JP2002214315A - Resonance frequency adjusting mechanism for loop gap resonator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resonance frequency adjusting mechanism for loop gap resonator dispensing with the exchange of a capacitance adjusting plate for controlling the capacitance of a loop gap resonator every change in aperture of the loop gap resonator. SOLUTION: This mechanism comprises the capacitance adjusting plate constituted so that the distance from a gap part is variable by arranging the gap part so as to cover the outside of a loop member cylindrically formed by a conductive material and having the gap in the direction substantially parallel to the axial center of the cylinder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement of a resonance frequency adjusting mechanism in a loop gap resonator used in an electron spin resonance (ESR) device.

[0002]

2. Description of the Related Art FIG. 1 shows a loop gap resonator and a resonance frequency adjusting mechanism described in Japanese Patent Publication No. 3-79670. The loop gap resonator is shown in FIG.
As shown in FIG. 1, the loop-shaped electrode 1 has a structure cut by a gap 2 substantially parallel to the axis of the loop, and a microwave current supplied through coupling with an external antenna circuit (not shown) is applied to the electrode 1. Flow over the surface. At this time, the loop electrode 1 becomes the inductance L, and the gap 2 becomes the capacitance C, thereby forming an LC resonator.

The resonance frequency of this loop gap resonator is determined by the loop length (loop diameter) and the size of the gap, that is, the shape. A method for changing the resonance frequency without changing the shape is shown in FIG. As has been
Inserting a capacitance adjusting plate 3 made of a dielectric material or the like into the gap 2 is performed. This is because the capacitance C is changed by inserting a dielectric into the gap, and the resonance frequency is changed. The resonance frequency is changed by moving the dielectric in the direction of the arrow to change the amount of dielectric inserted in the gap. It can be changed continuously.

In such a configuration, the electromagnetic field distribution of the loop gap resonator has a shape as shown in FIG. Under such an electromagnetic field distribution, when a dielectric is inserted halfway into the gap 2 as shown in FIG. 1 for frequency adjustment, the electric field concentrates on the dielectric, and the gap 2
Since the electric field is weakened in the portion without the dielectric, the vertical symmetry of the electromagnetic field distribution in the resonator is broken, and the electromagnetic field distribution itself changes as the capacitance adjusting plate 3 moves.

[0005] Such a phenomenon is very inconvenient in an apparatus such as an ESR imaging apparatus in which the spatial intensity distribution of the microwave magnetic field inside the loop gap resonator is problematic. A loop gap resonator and a resonance frequency adjustment mechanism disclosed in Japanese Patent Application Laid-Open No. 9-184814 have been newly proposed to solve such inconveniences.

FIG. 3 shows a loop gap resonator in which the symmetry of the electromagnetic field distribution inside the resonator is improved. The loop gap resonator forms a loop portion 1 by bending a central portion of a thin plate electrode having a predetermined width and a predetermined length into a cylindrical shape, and forms a gap extension electrode 4 in which both ends of the thin plate electrode face each other at a gap portion. Are bent so as to protrude in parallel toward the outside of the loop.

By inserting the capacitance adjusting plate 3 made of a dielectric or the like into the gap 2 formed between the two opposing gap extending electrodes 4, the resonance frequency of the loop gap resonator is increased. An adjustment mechanism is formed. The capacitance adjusting plate 3 is fixed to a distal end portion of the support 5 by a fixing member such as a screw (not shown), and by moving the support plate 5 forward or backward by a driving mechanism (not shown), The amount of insertion of the capacitance adjusting plate 3 is adjusted, and the capacitance C is controlled. By forming the capacitance adjusting plate 3 and the gap 2 in such a structure,
The distortion of the symmetry of the electromagnetic field distribution inside the loop gap resonator due to the adjustment of the resonance frequency can be greatly improved.

[0008]

However, in the ESR measurement using the loop gap resonator, since the sample used for the measurement may be of various sizes,
In order to measure a spectrum with high sensitivity, it is necessary to prepare loop gap resonators of various diameters in advance according to the size of the sample. When the loop gap resonator is replaced with another having a different diameter according to the size of the sample, not only the diameter of the loop portion changes, but also the inductance L of the loop portion 1 changes. Because of this, the optimum gap width also changes. Therefore, the thickness of the capacitance adjustment plate 3 inserted into the gap portion 2 for controlling the capacitance C also varies with the loop gap resonator. According to the gap width, it must be changed to a more appropriate thickness. As a result, when replacing the loop gap resonator with another one having a different diameter, not only the loop gap resonator but also the capacitance adjusting plate 3 must be replaced at the same time in accordance with the loop gap resonator. was there.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to control the capacitance of the loop gap resonator each time the aperture of the loop gap resonator is changed. An object of the present invention is to provide a resonance frequency adjustment mechanism of a loop gap resonator that does not require replacement of a capacitance adjustment plate.

[0010]

In order to achieve this object, a resonance frequency adjusting mechanism of a loop gap resonator according to the present invention is formed in a cylindrical shape by using a conductive material, and has a direction substantially parallel to the axis of the cylinder. A capacitance adjusting plate disposed so as to cover the gap portion from outside the loop member and configured to be able to change the distance from the gap portion with respect to the loop member having the gap portion. It is characterized by.

Further, the capacitance adjusting plate is made wider than the width of the gap portion.

Further, the capacitance adjusting plate is made of a conductive material such as a metal or a dielectric such as a ceramic.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 is an embodiment of the resonance frequency adjusting mechanism of the loop gap resonator according to the present invention. 4, the same parts as those in FIGS. 1 and 3 are denoted by the same reference numerals.

In FIG. 1, reference numeral 1 denotes a loop portion of the loop gap resonator. A gap portion 2 is provided in the cylindrical loop portion 1 in a direction substantially parallel to the axis of the cylinder. In the vicinity of the gap portion 2, a capacitance adjusting plate 6 that covers the gap portion 2 from the outside of the loop portion 1 so that the distance from the gap portion 2 can be changed substantially in the radial direction of the cylinder of the loop portion 1. Is provided. The capacitance adjusting plate 6 is desirably bent concentrically with substantially the same curvature as the curvature of the cylinder of the loop portion 1. However, the diameter of the loop portion 1 is sufficiently large, and May have a flat shape without curvature.

The capacitance adjusting plate 6 is usually made wider than the width of the gap 2 and is attached to the tip of the support 5 connected to a drive mechanism (not shown). Then, the capacitance adjusting plate 6 is moved closer to the gap portion 2 of the loop gap resonator by moving the support 5 forward or backward in a substantially radial direction of the cylinder of the loop portion 1 by a driving mechanism (not shown). Or away from the gap of the loop gap resonator.

FIG. 5 shows an embodiment of the entire structure of the loop gap resonator including the resonance frequency adjusting mechanism according to the present invention. In the figure, reference numeral 5 denotes a support for supporting the capacitance adjusting plate 6. A capacitance adjusting plate 6 is attached to one end of the support 5, and the other end is connected to a driving mechanism (not shown). The drive mechanism drives the support 5 by a method such as manual or electric drive, and moves the capacitance adjusting plate 6 closer to the gap 2 or away from the gap. still,
The capacitance adjusting plate 6 is made of a conductive material such as a metal or a dielectric such as a ceramic having a high dielectric constant and a small high-frequency loss.

The gap portion 2 of the plug-in type loop gap resonator 7 is arranged to face the capacitance adjusting plate 6. Since the loop portion 1 is made of a conductive material such as a metal, when the capacitance adjusting plate 6 is made of a conductive material such as a metal, the loop portion 1 and the capacitance adjusting plate 6 are formed. It is necessary to insulate the two so that they do not conduct with each other.

The loop section 1 is supported in the middle of the plug-in type loop gap resonator 7. The main body of the plug-in loop gap resonator 7 defines the maximum diameter of the sample that can be measured, and is made of a material having a low dielectric constant and a small high-frequency loss, such as glass, acrylic resin, and Teflon (registered trademark) resin. It has a cylindrical shape. The insertion type loop gap resonator 7 is prepared in advance of various diameters, such as a small diameter one and a large diameter one, and a screw (not shown) of the support plate 8 made of a non-magnetic material is looped. By removing the gap resonator from the shield case 9, it is possible to easily replace the gap resonator with one having a different diameter.

In addition, inside the shield case 9, an annular loop coil 10 for supplying microwave power to the loop portion 1 of the loop gap resonator 7 is additionally provided with a loop of the cylindrical loop gap resonator 7. The loop portion 1 is installed so as to be coaxial with the axis of the loop portion 1, and is moved closer to or away from the loop portion 1 of the loop gap resonator 7, thereby forming a loop with the loop portion 1. The degree of coupling with the coil 10 can be freely adjusted.

FIG. 6 is an equivalent circuit showing the relationship between the loop gap resonator 7 and the loop coil 10. The electromagnetic field of the microwave generated from the loop coil 10 acts on the loop portion 1 of the loop gap resonator 7 having a property as an antenna coil, and the loop portion 1 cooperates with the gap portion 2 having a property as a capacitor. Thus, an LC resonance circuit is formed. By moving the capacitance adjustment plate 6 closer to the gap 2 or moving the capacitance adjustment plate 6 away from the gap 2, the capacitance of the capacitor can be freely changed and the resonance frequency of the LC resonance circuit can be varied. so,
The microwave supplied from the loop coil 10 is tuned. This makes it possible to perform the best ESR detection.

In such a configuration, the resonance frequency adjusting mechanism of the loop gap resonator according to the present invention is used as follows. First, when it is desired to increase the resonance frequency of the loop gap resonator, the capacitance adjusting plate 6 is moved by the driving mechanism (not shown) to the gap portion 2 of the loop gap resonator.
Away from the capacitor C and reduce the value of the capacitance C. As a result, the resonance frequency of the loop gap resonator increases, and it becomes possible to tune to a higher frequency microwave.

When it is desired to lower the resonance frequency of the loop gap resonator, the capacitance adjusting plate 6 is moved closer to the gap 2 of the loop gap resonator by a drive mechanism (not shown) to increase the value of the capacitance C. This lowers the resonance frequency of the loop gap resonator and allows it to tune to lower frequency microwaves.

The plug-in loop gap resonator 7
When it is desired to exchange the capacitance adjusting plate 6 with another having a different diameter, the capacitance adjusting plate 6 is moved as far as possible from the gap portion 2 of the loop gap resonator by a drive mechanism (not shown). And the pluggable loop gap resonator 7 do not collide with each other. After the replacement of the plug-in loop gap resonator 7, the capacitance adjusting plate 6 is moved closer to the gap portion 2 of the loop gap resonator by a drive mechanism (not shown) to control the resonance frequency of the loop gap resonator to a desired value. I do.

The loop gap resonator used in the present invention does not have the gap extension electrode bent so as to protrude in parallel to the outside of the loop, and simply has the same structure as the axis of the cylinder of the cylindrical loop portion. Only a gap portion is provided as a narrow gap cut in a substantially parallel direction. Since the resonance frequency is simply controlled by approaching the capacitance adjustment plate toward the narrow gap, the operation of inserting the capacitance adjustment plate into the gap between the opposed gap extension electrodes as in the conventional case Is not required, and the capacitance adjusting plate 6 is replaced with the replacement of the pluggable loop gap resonator 7.
There is no need to adjust the thickness. As a result, even when the loop gap resonator is replaced, it is necessary to replace the capacitance adjustment plate 6 for controlling the capacitance C of the loop gap resonator with a capacitance adjustment plate 6 having a different thickness each time. Is gone.

[0025]

As described above, according to the resonance frequency adjusting mechanism of the loop gap resonator of the present invention, the gap is formed in a cylindrical shape by using a conductive material, and the gap is formed in a direction substantially parallel to the axis of the cylinder. A loop member having a capacitance adjusting plate arranged so as to cover the gap portion from the outside of the loop member and configured to be able to freely change the distance from the gap portion. Even when the diameter of the gap resonator is changed, it is not necessary to replace the capacitance adjusting plate for controlling the capacitance C of the loop gap resonator with a capacitance adjusting plate having a different thickness each time.

[Brief description of the drawings]

FIG. 1 is a diagram showing a resonance frequency adjusting mechanism of a conventional loop gap resonator.

FIG. 2 is a diagram showing a distribution of a resonance electromagnetic field of a loop gap resonator.

FIG. 3 is a diagram showing a resonance frequency adjusting mechanism of a conventional loop gap resonator.

FIG. 4 is a diagram showing a resonance frequency adjusting mechanism of the loop gap resonator according to the present invention.

FIG. 5 is a diagram showing a resonance frequency adjusting mechanism of the loop gap resonator according to the present invention.

FIG. 6 is a diagram showing an equivalent circuit of a loop gap resonator and a loop coil.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Loop part, 2 ... Gap part, 3 ... Capacitance adjustment plate, 4 ... Gap extension electrode, 5 ... Support body, 6 ... Capacitance adjustment plate, 7 ... Plug-in loop gap resonators
8 ... Support plate, 9 ... Shield case, 10 ... Loop coil.

Claims (3)

[Claims] 1. A loop member formed of a conductive material in a cylindrical shape and having a gap in a direction substantially parallel to the axis of the cylinder is disposed so as to cover the gap from the outside of the loop member. A resonance frequency adjusting mechanism for a loop gap resonator, comprising: a capacitance adjusting plate configured to change a distance from the gap portion. 2. The capacitance adjusting plate according to claim 1, wherein said capacitance adjusting plate is made wider than a width of said gap portion.
A resonance frequency adjustment mechanism of the loop gap resonator according to the above description. 3. The resonance frequency adjustment of the loop gap resonator according to claim 1, wherein the capacitance adjustment plate is made of a conductive material such as a metal or a dielectric such as a ceramic. mechanism.