Low loss wide band front end for NMR receiver

• US 4,450,408 A
• Filed: 12/11/1981
• Issued: 05/22/1984
• Est. Priority Date: 12/11/1981
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Tiemann, Jerome J.
• Primary Examiner(s): Tokar, Michael J.
• Application Number:
  US06/329,791
• Time in Patent Office: 893 Days
• Field of Search: 324/300, 324/318, 324/322
• US Class Current: 324/318
• CPC Class Codes: G01R 33/3621 NMR receivers or demodulators, e.g. preamplifiers, means for frequency modulation of the MR signal using a digital down converter, means for analog to digital conversion [ADC] or for filtering or processing of the MR signal such as bandpass filtering, resampling, decimation or interpolation
• CPC Class Codes: G01R 33/3628 Tuning/matching of the transmit/receive coil
• CPC Class Codes: H03H 7/38 Impedance-matching networks

Abstract

An inductive element of a multipole impedance transforming bandpass network of classical design such as Butterworth or Chebyshev, for example, is employed as a pick-up coil for sensing NMR signals. The network matches the high input impedance of an NMR receiver preamplifier to the low impedance of the pick-up coil. Simultaneously, and as a consequence of the impedance matching, the high preamplifier input impedance appears as a band width broadening element at the pick-up coil. By virtue of the multipole design of transformer, a bandwidth broader than the natural bandwidth of the pick-up coil is obtained and the transfer of the energy of the detected NMR signal to the preamplifier is maximized.

Claims

1. A low loss, wide band front end for sensing and coupling an NMR signal to a preamplifier of an NMR imaging receiver comprising:

a multi-pole impedance transforming bandpass network having first and second sets of coupled resonant circuits each formed by respective sets of inductive and capacitive elements, wherein the inductive elements in said first set of resonant circuits are operable simultaneously as a pick-up coil to sense said NMR signal and as operative elements of said multipole impedance transforming bandpass network; and

wherein

said second set of resonant circuits is operable to transform the input impedance of said preamplifier to an impedance level which matches the combined resistance of said first set of inductive elements in said first set of resonant circuits more closely than the untransformed input impedance of said preamplifier, wherein the transformed impedance level appears in parallel with said first set of resonant circuits and is operable to broaden the signal bandwidth thereof.

2. The low loss, wide band front end of claim 1 wherein the number of elements in said first set of inductive elements is one.

3. The low loss, wide band front end of claim 1 wherein the inductive elements of said first set of resonant circuits are operable as a pick-up coil to sense said NMR signals;

said second set of resonant circuits being coupled to a preamplifier exhibiting a known admittance; and

wherein said second set of resonant circuits operates to effectively cause the resistance corresponding to the real part of said preamplifier admittance to effectively appear as a dampening element in parallel with said first set of resonant circuits, said transformer resistance matching the combined resistance of said first set of inductive elements operative as a pick-up coil more closely than the resistance corresponding to the real part of said preamplifier admittance and acting to broaden the bandwith of said first set of resonant circuits.

4. The low loss, wide band front end of claim 2 or 3 including a capacitor coupling said first and second sets of resonant circuits.

5. The low loss, wide band front end of claim 2 or 3 wherein said multipole, impedance transforming bandpass network comprises a Butterworth circuit.

6. The low loss, wide band front end of claim 2 or 3 wherein said multipole, impedance transforming bandpass network comprises a Chebyshev circuit.