"The Noise Immunity of Gradiometer Coils for 14N NQR Land
Mine Detection: Practical Limitations"
B. H. Suits
Magnetic resonance measurements in the field, such as for land
mine detection using 14N nuclear quadrupole resonance (NQR),
must deal with large levels of environmental radio-frequency interference.
One approach to minimize the level of interference which enters the
NQR receiver is the use of a coil with no magnetic dipole moment. Such
a coil is, ideally, sensitive only to spatial gradients of the
magnetic fields and is referred to as a gradiometer. It is
straightforward to estimate the amount of reduction one can expect
for an ideal gradiometer. Here it is shown that for 14N
NQR land mine detection in practice, the ultimate level of
interference received can be expected to be significantly greater
than what one would expect solely due to these spatial gradients. This
is due to the fact that it is quite difficult to construct an
Applied Magnetic Resonance 25, 317-382 (2004).
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