US3171091A

US3171091A - Transformer encased in magnetic tape

Info

Publication number: US3171091A
Application number: US46920A
Authority: US
Inventors: Bernard M Goldsmith
Original assignee: Nytronics Inc
Current assignee: Nytronics Inc
Priority date: 1960-08-02
Filing date: 1960-08-02
Publication date: 1965-02-23
Anticipated expiration: 1982-02-23

Description

Feb. 23 1965 B. M. GoLDsMrrH 3,171,091

TRANsFoRMER ENcAsED 1N MAGNETIC TAPE i,

Filed Aug. 2, 1960 INVENTOR .Piena/au M GozpsM/vw ATTORNEY United States Patent O 3,171,091 TRANSFORMER ENCASED 1N MAGNETIC TAPE Bernard M. Goldsmith, Little Silver, NJ., assignor to Nytronics, Inc., Plrillipshurg, NJ., a corporation of New Jersey Filed Aug. 2, 1960, Ser. No. 46,920 14 Claims. (Cl. 336-83) This invention relates to electrical coil and transformer constructions and is particularly useful in miniaturized applications.

It is an object of the invention to provide an improved construction of the character indicated.y

Another object is to provide, in a miniaturized coil or transformer construction, a maximum possible inductance per unit volume.

Another object is to meet the above objects with a construction featuring a completely closed magnetic fluxconducting path to which a ywinding is linked.

A still further object is to achieve the above objects in a construction in which the possibility of `air gap development in any part of the flux-conducting path is reduced to zero.

A specific object is to achieve the above objects with a construction that lends itself to mass production with high reproducibility of electrical characteristics.

Other objects and various further features of novelty and invention will be pointed out or will occur to those skilled in the art from a reading of the following specification in conjunction with the accompanying drawings. In said drawings, which show, for illustrative purposes only, preferred forms of 4the invention:

FIG. 1 is an enlarged view in longitudinal section of a coil construction embodying features of the invention;

FIG. 2 is a view similar to FIG. l but showing a modification;

FIG. 3 is a view similar to FIG. 1 but showing application of the invention to a transformer;

FIG. 4 is an elevation of the transformer of FIG. 3, parts being shown in section in the plane 4 4 of FIG. 3; and

FIG. 5 is a simplified View similar to FIG. 3 but showing a modified transformer construction.

Briefly stated, my invention contemplates application to miniaturized coil and transformer constructions Wherein a winding is developed generally centrally on an elongated cylindrical core of magnetic flux-conducting material and wherein it is desired that the flux-conducting path toroidally envelop the winding without introducing any air gap in the magnetic-flux path. I have found that this can be achieved by applying high permeability tape or plastic as a circumferential envelopment of both the Wound and unwound exposed cylindrical parts of the core at both ends of the Winding, and by assuring that there is a residual compressed pressure contact of the high permeability plastic material on the unwrapped end parts of the core. Various forms of the invention will be described.

In FIG. 1, the invention is shown in application to a simple single coil comprising a plurality of closely adjacent turns of insulated wire on the central part of an elongated cylindrical core 11 of magnetic flux-conducting electrically insulating material. The core 11 may be a ferrite, or it may comprise powdered iron bonded in a thermosetting plastic or resin, such as Teflon.

Lead elements 12-13 may be securely mounted at the respective ends of the core 11 which, for the core materials recited above, will be electrically insulated. In the form shown, the lead elements 12-13 are cach received and bonded in a recess, as at 14, at an end of the core 11; and to enhance the bond, the inserted end of the lead element may be upset as by nail-heading machinery ICC core 11 and a similar surface 18 at the other end. The

respective ends of coil 10 may be brought out axially for wrapping and soldering, as at 19 to the lead 12, and at 20 to the lead 13. If desired, the core 11 may be provided with a longitudinal groove 21 to facilitate alignment and retention of the respective coil'ends, which are brought out for lead connection at 19-20.

In accordance with the invention, a continuous magnetic flux-conducting path is completed utilizing high permeability magnetic flux-conducting tape which, in the form shown, is a single or helical circumferential envelopment or layer 22 surrounding both wound and unwound parts of the core 11. To reduce to zero the possibility of air-gap development at the locations 17-18 Where the flux path is closed, I provide for compression contact of the high permeability plastic layer 22 with these end surfaces 17-18. In the form shown, such Contact is achieved by employment of a sleeve 23 circumferentially stressed in tension and, thus, holding not only circumferential contact at 17-18 but also tightly retaining the winding on the core.

The material of the sleeve 23 may be, in effect, a rubberband which is abnormally enlarged to receive insertion of the wound core and which is .allowed to compress with residual stress the remaining parts of the assembly. I prefer, however, to employ a sleeve 23 of irradiated polyethylene which goes by the trade name Thermofit,V being a product of Raytherm Corporation of Redwood City, California. In employing this material, it is initially supplied oversize, as suggested by the thickness dimension T in FIG. 1, the inner diameter being in excess of the outer diameter of the layer 22 prior to stressing. Such a sleeve 23 is assembled in co-axial relation with the rest of the parts and is, finally, shrunk into placeby application of heat. The material noted has the property of shrinking to about 60 percent of its original size so that if its size is initially selected to permit shrinkage only to, say, percent of its original size, then, to the extent that it has not been able to shrink completely, a permanent residual circumferential tension will be established in the sleeve 23 upon shrinking, and this tension will apply constant radial pressure to the plastic layer 22, at least at the desired points of firm contact, namely, at surfaces 17-18.

In a typical core construction of my invention, the

4core 11 is, as indicated, either of ferrite or bonded powdered iron. It may be of 0.070" diameter and 0.250" length. It is initially assembled with the lead elements 12-13 which may be of #26 wire. The turns of the coil 10 may be of #38 enameled magnetic wire, and the winding development may be a solenoid, universal, progressive universal, layer wound, bobbin wound, or insulated layer-wound type. The high permeability plastic material of the layer 22 may be a thermoplastic magnetic tape containing powdered iron in a suitable plastic vehicle, such as nylon, and I have found that satisfactory results may be achieved with that tape known as Ferrotron, being a product of Polypenco, Inc., of Reading, Pennsylvania. Such tape comes in various widths and thicknesses and is applied in one or more turns of helical development over the wound and unwound core 11 until the desired thickness is achieved. In the illustrative example, such thickness in the region of overlap with the single layer coil 10 shown may be such as to produce an outer diameter of layer 22 of 0.090.

Finally, shrunk sleeve 23. may be such Yas to produce a shrunk or nished thickness of about 0.010"v benglprocured in the unshrunk form with, for example, an inner diameter of 0.125" which would tend to shrink t 0.070" diameter butwhich, by virtue of the dimensions indicated above, will not be permitted to shrink all the way, thus establishing the residual tension and assuring pressure contact to complete the magnetic circuit.

In the arrangement` of FIG. 2, they leads 12-13 are omitted and the ends 25-26 of the winding 10 are loosely brought out. If desired, a small circumferential band 27 of adhesive tapemay be employed to bring the windingl endsl or leads 25-26V toward each other. In View of the similarity of parts, the same reference numbers have been used in FIG. 2.as in FIG. l, wherever applicable. In use, the coil of FIG. 2 may be supported intermedia-te the ends, as for example, by spring nger 28 frictionally engaging the sleeve 23. at a central location.

FIG; 2V also servesto illustrate a circuit-element filter, featuring very narrow band-pass characteristics when the core ofmaterial. 11 is' a magnetostiictive material as, for example, a magnetostrictive ferrite which has been initially magnetically polarized.v In such applications, the inductance presented; tothe leads 25-26 will be sharply dependent upon the mechanical-resonance characteristics of the core 11 (inthe longitudinal direction) and, if desired,a1se`cond;winding (not shown) may be wound adjacent to or over the winding 10 toy provide independent input and output circuits, that is, circuits which are electrically independent but whose coupling depends solelyuponA theV mechanical-resonance characteristics of the core 11.

In FIGS. 3 and 4, I illustrate' application of the invention. to a transformer construction in which the primary andsecondary windings yltland 10 are developed on separate cores 11411 of generally the same shape but. ar-

rangediin side-byLside relation, there-being a spacer 30' of? electrically insulating material preferred between adjacent parts of the winding 1040'. For convenience in description, the upper coil andcore 10-11may be similar to-that described in FIG. l, and corresponding parts of the lower coiland core 10'11' are, therefore, given thev same. reference numbers, but withy primed notation. It willibe noted that the coil 10' is amultilayer coil carried by the core 11'. Leads to the rst coil 10` are brought out at 12-13, and thoseto the second coil-10 are'brought outiat 12-13. For transformer action, it isfnecessary that'the core 11 and the core 11 shall be part of one and the same continuous ux path, and tol achieve this, in accordance with the invention, I cause the wrap22 of'high permeability material to bebanded to-and thus to overlapand'envelopfboth coils and 4both cores, as will be seen moreclearly inthe vie'wy of FIG.' 4.

This means, then, that the fluxV path" maybe considered to follow the arrows of FIG. 3 as, for'example, from left to right in the bodyk of core 11, thence dividing Vin parallel arms defined by stretches 32-33 of the high permeability materialv 22 at the right-hand end of the assembly of FIG. 3; from these points (stretches 32-33), the ux re-enters the core 11 and proceeds from right to left, for division into two parallel branches again in stretches 324335at the left hand of FIG. 3, and nally, re-enters the core 11.l In the form of FIG. 3, the use of tape 22 to envelop the coils as well as the unwound parts of the cores, means that the remaining parts -of the tape 22y will serve to shield the coils 10-10 against strayfluxes. The assembly is completed by employment of a compression sleeve 23', `such as described at 23 for FIG. 1 and, preferably, shrunk into stressed compressional contactgwith unwound extensive areas at the ends of both cores 11-11.

The arrangement of FIG. is simplified and somewhat schematic but serves to illustrate a modification of FIG. 3 in which separate tapes 35-36 are separately banded to corresponding ends of coresY 11-11; tapes 3S-36' thus complete -the ux path at the ends of the cores 11-11. Separate compressional sleeves may be applied over the tapes 35-36, but I indicate my preference that a single such sleeve 37 be employed to overlap both the tapes 35-36 and the windings 10-10.

It will be seen that I have described improved coil and transformer constructions featuring maximum inductance per unit volume. This result is achieved primarily by reducing air-gap development to zero and, thus, assuring continuous magnetic linx-path development. The construction lends itself to single layer, multi-layer and various other winding forms, and it may be easily fabrica-ted with great precision and reproducibility of electrical characteristics. or 357 may provide a tough protecting hide for the overall assembly.

While the foregoing description sets forth the principles of the invention in connection with specific apparatus, it is to be understood that this description is made only by way of example and not as a limita-tion of the scope of the invention as defined in the accompanying claims.

I claim:

1. An electrical coil construction, comprising an elongated cylindrical core of magnetic-flux conducting material, a winding including plurality of turns over a portion of said core short of the axial ends thereof, there being thus exposed a substantially continuous cylindrical core surfacev at each end of said winding, and magneticflux conducting means connecting said surfacesk independent of linkage to said winding, said last-delined means including plastic tape means of high-permeability material and circumferentially extending means radially inwardly compressing the high-permeability material into pressure contact with each of said end surfaces.

2. A construction according to claim 1, in which said tape means completely envelops said coil and is in pressurecontactfwithv said surfaces at the ends of said core.

3. A construction according to claim 1, and including a second elongated cylindrical core of magnetic flux-conducting material, a` second winding including turns carried by a portion of said second core intermediate the axial'ends thereof, whereby cylindrical end surfaces are exposedatboth ends of said second winding, said'tape means including a first portion of high-permeability material banded in-pressure con-tact with a first end surface of the first core and with a rst end surface of the second core, said 'tape means including a second portion of highpermeability material banded in pressure contact with both the opposi-te end surfaces of said cores.`

4. A transformer comprising two elongated cylindrical cores of magnetic flux-conducting material, separate windings including first turns carried intermediate the ends of a first core and second turns carried intermediate theends of the second core, said wound cores being dis'- posed side-by-side and having corresponding exposed cylindrical core surfaces at the respective ends of each of said windings, and tape means of high permeability material includinga irst portion banded in pressure Contact with" iii-'st corresponding adjacent end surfaces of said cores and a second portion banded in pressure contact with corresponding adjacent opposite end surfaces of said cores.

5. A transformer according to claim 4, and including a spacer of insulating material intermediate adjacent parts of the respective windings.

6. A transformer according to claim 4, in which said separate portions of tape are separate ltapes in pressure contact only withend surfaces of said cores.

7. A transformer according to claim 4, in which said tape means envelops both the unwound and wound portions of said cores and is in pressure Contact with said cores at the end surfaces thereof.

8. A coil construction comprising an elongated cylindricalcore of magnetic flux-conducting material, an electrical winding including a plurality of turns developed on Once assembled, the

outer sleeve

23 or 23` the core intermediate the axial ends thereof, whereby substantially circumferentially continuous cylindrical end surfaces of said core are exposed at both ends of said winding, and a tape of high permeability material continuously enveloping both the wound and unwound cylindrical portions of said core and circumferentially extending means radially inwardly compressing the highpermeability material into pressure Contact with said unwound portions.

9. A coil construction comprising an elongated cylindrical core of magnetic flux-conducting material, an electrical winding including a plurality of turns developed on the core intermediate the axial ends thereof, whereby substantially circumferentially continuous cylindrical end surfaces of said core are exposed at both ends of said winding, a tape of high permeability material continuously enveloping both the wound and unwound cylindrical portions of said core and in pressure contac-t with said unwound portions, and a sleeve of plastic material circumferentially enveloping said high permeability material in residual circumferential tension, whereby pressure Contact of said highly permeable material with the unwound cylindrical core ends is achieved.

10. A coil construction comprising an elongated core of magnetic flux-conducting electrically insulating material, leads carried at the respective ends of said core in electrically insulated relation with each other, an electrical Winding of insulated wire having turns developed on said core in closely adjacent relation to each other, said winding extending short of the axial ends of said core, whereby substantially circumferentially continuous surfaces of the core are exposed at both ends of said winding, the free ends of said winding being connected respectively to said leads, a layer of high permeability magnetic Eux-conducting plastic completely surrounding both wound and unwound cylindrical portions of said core, and a compression sleeve surrounding said ilux-conducting plastic and in intimate tensed contact therewith, whereby extensive pressure contact of said flux-conducting plastic with both unwound ends of said core is achieved.

11. Coil construction comprising an elongated core of magnetic flux-conducting electrically insulating material, an electrical winding of insulated wire having turns developed on said core in closely adjacent relation to each other, said winding extending short of the axial ends of said core, whereby substantially circumferentially continuous surfaces of the core are exposed at both ends of said winding, a layer of high permeability magnetic uxconducting plastic completely surrounding both wound and unwound cylindrical portions of said core, and a compression sleeve surrounding said flux-conducting plastic and in intimate tensed contact therewith, whereby extensive pressure contact of said ilux-conducting plastic with both unwound ends of said core is achieved.

l2. A device according to claim 11, in which said core is of magnetostrictive material.

13. A device according to claim 12, and including supporting means intermediate the axial ends of said core and supporting the assembly by contact with said sleeve.

14. A transformer including two elongated cylindrical cores of magnetic ilux-conducting material, a separate winding on each of said cores, said wound cores being disposed side-byside with the corresponding ends thereof adjacent one another, and tape means of high permeability material including a first portion banded in pressure contact with rst corresponding adjacent ends of said cores and a second portion banded in pressure contact with second corresponding adjacent ends of said cores.

References Cited in the file of this patent UNlTED STATES PATENTS 352,105 Zepernowsky Nov. 2, 1886 1,994,534 Robinson Mar. 19, 1935 2,457,806 Grippa lan. 4, 1949 2,79 1,753 Jeppson May 7, 1957 2,938,210 Harris May 24, 1960 2,966,704 OBrian et al. Ian. 3, 1961

Claims

1. AN ELECTRICAL COIL CONSTRUCTION, COMPRISING AN ELONGATED CYLINDRICAL CORE OF MAGNETIC-FLUX CONDUCTING MATERIAL, A WINDING INCLUDING PLURALITY OF TURNS OVER A PORTION OF SAID CORE SHORT OF THE AXIAL ENDS THEREOF, THERE BEING THUS EXPOSED A SUBSTANTIALLY CONTINUOUS CYLINDRICAL CORE SURFACE AT EACH END OF SAID WINDING, AND MAGNETICFLUX CONDUCTING MEANS CONNECTING SAID SURFACES INDEPENDENT OF LINKAGE TO SAID WINDING, SAID LAST-DEFINED MEANS INCLUDING PLASTIC TAPE MEANS OF HIGH-PERMEABILITY MATERIAL AND CIRCUMFERENTIALLY EXTENDING MEANS RADIALLY INWARDLY COMPRESSING THE HIGH-PERMEABILITY MATERIAL INTO PRESSURE CONTACT WITH EACH OF SAID END SURFACES.