Actively shielded gradient

The use of actively shielded magnetic field gradients has made the use of pulsed field gradients possible. The use of pulsed field gradients reduces experiment time, minimizes artifacts, and allows for further solvent suppression. 

For non-deuterated complexes, NMR experiments were performed on either Vaiian Unity600 or Varian Unity+500 spectrometers. The 600 MHz instrument was equipped with a triple resonance probe and a PTS synthesizer as a pseudo fourth channel. The 500 MHz spectrometer was a four channel instrument with a triple resonance probe with an actively shielded pulsed field gradient coil. All experiments were performed at 37 C. The heteronuclear experiments shown in Figure 1 were performed as described in Zhang et al (11) and Revington et al (24). For all 3D ex riments 32 transients were required for sufficient signal to noise. This necessitated the use of fewer increments and the use of linear prediction (25)... 

Figure 3.63. Gradient recovery after application of a 1 ms square gradient pulse of 0.25 Tm" (50% of maximum output). The sample is chloroform and data were acquired with an actively-shielded 5 mm inverse z-axis gradient probehead.

NMR imaging can be applied for different problems of network characterization. The following experiments were done with a VARIAN unity 200 MHz (wide bore) equipped with a homemade imaging probe of following specifications active-shielded design, maximum gradient 5 mT/cm RF part resonance frequency 67 MHz (deuterium), 200 MHz (protons) saddle coil or solenoid with different inner diameter (5 mm, 7 mm, and for deuterium coil 26 mm) temperature control between 0 °C and 120 °C. 

Figure 1 (A) Current diagram for conventional unshielded z gradient coil. (B) Current diagram for actively shielded z gradient coil.

Cryostat Active Shield Main Magnet Coil Passive Shims Active Shims Gradient Coil RF Coil... 

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