US2981688A - Ferrites for microwave applications - Google Patents

Description

April 25, 1961 E. ALBERS-SCHOENBERG 2,981,688

FERRITES FOR MICROWAVE APPLICATIONS Filed May 27, 1960 United States Patent'Oi'ice 22 3381: R CRO AV IC THPNS Albers schoenberg, Retlfield Village, Metuchen,

tele ram t efiect is: die we teraction of:

;N.'.I., assign r, by mesne assignments, Steatite Re- Search C6 f Delaware Filed Mam, 1 9 66, ser No. 32,387 Claims. (01. Zea-62.5

. mre t;su ate of ber 28,-19 l8, also abandoned. In application Serial No.

67,752 an unusual type of fe'rrite material is disclosed; Whereaslthe ordinary ferrite has a formula of xi/rom o,

and inwhich czy'is approximately l:1, tlie ferrites disclosed in said application Serial No. 67,752 havewan xzy ratio which is between 1.221 and 31-1 and preferably between ,1.6:1 and 2:1. These ferrites utilize 'MgOas the essential bivalent oxide. w Application, Serial No. 352,205 disc10ses that a certain group of ferrites disclosed in U.S. application Serial No; 67,752 having an xzy ratio of 1.2:1 to 3:1, have unusual properties making them particularly suitable as gyrator element which has very low losses'insuch ap:

plications.

Among other objects of the invention is to provide a ferromagnetic ferrite having low dielectric losses especially useful for microwave applications.

Another object of the invention is to provide a new connection with the accompanying drawing in which thesingle figure is a perspective view partly in cross section of" a circuitinventiomt h H Recently, the gyrator elements, referred to above,*com

em em the t s -eta 9 h prising wave guides including ferrite coresy have evolved as new circuit elements for microwave frequencies. Such gyrator elements are useful for phase' changer s,modulators and switches, for example. I: H

This type of new; circuitelementis a uniqueYdevice, since it violates the law of reciprocity; that is itdoes not have similar properties in both directions ,equally The planeof polarization of microwave propagation can be changedas the wave passes through the ferrite which is magnetized with a steady field. I This device can proper; 135 be .called a ferrite gyrator element! The ferrite. core has been named a Faraday plate. The actual effect upon (1) The spinning electrons which will precess about a force not'parallel to their axis of spin (similar to a y p 1 I I (2) .A steady magnetic, field parallel to the direction of propagation which acts as the aligning forceon the gyroscopic spinning electrons inthe ferrite,

(3) Circularly polarized waves in the wave guide which are propagated through the ferrite.

Actually, circularly polarized waves are not necessary since any linearly polarized wave can be considered as the resultant of two circularly polarized components of equal amplitudes which are rotating in opposite directions with equal angular velocities. Thus, one direction of circular polarization'will be in the same direction as the precession of the elemental electron gyroscope and the other direction of circular. polarizationwill be in the opposite direction to thatfofthe precession. It is evident that one component of circular polarization which has the same sense of circular direction as the precession of the elemental electron gyroscope in the ferrite will be rotated more than the normal amount due to angular velocities, While the other circularly polarized wave of the opposite direction will be rotated only the i normal amount, or less, than that, due, to its angular in which M represents one or more bivalent metal oxides velocity. Thus, at the exit end of the ferrite, there will be a relative phase shift between hoth circularly polarized components. When these are combined again into the linearly polarized wave, the plane of polarizationofthe latter is sh ifted ,with res pect to the plane of polarization before, it entered the ferrite. Another way of looking at phenomenon is to consider it as a relae change bf the velocities of propagation of the/circularly polarized waves. n a If very much attenuation of both circularly polarized waves occurs due to the loss characteristic of the ferrite,

thenfits efficiency as a transparent medium is poof. If the'two circularly polarized waves which emerge from the ferrite areattenuated unequally, then an elliptically polarized wave will result; n

' Difierent ferrites vary as to their attenuation proper ties "(or loss characteristics), ellipticity (or unequal 'attenuation of the two circularlypolarizedwaves), and rotation. In addition, as onewould expect, these propw erties" vary -as afunc'tion of the steady magnetic field.

Also,fthere is a resonance point present whenthe precessionfrequency of theclernental electron gyroscopes coincides witli that of the microwave frequency. This point is characterizedby complete absorption of the interacting circularly-polarizedwave, and thus, very high losses. Losses ina Faraday plate or'ferrite cores of such devices'may comprise dielectric losses, magnetic losses or rnay'bedu'e to some other unknown quality'of the core; For example, it is believed that the low losses and efiec tiveness of the core of thepresentinvention are not only due imitsmagneticand dieleotricproperties but that they are in. some. way associatedwith thepresence of more than one crystalline phase in the material due to the low proportion of Fe O with respect to the bivalent metal oxides. l 7 3 The ferri tes employed in the gyrato'r. of this invention not only have low losses but combine withthis property a fairly high rotation. These two properties are both dc sirable in a Faraday plate.

The ferrrtes f the gyr ator element of this invention comprise compositions which areessentially of the for inula x(MgO, MO)yFe O in which the MO represents a heavy metal oxide which is less than 10% by'weight of theentire composition (with the exception' of MnO which may be added in amounts up to 20% of "the corh n Patented Apr. 196 1 The MO may be entirely absent and may be MnO, ZnO,

CdO, CuO, NiO or any similar bivalent oxide. When oxide fluxes until a total of 20% of flux is obtained although with no more than 10% of the other bivalent oxide fluxes.

. Ferrites within the limits specified but containing over 55 mol percent of MgO are very satisfactory since they have a low susceptibility to compositional variations and may therefore be made with very. uniform properties. Increasing the MgO content to 55 mol percentreduces the maximum allowable iron oxide content to 44 mol percent and the maximum amount of MnO to 22 mol percent.

The properties of such ferromagnetic bodies which probably relate to their application in gyrator elements are as follows:.

(a) Initial permeability 10-40 at 1 me.

(b) Saturation magnetization, B of approximately 1500 'gausses.

(0) Dielectric constant of about 8 to 20.

(:1) Low magnetic losses at 1 me.

(e) Relatively low dielectric losses, tan 6, of about .05 at 1 mo. and about .001 at l0 c.p.s.

The dielectric constant of such bodies does not substantially change up to 10,000 mcs. However, the dielectric constant at these frequencies is diflicult to measure with accuracy. The initial permeability at 10,000 mcs. may be as low as unity. The magnetic losses at 10,000 mcs. vary somewhat, but are, at least,

. Magnesium oxi e Specific resistance 0.8)(10' ohm Power factor, tan 6 170x10 Initial permeability f.. (Approx) 30. Dielectric constant About 10.

At 10,000 mcs. the initial permeability is about 1.0.

EXAMPLE 2 A ferrite core is made of the following composition Parts byweight 2s Magnesium fluoride i 3 Manganese dioxide 6 Iron oxide 66 Approximate ratio of x:y=1.8:1. Firing temperature =1390 C.

This body has lower magnetic losses at 10,000 mes.

than the body of Example 1 and represents an improvement over such body in this respect.

When these bodies are inserted in the device of the drawing as the plate 20 in diameter of .6 cm. f.c. a gyr'ator element having exceptionally low losses and good performance is produced. The measurements of rotation were obtained on samples of 1 inch or 2.54 cm. length. Such circuit elements are useful for. one-way transmitting devices, for example, and since the rotation of the wave may be controlled by an external source of the magnetizing current they may also be used in electrically controlled attenuators, modulators and microwave switches.

The following tables give the essential features of further examples.

by one order of magnitude smaller than that of other ordinary ferrite materials.

The device shown in the drawing has a first rectangular wave guide 10 and a second rectangular wave guide 11 connected by a circular tube 12 in which the Faraday plate or ferrite 20 is placed. A magnetizing coil 21 surrounds the central portion of the circular tube 12 to magnetize the ferrite plate 20. Depending on the thickness of the plate or length of the ferrite 20, the amount of magnetization, etc., the wave in guide 1 1 will be rotated a certain number of degrees, in a clockwise direction, 90, for example. 'If any wave of the same frequency, etc., is passed from guide 11 through plate 20 and then to guide 10 this wave will be rotated 90 by Plate 20 'but if passed in a counter direction will not be rotated in the opposite direction (as would be expected by the law of reciprocity) but in the same direction. Any reflected wave would therefore be 180 out of phase with respect to the original wave. In the device shown, the central circular tube 12 is about the diameter of an ordinary cigarette.

EXAMPLE 1 A ferrite core is made by grinding, mixing and firing a composition of the following ingredients in the propor tions disclosed:

' Parts by weight Oalcined magnesite 21 Magnesium fluoride 1 Manganese dioxide 6 Zinc oxide 1 Iron oxidelFe o 71 EXAMPLES 3-6 Example 3 Example 4 Example 5 Example 6 7 Mol wt. Mol Wt. Mol Wt. Mol wt. -Per- Per- Per- Per- Per- Per Per- Percent cent cent cent cent cent cent .cent

M30 58 26. 3 58 28. 1 58 29. 1 58 27. 2 MnO 2 1. 9+ 10 10. 5 14 16. 2 5 5. 1 N10 1 9 F010: 40 71. 8 32 61. 5 28 55. 7 36 66. 9 Rotation, 2.54 cm.

or 1 inch, degrees 202 176 162 212 Losses Low Low Low Low.

I But sllghtly hlgher than 101. Examples 3-5.

V EXAMPLES 7-11 Ex. 7, Ex. 8, Ex. 9, Ex. 10, Ex. 11, Wt. Per- Wt. Per- Wt. Per- Wt. Per- Wt.'Percent cent cent cent cent MgO 25 30 30.5 MgO V 44 48 MgF- 3 8 .01 0 6 M11104.H|O 4. 5 4. 6 FerOr 66 51. 5 61 47. 6 69. 6 M01 ratio 1.8 1. 8 2. 3 2.3 1. 76

Mg0+MO FerO:

Examples 7 and 8 produce substantially the identical composition after firing and similarly Examples 9 and 10 produce the same end product. Example 11 illustrates a body prepared without additional flux. In order to obtain a satisfactory product from this composition the materials are mixed,'fired at around 1400 C. and-thereafter refired several times. I

Examples7 and 8 have low losses and a rotation of approximately 220 per inch.

Examples 9 and 10 have low losses and a rotation of approximately 180 per inch.

Example 11 has low losses and a rotation of approximately per inch.

When the term low losses" is employed it means that the losses are below 1.0 decibel, for example.

The features and principles underlying the invention described above in connection with specific exemplifications will suggest to those skilled in the art many other modifications thereof. It is accordingly desired that the appended claims shall not be limited to any specific features and details shown and described in connection with the exemplifications thereof.

I claim:

1. A ferromagnetic ferrite consisting essentially of a composition of the general formula x(MgO, MnO, Mo Fe,o,

in which MO consists of at least one bivalent metal oxide selected from the group consisting of ZnO, Q and NiO, in which xzy is between 1.2:1 and 3:1, the total amount of MO being less than 10% by weight of the entire composition, the amount of MnO being at least 1% and no more than by weight of said composition, and the total amount of MO and MnO being no more than 20% by weight of said composition, said ferrite having low dielectric losses, tan 6, of no more than about 0.05 at 1 mo. and of no more than about 0.001 at 10 c.p.s.

2. The ferrite of claim 1 in which the ratio of x:y is between 1.6:1 and 3:1.

3. A ferromagnetic ferrite consisting essentially of a composition of the general formula x(MgO, MnO) .yFe O in which any is between 1.2:1 and 3:1, the total amount of manganese oxide being between 1 and 20% by weight of the entire composition, said ferrite having low dielectric losses, tan 6, of no more than about 0.05 at 1 me. and of no more than about 0.001 at 10 c.p.s.

4. In a ferrite gyrator, a Faraday plate consisting essentially of a ferromagnetic plate of the composition of claim 3.

5. A fired, shaped ferrite body having low dielectric losses, tan 6, of no more than about 0.05 at 1 me. and of no more than about 0.001 at 10 c.p.s., formed by firing at a temperature of about 1390" 0., about 25 parts by weight of MgO, about 3 parts by weight of magnesium fluoride, about 6 parts by weight of manganese oxide calculated as M110, and about 66 parts by weight of ferric oxide.

References Cited in the file of this patent UNITED STATES PATENTS 2,565,861 Leverenz et a1. Aug. 28, 1951 2,576,456 Harvey Nov. 27, 1951 2,640,813 Berge June 2, 1953 2,644,930 Luhrs et al. July 7, 1953 2,715,109 AlbersSchoenberg Aug. 9, 1955 2,719,274 Luhrs Sept. 27, 1955 2,745,069 Hewitt May 8, 1956 2,748,353 Hogan May 29, 1956 2,877,183 Eckert Mar. 10, 1959 2,886,530 Greger May 12, 1959 FOREIGN PATENTS 697,219 Great Britain Sept. 16, 1953 735,375 Great Britain Aug. 17, 1955

Claims (1)

1. A FERROMAGNETIC FERRITE CONSISTING ESSENTIALLY COMPOSITION OF THE GENERAL FORMULA

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