CN106990372A - A kind of magnetic nuclear resonance radio frequency antenna circuit and its impedance matching methods - Google Patents
A kind of magnetic nuclear resonance radio frequency antenna circuit and its impedance matching methods Download PDFInfo
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- CN106990372A CN106990372A CN201610037087.9A CN201610037087A CN106990372A CN 106990372 A CN106990372 A CN 106990372A CN 201610037087 A CN201610037087 A CN 201610037087A CN 106990372 A CN106990372 A CN 106990372A
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- 238000000034 method Methods 0.000 title claims abstract description 23
- 238000012545 processing Methods 0.000 claims abstract description 5
- 230000003321 amplification Effects 0.000 claims abstract description 4
- 238000003199 nucleic acid amplification method Methods 0.000 claims abstract description 4
- 238000005481 NMR spectroscopy Methods 0.000 claims description 43
- 239000003990 capacitor Substances 0.000 claims description 24
- 230000014509 gene expression Effects 0.000 claims description 9
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- 230000015572 biosynthetic process Effects 0.000 description 2
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- 238000005259 measurement Methods 0.000 description 2
- 238000001208 nuclear magnetic resonance pulse sequence Methods 0.000 description 2
- 230000003068 static effect Effects 0.000 description 2
- 238000013459 approach Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 230000005415 magnetization Effects 0.000 description 1
- 230000005311 nuclear magnetism Effects 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 239000011435 rock Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N24/00—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects
- G01N24/08—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects by using nuclear magnetic resonance
- G01N24/081—Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/18—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging
- G01V3/32—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging operating with electron or nuclear magnetic resonance
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Abstract
The present invention provides a kind of magnetic nuclear resonance radio frequency antenna circuit and its impedance matching methods.The antenna circuit includes：Series resonant tank, it includes the radio frequency antenna element being connected in series, tuning capacitance unit and resistance unit；Radio-frequency power amplifier, it is used to carry out power amplification processing to input pulse signal；Radio-frequency transformer, its main coil is connected with the series resonant tank, is connected from coil with the radio-frequency power amplifier；Wherein, the capacitance values of tuning capacitance unit determine the resonant frequency of the magnetic nuclear resonance radio frequency antenna circuit, and the turn ratio of principal and subordinate's coil and/or the impedance value of resistance unit determine the impedance of the magnetic nuclear resonance radio frequency antenna circuit.The application can realize the relatively independent regulation of resonant frequency and impedance, simplify the impedance matching methods of NMR system antenna circuit.
Description
Technical Field
The invention relates to the field of oil and gas development and exploration, in particular to a radio frequency antenna circuit for nuclear magnetic resonance logging and lithology analysis and an impedance matching method thereof.
Background
Nmr logging and lithology instruments measure the amplitude and decay constants of the nmr signal from the spin nuclei, usually protons of the H element, of the rock in the formation. The amplitude of the initial signal is primarily indicative of the magnitude of the total porosity, while the time decay is decomposed into exponential decays, representing the transverse relaxation time. Relaxation times 1-2 are measures of spin-spin interaction, which provides information about the pore size, fluid type and permeability of the formation. These parameters are important petrophysical quantities, which are also the reason for the wide application of nuclear magnetism in the fields of well logging and well logging.
The measurement accuracy of nmr logging and lithology instruments is very sensitive to the noise ratio of the measured signal. The signal-to-noise ratio is determined primarily by the strength of the static magnetic field, the strength of the radio frequency field, and the relative orientation of the two fields in the sensing region. During a measurement procedure, the radio frequency field is used to flip the magnetization to the other face (usually perpendicular to the direction of the static magnetic field) in order to generate a nuclear magnetic resonance signal in the receiving antenna. The radio frequency antenna used in nuclear magnetic logging and lithology instruments typically operates at 400KHz to 40 MHz.
In order to effectively trigger the generation of the nuclear magnetic resonance phenomenon, a very strong radio frequency power signal needs to be generated, so that a power amplifier, antenna impedance matching and resonant frequency adjustment are indispensable. The power amplifier, the antenna impedance matching and the resonant frequency adjustment are matched with each other, so that a power output signal with stable gain is finally provided, and the pulse input signal can be amplified. In the prior art, most of the methods of series-parallel connection of a plurality of capacitors are adopted to realize impedance matching and resonant frequency adjustment, so that the application requirements are met.
In order to realize nuclear magnetic resonance tests of various pulse sequences, the power amplifier, the antenna impedance matching and the resonance frequency adjustment need to meet the application requirements of different methods, the energy consumption is reduced as much as possible, and the stability is improved. Fig. 1 and 2 show the structure of a conventional impedance matching and resonant frequency adjusting circuit. The mode of series-parallel connection of a plurality of capacitors is adopted to realize impedance matching and resonant frequency adjustment, and the application requirements are met. However, this method has a problem in that when any one of the capacitances is tuned, both the impedance and the resonant frequency are affected. Therefore, when the resonant frequency is adjusted and then the impedance is adjusted, the resonant frequency is changed again and cannot meet the requirement, or vice versa. This approach requires two or more capacitors to be iterated to achieve the desired resonant frequency and impedance. Therefore, the adjustment is very complicated, and due to the limitation of the precision when the capacitor is adjusted, an ideal effect is difficult to achieve.
Therefore, there is a need for a radio frequency antenna circuit that can independently perform impedance matching and resonant frequency adjustment.
Disclosure of Invention
The invention aims to solve the technical defect that the impedance and the tuning frequency of a radio frequency antenna circuit for nuclear magnetic resonance logging in the prior art cannot be independently adjusted.
The invention provides a nuclear magnetic resonance radio frequency antenna circuit, comprising:
a series resonant tank including a radio frequency antenna unit, a tuning capacitor unit and a resistance unit connected in series;
the radio frequency power amplifier is used for carrying out power amplification processing on the input pulse signal;
a radio frequency transformer, a primary coil of which is connected with the series resonance loop, and a secondary coil of which is connected with the radio frequency power amplifier;
the resonance frequency of the nuclear magnetic resonance radio frequency antenna circuit is determined by the capacitance value of the tuning capacitance unit, and the impedance of the nuclear magnetic resonance radio frequency antenna circuit is determined by the turn ratio of the main coil and the auxiliary coil and/or the impedance value of the resistance unit.
In one embodiment, a first end of the primary coil of the radio frequency transformer is connected to a first end of the tuning capacitor unit, a second end of the tuning capacitor unit is connected to a first end of the radio frequency antenna unit, a second end of the radio frequency antenna unit is connected to a first end of the resistor unit, and a second end of the resistor unit is connected to a second end of the primary coil of the radio frequency transformer.
In one embodiment, the tuning capacitance unit comprises an adjustable capacitance.
In one embodiment, when the nuclear magnetic resonance radio frequency antenna circuit is operated in a resonance state, the resonance frequency is adjusted according to the following expression:
wherein, L represents the built-in inductance of the radio frequency antenna unit, C represents the capacitance of the tuning capacitor unit, and ω represents the resonance frequency.
In one embodiment, when the nmr rf antenna circuit operates in a resonant state, the equivalent impedance of the nmr rf antenna circuit is:
wherein,Z0representing the input impedance, R, of the slave coilcRepresenting the impedance of the resistance unit, NSIndicating the number of turns of the slave coil, NPIndicating the number of turns of the primary coil.
According to another aspect of the present invention, there is also provided an impedance matching method for the above-mentioned nuclear magnetic resonance radio frequency antenna circuit, the method including:
adjusting the capacitance of the tuning capacitance unit to enable the series resonance circuit to work at a preset resonance frequency;
and adjusting the turn ratio of a main coil and a secondary coil of the radio frequency transformer and/or the impedance value of the resistance unit to determine the impedance of the nuclear magnetic resonance radio frequency antenna circuit.
In one embodiment, the step of adjusting the impedance of the nuclear magnetic resonance radio frequency antenna circuit is independent of the step of adjusting the resonant frequency of the nuclear magnetic resonance radio frequency antenna circuit.
In one embodiment, the step of adjusting the impedance of the nuclear magnetic resonance radio frequency antenna circuit comprises:
and adjusting the number of primary coil turns and/or the number of secondary coil turns of the radio frequency transformer.
Embodiments of the present invention first determine the resonant frequency and only adjust the size of one capacitor to adjust the resonant frequency. After the resonant frequency is adjusted, the impedance of the transformer is measured, and the turn ratio of the resistor and the transformer is adjusted to the optimal impedance. Therefore, the relative independent adjustment of the resonant frequency and the impedance can be realized, and the impedance matching method of the nuclear magnetic resonance system antenna circuit is simplified.
In addition, due to the limitation of the electrical characteristics of the capacitor, the adjustment precision of the capacitor generally cannot meet the impedance matching requirement of the nuclear magnetic resonance system. The embodiment of the invention avoids using the capacitor to adjust the matching impedance, adjusts the matching impedance by setting the turn ratio of the master coil and the slave coil of the radio frequency transformer, and can meet the requirement of flexibly setting the impedance of a system.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
FIG. 1 is a schematic diagram of a prior art circuit for adjusting resonant frequency and matching impedance using a capacitor network;
FIG. 2 is another circuit schematic of a prior art circuit for tuning resonant frequency and matching impedance using a capacitor network;
FIG. 3 is a schematic diagram of an exemplary embodiment of an RF nuclear magnetic resonance antenna circuit;
fig. 4 is a preferred example of an nmr rf antenna circuit according to an embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention are described in further detail below with reference to the accompanying drawings.
The embodiment of the invention provides a nuclear magnetic resonance radio frequency antenna circuit for nuclear magnetic resonance logging and lithology analysis processes. The structure of the rf antenna circuit is described in detail below with reference to fig. 3.
The rf antenna circuit mainly includes a series resonant tank 31, an rf power amplifier 32, and an rf transformer 33. The series resonant tank includes a radio frequency antenna unit 311, a tuning capacitor unit 312, and a resistor unit 313 connected in series.
The rf power amplifier 32 is used for performing power amplification processing on the input pulse signal. The primary winding of the rf transformer 33 is connected to the series resonant tank 31, and the secondary winding is connected to the rf power amplifier 32. When the nmr rf antenna circuit is operating in a resonant state, stable gain can be provided to the input pulse sequence only if the rf power amplifier 32 and the series resonant tank 31 achieve impedance matching and resonance.
In the antenna circuit of fig. 3, the capacitance value of the tuning capacitance unit determines the resonant frequency of the nuclear magnetic resonance radio frequency antenna circuit, and the turns ratio of the master and slave coils and/or the impedance value of the resistance unit determines the impedance of the nuclear magnetic resonance radio frequency antenna circuit. It should be noted that, the impedance of the whole antenna circuit is determined by adjusting the impedance of the resistance unit and the turns ratio of the primary coil and the secondary coil of the transformer, and the adjustment of the two parameters does not affect the resonant frequency. The relative independent adjustment of the resonance frequency and the impedance can be realized, which is very beneficial to improving the performance of the nuclear magnetic resonance system.
Specifically, a first end of the primary winding of the rf transformer 33 is connected to a first end of the tuning capacitor unit 312, a second end of the tuning capacitor unit 312 is connected to a first end of the rf antenna unit 311, a second end of the rf antenna unit 311 is connected to a first end of the resistor unit 313, and a second end of the resistor unit 313 is connected to a second end of the primary winding of the rf transformer 33. Preferably, the tuning capacitor unit 312 includes an adjustable capacitor to facilitate flexible adjustment of the capacitance value.
Fig. 4 is a preferred example of an nmr rf antenna circuit according to an embodiment of the invention. The impedance matching method is described in detail below with reference to fig. 4.
Current I of primary coil of RF transformerPWith current I from the coilSThe functional relationship of (a) can be expressed by the following expression:
wherein N isPNumber of turns of the main coil, NSThe number of turns of the slave coil.
Similarly, the voltage V of the primary winding of the RF transformerPVoltage V of slave coilSThe functional relationship of (a) can be expressed by the following expression:
the input impedance Z viewed from the coil end can be calculated from expressions (1) and (2)SThe expression function of (a) is as follows:
wherein Z isPRepresenting the impedance across the primary coil. As can be seen from expression (3), the input impedance looking into the coil end can be adjusted by changing the number of turns of the main coil or the secondary coil. With the circuit configuration in fig. 4, the input impedance Z viewed from the coil end can be further adjustedSExpressed as:
when the resonance is generated, the resonance frequency is increased,
and when resonance occurs, the equivalent impedance of the nuclear magnetic resonance radio frequency antenna circuit is as follows:
wherein L represents the built-in inductance of the RF antenna unit, C represents the capacitance of the tuning capacitor unit, ω represents the resonance frequency, Z0Representing the input impedance, R, of the slave coilcRepresenting the impedance of the resistance unit, NSIndicating the number of turns of the slave coil, NPIndicating the number of turns of the primary coil.
Generally, the resonance frequency ranges from 400KHz to 40MHz, and the resonance frequency can be set by adjusting the capacitance of the tuning capacitance unit using expression (5).
As can be seen from expressions (5) and (6), the adjustment of the resonance frequency and the calculation of the matching impedance are relatively independent processes.
Based on the analysis process, the specific process of the impedance matching method provided by the embodiment of the invention is as follows: firstly, adjusting the capacitance of a tuning capacitance unit to enable a series resonance loop to work at a preset resonance frequency; and then adjusting the turn ratio of a main coil and a secondary coil of the radio frequency transformer and/or the impedance value of the resistance unit to determine the impedance of the nuclear magnetic resonance radio frequency antenna circuit. Wherein the step of adjusting the impedance of the nuclear magnetic resonance radio frequency antenna circuit is independent of the step of adjusting the resonant frequency of the nuclear magnetic resonance radio frequency antenna circuit. And the step of adjusting the impedance of the nuclear magnetic resonance radio frequency antenna circuit comprises the step of adjusting the number of turns of a main coil and/or the number of turns of a secondary coil of a radio frequency transformer.
Therefore, after the resonant frequency is adjusted, the impedance of the whole circuit is determined by adjusting the size of the impedance adjusting resistor and the turn ratio of the primary coil and the secondary coil of the transformer, and the adjustment of the two parameters does not influence the resonant frequency. Thereby avoiding the tedious process of continuous iterative processing in the prior art.
Although the embodiments of the present invention have been described above, the above description is only for the convenience of understanding the present invention, and is not intended to limit the present invention. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (8)
1. A nuclear magnetic resonance radio frequency antenna circuit, comprising:
a series resonant tank including a radio frequency antenna unit, a tuning capacitor unit and a resistance unit connected in series;
the radio frequency power amplifier is used for carrying out power amplification processing on the input pulse signal;
a radio frequency transformer, a primary coil of which is connected with the series resonance loop, and a secondary coil of which is connected with the radio frequency power amplifier;
the resonance frequency of the nuclear magnetic resonance radio frequency antenna circuit is determined by the capacitance value of the tuning capacitance unit, and the impedance of the nuclear magnetic resonance radio frequency antenna circuit is determined by the turn ratio of the main coil and the auxiliary coil and/or the impedance value of the resistance unit.
2. The nuclear magnetic resonance radio frequency antenna circuit according to claim 1,
the first end of the primary coil of the radio frequency transformer is connected with the first end of the tuning capacitor unit, the second end of the tuning capacitor unit is connected with the first end of the radio frequency antenna unit, the second end of the radio frequency antenna unit is connected with the first end of the resistor unit, and the second end of the resistor unit is connected with the second end of the primary coil of the radio frequency transformer.
3. The nuclear magnetic resonance radio frequency antenna circuit according to claim 1,
the tuning capacitance unit includes an adjustable capacitance.
4. The nuclear magnetic resonance radio frequency antenna circuit according to any one of claims 1 to 3,
when the nuclear magnetic resonance radio frequency antenna circuit works in a resonance state, the resonance frequency is adjusted according to the following expression:
wherein, L represents the built-in inductance of the radio frequency antenna unit, C represents the capacitance of the tuning capacitor unit, and ω represents the resonance frequency.
5. The nuclear magnetic resonance radio frequency antenna circuit according to claim 4,
when the nuclear magnetic resonance radio frequency antenna circuit works in a resonance state, the equivalent impedance of the nuclear magnetic resonance radio frequency antenna circuit is as follows:
wherein Z is0Representing the input impedance, R, of the slave coilcRepresenting the impedance of the resistance unit, NSIndicating the number of turns of the slave coil, NPIndicating the number of turns of the primary coil.
6. An impedance matching method for a nuclear magnetic resonance radio frequency antenna circuit according to any one of claims 1 to 5, the method comprising:
adjusting the capacitance of the tuning capacitance unit to enable the series resonance circuit to work at a preset resonance frequency;
and adjusting the turn ratio of a main coil and a secondary coil of the radio frequency transformer and/or the impedance value of the resistance unit to determine the impedance of the nuclear magnetic resonance radio frequency antenna circuit.
7. The impedance matching method of claim 6, wherein the step of adjusting the impedance of the nuclear magnetic resonance radio frequency antenna circuit is independent of the step of adjusting the resonant frequency of the nuclear magnetic resonance radio frequency antenna circuit.
8. The impedance matching method of claim 6, wherein the step of adjusting the impedance of the nuclear magnetic resonance radio frequency antenna circuit comprises:
and adjusting the number of primary coil turns and/or the number of secondary coil turns of the radio frequency transformer.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201610037087.9A CN106990372B (en) | 2016-01-20 | 2016-01-20 | A kind of magnetic nuclear resonance radio frequency antenna circuit and its impedance matching methods |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107732457A (en) * | 2017-09-30 | 2018-02-23 | 苏州美柯医疗科技有限公司 | antenna element and array antenna |
| CN108828480A (en) * | 2018-06-05 | 2018-11-16 | 中国石油大学(北京) | Three-dimensional NMR imager array antenna decoupling method and device |
| CN112147554A (en) * | 2020-09-05 | 2020-12-29 | 武汉联影生命科学仪器有限公司 | Frequency matching and tuning device for receiving coil, cryogenic probe and magnetic resonance device |
| CN113433499A (en) * | 2021-06-29 | 2021-09-24 | 上海辰光医疗科技股份有限公司 | Magnetic resonance radio frequency coil structure for replacing connector |
| CN116084918A (en) * | 2023-02-28 | 2023-05-09 | 中石化江钻石油机械有限公司 | Lithology recognition system and lithology recognition method |
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| CN203204140U (en) * | 2013-04-12 | 2013-09-18 | 吉林大学 | Front-end signal conditioning module of receiving system of nuclear magnetic resonance water-researching machine |
| CN204457762U (en) * | 2014-12-31 | 2015-07-08 | 中国石油天然气集团公司 | A kind of high-power transmitting and apparatus for detecting weak signal |
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Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107732457A (en) * | 2017-09-30 | 2018-02-23 | 苏州美柯医疗科技有限公司 | antenna element and array antenna |
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| CN108828480A (en) * | 2018-06-05 | 2018-11-16 | 中国石油大学(北京) | Three-dimensional NMR imager array antenna decoupling method and device |
| CN112147554A (en) * | 2020-09-05 | 2020-12-29 | 武汉联影生命科学仪器有限公司 | Frequency matching and tuning device for receiving coil, cryogenic probe and magnetic resonance device |
| CN112147554B (en) * | 2020-09-05 | 2023-08-15 | 武汉联影生命科学仪器有限公司 | Frequency and matching tuning device of receiving coil, low-temperature probe and magnetic resonance device |
| CN113433499A (en) * | 2021-06-29 | 2021-09-24 | 上海辰光医疗科技股份有限公司 | Magnetic resonance radio frequency coil structure for replacing connector |
| CN116084918A (en) * | 2023-02-28 | 2023-05-09 | 中石化江钻石油机械有限公司 | Lithology recognition system and lithology recognition method |
| CN116084918B (en) * | 2023-02-28 | 2024-06-21 | 中石化江钻石油机械有限公司 | Lithology recognition system and lithology recognition method |
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