Solenoidal coil

The compact MRI system has an advantage for rf coil design because solenoid coils can be used in most applications. The solenoid coil has about three times better SNR than that of the saddle-shaped coil (14). Even if the saddle-shaped or birdcage coil is used in the quadrature mode, the solenoid coil will still have better SNR because an SNR gain of only about 1.4 times is obtained in that mode. 

Figure 2.2.13 shows an overview of the MRI system developed for salmon selection. A 0.2-T C-shaped yoked permanent magnet with a 25-cm gap [50-ppm homogeneity for 15-cm DSV (diameter spherical volume), weight 1.4 tons] is used for the magnet. For the rf coils, two solenoid coils with a 14-cm circular aperture and 14 cm x 18 cm oval aperture were developed. 

Dielectric losses arise from the direct capacitive coupling of the coil and the sample. Areas of high dielectric loss are associated with the presence of axial electric fields, which exist half way along the length of the solenoid, for example. Dielectric losses can be modeled by the circuit given in Figure 2.5.3. The other major noise source arises from the coil itself, in the form of an equivalent series resistance, Rcoii. Exact calculations of noise in solenoidal coils at high frequencies and small diameters are complex, and involve considerations of the proximity and skin depth effects [23],... 

All experiments were performed in a 1.9-T horizontal bore magnet (Oxford Instruments, Oxford, UK) with a dear bore diameter of 31 cm. Magnetic field gradients were produced by a 12-cm id water-cooled gradient set (Resonance Research, Billerica, MA, USA), capable of a maximum output of 300 mT m-1, and were driven by Techron 7700 amplifiers (Techron Inc., Elkhart, IN, USA). Rf excitation was accomplished using either a quadrature driven birdcage coil (Morris Instruments, Ottawa, ON, Canada), or an 8-tum laboratory-built solenoid coil, driven by an ENI LPI-10 1000 W amplifier or a Matec Model 525 class-C amplifier. 

Figure 2.38 Diagram of an NMR probe. The solenoid coils on the pole faces of the magnet produce the variable magnetic field. The direction of the magnetic field through the sample is indicated by M.

Bobbins for electronically controlled automatic transmissions for trucks, solenoid coils in control modules for five-speed automatic truck transmissions. 

FIGURE 7.1 RF coil geometries and their orientation with respect to the magnetic field, Bq (a) a saddle or Hehnoltz RF coil and (b) a solenoidal coil, shown here wrapped directly around a separation capillary. 

Providing that hid remains constant, the RF coil sensitivity is inversely proportional to the coil diameter for solenoidal coils of diameter greater than about 100 p,m. It can be shown theoretically and has been demonstrated experimentally that the sensitivity of a solenoidal coil is about three times that of a saddle coil of the same size [3], In order to translate the coil sensitivity into measurement of SIN defined by Equation 7.6, we also have to consider the noise characteristics of NMR microcoils. For coils of diameter less than 3 mm, the major noise source is from the resistance of the coil itself, and the noise from even lossy biological samples can be neglected [10]. 

Another important application of hyphenated NMR methods is to provide insights into processes that affect the separation. Eor example, online NMR detection of the water chemical shift was used to noninvasively probe intracapillary temperatures in CE separations with subsecond temporal resolution and spatial resolution on the order of 1 mm [111]. Lacey et al. [112] followed up this report with a second NMR study using a novel 2-turn vertical solenoidal coil to measure temperature increases of more than 50 C in a chromatographic frit of the type used in CEC. Insights into the mechanisms underlying cITP have also been investigated utilizing online NMR... 

An alternative to a saddle coil would be a solenoid coil which, however, would have to be oriented perpendicularly to the magnet bore and thus to the physical axis of the probe assembly. Due to spatial constraints, such an arrangement complicates considerably sample insertion, especially when the sample temperature has to be controlled and the assembly has to include an enveloping dewar for temperature control of the sample. ... 

Figure 3 A schematic drawing of a typical ECR ion source. The ions and electrons are confined in the plasma by the magnetic field generated by the solenoid coils and the hexapole magnet.

This is negligible compared to other circuit delays Solenoid Coil Detectors... 

The design of the solenoid coil and the pulse shaping circuit is important to assure triggering of the chronograph at a known point in space. 

C. Camera Chronograph, formerly called Solenoid Chronograph because it was used with the solenoid coil (See item c, above). 

Figure 7.3.1.2 S/N per unit sample volume as a function of coil diameter for solenoidal coils. The 1 Id and (1 /d )1 2 asymptotes do not account for the resistance of the lead and thus are not followed exactly by either theoretical or experimental data points. Adapted by permission of Academic Press, from Peck, T. L., Magin, R. L. and Lauterbur, P. C., J. Magn. Reson., B., 1995, 108, 114...

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