Magnetic field pulsing

A can be measured accurately, and the value of G8 need not be known precisely so long as it is the same for the two magnetic field pulses. This technique permits accurate measurement of diffusion coefficients for one substance dissolved in another or for self-diffusion of a single substance. By Fourier transforming the echo, diffusion coefficients for several substances can be determined. In conjunction with spatial localization methods provided by NMR imaging, studies of diffusion can be quite valuable, as we point out in Chapter 14. 

FIGURE 8.9 Magnetic field pulse schemes used in the measurement of g-pair lifetime and the separation of g- and f-pair RP kinetics. 

FIGURE 3.8 Schematic drawing illustrating the remote query nature of the passive, wireless magnetoelastic sensor. Magnetic field pulses, at a frequency near the resonant frequency of the sensor, are generated to vibrate the sensor. The excitation field is then turned off allowing the sensor to continue vibration at its resonant frequency. The transient sensor response is then converted to the frequency domain to extract the resonant information. 

FIGURE 9.9 Diagram showing the shape of a magnetic field pulse along the Z axis of an NMR sample tube. 

Intense THz magnetic field pulses allowed not only the induction of spin precession but also its extinction on demand. This was achieved by exciting the sample by a pair of THz pump pulses which were delayed with respect to one another the second, delayed pulse induced a precessional motion that was out of phase with the precession due to the first pulse, and thereby stopped the spin precession. This is shown in Figure 6.15(e) for a pump pulse pair delayed by 6.5 precession cycles. Similar sequences of pulses (of much lower frequencies) have been used in nuclear spin resonance to investigate molecular structure. The extension to the THz domain (THz-ESR) would require, however, magnetic field strengths about 100 times stronger than currently available in the Department. 

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