US2671884A - Microwave magnetic control - Google Patents

Description

March 9, 1954 J. F. zALEsKl MICROWAVE MAGNETIC CONTROL Filed Sept. 19, 1950 @Maw/ms Patented Mar. 9, 1954 MICROWAVE MAGNETIC CONTROL John F. Zaleski, Valhalla, N. Y., assignor tc General Precision Laboratory Incorporated, a corporation of New York Application September 19, 1950, Serial No. 185,593

(Cl. S33-98) 7 Claims. y1

This invention relates to microwave magnetic control circuits for control of microwave energy by means of a magnetic substance.

In the art of control of microwave energy, improved means have been lacking for switching, attenuation and modulation of the energy. The straightforward switching methods of directcurrent and low alternating-current practice are not applicable to microwave energy because of the radically diierent behavior of such energy. Microwave switching means have, therefore, in most cases included wave traps to eliminate radiation losses, precise sliding parts, or accurately made fiexible wave guides. Means for attenuation of high power and for modulation are at present correspondingly cumbersome. e

The instant invention employs a magnetic substance which may be either ferromagnetic, paramagnetic or diamagnetic. This substance is positioned within a confined microwave eld, as within a wave guide, a resonant cavity, or any other microwave transmission component. A solenoid is so positioned that when electrically excited its field magnetizes the magnetic substance, and the resulting change in the magnetic substance changes the impedance which the associated microwave transmission component presents to microwave energy transmitted through it.

The purpose then of this invention is to provide means including a magnetic substance for controlling the magnitude of microwave energy passing through it or near it.

More specically, the purpose of this invention is to provide magnetic means for changing the impedance of a microwave transmission component.

A further understanding of the invention may be obtained from the detailed description and the drawings, in which:

Figure 1 illustrates a microwave resonant cavity in a circuit embodying the invention.

Figures 2 and 3 illustrate graphically the operation of the invention.

Figure 4 illustrates an alternative embodiment of the invention.

Referring now to Fig. 1, a source of micro- Wave energy is represented by the rectangle II. 'This source may be any type of generator such as a magnetron or a hot cathode electric discharge tube, or in general the rectangle II may represent any circuit carrying microwave energy. This energy is applied to a microwave guide of any type, such as the rectangular hollow guide I2, of suitable dimensions for transmitting 2 microwave energy of the frequency generated by the source II.

The guide I2 is connected through an appropriate impedance-matching device such as the iris I3 to the interior of a tunable microwave cavity I 4. This cavity may have any desired shape, such as that of a hollow right circular cylinder, a sphere, a parallelepiped, a coaxial cylinder, or a partial-coaxial cavity. For the purposes of the present description a hollow right circular cylinder has been chosen, the specific details of which will be more fully described hereinafter.

From the cavity I4 the microwaves are conducted through a matching iris I6 and a rectangular guide II to a matched load represented by the rectangle I8. Preceding the load I8 there is connected a microwave power meter I9 which may be any one of the several well-known types, with an associated indicator 2|.

Returning now to the cylinder cavity I4, this cavity is tunable by longitudinal adjustment of a piston 22 loosely tted in the cylinder. The piston 22 is supported by a threaded rod 23 that extends through the end plate 24 and is adjusted by a knurled nut 26 rotatable about the rod and constrained from moving upward by a flange 21 engaging a ring 28 affixed to the end plate 24 of the cavity. The rod is constrained against rotation by a tongue 29 which projects from the end f plate 24 into a longitudinal slot or spline 3I cut in the rod 23. The cavity may be of such a size as to support only the principal mode of field conguration at the applied frequency, in which case no microwave energy will leak past the piston 22. If, however, the cavity is made larger to secure the advantage of a larger Q (gure of merit), a higher mode will be supported in addition and some energy will exist in resonations in that mode. This energy will to some extent reach the space behind the piston. In order to absorb this energy, the rear face of the piston is coated with a thick layer 32 of a solid aggregate of finely divided iron in a matrix.

A short rod or stub 33 is pressed into an axial recess 34 in the end disc 36 of the tunable cavity portion of the cylinder, so that the stub projects into the interior space of the tunable cavity. The stub 33 is constructed of a solid aggregate preferably consisting of finely-divided coppery coated iron filings embedded in a matrix of polystyrene. Although the iron particles are numerous and are close together in their matrix, in general each particle is insulated by the polystyrene from the others. Other magnetic materials can be employed, although with less eiciency.

However, if so, it is preferable that they be in the form of small particles substantially or partly insulated from each other and immobilized in a solid matrix.

Surrounding the cylinder Iii is a wire coil or solenoid 31 in such a position that when energized its eld magnetizes the stub 33. The coil 31 is energized by direct current, represented by a battery 38, when the switch 39 is closed.

As is well known, a cavity such as the cylinder I4 resonates at a definite microwave frequency determined by the position of the piston. When microwave energy is transmitted 'from the guide I2 through the cavity to the guide I1, the cavity acts as a shunt tuned circuit of highquality and rejects incoming energy of all frequencies except that frequency to which it is tuned. Therefore only that frequency is permitted by the cavity to pass from the guide I2 to guide I1, with only a slight reduction in power. All other frequencies are very highly attenuated. 'This behavior of the cavity is graphically illustrated in Fig-2, in which when microwave power is applied to the cavity andthe resonant frequency of the cavity is -varied by adjustment of its piston, the adjustment positions are plotted against the output power, as measured at the meter 2l, Fig. 1. A similar resonance curve would be obtained by holding the cavity adjustment constant and varying the frequency of the incident microwave power.

Tests have shown that if a stub of magnetic materiahsuch as vthe stub 33, is placed in such a cavity in any one of a number of positions, and if the stub be magnetized in any manner such as'by energizing a surrounding solenoid, such as the solenoid 31, then the resonant frequency of thecavity is thereby changed. This change of resonant frequency is a nonlinear function, and is represented by the curve of Fig. 3. If the magnetic eld strength be variedfrom A to B on this curve, the resonant frequency of the cavitf,7 will change from F2 to F1. Such a change in resonant frequency will permit power to pass throughthe cavity, as indicated in Fig. 2so that by increase of the magnetic field of the coilthe microwave-energy to theload I8, Fig. l, has in effect been switched on. By proper selection-of resonant frequency adjustments the other side of -the resonant curve may of course, be usedy'as for example, in Fig. 2 by-adjustment to operate between F and Fi. Thus the switch39, Fig. ..1 is employed to control the flowof microwave power, and may be-alternatively arranged so that .when it is moved to itslclosed position it either starts or stops the flow of 'microwave power. Because of the high efficiency of any microwavecavity, and because the control of power .is effected withoutmechanical movement within the microwave guides or cavityVthis'control ofmicrowave power is exceedingly convenient, 'and is applicable to the lowest microwave powersas `well as to the highest.

Another condition occurs when the input microwave frequency is intermediate between the resonant frequency of the cavity with the switch open and that with the switch closed. Then closing or opening the switch results in a momentary pulseof output power as the cavity'tuning sweeps past the microwave frequency, and furnishes a method of securing microwave pulses that are exceedingly short. For instance, if in Fig. 3 a eld change from A to C be made, causing a frequencychange from F to F2, then as indicated in Fig. 2 the microwave lpower will be passed While the magnetic field in the coil 31, Fig. l, is building up, when the cavity resonance sweeps past its peak, but the microwave power will be prevented from passing when the switch is either open or closed. The shortness of the pulse will be limited only by the speed of buildup of the magnetic field of the coil 31. A similar pulse will be transmitted when the switch is opened. By passing periodically changing or alternating current through the coil, pulses of microwave power will of course, be periodically allowedto pass .through the cavity.

Instead of placing magnetic material in a cavity as Villustrated in Fig. 1, it may be placed directly in a waveguide 4I, Fig. 4, as at 42. If placed to. form a post projecting into the interior of a .rectangular hollow guide through a broad face thereof, lit has the properties of a shunt capacitance if shorter than where A is the free space wavelength of impinging microwave energy, and `of an inductance if longer. If it is surrounded by a solenoid 43, changes the magnetic field thereof will cause changes in the-impedance which the post -prescntsto impinging microwave energy, thus controlling to some degree the magnitude of the Vmicrowave. power passing through the guide.

This effect'is of course, by nomeans so marked asis the-effect in a resonant cavity but is usefuliforzsome purposes because broadband in its frequency transmission characteristics.

What isA claimed is:

l. A generator of short microwave energy pulses comprising, a microwave generator producing microwave energy at a selectedfixed frequency, ami'crowave resonant cavity tunedto a frequency which departs from the :frequency of said'generated energy by a small amountinone sense, means for impressing Vsaid generated .energy onsaid cavity, an output circuit connected tosaid cavity, a member composedof .magnetic material positioned in said cavity, means forgenerating-a -magnetic lfield the ilux of whichslinks said magnetic member, land. means for laltering said .magnetic eld so that when soaltered .the resonant cavity is tuned to a frequency which departs fromthe frequency of the generated signalbya small amount in a sense` opposite to said rstmentioned sense.

2. A generator of short microwave energy pulsesA as Vset forth in claim 1 wherein saidmagnetic material comprises comminuted .-iron Vemrbedded. in aninsulatingmatrix.

3. A generator of short microwave energy pulses as set forth inl claim 1 wherein said-magnetic material consists of comminuted ironhaving a highly conductive coating embedded man insulating-matrix.

4. A generator of short microwave energy pulsescomprising, a microwave generator 4producing microwave energy at a selected-fixed frequency, amicrowaveresonant cavitytuned to a frequency which differs from the frequency of said Agenerated energy by a predetermined amount in .one sense, means for impressing said generated energyv on said cavity, an output circuit connected to said cavity, a member composed of magnetic material. positioned in said cavity, a solenoid surroundingsaid cavity .and said member, a circuit energizing said solenoid producing a magnetic eld of such intensity .in said magnetic member that 4the resonant cavity is tuned to a frequency diiiering from the frequency of said generated energy in a sense opposite from said rst mentioned sense, and switching means in said energizing circuit for selectively energizing and cle-energizing said solenoid.

5. A generatoi of short microwave energy pulses as set forth in claim 4 wherein said magnetic material comprises comminuted iron embedded in an insulating matrix.

6. A generator of short microwave energy pulses as set forth in claim 4 wherein said magnetic material consists of comminuted iron having a highly conductive coating embedded in insulating matrix.

7. A magnetic microwave control comprising, a source of microwave energy of a predetermined xed frequency, a microwave resonant cavity, a transmission circuit interconnecting said source and said resonant cavity, a utilization circuit, a 20 second transmission circuit interconnecting said resonant cavity and said utilization circuit, a rod composed of comminuted iron particles having a highly conductive coating embedded in an insulating matrix positioned in said cavity and extending longitudinally of the aXis thereof, and means for generating a variable magnetic eld the iiuX of which links said magnetic member. JOHN F. ZALESKI.

References Cited in the lle of this patent UNITED STATES PATENTS Number Name Date 2,197,123 King Apr. 16, 1940 2,241,976 Blewett et a1. May 13, 1941 2,286,428 Mehler June 16, 1942 2,396,044 Fox Mar. 5, 1946 2,402,948 Carlson July 2, 1946 2,453,453 Norton Nov. 9, 1948 2,511,610 Wheeler June 13, 1950 2,560,859 Gutton et a1. July 17, 1951

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