Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
2001-06-26
2003-04-08
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S315000, C324S307000
Reexamination Certificate
active
06545474
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to apparatuses in which a superconductor is allowed to capture a magnetic field and used as a magnetic field generation source, such as a nuclear magnetic resonance apparatus, permanent magnet magnetization apparatus, magnetic field floating apparatus, electric motor, power generator, magnetic field separation apparatus, magnetic field press apparatus, ferromagnetic field generation apparatus, and flywheel power storage apparatus. The present invention particularly relates to a technology for controlling and stabilizing a generated magnetic field and a distribution of the field in desired sizes.
2. Description of Related Art
A nuclear magnetic resonance is a phenomenon seen in a magnetic system including a magnetic moment and angular momentum, and is a resonance phenomenon in a frequency (Larmor frequency) inherent in the magnetic system. For example, as shown in
FIG. 1
, a static magnetic field H
o
made by a magnet is applied to a sample, and a vibration magnetic field H
i
is further applied to the sample from a direction vertical to the static magnetic field via a transmission coil. At present, a pulse nuclear magnetic resonance (NMR) apparatus is a mainstream, in which a very short (3 to 6 &mgr;s) and strong high-frequency pulse is applied to the sample, and all signals spreading in a chemical shift are simultaneously resonated and simultaneously observed.
Moreover, in order to obtain a sectional image, magnetic fields whose strength differs with a position called a gradient magnetic field is superimposed onto the static magnetic field, and a position is identified by shifting a resonance frequency for each position. An image method of exciting (selectively exciting) a predetermined section only by a necessary thickness with a high frequency, subsequently applying the gradient magnetic field in two directions in the section, and obtaining the sectional image by a two-dimensional Fourier method is generally used.
The aforementioned nuclear magnetic resonance apparatus (hereinafter referred to as an NMR apparatus) utilizing the aforementioned nuclear magnetic resonance phenomenon is basically constituted of a magnet for forming the static magnetic field, a coil for generating another high-frequency pulse and detecting an NMR signal, a receiver for receiving the NMR signal, and the like. Data useful in analyzing a structure of an organic compound, such as a chemical shift amount of each atom and spin-spin coupling constant can be obtained by the NMR apparatus.
Moreover, a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus) utilizing the nuclear magnetic resonance phenomenon is constituted of: at least a magnet as static magnetic field generation means; gradient magnetic fields for applying space information to the signal; a high-frequency irradiation system; an NMR signal detection system; probe coils which surrounds a test object such as a human body and actually performs high-frequency irradiation and signal detection; and controllers for controlling these components and processing the obtained signal. A space distribution of a nuclide which generates the signal is visualized by the nuclear magnetic resonance (NMR) signal obtained by irradiating the test object disposed in the presence of the static magnetic field with the high frequency. Since the MRI apparatus does not use a ray, the apparatus is safe, a sufficient resolution is obtained, and a practical value is remarkably high.
On the other hand, as a method for magnetizing a bulk superconductor, a field cooling method and a pulse magnetizing method have heretofore been known.
The field cooling method (FC method) is general, and comprises applying a uniform external magnetic field to the superconductor to be magnetized by a superconducting magnet or the like using a superconducting coil at a temperature not less than a superconducting transition temperature. While the magnetic field is kept as it is, and the magnetic field exists inside the superconductor, the superconductor is cooled at a temperature lower than the superconducting transition temperature. When the external magnetic field is reduced at the kept temperature, the magnetic field tends to go out of the superconductor by a repulsive force of magnetic flux lines. However, when there is a portion for restraining the magnetic flux line in the superconductor, the magnetic flux line is pinned. Therefore, even when the external magnetic field turns to zero, and the magnetic field in a sample outer edge decreases to zero, the magnetic field remains in the superconductor. In this case, a superconducting current flows in a portion having a magnetic field gradient inside the superconductor, and a size of the current becomes equal to that of a critical current density Jc. According to the principle, when a sufficiently large external magnetic field is formed and the superconductor is magnetized, the magnetic field gradient is formed to a sample center. The superconductor is magnetized until a material property is obtained. Moreover, when the applied magnetic field is lower than the material property, the superconductor is magnetized to achieve the size of the applied magnetic field at maximum.
For the pulse magnetization, an apparatus therefor is simple. In the apparatus the superconductor to be magnetized is cooled at a temperature lower than the superconducting transition temperature. While the temperature is controlled and kept to be constant, the pulse magnetic field is applied. The magnetic flux line having penetrated the superconductor in a pulse magnetic field increase process is captured inside the superconductor by a pinning force in a magnetic field decrease process.
As the static magnetic field generating magnet constituting the nuclear magnetic resonance apparatus, a resistive magnet of 0.5 to 2.2 T, and a superconducting magnet of 0.5 to 18.8 T have heretofore been used, and a permanent magnet is also used in some case. The static magnetic field generating magnet of the nuclear magnetic resonance apparatus has an enhanced sensitivity for a ferromagnetic field, and enables analysis of a large amount of detailed information. Therefore, the superconducting magnet using a superconducting material is superior in the strength, stability and uniformity of the magnetic field.
Therefore, in the recent nuclear magnetic resonance apparatus, the superconducting magnet using a superconducting coil formed of a metal-based superconducting wire material such as niobium and titanium is used to form a main magnetic field (static magnetic field). However, when the superconducting coil is utilized, liquid helium is used to cool the coil at an extremely low temperature. This raises a problem that a large amount of expensive liquid helium is required and running cost is high.
Moreover, the metal-based superconducting wire material such as niobium and titanium is produced by a complicated manufacturing process and thermal treatment. Therefore, the superconducting coil is much more expensive than a usual electromagnet coil formed of a copper wire, and the apparatus main body becomes extremely expensive. Additionally, utilization of a refrigerant (liquid helium and liquid nitrogen) essential for operating the superconducting magnet requires a special technique, and is technically complicated and intricate. Therefore, it is difficult to handle that the utility is a simple technique. These big problems hinder a high-performance nuclear magnetic resonance apparatus from spreading.
Furthermore, since the superconducting magnet requires a large cooling structure, and a leak magnetic field is also huge, an exclusive room for installing the magnet is necessary. This remarkably limits an apparatus installation condition, and also limits an apparatus utilization field.
On the other hand, an example of a small and simple nuclear magnetic resonance apparatus is proposed in Japanese Patent Application Laid-Open No. 135823/1997, in which a direct cooling type superconducting mag
Ito Yoshitaka
Nakamura Takashi
Oka Tetsuo
Uzawa Jun
Yabuno Ryohei
Griffin & Szipl, P.C.
Lefkowitz Edward
Riken
Shrivastav Brij B.
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