JP3103441B2 - Tuning method of NMR probe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tuning system for an NMR probe.

[0002]

2. Description of the Related Art In a nuclear magnetic resonance apparatus (NMR), it is necessary to change the frequency of RF according to the nucleus to be measured. It is necessary to match with. This is the tuning of the probe, in which RF at a frequency corresponding to the measurement nucleus is input to the probe and the tuning state and the matching state are adjusted so that the level of the reflected wave from the probe is minimized.

[0003] Specifically, it is as follows. For a probe whose circuit configuration can adjust tuning and matching independently of each other, for example, first operate a tuning adjustment knob of the probe and then operate the Search for the position where the reflected wave level of the probe becomes minimum and fix it at that position. Then, operate the knob for adjusting the alignment of the probe to search for the position where the reflected wave level from the probe becomes the minimum and find that position. If fixed, tuning is completed. However, in a probe in which matching and tuning are combined, if the matching state is adjusted, the tuning state also changes. Therefore, tuning is performed in the following procedure.

First, matching and tuning are adjusted to standard values corresponding to the measurement nucleus. Next, the tuning adjustment knob is operated to search for a position where the level of the reflected wave from the probe is minimized, and the level of the reflected wave from the probe at that time is recorded. Operate the alignment knob slightly in either direction. The tuning adjustment knob is again operated so that the level of the reflected wave from the probe is minimized while the matching adjustment knob is kept as it is, and the level of the reflected wave from the probe at that time is recorded. Compare the reflected wave level recorded in step 2 with the reflected wave level recorded in step 2. If the reflected wave level recorded in step 3 is smaller, move the matching adjustment knob a little further in the direction operated by. If the wave level is higher, slightly move the adjustment knob in the direction opposite to the direction in which it was operated. By repeating ~, the knob for matching adjustment is fixed at the position where the reflected wave level from the probe is minimized,
In this state, the tuning knob is operated so that the level of the reflected wave from the probe is minimized.

[0005]

However, in the past, the tuning of the probe was performed manually,
The tuning required not only a long time but also skill.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide an NMR probe tuning method capable of performing probe tuning in a short time and with high accuracy. .

[0007]

In order to automate the tuning of the probe, it is conceivable to execute the above-mentioned conventional procedure by a processor. However, the above-mentioned procedure is based on a so-called successive approximation method. When tuning a probe in which tuning and matching are combined, the matching state must be changed slightly and tuning must be performed each time. Shortening cannot be expected.

However, the present inventor has found that when the tuning and matching are at standard positions and roughly match, the level of the reflected wave from the probe can be approximated by a quadratic function of the matching position. That is, the alignment position is M, and the alignment position is M
Let RFL be the reflected wave level when tuning is performed at
It has been found that when b and c are coefficients, RFL = aM ² + bM + c (1) may be satisfied. This has been confirmed by various experiments.

_{Accordingly, M 1, M 2, RFL} 1 reflected wave level each time taking a tuned three alignment positions of M _3, RFL _2,
When was _{RFL 3, RFL 1 = aM 1} 2 + bM 1 + c ... (2) RFL 2 = aM 2 2 + bM 2 + c ... (3) RFL 3 = aM 3 2 + bM 3 + c ... because it is (4), From these equations (2) to (4), the reflected wave level
RFL an inflection point M _i which is the smallest can be obtained by the following equation.

[0010] ^{_{M i = [M 1 2 (}} RFL 2 -RFL 3) + M 2 2 (RFL 3 -RFL 1) + M 3 2 (RFL 1 -RFL 2)] / 2 [M 1 (RFL 2 -RFL ₃ ) + M ₂ (RFL ₃ -RFL ₁ ) + M ₃ (RFL ₁ -RFL ₂ )] (5) Therefore, the tuning method of the NMR probe of the present invention employs at least three positions near the optimum matching position. Find the level of the reflected wave from each probe, find the optimal matching position based on the position and the reflected wave level,
The tuning is performed by tuning at the optimum matching position.

[0011]

In the present invention the effect of the action and the present invention, first detects for example the reflected wave level RFL ₁ at three positions in the vicinity of the optimal alignment position _{M 1, M 2, M 3} , RFL 2, RFL 3, M _1, M _2,
Using the values of M ₃ , RFL ₁ , RFL ₂ , and RFL ₃ , the optimum matching position is obtained by the above equation (5), and then tuning is performed at the optimum matching position.

Accordingly, the number of steps for tuning is very small as compared with the conventional tuning by the successive approximation method, so that the time required for tuning can be greatly reduced as compared with the conventional one.

[0013]

Embodiments will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of an embodiment of a tuning method of an NMR probe according to the present invention, in which 1 is an NMR spectrometer, 2 is a power amplifier, 3 is a directional coupler, and 4 is a level detector. , 5 control device, 6 denotes an input device, 7 drives, 8 probe, L is the sample coil, C ₁ is a tuning adjustment capacitor, C ₂ indicates a matching adjusting capacitor.

The NMR spectrometer 1 is a device for performing NMR spectroscopy, and includes a power amplifier 2 for generating RF. The directional coupler 3 supplies the RF generated from the power amplifier 2 to the probe 8, and supplies the reflected signal from the probe 8 to the level detector 4. The level detector 4 detects the level of the reflected signal supplied from the directional coupler 3, for example, a peak level.

The control device 5 performs the tuning process of the NMR probe according to the present invention, and is composed of a microprocessor and its peripheral circuits. And the control device 5
Has a tuning table in which a matching position and a standard tuning position are written for each measurement nucleus as shown in FIG. According to FIG. 2, the matching position for carbon is
_MC1 , _MC2 , and _MC3 are set, and the standard tuning position is T
_C0 is set. The same applies to other measurement nuclei. Here, it is natural that the three points set as the matching positions are located near the standard matching position of the measurement nucleus. It is clear that the matching position and the standard tuning position of these three points can be obtained empirically and experimentally. Note that when A matching position, capacity of the matching adjustment capacitor C ₂ is mechanical position means a capacitor C ₂ is voltage control for matching adjustment of the contact when it is intended to be mechanically operated Means the applied voltage. The same applies to the tuning position.

The input device 6 is composed of a keyboard or the like.
The driving device 7 adjusts the tuning position of the tuning adjustment capacitor C ₁ ,
It indicated tuned position alignment position of the alignment adjusting capacitor C ₂ from the respective control unit 5, and sets the matching position. When the tuning adjusting capacitor C ₁ is intended to be operated by a mechanical rotation driving device 7 is provided with for example a stepping motor or the like, the rotation axis of the tuning adjustment capacitor C ₁ and the rotation axis of the motor It is coupled by a flexible shaft or the like, when the tuning position from the control unit 5 is instructed rotates until the indicated tuned position the rotation axis of the tuning adjustment capacitor C _1. Also, when the tuning adjusting capacitor C ₁ is a voltage-controlled, the drive unit 7 when a control voltage generating circuit, the tuning position from the control unit 5 is instructed, corresponding to the tuning position control It generates a voltage applied to the tuning control capacitor C _1. The same applies to the matching adjusting capacitors C _2.

The probe 8 includes a sample coil L, a tuning adjustment capacitor C ₁ , a matching adjustment capacitor C ₂ , a coupling capacitor C _{3 and the} like. The matching and tuning are coupled by the coupling capacitor C ₃ . I have.

Next, the operation of the configuration shown in FIG. 1 will be described. When the measurement nucleus is inputted from the input device 6 and the start of tuning is instructed, the control device 5 refers to the tuning table and takes in the matching position with respect to the specified measurement nucleus, and the first matching position M ₁ To the driving device 7. This alignment adjustment capacitor C ₂ is positioned in the alignment position M _1. And the control device 5 is a driving device 7
Is instructed to perform a synchronous sweep in a predetermined range. This tuning control capacitor C ₁ is tuned located over the indicated range is changed, the tuning sweep is performed. The tuning sweep all of the tuning position, i.e. may be performed on the entire variable range of tuning adjustment capacitor C _1, also a predetermined range determined in advance around the standard tuning position written in the tuning table The sweep may be performed. Then, during a tuning sweep, the control unit 5 takes in the reflected wave level from the level detector 4, and stores the minimum value as RFL _1. Incidentally, it is natural that RF of the frequency corresponding to the measurement nucleus is generated from the power amplifier 2 prior to this processing.

When the above processing is completed, the control device 5 instructs the drive device 7 to the _second matching position M2, performs the tuning sweep in the same manner as described above, and determines the minimum value of the reflected wave level at that time. Store as RFL ₂ . Similarly conducted for the third aligning position M _3, stores the minimum level of the reflected wave at the time of the tuning sweep as RFL _3.

[0020] The control unit 5 and the above process ^{_{ends, M i = [M 1 2}} (RFL 2 -RFL 3) + M 2 2 (RFL 3 -RFL 1) + M 3 2 (RFL 1 -RFL 2) _{] / 2 [M 1 (RFL} 2 -RFL 3) + M 2 (RFL 3 -RFL 1) + M 3 (RFL 1 -RFL 2)] wherein sought inflection point M _i by the optimal alignment position this position And The relationship between the matching position and the reflected wave level at this time is as shown in FIG. 3, for example.

[0021] obtaining the optimal alignment position M _i in the above manner, the control unit 5 instructs the optimum alignment position M _i to the drive device 7, and instructs the tuning sweep. Then, the control device 5 takes in the reflected wave level from the level detector 4 during the tuning sweep, searches for a tuning position where the reflected wave level is minimized, and instructs the driving device 7 when the search is performed.

By executing the above processing, the matching adjustment capacitor C ₂ is set at the optimum matching position, and the tuning adjustment capacitor C ₁ is set at the optimum tuning position, and tuning is completed.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above-mentioned embodiment, the optimum matching position is obtained by performing the tuning sweep at each of the three matching positions. However, if there is a concern about adverse effects such as noise, the matching positions are further shifted. By performing the tuning sweep and repeating the above calculation, the optimum matching position can be obtained with higher accuracy. For example, if the reflected wave levels RFL ₁ , RFL ₂ , RFL ₃ , and RFL ₄ are obtained at _four matching positions M ₁ , M ₂ , M ₃ , and M ₄ , respectively, M ₁ , M ₂ , M ₃ , and RFL _1, RFL _2, RFL ₃ can be obtained a single inflection point using, also _{M 2, M 3, M 4} , RFL 2, RFL 3,
Another inflection point can be found using RFL ₄ .
Therefore, if the inflection points are obtained in all such combinations and the average value thereof is set as the optimum inflection point, the optimum inflection point can be obtained without being affected by noise.

Further, with reference to the inflection points obtained from the three matching positions, the minimum reflected wave level is further obtained for some of the matching positions, and each point composed of the combination of the matching position and the reflected wave level is reduced to a minimum of 2 points. The inflection point may be obtained by performing curve fitting by a multiplication method. Further, in the above embodiment, the separate control device 5 is provided for performing the tuning process. However, the control may be performed by the host computer of the NMR measurement device.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration example of a tuning table.

FIG. 3 is a diagram illustrating an example of a relationship between a matching position and a reflected wave level.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... NMR spectrometer, 2 ... Power amplifier, 3 ... Directional coupler, 4 ... Level detector, 5 ... Control device, 6 ... Input device,
7: drive unit, 8: probe, L: sample coil, C
₁ : Tuning adjustment capacitor, C ₂ : Matching adjustment capacitor.

Claims (1)

(57) [Claims] In each of at least three positions near an optimum matching position, a level of a reflected wave from the probe is obtained, an optimum matching position is obtained based on the position and the reflected wave level, and tuning is performed at the optimum matching position. A tuning method of an NMR probe, characterized in that tuning is performed by performing the following.