APPARATUS FOR VARYING THE MAGNETIC FIELD FOR A MAGNETIC RESONANCE ELEMENT

Abstract: Apparatus for varying the magnetic field in a magnetic resonant element which comprises a magnetic yoke (1) with one or more magnets (4, 5) mounted within the magnetic yoke (1) so as to generate a substantially uniform magnetic field in the magnetic yoke (1) and a plurality of magnetic resonance elements (6, 7) located in the magnetic field formed by the magnet (4, 5) and including adjusting means (11, 12) for varying the magnetic reluctance between the magnetic yoke (1) and the magnet (4, 5) at a position which is opposite the position of the plurality of magnetic res­ onance elements (6, 7). The magnetic reluctance can be varied to arrive at the desired strength of the magnetic field.

Description: Field of the Invention: This invention relates in general to a magnetic apparatus for applying a magnetic field to magnetic resonance elements and, in particular, to such type of apparatus, having an improved means for adjusting the magnetic field. Description of the Prior Art: In prior art filters using magnetic resonance elements such as YIG (yttrium, iron and garnet) and the like, it is customary to use a permanent magnet or an electro-magnet to apply a biasing magnetic field to the magnetic resonance element. In a filter, the filtering frequency of which is fixed, a permanent magnet is used because the permanent magnet is small and consumes substantially no power. FIGS. 7 and 8 illustrate a prior art magnetic apparatus for applying a bias magnetic field to a magnetic resonance element in a filter. FIG. 7 is a section view of the filter illustrated in FIG. 8. A magnetic yoke 1 made of soft magnetic material such as iron is formed with a gap portion bordered by threads 1a. A disc 2 is formed with external threads which mate with the threads 1a so as to allow the disc 2 to be adjusted upwardly and downwardly relative to FIG. 7 so as to adjust the magnetic gap. The upper surface of the disc 2 is formed with a number of depressions 2a into which a suitable tool can be inserted for rotating the disc 2 for adjusting it relative to the yoke 1. A permanent magnet 4 is attached to a plate 3 which is attached to the disc 2 as illustrated. A second permanent magnet 5 is attached to a lower surface of the yoke 1 and a magnetic field exists between the permanent magnets 4 and 5 so as to provide magnetic bias for magnetic resonance elements 6 and 7 mounted on a high frequency circuit board or plate 10 and which is attached to the walls of the yoke 1 between the magnets 4 and 5 as illustrated. A pair of thin plate-shaped magnetic resonance elements (YIGs) 6 and 7 are mounted on the circuit board or plate 10 in the magnetic field between the magnets 4 and 5. The magnetic resonance elements 6 and 7 may form YIG filters having two stages, for example. A microstrip line 8, illustrated in FIG. 8, extends across the magnetic resonance elements 6 and 7 and provides input and output. A ground conductive layer 9 is deposited on the entire surface on one side of the plate or board 10 and provides a ground conductive layer. In the apparatus of FIGS. 7 and 8, the magnetic field may be adjusted by rotating the disc 2 so as to move the magnet 4 toward or away from the magnet 5 so as to adjust the density of the magnetic field in which the elements 6 and 7 are mounted. It is necessary and desirable that the magnetic fields applied to the magnetic resonance elements 6 and 7 have the same intensity so that the resonant frequencies of the magnetic resonance elements will be the same, but in the apparatus of FIGS. 7 and 8, the magnetomotive forces of the magnets 4 and 5 are not uniform in a practical example. Thus, as shown in FIGS. 9 and 10, the resonant frequency and the intensity of the magnetic fields of the magnetic resonant elements will be changed when the magnetic 4 is moved by rotating the disc 2 and these variations depend upon the inside configurations of magnets 4 and 5. In a particular example, the diameter of the magnets 4 and 5 was 25mm. When the structure of FIGS. 7 and 8 are rotated on the disc 2 to vary and adjust the intensities of the bias magnetic fields the fields will not be uniform. The prior art magnetic apparatus illustrated in FIGS. 7 and 8 has a number of defects. Even if the magnets 4 and 5 are rotated, it is very difficult to maintain the intensity of the bias magnetic fields applied to the magnetic resonance elements 6 and 7 equal. Also, when the disc 2 is rotated, the parallel relationship of the magnets 4 and 5 is changed or the position of the magnets 4 and 5 are displaced in the lateral direction which varies the filter characteristics of the filter formed by the magnetic resonance elements 6 and 7. As explained above, in the apparatus of FIGS. 7 and 8, adjustment of the magnetic field acting on the magnetic resonance elements is done by mechanically shifting one of the magnets. An apparatus working by the same principle, however with a completely different embodiment, is described in US-A-4,468,643. Pole pieces can be tilted with respect to each other in any direction by tapered screws within a certain limit. Thus, the magnetic field is changed at the locations of two magnetic resonance elements. A completely different principle for adjusting the magnetic field acting on a magnetic resonance element is described in GB-A-441,740. The magnetic yoke of the arrangement is provided with a hole into which a movable piece of ferro-magnetic material is inserted. The more completely the piece fills the hole, the less will be the reluctance of the magnetic circuit and the greater the field strength in a main air gap in which a discharge device for a magnetron oscillator is placed. It is the object of the present invention to provide a magnetic apparatus comprising a plurality of magnetic resonance elements, which apparatus allows the magnetic bias on the magnetic resonance elements to be adjusted as independently and as accurately as possible. SUMMARY OF THE INVENTION The magnetic apparatus of the present invention comprises: a magnetic yoke having an inside opening, a first magnet and a second magnet provided in said inside opening, forming a gap between said first magnet and said second magnet and forming substantially uniform magnetic field in said gap, a plurality of magnetic resonance elements spaced apart from one another in a plane within and perpendicular to said magnetic field in said gap, and adjusting means for varying magnetic reluctance between said yoke and one of said magnets, said adjusting means comprises respective separate adjusting means disposed within the material of said yoke at positions opposite the different magnetic resonance elements, viewed in the direction of the substantially uniform magnetic field, whereby the magnetic fields applied to the different magnetic resonance elements may be independently adjusted. As an adjusting means is provided for each of said magnetic resonance elements, and as each adjusting means is mounted at a position opposing the respective element the magnetic bias on the magnetic resonance elements can be adjusted rather independently and accurately for all elements. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of the invention; FIG. 2 is a perspective view of the invention; FIG. 3 is a graph illustrating the characteristic of the YIG filter of the invention; FIGS. 4, 5 and 6 illustrate a characteristic of the filter according to the present invention. FIG. 7 is a sectional view of a magnetic adjusting means of the prior art; FIG. 8 is a perspective view of the apparatus of FIG. 7; FIG. 9 is a distribution characteristic graph illustrating magnetic resonant frequency; and FIG. 10 is a distribution characteristic graph illustrating magnetic field. DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention is illustrated in FIGS. 1 and 2; it comprises a magnetic yoke 1 of generally rectangular shape as illustrated in FIGS. 1 and 2 with a first permanent magnet 4 attached to the top surface of the inside opening of the yoke and a second magnet 5 attached to the bottom surface relative to FIGS. 1 and 2 of the yoke. The magnets 4 and 5 establish a substantially uniform magnetic field within the magnetic yoke 1. A plurality of magnetic resonance elements 6 and 7 are mounted in the magnetic field generated by the magnets 4 and 5 and are mounted on a printed circuit board 10 which has a conductive layer 9 on one surface thereof and the magnetic resonance elements 6 and 7 are mounted on the other surface. Magnetic adjusting means 11 and 12 are provided in the top surface of the yoke 1 and comprise a pair of threaded openings 1b and 1c into which are received headless bolt adjusting elements 11 and 12. The headless bolt magnetic adjusting elements 11 and 12 are made of a suitable magnetic material as, for example, iron and are formed with slots 11a and 12a to allow them to be adjusted upwardly and downwardly relative to FIG. 1 so as to adjust the magnetic coupling of the yoke 1 and, thus, vary the magnetic reluctance in the yoke which changes the magnetic field between the magnets 4 and 5 which is applied to the magnetic resonance elements 6 and 7. The magnetic resonance elements 6 and 7 may be YIG elements and they may form FIG filters having two stages and an input and output microstrip line 8 is coupled to the magnetic resonance elements 6 and 7. The headless bolts 11 and 12 are made of soft magnetic material such as iron and may be of the same material as the magnetic yoke 1. The magnetic reluctance can be adjusted with a screwdriver which is inserted into the grooves 11a and 12a of the headless bolts 11 and 12 to rotate them to adjust them upwardly and downwardly in the threaded openings 1b and 1c to adjust the magnetic reluctance between the magnet 4 and the magnetic yoke 1 and thereby to vary each of the bias magnetic fields which is applied to the magnetic resonance elements 6 and 7, respectively. Thus, the biasing magnetic fields can be made to be equal or different from each other as desired. In the magnetic apparatus illustrated in FIGS. 1 and 2, the magnets 4 and 5 are not moved relative to the yoke, but are maintained in a fixed position and, thus, the spacing between the magnets 4 and 5 does not vary and the magnetic fields which are applied to the magnetic resonance elements 6 and 7 can be easily and accurately varied by the headless bolts 11 and 12. Thus, there will be no deterioration of the high frequency characteristic such as isolation of the high frequency circuit board 10 which occurs when the magnets 4 or 5 are moved as in the prior art. Also, since the headless bolts 11 and 12 can be rotated independent from each other, the resonant frequencies of the magnetic resonance elements 6 and 7 can be independently adjusted so that filter characteristics will be excellent and the optimum point of the filter can be easily determined. The diameters of the threaded openings 1b, 1c and the headless bolts 11 and 12 can be adjusted so as to have larger or smaller diameters so as to increase the variable range of the magnetic field adjustment. Since the magnets 4 and 5 are fixedly attached to the magnetic yoke 1, the shape of the magnets 4 and 5 is not limited to a disc shape, but can be any desired shape such as rectangular shaped or other selected shape. Thus, the magnetic apparatus can be formed to be smaller than those of the prior art. FIG. 3 illustrates a measured result of the filter characteristic of the magnetic apparatus in FIGS. 1 and 2. FIG. 3 is a graph illustrating the characteristic of the YIG filter where the diameter of the headless bolts 11 and 12 is 4mm. As illustrated in FIG. 3, curve a indicates the characteristic where the headless bolts 11 and 12 are completely removed from the internal threaded openings 11b and 11c and the minimum insertion loss is 10dB. Curves b illustrate the characteristic when one of the headless bolts 11 or 12 is removed from the yoke and the minimum insertion loss is 26dB. Curves c illustrate the characteristic when the other of the headless bolts 11 or 12 is removed from the yoke and the minimum insertion loss is 26dB. Curve d illustrates the characteristic in which the headless bolts 11 and 12 are both inserted into the internal threaded openings 11b and 11c and the minimum insertion loss is 5dB. It can be seen from the graph of FIG. 3 that the center band pass frequency can be varied over a range of 150MHz. FIGS. 4, 5 and 6 are graphs in which the headless bolts 11 and 12 are both inserted into the internal threaded openings 11b, 11c and then are, respectively, adjusted to obtain the optimum filter characteristic. FIG. 4 illustrates the minimum insertion loss of 3.0dB and the bandwidth where the insertion loss is lower than the minimum insertion loss by 3dB is 11.7MHz. FIG. 5 illustrates a filter wherein the minimum insertion loss is 2.7dB; the bandwidth where the insertion loss is lower than the minimum insertion loss by 3dB is 12.5MHz. In FIG. 6, the minimum insertion loss is 2.3dB and the bandwidth where the insertion loss is lower than the minimum insertion loss by 3dB is 11.0MHz. FIGS. 4, 5 and 6 illustrate that the center frequency of the bandpass filter can be varied over a range from 1660 to 1825MHz. Also, the minimum insertion loss of 5-10dB before adjustment as illustrated by curves a and b in FIG. 3 can be improved so as to be 2-3dB as illustrated in FIGS. 4, 5 and 6 by adjusting the filter characteristic so that they are optimum. Modification of the magnetic apparatus of the invention can be made as that, for example, a pair of magnetic apparatuses such as illustrated in FIGS. 1 and 2 with a common magnetic yoke can be utilized and the high frequency circuit board 10 can be sandwiched between two upper and two lower magnets. A plurality of headless bolts opposing the magnets of both the upper and lower ends of the yoke can be provided which are varied and adjusted to thereby vary and adjust the magnetic fields which are applied to the plurality of magnetic resonance elements. Also, in the magnetic apparatus illustrated in FIGS. 1 and 2, the magnet 5 can be eliminated and the apparatus can be operated with only the magnet 4. The invention provides a magnetic apparatus in which magnetic fields can be independently adjusted, said fields being applied to magnetic resonance elements.

Claims: A magnetic apparatus comprising: a magnetic yoke (1) having an inside opening, a first magnet (4) and a second magnet (5) provided in said inside opening, forming a gap between said first magnet (4) and said second magnet (5) and forming substantially uniform magnetic field in said gap, a plurality of magnetic resonance elements (6, 7) spaced apart from one another in a plane within and perpendicular to said magnetic field in said gap, and adjusting means (11, 12) for varying magnetic reluctance between said yoke (1) and one of said magnets (4, 5), characterized in that said adjusting means (11, 12) comprises respective separate adjusting means (11, 12) disposed within the material of said yoke (1) at positions opposite the different magnetic resonance elements (6, 7), viewed in the direction of the substantially uniform magnetic field, whereby the magnetic fields applied to the different magnetic resonance elements (6, 7) may be independently adjusted. A magnetic apparatus according to claim 1, characterized in that each adjusting means is a threaded bolt (11, 12) rotatable within a threaded opening (1b, 1c) within said yoke (1).

Inventors: ITO, SEIGO, MURAKAMI, YOSHIKAZU
Applicants: SONY CORPORATION
Application year: 1985
Main classification: H01P1
IPC codes: G01R33, H01P1, H01P7