Baluns, a fine balance and impedance adjustment module, a multi-layer transmission line, and transmission line NMR probes using same

• US 20090140824A1
• Filed: 11/20/2008
• Published: 06/04/2009
• Est. Priority Date: 11/21/2007
• Status: Active Grant

• Current Assignee: Brandeis University
• Original Assignee: Brandeis University
• Inventors: Herzfeld, Judith, Hu, Jianping
• Granted Patent: US 7,936,171 B2
• Time in Patent Office: Days
• US Class Current: 333/26
• CPC Class Codes: H01P 5/02 with invariable factor of coupling H01P5/12 takes precedence choke joints H01P1/04, H01P1/06
• CPC Class Codes: H01P 5/10 for coupling balanced lines or devices with unbalanced lines or devices

Abstract

A pseudo-Marchand balun, compound balun and tunable multi-resonant coaxial balun, and NMR probes employing each such balun, and a fine balance and impedance adjustment module and a multi-layer transmission line for use in such NMR probes.

Claims

1. An improved Marchand balun comprising:

a first defined length transmission line having a center conductor and a shield;

a second transmission line having a center conductor and a shield;

one end of the center conductors providing a balanced output/input, the other end of said second transmission line center conductor providing the unbalanced input/output;

the shield of each transmission line being connected to ground; and

a capacitor interconnected between the other end of said first defined length transmission line and ground.

2. The improved Marchand balun of claim 1 in which said defined wavelength transmission line is less than ¼

wavelength.

3. The improved Marchand balun of claim 1 in which said defined wavelength transmission line has a length greater than

$\left(\frac{n}{2}\right)$

λ

and less than

$\left(\frac{1}{4}+\frac{n}{2}\right)<br><br>\mathrm{\lambda <br><br>}$

where n is a whole number.

4. The improved Marchand balun of claim 1 further including an in-line filter at the balanced output of said second transmission line.

5. A compound balun comprising:

a transmission line system having a center conductor and at least three concentric shields forming a first transmission line between said center conductor and said first shield, a second transmission line between said first and second shields, and a third transmission line between said second and third shields;

said first transmission line receiving unbalanced input/output having at least three multi-band frequency signals at one end and providing a multi-band balanced output/input at the other;

said second and third transmission lines forming a choke to suppress the common mode current in the shield of the first transmission line at high frequency.

6. The compound balun of claim 5 in which there is a fourth concentric shield forming a fourth transmission line between said third and fourth shields.

7. The compound balun of claim 5 further including a first reactive load between said second and third transmission lines.

8. The compound balun of claim 7 in which said first reactive load includes first and second sections spaced from each other about the periphery of said second and third shields.

9. The compound balun of claim 8 in which each said first and second section includes a reactive transmission line having one end of its center conductor connected to one of said second and third shields and one end of its shield connected to the other of said second and third shields, the other ends of said reactive transmission line'"'"'s shield and center conductor being connected to a capacitor for adjusting the choke for middle and low frequencies, respectively.

10. The compound balun of claim 6 further including a second reactive load between said third and fourth transmission lines.

11. The compound balun of claim 10 in which said second reactive load includes third and fourth sections spaced from each other about the periphery of said third and fourth shields.

12. The compound balun of claim 7 in which each said third and fourth sections include a reactive transmission line having one end of its center conductor connected to one of said third and fourth shields and one end of its shield connected to the other of said third and fourth shields, the other ends of said reactive transmission line'"'"'s shield and center conductor being connected to a capacitor for adapting the choke for low frequency.

13. The compound balun of claim 5 in which the space between said second and third shields includes a dielectric member.

14. The compound balun of claim 5 in which the space between said first and second shields includes a static dielectric member and a moveable dielectric member movable toward and away from said static dielectric member for adjusting the suppression of the common mode current at the highest frequency.

15. A tunable multi-resonant coaxial balun comprising:

a segmented main transmission line having an unbalanced input at one end and one of the balanced output terminals at the other;

an adjustable transmission line having an inner conductor and shield with at least one dielectric member movable to and fro longitudinally between the inner conductor and shield for defining at least two adjustable transmission lines sections and adjusting the dielectric constant thereof for varying the output impedance of the adjustable transmission line to match the output impedance of the main transmission line at high frequency.

16. The tunable coaxial balun of claim 15 in which there is a number, n, of said dielectric members defining a number, up to n+1, of adjustable transmission line sections.

17. The tunable coaxial balun of claim 15 further including a first and second capacitor at the output ends of each transmission line and/or a third capacitor connected between the input end of the adjustable transmission line and ground for adjusting the adjustable transmission line to match the output impedance of the segmented main transmission line at lower frequency when there are two channels.

18. The tunable coaxial balun of claim 17 further including a low frequency trap and either an impedance module or a low frequency module, connected respectively to the bottom or top of the tunable balance module, for adjusting the output terminal at the top of tunable balance module to match the output impedance of the segmented main transmission line (along with the said first and/or second capacitor at the output ends of said segmented main transmission line and adjustable transmission line) at the lowest frequency, when there are three channels.

19. A pseudo-Marchand balun NMR probe comprising:

a base including at least one pseudo-Marchand balun, and a tuning and matching circuit associated with each pseudo-Marchand balun; and

a probe body including a balanced pair of segmented main transmission lines at the proximate end interconnected with a sample coil at the distal end.

20. The multi-resonant pseudo-Marchand balun NMR probe of claim 19 further including in said base common null point modules connected to each of the outputs of said at least one pseudo-Marchand balun.

21. The multi-resonant pseudo-Marchand balun NMR probe of claim 19 in which in said probe body a fine balance and impedance adjustment module is interconnected between said balanced pair of segmented main transmission lines and said sample coil.

22. The multi-resonant Marchand balun NMR probe of claim 19 in which there are a plurality of said pseudo-Marchand baluns and said pseudo-Marchand balun NMR probe is multi-resonant.

23. The multi-resonant pseudo-Marchand balun NMR probe of claim 19 in which each said multi-resonant pseudo-Marchand balun includes a first defined length transmission line having a center conductor and a shield;

a second transmission line having a center conductor and a shield;

one end of the center conductors provides a balanced output/input, the other end of said second transmission line center conductor providing the unbalanced input/output;

the shield of each transmission line being connected to ground; and

a capacitor interconnected between the other end of said first defined length transmission line and ground.

24. A multi-resonant compound balun NMR probe comprising:

a base including at least one tuning and matching circuit; and

a probe body including a segmented main transmission line interconnected to said at least one tuning and matching circuit;

a multi-resonant compound balun connected to said main transmission line and a sample coil interconnected to said multi-resonant compound balun.

25. The multi-resonant compound balun NMR probe of claim 24 in which said multi-resonant compound balun includes a transmission line system having a center conductor and at least three concentric shields forming a first transmission line between said center conductor and said first shield, a second transmission line between said first and second shields, and a third transmission line between said second and third shields;

said first transmission line receiving unbalanced input/output at least three frequencies at one end and providing a multi-band balanced output/input at the other;

said second and third transmission lines forming a choke to suppress the common mode current in the shield of the first transmission line at high frequency.

26. The multi-resonant compound balun NMR probe of claim 24 further including in said base a common null point module interconnected between said at least one tuning and matching circuit and said main transmission line.

27. The multi-resonant compound balun NMR probe of claim 24 further including in said probe body a fine balance and impedance adjustment module interconnected between said multi-resonant compound balun and said sample coil.

28. A multi-resonant compound balun NMR probe comprising:

a base including at least one tuning and matching circuit; and

a multi-resonant compound balun interconnected therewith; and

a probe body including a balanced pair of segmented main transmission lines at the proximate end and a sample coil at the distal end.

30. The multi-resonant compound balun NMR probe of claim 28 further including a transmission line extension in series between said common point module and said multi-resonant compound balun.

32. The multi-resonant compound balun NMR probe of claim 28 in which said multi-resonant compound balun includes a transmission line system having a center conductor and at least three concentric shields forming a first transmission line between said center conductor and said first shield, a second transmission line between said first and second shields, and a third transmission line between said second and third shields;

said first transmission line receiving multi-band unbalanced input/output at one end and providing balanced output/input at least three frequencies at the other end;

said second and third transmission lines forming a choke to suppress the common mode current in the shield of the first transmission line at high frequency.

29. The multi-resonant compound balun NMR probe of claim F1 further including a common null point module interconnected between said at least one tuning and matching circuit and said multi-resonant compound balun.

31. The multi-resonant compound balun NMR probe of claim 29 further including a fine balance and impedance adjustment module interconnected between said sample coil and said main transmission line.

33. A multi-resonant tunable coaxial balun NMR probe comprising:

a base including at least one tuning and matching circuit; and

a probe body having a multi-resonant tunable coaxial balun connected to said at least one tuning and matching circuit at the proximate end and a sample coil at the distal end.

34. The multi-resonant tunable coaxial balun NMR probe of claim 33 in which said multi-resonant tunable coaxial balun includes a segmented main transmission line having an unbalanced input at one end and one of the balanced output terminals at the other;

an adjustable transmission line having an inner conductor and shield with at least one dielectric member movable to and fro longitudinally between the inner conductor and shield for defining at least two balun transmission line sections and adjusting the dielectric constant thereof for varying the output impedance of the balun transmission line to match the output impedance of the main transmission line at high frequency.

35. The multi-resonant tunable coaxial balun NMR probe of claim 33 further including in said base a common null point module interconnected between said at least one of said tuning and matching circuits and said multi-resonant tunable coaxial balun.

36. A fine balance and impedance adjustment module comprising:

a pair of transmission line sections having the same or different characteristic impedances and having their shields connected together;

a dielectric medium in each shield;

a center conductor passing through said dielectric medium and snugly fit therein to permit movement and repositioning of said center conductor relative to said shields for adjustment of high frequency impedance and balance; and

a capacitor connected to each center conductor for adjusting lower frequency impedances and balances.

38. The fine balance and impedance adjustment module of claim 36 in which said capacitors are variable.

37. The fine balance and impedance adjustment module of claim 361 in which said capacitors are unequal.

39. A multi-layer transmission line comprising:

an inner metal sleeve;

an outer metal sleeve;

a longitudinally aligned stack of metal (normally copper) disks that alternately make contact with the inner or outer sleeve of the transmission line, and are separated by dielectric material that makes contact with both sleeves.

40. The multi-layer transmission line of claim 39 further including a top coaxial transmission line section.

41. The multi-layer transmission line of claim 40 further including an adjustable dielectric, which can be moved into and out of said top coaxial transmission line section to accomplish the fine adjustment of the electrical length.