Non-resonant magnetic resonance transmitter with power factor correction

Patent metadata

Field	Value
Publication number	US-9689937-B2
Application number	US-201314067567-A
Country	US
Kind code	B2
Filing date	Oct 30, 2013
Priority date	Oct 30, 2013
Publication date	Jun 27, 2017
Grant date	Jun 27, 2017

Abstract

A non-resonant transmitter for a magnetic resonance (MR) system, such as a nuclear magnetic resonance (NMR) system, is described herein. The transmitter includes a coil for applying NMR pulse sequences to a substance. The coil is coupled to a circuit that includes a capacitor, a number of switches, and a power source. The transmitter operates in two modes. In a charging mode, the switches decouple the coil from the capacitor and the capacitor is charged by the power source. In a discharging mode, a radio frequency pulse is generated and the switches couple and decouple the coil from the capacitor so that the capacitor provides power to the coil. The addition of the capacitor improves the power factor of the circuit and reduces power draw from the power source.

First claim

What is claimed is:

1. A non-resonant magnetic resonance (MR) device for transmitting radio frequency pulses, the device comprising:
a coil for transmitting the radio frequency pulses;
a circuit configured to operate in a charging mode and a discharging mode, wherein the circuit comprises:
a capacitor;
a power source coupled to the capacitor; and
at least one switch that selectively couples the coil to both the capacitor and the power source;
wherein, in the charging mode, (i) the at least one switch decouples the coil from the capacitor and (ii) the power source charges the capacitor; and
wherein, in the discharging mode, the at least one switch alternatingly (i) couples the coil to both the capacitor and the power source and (ii) decouples the coil from both the capacitor and the power source at a frequency selected to generate the radio frequency pulses.

2. The device of claim 1 , wherein the capacitor comprises a capacitance of at least 1 pico-Farad.

3. The device of claim 1 , wherein the capacitor and the power source power the coil when the at least one switch couples the coil to the capacitor.

4. The device of claim 1 , wherein the circuit comprises a plurality of switches coupled between the capacitor and the coil and configured to selectively couple the coil to both the capacitor and the power source.

5. The device of claim 4 , wherein the plurality of switches comprises transistors.

6. The device of claim 5 , wherein the plurality of switches are arranged in an H-bridge.

7. The device of claim 5 , further comprising:
a driver coupled to the circuit and configured to control operation of the plurality of switches.

8. The device of claim 7 , wherein the operation of the switches generates the radio frequency pulses.

9. The device of claim 1 , wherein the device is part of a wellbore logging tool.

10. A method for transmitting radio frequency pulses, the method comprising:
(i) decoupling a capacitor from a coil to charge the capacitor over a first time period using a power source; and
(ii) alternatingly coupling the coil to both the capacitor and the power source and decoupling both the capacitor and the power source from with the coil to generate a radio frequency pulse over a second time period; wherein
the coupling and decoupling of processes (i) and (ii) are performed using a plurality of switches.

11. The method of claim 10 , wherein the coupling and decoupling in process (ii) comprises coupling and decoupling both the capacitor and the power source with the coil a plurality of times to generate the radio frequency pulse over the second time period.

12. The method of claim 11 , further comprising repeating processes (i) and (ii) a plurality of times to generate a plurality of radio frequency pulses that are each separated from adjacent radio frequency pulses by respective instances of the first time period.

13. The method of claim 10 , wherein the plurality of switches comprises a plurality of transistors.

14. The method of claim 10 , further comprising
applying the radio frequency pulse to a formation.

15. A non-resonant magnetic resonance (MR) device for transmitting radio frequency pulses, the device comprising:
a coil for transmitting the radio frequency pulses;
a circuit configured to operate in a charging mode and a discharging mode, wherein the circuit comprises:
a capacitor arranged in parallel with the coil;
a power source that is coupled to the capacitor; and
a plurality of transistors coupled between the capacitor and the coil and configured to selectively couple the coil to both the capacitor and the power source; and
wherein, in the charging mode, (i) the plurality of transistors decouple the coil from the capacitor and (ii) the power source charges the capacitor; and
wherein, in the discharging mode, the plurality of transistors alternatingly (i) couple the coil to both the capacitor and the power source and (ii) decouple the coil from both the capacitor and the power source at a frequency selected to generate the radio frequency pulses.

16. The device of claim 15 , wherein the capacitor comprises a capacitance of at least 1 pico-Farad.

17. The device of claim 15 , further comprising:
a driver coupled to the circuit and configured to control operation of the plurality of transistors.

18. The device of claim 17 , wherein operation of the transistors generates the radio frequency pulses.

19. The device of claim 15 , wherein the device is part of a wellbore logging tool.

Assignees

• Schlumberger Technology Corp

Inventors

• Song Yi-Qiao
• Mandal Soumyajit

Classifications

• G01V3/32

  operating with electron or nuclear magnetic resonance · CPC title

• G01R33/34092 Primary

  RF coils specially adapted for NMR spectrometers · CPC title

• G01N24/081

  Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity · CPC title

• G01R33/3614

  RF power amplifiers · CPC title

• G01R33/3607

  RF waveform generators, e.g. frequency generators, amplitude-, frequency- or phase modulators or shifters, pulse programmers, digital to analog converters for the RF signal, means for filtering or attenuating of the RF signal · CPC title