JP2006258779A - Rectangular type resonator for electron spin resonance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a rectangular type resonator which enables high-sensitivity measurement of electron spin resonance, has a high Q-value, and introduces an external modulated magnetic field. <P>SOLUTION: This resonator is a TE<SB>102</SB>rectangular type resonator, has at least one cut line in the direction parallel to the flow of current formed in the direction of energy propagation of a microwave, and has neither a cut line nor a connecting part in the direction perpendicular to this, in a wall surface made up of an electric conductor. The resonator is composed of its lower part 31 and its upper part 32 which separate in the direction of the cut line. At the wall surface through which an AC magnetic field is intended to be guided into the resonator from outside, a conductor thickness is not larger than 0.3 mm, and a cut line whose width is between 1 mm and 5 mm is formed. Moreover, the quantity of reflection of an electromagnetic wave from the resonator can be adjusted in this resonator, by inserting two conductors or more at fixed intervals in a direction of vertically piercing the wall of the longitudinal diameter part of a waveguide being connected to the resonator, and adjusting the insertion length of these conductors. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a measurement technique using a microwave, and particularly to provide a resonator that realizes a small and highly sensitive measurement in an electron spin resonance apparatus.

  In the observation of the electron spin resonance signal, a sample placed in a magnetic field is irradiated with microwaves to detect absorption of the microwaves caused by the electron spin resonance phenomenon. At this time, a resonator is used to efficiently detect slight microwave absorption. Generally, a method is adopted in which the resonator is adjusted so that the reflection of the microwave irradiated to the sample placed in the resonator is minimized, and the increase in reflection due to the absorption of the microwave caused by the magnetic field sweep is detected. It has been. At this time, in order to reduce electrical noise, a modulation magnetic field having a frequency of about 100 kHz is applied in addition to the main magnetic field, and the sensitivity is improved by detecting only the signal modulated at 100 kHz.

There are a plurality of types of resonators used for electron spin symbiosis. Generally, a TE ₀₁₁ cylindrical resonator and a TE ₁₀₂ rectangular resonator are used. Although the cylindrical resonator has good resonance characteristics (Q value = 100,000 or more), the width in the magnetic field direction is relatively large and the Q value is greatly reduced when measuring an aqueous solution sample. On the other hand, the rectangular resonator can narrow the width of the resonator sandwiched between the magnets that provide a magnetic field necessary for measurement, and therefore it is relatively easy to manufacture a magnetic field supply magnet. However, the Q value is low and it is not suitable for high sensitivity measurement.

As a prior art related to a rectangular resonator, Japanese Patent Application Laid-Open No. 2004-286757 proposes a shape in which an external modulation magnetic field for electron spin resonance measurement is easily introduced into the resonator, but is formed in the direction of microwave energy propagation. A high Q value cannot be obtained because it has a connection portion in a direction orthogonal to the current flow.
JP 2004-286757 A

  The cylindrical resonator has a high Q value and enables highly sensitive electron spin resonance measurement. However, measurement using a microwave in the most common X band frequency band requires a resonance space of at least 50 × 50 mm or more. The electromagnet needs to be capable of supplying a magnetic field of about 330 mT with a pole piece interval of about 60 mm or more. For this reason, an electromagnet part becomes large and the apparatus currently marketed is size 400 (w) X500 (D) X500 (H) mm or more and the weight of 100 kg or more. If the gap between the pole pieces can be reduced without reducing the measurement sensitivity, the apparatus can be reduced in size and cost. In order to solve this problem, the present invention proposes a structure having a high Q value and enabling practical high-sensitivity electron spin resonance measurement in a rectangular resonator suitable for miniaturization.

The resonator proposed by the present invention is a TE ₁₀₂ rectangular resonator, and has at least one cut line in a direction parallel to a current flow formed in a direction of microwave energy propagation on a wall surface made of an electric conductor. In addition, there is no cut and no connection portion in a direction orthogonal to this.

  Furthermore, in the resonator according to the present invention, the conductor thickness of at least the wall surface of the AC magnetic field to be introduced into the resonator from the outside is 0.3 mm or less.

  In addition, the resonator according to the present invention is characterized in that the width of the cut is between 1 mm and 5 mm at least in the cut of the conductor on the wall surface to introduce an AC magnetic field into the resonator from the outside.

  In addition, in the above resonator, two or more conductors are inserted at a predetermined interval in a direction perpendicularly penetrating the wall of the long diameter portion of the waveguide connected to the resonator, and the insertion length of the conductors The amount of reflection of the electromagnetic wave from the resonator can be adjusted by adjusting.

  Good resonance characteristics (high Q value) can be obtained by comprising an integral conductor in the electric field direction. This structure is easy to manufacture and contributes to cost reduction. Furthermore, an external modulation magnetic field is introduced inside by providing a slit on the side surface. At this time, since the slit is provided in a direction not cutting the electric field, a decrease in the Q value is suppressed. The coupling adjustment of the microwave of the resonator is relatively easily performed by a stub provided in the H corner waveguide to be connected.

  By using the present invention as described above, a rectangular resonator having good resonance characteristics is realized. As a result, the entire apparatus can be reduced in size and cost without reducing the current measurement sensitivity.

  Examples of the present invention will be described below.

  FIG. 1 shows a general rectangular resonator 11. The microwave is introduced into the resonator from the microwave inlet 12 through the waveguide, and forms a microwave magnetic field 14 in the resonator 11 in the resonance state. At this time, the microwave electric field is formed in a direction perpendicular to the magnetic field. When performing electron spin resonance measurement, the sample is inserted in the vertical direction from the sample insertion port, so that an electric field that affects the resonance characteristics (Q value) at the time of measurement is formed on the wall surface in the direction along the energy propagation direction 15. Electric field. By providing a connection surface or a cut (slit) along the cut surface 21 shown in FIG. 2, a resonator having a high Q value can be obtained without blocking the microwave electric field. In FIG. 2, a cut surface is drawn between the upper and lower surfaces. The position of the cut surface is preferably in the middle of the upper and lower walls in the resonator, and the Q value is lowered as the distance is shifted. However, if the sensitivity is within the allowable range required for the measurement using the resonator, it is not necessary to be strictly at the intermediate position.

  FIG. 3 shows a resonator lower portion 31 and a resonator upper portion 32 having a connection surface 33 at a position corresponding to the cut surface 21 shown in FIG. The connection surface 33 may be fixed mechanically. Screw holes may be made on the side or front and back surfaces and fixed to the metal plate, or may be sandwiched from above and below.

  FIG. 4 shows a slit 41 provided on the side surface for introducing an external modulation magnetic field. In order to positively introduce a modulation magnetic field applied from the outside into the resonator 11, a plurality of the aforementioned cuts are provided as the slits 41. The slits 41 are required to be parallel to the cut surface 21 shown in FIG. 2 and have a width between 1 mm and 5 mm, but the number of slits 41 is arbitrary. When the number of slits 41 increases and the opening width increases, the external modulation magnetic field is easily introduced inside, but the Q value of the resonator decreases. In designing, the magnitude of the modulation magnetic field and the trade-off of the Q value must be considered.

  FIG. 5 shows a state in which the H corner waveguide 52 is connected to the resonator. Here, the resonator lower portion 31 and the resonator upper portion 32 are fixed by a fixing plate 51 and a flange provided at the waveguide end. The microwave coupling of the resonator is adjusted by inserting and removing the stub 53 installed at the center of the corner portion of the H corner waveguide 52.

  FIG. 6 shows the resonance characteristics of the manufactured resonator as an absorptance with respect to the microwave frequency. A quartz cell for measuring electron spin resonance of an aqueous solution was filled with distilled water, and this was set in a resonator and measured. A high Q value of 4000 or more was obtained, and it was confirmed that highly sensitive electron spin resonance measurement using a compact rectangular resonator was made possible by the present invention.

It is a figure which shows a general rectangular resonator and the microwave magnetic field formed inside. It is a figure which shows the Example which makes the cut of this invention. It is a figure which shows the structure of the resonator which consists of two upper and lower parts. It is a figure which shows the Example which puts a slit in a resonator. It is a figure which shows the Example which connected the H corner waveguide to the resonator. It is the figure which showed the resonance characteristic of the resonator by the absorption factor with respect to a microwave frequency.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Rectangular type resonator 12 Microwave introduction port 13 Sample insertion port 14 Microwave magnetic field 15 Energy propagation direction 21 Cut surface 31 Resonator lower part 32 Resonator upper part 33 Connection surface 41 Slit 51 Fixing plate 52 H corner waveguide

Claims (4)

On the wall surface made of an electrical conductor, there should be at least one cut in the direction parallel to the current flow formed in the microwave energy propagation direction, and there should be no cut and no connection in the direction perpendicular to this. A TE ₁₀₂ rectangular microwave resonator characterized. The resonator according to claim 1, wherein a conductor thickness of at least a wall surface of the AC magnetic field to be introduced into the resonator from the outside is 0.3 mm or less. 3. The resonator according to claim 2, wherein the width of the cut is between 1 mm and 5 mm at least in the cut of the conductor on the wall surface to introduce an AC magnetic field into the resonator from the outside. By inserting two or more conductors at regular intervals in a direction that penetrates the wall of the long-diameter portion of the waveguide connected to the resonator vertically, and adjusting the insertion length of the conductor, 4. The resonator according to claim 1, wherein the amount of reflection of electromagnetic waves can be adjusted.

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