Patent Grant
6933799
The present invention relates to a method of controlling an intermodulation distortion of a non-reciprocal device, ferrimagnetic material suitable for implementing the method, and a non-reciprocal device using the ferrimagnetic material.
Worldwide-scale introduction of a ‘Code Division Multiple Access (CDMA)’ method has recently been pursued in the field of mobile communications being used compact mobile communications device such as cellular phones, personal-handy phones or microcellular phones. In association with such a tendency, an intermodulation distortion (hereinafter called ‘IMD’) of a non-reciprocal device used in mobile communications, such as an isolator or a circulator, has come to gain attention despite the IMD having thus far posed no problem in a conventional analog communications scheme. The IMO corresponds to an undesired signal which would additionally arise when two or more signals are supplied to a non-linear device, which is used in non-reciprocal device. For instance, when two signals, one having a frequency f1 and the other having a frequency f2, are simultaneously input to a non-reciprocal device, there arise frequency components other than the signals of frequencies f1 and f2 such as a sideband having a frequency of (2f1−f1) and a sideband having a frequency of (2f2−f1). These sidebands will cause crosstalk or noise. Therefore, sidebands must be suppressed.
The IMD can be suppressed, by applying a sufficiently strong direct current magnetic field (hereinafter called ‘d.c. magnetic field’ simply) to a ferrimagnetic member (i.e. a member made of ferrimagnetic material) from a magnet provided in a non-reciprocal device. However, application of the d.c. magnetic field involves production of side effects; that is, shifting of a frequency band assigned to a non-reciprocal device toward a higher frequency and narrowing of the frequency band of interest, thus degrading the performance of the non-reciprocal device. Further, demand for a more compact and thinner non-reciprocal device hinders application of a sufficient d.c. magnetic field to the ferrimagnetic member.
The compact mobile communications device is battery-powered, and then, use of a low-loss device is indispensable for realizing long-time operation of the compact mobile communications device. In a case where the compact mobile communications device is equipped with a non-reciprocal device, the compact mobile communications device is also desired to have a low-loss characteristic. Not only a compact mobile communications device serving as a ‘Terminal Station’ but also an apparatus serving as ‘Base Station’ provides small coverage areas, and hence an amplifier for use of a small amount of power has been used for the apparatus. Further, a non-reciprocal device to be used as a Base Station is also desired to have a low-loss characteristic.
Also, important characteristics of a ferrimagnetic material used in a non-reciprocal device are to have a characteristic of a sufficiently low ferromagnetic resonance linewidth (hereinafter called ‘FMR linewidth’ and also represented as ‘ΔH’), which acts as a magnetic loss term.
In a non-reciprocal device, the ferrimagnetic member is used in combination with a magnet, and hence a saturation magnetic flux density of the ferrimagnetic material forming the ferrimagnetic member is ideal in assuming that a temperature coefficient may compensate for the temperature characteristic of a magnet. A close correspondence exists between the temperature coefficient of the saturation magnetic flux density and curie temperature (hereinafter represented as ‘Tc’). Ferrimagnetic material is usually desired to have high curie temperature in response to a magnet which is less susceptible to temperature change.
Japanese Patent Publication No. 31288/1981 (Kokoku 56-31288) describes the technique of arbitrarily changing the value of saturation magnetic flux density, by changing the composition ratio of yttrium-calcium-vanadium-iron garnet ferrite (hereinafter called or represented as ‘Y—CaV—Fe garnet ferrite’) substituted by indium (In) and aluminum (Al).
However, the above-mentioned material, i.e. the Y—CaV—Fe garnet ferrite, has a curie temperature as low as 160° C. or less. Therefore, a non-reciprocal device formed of the Y—CaV—Fe garnet ferrite encounters a practical problem of the non-reciprocal device being limited to use at a certain temperature or below. Further, In is a rare natural resource, and hence a ferrite containing In would become costly.
Accordingly, the present invention has been aimed at providing—
The present invention has also been aimed at providing—
The present invention has further been aimed at providing—
To these ends, according to the present invention, a ferromagnetic resonance linewidth of ferrimagnetic material contained in a non-reciprocal device is controlled in order to control an intermodulation distortion of the non-reciprocal device. According to this control method, even in a case where a sufficient d.c. magnetic field cannot be applied to the ferrimagnetic member, the intermodulation distortion of the non-reciprocal device can be improved, thereby sufficiently responding to demand for a compact and thinner non-reciprocal device.
A non-reciprocal device comprises ferrimagnetic member and a magnet for applying a d.c. magnetic field thereto.
The reason for the above-described effect; that is, the IMD decreasing with increasing intensity of the d.c. magnetic field applied to the ferrimagnetic member by the magnet, is as follows:
In a case where a strong d.c. magnetic field is applied to ferrimagnetic member, the influence of a demagnetizing field developing in the vicinity of a non-magnetic phase in ferrimagnetic material forming the ferrimagnetic member and the influence of a crystalline magnetic anisotropy or a like characteristic are weaker than the influence of the applied magnetic field, wherewith procession motions of spins generating in magnetic material are aligned uniformly into one direction, thus causing a circular motion.
In reality, a decreasing in the operational performance of a non-reciprocal device and demand for a compact and thinner non-reciprocal device hinder application of a sufficient d.c. magnetic field.
In order to solve these problems, the present invention controls an IMD by controlling a FMR linewidth of the ferrimagnetic member or the ferrimagnetic material forming the ferrimagnetic member contained in a non-reciprocal device.
In general, the FMR linewidth of a polycrystal ΔH can be expressed as follows:
ΔH=ΔHi+ΔHp+ΔHa (1)
where,
A FMR linewidth of a single crystal ΔHi, which is one of the proper values of a single crystal, is said to assume a value of 0.5[Oe], and this linewidth is negligible at the time of discussion of a FMR linewidth of a polycrystal. Next will be described an increment ΔHp (here, especially, the ΔHp denotes an increment contributed from pores) and an increment ΔHa.
<Influence of Demagnetizing Field Developing in the Vicinity of Pores>
With regard to a increment ΔHp, E. Shlomann has provided the following equation (2):
ΔHp=1.47(4πMs)p (2)
where “p” designates porosity.
As can be seen from
<Increment ΔHa>
An increment ΔHa is expressed as
ΔHa∝(K1)2/(Ms)3 (3)
where
Table 1 shows characteristic values of yttrium-calcium-vanadium-zirconium-iron garnet ferrites (hereinafter called and also represented as ‘Y—CaV—Zr—Fe garnet ferrite’) employing different amounts of zirconium (Zr) for substitution, on the condition that saturation magnetization is around 1250 Gauss.
Machida et al. have reported that substitution with Zr is effective for decreasing magnetic anisotropy. In Table 1, all the samples are substantially equal in terms of saturation magnetic flux density and porosity. Provided that porosity assumes a value of 0.3% and saturation magnetic flux density assumes a value of 1250 Gauss, a increment ΔHp assumes a value of about 6[Oe] according to the above-mentioned equation (2). All the samples are equal and assume a contribution of about 6[Oe]. Accordingly, a difference of each FMR linewidth ΔH among the samples provided in Table 1 can be considered to be attributable to a difference in ΔHa terms of the samples, the difference having been caused by variation in magnetic anisotropy resulting from a difference in the amounts of Zr used for substitution.
As mentioned above, the IMD can be controlled by controlling the non-magnetic phase and magnetic anisotropy of ferrimagnetic material. In other words, the only requirement for reducing an IMD is that the FMR linewidth ΔH be reduced; namely, that non-magnetic phase or magnetic anisotropy of ferrimagnetic material be reduced.
Of the non-magnetic phase and magnetic anisotropy, both being relevant to a FMR linewidth, magnetic anisotropy is defined by properties of ferrimagnetic material. Accordingly, the FMR linewidth is controlled by changing composition of ferrimagnetic material, to thereby control an IMD.
Next will be described the composition of ferrimagnetic material suitable for suppressing generation of an IMD. Preferable ferrimagnetic material has a composition expressed by the following general formula:
(Y3−2x−z+wCa2X+Z)(Fe5−x−y−z−wVxAlyZrz)O12,
The ferrimagnetic material having the abovementioned composition has a FMR linewidth smaller than 15[Oe] and is effective for suppressing generation of an IMD. Further, the value of saturation magnetic flux density of the ferrimagnetic material can be adjusted, arbitrarily, and the ferrimagnetic material has a comparatively high curie point. Within the range where the FMR linewidth assumes a value smaller than 15[Oe], the IMD can be reduced to a value of −75 dBc or less, which practice poses no substantial problem at the time of use of an isolator.
The ferrimagnetic material having the above-mentioned composition according to the present invention can realize a balance between the curie point representing magnetic stability relative to temperature variation and the FMR linewidth and simultaneously satisfy practical requirements of the curie point and the FMR linewidth.
In the general formula, Zr has characteristics similar to those of In, and further, Zr is inexpensive or cheap than In. Elements V, Al, and Zr are substituted such that merits and demerits, which would be caused by substituting the elements, cancel each other, and hence, a loss characteristic and a temperature characteristic are set to preferable values.
Within the range of the “w” term of the above-mentioned chemical formula, there was obtained a compact crystal having only a garnet structure and a grain size of 15 μm or more. Outside the range of the “w” term of the above-mentioned chemical formula, an inhomogeneous phase other than a garnet phase undesirably generates in a crystal.
The relationship between the amount of elements V, Al, and Zr which have been used as substitution elements and the saturation magnetic flux density 4πMs at room temperature can be readily estimated by the following empirical formula (±7% within the range of 0≦z≦0.3).
4πMs=17801−1750x−1400y+1000z−1200z2
Thus, from the relationship between the amount of respective substitution element and the saturation magnetic flux density 4πMs, a material characteristic of a composition can be compared to that of other compositions having the same amount of saturation magnetic flux density to the composition. This will be described by reference to examples.
After having been sintered raw materials Y2O3, CaCO3, Fe2O3, ZrO2, V2O5, and Al(OH)3 were weighed so as to assume a target composition (Y3−2x−z+wCa2X+Z)(Fe5−x−y−z−wVxAlyZrz)O12. After having been wet-mixed by means of a ball mill for 20 hours, the materials were calcined at 1100 to 1200° C. for four (4) hours in the air. The thus-calcined materials were transferred to the ball mill and subjected to compression molding after having been subjected to wet grinding for 20 hours. The optimum temperature of the thus-obtained mold was selected from the range of 1250 to 1450° C. such that the FMR linewidth ΔH of the composition was minimized and a particle size of 15 μm or more was obtained. The mold was sintered for six (6) hours in oxygen. X-ray diffraction of the thus-obtained sintered compact (sintered material) indicates that the sintered compact has a garnet single phase.
Here, according to the Bond Method, a ball sample having a diameter of 1.0 mm (SAMPLE) was formed from a fragment sample of the sintered compact. Then, according to the Reflection Method, the FMR linewidth of the SAMPLE was determined at 10 GHz. Also, the saturation magnetic flux density and the curie temperature of the SAMPLE were determined through use of a Vibrating Magnetometer. Table 2 shows results (such as curie temperature and FMR linewidth) for the compositions computed through use of the above-mentioned empirical formula as to have a saturation magnetic flux density 4πMs of 1250 Gauss or thereabouts. In Table 2, Nos. 1 through 18 are assigned to the SAMPLE respectively used for determination. Here, “w” was set such that 0.01≦w≦0.03.
Material No. 1 is a conventional Y—Al—Fe garnet ferrite having a saturation magnetic flux density 4πMs of 1230 Gauss. Each of Materials Nos. 2 through 18 also has a saturation magnetic flux density 4πMs of 1250 Gauss or thereabouts (within the range of 1210 through 1286 Gauss).
With regard to FMR linewidth ΔHK which is relevant to an IMD, that of Material No. 1 has a value of 45[Oe], in contrast, that of each of Material Nos. 2 through 18 has a value smaller than 15[Oe]. Accordingly, with regard to an IMD, all Material Nos. 2 through 18 are improved as compared with conventional Material No. 1.
With regard to the curie temperature Tc, which is relevant to a temperature characteristic, that of Material No. 1 assumes a value of 224° C., in contrast, that of Material Nos. 8 through 18, each having a composition expressed by a general formula, assumes the range from 180° C. to 259° C. In comparison with conventional Material No. 1, it is seen that a composition—which suppresses an IMD expressed by a FMR linewidth and improves a temperature characteristic—satisfies the following requirements:
Regarding the sintered compact having a saturation magnetic flux density 4πMs of 1750 Gauss or thereabouts, the SAMPLE was made in the same manner as in Example 1. The characteristics of the SAMPLE were determined, and results are shown in Table 3. In Table 3, Material No. 21 designates a ‘conventional’ yttrium-iron garnet ferrite, which is non-substituted by Zr, (hereinafter called and also represented as ‘Y—Fe garnet ferrite’), and Material Nos. 22 through 26 designate materials employed in Example 2.
With regard to the FMR linewidth ΔH, which is relevant to an IMD, that of Material No. 21 assumes a value of 25[Oe], in contrast, that of each of Material Nos. 22 through 26 assumes a value smaller than 15[Oe]. Accordingly, as compared with conventional Material No. 21, all Material Nos. 22 through 26 are improved in terms of an IMD.
With regard to the curie temperature, that of Material No. 21 assumes a value of 275° C., in contrast, that of each of Material Nos. 22 through 26 assumes a value lower than 275° C. Of Material Nos. 22 through 26, Material Nos. 22 and 26 have a curie temperature Tc of 261° C. and exhibit substantially the same temperature dependence as does Material No. 21.
In contrast with the case of conventional Material No. 21, the summary of the data provided in Table 3 shows that generation of an IMD is suppressed and an optimum composition capable of realizing equivalent temperature dependence satisfies the following requirements:
Regarding the sintered compact having a saturation magnetic flux density 4ρMs of 750 Gauss or thereabouts, the SAMPLE was made in the same manner as in Example 1. The characteristics of the SAMPLE were determined, and the results are shown in Table 4. Material No. 0.31 designates a conventional Y—Al—Fe garnet ferrite, which is a sample formed from material having a saturation magnetic flux density 4πMs of 750 Gauss. Material Nos. 32 through 43 are samples formed from materials having saturation magnetic flux densities 4πMs from 740 to 780 Gauss.
With regard to the FMR linewidth ΔH which is relevant to an IMD, that of Material No. 31 assumes a value of 30[Oe], in contrast, that of Material No. 33 and that of each of Material Nos. 38 through 43 assume a value smaller than 15[Oe].
With regard to the curie temperature Tc, that of Material No. 31 assumes a value of 175° C.; that of Material No. 34 assumes a value of 179° C.; and that each of Material Nos. 40 through 42 assumes a value higher than 175° C. and within the range of 177 to 196° C.
In contrast with conventional Material No. 31, materials having a saturation magnetic flux density 4πMs of 750 Gauss or thereabouts can suppress generation of an IMD and an equivalent or superior temperature characteristic, so long as the material satisfies the following requirements:
Next will be described an application example in which ferrimagnetic material having a composition of (Y2.58Ca0.46)(Fe4.49V0.19Zr0.08Al0.2)O12 (x=0.19, y=0.2, z=0.08, and w=0.02) was used for an isolator. To put it more concretely, in the application example, the ferrimagnetic member applied the isolator is formed from the ferrimagnetic material. Here, the ferrimagnetic material has the following properties:
While, for comparison, another ferrimagnetic member was formed from conventional Y—Al—Fe garnet ferrite (FM-MEMBER B), and then, another isolator was fabricated using the FM-MEMBER B (hereinafter called ‘ISOLATOR B’). In other words, ISOLATOR B is one example of the prior arts.
Here, the Y—Al—Fe garnet ferrite has the following properties:
As is evident from
As is evident from
Next will be described an application example in which ferrimagnetic material having a composition of (Y0.82Ca0.2)(Fe4.83V0.05Zr0.1)O12 (x=0.05, y=0, z=0.1, and w=0.02) was used for an isolator. To put it more concretely, in the application example, the ferrimagnetic member applied the isolator is formed from the ferrimagnetic material. Here, the ferrimagnetic material has the following properties:
While, for comparison, another ferrimagnetic member was formed from conventional Y—Fe garnet ferrite, which is non-substituted (FM-MEMBER D), and then, another isolator was fabricated using the FM-MEMBER D (hereinafter called ‘ISOLATOR D’). In other words, ISOLATOR C is also one example of the prior arts. Here, the Y—Fe garnet ferrite has the following properties:
As is evident from
As is evident from
The magnet 4 applies a d.c. magnetic field to the ferrimagnetic members 21 and 22 and the center conductor 1. While, there may be employed two magnets 4, which would be placed on the respective sides of the ferrimagnetic members 21 and 22. Yokes 5 and 6 are magnetically connected to the magnet 4. In the illustrated example, the yokes 5 and 6 double as a package case for covering the ferrimagnetic member 21 and 22, the center conductor 1, ground conductors 31 and 32, and the magnet 4.
A substrate 7 of the distributed parameter isolator is equipped with capacitors and resistors required for effecting the operation of the non-reciprocal device. There is formed an aperture 71 in the substrate 7, and the ferrimagnetic member 22 is disposed within the aperture 71. Here, reference numerals 8, 9, 10 and 11 designate as follows respectively:
The non-reciprocal device shown in
As mentioned above, the present invention yields the following advantages:
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-103194 | Apr 1998 | JP | national |
| 11-17254 | Jan 1999 | JP | national |
This application is a continuation of PCT/JP99/01996 filed Jan. 14, 1999.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3563898 | Neichi et al. | Feb 1971 | A |
| 4236125 | Bernard et al. | Nov 1980 | A |
| 5926073 | Hasegawa et al. | Jul 1999 | A |
| Number | Date | Country |
|---|---|---|
| 1 321 511 | Jun 1973 | GB |
| 56-10767 | Mar 1981 | JP |
| 56-31288 | Jul 1981 | JP |
| 3-288406 | Dec 1991 | JP |
| 7-61821 | Mar 1995 | JP |
| 7-157313 | Jun 1995 | JP |
| 8-288116 | Nov 1996 | JP |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP99/01996 | Jan 1999 | US |
| Child | 09689696 | US |
