JP2008002933A - Loop gap resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow continuous ESR measurement over a wide frequency band by one loop gap resonator. <P>SOLUTION: A plurality of loops are connected with a variable-length gap extension electrode. The length of the gap extension electrode is varied to vary a resonance frequency. The gap extension electrode is divided into two parts, which slide each other while maintaining electric contact to vary an inter-loop distance. A change in the length of the gap extension electrode of 5 mm gives a nearly double resonance frequency change. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  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) apparatus.

  The loop gap resonator is one of the most commonly used ESR detectors along with the cavity resonator. The loop gap resonator is most often used when measuring a sample having a large dielectric loss such as a low-frequency ESR or an aqueous solution that handles a living body. The feature of the loop gap resonator is that the density of the generated high-frequency magnetic field is very high compared to other ESR resonators (for example, cavity resonators). On the other hand, the Q value representing the characteristics of the resonator is also low.

The basic operation of the loop gap resonator is summarized in FIG. According to Non-Patent Documents 1 and 2, the resonance frequency of the loop gap resonator is determined by the configuration of the loop and the gap, and can be approximated by equations A and B shown in the figure. (A) is a model when there is one loop and two gaps, and (b) is a model when there are two loops and one gap. From the expression B in (b), it can be seen that in a loop gap resonator having a plurality of loops, the resonance frequency is proportional to W ^−0.5 and t ^0.5 .

  FIG. 2 shows a loop gap resonator and a resonance frequency adjusting mechanism described in Japanese Patent Publication No. 3-79670. As shown in FIG. 2, this loop gap resonator has a structure in which a loop-shaped electrode 1 is cut by a gap 2 substantially parallel to the axis of the loop, and is supplied through coupling with an external antenna circuit (not shown). Microwave current flows through the surface of the electrode 1. At this time, the LC electrode is configured with the loop electrode 1 as the inductance L and the gap 2 as the capacitance C.

  The resonance frequency of the loop gap resonator is determined by the loop length (loop diameter) and the size of the gap, that is, the shape of the loop electrode 1. As a method of changing the resonance frequency without changing the shape of the loop electrode 1, As shown in FIG. 3, 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. By changing the amount of dielectric insertion in the gap by moving the dielectric in the direction of the arrow, the resonance frequency is changed. It is possible to change continuously.

  In such a configuration, the electromagnetic field distribution of the loop gap resonator is as shown in FIG. Under this electromagnetic field distribution, when the dielectric plate is inserted partway through the gap 2 as shown in FIG. 3 for frequency adjustment, the electric field concentrates on the dielectric portion, and the dielectric of the gap 2 Since the electric field is weakened at the portion where there is no plate, 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.

  Such a phenomenon is a very inconvenient phenomenon in an apparatus such as an ESR imaging apparatus that performs measurement based on the spatial intensity distribution of the microwave magnetic field inside the loop gap resonator. In order to solve such inconveniences, a loop gap resonator and a resonance frequency adjusting mechanism disclosed in Japanese Patent Laid-Open No. 9-184814 have been newly proposed.

  FIG. 4A shows a loop gap resonator in which the symmetry of the electromagnetic field distribution inside the resonator is improved, and FIG. 4B shows an equivalent circuit thereof. The loop gap resonator is formed by bending a central portion of a thin plate electrode having a predetermined width and a predetermined length into a cylindrical shape to form a loop portion 1, and both ends of the thin plate electrode are formed as gap extension electrodes 4 opposed at a gap portion. It is 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 extension electrodes 4, the resonance frequency adjusting mechanism of the loop gap resonator can be realized. It is formed. The capacitance adjusting plate 3 is fixed to a tip 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 drive mechanism (not shown). By doing so, the insertion amount of the capacitance adjusting plate 3 into the gap 2 is adjusted, and the capacitance C is controlled. By making the capacitance adjusting plate 3 and the gap portion 2 in such a structure, it becomes possible to greatly improve the symmetry distortion of the electromagnetic field distribution generated inside the loop gap resonator accompanying the resonance frequency adjustment. It was.

Journal of Magnetic Resonance, vol. 47, 515 (1982) Journal of Magnetic Resonance, vol. 58, 243 (1984) Japanese Patent Publication No. 3-79670 Japanese Patent Laid-Open No. 9-184814 JP 2002-214315 A JP 2002-350525 A

  By the way, various loop gap resonators have been developed and used so far, and all are intended to be used at a single frequency. Usually, a certain amount of frequency fine adjustment mechanism is provided, but since it has only an adjustment range within a certain frequency band, an ESR spectrum cannot be acquired across different frequency bands with one resonator. . Specifically, for example, the ESR spectrum for each frequency band such as 5 GHz, 10 GHz, and 20 GHz cannot be acquired without exchanging the detector.

  For example, frequency bands used for typical ESR devices include L band (~ 1 GHz), S band (~ 2 GHz), X band (~ 9 GHz), K band (~ 17 GHz), Q band (~ 34 GHz), etc. There is a frequency band. When conducting research related to the motility of materials, the appearance of the spectrum differs depending on the frequency band, so measurements are usually made by exchanging the detector for a dedicated frequency band.

  Even if it is desired to continuously change the measurement frequency, a normal detector can resonate only in a certain frequency band, so that there is a problem that only a spectrum in a discrete frequency band can be obtained.

  An object of the present invention is to provide a technique that enables continuous ESR measurement in a very wide frequency band with one loop gap resonator in view of the above points.

In order to achieve this object, a loop gap resonator according to the present invention includes:
A feature is that a plurality of loops are connected by a gap extending electrode whose length can be varied, and the resonance frequency is varied by varying the length of the gap extending electrode.

  In addition, the gap extension electrode is divided into two parts, and is configured to be able to change the distance between the loops by sliding while maintaining electrical contact with each other.

  Further, the plurality of loops are characterized in that resonance axes are parallel to each other.

According to the loop gap resonator of the present invention,
Since the gap extension electrode that can change the length between multiple loops is connected, and the length of the gap extension electrode is changed, the resonance frequency is changed.
A single loop gap resonator can enable continuous ESR measurement in a very wide frequency band.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 5 shows an embodiment of a loop gap resonator according to the present invention. In the present invention, as shown in the figure, a cylindrical large loop 6 having a radius r _{0 and} a cylindrical small loop 7 having a radius r ₁ are formed by a gap extension electrode 8 having a width t and a length W, and the resonance axes of the two loops. Are connected in parallel, and the length W of the gap extension electrode 8 can be varied. As an actual structure, the gap extension electrode 8 is divided into two parts, and is configured to be able to change the distance between the loops by sliding while maintaining electrical contact with each other. To work. First, in a state where the sample 9 is set in either the large loop 6 or the small loop 7, a microwave having a predetermined frequency is introduced through the coupling loop 10 or the like, and an electromagnetic field is introduced into the loop gap resonator. Cause resonance. Next, the length W of the gap extension electrode 8 is adjusted so that resonance occurs at a target frequency. When resonance occurs, a static magnetic field (not shown) applied to the sample 9 is swept and the ESR spectrum is measured.

  FIG. 7 shows the relationship between W and resonance frequency obtained by numerical calculation. From this, it can be seen that the resonance frequency changes approximately twice from 21 GHz to 11 GHz with a change of ΔW = 5 mm. As a result, it is possible to observe ESR across a plurality of frequency bands with only one loop gap resonator without replacing the resonator.

  The present invention can be modified. That is, the number of gaps provided in the loop gap resonator is not always one. In the case of a loop gap resonator having a plurality of gaps, a small loop with a mechanism capable of changing the length of the gap extension electrode is provided for some of them, and the entire loop gap resonator has three or more large and small sizes. The resonance frequency may be varied by configuring the loops and varying the lengths of the gap extension electrodes. In that case, the resonance axis of the small loop is set to be parallel to the resonance axis of the central large loop. By doing so, it is possible to realize a greater change in the resonance frequency of the loop gap resonator.

  Widely applicable to ESR devices.

It is a figure which shows an example of the conventional loop gap resonator. It is a figure which shows an example of the conventional loop gap resonator. It is a figure which shows an example of the conventional loop gap resonator. It is a figure which shows an example of the conventional loop gap resonator. It is a figure which shows one Example of the loop gap resonator concerning this invention. It is a figure which shows the operation example of the loop gap resonator concerning this invention. It is a figure which shows the numerical calculation example of the loop gap resonator concerning this invention.

Explanation of symbols

1: loop part, 2: gap part, 3: capacitance adjusting plate, 4: gap extension electrode, 5: indicator, 6: large loop, 7: small loop, 8: gap extension electrode, 9: sample, 10 : Coupling loop

Claims (3)

A loop gap resonator characterized in that a plurality of loops are connected by a gap extension electrode whose length can be changed, and the length of the gap extension electrode is changed to change the resonance frequency. The loop gap resonator according to claim 1, wherein the gap extension electrode is divided into two parts, and is configured to be able to change a distance between the loops while maintaining electrical contact with each other. The loop gap resonator according to claim 1, wherein resonance axes of the plurality of loops are parallel to each other.

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