JP2002350525A - Resonance frequency control mechanism of loop gap resonator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resonance frequency control mechanism of a loop gap resonator which controls the resonance frequency in a wider frequency range with improving the detection sensitivity of the loop gap resonance used in an electron spin resonance(ESR) apparatus. SOLUTION: The control mechanism comprises at least dielectric layers on both side of a conductor plate grounded by itself and the conductor plate is inserted in the gap of a loop gap resonator and movable in the gap to adjust the resonance frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in 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.

[0003] The resonance frequency of this loop gap resonator is determined by the loop length (diameter of the loop) and the size of the gap, that is, the shape of the loop electrode 1. As a changing method, as shown in FIG. 1, a capacitance adjusting plate 3 made of a dielectric or the like is inserted into the gap 2. This is to change the resonance frequency by changing the capacitance C by inserting a dielectric into the gap, and to change the resonance frequency by moving the dielectric in the direction of the arrow to change the amount of the 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 the dielectric plate is inserted halfway into the gap 2 as shown in FIG. 1 for frequency adjustment, the electric field concentrates on the dielectric portion and the dielectric material in the gap 2 Since the electric field is weakened in the portion without the plate, the vertical symmetry of the electromagnetic field distribution in the resonator is broken, and the electromagnetic field distribution itself changes with the movement of the capacitance adjusting plate 3.

[0005] Such a phenomenon is extremely inconvenient in an apparatus such as an ESR imaging apparatus that performs measurement based on a spatial intensity distribution of a microwave magnetic field inside a loop gap resonator. Japanese Patent Application Laid-Open No. 9-18481 proposes a new method for solving such inconvenience.
No. 4 discloses a loop gap resonator and a resonance frequency adjusting mechanism thereof.

FIG. 3A shows a loop gap resonator in which the symmetry of the electromagnetic field distribution inside the resonator is improved, and FIG.
Indicates an equivalent circuit thereof. 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 also 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 a support 5 made of a conductor such as copper by a fixing member such as a screw (not shown), and the support plate 5 is moved forward or backward by a driving mechanism (not shown). By doing so, the amount of insertion of the capacitance adjusting plate 3 into the gap 2 is adjusted, and the capacitance C is controlled. With such a structure of the capacitance adjusting plate 3 and the gap portion 2, it is possible to greatly improve the distortion of the symmetry of the electromagnetic field distribution inside the loop gap resonator due to the adjustment of the resonance frequency. .

[0008]

However, in a loop gap resonator having such a structure, the loop electrode 1
And the capacitance adjustment plate 3 are both floating in the air, so that a stray capacitance is generated between the resonance circuit and the ground, and the capacitance adjustment plate 3 Since the capacitance C composed of the gap extension electrode 4 and the gap C wears clogs, the capacitance C cannot be adjusted to a small value. As a result, the resonance frequency f of the loop gap resonator can be varied over a wide range. There was a problem that it was not possible.

In order to avoid this problem and make the resonance frequency f of the loop gap resonator variable over a wide range, the absolute value of the capacitance C is increased and the effect of stray capacitance is sufficiently ignored. To be able to
In other words, it is necessary to widen the gap 2 so that a thicker capacitance adjusting plate 3 can be inserted into the gap 2. With such a configuration, the value of the inductance L of the loop electrode 1 is reduced. It will be smaller. The detection sensitivity of the loop gap resonator is proportional to the Q value of the loop gap resonator, and the Q value of the loop gap resonator is proportional to the value of the inductance L of the loop electrode 1 (Q∝ω
L, where ω = 2πf), a decrease in the value of the inductance L of the loop electrode 1 means that the detection sensitivity of the loop gap resonator decreases. A decrease in the detection sensitivity of the loop gap resonator leads to a problem that the image quality of the ESR imaging image is reduced.

The present invention has been made in view of the above points, and has as its object to control the resonance frequency f in a wider frequency range while improving the detection sensitivity of a loop gap resonator. It is an object of the present invention to provide a mechanism for adjusting the resonance frequency of a loop gap resonator.

[0011]

In order to achieve this object, a resonance frequency adjusting mechanism for a loop gap resonator according to the present invention comprises at least a dielectric layer on both sides in a gap of the loop gap resonator, and The antenna itself is characterized in that the resonance frequency is adjusted by inserting a grounded conductive plate and moving the conductive plate within the gap.

[0012] Further, a conductive material layer is provided on the surface of the dielectric layer.

Further, the conductive plate is characterized in that it is made to reciprocate in a direction in which the distance from the center axis of the loop gap resonator changes.

Further, a loop gap resonator having a structure in which a loop-shaped electrode is cut by a gap substantially parallel to the axis of the loop, and the loop-shaped electrode for extending the gap outside the loop gap resonator A pair of extension electrodes provided in the cut portion of the, and between the pair of extension electrodes, at least a dielectric layer is provided on both surfaces, and a conductor plate that is itself grounded is arranged. A moving mechanism that reciprocates in a direction in which the distance from the center axis of the loop gap resonator changes.

Further, a conductive material layer is provided on the surface of the dielectric layer.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4A is an embodiment of the resonance frequency adjusting mechanism of the loop gap resonator according to the present invention, FIG. 4B is an enlarged view of a main part thereof, and FIG.
The equivalent circuit is shown. 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 a loop gap resonator. 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 also 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.

In the gap 2 formed between the two opposed gap extension electrodes 4, there is provided a capacitance adjusting plate 6 made of a conductor such as copper and itself set to a ground potential. Inserted. Thereby, a resonance frequency adjusting mechanism of the loop gap resonator is formed. Dielectrics 7 made of ceramics such as alumina are attached in layers to both surfaces of the capacitance adjusting plate 6 for the purpose of increasing the capacitance between the capacitance adjusting plate 6 and the gap extension electrode 4. Then, by moving the capacitance adjusting plate 6 forward or backward by a driving mechanism (not shown), the insertion amount of the capacitance adjusting plate 6 into the gap 2 is adjusted, and the capacitance C is controlled.

In this embodiment, the capacitance adjusting plate 6 and the gap 2 are formed in a three-layer sandwich structure of such a dielectric and a conductor, thereby forming a divided capacitor and passing through a conductor path. To set the capacitance adjusting plate 6 to the ground potential. As a result, it is possible to eliminate the stray capacitance, which has clogged in the resonance frequency adjusting mechanism of the conventional loop gap resonator, to reduce the lower limit value of the capacitance C, and to reduce the resonance frequency f of the loop gap resonator. It has become possible to vary up to a frequency range higher than the value.

Also, since the value of the capacitance C can be reduced by the amount of the stray capacitance that has worn the clogs, the value of the inductance L of the loop electrode 1 can be increased, and when compared at the same resonance frequency f, the loop gap resonance The Q value of the vessel could be increased. As a result, it has become possible to provide a resonance frequency adjustment mechanism of the loop gap resonator that can control the resonance frequency f in a wider frequency range while improving the detection sensitivity of the loop gap resonator.

The present invention can have various modifications. For example, a conductive material layer 9 such as copper or gold is formed on the surface of a capacitance adjusting plate 6 made of copper or the like via a dielectric insulating film 8 instead of the dielectric layer 7 such as a ceramic. Alternatively, a capacitor having a multilayer structure including the conductive material layer 9, the insulating film 8, and the capacitance adjusting plate 6 may be formed. In this case, it is necessary to prevent a short circuit between the conductive material layer 9 and the gap extending electrode 4. Therefore, at least a surface of the conductive material layer 9 or a surface of the gap extending electrode 4 is coated with an insulating film, so that both of them can be prevented. Need to be kept in an insulated relationship.

[0022]

As described above, according to the resonance frequency adjusting mechanism of the loop gap resonator of the present invention, at least the dielectric layers are provided on both sides in the gap of the loop gap resonator, and the dielectric layer itself is grounded. By inserting the conductor plate and moving the conductor plate in the gap, the resonance frequency f is adjusted, so that the detection sensitivity of the loop gap resonator is improved, and the width is wider. It has become possible to provide a resonance frequency adjustment mechanism of a loop gap resonator capable of controlling the resonance frequency f in a frequency range.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of a resonance frequency adjusting mechanism of a 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 an embodiment of a resonance frequency adjusting mechanism of the loop gap resonator according to the present invention.

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

[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 ... dielectric layer, 8 ... insulating film, 9 ... conductive material layer.

Claims (5)

[Claims] In a gap of a loop gap resonator, at least a dielectric layer is provided on both sides, and a grounded conductive plate is inserted therein, and the conductive plate is moved in the gap. And a resonance frequency adjusting mechanism for adjusting a resonance frequency of the loop gap resonator. 2. The resonance frequency adjusting mechanism for a loop gap resonator according to claim 1, wherein a conductive material layer is provided on a surface of said dielectric layer. 3. The loop gap resonator according to claim 1, wherein the conductor plate is reciprocated in a direction in which a distance from a center axis of the loop gap resonator changes. Resonance frequency adjustment mechanism of the vessel. 4. A loop gap resonator having a structure in which a loop-shaped electrode is cut by a gap substantially parallel to the axis of the loop, and the loop-shaped electrode extends the gap out of the loop gap resonator. A pair of extension electrodes provided in the cut portion of the, and between the pair of extension electrodes, at least a dielectric layer is provided on both surfaces, and a conductor plate that is itself grounded is arranged. A moving mechanism for reciprocating in a direction in which the distance from the center axis of the loop gap resonator changes. 5. The resonance frequency adjusting mechanism for a loop gap resonator according to claim 4, wherein a conductive material layer is provided on a surface of said dielectric layer.