JPH11133129A - NMR magnet device - Google Patents

Abstract

(57) [Problem] To provide an NMR magnet apparatus in which oscillation does not easily occur even if the length of a power supply cable is changed. SOLUTION: A main magnetic field generating means for generating a substantially uniform static magnetic field, a shim coil for correcting the homogeneity of the static magnetic field, a shim power supply for supplying a correction current to the shim coil, and a power supply cable for connecting the shim coil and the shim power supply. In the NMR magnet apparatus, a resistor close to the impedance value of the power cable was connected to the coil end of the shim coil in parallel with the shim coil via a capacitor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnet device used in an NMR device.

[0002]

2. Description of the Related Art FIG. 1 shows the structure of a conventional NMR magnet apparatus. Inside the magnet apparatus 1 for NMR,
The main magnetic field coil 2 is wound and generates a static magnetic field of tens of thousands to several hundred thousand gauss. Since a very strong static magnetic field is required for NMR measurement, a superconducting coil utilizing a superconducting phenomenon is generally used as the main magnetic field coil 2.

In order to observe NMR, it is required that the static magnetic field has a very high magnetic field strength and a very high uniformity. Lack of uniformity. Therefore, inside the main magnetic field coil 2, a magnetic field correction coil 3 (hereinafter, abbreviated as a shim coil 3) for correcting distortion of a static magnetic field.
The static magnetic field generated by the main magnetic field coil and the correction magnetic field generated by the shim coil are added to improve the uniformity of the static magnetic field.

An NMR measurement is performed by placing the measurement sample 4 in a highly uniform static magnetic field thus produced.

[0005]

By the way, a magnetic field correction power supply 5 (hereinafter, referred to as a power supply) for supplying a DC current to the shim coil 3.
The abbreviated shim power supply 5) is a stabilized power supply using a transformer, and therefore needs to be kept away from the NMR magnet apparatus 1 so as not to be affected by a strong magnetic field. For this reason, the shim power source is placed at a place distant from the NMR magnet apparatus 1 and is connected to the shim coil 3 using a long power cable (about 10 meters).

However, in such a configuration, since the shim coil 3 acts as a load at the end of the long power cable, there is a problem that oscillation is extremely likely to occur in the shim power supply 5 including an operational amplifier having a large gain in the circuit configuration. .

Normally, the length of the power supply cable is set to a length at which oscillation does not easily occur (ie, a length at which high-frequency waves from the shim power source are hardly reflected) to suppress the oscillation of the shim power source 5. If the length of the power supply cable is changed due to restrictions such as installation conditions of the NMR apparatus, the possibility that oscillation occurs in the shim power supply 5 cannot be denied.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide an NMR system which does not easily oscillate even if the length of a power cable is changed.
An object of the present invention is to provide a magnet device for a vehicle.

[0009]

In order to achieve this object, an NMR magnet apparatus according to the present invention comprises: a main magnetic field generating means for generating a substantially homogeneous static magnetic field; a shim coil for correcting the homogeneity of the static magnetic field; In an NMR magnet apparatus comprising a shim power supply for supplying a correction current to a shim coil and a power supply cable connecting the shim coil and the shim power supply, the coil end of the shim coil, in parallel with the shim coil, the impedance value of the power supply cable. It is characterized in that close resistors are connected via a capacitor.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows an NM implementing the present invention.
This is a magnet device for R. In the figures, 1 to 5 represent NMR, respectively.
1 shows a magnet device, a main magnetic field coil, a shim coil, a measurement sample, and a shim power supply, which are the same as those in FIG. Among them, an enlarged view of the connection portion between the shim coil 3 and the power cable, which is surrounded by a circle, is shown on the right side of the figure of the NMR magnet apparatus 1.

In the figure, a resistor 6 having a value close to the impedance of the power cable is connected to the coil end of the shim coil 3 via a capacitor 7 so as to be parallel to the shim coil 3. This is to suppress the reflection of the high frequency coming from the shim power supply by terminating the tip of the power supply cable with the resistor 6 having a resistance value close to the value of the impedance of the power supply cable. Actually, the impedance of the power cable used between the shim coil 3 of the NMR and the shim power supply 5 is about 100Ω,
For example, a resistor of 100Ω is connected.

Since the shim coil 3 is generally formed by combining a plurality of electromagnetic coils to correct a static magnetic field, a resistor of 100Ω is connected to each coil end.

As described above, by terminating the circuit in front of the shim coil 3 provided at the end of the power cable, even if the length of the power cable is changed due to installation circumstances or the like, the impedance is not changed. Is less. As a result, it is possible to provide an NMR magnet device in which oscillation hardly occurs.

The reason why the DC current flowing through the resistor 6 is cut by the capacitor 7 is that the shim coil 3
It has to do with the flow of current. That is, since the electric resistance of the shim coil 3 is several Ω to several tens of Ω, if the resistor 6 of 100 Ω is directly connected in parallel with the shim coil 3, the DC current flowing through the shim coil 3 has a non-negligible effect.

In consideration of the characteristics of the shim power supply 5, a capacitor having characteristics such that the impedance is reduced with respect to a frequency (several MHz or more) where oscillation is likely to occur is used as the capacitor 7.

[0016]

As described above, according to the present invention, it is possible to provide an NMR magnet apparatus in which the oscillation of the shim power supply does not easily occur even when the length of the power supply cable is changed due to restrictions on installation conditions and the like. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional example.

FIG. 2 is a diagram showing one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... NMR magnet apparatus, 2 ... Main magnetic field coil, 3 ... Shim coil, 4 ... Measurement sample, 5 ... Shim power supply, 6 ...
Resistor, 7 ... capacitor.

Claims (1)

[Claims] 1. A main magnetic field generating means for generating a substantially homogeneous static magnetic field, a shim coil for correcting homogeneity of a static magnetic field, a shim power supply for supplying a correction current to the shim coil, and a power cable connecting the shim coil and the shim power supply. An NMR magnet device comprising: an NMR magnet device comprising: a resistor near the impedance value of the power cable connected to a coil end of the shim coil in parallel with the shim coil via a capacitor;