US 3382472 A
Description (OCR text may contain errors)
May 7, 1968 J. A. MAASS 3 5 RELATIVELY MOVABLE COILS IN SLOTTED CORES Filed July 6, 1966 INVENTOR, JOACHIM A. MAASS United States Patent 3,382,472 RELATIVELY MOVABLE COILS IN SLOTTED 'CORES Joachim A. Maass, 3212 Querns Road, Belmar, NJ. 07719 Filed July 6, 1966, Ser. No. 563,652 6 Claims. (Cl. 336-119) ABSTRACT OF THE DISCLOSURE A transformer with an inductive coupling coefficient that is adjustable over a wide range having two ferromagnetic bases with each base having a surface with the slot and a wire disposed in each slot. The surfaces are held in abutment and rotating the surfaces with respect to each other varies the coupling coefiicient between the wires in the slots.
The present invention relates to transformers and more particularly to transformers with an adjustable inductive coupling coefiicient.
When the flux field of one inductance coil is linked with the turns of another inductance coil, the coils are considered to be inductively coupled. The effect of the coils on each other is called the mutual inductance. If one of the coils has an inductance L and the other has an inductance L the maximum value of mutual inductance has been theoretically calculated as /L L In actuality this maximum has not been obtained and, accordingly, it has been useful to describe the ratio of actual mutual inductance, M, of two coils to the theoretical maximum VIE; as the coefficient of coupling, k, which is expressed by the formula w LlLz As the actual mutual inductance increases, the value of the coefficient of coupling approaches 1. In practice, coupling coefiicients larger that .33 have not been obtained for mutual inductance with air core transformers or .5 in the case of powered-iron core transformers. Overlapping windings have been used to achieve slightly higher coupling coeflicients. The difiiculty in obtaining a large cou pling coefiicient is due to the fact that the coils including those wound on the same coil form, produce flux fields which are not entirely common to the conductors of which the inductance coils are made.
In the past, values of mutual inductance of .5 or slightly higher have been acceptable for most uses. However, the increase in the number and kind of devices employing double tuned filters such as broad band if. amplifiers have presented a need for inductive couplings by means of coils with very small inductance values and large adjustable coefficients of coupling. The present invention fulfills this need.
An object of this invention is the provision of an inductive coupling with an adjustable coefiicient of coupling.
Another object is to provide an adjustable inductive.
coupling with a wide range of coupling coefiicient values including very high coupling coefficients.
A further object is the provision of a high mutual inductance between elements with small inductive values.
Still another object is to provide a transformer that is easy to construct and adjust.
The exact nature of this invention as well as other objects and advantages thereof Will be readily apparent from consideration of the following specification relating to the annexed drawing in which:
FIG. 1 is an exploded view, partly in section, of a preferred embodiment of the invention;
FIG. 2 illustrates an exploded view, of a modification of the invention; and
FIG. 3 shows an exploded view, partly in section, of yet another modification of the invention.
Referring now to the drawings wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIG. 1 (which illustrates a preferred embodiment) first and second ferromagnetic bases 11, 12, illustrated as circular discs, said bases being rotatably mounted on shaft 13 so that they abut each other and can be rotated with respect to each other. Base 11 is provided with a pair of holes 14, 15, and base 12 with a correspondingly aligned pair of holes 16, 17. Arc shaped recesses or slots 18', 19, extend between the ends of the holes on the mutually opposing sides of the bases 11 and 12, respectively, the slots also being mutually aligned. In base 11, wire 20 passes through hole 14, along slot 18 and through hole 15 to form one of the coils in the transformer. The other coil is formed in base 12 by wire 21 which passes through hole 16, along slot, 19 and through hole 17 so as to make the two coils mirror images of each other when directly opposed. In this position practically all of the magnetic field that could be produced by one or both of the wires will be confined in the ferromagnetic material in such a manner that the flux field will be almost completely common to both coils thereby yielding a high mutual inductance. As the bases are rotated with respect to each other the portion of the coils opposing each other, and therefore sharing the same field, decreases thereby decreasing the mutual inductance and coeflicient of coupling. If the relative rotation is continued until no portion of the two coils are overlapping, the ferromagnetic material then acts to prevent the two fields from being common thus providing a coefficient of coupling that is substantially zero.
It is apparent that extra turns may be added as necessary and that more than one coil may be mounted on each base. FIG. 2 shows an embodiment wherein wire 20 in base 11 is provided with a plurality of turns and wire 22 is also wound to provide an additional inductance coil. Wires 21 and 23 are shaped on base 12 to provide mirror images of coils made by Wires 20 and 22, respectively, when directly opposed. Additional holes and slots may be provided as necessary.
In some cases it is not possible to wind the necessary plurality of turns as shown in FIG. 2. Another embodiment, providing for more turns in the wire, is shown in FIG. 3. In this embodiment, slots 18 and 19 comprise parallel straight slot sections connected at their ends by arc shaped slot sections whose concave side face each other. A plurality of turns may be wound in slot 18 with a mirror image of the coil (not shown) formed in base 12. Mutual inductance can be lowered to almost zero by rotating the bases so that the straight portions of slots 18 and 19 are perpendicular to each other. The mutual inductance will be low even though the oppositely disposed coils are not shielded from each other by the bases because of the orthogonally arranged lines of force.
Various modifications may obviously be resorted to by those skilled in the art without departing from the spirit and scope of the invention, as hereinafter defined disposed in said slot in said second base, and means for holding the slotted surfaces of said bases in abutment and for substantially confining said first and second wires in ferromagnetic material, said means including means for allowing movement of said surface and slot of one of said bases relative to said surface and slot of the other of said bases, said slots being positioned such that relative movement of said surfaces varies the alignment and inductive coupling coefficient between said first and second wires.
2. The device as claimed in claim 1 and wherein said first and second bases each include at least two holes therethrough and the ends of the first wire pass through the holes in said first base and the ends of the second wire pass through the holes in said second base.
3. The device as claimed in claim 1 and wherein the slot and wire in said first base is a mirror image of the slot and wire in said second base when directly opposed- 4. The device as claimed in claim 1 and wherein the slots in said first and second bases each have parallel straight portions connected at their ends by arcuate por tions.
5. The device as claimed in claim 4 and wherein the first and second wires each comprise a plurality of loops.
6. The device as claimed in claim 5 and wherein the recess and wire in said first base is a mirror image of the recess and wire in said second base when directly opposed.
References Cited UNITED STATES PATENTS 2,894,231 7/1959 Krasno 336 X 2,900,612 8/1959 Tripp 336123 2,921,280 1/1960 Litwin et a1. 336120 3,090,933 5/1963 Henry-Baudot 336-120 3,179,909 4/1965 Cheney 336-120 FOREIGN PATENTS 224,976 1924 Great Britain.
DARRELL L. CLAY, Primary Examiner.
T. I. KOZMA, Assistant Examiner. I