JP2874988B2 - Sample coil for NMR - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sample coil used in a nuclear magnetic resonance apparatus (NMR), and in particular, generates a high-frequency magnetic field for exciting a sample and generates the high-frequency magnetic field from the sample. The present invention relates to a sample coil for NMR used for detecting a high-frequency signal generated.

(Prior art)

Conventionally, a solenoid coil or a saddle coil has been used to generate a high-frequency magnetic field for NMR and simultaneously detect a resonance frequency. These have the drawback that when the frequency of the high frequency increases, the dielectric loss of the sample increases when the dielectric constant of the sample increases, and the coil length approaches one-quarter of the wavelength and the performance decreases. . Alderman-Grant (Al) is used as a high-frequency magnetic field generation detector having a structure that reduces such defects and is characterized by high sensitivity even at high frequencies.
A coil called a derman-Grant type or a resonator type is known (DWAlderman and DMGrant: Journal)
of Magnetic Resonance 36,447 (1979)). FIG. 4 is a perspective view and FIG. 5 is an exploded view of the parts. This coil has an outer cylindrical shape, and has two guard rings G1 and G2 made of band-shaped conductors spaced apart from each other at an upper portion and a lower portion inside the cylinder, and a dielectric sheet wound therearound. D (in FIG. 4, the reference numerals are shown, but the components themselves are not shown for clarity of the drawing), and wound around the dielectric sheet D facing each other with a gap therebetween. It consists of a pair of H-shaped conductive sheets (H-shaped coils) H1 and H2 of the same shape. The H-shaped coils H1 and H2 are shaped so as to cover vertical bands B1 and B2 extending in the axial direction of the cylinder and guard rings G1 and G2.
Wings W1 to W4 extending from both the upper and lower ends to both sides
W5 to W8. Wing section W1 of H-shaped coil H1
WW4 and the wings W55W8 of the H-shaped coil H2 are separated from each other. The high-frequency magnetic field generated by this coil is divided into vertical bands B1, B2 and guard ring G.
1, a region surrounded by G2, the direction of which is perpendicular to the plane of FIG. This coil has higher frequency and higher sensitivity than the conventional solenoid coil and saddle coil as described above. FIG. 6 shows an equivalent circuit of this coil. The inductances B1 and B2 of this equivalent circuit correspond to the vertical band portions B1 and B2 of the H-shaped coils H1 and H2, respectively, and the capacitances W1 to W8 respectively correspond to the wing portions W1 and W2.
It is formed between W8 and guard rings G1, G2. The guard rings G1 and G2 have a large effect of preventing a dielectric loss from occurring due to the generation of a high-frequency electric field between the conductive sheets H1 and H2, in addition to the function of forming the capacitances W1 to W8. The excitation pulse is applied between COLD and HOT in the figure, and the signal is extracted therefrom. The frequency of this coil cannot be changed even if a variable capacitor is provided between COLD and HOT in the figure.

However, the resonator type coil as described above,
Although it operates at high sensitivity and high frequency, it cannot be used at two types of frequencies (double tuning) or higher frequencies, so it is very difficult to use. In nuclear magnetic resonance signal measurement, a high frequency magnetic field having two different frequencies is often used, such as decoupling and NMR lock. Therefore, in such a measurement, the resonator type coil has low practical value.

Against this background, a distributed tuning type coaxial cable is connected to the resonator type coil to perform a double tuning operation at two different frequencies (US Pat. No. 4,833,412). ).

[Problems to be solved by the invention]

However, in the above-mentioned prior art, since a coaxial cable is used as a component, a large-sized coaxial cable with a high Q must be arranged near the resonator type coil, so that the size of the coil itself becomes large, It cannot fit into the limited NMR probe, and the magnetic field created by the coaxial cable causes distortion in the static magnetic field of NMR, and high resolution cannot be obtained.
As is clear from the specification of the above-mentioned patent, there is a difficulty in manufacturing due to a complicated configuration.

The present invention has been made in view of such a situation, and an object of the present invention is to solve the above-described problem of the conventional resonator type coil capable of performing double tuning operation, and to add two types of frequencies by adding a simple configuration. And a small, high-resolution resonator-type NMR sample coil.

[Means for solving the problem]

The NMR sample coil of the present invention, which achieves the above object, has a substantially cylindrical outer shape, and two guard rings made of band-shaped conductors spaced apart from each other at an upper portion and a lower portion inside the cylinder, A dielectric sheet wound around them and a pair of H-shaped conductive sheets of substantially the same shape wound facing each other with a gap therebetween on the outside of the dielectric sheet. The body sheet is composed of a vertical band extending in the axial direction of the cylinder, and a resonator type coil having a shape covering the periphery of the two guard rings and having wings extending to both sides from the upper end and the lower end of the vertical band. In the sample coil for use, one or more inductances are connected in series between the lower ends of a pair of H-shaped conductive sheets, one vertical band portion, the upper wing portion, and the other vertical band. , The first resonant circuit formed by connecting the wing portion of the lower end, one of the vertical band part,
One vertical band portion, an upper wing portion, the other vertical band portion, one or more inductances connected in series, and a second resonance circuit configured by connecting one vertical band portion; Further, one of the injection points of the high frequency to be injected into the first resonance circuit is provided on one guard ring.

[Action]

Since the NMR sample coil of the present invention is configured so that one or more inductances are connected in series between the lower ends of a pair of H-shaped conductive sheets of the resonator type coil and two resonance circuits are provided, With the addition of a simple configuration, double tuning can be performed at two frequencies, and the practicality of the resonator type coil is improved. Moreover, since the connecting inductance does not need to be placed near the resonator type coil, the size of the probe does not need to be large, and the static magnetic field of NMR can be distorted compared to the case of using a coaxial cable. Low and high resolution can be obtained. Further, according to the present invention, the size of the probe may be small, and the probe is advantageous as a high-resolution NMR probe such as an SCM type high magnetic field NMR probe in which the space factor is the most important. Also, since no coaxial cable is used, NMR
No signal (background) is generated. Furthermore, the first
Because one of the high-frequency injection point that is injected into the resonant circuit is provided on one of the guard ring, it is possible to suppress the generation of parasitic inductance, take the isolation between f ₁ and f ₂ Cross Talk can be prevented, operation can be stabilized, and circuit efficiency can be improved.

〔Example〕

Next, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows the entire configuration of an NMR sample coil of the present invention. FIG. 2 shows an equivalent circuit thereof. This NMR
As a sample coil for use, a resonator type coil 1 similar to that shown in FIG. 4 was used, and extrapolation inductances L1 and L2 were attached to leads extending below guard rings G2 of two H-shaped coils H1 and H2 of this coil 1. To form two resonance circuits for the resonator type coil 1 and perform double tuning with these resonance circuits. In FIG. 1, the resonator type coil 1 is the same as that of FIG. 4, and the description of each part is omitted. However, the dielectric sheet D is generally made of a high frequency material such as "Teflon" (trade name).
Use a high dielectric material. It is necessary to select a material for this dielectric according to the application. VC1 to VC4 shown are variable capacitors, which are used for tuning and matching the frequencies f1 and f2.
Extrapolated inductance L connected to H-shaped coils H1, H2
1. Extrapolated capacitances C1 and C2 between the other ends of L2 are commercially available capacitors. Then, the excitation pulse of the frequency f1 is applied between the lead of one H-shaped coil H2 and the guard ring G2 as shown in the figure, and the excitation pulse of the frequency f2 is applied between the extrapolation inductances L1 and L2. Connected so that

The operation of this sample coil for NMR will be described with reference to the equivalent circuit of FIG.
Are used for tuning and matching of the frequencies f1 and f2, as described above, and thus may be omitted in the approximate calculation of the resonance frequency. Therefore, the main part of the resonance circuit on the frequency f1 side is as shown in FIG. The resonance frequency f1 of this resonance circuit is f1 = 1 / (2π) [(B1 + B2) {Wu · W1 / (Wu + W1)}]
^-1/2 . Here, Wu = (W1 + W2) (W5 + W6) / (W1 + W2 + W5 + W6), W1 = (W3 + W4) (W7 + W8) / (W3 + W4 + W7 + W8).

The main part of the resonance circuit on the frequency f2 side is as shown in FIG. 3 (b). The resonance frequency f2 of this resonance circuit
Is f2 = 1 / (2π) [(B1 + L1 + B2 + L2) ｛Wu · C3 / (Wu + C
3)｝] ^-1/2 . Here, C3 = C1 · C2 / (C1 + C2).

As described above, the two frequencies of f1 and f2 are simultaneously or selectively applied, and the vertical band portions B1 and B2 and the guard ring G are applied.
1. High-frequency magnetic fields of these frequencies can be generated in a region surrounded by G2.

In the above example, two extrapolated inductances L1 and L2 are connected between the leads of the H-shaped coils H1 and H2, but only one extrapolated inductance L1 or L2 may be connected. Further, it is apparent that the present invention can be variously modified without being limited to these embodiments.

As described above, in the present invention, simply adding a simple circuit including one or more inductances to the conventional resonator type coil does not increase the probe size,
A double-tunable high-resolution probe can be realized without generating distortion in the static magnetic field of NMR.

〔The invention's effect〕

The NMR sample coil of the present invention is configured so that one or more inductances are connected in series between the lower ends of a pair of H-shaped conductive sheets of the resonator type coil and two resonance circuits are provided. With the addition of a simple configuration, double tuning can be performed at two frequencies, and the practicality of the resonator type coil is improved. Moreover, since the connecting inductance does not need to be placed near the resonator type coil, the size of the probe does not need to be large, and the static magnetic field of NMR can be distorted compared to the case of using a coaxial cable. Low and high resolution can be obtained. Also, according to the present invention, the size of the probe can be small, and the space factor is the most important.
This is advantageous as a high-resolution NMR probe such as an SCM type high magnetic field NMR probe. Further, since no coaxial cable is used, there is no generation of an NMR signal (background).

Further, since one of the injection points of the high frequency injected into the first resonance circuit is provided on one guard ring,
It is possible to suppress the generation of parasitic inductance, take the isolation between f ₁ and f ₂ can be prevented crosstalk, the operation is improved circuit efficiency as well as stable.

[Brief description of the drawings]

FIG. 1 is a diagram showing the overall configuration of an NMR sample coil of the present invention, FIG. 2 is an equivalent circuit diagram thereof, FIG. 3 is a diagram showing a main part of a resonance circuit, and FIG. 4 is a perspective view of a resonator type coil. FIG. 5 is an exploded view of the parts, and FIG. 6 is an equivalent circuit diagram thereof. 1 ... Resonator type coil, G1, G2 ... Guard ring,
D: dielectric sheet, H1, H2: H-shaped conductive sheet (H-shaped coil), B1, B2: vertical band portion, W1 to W4,
W5~W8 ...... wings, L _1, L2 ...... extrapolation inductance, VC1~4 ...... variable capacitor, C1, C2 ...... extrapolation capacitance

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 24/00-24/12 A61B 5/055

Claims (1)

(57) [Claims] An outer shape is substantially cylindrical, and two guard rings made of band-shaped conductors are provided at upper and lower portions of the inside of the cylinder so as to be separated from each other, and a dielectric material is wound around the two guard rings. A sheet and a pair of substantially identical H-shaped conductive sheets wound around the outside of the dielectric sheet with a gap therebetween, and each of the H-shaped conductive sheets are arranged in the axial direction of the cylinder. In the NMR sample coil consisting of a resonator type coil having a vertical band portion extending and a wing portion which is formed to cover the periphery of the two guard rings and extends to both sides from the upper end and the lower end of the vertical band portion, one pair of H One or more inductances are connected in series between the lower ends of the shaped conductive sheet, and one vertical band portion, an upper wing portion, the other vertical band portion, a lower wing portion, and one vertical band are connected. A first resonance circuit formed by connecting the first and second vertical bands, one vertical band, an upper wing, the other vertical band, one or more inductances connected in series, and one vertical band are connected. A second resonance circuit to be configured, and one of the high-frequency injection points injected into the first resonance circuit is provided on one of the guard rings. coil.