Formula: see text] is sufficient to estimate the impact of [Formula: see text] inhomogeneity on the FID in cases where [Formula: see text] inhomogeneity causes less than an order of magnitude decrease in the relaxation times governing the FID.

scholarly journals The Influence of Single-Walled Carbon Nanotubes on the Dynamic Properties of Nematic Liquid Crystals in Magnetic Field

Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4031 ◽  
Author(s):  
Cirtoaje ◽  
Petrescu
Keyword(s):  
Magnetic Field ◽  
Liquid Crystals ◽  
Dynamic Properties ◽  
Relaxation Times ◽  
Continuum Theory ◽  
Elastic Continuum ◽  
Walled Carbon Nanotubes ◽  
The Impact ◽  
The Magnetic Field ◽  
Good Agreement

This article aims to study the impact of carbon nanotube dispersions in liquid crystals. A theoretical model for the system’s dynamics is presented, considering the elastic continuum theory and a planar alignment of liquid crystal molecules on the nanotube’s surface. Experimental calculation of the relaxation times in the magnetic field was made for two cases: when the field was switched on (τon), and when it was switched off (τoff). The results indicate an increase of the relaxation time by about 25% when the magnetic field was switched off, and a smaller increase (about 10%) when the field was switched on, where both were in good agreement with the theoretical values.

OPTICAL NUTATION AND FREE INDUCTION DECAY IN MAGNETOACTIVE INDIUM ANTIMONIDE

1999 ◽  
Vol 08 (03) ◽  
pp. 431-441
Author(s):  
J. THOMAS ANDREWS ◽  
PRATIMA SEN
Keyword(s):  
Magnetic Field ◽  
Indium Antimonide ◽  
Free Induction Decay ◽  
Field Amplitude ◽  
Lead Salt ◽  
Thin Sample ◽  
Crystal Laser ◽  
Amplitude Increase ◽  
Free Induction ◽  
Numerical Estimations

Using the density matrix approach, the effect of magnetic field on optical nutation and free induction decay (FID) has been investigated analytically in direct gap semiconductors. The numerical estimations made for a thin sample of bulk InSb duly irradiated by a Lead salt (PbEuSeTe) diode laser exhibit an enhancement in the beat signal intensity of the nutating output at large magnetic fields. The numerical analysis of free induction decay in InSb crystal–laser interacting system yield the results that both the decay time as well as transmitted field amplitude increase with increasing magnetic field.

Advancement and validation of surface nuclear magnetic resonance spin-echo measurements of T2

Geophysics ◽  
2014 ◽  
Vol 79 (2) ◽  
pp. EN15-EN23 ◽  
Author(s):  
Elliot Grunewald ◽  
Rosemary Knight ◽  
David Walsh
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Pore Size ◽  
Free Induction Decay ◽  
Field Experiments ◽  
Spin Echo ◽  
Coarse Grained ◽  
Background Magnetic Field ◽  
Free Induction ◽  
Nuclear Magnetic

Obtaining reliable estimates of hydrogeologic properties from nuclear magnetic resonance (NMR) measurements requires the ability to measure NMR relaxation parameters that are most sensitive to pore-scale geometry. Conventional surface NMR measurements of the free induction decay yield accurate estimates of the relaxation time parameter [Formula: see text], but it has been shown that this parameter can exhibit limited sensitivity to pore size and permeability. We evaluated an improved surface-NMR scheme that uses spin-echo signals to estimate the more robust and readily usable relaxation parameter [Formula: see text]. The acquisition methodology builds upon previous spin-echo schemes and incorporates robust phase-cycling procedures, which remove responses that can potentially interfere with the echo signals. A new two-stage linear inversion was used to derive quantitative estimates of [Formula: see text] with depth. The method was evaluated in two field experiments at sites in the central and western United States. At one site, NMR logging measurements in a nearby borehole provided the first opportunity to compare [Formula: see text]-values estimated by surface NMR to [Formula: see text]-values determined from the logging data. The surface and logging results showed very close agreement at depths where [Formula: see text] is long, but echoes cannot be detected from depths where [Formula: see text] is shorter than the minimum echo time. As anticipated, we found that [Formula: see text] derived from spin echoes was generally much longer than [Formula: see text], derived from the free induction decay. We explain the observed differences by considering the magnitude of inhomogeneity in the background magnetic field. We note that [Formula: see text] exhibited greater variation and sensitivity to pore size than [Formula: see text] in coarse-grained materials, while [Formula: see text] provided greater sensitivity in fine-grained materials where no echo signal was detected. Given these complementary advantages of [Formula: see text] and [Formula: see text] measurement, we advocate adoption of a framework combining spin-echo and free induction decay data to improve characterization of groundwater aquifers.

Optical free-induction decay of paramagnetic molecules in magnetic field

Laser Physics ◽  
2019 ◽  
Vol 30 (1) ◽  
pp. 015204 ◽  
Author(s):  
Evgeniy N Chesnokov ◽  
Lev N Krasnoperov ◽  
Vitaly V Kubarev
Keyword(s):  
Magnetic Field ◽  
Free Induction Decay ◽  
Free Induction ◽  
Paramagnetic Molecules

scholarly journals A new limit of the 129Xenon Electric Dipole Moment

2019 ◽  
Vol 219 ◽  
pp. 02003
Author(s):  
Fabian Allmendinger ◽  
Ilhan Engin ◽  
Olivier Grasdijk ◽  
Werner Heil ◽  
Klaus Jungmann ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Dipole Moment ◽  
Electric Dipole Moment ◽  
Electric Dipole ◽  
Free Induction Decay ◽  
Low Noise ◽  
Upper Limit ◽  
Free Induction ◽  
Field Fluctuations ◽  
Spin Species

We report on the first preliminary result of our 129Xe EDM measurement performed by the MIXed collaboration. The aim of this report is to demonstrate the feasibility of a new method to set limits on nuclear EDMs by investigating the EDM of the diamagnetic 129Xe atoms. In our setup, hyperpolarized 3He serves as a comagnetometer needed to suppress magnetic field fluctuations. The free induction decay of the two polarized spin species is directly measured by low noise DC SQUIDs, and the weighted phase difference extracted from these measurements is used to determine a preliminary upper limit on the 129Xe EDM.

Magnetic-field quantum beats in two-photon free-induction decay

1978 ◽  
Vol 3 (5) ◽  
pp. 172 ◽  
Author(s):  
N. P. Economou ◽  
P. F. Liao
Keyword(s):  
Magnetic Field ◽  
Free Induction Decay ◽  
Quantum Beats ◽  
Two Photon ◽  
Free Induction

scholarly journals Lineshape of Magnetic Resonance and its Effects on Free Induction Decay and Steady-State Free Precession Signal Formation

2020 ◽  
Vol 2020 ◽  
pp. 1-17
Author(s):  
C. H. Ziener ◽  
M. Uhrig ◽  
T. Kampf ◽  
V. J. F. Sturm ◽  
F. T. Kurz ◽  
...  
Keyword(s):  
Steady State ◽  
Magnetic Resonance ◽  
Free Induction Decay ◽  
Relaxation Times ◽  
Fast Method ◽  
Signal Decay ◽  
Microscopic Field ◽  
Free Induction ◽  
Vessel Networks ◽  
Sequence Parameters

Magnetic resonance imaging based on steady-state free precision (SSFP) sequences is a fast method to acquire T1, T2, and T2∗-weighted images. In inhomogeneous tissues such as lung tissue or blood vessel networks, however, microscopic field inhomogeneities cause a nonexponential free induction decay and a non-Lorentzian lineshape. In this work, the SSFP signal is analyzed for different prominent tissue models. Neglecting the effect of non-Lorentzian lineshapes can easily result in large errors of the determined relaxation times. Moreover, sequence parameters of SSFP measurements can be optimized for the nonexponential signal decay in many tissue structures.

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