JPS5945097B2 - High frequency circuit of nuclear magnetic resonance apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high frequency circuit for a nuclear magnetic resonance apparatus for supplying a high frequency wave for excitation to a sample or for receiving a resonance signal from the sample.

Nuclear magnetic resonance apparatuses have made remarkable progress in recent years, and pulsed Fourier type nuclear magnetic resonance apparatuses have come to dominate.

In a pulsed Fourier transform type nuclear magnetic resonance apparatus, a high-frequency circuit is provided to irradiate the sample with a high-frequency pulse for excitation that is amplified by an output amplifier or to detect a resonance signal from the sample. There is. In recent years, in order to perform spin decoupling or observation of multiple types of nuclei, devices that can irradiate or detect not only a single frequency but also high-frequency waves having two or more types of frequencies at the same time have been required and manufactured. It has reached this point. The circuit for decoupling two different nuclides uses two types of high frequency frequencies f, , f,
It is classified as follows.

(1) One that uses a double-tuned circuit as shown in Figure 5a.

In the same figure, S is the sample tube, Ls is the irradiation coil, C is f,
σ is a capacitor that contributes to the tuning of f2, and σ is a capacitor that contributes to the tuning of f2. The irradiation coil Ls is directly connected to the capacitor C, and is connected to the capacitor C' via a fl trap circuit A consisting of an LC resonant circuit whose constant is selected to prevent the passage of f. , a tuned circuit shown in the equivalent circuit of FIG. 5b is established, and the frequency f. For , a tuned circuit shown by the equivalent circuit in FIG. (2) It is tuned only to the resonance frequency of one nuclide, and is not tuned to the other nuclide. (3) Non-synchronization with respect to both nuclides.

Among these circuits, (2) and (3) have non-tuned circuit parts, so the irradiation power may not be efficiently supplied to the sample. It cannot be said to be an effective method for samples with large binding constants. In addition, (1) is effective when the difference between f and f is large, but when f and f are close to each other, the trap circuit does not work effectively and tuning becomes impossible. There is a problem that it cannot be removed.

Moreover, not only this, but power consumption due to the inductance L included in the trap circuit cannot be ignored, and the sample cannot be effectively irradiated with high frequency waves from the power amplifier. The present invention has been made in view of the above-mentioned points, and by using a double-tuned circuit that does not require a trap circuit, it is possible to efficiently irradiate a sample with two different high-frequency signals Fl, f. , or the frequency F from the sample
It is an object of the present invention to provide a high frequency circuit for a nuclear magnetic resonance apparatus that can efficiently detect resonance signals of l and f2.

The double-tuned circuit illustrated in FIG. In this case, a trap circuit was indispensable so that two tuned circuits could exist separately by trapping one frequency.

However, the double-tuned circuit used in the present invention prepares two independent LC resonant circuits with different resonant frequencies and arranges the coils of the two LC resonant circuits on the same axis so as to mutually couple them. Therefore, a double-tuned circuit can be constructed without the need for a trap circuit, which is a major feature of the present invention. Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows the configuration of an embodiment of the present invention, and in the figure, 1 is a first power amplifier.

The excitation high frequency signal of frequency f1 amplified in the power amplifier is supplied to the tuning circuit section 3 via the mixer 2. The tuning circuit section 3 is matched with the mixer 2 by matching capacitors 4 and 5. Reference numeral 6 denotes a second power amplifier, which amplifies the high frequency signal for excitation of frequency F2 and supplies it to the tuning circuit section 3 via the mixer 2.

The mixer 2 is for preventing interference between the first and second power amplifiers. Reference numeral 7 denotes a variable capacitor for setting a tuning frequency range, and together with a coil 9 placed near the sample tube 8, constitutes a tuning circuit.

10 is a sample placed in a sample tube 8.

A coil 11 is disposed coaxially with the coil 9 and near the sample tube 8, and is connected to a variable capacitor 12.

In the above configuration, the inductances of the coil 9 and the coil 11 are Ll and L2, respectively, and the variable capacitors 7 and 12 are
Let the capacities of Cl and C2 be respectively.

If the coil 11 and the variable capacitor 12 were not present, the tuned circuit section 3 would have a single resonance point determined by L1 and C1, but in reality, the resonant circuit consisting of the coil 11 and the variable capacitor 12 is connected to the coil 9 and the coil. 11, the tuned circuit section 3 has two resonance points as shown in FIG. 2a. And Ll, L
2 is fixed, the frequency of one resonance point can be controlled mainly by appropriately selecting the value of C1, and the frequency of the other resonance point can be controlled arbitrarily by mainly selecting the value of C2 appropriately. Can be set to However, since mutual inductance due to mutual coupling between the coils 9 and 11 exists between the two resonant circuits, the two influence each other, and the two frequencies cannot be varied completely independently. Here, the resonance frequencies of the two nuclei to be observed or decoupled are F,, f2, f1 is mainly determined by C1, and F, is mainly determined by C2. shall be.

First, the value C1 of the variable capacitor 7 is adjusted so that one resonance point p is set at f1. After that, the value C2 of the variable capacitor 12 is adjusted so that another resonance point q is F.
Set to 2. Then, due to the influence of the mutual inductance mentioned above, the resonance point p adjusted earlier becomes f1
Since it has deviated slightly from the point, C1 is adjusted again so that the resonance point p is set at f1. Thereby,
Since the resonance point q deviates very slightly from the resonance point f, adjust C2 again so that the resonance point q is set to F, and by repeating this operation multiple times, the frequency f of each resonance point can be adjusted.
! , F2 can be exactly matched. Thus,
Output signals from the first and second power amplifiers 1 and 6 are supplied to coils 9 and 11 via a coupler 2.

As a result, the frequencies Fl and f2 are transmitted through the coils 9 and 11.
The sample 10 in the sample tube 7 is irradiated with a high-frequency magnetic field. In this case, when the high frequency power supplied from the power amplifier 1 or 6 is supplied to one of the coils 9 and 11, it is also consumed in the other coil because the two coils are coupled. Since the two coils are placed near the sample, the above-mentioned consumed high-frequency power will be irradiated onto the sample, and as mentioned above, there will be unnecessary consumption (wasted here) due to the inductance L included in the trap circuit. Compared to the conventional example in which the high frequency power generated by the power amplifier is not irradiated onto the sample), the high frequency power from the power amplifier can be effectively irradiated onto the sample with almost no loss. Furthermore, since no TRAB circuit is used, even when f1 and F2 are very close, they can be easily synchronized and used for irradiation or detection, no different from when they are far apart. In the above embodiment, the output signals of the first and second power amplifiers 1 and 6 are guided to the tuning circuit section 3 via the coupler 2, but as shown in FIG. It is also possible to feed the output signals of the amplifiers 1, 6 directly to the coil 9 in parallel.

In FIG. 3, the same components as in FIG. 1 are given the same numbers, and their explanations are omitted. The variable capacitor 13 and the capacitor 14 are provided to match the power amplifier 1 and a tuning circuit consisting of the coil 9 and the variable capacitor 7. With such a circuit, it is possible to effectively irradiate the sample with high frequencies having two different frequencies Fl and f2, similar to the embodiment shown in FIG. Furthermore, in the embodiments described above, an example was described in which the present invention was applied to a tuning circuit including an irradiation coil for performing spin decoupling, but an embodiment in which the present invention was applied to a detection coil is shown in FIG. Shown below. The difference from the embodiment shown in FIG. 3 is that since it is a detection system, the power amplifiers 1 and 6 are replaced with preamplifiers 16 and 15. In this embodiment as well, due to the mutual coupling between the coil 9 and the coil 11, the tuned circuit section 3 has two resonant frequencies Fl and f.
2, and the free induction damped signals with their respective frequencies are sent to subsequent processing (not shown) via preamplifiers 16 and 15, respectively. Note that the present invention is not limited to the above-described embodiments, but can be similarly applied to a high-frequency circuit equipped with a type of coil that serves both detection and irradiation.

[Brief explanation of the drawing]

1, 3, and 4 show an embodiment of the present invention, and FIG. 2 is a diagram for illustrating resonance points of a high frequency circuit.
FIG. 5 is a diagram for explaining an example of a conventional demodulation circuit. 1, 6: power amplifier, 2: coupling circuit, 3: tuning circuit section,
4, 14: Capacitor, 5, 7, 12, 13: Variable capacitor, 8: Sample tube, 9, 11: Coil, 10: Sample,
15, 16: Preamplifier.

Claims (1)

[Claims] 1 A first circuit placed near the sample and connected to a circuit for irradiating the sample with two types of high frequency waves of different frequencies or a circuit for detecting two types of high frequency signals of different frequencies generated from the sample. a first variable capacitor connected in parallel to the first coil; and a second coil disposed coaxially with the first coil so as to be mutually coupled to the first coil. A high frequency circuit for a nuclear magnetic resonance apparatus, comprising a second variable capacitor connected in parallel to the second coil.