In Fourier Transform NMR, a free induction decay (FID) is the observable NMR signal generated by non-equilibrium nuclear spin magnetisation precessing about the magnetic field (conventionally along z). In Physics, Larmor precession (named after Joseph Larmor) refers to the Precession of the Magnetic moments of Electrons atomic In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges This non-equilibrium magnetisation is generally created by applying a pulse of resonant radio-frequency close to the Larmor frequency of the nuclear spins. In Physics, resonance is the tendency of a system to Oscillate at maximum Amplitude at certain frequencies, known as the system's In Physics, Larmor precession (named after Joseph Larmor) refers to the Precession of the Magnetic moments of Electrons atomic In Quantum mechanics, spin is a fundamental property of atomic nuclei, Hadrons and Elementary particles For particles with non-zero spin
If the magnetisation vector has a non-zero component in the xy plane, then the precessing magnetisation will induce a corresponding oscillating voltage in a detection coil surrounding the sample. Faraday's law of induction describes an important basic law of electromagnetism which is involved in the working of Transformers Inductors and many forms of This time-domain signal is typically digitised and then Fourier transformed in order to obtain a frequency spectrum of the NMR signal i. This article specifically discusses Fourier transformation of functions on the Real line; for other kinds of Fourier transformation see Fourier analysis and e. the NMR spectrum. A spectrum (plural spectra or spectrums) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum.
The duration of the NMR signal is ultimately limited by T2 relaxation, but mutual interference of the different NMR frequencies present also causes the signal to be damped more quickly. In nuclear magnetic resonance (NMR spectroscopy and magnetic resonance imaging (MRI the term relaxation describes several processes by which nuclear Magnetization In physics interference is the addition ( superposition) of two or more Waves that result in a new wave pattern When NMR frequencies are well-resolved, as is typically the case in the NMR of samples in solution, the overall decay of the FID is relaxation-limited and the FID is approximately exponential (with a time constant T2 or more accurately T2*). FID durations will then be of the order of seconds for nuclei such as 1H. If NMR lineshapes are not relaxation-limited (as is commonly the case in solid-state NMR), then the NMR signal will generally decay much more quickly e. Solid-state NMR ( SSNMR) spectroscopy is a kind of Nuclear magnetic resonance (NMR spectroscopy characterized by the presence of anisotropic (directionally dependent g. microseconds for 1H NMR.
Particularly if a limited number of frequency components are present, the FID may be analysed directly for quantitative determinations of physical properties, such as hydrogen content in aviation fuel, solid and liquid ratio in dairy products (Time-Domain NMR).
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