Inhomogeneous magnetic field

Figure 5a. Variation in the magnetic properties of metal clusters are investigated by measuring the depletion of a highly collimated cluster beam by an inhomogeneous magnetic field, A1 clusters at zero and high field, showing that only small clusters are appreciably deflected.

By performing sequential SG experiments it can be shown that electron spin has much in common with photon polarization. In a typical arrangement the beam from the oven is first passed through an SGZ apparatus with the inhomogeneous magnetic field in the z-direction. Suppose the one (S ) component from this experiment is blocked and the second (5+), is allowed to pass into another SGZ apparatus. The beam emerging from the second device will be found to have no S component, exactly as for two parallel polaroids. 

Another approach to water and fat selective imaging which is also based on chemical shift elfects should be mentioned here The so-called Dixon method works with phase shifts in asymmetric spin-echo versus symmetric spin-echo acquisition. This method was shown to provide high-quality chemical shift selective images even in the presence of an inhomogeneous magnetic field. However, extreme high sensitivity to only one component seems to be obtained more difficult. 

As a first step let us expand the inhomogeneous magnetic field at a point, r, as a Taylor series ... 

The SQUID obviously has several potential advantages for on-line applications. It can operate at very low inhomogeneous magnetic fields, avoiding the need for large expensive shimmed magnets. It also does not require tuning and has very low power requirements. However there are also severe technical limitations to be overcome before it can be used in on-line commercial operations. The whole SQUID needs to be immersed in liquid helium and a conventional RF coil is still needed to excite the NMR resonance. It remains to be seen whether such devices will find future on-line application in horticulture. 

Eujiwara, M. Chie, K. Sawai, J. Shimizu, D. Tanimoto, Y. On the Movement of Paramagnetic Ions in an Inhomogeneous Magnetic Field. J. Phys. Chem. B 2004, 108, 3531-3534. 

A sample of a diamagnetic substance placed in an inhomogeneous magnetic field is acted on by a force that tends to push it away from the strongfield region. This force is proportional to the diamagnetic susceptibility of the substance, which is defined as the ratio of the induced moment, /x, to the field strength, H ... 

If l( ) is the time-dependent Larmor frequency, the precession phase (0 in Figure 7.1) can be expressed in an inhomogeneous magnetic field according to ... 

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