Magic-sandwich echo sequenc

More sophisticated NMR techniques have been also applied to measure the crystallinity in PVA cryogels [58]. For instance, pulsed mixed magic-sandwich echo sequences have been applied in a low-field NMR spectrometer [58]. This kind of pulse sequence provides near-quantitative refocusing of the rigid contribution to the initial part of proton free induction decay [58], allowing for a more quantitative determination of crystallinity in these gels. The results so obtained essentially confirm those shown in Fig. 10. 

Fig. 24. Top Magic-echo sequence, TREV-16TS, for solid-state imaging with (a) ideally pulsed (b) nonideally pulsed and (c) sinusoidal field gradients. On-resonance RF irradiations along x and — x are sandwiched by 90° pulses (magic sandwich). The hatched magic sandwich consists of four magic sandwiches. Bottom Projections of the one-dimensional test sample (admantane powder) obtained with the TREV-16TS sequence (r = 30 ps) and the field gradients shown in Fig. 18. The RF field was set at 100 kHz. (Adapted from Matsui et al.296 with permission.)...

Fig. 3.4.3 Pulse sequence for generation of the magic echo. The magnetization dephases for a time 2r by free precession before and after refocussing by the magic sandwich of length At.

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