JP5561669B2 - NMR probe - Google Patents

Description

  The present invention relates to an NMR probe used in an NMR apparatus, and more particularly to an NMR probe capable of observing and irradiating two types of nuclei.

  The NMR device irradiates a sample to be measured placed in a static magnetic field with a high-frequency signal, then detects a minute high-frequency signal (NMR signal) emitted from the sample to be measured, and the molecular structure information contained therein Is a device for analyzing molecular structure by extracting.

  FIG. 1 is a schematic configuration diagram of an NMR apparatus. The high frequency signal oscillated from the high frequency oscillator 1 is controlled in phase and amplitude by the phase controller 2 and the amplitude controller 3 and sent to the power amplifier 4.

  The high-frequency signal amplified to the power required to excite the NMR signal by the power amplifier 4 is sent to the NMR probe 6 through the duplexer 5 and from a sample coil (not shown) placed in the NMR probe 6. The sample to be measured is irradiated as a high frequency pulse.

  After high frequency irradiation, a minute NMR signal emitted from the sample to be measured is detected by a sample coil (not shown) placed in the NMR probe 6, sent to the preamplifier 7 through the duplexer 5, and amplified.

  The receiver 8 converts the high-frequency NMR signal amplified by the preamplifier 7 to an audio frequency that can be converted into a digital signal, and simultaneously controls the amplitude. The NMR signal frequency-converted to the audio frequency by the receiver 8 is converted to a digital signal by the analog-digital data converter 9 and sent to the control computer 10.

  The control computer 10 controls the phase controller 2 and the amplitude controller 3, performs Fourier transform processing on the NMR signal captured in the time domain, and automatically corrects the phase of the NMR signal after Fourier transform, and then the NMR spectrum. Display as.

There are several types of high frequency applied to the NMR probe 6. Specifically, a high frequency corresponding to the resonance frequency of the nuclide as shown in FIG. 2 is applied to the NMR probe. In the figure, the chemical symbol on the left represents the type of observation nucleus, the numerical value on the right represents the resonance frequency of the observation nucleus when placed in a static magnetic field of 18 Tesla (T), and the unit is megahertz (MHz). Generally, it is divided into a nuclear group that resonates in a relatively high frequency band such as ³ H nucleus to ¹⁹ F nucleus and a nuclear group that resonates in a relatively low frequency band such as ²⁰⁵ Tl nucleus to ¹⁰³ Rh nucleus. The former high frequency is called HF and the latter high frequency is called LF.

Conventional techniques related to the present invention include NMR probes as shown in FIGS. In these examples, general f1 (HF nucleus, eg ¹ H nucleus) and f2 (LF nucleus, eg ¹³ C nucleus) were assumed. These NMR probes have decoupling circuits for separating two high frequencies.

  FIG. 3 shows a mixed type of the circuit system shown in FIG. 5. FIG. 3 (a) shows that the capacitors C1, C2, and C3 for the circuit configuration of the f1 signal are connected to the ground potential partition plate. FIG. 3B shows a case where the two separation circuits are placed on the opposite side of the helical resonator L1 and the coaxial resonator CR1, and FIG.

In FIG. 3A, f1 is approximately the resonance frequency of a balanced parallel resonance circuit composed of the combined capacitance of the sample coil L _S and (C2, C3), and C1 is its matching capacitance. Approximately, f2 is an unbalanced parallel resonant frequency due to the combined induction consisting of (L1, L _S , CR1) and C5, and C6 is its matching capacitance.

  F1 in FIG. 3 (b) is substantially the same as f1 in FIG. 3 (a), except that C1, C2, and C3 are not on the sample coil LS side but on the resonator L1 and CR1 side. . In summary, there is no significant difference.

  FIG. 4 shows a method of resonating two high frequencies using only one separation circuit. In this example, since there is no separation circuit on the LF side, the leakage of the HF signal to the f2 terminal side increases. However, an LF signal resonance circuit can be easily configured through a corresponding capacitor C7.

  FIG. 4A is often used when the LF side circuit is an unbalanced circuit and the frequency range of the LF signal is wide. FIG. 4B is a circuit in which the LF side circuit is a balanced circuit and is often used when large RF power is input, but the frequency range of the signal is narrowed.

In FIG. 4A, f1 is approximately a balanced parallel resonant frequency composed of the combined capacitance of the sample coils L _S and (C2, C3 and C7, C5), and C1 is the matching capacitance. Approximately, f2 is an unbalanced parallel resonant frequency consisting of a combined induction consisting of (L _S , CR1 induction term) and a combined capacitance of (C3, C7, C5), and C6 is its matching capacitance. .

In FIG. 4B, f1 is approximately a balanced parallel resonant frequency composed of the combined capacitance of the sample coils L _S and (C2, C3 and C7, C5), and C1 is the matching capacitance. Approximately, f2 is a balanced parallel resonant frequency consisting of a combined induction consisting of (L _S , CR1 induction term) and a combined capacitance of (C4, C3, C7, C5), and C6 is its matching capacitance. is there.

Japanese Patent Laid-Open No. 10-2947

In order to prove the difference from the technique presented in the present invention, FIG. 5 shows a schematic diagram of a conventional NMR probe. Needless to say, the sample coil L _S side has a metallic cover, and the cover is integrated with the chassis in terms of potential by fitting, screwing, joining, or the like.

  In the conventional NMR probe, the helical coils L1 and L2 of the separation circuit resonating with f1 or the coaxial resonators CR1 and CR2 are placed close to the chassis. Therefore, there is a problem that not only the two separation circuits are mainly coupled by mutual inductance (transformer coupling), but also the coupling is complicated by capacitive coupling because of high impedance.

  As a result, in the conventional type NMR probe, HF and LF interfere with each other, resulting in a decrease in resonance efficiency. Further, as a result of interference, mutual signal leakage cannot be ignored, resulting in a decrease in sensitivity.

FIG. 6 shows a simulation close to the experimental result of the frequency characteristics of the circuit configuration as shown in FIG. It can be seen that the isolation at the frequency f2 corresponding to the ¹³ C nucleus is about −10 several dB, and leaks considerably on the HF side.

The isolation of the frequency ^{1 of the 1} H nucleus is quite good because an HF block filter (not shown) is intentionally inserted in the pass circuit. In the absence of this filter, the isolation is still reduced to about -20 dB.

  For performance evaluation, in order to suppress interference between circuits, isolation of approximately −30 dB or more is necessary. However, in the prior art, such a separation circuit interferes with each other, so that −20 dB is the limit. End up.

  In such a state, the coupling between the circuits cannot be ignored from each signal line (usually having a coaxial signal line) to the external amplifier circuit, and an unnecessary ghost signal appears, Further reduce the signal efficiency.

  In addition, regarding Q in terms of Q parameters for evaluating a circuit with a normal circuit configuration, the Q obtained when a capacitor is arranged in a sample coil and a parallel resonant circuit is configured is approximately 250 (for example, at 400 MHz) However, if the separation circuit is configured as described above, the Q value decreases and may be about ˜200.

  The reason for this is that the electromagnetic fields around the adjacent resonators overlap each other and the resonance impedance is lowered due to the presence of the separation circuit. Therefore, it has been expected to develop a technique that can bring out the performance of the original sample coil while providing such a separation circuit.

  In view of the above points, an object of the present invention is to provide an NMR probe that can bring out the high performance of a sample coil even when a plurality of separation circuits are arranged at close positions.

In order to achieve this object, the NMR probe according to the present invention comprises:
A sample coil with two terminals A and B;
A cylindrical body in which two closed spaces C and D are formed by a ground wall conductor cylinder wall and a plurality of ground potential conductor walls partitioning the inside of the cylinder in the vertical direction;
The separation circuit E is stored in the closed space C, one end of the separation circuit E is connected to the sample coil terminal A through a hole formed in the partition wall, and the other end of the separation circuit E is connected to the closed space C. Ground directly or indirectly through a capacitive element to the partition wall of the closed space C,
Furthermore, the separation circuit F is stored in the closed space D, and one end of the separation circuit F is connected to the sample coil terminal B through a hole formed in the partition wall. An end is directly grounded to the partition wall of the closed space D or indirectly through a capacitive element to form a resonance circuit that can be double-tuned to the HF frequency and the LF frequency,
The HF is input from a terminal A or a terminal B of the sample coil, and the LF is input from a ground terminal of the separation circuit E or a ground terminal of the separation circuit F.

  The separation circuits E and F are helical resonators or coaxial resonators.

The line lengths of the separation circuits E and F are characterized by being a length corresponding to (2n-1) times a quarter wavelength of the resonating high frequency. However, n is a natural number.

According to the NMR probe of the present invention,
A sample coil with two terminals A and B;
A cylindrical body in which two closed spaces C and D are formed by a ground wall conductor cylinder wall and a plurality of ground potential conductor walls partitioning the inside of the cylinder in the vertical direction;
The separation circuit E is stored in the closed space C, one end of the separation circuit E is connected to the sample coil terminal A through a hole formed in the partition wall, and the other end of the separation circuit E is connected to the closed space C. Ground directly or indirectly through a capacitive element to the partition wall of the closed space C,
Furthermore, the separation circuit F is stored in the closed space D, and one end of the separation circuit F is connected to the sample coil terminal B through a hole formed in the partition wall. An end is directly grounded to the partition wall of the closed space D or indirectly through a capacitive element to form a resonance circuit that can be double-tuned to the HF frequency and the LF frequency,
The HF is input from the terminal A or the terminal B of the sample coil, and the LF is input from the ground terminal of the separation circuit E or the ground terminal of the separation circuit F.
Even if a plurality of separation circuits are arranged at close positions, it has become possible to provide an NMR probe that can bring out the high performance of the sample coil.

It is a figure which shows an example of the conventional NMR apparatus. It is a figure which shows an example of the nuclide measured by NMR, and its resonant frequency. It is a figure which shows an example of the conventional NMR probe. It is a figure which shows another example of the conventional NMR probe. It is a figure which shows another example of the conventional NMR probe. It is a figure which shows the frequency characteristic of the conventional NMR probe. It is a figure which shows one Example of the NMR probe concerning this invention. It is a figure which shows an example of the separation circuit used for the NMR probe of this invention. It is a figure which shows the frequency characteristic of the NMR probe concerning this invention. It is a figure which shows another Example of the NMR probe concerning this invention. It is a figure which shows another Example of the NMR probe concerning this invention. It is a figure which shows the frequency characteristic of the NMR probe concerning this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 7 shows an embodiment of the NMR probe according to the present invention. FIG. 7A is a typical schematic diagram of the present invention, and FIG. 7B is a diagram showing an actual circuit configuration.

In this embodiment, there is an NMR probe sample coil L _S used for observation and / or irradiation. There is an independent resonant box that connects to each end node of the coil. These resonant boxes have a structure that resonates at a specific frequency by coexisting with a device installed inside the resonant box.

  The respective resonance boxes are connected to each other in a column, that is, aligned in the direction of the static magnetic field. The connecting portion forms a strong RF ground plane chassis by bonding. The resonant box is formed in a cylindrical shape in the same direction as the cylinder, and after connection, the cylindrical box-shaped chassis has a certain length with the same diameter (cylindrical diameter: 2R, where R is a radius) sharing the same central axis. It becomes.

  One of the resonance boxes has a device 1 (eg, L1; a conductor path cut out from a certain length is coiled), surrounded by a ground plane cylindrical box, and shielded from the outside. One end of the device is connected to a terminal 1 for taking the device 1 out as an electrode.

  There are a case where the terminal 1 is taken out so as not to contact the surroundings by making a hole in the resonance box, and a case where an insulating bushing (made of ceramic or resin) is bitten in the hole and penetrated through the hole. is there. The other end of the device 1 may be directly grounded to the resonance box or may be grounded to the resonance box via the capacitor C4. In general, a method using a capacitor is frequently used.

  In addition to the terminals, two other through holes or terminals with second and third insulating bushings are attached to the plane portion (upper and lower end faces in the figure) that cuts the cylindrical axis of the resonance box.

  Another cylindrical resonance box connected in cascade connection includes the device 2 as in the previous resonance box, and has one similar terminal on each of the upper and lower end faces. One end of the device 2 is connected to the terminal 2, and the other end of the device 2 may be directly grounded to the resonance box or may be grounded to the resonance box via the capacitor C5. In general, a method using a capacitor is frequently used.

The final wiring when the two resonance boxes are joined in the longitudinal direction with their cylindrical axes aligned is called the box 1 for the resonance box described above and the box 2 for the resonance box described later. The electrode terminal 2 is inserted through the hole of the terminal 3 formed in the lower end surface of the box 1. In this state, a conductor line is extended from the terminal 2 of the box 2 and connected to the terminal 2 following one end of the sample coil L _S placed on the upper end surface of the box 1.

  The length of the extension line is good in terms of RF when about 1/3 of the length of a high-frequency quarter wavelength of f1 (HF) required for resonance is in the box 1. Will give. In this embodiment, since 180 to 190 mm corresponds to a quarter wavelength, it is sufficient to consider about 60 to 63 mm.

  However, as a modification, it is needless to say that the length may be (2n-1) times (n is a natural number) of a quarter wavelength.

Terminal 2 of the box 1 is joined to one end of the sample coil L _S, the terminal 1 of the box 1 is joined to the other end of the sample coil L _S. By doing so, each device in the two resonance boxes 1 and 2 is joined to both ends of the sample coil L _S.

By the way, assuming that an NMR probe that resonates with ¹ H nuclei at 400 MHz is assumed as the device placed in the resonance box, for example, the length of the 1/4 wavelength resonance size that is the minimum unit that resonates at 400 MHz, that is, 180 to 190 mm. A conductor path having a certain length is coiled to a size that can be installed in a resonance box.

  FIG. 8 shows a device mounted on the resonance box 1. The thicker the conductor, the better. In the example shown in the figure, the outer diameter of the conducting wire is ˜3 mm, the coil winding pitch space is ˜2.6 mm, and the coil winding thickness is ˜8 mm. When this coexists with the resonance box 1, it resonates at a desired frequency to form a helical resonator CR1 (L1).

  The same applies to the resonance box 2, and the wound conductor path is mounted in the resonance box to form the helical resonator CR2 (L2).

  In addition, since the high-frequency current flows only on the surface due to the skin effect, the conductor path may be a hollow pipe-like shape, and may be a type of line that is filled with a resin or the like inside the hollow and covered with metal at both ends. Needless to say.

The completed boxes 1 and 2 are connected, and an auxiliary line in the box 1 serving as an electrode extension path of the box 2 is wired. Both ends of the sample coil L _S are connected to the terminal 1 and the terminal 2 of the box 1.

The individual resonance boxes are integrated with the chassis, which is a ground plane, to form circuits that do not interfere with each other. The resonance box 1 is provided with tuning capacitors C2 and C3 and a matching capacitor C1 that constitute a resonance circuit of f1 (a high frequency that resonates with HF band nuclei such as ¹ H nuclei).

f2 (a high frequency that resonates with a nucleus in the LF band such as a ¹³ C nucleus) forms a balanced circuit or an unbalanced circuit through a separation circuit composed of a helical resonance circuit. That is, the terminal opposite to the terminal 1 of the inclusion device CR1 (L1) of the resonance box 1 is grounded via the capacitor C4 or directly grounded.

  Further, from the terminal 2 provided on the upper end face of the resonance box 1 to the terminal 3 provided on the lower end face of the resonance box via the auxiliary line (that is, the terminal 2 provided on the upper end face of the resonance box 2). The internal device CR2 (L2) of the resonance box 2 is grounded via the capacitor C5 or directly grounded to form a resonance circuit having an LF frequency (f2).

  The node CR on the terminal 3 side of the device CR2 (L2) in the resonance box 2 is connected to the LF side input / output circuit via the matching capacitor C6.

9A and 9B show the simulation results of the frequency characteristics at that time. The Q value ( ¹ H) of HF is ˜230, and the Q value ( ¹³ C) of LF is ˜112. By storing the two separation circuits CR1 and CR2 in separate resonance boxes, mutual interference between the separation circuits is achieved. Was suppressed, and the Q value showed a significant improvement.

In this embodiment, the position at which HF is input to the resonance circuit is on the connection terminal of the sample coil L _S and the separation circuit in the resonance box 1, but this is on the opposite terminal of the sample coil L _S. It may be.

  In this embodiment, the position where the LF is input to the resonance circuit is the ground end to the partition wall of the separation circuit on the resonance box 2 side, but this is connected to the partition wall of the separation circuit on the resonance box 1 side. It may be a ground end.

  The partition wall that partitions the resonance box 1 and the resonance box 2 has a single-layer structure in this embodiment, but may have a multilayer structure of two or more layers.

  FIG. 10 shows another embodiment of the present invention. In the example of FIG. 10, a portion corresponding to the CR of the first embodiment is replaced with a coaxial resonator. Mutual interference between coaxial resonators is suppressed, and excellent resonance characteristics are exhibited with respect to HF and LF.

11, in addition to the double tuned HF and LF, is an example of further adding the resonant circuit of the NMR lock frequency f3 for ² D nucleus.

  Usually, an LC parallel resonance circuit is used to form a separation circuit, and a resonance circuit for the f3 signal is formed. The element indicated by * 1 is the separation circuit. In order to reduce leakage on the HF side, an HF blocking filter may be combined at the same time.

FIG. 12 shows frequency characteristics simulating performance in an actual machine. Here, the ¹ H nucleus was 400 MHz, the ¹³ C nucleus was 100 MHz, and the ² D nucleus (lock) was 61 MHz.

FIG. 12A shows transmission characteristics and reflection characteristics when the ¹³ C nuclear input / output terminal is viewed from the ¹ H nuclear input / output terminal. Figure 12 (b) is a transmission characteristic and the reflection characteristic when viewed O pin for ² D lock core from the input-output terminal ¹³ C nuclei. FIG. 12 (c) is a transmission characteristic and the reflection characteristic when viewed O pin for ¹ H nucleus from ² D input terminal lock nucleus. In both cases, high isolation is obtained between the terminals.

  Thus, since the present invention can constitute a non-interference type resonance circuit, the mutual crosstalk characteristics are greatly improved. Further, since the separation circuit is spatially separated, it is difficult for discharge to occur, and the manufacturing convenience is increased.

  It can be widely used for NMR measurement when it is necessary to resonate the probe simultaneously with the resonance frequency of the HF nucleus and the resonance frequency of the LH nucleus.

1: high frequency oscillator, 2: phase controller, 3: amplitude controller, 4: power amplifier, 5: duplexer, 6: NMR probe, 7: preamplifier, 8: receiver, 9: analog-digital data converter 10: Control computer

Claims (3)

A sample coil with two terminals A and B;
A cylindrical body in which two closed spaces C and D are formed by a ground wall conductor cylinder wall and a plurality of ground potential conductor walls partitioning the inside of the cylinder in the vertical direction;
The separation circuit E is stored in the closed space C, one end of the separation circuit E is connected to the sample coil terminal A through a hole formed in the partition wall, and the other end of the separation circuit E is connected to the closed space C. Ground directly or indirectly through a capacitive element to the partition wall of the closed space C,
Furthermore, the separation circuit F is stored in the closed space D, and one end of the separation circuit F is connected to the sample coil terminal B through a hole formed in the partition wall. An end is directly grounded to the partition wall of the closed space D or indirectly through a capacitive element to form a resonance circuit that can be double-tuned to the HF frequency and the LF frequency,
The NMR probe, wherein the HF is input from a terminal A or a terminal B of the sample coil, and the LF is input from a ground terminal of the separation circuit E or a ground terminal of the separation circuit F. The NMR probe according to claim 1, wherein the separation circuits E and F are helical resonators or coaxial resonators. 3. The NMR probe according to claim 1, wherein the line length of the separation circuits E and F is a length corresponding to (2n-1) times a quarter wavelength of a resonating high frequency. However, n is a natural number.

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