US2494502A

US2494502A - Electrical capacitance device

Info

Publication number: US2494502A
Application number: US542192A
Authority: US
Inventors: Harold E Barnes
Original assignee: FERRIS INSTR LAB
Current assignee: FERRIS INSTR LAB; FERRIS INSTRUMENT LABORATORIES
Priority date: 1944-06-26
Filing date: 1944-06-26
Publication date: 1950-01-10
Anticipated expiration: 1967-01-10

Description

Jame m, 19% H. E. BARNE$ 5 ELECTRICAL CAPACITANCE DEVICE Filed June 26, 1944 5 Sheets-Sheet l HAROLD E. BARNES INVENTOR ATTORNEY Jan. 10, 1950 H. E. BARNES 2,494,502

ELECTRICAL CAPACITANCE DEVICE Filed June 26, 1944 3 Sheets-Sheet 2 PEG. 2

@ sl sa SIQRSZ 5% RI RI 52 HAROLD E. BARNES ENVENTOR ATTORNEY 1950 H. E. BARNES 2,494,502

ELECTRICAL CAPACITANCE DEVICE Filed June 26, 1944 3 Sheets-Sheet 3 HAROLD E. BARNES INVENTOR ATTORNEY Patented Jan. 10, 1950 ELECTRICAL CAPACITANCE DEVICE Harold E. Barnes, East Orange, N. .L, assignor to Ferris Instrument Laboratories, Boonton, N. 1., a corporation of New Jersey Application June 26, 1944, Serial No. 542,192

1 Claim.

My present invention broadly relates to improvements in electrical capacitance devices, and particularly in such devices as may be required to serve unreplaced in a single unit in otherwise changeable circuits therein having to handle high, very high and ultra high frequency electrical alternating currents; and my present application for patent is a continuation-in-part of an application for Letters Patent of the United States by me filed April 14, 1942, given Serial No. 438,884, now abandoned.

A first object of my present invention is to bring about such a high degree of stability in the building of the mechanism of the capacitance device involved that due to it, in conjunction with circuits of a single unit designed to handle high, very high and ultra, high frequency electrical alternating currents with exceptional precision with respect to all of the currents, the usual mechanical irregularities that would normally bring about failure to reach this goal would thereby be substantially abolished. In this connection, the number of parts is reduced to an absolute minimum, the rigidity of the respective parts is not left in doubt, artificial afiixing of respective parts to each other is substantially abolished, the adaptability of the parts for stable. mounting is not left in doubt, the truenesses of the respective active capacitance surfaces are not left in doubt and reasonably perfect control of the dielectric spacing between the active capacitance surfaces is not left in doubt.

A highly important object of my present invention from the point of view of its electrical activities under the. operating conditions in which I am particularly interested is the one of making the device involved effectively less pregnant with impediments to unfettered electrical activities while the electrical energy involved is actually in action within the confines of the respective parts of the capacitance device involved, and I have in mind in particular those impediments to free movements of'the electrical activities within the confines of such devices due to the inherent therein inductive reactances and ohmic resistances. In this connection, it is axiomatic that a given amount of electrical energy with a given amount of force behind it will move more freely in a broad'path than in a. narrow path in proportion to the ratio between the broadness and the narrowness, and that the difference in potential between any two points in the path of movilig increases in proportion to the reductions in cross-sectional areas of the paths involved; plus it being'necessary to take into account in dealing with electrical alternating currents that the inductive reactances increase with increase of frequency.

With the electrical phenomena being as stated,

'in working up a capacitance device in accordance with my present invention for a required coverage in the generation of electrical alternating currents ranging in frequency from 20 to 250 megacycles as one stringent example, it was found that it was altogether due to the bringing to bear the remedies I apply to reducing the inherent impediments involved that the results thereby attained fully measured u to the precision requirements involved, the significant reasons for which will later be more in full set forth.

In considering the importance of my present invention in connection with high, very high and ultra high frequency work of the kind involved, another pertinently important matter is that in using the capacitance device involved with artificial inductance to form tunable circuits, its variation in capacitance more often than not will have to be devised so as to follow some exponential law depending upon the characteristics of the inductance with which used. The versatile in this respect means my present invention brings to bear for accomplishing this object will later be more in full set forth.

It is believed that other lesser important objects of my present invention will be readily apparent to those competently familiar with the particular art.

Having broadly outlined the underlying objects of my present invention, with the aid of the illustrative figures of the accompanying drawings in which repeated lik symbols refer to like in function at lea-st parts, it will now be more fully elaborated upon and described in the treatment to follow.

Fig. l constitutes a perspective view of my capacitance device in a form somewhat incomplete in assembly.

Fig. 2 constitutes an end cross-section of Fig. 2 through the mid portions of the elements Ti and T2 view.

Fig. 3 adds to a side view of element RI of Figs. 2 and 3 the assembly elements missing in Fig. 2.

Fig. 4 schematically illustrates three ways in which the capacitance device of my present invention can become the capacitance element of an electrical circuit.

Fig. 1 displays in perspective the novel nature of the capacitance device of my present invention, and due to the special features of its novelty, with careful design of inductances, I have been able to make it serve most satisfactorily as a sole variable in capacitance electrical capacitance device in a sole generator of a signal generator covering with margin to spare at both ends the very high and ultra high frequency range of to 250 megacycles. This certain capacitance device of my present invention is further displayed in Figs. 2 and 3 in life size by being drawn to actual scale.

In the figures in which the symbols SI and S2 occur, they display substantially duplicate stators each terminated in a cylindrical terminal symbolized by TI and T2, respectively, preferably manufactured to be integral therewith;

and where RI occurs it displays a unitary rotor supported by a pivoted support T3 preferably manufactured integral therewith. Each stator is indicated as having a sloping side to match a corresponding sloping side of the rotor to give each more surface overlapping with the other. In the case of a choice of stator, rotor, terminals and support material, preference is given to materials having the best obtainable electrical conductivity, and unless some special advantage is to be obtained by not doing so, it is preferred to make all of them solid throughout. In the case of the pivoted at P upright lever N, it is also preferred that it be solid and integral with support T3.

To make the capacitance involved variable, the first step is the one of moving the rotor RI up or down as the direction of variation may require in its interposed relation to the two stators, and because the force of gravity is entirely relied upon for the downward movement, it is important to so mount the stators that the plane of the cross-section of Fig. 2 is maintained in parallel to the lines of force of gravitation, this kind of mounting being displayed by what is shown in Fig. 2. With lever N being integral with support T3 and rotor RI, either by manufacture or assembly, Fig. 3 makes it pictorially clear that any right or left movement of it will be correspondingly converted into upward or downward movement of rotor RI. A second step of making the capacitance involved variable is the one of selectively connecting up the dielectric spacings in the respective three manners diagrammatically displayed in Fig. 4 whereby, other things being equal, with the dielectric spacings in parallel the maximum of capacitance is obtainable, with only one dielectric spacing in circuit the capacitance obtainable is reduced to about one-half and with the two dielectric spacings in series the capacitance obtainable is reduced to a minimum.

To gain control over any law the capacitance variations will follow, the cam C displayed in Fig. 3 is my answer. As displayed, a roller D is mounted on one side of lever N, preferably near its upper end to gain the maximum of leverage, and a cam C is so mounted along with an indicated knob K that its rim makes and maintains contact with the roller rim, the contact being maintained substantially perfect because it is unrelentingly called upon to withstand all of the force of gravity acting on the solid masses of rotor RI and support T3 which force, because of the combined weight of the massive elements involved, is most effective in keeping the elements involved rigidly anchored to the location determined by cam C. A knob K may be used to control cam C, and to make the control easier under the pressure exerted by roller D, gear mechanism interposed therebetween is a ready answer.

I have found that the cam C may be shaped to cause by its rotation variations in the resulting capacitance following any exponential law that may be found to be wanted in using my device with inductances in electrical circuits, and have used this helpful attribute in many ways including compromising to meet an approximate average with six separate inductance units found necessary to cover six bands in the 20 to 250 megacycle range of the signal generator previously mentioned. This accomplishment has materially facilitated the laying out of the scale divisions covering the whole range of frequency operations on a single panel dial associated with knob K and C. Because Fig. 3 is drawn to full scale including cam C, due to the lack of drawing sheet space therefor, as shown, a portion of it is indicated as having been left out.

In connection with safeguarding against lost motion in the joint pivoting of support T3 and lever N, as evidenced by the support T3 being marked as having a cross-section of one square inch, the journaling' of the pivoting is even greater than one inch in diameter and is 1ongitudinally effective for at least one inch, from which it is clearly obvious that due to the very light duty involved the safeguarding against lost motion has been worked out to be substantially perfect. Also, that due to support T3 having a cross-section of one square inch, rotor RI is too firmly anchored to at any time swing the least bit out of place, and that because RI and T3 are massive in all respects, they are substantially immune to vibrations of any kind, or at least at any frequency sufficiently high to be detectable. Clearly, what applies to RI with respect to vibrations applies with more force to stators SI and S2.

.As to making my capacitance device much more effectively than usual less pregnant with impediments to unfettered electrical activities while" the electrical energy involved is actually in action within the confines of its respective parts, I have found that in the absence of so doing the magnitudes of inherent inductances found within the confines of capacitance devices in general impose frequency limits beyond which it becomes mechanically impossible to devise artificial inductances with sufficiently low inductances as to be able to extend the frequencies of operations high enough to meet present day needs therefor, and it was in a search for an answer therefor that I came upon my present invention.

Referring to Figs. 1 and 2, they display in terminals TI and T2 three-quarter inch in diameter cylindrical channels through which to freely feed any quota of electrical energy being dealt with into the greatly expanded bodies of stators SI and S2, so that from then on the paths to the areas marked out by the respective dielectric spacings become in effectsubstantially infinite in number with whatever little crowding there may initially be becoming greatly diminished as the respective distances from entry increase, plus the .further great advantage that none of the distances are at all excessive and the overall average distance, being as it is nothing over two inches, being insignificant compared to what has previously prevailed in typical variable capacitance electrical capacitance devices.

i To 'keep the capacitances low enough to serve in the region of ultra high frequencies involved, I connect up so that the capacitances between rotor RI and stators Si and S2 respectively, are used in a, series relation. From a glance at Fig. 2 in particular, it is perfectly clear that with this connectionany quota of electrical energy coming into action through either terminal Tl or T2 finds from there on to the other terminal an unusually wide spread path, so that the consequential inherent inductance bottle-neck is pro-- portionately dissipated over the wide spread path it is compelled to defend so to say. While so connected up, it is desirable to maintain rotor Rl at ground potential as by its indicated connection through support T3 to the grounding- G of Fig. 3.

When connecting up so as to bring the respective capacitances in parallel, as shown in the left hand one of the three different forms of connecting up displayed by Fig. 4, the support T3 is normally used as a feed in terminal for rotor RI. From a glance at Fig. 3 in particular, it is perfectly clear that due to rotor RI being made most unusually wide, there are unusually wide paths to the respective terminals TI and T2 which also prevents any effective crowding between the respective energy movements to the respective dielectric spacings. When the connecting up is reduced to rotor RI and one only of the stators, also displayed by Fig. 4, it is perfectly clear that this single duty given to rotor RI serves to make its task of dissipating inherent inductive reactance even lighter.

Referring to Fig. 4, its display of provision for a choice between a coil form of artificial inductance L and a rod form of artificial inductance L" typifies what has to be done in handling in a single unit electrical alternating currents of high, very high and ultra high frequencies, as somewhere in the range in moving upward rods only give low enough inductances to permit of carrying on with the minimum in series capitances connecting up. The indicated switching mechanisms IS and GP for making these choices may be automatically controlled from knob K of Fig. 3.

The deductions herein offered as to the relative potencies of the ohmic resistances and inductive reactances in particular under diflierent conditions of confinement, distance of travel and frequencies of reoccurrence are not solely based on technological theorizing, as it is a simple matter to detect and measure the same as between two separated points on or within the conductil'lg mediums involved with commercially available instruments plenty enough sensitive for the purpose.

Of all of the dimensions of the highly conductive mediums involved, three-eighths of an inch is the smallest, it being the bottom crosswise dimension of each of the stators, each of which has a top crosswise dimension of one and nine sixteenths of an inch, making the average crosswise dimension of each stator close to one inch. Since each stator is four inches long, the average area of the path through which the electrical energy moves is accordingly of the order of four square inches, and it is perfectly clear that the corresponding area in the case of the rotor is more than twice that amount. Because no part of the energy involved has to travel as much as three inches in any one unit per se, it is perfectly clear that the usual inherent ohmic resistance and inductive reactance bottle-neck has been majorly wiped out even in cases of ultra high frequency electrical alternating currents in so far as the variable capacitance device of my present invention is concerned.

To make the dielectric action throughout the respective areas thereof substantially uniform, the displayed sloping surface facing the same are painstakingly smoothed to the right slope, and, in assembling the parts for use, the sloping surfaces are painstakingly adjusted to be substantially parallel to each other when the spacings are reduced to minimums without making contact therebetween. As displayed by Fig. 2, the sloping of the surfaces of the particular device I have described as a typical example of what is required in the practice of my present invention is approximately 27 degrees, and in spite of this quite considerable degree of sloping, the smallest one of all of the dimensions is the quite substantial one of three-eighths of an inch previously mentioned. In other words, the all important massiveness responsible for the highly significant results that have been obtained in the exceedingly stringent field of operations herein dealt with completely permeates all zones of activities.

From the foregoin statements with respect to the abnormally large physical dimensions employed in the make-ups of the respective elements of the variable capacitance electrical capacitance device of my present invention, it is perfectly and technologically clear that they as a matter of fact greatly exceed anything needed from a straight out physical properties point of View, and would, therefore, be physical freaks from any practical and economical points of view if the special electrical per se need therefor did not exist.

While I have described my present invention in certain confined respects, it is apparent that modifications may be made, and that no limitations are intended other than those imposed by the respective scopes of the appended claim.

What I claim as new, and desire to secure by Letters Patent of the United States is as follows:

A variable electrical capacitance device having low overall inherent inductance making it suitable for use with bar type inductances in electrical resonant circuits operating at frequencies of the order of 250 megacycles per second or more, comprising a movable element formed of an elongated solid block of conducting material having a uniform trapezoidal cross section forming a pair of parallel faces and a pair of similarly and oppositely slanted plane faces, all the sides of said trapezoidal cross-section having dimensions of the same order of magnitude, and a pair of symmetrically arranged fixed independent relatively insulated fixed stator sections, each stator section being formed as a solid block of conductive material of massive configuration having a plane face parallel to and spaced uniformly from a respective one of said slanting plane faces of said movable element, each said stator section having a trapezoidal cross-section whose sides have dimensions of the same order of magnitude, said movable element being mounted for adjustment adapted to maintain said plane faces in substantially parallel variably spaced relation throughout the entire range of said adjustment and a pair of substantially cylindrical terminal post members each integrally formed with a respective one of said stator sections, and each extending outward from a face of its stator section adjoining its said plane face; said two terminal post members being adjacently parallel and of substantially equal extent, whereby they are adapted to be directly connected to a bar-type inductance element of minimum in- REFERENCES CITED The following references are of record in the file of this patent:

' UNITED STATES PATENTS Number Number Name Date Crosley May 19, 1925 Wittgenstein Apr. 19, 1927 Volet July '7, 1936 Melicharek Dec. 27, 1938 Eickemeyer Mar. 26, 1940 Rinia Apr. 15, 1941 Caplin et a1. July 18, 1944 FOREIGN PATENTS Country Date Great Britain May '7, 1925 Great Britain Sept. 14, 1934 France Apr. 1, 1925