NMR RF PROBE COIL EXHIBITING DOUBLE RESONANCE
The present invention describes NMR probe coils that are designed to operate at two different frequencies, producing a strong and homogenous magnetic field at both the frequencies. This single coil, placed close to the sample, provides a method to optimize the NMR detection sensitivity of two different channels. In addition, the present invention describes a coil that generates a magnetic field that is parallel to the substrate of the coil as opposed to perpendicular as seen in the prior art. The present invention isolates coils from each other even when placed in close proximity to each other. A method to reduce the presence of electric field within the sample region is also considered. Further, the invention describes a method to adjust the radio-frequency tuning and coupling of the NMR probe coils.
1 . An apparatus for an NMR probe comprising:
two sets of RF coils forming a sample region between them for positioning an NMR sample wherein each set of RF coils consists of conductive material patterned on a dielectric substrate; and
is resonant at two distinct radio frequencies, wherein the magnetic fields generated at the two resonance frequencies are orthogonal to each other; and
said magnetic fields employed to excite and detect NMR signals at said resonance frequencies.
2 . The NMR probe of claim 1 , wherein the current-carrying elements of each coil set at one of the two resonance frequencies are exclusive of the current-carrying elements at the other frequency.
3 . The NMR probe in claim 2 , wherein one coil is placed on one side of the dielectric substrate and the other coil on the opposite side of the dielectric substrate.
4 . The NMR probe in claim 2 , wherein the two coils are patterned on two dielectric substrates, which are subsequently fastened together.
5 . The NMR probe in claim 2 , wherein the two coils are placed on the same side of the dielectric substrate, and one coil is placed within the other coil.
6 . The NMR probe of claim 1 , wherein there is capacitive coupling between the two coils across the substrate at one of the two frequencies, and current-carrying elements of the coil set.
7 . The NMR probe of claim 1 , wherein the current-carrying elements of each coil set at the two frequencies are the same, whereby the two resonances are produced due to differences in the current density distribution at the two frequencies.
8 . An NMR probe coil comprising conductive elements patterned on a dielectric substrate forming a resonant device, wherein the current in the coil at the resonance frequency flows through a central conductor, and flows back in the reverse direction through distal conductors, and the corresponding magnetic field within the sample region is substantially parallel to the dielectric substrate.
9 . A method to improve the homogeneity of the magnetic field of the NMR probe coil of claim 8 , achieved by making the central conductor wider near the middle and tapering near the ends along the long axis of the coil.
10 . An apparatus for an NMR probe comprising a fixed inductive coupling loop which is used to transfer energy into and out of the RF coils, wherein the loop is terminated by a network of adjustable capacitors which can be adjusted to achieve tuning and coupling of the RF coils.
11 . The NMR probe in claim 11 , where the said coupling loop is fabricated from normal metallic conductors.
12 . The NMR probe in claim 11 , where the said coupling loop is fabricated from high temperature superconductors.