Transverse gradient coils

FIGURE 24J A filamentary, singie-tum, saddle transverse gradient coil set and patterns for a typical unshielded transverse gradient coil is shown. 

Schenck, J. F., M. A. Hussain, and W. A. Edelstein, 1987, Transverse gradient coils for nuclear magnetic resonance imaging, U.S. Patent number 4646024. 

FIGURE 6 Cutaway drawing of magnet geometry. A four-coil geometry is used to produce the static field. The inner coil shown is for the transverse gradient field. (Courtesy of GE Medical Systems.)... 

In simple shear flow where vorticity and extensional rate are equal in magnitude (cf. Eq. (79), Sect. 4), the molecular coil rotates in the transverse velocity gradient and interacts successively for a limited time with the elongational and the compressional flow component during each turn. Because of the finite relaxation time (xz) of the chain, it is believed that the macromolecule can no more follow these alternative deformations and remains in a steady deformed state above some critical shear rate (y ) given by [193] (Fig. 65) ... 

Fio. 9.3.4 Excitation with a surface coil of 9 mm diameter in a Bo gradient of the order of lOT/m by the NMR-MOUSE (a) Series train of CPMG echoes from a carbon-black filled SBR section of an intact car tyre with a steel belt. A fit of the echo envelope with an exponential decay function yields a transverse relaxation time Ti [Eidl]. (b) Variation of the pulse duration in an a — te/l — Ta — ts/ i- pulse sequence for different rf frequencies. For each frequency maxima and minima are observed which define the nominal 90° and 180° pulse widths. With decreasing rf frequency the distance of the sensitive volume from the rf coil increases. A frequency of 17.5 MHz correspond to depths of 0-0.5 mm, 16MHz to 0.5-1.0mm, and 16.5 MHz to 1.0-1.5 mm into the sample [Gut3], (c) Hahn- and solid-echo envelopes for a sample of carbon-black filled cross-linked SBR. The Hahn-echo decay is faster because of residual dipolar couplings which are partially refocused by the solid-echo [Gut3]. (d) Multi-echo excitation. 

Shear flow can be roughly separated into the inclined extensional flow brought by the transverse velocity gradient, and the rotating flow, as illustrated in Fig. 7.8. The extensional flow leads to the major deformation of polymer coils, while the rotating flow makes tumbling of polymer coils upon flow. The latter realizes the... 

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