Search results for "Free induction decay"
showing 10 items of 12 documents
Systematic and statistical uncertainties of the hilbert-transform based high-precision FID frequency extraction method.
2021
Abstract Pulsed nuclear magnetic resonance (NMR) is widely used in high-precision magnetic field measurements. The absolute value of the magnetic field is determined from the precession frequency of nuclear magnetic moments. The Hilbert transform is one of the methods that have been used to extract the phase function from the observed free induction decay (FID) signal and then its frequency. In this paper, a detailed implementation of a Hilbert-transform based FID frequency extraction method is described, and it is briefly compared with other commonly used frequency extraction methods. How artifacts and noise level in the FID signal affect the extracted phase function are derived analytical…
Characterization of water mobility in dry and wetted roasted coffee using low-field proton nuclear magnetic resonance
2007
Abstract Roasted and ground coffee was studied by low-field 1 H nuclear magnetic resonance at various water contents and temperatures. The spin–spin relaxation times ( T 2 ) were measured with single pulse free induction decay (FID) and Carr–Purcell–Meiboom–Gill (CPMG) sequences. Four relaxing components were distinguished: the solid population was observed with FID sequence at T 2s ∼9 μs; the other three populations, measured with the CPMG sequence, corresponded to an apolar phase, the coffee oil, and two polar phases. The two polar populations, observed at T 2m ∼6 ms and ∼27 ms (for coffee with 50% water content at 90 °C) were attributed to water in cell wall polymers and in water filling…
Everything you wanted to know about phase and reference frequency in one- and two-dimensional NMR spectroscopy
2019
The fundamental concept of phase discussed in this tutorial aimed at providing students with an explanation of the delays and processing parameters they may find in nuclear magnetic resonance (NMR) pulse programs. We consider the phase of radio-frequency pulses, receiver, and magnetization and how all these parameters are related to phases and offsets of signals in spectra. The impact of the off-resonance effect on the phase of the magnetization is discussed before presenting an overview of how adjustment of the time reference of the free induction decay avoids first-order correction of the phase of spectra. The main objective of this tutorial is to show how the relative phase of a pulse an…
13C-Decoupled J-Coupling Spectroscopy Using Two-Dimensional Nuclear Magnetic Resonance at Zero-Field
2017
We present a two-dimensional method for obtaining 13C-decoupled, 1H-coupled nuclear magnetic resonance (NMR) spectra in zero magnetic field using coherent spin-decoupling. The result is a spectrum determined only by the proton–proton J-coupling network. Detection of NMR signals in zero magnetic field requires at least two different nuclear spin species, but the proton J-spectrum is independent of isotopomer, thus potentially simplifying spectra and thereby improving the analytical capabilities of zero-field NMR. The protocol does not rely on a difference in Larmor frequency between the coupled nuclei, allowing for the direct determination of J-coupling constants between chemically equivalen…
Solid-liquid nuclear magnetic resonance relaxation and signal amplitude relationships with ranking of seasoned softwoods and hardwoods
2006
In 1H NMR (Nuclear Magnetic Resonance) relaxation measurements for a set of eight hardwood and softwood samples, each Free Induction Decay (FID) is fit by the sum of a “Solid” signal of the form A exp[−c(t/Ts)2] [1−g(t/Ts)2+h(t/Ts)4] plus a “Liquid” signal B exp(−t/T2 FID). Distributions of longitudinal (T1) relaxation times were computed separately for the Solid and Liquid components, giving also the Solid/Liquid 1H ratio α. From measurements on the samples dried, seasoned, and hydrated, the moisture content, (Liquid/Solid weight ratio) was found to be approximately 0.50/α. For each of the “Seasoned” samples (10-13% moisture content) a single T1 peak was found for the Solid and two for the…
Transient nutations decay: The effect of field-modified dipolar interaction
1999
The anomalous behavior of transient nutations is experimentally investigated in a set of two-level $(S=\frac{1}{2})$ spin systems differing only in spin concentration. Our results show that the non-Bloch power dependence of the decay rate of transient nutations is a concentration-dependent effect, which is more and more pronounced in more and more concentrated samples. The experimental results are interpreted in the framework of the recent theory by Shakhmuratov et al. [Phys. Rev. Lett. 79, 2963 (1997)] and support the hypothesis that the anomalous decay of transient nutations in solids originates from radiation-induced changes of the dipolar field, rather than from residual fluctuations of…
Second-harmonic free-induction decay in a two-level spin system
1983
Denoising of MR spectroscopy signals using total variation and iterative Gauss-Seidel gradient updates
2015
We present a fast variational approach for denoising signals from magnetic resonance spectroscopy (MRS). Differently from the TV approaches applied to denoising of images, this is the first time to our knowledge that it has been used for the processing of free induction decay signals from single-voxel spectroscopy (SVS) acquisitions. Another novelty in this study is the direct use of the Euler Lagrange formulation coupled with Gauss Seidel gradient updates to improve the speed of iteration and reduce ringing. Results from brain MRS signals show improvement in signal to noise ratio as well as reduction in estimation error in the quantification of metabolites.
Optimal control of the inversion of two spins in Nuclear Magnetic Resonance
2012
International audience; We investigate the optimal control of the inversion of two spin 1/2 particles in Nuclear Magnetic Resonance. The two spins, which differ by their resonance offset, are controlled by the same radio frequency magnetic field. Using the Pontryagin Maximum Principle, we compute the optimal control sequence which allows to reach the target state in a given time, while minimizing the energy of the magnetic field. A comparison with the time-optimal solution for bounded control amplitude realizing the same control in the same time is made. An experimental illustration is done using techniques of Nuclear Magnetic Resonance.
A new limit of the 129 Xenon Electric Dipole Moment
2019
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.