US3611223A

US3611223A - Magnetic apparatus for producing homogeneous field

Info

Publication number: US3611223A
Application number: US856939A
Authority: US
Inventors: Yoshiharu Utsumi; Goh Miyajima
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1968-09-11
Filing date: 1969-09-11
Publication date: 1971-10-05
Anticipated expiration: 1988-10-05

Abstract

A magnetic apparatus comprising a rectangularly shaped yoke through which flux passes; a pair of magnetic poles for producing a strong unidirectional field therebetween; and a pole piece assembly comprising a pair of pole pieces and a supporting member provided with a pair of holes; the pole pieces being inserted into respective holes and fixed to the supporting member.

Description

United States Patent 1 3,61 1,223

[72] Inventors Yoshiharu Utsumi; [56] References Cited Goh Miyajima, both of Katsuta-shi, Japan UNITED STATES PATENTS [211 856,939 2,962,636 11/1960 Purcell 335/296 1221 Filed Sew-1111969 3,182,23l 4/1965 Gang 61:11 335/281 1451 Patented 3,188,531 6/1965 Boswell 335/281 [731 Assign 3,211,965 10/1965 Williamsetal. 335/296 3,437,963 4/1969 Gang 6161.... 335/298 Pmmy 3,253,194 5/1966 Parker 335/298 ux [33] Japan l3l l 43/64954 Primary ExaminerG. Harris Armrney-Craig, Antonelli, Stewart & Hill [54] MAGNETIC APPARATUS FOR PRODUCING f ABSTRACT: A magnetic apparatus comprising a rectangug g larly shaped yoke through which flux passes; a pair of mag- (521 US. Cl 335/298, netic poles for producing a strong unidirectional field 335/296 therebetweenyand a pole piece assembly comprising a pair of [51] Int. Cl H011 3/00 pole pieces and a supporting member provided with a pair of [50] Field of Search 335/296, holes; the pole pieces being inserted into respective holes and 297, 298, 301, 281 fixed to the supporting member.

PATENTEUHBI 5|9n 3.611.223

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ATTORNEY 5 MAGNETIC APPARATUS FOR PRODUCING HOMOGENEOUS FIELD BACKGROUND OF THE INVENTION This invention relates to improvements in a magnetic apparatus, and more particularly, to a magnetic apparatus able to produce a strong unidirectional magnetic field. A homogenous or uniform field is extremely useful, for example, in attaining high resolution in gyromagnetic systems.

Gyromagnetic resonance is explained in many publications and patents, for example, US. Reissue Pat. No. 23,950 entitled Method and Means for Chemical Analysis by Nuclear Inductions;" the article Nuclear Introduction" by Felix Bloch in Physical Review, Vol. 70, page 460 and an article entitled The Nuclear Induction Experiment," written by Bloch, Hansen and Packard appearing in Physical Review, Vol. 70, page 474. Very briefly, gyromagnetic resonance analysis comprises the placing of a sample of matter to be investigated within an extremely strong and uniform unidirectional mag netic field. To the sample and at right angles to the polarizing field is applied a radio frequency magnetic field. At precisely the correct combination of these two fields the nuclei of the sample experience a gyromagnetic resonance and emit an electromagnetic signal which is detected and displayed.

From the gyromagnetic resonance signal it is possible to obtain a wealth of information, both quantitative as well as qualitative, about the chemical and physical nature of the sample investigated. As the art has advanced a need has grown for high degrees of resolution, but in order to obtain such high resolution, it is important that the sample be subjected to a completely homogenous magnetic field intensity. In the past, numerous apparatus have been used to obtain uniform magnetic fields. Generally great care is given to the winding of a powerful electromagnet for producing the field and to providing uniform pole pieces and proper alignment of the pole pieces upon the coil structure. However, even after these tedious preparations, additional homogeneity is often desired.

Especially in a high resolution nuclear magnet spin resonance measuring device, the degree of variation of magnetic homogeneity in the sample located between the pole pieces should be smaller than for a polarizing magnetic field of l4,l oersteds. In other words, the requirement is such that there must not be any uneveness of more than 0.00M oersteds per unit volume of a sample participating in the magnetic resonance. Generally, to obtain such extremely high homogeneity, such measures as adjustment of parallelism and of the relative center between the pole pieces are employed. In addition to these, a compensation coil for further adjusting and improving magnetic homogeneity has been employed, and the sample to be investigated is rotated at a desired speed to further improve the homogeneity.

Practically, the thus obtained high homogenous magnetic field must be maintained for a long period because variation of the magnetic field in a short period necessarily requires troublesome adjustment of the magnetic field every time.

To obtain such stable high homogeneity in a gyromagnetic apparatus with permanent magnet poles, the permanent magnet poles are accommodated in a constant temperature bath, and in the case of electromagnetic poles the pole temperature, which results from self-heating due to the exciting current, is regulated by control of the flow amount of cooling water. However, in spite of such temperature regulation, it is impossible to prevent a small temperature variation in the poles. Owing to this small temperature variation which has been unavoidable in the conventional arrangement the distance between the pole pieces tends to vary. Since the temperature variation which causes the variation of distance between the pole pieces cannot be avoided entirely, it is desired that the distance variation under consideration should be kept at a very low level for a long period even if there is temperature variation.

Accordingly, a main object of the invention is to provide a magnetic field generating device for a gyromagnetic apparatus providing an extremely homogenous magnetic field for a long period.

Basically, the present invention provides a magnetic field generating device in which a pair of pole pieces for providing a homogenized magnetic field are constructed in one body.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of the novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

FIG. 1 is a longitudinal view of a conventional gyromagnetic apparatus;

FIG. 2 is a longitudinal view of a novel gyromagnetic field generating apparatus embodying the present invention;

FIG. 3 is a partial sectional view of a magnetic construction showing a pole piece assembly according to the invention; and

FIG. 4 is a partial sectional view of another embodiment of a pole piece assembly according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. I, there is shown in a longitudinal view a conventional magnetic field generating apparatus, which comprises a rectangularly shaped yoke l, a pair of magnetic poles 2 and 2' provided with frustoconical portions 5 and 5' for producing a unidirectional magnetic field, a pair of coils 3 and 3' for magnetizing or magnetically exciting the magnetic poles, and a pair of

pole pieces

4 and 4 for homogenizing the magnetic field produced by the magnetic poles.

In a central space formed between the pole pieces the magnetic field should be homogenous for a long period. However, as shown in FIG. 1, the magnetic poles 2 and 2' are fixed to the rectangularly shaped yoke 1. In this case, when the lateral length of the yoke is 500 millimeters and the distance between the pole pieces is 25 millimeters; for example, variation of the distance between the poles is 2 X10" even though temperature variation of the pole pieces is only one hundredth. Such variation of distance cannot be tolerated in a gyromagnetic apparatus because the upper limit of variation in homogeneity is 10 in this apparatus.

Referring to FIG. 2, an improved magnetic apparatus, which comprises a rectangularly shaped yoke 10, a pair of magnetic poles l2 and 12' fixed to the yoke 10 and provided with frustoconical portions 14 and I4, and a pair of pole pieces 22 and 22' being constructed in one body through a pair of supports 20 made of nonmagnetic material, is shown. A pole piece assembly, comprising the pole pieces 22 and 22' and supports 20, is fixed to the magnetic pole I4 through a spacer plate 18 made of nonmagnetic material. The pole piece assembly, the spacer plate and the magnet pole 14 are joined by a suitable adherent such as epoxy type adherent material.

Because the pole pieces are fixedly connected to each other, the constant distance between the pole pieces is maintained for a long period even if there is variation in the pole temperature by virtue of environment or any other thermal effects. And furthermore, there is no necessity to adjust the parallelism of the pole pieces during every operation time. These are very important and useful conveniences for a gyromagnetic apparatus, such as a very high resolution nuclear gyromagnetic resonance apparatus.

Though the aforementioned pole piece assembly is fixed to the magnetic pole, it is required that a small clearance 26 for absorbing or moderating the effects of thermal expansion or shrinkage of the constructing members he formed between at least one of the magnetic poles and the pole piece assembly, as shown in FIG. 2. Of course there is small variation in the width of clearance in this embodiment, and even if such variation takes place, the volume of the clearance being much smaller than that of the free space 24, variation in magnetic field in the free space 24 is negligibly small. This is particularly true because no variation occurs in the distance between the pole pieces. Deformations or changes of the yoke and magnetic poles do not effect deformation of the pole piece assembly in theimproved magnetic apparatus.

in FIG. 3, a pole piece assembly is fixed to the yoke 30 by bolts 46 and 46'. The pole piece assembly comprises a pair of

pole pieces

37 and 37 having a frustoconical shape and being inserted into and fixed to

respective holes

39 and 39 provided in the support members 32 and 32', made of nonmagnetic material. The pole pieces are respectively secured to the support members by a suitable'adherent material 52. The support members 32 and 32' are assembled to each other through

bolts

48 and 56 so as to provide a central hollow 41. A bolt 42 and nut 40 are also screwed through the support members. A unidirectional homogenous magnetic field is produced in a central space 50 between the pole pieces 37 and 37'. A pair of magnetic poles 44, which are provided with

frustoconical portions

34 and 34 made of magnetic material are spaced from the surfaces of the frustoconical pole pieces 37 and 37' by means of adjusting means 36 which abut the pieces 37 and 37'. Adjusting rings 36 are screwed to respective projections 58 and 58' which are secured to the surfaces of portions 34 and 34- of the magnetic poles. The adjusting rings 36 are not affixed to pole pieces 37 and 37', but each will slidably rotate along the surface of pole pieces 37 and 37', as the rings are turned, thereby varying the spacing between the

pole pieces

34, 34' and 37, 37' respectively. Each ring contains holes 38 in which a turning element, such as a handling rod may be inserted. By turning the adjusting rings the magnetic uniformity and homogeneity can be changed and adjusted.

'These rings are means for fine adjustment of the magnetic unifonnity and homogeneity.

FIG. ,4 shows another example with respect to a pole piece assembly whereina pair of pole pieces 62 and 62' having frustoconical shape are inserted and fixed by suitable adherent material 72 to

respective holes

61 and 61 provided in the supporting

members

60 and 60. One of the supporting members is divided into two blocks and the blocks are connected through bolts 64, with clearances 66 provided between the blocks, so that deformation of the assembly may be absorbed thereby. it is noted that in the embodiments mentioned above the distance between the pole pieces is always maintained constant. If necessary, the magnetic homogeneity may be adjusted by turning the bolt.

According to our investigations, it has been found that in the novel magnetic apparatus of the invention the variation of magnetic field is less than about one tenth to one hundredth compared with conventional ones under the same temperature variation. Further, it is a dominant feature of the invention that the dependency of field homogeneity on temperature variation is extremely small. In an example of the invention, variation in the field homogeneity was less than per week in an air bath thermosetting box of temperature stability of 0.1 C. On the contrary, in the conventional magnetic apparatus, as shown in FIG. 1, variation in field homogeneity was l0 per 8 hours in an air bath thermosetting box of temperature stability of 0.0l C. This is a very important advantage for high resolution nuclear resonance apparatus. Even in the invention field homogeneity, flatness of field contour and magnetic stability can be adjusted by employment of adjusting coils, a sample rotation in the field and other desirable manners.

While there have been shown and described specific examples of the present invention, modifications thereto will readily occur to those skilled in the art. It is not intended, therefore,

ma etic poles and includin a pair of spaced pole pieces de mmg said main gap there etween and support means made of nonmagnetic material mounted on said yoke without contact with said magnetic poles for fixedly supporting said pole pieces relative to each other so that the said main gap therebetween is maintained constant, said support means supporting said pole pieces in spaced relationship to the associated magnetic poles immediately adjacent thereto so as to provide auxiliary gaps therebetween, whereby each of said pole pieces is supported only by said support means.

2. A magnetic field generating apparatus as defined in claim 1, wherein said support means includes a supporting member of nonmagnetic material provided with a pair. of aligned holes and a central hollow, said pole pieces being inserted into the respective holes on either side of said hollow, whereby said pole pieces are supported without providing any mechanical stress.

3. A magnetic field generating apparatus as defined in claim 2, and further including adjusting means positioned on the end of each pole piece facing a respective magnetic pole for adjusting the homogeneity of the field produced between said pole pieces including a projection made of magnetic material extending from each magnet pole and an adjusting ring spaced from each pole piece and threadedly engaging a respective projection.

4. A field generating apparatus for use on a gyromagnetic resonance spectrometer comprising a yoke through which flux passes; a pair of magnetic poles fixed to the yoke for producing a unidirectional magnetic field; and a pole piece assembly which comprises a supporting member made of nonmagnetic material provided with a pair of holes and having a hollow and a pair of pole pieces made of magnetic material being inserted and fixed to the respective holes on either side of said hollow, said pole piece assembly being secured to said yoke and being slightly movable relative to the magnetic poles, said supporting member being composed of a pair of blocks interconnected by adjustable coupling means for adjusting the homogeneity of the field generated in said hollow.

5. A field generating apparatus for use in a gyromagnetic resonance spectrometer comprising a rectangular yoke through which flux passes; a pair of magnetic poles fixed to said yoke for producing a unidirectional magnetic field; a pair of supporting members made of nonmagnetic material provided with a pair of frustoconical-shaped holes; a pair of frustoconical-shaped pole pieces inserted into and fixed to the respective holes of the supporting members, the pole pieces being mechanically separated from the opposing magnetic poles and said supporting members being secured to said yoke, whereby a constant distance between the pole pieces is maintained.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 42, "than should read-"than 1o Column 2, line 38, "2 x 10 should read-2 x 10 Column 2, line 42, "10 should reacli0 -1.

Column 3, line 21, "34"' should read-34'-.

should read-- 10 Column 3, line 54, "1O should read--l0 Column 3, line 50, "10

(SEAL) Attestz EDWARD M FLETCHER ,JR Attesting Officer ROBERT GOTTSCHALK Commissioner of Patents DRM PO-105O (O-69) USCOMM-DC 60376'P69 0.5. GOVERNIIINT PRlNT HG OFFICE l9! 0-366-331

Claims

1. A magnetic field generating apparatus for producing a homogeneous magnetic field in a main gap, comprising magnetic field generating means including a pair of spaced magnetic poles and a yoke of magnetic material interconnecting said poles, and a pole piece assembly disposed in the space between said magnetic poles and including a pair of spaced pole pieces defining said main gap therebetween and support means made of nonmagnetic material mounted on said yoke without contact with said magnetic poles for fixedly supporting said pole pieces relative to each other so that the said main gap therebetween is maintained constant, said support means supporting said pole pieces in spaced relationship to the associated magnetic poles immediately adjacent thereto so as to provide auxiliary gaps therebetween, whereby each of said pole pieces is supported only by said support means.

2. A magnetic field generating apparatus as defined in claim 1, wherein said support means includes a supporting member of nonmagnetic material provided with a pair of aligned holes and a central hollow, said pole pieces being inserted into the respective holes on either side of said hollow, whereby said pole pieces are supported without providing any mechanical stress.