US1608560A

US1608560A - Coil system

Info

Publication number: US1608560A
Application number: US111074A
Authority: US
Inventors: Lester L Jones
Original assignee: Individual
Current assignee: Individual
Priority date: 1926-05-22
Filing date: 1926-05-22
Publication date: 1926-11-30
Anticipated expiration: 1943-11-30

Description

Patented Nov. 30, 1926.

UNITED STATES LESTER I4. JONES, OF ORADELL, NEW JERSEY.

COIL SYSTEM.

Applicationfiled May 22,

This invention relates to an inductance coil system and relates more particularly to a coil system especially designed for radio circuits of the sharply tuned or selective type; and has special reference to the provision of a coil system which is self-shielded magnetically and electrostatically.

As is well known, it is a desideratum in certain types of selective and sensitive radio receiving apparatus and in apparatus employable near transmitting stations to construct the inductance coils of the receiving apparatus so that they are uncoupled magnetically and electrostatically to other coils and apparatus in the receiving circuit or to the transmitting apparatus. To accomplish the magnetic uncoupling of the coils to other apparatus, various types of coil windings have hitherto been designed, such as double D windings, toroid windings and binocular coils; and to accomplish the electrostatic uncoupling of such coils to surrounding apparatus, it has been common to employ separate electrostatic shields. These prior types of coil windings have, however, been found insufficient to produce the desired result-s on account of their relatively large external fields near the coil which produce considerable coupling to other parts and even between similar coils when placed at a moderate distance apart. To reduce the intermagnetic couplings between similar coils in a radio receiving set with the use of such prior structures, it has been found necessary to so relatively arrange the coils one with respect to the other in the radio receiving set as to minimize the reacting fields. Other structural difficulties, such as the large volume of winding required and the difficulty of windinc;- methods, have also hindered the use of these prior and known types of winding coils.

A prime desideratum of my present invention resides in the provision of an inductance coil system designed and constructed so that the external magnetic field is reduced to such a minimum that the coil is substantially decoupled magnetically from surrounding apparatus and may be placed in close proximity to other similar coils of a radio receivingsystem without intermag- Y netically reacting with the same.

A further prime desideratum of the invention resides in the provision of a coil system whlch is self-electrostatically shield- 1926. Serial No. 111,074.

ed, that is, which requires no additional or separate electrostatic shield structure, the coil system being so designed and constructed that even when employed in a sharply tuned circuit, the same will be so perfectly shielded electrostatically that the hand of the operator maybe brought to touch and surround the coil structure without detuning the circuit.

It is a further principal object of my present invention to so design and construct the inductance coil system that the mathematical and empirical conditions which sat isfy the relations to produce the magnetic shielding also satisfy the relations to produce the static shielding so that the coil system is both electromagnetically and electrostatically decoupled from surrounding ap paratus, permitting not only the close arrangement of a plurality of coil structures to producea compactly organized radio receiving set, but permitting the same to be constructed Without the use of electrostatic shielding devices.

To the accomplishment of the foregoing and such other objects as will hereinafter appear, my invention consists in the elements and their relation one to the other as hereinafter more particularly described and sought to be defined in the claims; reference being had to the accompanying draws ings which show the preferred embodiment of my invention, and in which:

Fig. 1 is a cross-sectional view of the coil system of my invention, and

Fig. 2 is a view of the same showing the relation between the magnetic field of the unshielded inner coil and the residual magnetic field of the coil system as a whole.

Referring now in detail to the drawings, and having reference first to Fig. 1 thereof, the coil system of my invention is shown to comprise an inner coil section A and an out ter coil section B both preferably made in the form of solenoids arranged in coaxial relation, the inner coil section being wound on a drum 10 made of insulating material and the outer coil section being wound on a drum 11 made of insulating material, the said'coil sections being related in the manner specified hereinafter so that the outer coil section B forms a magnetic and electrostatic shield for the inner coil section A.

The coil. sections'A and B are connected together at contiguous ends by the conductor 12 so that the instantaneous currents traversing the coil sections are in opposite directions, or in other words, so that opposing fluxes of different magnitudes are produced in the core of the inner coil section A. Preferably as shown the outer coil joins the inner coil at the same axial end so that the two coils may be wound in the same direction. The free end 13 of the inner coil section A is the high potential end and is connected to the high potential point of the radio receiving circuit, and the free end 14 of the outer coil section is the ground end and is connected. in use to a point of ground potential in the radio receiving circuit. For reasons to be pointed out hereinafter, the outer coil preferably overlaps the inner coil and preferably so that the line joining their ends makes an angle of approximately 45 with the axis of the coils, as clearly shown in Fig. 1 of the drawings.

To produce the magnetic decoupling of v the-coil system, I have discovered that the ratio of the turns of the two coil sections must bear a definite and quite accurate rela tion to the ratio of the areas of the two coils. This relation is that the product ofthe area and the number. of turns on one coil section must be substantially equal'to the product- 'of the area and the number of turns of the other'coil section. The satisfaction of this condition reduces to a minimum the magnetic coupling between the coil system and a uniform magnetic field, as well as the magnetic coupling of the coil system with other similar coils. This will be best understood when it is seen that'if the coil system of my invention be placed in a uniform magnetic field of variable intensity, which field is directed for point of illustration along the axes of the coils, the E. M. F. induced in the inner coil section is equal. to the E. M. F.

induced in the outer coil section, since the induced E. M. F. in a coil section is a linear function of the number of turns and the total flux threading the coil. Since the product of the area and number of turns for one coil is equal to the product of the number of turns and the area for the other coil, it follows that the induced E. M. F.s are equal. Conversely, it will therefore be seen that the resultant field at a distance is zero, since the field produced by one coil section neutralizes at a distance the field produced by the other coil section. If the field be not parallel to the axis as assumed. the samel'condition exists, since the field threading the coil is to be taken as the product ofthe field intensity and the cosine of the angle between the coil axis and the direction of the field, this angle being the same for both coil sections. a To produce the static decoupling or shielding of the coil system. I have discovered that the coil system should be so constructed that the self-inductanceof the, outer coil section B be made substantially equal to the mutual inductance between the two coil sections A and B. When this condition is satisfied, there results the novel effect of no potential drop along the outer coil due to the high frequency currents flowing; so that the whole surface of the outer coil is at substantially one potential. If this potential be made the ground potential as shown in the preferred use of the coil system, it will be seen that the coil system is substantially completely electrostatically shielded.

To make the self-inductance of the outer coil section 13 equal to the mutual inductance between the coils, I have found first that the ratio of the turns of the two coils must bear the same relation to the ratio of the area of the two coils as is necessary to satisfy the requirement of producing. the magnetic shielding of the coil system hereinbefore described. Thus the product of the area and number of turns of one coil should be equal to the product of the area and the number of turns of the other coil. satisfying this condition, which is the same for producing magnetic decoupling, it is generally necessary only to make the length of the outer coil slightly greater-than the length of the inner coil, as clearly shown in the drawings. This difference in coil length may be utilized as shown to improve the electrostatic shielding of the high potential end of the inner coil, or, where this is not of primary importance, the inner and outer coils may be related symmetrically with a little overhanging of the outer coil at each end. The latter slightly impairs the electrostatic shielding of the high potential end of the inner coil but slightly improves the magnetic shielding of the coil system.

\Vhen exactcompliance with the lastnientioned condition is effected, I have found that it is possible to place ones hands about the outer coil without detuning, even though this coil be connected in a sharply tuned circuit.

To produce a coil system of high efiiciency, I have found that the ratio of areas of the coil sections should bear a given relation. Generally the ratio of areas of the outer to the inner coil section may be between 5 to 1 and 1 to 1, and for producing the greatest. efficiency the ratio of areas should be about 2, 2.1 and 2.2 for coils having ratios of 1.26, 1.58 and 2.1 respectively, of outer coil diam eter to, length. These area ratios are considered desirable because they give a maximum inductance for a given length of coil system having a constant outside diameter when the inner coil is wound with a constant number of turns. This is a practical commercial limitation becauseother electrical and structural conditions impose certain limitations on coil diameters and coil lengths. The maximum number of turns per inch that After.

lilil Magnetically considered, the magnetic flux can be wound on the solenoid form is usually determined by the wire diameter especially at short waves where multilayer or banked windings cause a large decrease in coil efiiciency. Where the area ratio of outer coil to inner coil is about 2 I also obtain a high degree of static shielding with low distributed capacity in addition to obtaining maximum inductance with minimum resistance.

The results of magnetic and electrostatic shielding produced by my coil construction may also be visualized by consideration of the magnetic and electrostatic fields pro.- duced by the inter-acting coil sections.

through the inner coil due to the current in the inner coil, which flux is the more intense flux, is slightly reduced by the opposing flux through the inner coil due to the current in the outer coil. The inductance of the coil system arises primarily because" the inner coil section has in its core a rela- -sbf 175at a-point along the axis of the coil, partially neutralized by the flux of theouter coil. This partially neutralized flux witlziin,

tivelyintense magnetic field which is only the coil has for its return path the annular space between the coils. That portion of the flux of the inner coil which would tend {30 return outside the outer coil is neutralize follows, therefore, that the outer coil section confines the magnetic flux and is effective as a magnetic shield. I

Electrostatically considered, we may first assume that we may neglect the potential drop along the outer coil section due to the resistance of the coil, since for the sharply tuned circuits in which these coils are to be used, the ratio of inductive to resistive drop is greater than to 1. Now the inductive drop along the outer coilmust be due to the magnetic flux linkages with this coil. Sinc practically the entire flux threading the coil system passes through the core of the inner.

coil and back in the annular space betweenthe coils, there is no resultant flux linkage with the outer coil. This statement is to be modified only with respect to the residual flux which I have found issues radially from the center of the coil system and tends to produce neutralizing flux linkages in the hal es of the outer coil as illustrated in Fig. 2 of the drawings, which will be referred to hereinafter. Looking at the phenomenon from the viewpoint of self and mutual inductances, the inductive drop along the return flux of the outer coil; It

much greater than the self-inductance of the outer coil, the fraction of inductance of the inner coil lost due to the reverse mutual is inconsequential.

The manner of designing and constructing the coil system of my present invention will in the main be fully apparent from the above detailed description thereof. The uses and the manifold advantages, especially in radio frequency circuits of the tuned and selective types, will, it is thought, be also manifest from the above. To show the substantial elimination of the magnetic field surrounding the coil system, I reproduce graph) the small magnetic residual field of the coil system as a whole. Thus it will be-seen, viewing Fig. 2 of the drawings, that While the inner coil (unshielded) has a value the,.value of the residual when the coil is 'cbn'nected to its. outer shielding section falls at the 'i'same point to a value too small for ,measiire'ment. Comparing points along a centralgline normal to the axis of the coil,

he field of the unshielded coil at a point rom the coil :center equal to four times the "-radiusz'f'of the coil .is 104, while a similar point: of the shielded coil has a recorded value of G. v

= While I have-shown and described my invention in the preferred form, it will be apparent that many changes and modifications may be made in the structure disclosed without departing from the spirit of the invention,?defined in the following claims.

'I-claim:

' 1. A coil system comprising an inner coil section and an outer soil section connected to produce opposing fluxes of different magnitudes in the core of the inner coil section, the product of the number of turns and area of the inner coil section being related to the product of the number of turns and area of the outer coil section to produce neutralizing magnetic fields at a distance.

2.;A coil system comprising inner and outer coa'xially arranged cylindrical coil sections connected to produce opposing fluxes of different magnitudes in the core of the inner coil section and a flux in the annular space between the coil sections, the product of the number of turns and area of the inner the outer coil due to its self-inductance is coil section being related to the product of neutralized by the voltage drop due to the induced voltage arising from the mutual inductance of the two coils, these being equalized. Similarly the voltage drop along the inner coil is neutralized in part by the mutual inductance between the coils, but

the self-inductance of the inner coil being the number of turns and area of the outer coil section to produce neutralizing magnetic fields at a distance.

3. A coil 5 stem comprising an inner inductance coi section and an outer shielding coil section connected so that the instantaneous currents traversing the same are in tance coil section being equal to the product of the number of turns and area of the out 5 er shielding coil section.

v 4. Aj'co'il system comprising inner and outer coairially arranged cylindrical coil unctions connected so that the instantaneous currents traversing the same are in opposite directions producing opposing fluxes of different magnitudes in the core of the inner coil section and a flux in the annular space between the coil sections, the product of the number of turns and the area of the inner e il section being equal to the product of e'number of turns and area of the outer coil section.

5. A coil system comprising an inner coil section and an outer coil section connected so that the instantaneous currents traversing the same are in opposite directions, the ratio of areas of the outer to the inner coil sections being between five to one and one and one-half to' one, and the product of the number of turns and the area of the inner coil section being equal to the product of the number of turns and area of the outer coil section.

6. A coil system comprising an inner coil sect-ion and an outer coil section connected so that the instantaneous currents traversing the same are in opposite directions, the ratio of areas of the outer to the inner coil sections being substantially two to one, and

the product of the number of turns and the area of the inner coil section being equal to the product of the number of turns and area of the outer coil section.

7. A coil system comprising an inner coil section and an outer coil section connected to produce opposing fluxes of different magnitudes in the core of the inner coil section, the self-inductance of the outer coil section being equal to the mutual inductance be tween the coil sections, whereby the outer coil section forms a static shield for the coil system.

8. A coil system comprising inner and outer coaxially arranged cylindrical coil sections connected to produce opposing fluxes of different magnitudes in the core of the inner coil and a flux in the annular s ace between the coils, the self-inductance o the outercoil section being equal to the mutual inductance between the coil sections whereby the outer coil section forms a static shield for the coil system.

9. A coil system comprising inner and outer coaxially arranged cylindrical coil sections connected to produce opposing fluxes of different magnitudes in the core of the inner coil and'a flux in the annular space nected to produce opposing fluxes of differ.

ent magnitudes in the core of the inner coil section, the product of the number of turns and area of the inner coil section being related to the product of the number of turns and area of the outer coil section to produce neutralizing magnetic fields at a distance 7 and so that the self-inductance of the outer coil section is equal to the mutual induc tan e between the coil sections.

11. A coil system comprising an inductance coil section and a shielding coil section connected thereto, the area turns of the coil sections being related to produce neutralizing magnetic fields at a distance and so that the self-inductance of the shielding coil section equals the mutual inductance between the coil sections, whereby the shielding coil section forms a static and magnetic shield for the inductance coil section.

12. A coil system comprising an inner inductance coil section and an outer shielding co'l section connected so that the instantaneous currents traversing the same are in opposite directions, the product of the number of turns and area of the inner inductance coil section being equal to the product of the number of turns and area of the outer shielding coil section, and the length of the outer coil section being slightly greater than the length of the inner coil section whereby the outer coil section forms the static and magnetic shield for the coil system.

13. A coil system comprising an inner coil section and an outer coil section connected so that the instantaneous currents traversing thesame are in opposite directions, the ratio of areas of the outer to the inner coil sections being substantially two to one, and the product of the number of turns and the area of the inner coil section being equal to the product of the number of turns and area of the outer coil section,

/ and the length of the outer coil section being LESTER L. JONES.