Apparatus for Nuclear Magnetic Resonance

Abstract

Apparatus and procedures are described for the high-resolution measurement of resonance shifts and for the observation of broad line shapes. Included are a discussion of magnet design and a summary of empirical results obtained in the construction and field homogenization of two large permanent magnets. Narrow, complex resonance lines, with components separated by as little as a milligauss, are resolved by a combination of homogeneous applied magnetic field, small samples, and slow-sweep field modulation. Broad absorption line shapes are plotted at fixed frequency by a system incorporating a regenerative oscillator, a narrow band amplifier, a recording potentiometer, and an electronic control for varying the applied magnetic field linearly in time. A simple cryostat provides stable temperatures from 85° to 500°K. In the case of samples with short spin-lattice relaxation times, such as the metals, improved signal-to-noise ratios are obtained by adjusting the oscillator to super-regenerative operation and observing the frequency modulation associated with the dispersive component of the resonance.

A broadband single-chip transceiver for multi-nuclear NMR probes

“…11 In order to obtain a high signal-to-noise ratio (SNR) and access the information hidden in NMR spectra, strong and homogeneous magnetic fields are required. 12,13 The realization of strong and homogeneous miniaturized magnets is the main obstacle towards low-cost portable NMR tools, possibly solved by Halbach configurations of permanent magnets. 14,15 NMR systems also require relatively complex RF electronics for resonance excitation and signal detection.…”

Forty years of Progress in Nuclear Magnetic Resonance Spectroscopy

“…Bloch [6] and Purcell [7] receive Nobel Prize for NMR 1953 Bloch equations for NMR relaxation [6,32] 1953 Overhauser effect [18] 1953 Theory for effects of exchange on NMR spectra [33,34] 1954 Carr-Purcell spin echoes [35] 1955 Solomon equations for NMR relaxation [36] 1955 Relaxation in the rotating frame [37] 1956 Early NMR studies on body fluids and tissues [120,121] 1953-1958 Sample-spinning used for resolution improvement [32] Field gradient shimming with electric currents [38] Magnetic flux stabilization (Varian) Spin-decoupling [39] Variable temperature operation ( [40] and Varian) 1957 Redfield theory of relaxation [41] 1957 Analysis of second-order spectra [42,43,92,93] 1957 NMR spectrum shown to be Fourier transform (FT) of Free Induction Decay (FID) [44] 1958 Magic angle spinning used for high resolution studies of solids [19,20] 1959 Blood flow measurements in vivo [47] 1959 Vicinal coupling constant dependence on dihedral angle [48] 1961 First 60 MHz field/frequency locked NMR spectrometer (Varian A60) 1962…”

Hyperpolarised 1H–13C Benchtop NMR Spectroscopy

“…Of particular interest are permanent magnet spectrometers with magnetic field strengths of 1-2 T that have the capability to record high-resolution NMR spectra [1]. Whilst several of the original NMR discoveries were made using permanent magnet NMR spectrometers [2][3][4][5][6][7][8][9], their usage became limited once strong and stable superconducting electromagnets became readily available [10][11][12]. In the early 2000s, the prospect of cheap, cryogen-free, and compact NMR spectrometers prompted the resurgence of permanent magnet-based systems [13].…”