Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Magnet structure or material
Patent
1987-01-22
1988-09-27
Harris, George
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Magnet structure or material
324318, H01F 500
Patent
active
047744863
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a coil used for a nuclear magnetic resonance (NMR) imaging diagnostic apparatus, and more particularly to inclined magnetic field coils used for obtaining position information in an NMR imaging diagnostic apparatus.
BACKGROUND ART
FIG. 1 shows a magnetic portion of a conventional superconductive NMR imaging diagnostic apparatus, comprising a superconductive main coil 2 contained in a cryostat 1, inclined magnetic field coils 3, 4 and 5 disposed inside the main coil 2, a bobbin 6, and a bed unit 7, so that an examinee is positioned within the bobbin 6. The inclined magnetic field coils comprising two pairs of X-direction coils 3, 3 . . . , each having a saddle-like shape and disposed transversely, two pairs of Y-direction coils 4, 4 . . . , each having a saddle-like shape and disposed vertically, and a pair of Z-direction solenoid-type coils 5, 5 disposed longitudinally, are mounted on the bobbin 6 formed of a non-conductive material.
The coils 3, 4, 5 are mounted on the bobbin 6 in such a manner that the windings 9, 9 . . . of each coil, as shown in FIG. 2, are secured to the bobbin 6 by a band 10, such as a glass fiber tape, or the windings 9, 9 . . . , as shown in FIG. 3, are press-contacted by bolts 12, 12 . . . through a pressure plate 11.
In such an apparatus, the inclined magnetic coils 3, 4 and 5 are excited by the intense DC magnetic field generated by the main coil 2, at which time a current flowing in the coils, as shown in FIG. 4(a), is of pulse-like wave form, so that the coils 3, 4 and 5 each generates an electromagnetic mechanical force, thereby vibrating as the current varies as shown in FIG. 4(b).
The electromagnetic mechanical force generated in the coils 3, 4 and 5 is similar in wave form to the current shown in FIG. 4(a). Hence, the frequency component of the mechanical force is distributed over a wide frequency domain of DC to kHz, vibrations and noises caused thereby having the similar frequency component.
The conventional inclined magnetic field coil, whose windings are fixed directly to the bobbin, transmits its vibrations to the bobbin directly. As a result, a problem has occurred in that noises emitted together with the vibrations of the bobbin cause pain to the examinee positioned inside the bobbin.
SUMMARY OF THE INVENTION
In order to solve the above problem, the present invention has been designed to provide a coil used for a nuclear magnetic resonance imaging diagnostic apparatus which reduces vibrations and noises. Such a coil, according to a first embodiment of the invention, comprises inclined magnetic field coils fixed to a bobbin with a vibrationproofing material interposed therebetween.
In this embodiment, the audible high frequency components in the wide frequency component range of the generated noises is attenuated from the vibrations transmitted from the coil to the bobbin through the vibrationproofing material, such as rubber. In this case, when the characteristic frequency depending on the mass of coil and on the spring constant of the vibrationproofing material is represented by f.sub.n, the attenuated frequency component is .sqroot.2.times.f.sub.n or more.
In the first embodiment, by adding a mass body of non-magnetic material, such as stainless steel to the inclined magnetic field coils, the coil mass increases and the characteristic frequency of the coil lowers to expand the frequency domain having the damping effect.
A coil according to a second embodiment of the invention comprises inclined magnetic field coils and a bobbin which are integrally molded by a damping material.
In the second embodiment, since the coils and bobbin are integrally molded by damping material, such as epoxy derivative binary reaction type resin, the damping effect is extremely high, thereby remarkably reducing an abrupt damped vibration generated during the rising and the falling of the current.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partially cutaway perspective view of the principal portion of a conventional nuclear ma
REFERENCES:
patent: 4636729 (1987-01-01), Maurer et al.
patent: 4639672 (1987-01-01), Beaumont
Patent Abstracts of Japan, vol. 9, No. 86, Apr. 16, 1985 59-216045, Hitachi Seisakusho.
Harris George
Mitsubishi Denki & Kabushiki Kaisha
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