BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
FIGS. 1A and 1B are schematic views of an outline structure of a probe for an NMR signal provided with a solenoid coil;
FIG. 2 is a view showing an example of a positional relation between a sample tube and the solenoid coil;
FIG. 3 is a view showing a static magnetic field intensity distribution in the case that a static magnetic field compensating member is not provided;
FIG. 4 is a view showing the static field magnetic intensity distribution in the case of applying the present invention;
FIGS. 5A and 5B are brief views and three-dimensional views of a solenoid coil in accordance with an embodiment 1;
FIGS. 6A and 6B are brief views and three-dimensional views of a solenoid coil in accordance with an embodiment 2;
FIG. 7 is a brief view of a solenoid coil in accordance with an embodiment 3; and
FIG. 8 is a view showing an effect of the present invention determined by a calculation.
DETAILED DESCRIPTION OF THE INVENTION
A description will be given below of embodiments, however, the present invention is not limited to the following embodiments.
Embodiment 1
FIGS. 1A and 1B are explanatory views showing an example of a positional relation between a probe and a solenoid coil in an NMR signal acquiring apparatus. A direction of a static magnetic field is different between FIGS. 1A and 1B. A static magnetic field in a static magnetic field direction 3 is formed by a static magnetic field generating apparatus such as a superconducting magnet or the like. A solenoid coil 100 aimed by the present invention is constituted by a main solenoid coil and a static magnetic field compensating member which are not illustrated in this case, is mounted to a probe 11, and is arranged near a center of a static magnetic field in such a manner that a coil axis orthogonal to the static magnetic field direction 3. The main solenoid coil is compensated so as to resonate at a predetermined frequency, by a resonance circuit 12 arranged within the probe. The solenoid coil and the apparatus in an outer side of the probe exchange a high-frequency signal via a coaxial cable or the like through the resonance circuit. As shown in FIG. 1, a probe longer direction may come to a horizontal direction or a vertical direction in accordance with the direction of the static magnetic field direction 3.
FIG. 2 is an explanatory view showing an example of a positional relation between a sample tube 4 and the solenoid coil in the NMR signal acquiring apparatus. In this case, only a main solenoid coil 1 is shown, and a static magnetic field compensating member is omitted. Since a direction of the static magnetic field is frequently expressed by z, an axial direction of the sample tube is frequently expressed by y, in an NMR system, a coordinate axis in FIG. 2 is based on this. A sensitive area of the main solenoid coil 1 protrudes and expands in a coil axial direction than both ends of the main solenoid coil as shown in FIG. 2.
FIGS. 3 and 4 are views comparing effects of the present invention. FIG. 3 shows a case that the static magnetic field compensating member is not arranged. In the case of being constituted only by the main solenoid coil without arranging the static magnetic field compensating member, a static magnetic field intensity is a fixed value near a center of the main solenoid coil 1 as shown in FIG. 3, however, is not fixed as being closer to both ends. This is based on a knowledge of an electromagnetism that a magnetic field intensity within an infinite cylinder placed in the static magnetic field is constant, but the magnetic field intensity is not constant as being closer to an end portion within a cylinder having a finite length.
FIG. 4 shows a case that a static magnetic field compensating ring 21 is provided in an outer side in an axial direction of the main solenoid coil 1. A solenoid coil 100 is constructed by combining the main solenoid coil and the static magnetic field compensating member. Since to arrange the static magnetic field compensating ring 21 in the outer side in the axial direction of the main solenoid coil 1 deserves to elongate the length of the cylinder having the finite length in the coil axial direction, a point at which the magnetic field intensity starts changing moves to an outer side in the coil axial direction. As a result, a homogeneity of the static magnetic field is improved in the sensitive area of the main solenoid coil 1. A magnetic field distribution generated by the static magnetic field compensating ring 21 being magnetized is in proportion to a product of a susceptibility per volume of a material constituting the static magnetic field compensating ring 21 and a volume. Accordingly, it is not necessary that the susceptibility per volume of the material constituting the static magnetic field compensating ring 21 is necessarily identical to the susceptibility per volume of the solenoid coil, and it is sufficient that they have the same sign.
FIG. 5A is a brief view and FIG. 5B is a three-dimensional view showing one example of a first means, in the case that the static magnetic field compensating ring 21 is placed one turn by one turn in both ends of the main solenoid coil 1 which is wound at two turns step by step. In the three-dimensional view of FIG. 5B, a hatched part corresponds to the static magnetic field compensating ring 21. A manufacturing example will be shown below. At a time of manufacturing the main solenoid coil 1 by using the copper and aluminum composite material mentioned above, in the case that the material has a negative magnetic susceptibility although being small, it is preferable to manufacture the static magnetic field compensating ring 21 by applying a material having the same negative magnetic susceptibility, for example, a polyimide varnish or the like to a bobbin 31. On the contrary, in the case that the material constructing the main solenoid coil has a positive magnetic susceptibility per volume, the static magnetic field compensating ring 21 can be manufactured by mixing a material having a positive susceptibility, for example, an aluminum nitride or the like to the polyimide varnish so as to apply. An applying amount can be calculated by the susceptibility per volume of the material constructing the main solenoid coil 1 and the susceptibility per volume of the applied material. In the case that it is unknown, the applying amount may be compensated by applying little by little and observing an effect of the static magnetic field compensation obtained by actually acquiring the NMR signal.
Embodiment 2
FIG. 6A is a brief view and FIG. 6B is a three-dimensional view showing one example of a second means, in the case that the static magnetic field compensating ring 21 is placed one turn by one turn in both ends of the main solenoid coil 1 which is wound at two turns spirally, by the same material on an extension of both ends. In the three-dimensional view of FIG. 6B, a hatched part corresponds to the static magnetic field compensating ring 21. In the case of the second means, the static magnetic field compensating ring 21 can be formed by the conductive material or the insulant, however, if it is made of the same material as the main solenoid coil, it is unnecessary to compensate the magnetic susceptibility. Accordingly, there is obtained an advantage that it is easy to manufacture.
Embodiment 3
FIG. 7 is a brief view showing one example of a third means, in the case that the static magnetic field compensating rings 21 made of the same material but divided in a circumferential direction are placed one turn by one turn in both ends of the main solenoid coil 1 which is wound at two turns step by step, so as to be spaced at the same distance as the winding interval of the main solenoid coil 1 from the end portion of the main solenoid coil.
Embodiment 4
FIG. 8 is one example of a result of calculation expressing an effect of the present invention. A horizontal axis indicates a length in a coil axial direction, and a vertical axis indicates a displacement from the static magnetic field intensity of a coil center. A left half corresponds to a case that the static magnetic field compensating member is not provided, and indicates the static field magnetic field distribution on φ4.2 mm in the solenoid coil in which a tape-like wire rod having a line width 1.4 mm is wound at five turns in a spiral shape having φ6.4 mm and a pitch 1.4 mm. A right half indicates the static magnetic field distribution in a case of adding one turn of static magnetic field compensating ring by the same material in both ends of the same solenoid coil. Positions at ±4 mm in the y axis correspond to both ends of the main solenoid coil, however, it is known that the static magnetic field intensity distribution near both ends of the main solenoid coil is suppressed to about one half by the static magnetic field compensating ring.
It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.
Patent Application
20080074221
