JPH0431069B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a coil device used in a probe of a nuclear magnetic resonance apparatus (NMR apparatus), and particularly to a coil structure that can increase sensitivity.

[Prior art]

In an NMR device, a probe containing a sample is placed in a uniform static magnetic field, and a high-frequency magnetic field for excitation is irradiated from a coil placed close to the sample within the probe. The NMR spectrum is received by a receiver, sent to a computer via a receiving circuit, and subjected to Fourier transform processing to obtain an NMR spectrum. At this time, the sensitivity of the NMR device is greatly influenced by the quality of the coupling between the coil and the resonator of the sample, so great attention is paid to the shape and structure of the coil. In the case of NMR devices using superconducting magnets, for example, a cylindrical saddle-shaped coil as shown in FIG. 6 has been commonly used. In the saddle-shaped coil shown in Fig. 6, two spirally wound coil parts 1 and 2 are arranged symmetrically around the cylindrical axis Z around a cylindrical region of radius R in which a sample tube containing a sample is arranged. has been done. This spirally wound coil portion consists of straight portions 1A, 2A parallel to the cylindrical axis Z, and arcuate portions 1B, 2B lying in a plane perpendicular to the cylindrical axis Z. FIG. 7 shows a cross-sectional view of the linear portion A taken along a plane perpendicular to the cylindrical axis Z. The linear portions 1A and 2A are arranged symmetrically on the circumference of the radius R with the Y plane in between. A high frequency magnetic field is generated in the X direction by the coil.

The idea common to conventional coils as mentioned above is
Two spiral-wound coil parts 1 and 2 with the same shape are arranged facing each other from both sides with a cylindrical area in between, and therefore the number of turns of the coil is an even number such as 2, 4, 6, 8, etc. It will be a turn.

By the way, in recent years it has become possible to obtain strong static magnetic fields using superconducting magnets, and along with this, the observation frequency has also been increased from about 400 MHz to 500 MHz and 600 MHz. In order to increase the observation frequency in this way, the sample coil should have a small inductance that can increase the tuning frequency, and a high Q.
A device that can increase the signal-to-noise ratio and sensitivity is required.

Conventionally, the two-turn coil shown in FIG. 6, which has the smallest number of turns and can minimize inductance, has been used in such cases. However, even if such a coil is used, the inductance cannot be made sufficiently small, and in the past, this coil has had to be used even though it is undesirable.

Therefore, the present inventor proposed a novel one-turn coil as shown in FIG. 8, in which the winding is arranged on the Y axis in FIG. 7, which would never be arranged based on the conventional concept described above. FIG. 8a shows the shape when punched out from the conductor plate, and FIG. 8b shows the state when it is formed into a cylindrical shape. In Figures 8a and 8b, the coil is a straight conductor L parallel to the cylindrical axis Z.
1, L2, and an arc-shaped conductor L for forming a coil by connecting the linear conductors L1, L2 in series.
3. L4, second arc-shaped conductors L5 to L8, and lead L9 for connecting the coil to an external circuit.
It consists of L10. As can be seen from the fact that they are not connected to each other, the second arc-shaped conductors L5 to L8 do not have a role as a coil, and are located at the center point O of the cylindrical area where the sample is placed. By arranging a conductor having substantially the same shape at a position symmetrical to the first arc-shaped conductor, it is provided for the purpose of compensating for disturbances of the same degree in the static magnetic field.

According to such a proposed coil, a one-turn coil having a smaller inductance than a conventional two-turn coil can be realized. Moreover, in this proposed coil, the linear conductor L that plays the role of the coil
1. YZ where L2 is perpendicular to the axis of the high frequency magnetic field (X axis)
Although the straight conductor is placed on a plane, the high-frequency magnetic field strength generated in the X-axis direction at the center origin O of the cylindrical area where the sample is placed by the straight conductor placed at this position is different from that of the straight conductor at any other position. Since it is stronger than when it is placed, it has a high Q as a coil.

Therefore, this proposed coil realizes a coil with low inductance and high Q, but even if this proposed coil is used in an actual device, the Q of the tuned circuit will be low.
was not as high as expected. The reason for this is that in an actual NMR probe, the proposed coil is placed at the center of the static magnetic field, a lead wire is extended from this coil, and a tuning capacitor is connected at a position away from the coil to form a resonant circuit. This is because the inductance and stray capacitance of the lead wires prevented the Q of the tuned circuit (resonant circuit) from becoming as good as expected.

Therefore, an object of the present invention is to realize a coil device that can increase the Q of a tuning circuit by incorporating a tuning capacitor into the proposed coil.

[Means for solving problems]

To achieve this objective, the present invention
A coil device for an NMR probe is a coil device that is wound around a cylindrical sample region and generates a high-frequency magnetic field in a direction perpendicular to the axis of the cylinder, and includes:
A pair of straight conductive pieces extending in a direction parallel to the cylindrical axis and arranged approximately symmetrically across the cylindrical axis, and connecting the tips of the pair of straight conductive pieces to each other. comprising a first arcuate conductive piece for forming a coil, and a second arcuate conductive piece for connecting the other ends of the pair of linear conductive pieces, The first arc-shaped conductive piece extends continuously along the outer periphery of the cylindrical region to connect the pair of linear conductive pieces, and the second arc-shaped conductive piece A capacitor is inserted in the middle of the conductive piece, and the second arc-shaped conductive piece is connected to an external circuit through a connecting part between the pair of linear conductive pieces. There is.

[Effect]

In the proposed coil, the present invention provides a second conductor to compensate for the presence of the first arc-shaped conductors L3 and L4.
The second arc-shaped conductor L5 to L8 are provided, and a tuning capacitor is inserted into the second arc-shaped conductor. In this way, since a tuned circuit (resonant circuit) is formed by the coil structure alone, the Q of the tuned circuit can be dramatically increased compared to the conventional method in which the lead image is extended and a tuning capacitor is connected. become.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail using the drawings.

FIG. 1 is a perspective view showing an example of a coil device for an NMR probe embodying the present invention. This coil device differs from the proposed coil shown in FIG. 8b in that capacitors are inserted between the arcuate conductors L5 and L6 and between L7 and L8. In this example, a second cross-sectional view showing a cross-sectional view of the coil cut along a plane perpendicular to the cylindrical axis Z at the position of the second arc-shaped conductor is used.
As can be seen from the figure, arc-shaped conductors L5, L6 and L
By providing an overlapping portion between 7 and L8 and insulating the overlapping portion by sandwiching a dielectric film F, the overlapping portion has a capacitance, thereby forming a capacitor.

Therefore, if the coil in Figure 1 is represented as an equivalent circuit, it will be as shown in Figure 3, where the inductance and capacitors C1 and C2 are mainly contributed by the linear conductors L1 and L2.
A parallel resonant circuit is constructed with the combined capacitance of . In this resonant circuit, there is no lead wire or the like between the coil and the capacitor as in the conventional case, and the tuning capacitor is built into the coil, so the Q of the resonant circuit is extremely high.

FIG. 4 shows another embodiment of the present invention. In this embodiment, in addition to the configuration shown in FIG. 1, commercially available small chip capacitors C5 and C6 are attached to the arc-shaped conductors L5 and L6, are connected to each other by a third arc-shaped conductor L11, and this arc-shaped conductor L1
Lead L12 is pulled out from 1. Accordingly, the lead L10 in the coil of FIG. 1 is removed.

If the coil of this embodiment is represented as an equivalent circuit, it will be as shown in Fig. 5. Since the inductance of the coil is canceled by the capacitor C5 and is substantially reduced, the resonance frequency will be higher than that of the coil of Fig. 1. (tuned frequency) can be increased.

In addition, in each of the above embodiments, the capacitor constructed by sandwiching the dielectric film F between arc-shaped conductors is
It goes without saying that the small chip capacitors partially used in the illustrated embodiment may be substituted.

In addition to being punched out from a conductor plate as described above, the coil of the present invention can also be formed by attaching a conductor wire to a bobbin, by vapor deposition technology on the surface of a bobbin, or by forming a printed circuit on a substrate with or without flexibility. It can be manufactured by forming it as.

Further, in the above embodiment, the linear conductors are arranged exactly symmetrically with respect to the Z axis, but the linear conductors only need to be arranged substantially symmetrically, and a slight deviation is allowed.

〔Effect of the invention〕

As detailed above, according to the present invention, a coil device for an NMR probe is realized which has small inductance, can be used up to high frequencies, and has a high resonant circuit Q, so that the observation frequency of the NMR device can be further increased. At the same time, it becomes possible to dramatically improve sensitivity.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an example of a coil device for an NMR probe embodying the present invention, and FIG. 2 is a cross section of the coil taken along a plane perpendicular to the cylindrical axis Z at the positions of the second arc-shaped conductors L5 to L8. 3 is a diagram showing an equivalent circuit of the coil in FIG. 1, FIG. 4 is a perspective view showing another embodiment of the present invention, and FIG. 5 is a diagram showing an equivalent circuit of the coil in FIG. 4. 6 and 7 are diagrams for explaining a conventional saddle-shaped coil, and FIG. 8 is a diagram for explaining a novel coil proposed by the present inventor. L1, L2...Straight conductor, L3-L8...Circular conductor, F...Dielectric film, C1-C6...Capacitor.

Claims (1)

[Scope of Claims] 1. A coil device that is wound around a cylindrical sample region and generates a high-frequency magnetic field in a direction perpendicular to the axis of the cylinder, which extends in a direction parallel to the axis of the cylinder. A pair of linear conductive pieces arranged substantially symmetrically across an axis, and a first arcuate conductive piece for connecting the tips of the pair of linear conductive pieces. and a second arcuate conductive piece for connecting the other ends of the pair of linear conductive pieces to form a coil, the first arcuate conductive piece being The linear conductive pieces extend continuously along the outer periphery of the cylindrical region to connect the pair of linear conductive pieces, and a capacitor is inserted in the middle of the second arcuate conductive piece, and the The second arcuate conductive piece is connected to an external circuit through a connecting portion between the pair of linear conductive pieces.
Coil device for NMR probe. 2. The coil according to claim 1, wherein the conductive piece is formed of a plate-shaped conductor. 3. A patent in which the first and second arcuate conductive pieces are provided in pairs symmetrically across the sample area, and a capacitor is inserted into each of the pair of second arcuate conductive pieces. An NMR probe coil device according to any one of claims 1 to 2.