JP4027877B2 - Loop gap resonator - Google Patents

Description

  The present invention relates to a loop gap resonator used in an electron spin resonance method for imaging a sample structure such as a biological material.

  Recently, in order to know the structure of a material in a non-destructive manner, an electron spin resonance method has been used, and a loop gap resonator has been applied thereto. FIG. 1 shows a conventional loop gap resonator. In the figure, reference numeral 1 denotes a loop gap resonator, and reference numeral 2 denotes a low dielectric constant cylindrical support made of Teflon (registered trademark) having a cavity x. A gap portion 3 is formed on the outer peripheral surface of the cylindrical support 2 along the axial direction of the cylinder at a predetermined angle, for example, at an interval of 180 °, and a cylindrical arc resonator called a loop portion sandwiching the gap portion 3. The main bodies 4a and 4b are fixed.

  In the loop gap resonator, the loop portions 4a and 4b correspond to the coil (L) and the gap portion 3 corresponds to the capacitor (C), and the resonance frequency of the resonator is defined by these electrical parameters. If there is only one gap part that interrupts the loop part, it functions as a loop gap resonator. However, in the example of FIG. 1, microwaves are input by providing two gap parts symmetrically in front and back. In this case, the spatial uniformity of the magnetic flux density is improved (Patent Document 1).

  Inside the gap portion 3, cylindrical arc-shaped microwave electric field shields 5a and 5b called bridge portions are provided via a cylindrical support 2 (dielectric material), and the micro electric field generated in the gap portion 3 is hollow. The micro magnetic field generated in the cavity x is prevented from leaking out of the resonator from the gap 3 so as not to leak into x (Patent Documents 2 and 3). Thereby, the electric field component and the magnetic field component of the resonant microwave are separated, and only the magnetic field component is configured to act on the sample. The loop portions 4a and 4b and the bridge portions 5a and 5b are formed of a nonmagnetic conductor, for example, a copper plate.

  For example, in order to know the structure of a biological material in a non-destructive manner using such a loop gap resonator 1, after inserting a biological sample into the cavity x of the cylindrical support 2 of the loop gap resonator 1. The microwave of the constant frequency is irradiated to the loop gap resonator 1 from the outside to generate the resonance of the microwave in the resonator in which the biological sample is inserted, and the magnetic field (not shown) disposed in the vicinity of the resonator. A modulation coil and a DC magnetic field generator superimpose an AC magnetic field and a DC magnetic field, apply them to the sample in the resonator, and obtain an electron spin resonance signal from the spectrum obtained by sweeping the DC magnetic field. This is signal-processed, and the structure of the biological sample is imaged, that is, imaging measurement is performed.

  The modulation magnetic field applied to the sample increases the detection sensitivity of the electron spin resonance signal as the modulation frequency increases, and as the intensity distribution becomes more uniform, the distortion of the image contrast becomes more uniform. Therefore, it is required to design the apparatus so that a modulation magnetic field having a higher modulation frequency and a more uniform intensity distribution can be applied.

JP-A-58-127154.

Japanese Patent Laid-Open No. 62-123342.

Japanese Patent Laid-Open No. 62-123343.

JP-A-5-249215.

  By the way, in the loop gap resonator 1 as described above, as shown in FIG. 2, the modulation magnetic field generated by the magnetic field modulation coil (not shown) increases on the conductive walls of the loop portions 4a and 4b as the frequency increases. It becomes easy to generate the eddy current i. The generated eddy current i works so as to relax the magnetic flux B of the applied modulation magnetic field, so that the modulation magnetic field cannot pass through the conductive wall, and is generated by the magnetic flux entering from the upper and lower openings of the loop gap resonator 1. However, the modulation magnetic field acting on the biological sample is not formed, and as a result, the intensity of the modulation magnetic field becomes weaker toward the center of the resonator in the loop gap resonator 1 and the intensity of the modulation magnetic field becomes uniform. There was a problem that could not be made.

  Further, when the modulation frequency of the magnetic field is increased, a phenomenon called “skin effect” occurs in which the magnetic flux density that can be transmitted from the outer wall of the loop gap resonator 1 to the inside decreases, and the magnetic field with a high modulation frequency cannot reach the inside of the resonator. There was a problem.

  In view of the above points, an object of the present invention is to provide a loop gap resonator that can achieve a uniform modulation magnetic field inside the loop gap resonator with a simple configuration.

In order to achieve this object, the loop gap resonator of the present invention includes:
A low dielectric constant cylindrical support;
A gap formed along the axial direction of the cylinder on the outer peripheral surface of the cylindrical support;
A cylindrical arc-shaped loop portion formed of a conductor and fixed to the outer peripheral surface of the cylindrical support with the gap portion interposed therebetween;
In a loop gap resonator formed of a conductor and provided with a bridge portion for shielding a microwave electric field provided inside the gap portion via the cylindrical support,
Both the loop part and the bridge part are provided with slits in a direction intersecting with the axial direction of the cylinder , and the slits are planes where the positions carved in both the loop part and the bridge part are orthogonal to the cylindrical axis of the resonator. It is characterized by being arranged in line .

  Further, the direction intersecting the axial direction of the cylinder is characterized in that it is a direction that does not block the transmission path of the microwave current flowing through the loop portion.

  In addition, a plurality of the slits are provided.

A low dielectric constant cylindrical support, a gap formed on the outer peripheral surface of the cylindrical support along the axial direction of the cylinder, and a conductor, and on the outer peripheral surface of the cylindrical support sandwiching the gap In a loop gap resonator including a cylindrical arc-shaped loop portion to be fixed, and a bridge portion that is formed of a conductor and shields a microwave electric field provided inside the gap portion via the cylindrical support. Both the loop part and the bridge part are provided with slits in a direction intersecting with the axial direction of the cylinder , and the slits are engraved in both the loop part and the bridge part at right angles to the cylindrical axis of the resonator. Since they are arranged on a plane, the modulation magnetic field inside the loop gap resonator can be made uniform with a simple configuration.

  FIG. 3 shows an embodiment of a loop gap resonator according to the present invention. In the figure, reference numeral 1 denotes a loop gap resonator, and 2 denotes a low dielectric constant cylindrical support made of Teflon (registered trademark) having a cavity x. A gap portion 3 is formed on the outer peripheral surface of the cylindrical support 2 along the axial direction of the cylinder at a predetermined angle, for example, at an interval of 180 °, and a cylindrical arc resonator called a loop portion sandwiching the gap portion 3. The main bodies 4a and 4b are fixed. Note that the angle is not necessarily limited to 180 °.

  In the loop gap resonator, the loop portions 4a and 4b correspond to the coil (L) and the gap portion 3 corresponds to the capacitor (C), and the resonance frequency of the resonator is defined by these electrical parameters. If there is only one gap part that interrupts the loop part, it functions as a loop gap resonator. However, in the example of FIG. 3, microwaves are input by providing two gap parts symmetrically in front and back. In this case, the spatial uniformity of the magnetic flux density is improved. Note that the number of the gap portions is not necessarily limited to two.

  Inside the gap portion 3, cylindrical arc-shaped microwave electric field shields 5 a and 5 b called bridge portions are provided via the cylindrical support 2, and the microwave electric field generated in the gap portion 3 leaks into the cavity x. The micro magnetic field generated in the cavity x is prevented from leaking out of the resonator from the gap portion 3. Thereby, the electric field component and the magnetic field component of the resonance microwave are separated, and only the magnetic field component is configured to act on the sample. The loop portions 4a and 4b and the bridge portions 5a and 5b are formed of a nonmagnetic conductor, for example, a copper plate.

  In both of the loop portions 4a and 4b and the bridge portions 5a and 5b, a plurality of slits 6 (in the example of FIG. 3) in a direction intersecting with the axial direction of the cylinder, more preferably in a direction orthogonal to the axial direction of the cylinder. 4). These slits 6 are arranged so that the positions carved in the loop parts 4a and 4b and the positions carved in the bridge parts 5a and 5b are arranged on a plane perpendicular to the cylindrical axis of the resonator.

  When a modulation magnetic field (alternating magnetic field) is applied from outside the loop gap resonator, an eddy current is usually generated and acts in a direction to cancel the applied magnetic field, but a slit 6 is provided as shown in FIG. Thus, the eddy current transmission path is interrupted, the generation of eddy current is suppressed, and the loss of the modulation magnetic field (alternating magnetic field) does not occur.

  Also, thanks to the slit 6, the modulated magnetic field can pass through the open space of the slit 6 without being disturbed by the skin effect on the surface of the loop portions 4 a and 4 b constituting the outer wall of the loop gap resonator. The sample inside the loop gap resonator can be reached directly.

  On the other hand, of the microwave energy resonating by forming a standing wave inside the loop gap resonator, the electric field component is orthogonal to the cylindrical axis of the loop gap resonator in the loop portions 4a and 4b of the loop gap resonator. An annular alternating current is formed in the direction in which the slit 6 is formed. However, as shown in FIG. 3, if the slit is cut in the plane direction orthogonal to the axial direction of the cylinder, the slit 6 does not block the current path of the microwave current. An excellent effect of not causing loss of microwaves can be obtained.

  Therefore, if the slit 6 in the horizontal direction orthogonal to the cylindrical axis of the loop gap resonator is engraved in the loop portion and the bridge portion of the loop gap resonator, the resonance of the microwave energy stored in the resonator is not caused. It is possible to measure the electron spin resonance signal in a state where the instrument maintains a high Q value.

  In addition, since the modulated magnetic field is directly applied to the sample from the open space of the slit 6, a uniform modulated magnetic field enters the loop gap resonator, and measurement with high sensitivity becomes possible.

  In order to introduce a microwave into a new loop gap resonator constructed by the method as shown in FIG. 3, the coupling coil 7 is brought close to the loop gap resonator 1 as shown in FIG. A microwave magnetic field may be induced in the resonator 1 and the coupling coil 7 and the loop gap resonator 1 may be magnetically coupled.

  It can be used for a loop gap resonator for an electron spin resonance apparatus.

It is a figure which shows the conventional loop gap resonator. It is a figure which shows the problem 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 method of introduce | transducing a microwave into a loop gap resonator.

Explanation of symbols

1: loop gap resonator, 2: cylindrical support, 3: gap part, 4a: loop part, 4b: loop part, 5a: bridge part, 5b: bridge part, 6: slit, 7: coupling coil

Claims (3)

A low dielectric constant cylindrical support;
A gap formed along the axial direction of the cylinder on the outer peripheral surface of the cylindrical support;
A cylindrical arc-shaped loop portion formed of a conductor and fixed to the outer peripheral surface of the cylindrical support with the gap portion interposed therebetween;
In a loop gap resonator formed of a conductor and provided with a bridge portion for shielding a microwave electric field provided inside the gap portion via the cylindrical support,
Both the loop part and the bridge part are provided with slits in a direction intersecting with the axial direction of the cylinder , and the slits are planes where the positions carved in both the loop part and the bridge part are orthogonal to the cylindrical axis of the resonator. A loop gap resonator characterized by being arranged in a row . 2. The loop gap resonator according to claim 1, wherein the direction intersecting the axial direction of the cylinder is a direction that does not block a transmission path of a microwave current flowing through the loop portion. The loop gap resonator according to claim 1, wherein a plurality of the slits are provided.

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