NMR probe circuit with nodal impedance bridge

• US 7,187,176 B2
• Filed: 02/08/2005
• Issued: 03/06/2007
• Est. Priority Date: 02/08/2005
• Status: Active Grant

• Current Assignee: Bruker Biospin Corporation (Bruker Corporation)
• Original Assignee: Bruker Biospin Corporation (Bruker Corporation)
• Inventors: Lim, Yit Aun, Maas, Werner E.
• Primary Examiner(s): Arana; Louis M.
• Application Number:
  US11/053,452
• Publication Number:
  US 20060176057A1
• Time in Patent Office: 756 Days
• Field of Search: 324/322, 324/318
• US Class Current: 324/322
• CPC Class Codes: G01R 33/3635 Multi-frequency operation

Abstract

A nuclear magnetic resonance (NMR) probe circuit is used with a sample coil tuned to a primary frequency f₁. The circuit is arranged to have a plurality of points of electric field minima at the f₁ frequency. One or more additional frequencies may be coupled to the circuit at these points, without interaction with f₁. The probe circuit also uses an impedance coupled between two of the minima points that affects the frequency response at the additional frequency or frequencies, without affecting the frequency response at f₁. The impedance may be made adjustable to allow tuning of the relative frequency resonances.

Claims

1. A nuclear magnetic resonance probe circuit comprising:

an inductive sample coil;

a resonator circuit electrically connected to the sample coil to form a combined circuit that is resonant at frequency f₁, the resonator circuit having a plurality of points of electric field minima for an RF signal at the frequency f₁;

an input port connected to a one of said minima points via which an electrical signal at a frequency f₂ that is lower than frequency f₁ is input to the resonator circuit; and

an impedance connected between the two of said minima points that significantly modifies the frequency response of the probe circuit at frequency f₂, but has a negligible effect on the frequency response of the probe circuit at frequency f₁.

2. A probe circuit according to claim 1 wherein the impedance is adjustable.

3. A probe circuit according to claim 2 wherein the impedance comprises an adjustable capacitor.

4. A probe circuit according to claim 2 wherein the impedance comprises an adjustable inductor.

5. A probe circuit according to claim 1 wherein the impedance comprises a parallel combination of at least one inductor and one capacitor.

6. A probe circuit according to claim 1 wherein the impedance comprises a series combination of at least one inductor and one capacitor.

7. A probe circuit according to claim 1 wherein the impedance is electrically in parallel with the sample coil.

8. A probe circuit according to claim 1 wherein the input port is a first input port, and wherein the resonator circuit comprises a second input port connected to a second one of said minima points via which an electrical signal at a frequency f₃ is input to the resonator.

9. A probe circuit according to claim 1 wherein the resonator circuit comprises a transmission line.

10. A probe circuit according to claim 9 wherein the transmission line is a first transmission line, and wherein the resonator circuit comprises a plurality of transmission lines separated by said minima.

11. A probe circuit according to claim 1 wherein the resonator circuit is balanced such that an electric field minimum for the frequency f₁ is located at the center of the sample coil.

12. A nuclear magnetic resonance probe circuit comprising:

an inductive sample coil;

a resonator circuit electrically connected to the sample coil to form a combined circuit that is resonant at frequency f₁ and balanced so that a point of electric field minimum is located at a center of the sample coil, the resonator circuit comprising a plurality of transmission lines and having a plurality of additional points of electric field minima for an RF signal at the frequency f₁;

a first input port connected to a first one of said minima points via which an electrical signal at a frequency f₂ that is lower than frequency f₁ is input to the resonator circuit;

a second input port connected to a second one of said minima points via which an electrical signal at a frequency f₃ that is lower than frequency f₂ is input to the resonator circuit; and

an impedance connected between the first and second minima points that significantly modifies the frequency response of the probe circuit at frequencies f₂ and f₃, but has a negligible effect on the frequency response of the probe circuit at frequency f₁.

13. A method of producing a nuclear magnetic resonance probe circuit having an inductive sample coil and a resonator circuit electrically connected to the sample coil to form a combined circuit that is resonant at a frequency f₁, the resonator circuit having a plurality of points of electric field minima for an RF signal at the frequency f₁, the method comprising:

coupling a signal at frequency f₁ to the resonator circuit at a point away from said minima points;

coupling a signal at a frequency f₂ that is lower than frequency f₁ to the resonator circuit at one of said minima points; and

providing an impedance connected between two of said minima points that significantly modifies the frequency response of the probe circuit at frequency f₂, but has a negligible effect on the frequency response of the probe circuit at frequency f₁.

14. A method according to claim 13 wherein the impedance is adjustable, and may be adjusted to change the frequency response of the probe circuit at the frequency f₂.

15. A method according to claim 13 wherein the impedance comprises a combination of at least one inductor and one capacitor.

16. A method according to claim 13 wherein the impedance is electrically in parallel with the sample coil.

17. A method according to claim 13 wherein the input port is a first input port, and wherein the resonator circuit comprises a second input port connected to a second one of said minima points via which an electrical signal at a frequency f₃ is input to the resonator.

18. A method according to claim 17 wherein the impedance is adjustable, and may be adjusted to change the frequency response of the probe circuit at the frequencies f₂ and f₃.

19. A method according to claim 13 wherein the resonator circuit comprises a transmission line.

20. A method according to claim 13 wherein the resonator circuit is balanced such that an electric field minimum for the frequency f₁ is located at the center of the sample coil.