JP2003014835A - Nmr probe and its adjustment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an NMR probe where a resonance frequency has been reduced while maintaining a high Q value and a method for adjusting the NMR probe for reducing a resonance frequency while maintaining a high Q value when the resonance frequency of a resonance circuit is high originally and when a transmission/reception coil is cut excessively to increase the resonance frequency. SOLUTION: The NMR probe comprises a transmission/reception coil for irradiating a sample with a high-frequency magnetic field and at the same time radiating it from the sample, a winding frame of a coil that is made of an insulator and wounds the transmission/reception coil, two lead sections being withdrawn from the transmission/reception coil, a shield member that is provided inside the winding frame for forming a capacitor at an area to the lead section via the winding frame, a coil cover that is made of an insulator and covers the transmission/reception coil and the lead section from the outside, and an electrode member that is provided outside the coil cover for forming a capacitor while striding over the two leads via the coil cover.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an NMR probe used in an NMR apparatus and a tuning frequency adjusting method thereof.

[0002]

2. Description of the Related Art In an NMR apparatus, an NMR probe equipped with a transmission / reception coil, a transmission / reception circuit, etc. is placed in a strong magnetic field,
The sample in the probe is irradiated with a high frequency magnetic field. There is a tuning circuit that tunes to the resonance frequency of the measurement nucleus, a resonance circuit for traps, etc. in this transmission / reception circuit, but the tuning frequency or resonance frequency of these circuits must be finely adjusted. The element is used.

Generally, variable capacitors and variable inductors are known as frequency variable elements, but in the conventional variable inductor, the ferrite core is inserted into and removed from the coil to vary the inductance, and the variable inductor is placed in a strong magnetic field. And NMR that does not disturb high magnetic field homogeneity
It cannot be used as a probe. Therefore, conventionally, a variable capacitor has been used as a frequency variable element, but in recent years when a superconducting magnet is used and the resonance frequency has risen to several hundred MHz, the lead wire portion has inductance,
Since the LC resonance mode is created, there is a problem that the application range is narrowed if only the variable capacitor is used for the purpose of tuning. Further, if the function of the resonance circuit as the capacitance is relied on by an external variable capacitor, there is a problem that the Q value of the whole resonance circuit is lowered.

Therefore, recently, the variable capacitor is
It is generally used for fine adjustment of the resonance frequency of the MR probe, and for the rough setting of the resonance frequency of the NMR probe, not the variable capacitor but the capacitance formed by the lead wire and the shield member is generally used. Figure 1
Is a schematic representation of the structure of such a recent NMR probe. In the figure, 1 is a transmission / reception coil.
The transmission / reception coil 1 has a role of irradiating the sample with a high-frequency magnetic field and a role of detecting an NMR signal emitted from the sample. Further, the transmission / reception coil 1 is wound on the outside of a cylindrical winding frame (coil bobbin) 4 made of an insulating material such as glass, and from the outside, a cylindrical coil cover made of an insulating material. Covered with 5.

From the lower end of the transmitting / receiving coil 1, the tuning circuit 7
Two lead portions 2 are drawn out toward. The two lead portions 2 are locations where the resonating high-frequency voltage amplitudes are maximized in opposite phases to each other, and the cylindrical shield member 3 made of a conductor is provided with the insulator winding frame 4 interposed therebetween. Is facing. As a result, the lead portion 2, the winding frame 4, and the shield member 3 form a capacitor having a high Q value in which the lead portion 2 and the shield member 3 are electrodes and the winding frame 4 itself is a dielectric portion. Since the capacitor having such a configuration has less loss than when an external capacitor is soldered, a resonant circuit having a high Q value can be obtained.

FIG. 2 illustrates such a resonance circuit as an equivalent circuit. In FIG. 2, (a) shows an example in which an LC resonance circuit is composed of an unbalanced circuit, and (b) shows an example in which an LC resonance circuit is composed of a balanced resonance circuit. The capacitor C ₁ having a high Q value, which uses the lead portion 2 and the shield member 3 as electrodes and the winding frame 4 itself as a dielectric portion, is arranged in parallel with the tuning capacitors C _{2 to} C _4, and the transmission / reception coil L
Together with ₁ constitutes an LC parallel resonance circuit. And
The main capacitance role of the LC parallel resonant circuit is placed on the capacitor C ₁ , and the tuning capacitors C _{2 to} C ₄ are provided only for fine adjustment of the resonant frequency. In the figure, C ₅ is a matching variable capacitor for matching the external high frequency source with the LC resonance circuit.

[0007]

As described above, in such a configuration, a tuning variable capacitor is provided to tune the resonance frequency of the entire LC resonant circuit to a predetermined frequency. When the resonance frequency of the entire LC resonance circuit deviates from the predetermined frequency beyond the variable range of (1), there is a problem in that it cannot be tuned to the predetermined frequency.

In such a case, when adjustment is required in the direction of increasing the frequency, a part of the transmission / reception coil 1 or a part of the lead portion 2 which is drawn from the transmission / reception coil 1 and forms a shield member 3 and a capacitor. Fine adjustment of the frequency has been performed by cutting out the portion to reduce the area and reduce the inductance component or capacitance component of the LC resonance circuit.

However, in such fine adjustment, if a part of the transmission / reception coil 1 or a part of the lead portion 2 is cut off too much, the inductance component or the capacitance component of the resonance circuit becomes too small, and the resonance frequency. Became too high, and it became difficult to lower it to the target level this time, and the transmission / reception coil 1 had to be recreated. On the other hand, on the contrary, when adjustment is required in the direction of lowering the frequency, the area of the transmission / reception coil 1 and the lead portion 2 cannot be increased, so that it is necessary to add a less efficient fixed capacitor to the LC resonance circuit. Therefore, there is a problem that the Q value of the entire LC resonance circuit is lowered.

In view of the above points, the present invention is directed to a case where the resonance frequency of the resonance circuit is originally too high,
Alternatively, when the resonance frequency becomes high by cutting off the lead portion too much, the resonance frequency is reduced while maintaining the high Q value, and the resonance frequency is reduced while maintaining the high Q value. It is to provide a method for adjusting an NMR probe.

[0011]

In order to achieve this object, an NMR probe and a method for adjusting an NMR probe according to the present invention include irradiating a sample with a high-frequency magnetic field and
A transmitter / receiver coil for detecting an NMR signal emitted from the sample, a coil winding frame made of an insulator and wound around the transmitter / receiver coil, two lead portions pulled out from the transmitter / receiver coil, and inside the winding frame. A shield member that is provided and forms a capacitor between the lead portion and the lead frame via a winding frame; a coil cover that is made of an insulator and covers the transmission / reception coil and the lead portion from the outside; and a coil cover that is provided outside the coil cover. , And an electrode member that forms a capacitor across the two lead portions via the coil cover.

Further, the electrode member is characterized in that it is a conductor wire wound on the outside of the coil cover, or a conductor foil arranged across the two lead portions from above the coil cover.

The sample is irradiated with a high-frequency magnetic field, and a transmitter / receiver coil for detecting an NMR signal emitted from the sample, a coil winding frame made of an insulator and wound around the transmitter / receiver coil, and a coil drawn out from the transmitter / receiver coil. 2
A lead member of a book and a shield member that is provided inside the winding frame and forms a capacitor between the lead portion and the winding unit via a winding frame; A method for adjusting an NMR probe including a coil cover for covering, comprising providing an electrode member on the outside of the coil cover so as to form a capacitor across the two lead portions via the coil cover.
The feature is that the tuning frequency of the probe is adjusted.

Further, the electrode member is characterized in that it is a conductor wire wound on the outside of the coil cover, or a conductor foil arranged so as to straddle two lead portions from above the coil cover.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 shows NMR according to the present invention.
1 shows an example of a probe. In FIG. 3, FIG.
The same reference numerals are given to the same portions as.

In the figure, reference numeral 1 is a transmission / reception coil. The transmission / reception coil 1 has a role of irradiating the sample with a high-frequency magnetic field and a role of detecting an NMR signal emitted from the sample. Further, the transmission / reception coil 1 is wound on the outside of a cylindrical winding frame (coil bobbin) 4 made of an insulating material such as glass, and from the outside, a cylindrical coil cover made of an insulating material. Covered with 5.

From the lower end of the transmission / reception coil 1, a tuning circuit 7
Two lead portions 2 are drawn out toward. The two lead portions 2 are locations where the resonating high-frequency voltage amplitudes are maximized in opposite phases to each other, and the cylindrical shield member 3 made of a conductor is provided with the insulator winding frame 4 interposed therebetween. Is facing. As a result, the lead portion 2, the winding frame 4, and the shield member 3 form a capacitor having a high Q value in which the lead portion 2 and the shield member 3 are electrodes and the winding frame 4 itself is a dielectric portion. Since the capacitor having such a configuration has less loss than when an external capacitor is soldered, a resonant circuit having a high Q value can be obtained.

In such a configuration, in order to enable the resonance frequency of the entire resonance circuit to be tuned to the resonance frequency of the observation nucleus by an external tuning variable capacitor (not shown), the resonance frequency of the entire resonance circuit is set in advance. Must be within specified standards. If the resonance frequency of the whole resonance circuit is too low and exceeds the specified standard range, the resonance frequency of the whole resonance circuit may change depending on the external tuning variable capacitor.
When it is not possible to tune to the resonance frequency of the observation nucleus, that is, when adjustment is required to increase the resonance frequency of the entire resonance circuit, a part of the transmission / reception coil 1 or the transmission / reception coil 1 is pulled out and shielded. A part of the lead portion 2 forming the capacitor with the member 3 is cut off to reduce the area, and the inductance component of the LC resonance circuit
Alternatively, by decreasing the capacitance component, the frequency is finely adjusted in the direction of increasing the frequency.

However, in such fine adjustment, if a part of the transmission / reception coil 1 or a part of the lead portion 2 is cut off too much, the inductance component or the capacitance component of the resonance circuit becomes too small, and the resonance frequency is reduced. Became too high, and it became difficult to lower it to the target level this time, and the transmission / reception coil 1 had to be recreated. Or, conversely, the resonance frequency of the whole resonance circuit is too high, exceeding the specified standard range, and the resonance frequency of the whole resonance circuit cannot be tuned to the resonance frequency of the observation nucleus by an external tuning variable capacitor. In such a case, that is, when the resonance frequency of the entire resonance circuit needs to be lowered, the area of the transmission / reception coil 1 and the lead portion 2 cannot be increased. There is a problem in that an additional measure is required and the Q value of the entire LC resonant circuit is lowered.

In order to solve such a problem, according to the present invention, a conductor wire 6 of 0.5 mmφ or less is formed on the outside of a coil cover 5 which is made of an insulator and covers the transmission / reception coil 1 and the lead portion 2 from the outside. Preferably, the conductor wire 6 having a diameter of 0.2 to 0.3 mm is wound about 1 to 3 turns. As a result, a capacitor having the same function as the external fixed capacitor is formed across the two lead portions 2 via the coil cover 5, so that it is not necessary to add an inefficient external fixed capacitor. Become.

This newly formed capacitor is a capacitor having a high Q value, in which the conductive wire 6 and the two lead portions 2 are electrodes, and the coil cover 5 itself is a dielectric portion. The coil cover 5 is sandwiched between the conductors 6 to bridge the spaces. This is because the one lead portion 2 and the conducting wire 6 form a first capacitor, and the other lead portion 2 and the conducting wire 6 form a second capacitor. Means that the conducting wire 6 is connected in series.

Such a resonance circuit of the present invention is called an equivalent circuit.
4 is shown in FIG. In FIG. 4, (a) is
An example of configuring an LC resonant circuit with an unbalanced circuit, (b) is a flat
An example in which an LC resonance circuit is configured by an equilibrium resonance circuit is shown.
Using the lead part 2 and the shield member 3 as electrodes,
A capacitor C having a high Q value, which uses the frame 4 itself as a dielectric portion. ₁
Is a tuning variable condenser C_Two~ C_FourIt is placed in parallel with and sends and receives
Coil L₁Together, they form an LC parallel resonance circuit.
And the role of the main capacitance of the LC parallel resonant circuit
Is the capacitor C₁The tuning variable condenser C_Two~ C_Four
Is only provided for fine adjustment of the resonance frequency.
Yes. In the figure, C₅Is an LC resonance with an external high frequency source
It is a matching variable capacitor for matching with the circuit.

This time, it is formed by one lead portion 2 and the conducting wire 6.
The removed first capacitor is C₆Equivalent to another
Second capacitor formed by the lead portion 2 and the conducting wire 6
Is C ₇Equivalent to. And these two capacitors
C₆, C₇Between, the conductor 6 wound around the coil cover 5
And are connected in series. The capacitors of these capacitors
Since the passitance component is relatively small, the loss is small, so
Lower the resonant frequency of the entire resonant circuit without reducing the Q value.
If you need to make fine adjustments,
You can

In the above embodiment, the conductor wire 6 is wound around the outside of the coil cover 5, but instead of the conductor wire 6, a conductor foil 8 having a width of about 0.5 mm is used as shown in FIG. It is also possible to dispose the lead portion 5 over the two lead portions 2. In this case, the area where the lead portion 2 and the conductor foil 8 overlap (hatched portion) becomes the capacitor,
The conductor foil 8 in the other portion plays a role of a conductor wire that connects the regions where the lead portion 2 and the conductor foil 8 overlap with each other in series. In this case, the conductor foil 8 need not be wound around the entire circumference of the coil cover 5.

[0025]

As described above, according to the NMR probe and the method for adjusting the NMR probe of the present invention, the sample is irradiated with the high frequency magnetic field, and the transmitter / receiver coil for detecting the NMR signal emitted from the sample and the insulator are used. A coil winding frame for winding the transmission / reception coil, two lead portions drawn out from the transmission / reception coil, and a capacitor provided inside the winding frame and between the lead portion and the winding frame. Made of an insulator and a shield member that forms
Since the coil cover that covers the transmission / reception coil and the lead portion from the outside and the electrode member that is provided on the outside of the coil cover and that forms the capacitor across the two lead portions via the coil cover are provided, When the resonance frequency is originally too high, or when the resonance frequency becomes high by cutting the transmitting / receiving coil or the lead part too much, the resonance frequency is reduced while maintaining the high Q value.
It is possible to provide a probe and a method for adjusting an NMR probe that reduces a resonance frequency while maintaining a high Q value.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional NMR probe.

FIG. 2 is a diagram showing an equivalent circuit of a conventional NMR probe.

FIG. 3 is a diagram showing an example of an NMR probe according to the present invention.

FIG. 4 is a diagram showing an example of an equivalent circuit of an NMR probe according to the present invention.

FIG. 5 is a diagram showing another example of the NMR probe according to the present invention.

[Explanation of symbols]

1 ... Transmit / receive coil, 2 ... lead part, 3 ... shield part
Material, 4 ... Reel, 5 ... Coil cover, 6 ... Conductor, 7 ...
..Tuning circuits, 8 ... Conductor foil, L₁... Transmitting and receiving coils, C₁
... Capacitors, C_Two~ C_Four... Synchronizing variable capacitors, C₅...
Matching variable condenser, C ₆... First capacitor, C₇... Second
Capacitors.

Claims (4)

[Claims] 1. A transmission / reception coil for irradiating a sample with a high-frequency magnetic field and for detecting an NMR signal emitted from the sample, a coil winding frame made of an insulator and around which the transmission / reception coil is wound, and drawn out from the transmission / reception coil. Two lead parts, a shield member provided inside the winding frame and forming a capacitor between the lead part and the winding frame, and an insulating body to form a transmitting / receiving coil and a lead part. An NMR probe comprising: a coil cover that is covered from the outside; and an electrode member that is provided on the outside of the coil cover and that forms a capacitor across two lead portions via the coil cover. 2. The electrode member is a conductor wire wound on the outside of the coil cover, or a conductor foil arranged across the two lead portions from above the coil cover. 1. The NMR probe according to 1. 3. A transmission / reception coil for irradiating a sample with a high-frequency magnetic field and for detecting an NMR signal emitted from the sample, a coil winding frame made of an insulator and wound around the transmission / reception coil, and drawn out from the transmission / reception coil. Two lead parts, a shield member provided inside the winding frame and forming a capacitor between the lead part and the winding frame, and an insulating body to form a transmitting / receiving coil and a lead part. A method for adjusting an NMR probe including a coil cover that is covered from the outside, wherein an electrode member that forms a capacitor is provided on the outside of the coil cover via the coil cover and between two lead portions. A method for adjusting an NMR probe, comprising adjusting the tuning frequency of the NMR probe. 4. The electrode member is a conductor wire wound on the outside of the coil cover, or a conductor foil arranged across the two lead portions from above the coil cover. 3. The method for preparing an NMR probe according to item 3.