NMR RF probe coil exhibiting double resonance
NMR probe coils 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 MAR probe coils.
1. A nuclear magnetic resonance probe, comprising:
a first radiofrequency coil patterned on a dielectric substrate, said first radiofrequency coil formed of conductive material, said first radiofrequency coil generating a first magnetic field that is resonant at a first radiofrequency;
a second radiofrequency coil patterned on said dielectric substrate, said second radiofrequency coil formed of conductive material, said second radiofrequency coil generating a second magnetic field that is resonant at a second radiofrequency,
said first radiofrequency coil and said second radiofrequency coil forming a first double-resonance apparatus;
a second double-resonance apparatus positioned substantially parallel to said first double-resonance apparatus; and
a sample region formed between said first double-resonance apparatus and said second double-resonance apparatus, said sample region configured to receive a nuclear magnetic resonance sample, wherein said second magnetic field is orthogonal to said first magnetic field at their respective resonant frequencies in said sample region,
said first radiofrequency coil patterned on a side of said dielectric substrate that is proximal to said nuclear magnetic resonance sample, said second radiofrequency coil patterned on an opposite side of said dielectric substrate that is distal to said nuclear magnetic resonance sample,
said first radiofrequency coil being a figure-eight racetrack resonator on a first side of said dielectric substrate and said second radiofrequency coil being a spiral resonator on a second side of said dielectric substrate,
wherein said first magnetic field and said second magnetic field excite or detect respective nuclear magnetic resonance signals at said first radiofrequency and said second radiofrequency alternately or simultaneously.
2. A nuclear magnetic resonance probe as in claim 1 , further comprising:
said first radiofrequency coil including a first set of current-carrying elements and said second radiofrequency coil including a second set of current carrying elements,
said first set of current-carrying elements set at said first radiofrequency being exclusive of said second set of current-carrying elements set at said second radiofrequency.
3. A nuclear magnetic resonance probe as in claim 1 1 , further comprising:
said figure-eight racetrack resonator generating said first magnetic field substantially parallel to a plane of said dielectric substrate, and
said spiral resonator generating said second magnetic field substantially perpendicular to the plane of said dielectric substrate.
4. A nuclear magnetic resonance probe as in claim 1 , further comprising:
a Faraday shield positioned between said first and second radiofrequency coils, wherein said Faraday shield reduces an electric field generated by said second radiofrequency coil but does not affect said first magnetic field generated by said first radiofrequency coil.
5. A nuclear magnetic resonance probe as in claim 1 , further comprising:
said dielectric substrate formed of two (2) substrates that are fastened together, and
said first and second radiofrequency coils patterned on said two (2) substrates, respectively.
6. A nuclear magnetic resonance probe as in claim 1 , further comprising:
said first and second radiofrequency coils patterned on a single side of said dielectric substrate, wherein said first radiofrequency coil is positioned within said second radiofrequency coil.
7. A nuclear magnetic resonance probe as in claim 6 , further comprising:
said first radiofrequency coil being a figure-eight spiral resonator and said second radiofrequency coil being a spiral resonator.
8. A nuclear magnetic resonance probe as in claim 7 , further comprising:
said figure-eight spiral resonator generating said first magnetic field substantially parallel to a plane of said dielectric substrate, and
said spiral resonator generating said second magnetic field substantially perpendicular to the plane of said dielectric substrate.
9. A nuclear magnetic resonance probe as in claim 1 , further comprising:
capacitive coupling between a first set of current-carrying elements of said first radiofrequency coil and a second set of current-carrying elements of said second radiofrequency coil across said dielectric substrate at said first radiofrequency, at said second radiofrequency, or at both of said first and second radiofrequencies.
10. A nuclear magnetic resonance probe as in claim 1 , further comprising:
said first radiofrequency coil and said second radiofrequency coil including a set of current-carrying elements,
whereby resonances of said first and second sets of current-carrying elements are produced due to differences in current density distribution at said first and second radiofrequencies.
11. A nuclear magnetic resonance probe as in claim 1 , further comprising:
a fixed inductive coupling loop used to transfer energy into and out of said first and second radiofrequency coils, said coupling loop terminated by a network of adjustable capacitors that are adjustable to achieve tuning and coupling of said first and second radiofrequency coils.
12. A nuclear magnetic resonance probe as in claim 11 , further comprising:
said coupling loop formed of high temperature superconductors.
13. A method of minimizing interaction between two (2) coils positioned in close proximity to each other, comprising the steps of:
patterning a first coil on a dielectric substrate, said first coil generating a first magnetic field resonant at a first frequency;
patterning a second coil on said dielectric substrate, said second coil generating a second magnetic field resonant at a second frequency, said first and second radiofrequency coils defining a nuclear magnetic resonance probe coil;
patterning a central conductor in said first radiofrequency coil or said second radiofrequency coil, such that a current in said probe coil at said first or second frequency flows through said central conductor and generates said first or second magnetic fields, respectively, parallel to a plane of said dielectric substrate; and
positioning said first and second coils on said dielectric substrate such that said first magnetic field at said first frequency is orthogonal to said second magnetic field at said second frequency, wherein a net magnetic flux generated by said first coil and flowing through said second coil is substantially zero (0).
14. A nuclear magnetic resonance probe, comprising:
a first radiofrequency coil patterned on a dielectric substrate, said first radiofrequency coil formed of conductive material, said first radiofrequency coil generating a first magnetic field that is resonant at a first radiofrequency;
a second radiofrequency coil patterned on said dielectric substrate, said second radiofrequency coil formed of conductive material, said second radiofrequency coil generating a second magnetic field that is resonant at a second radiofrequency;
said first radiofrequency coil and said second radiofrequency coil forming a first double-resonance apparatus;
a second double-resonance apparatus positioned substantially parallel to said first double-resonance apparatus; and
a sample region formed between said first double-resonance apparatus and said second double-resonance apparatus, said sample region configured to receive a nuclear magnetic resonance sample, wherein said second magnetic field is orthogonal to said first magnetic field at their respective resonant frequencies in said sample region, wherein said first magnetic field and said second magnetic field excite or detect nuclear magnetic resonance signals at said first radiofrequency and said second radiofrequency alternately or simultaneously,
said first radiofrequency coil or said second radiofrequency coil being substantially in the shape of a figure-eight, such that a central conductor is patterned along a substantial center of said first or second radiofrequency coils and along a longitudinal axis of said first or second radiofrequency coils, wherein current in said probe at said first or second radiofrequencies flows through said central conductor,
wherein said first or second radiofrequency coil carries current in counter directions on opposite sides of said nuclear magnetic resonance sample, such that said first and second magnetic fields in said sample region are additive and are generated substantially parallel to said dielectric substrate.
15. A nuclear magnetic resonance probe as in claim 14 , further comprising:
a fixed inductive coupling loop used to transfer energy into and out of said first and second radiofrequency coils, said coupling loop terminated by a network of, adjustable capacitors that are adjustable to achieve tuning and coupling of said first and second radiofrequency coils,
said coupling loop formed of high temperature superconductors.
16. A nuclear magnetic resonance probe as in claim 14 , further comprising:
said central conductor having two (2) end portions along said longitudinal axis of said first or second radiofrequency coil, said two (2) end portions defining a middle portion, said middle portion having a predetermined width, said two (2) ends being tapered relative to said middle portion in order to improve homogeneity of said first and second magnetic fields.