US2438592A - Electrical condenser - Google Patents

Description

March 30, 1948. 5. Y. WHITE 2,438,592

ELECTRICAL CONDENSER Original Filed Dec. 8-, 1942 3 Sheets-Sheet 1 IN V EN TOR.

7WMe4/Z 7 viii wit 41.

March 30, 1948. s; Y. WHITE ELECTRICAL CONDENSER 3 Sheets-Sheet 2 Original Filed Dec. 8, 1942 S. Y. WHITE ELECTRICAL CONDENSER Original Filed Dec. 8, 1942 March 30, 1948.

3 Sheets-Sheet 3 INVENTOR.

cient to cover the projections.

. Patented Mar. 3c, 1948 ELECTRICAL CONDENSER Sidney Y. White, Wilmette, Ill., assignor to Victor S. Johnson, Chicago, 111.;

Alex Thomson, ad-

ministrator of said Johnson, deceased Original application December 8, 1942, Serial No. 468,195. Divided and this application October 15, 1943, Serial No. 506,374

3 Claims. (01. 175 -41) This invention relates to condensers of small size adapted to be used in radio and other electrical circuits.

It is an object of the invention to provide a condenser adapted to be adjusted substantially to a desired capacity by unit amounts through grinding. Such a condenser may advantageously comprise a dielectric base having integral therewith a multiplicity of spaced, abruptly rising projections on a face thereof, and a conductive metallic body covering said face to a depth sumare desirably of uniform shape and size.

The present application is a division of my pending application Serial No. 468,195, filed December'8, 1942, for Precision radio apparatus. The entire disclosure of said application is made apart of the present specification by reference.

Other objects and advantages will hereinafter appear.

In the drawing forming part of this specification Fig. 1 is a plan view of the body of an improved condenser which may be reduced in capacity to predetermined accuracy by grinding, and which may then be employed toadvantage in radio circuits;

Fig. 2 is a view in sectional elevation of the body of the condenser of Fig. 1;

Fig. 3 is a fragmentary view illustrative of a difficulty which the condenser of Figs. I and 2 is designed to overcome;

Fig. 4 is a fragmentary view in sectional elevation showing the grindin away of surplus capacity units of the condenser of Fig. 1 to produce a condenser of the desired fixed capacity;

Fig. 5 is a fragmentary view in sectional elevation further illustrating the effect of the grinding of the condenser of Figs. 1 and 2; and

Fig. 6 is a fragmentary plan view further illustrating the eiiect of the-grinding of Fig. 4.

The invention of the present application is not limited in utility to its employment in the illustrative apparatus of Serial No. 468,195. The use made in Serial No. 468,195 of the condenser which forms the subject of the present application is, however, illustrative of an important field of use of this condenser and is here briefly referred to for the purpose of indicating the importance and value of the structures herein claimed.

In Serial No. 468,195 disclosure is made of mobile radio apparatus for transmitting and receiving radio waves of ultra-high frequency. Such apparatus is subject to violent physical shock and to extreme variations of temperature. It is re- The projections quired to admit of extremely precise preset dial tuning and consistently and dependably provides for such tuning through the employment of highly disciplined tunable circuits in which no casual effects bearing on frequency are admitted, in which the parts are of rugged construction. and in which the circuit elements all have such definite and stable response to variations of temperature that variation of frequency with temperature may be reduced in the combination to a value of extremely low order. No wiring is employed in the tunable circuits.

In Serial No. 468,195 disclosure is made of a tuned circuit assembly comprising an inductance coil and a tank condenser, massive terminal blocks of the coil serving also as a conductive holder for the condenser. The condenser of Figs. 1, 2, 5 and 6 is particularly designed for use in a combination of this kind, although it very evidently has other fields of utility.

Both the real and apparent inductance of the tuned circuit assembly lower the frequency as the temperature increases, so a slightly negative temperature coeflicient condenser is used for tuning the circuit to provide a balance, resulting in very small change in frequency with temperature.

The condenser is desirably of the type that have very small temperature coefliicients of dielectric constant, and are quite satisfactory. It is difiicult,.however, to manufacture these condensers to a high degree of accuracy with respect to capacity, as for instance 0.1% or 0.2%, so that re course is desirably had to making the condenser.

tool large in capacity by a comfortable amount, and then grinding ofi the excess capacity. This can be well accomplished in condensers of this type, since the heat developed during grinding does not substantially change the dielectric constant of the condenser, and when the condenser cools off it will be substantially of the desired capacity.

A serious difficulty arises, when the ground condensers are either aged or heat cycled, in that they change capacity by a rather important amount, as for instance 1%. This difliculty is overcome by the present invention.

is not a clean sharp break between the silverremaining on thecondenser and the exposed ceramic left after grinding off the silver. The nature of this intermediate zone is illustratedin the plan view of Fig. 3 and in the elevation view of Fig. 4, and is attributable to the combined roughness of the grinding wheel 23, the rounding of the wheel edge. and the non-linear surface of the ceramic 285. As will be seen from an examination of Figs. 8 and 4, the intermediate ground zone includes little islands 23B of silver,

and little peninsulas of silver, the latter connected by narrow random necks 238 of silver to the main silver body 239. There is no definite pattern at all, but simply a rough surface of mingled silver and ceramic of all possible detail. It has been found that the explanation for the inevitable lowering of capacity of such a ground condenser'is due to the oxidation of the necks connecting these peninsulas of capacity with the mainland of silver. It has not been found practical, even by using a diamond wheel, to avoid this intermediate zone, because of its extremely small dimensions.

To overcome this indefinitenss, and still allow, grinding to capacity, the improved condenser 2% shown in Figs. 1, 2, 5 and 6 is provided. The ceramic base 24 i of this type of condenser is produced by pressing, and not by extrusion, and the specific improvement lies in the provision of a number of pyramids 242, so that the base resembles a waffle iron. Silver is'flowed into the base 24! and over the tops of these pyramids 2 32 to form one plate 243 of the condenser. The silver is also flowed over the other side of the base it! which has no detail, to form the other plate 2% of the condenser. As shown in Fig. 5, a wheel 245 of very small radius is used to grind the silver off the top of these pyramids and to grind away the pyramids to a depth suficient to clean off any ambiguous traces of silver which might otherwise be left on the tops of the pyramids because of the depth of detail in the surface of the ceramic. Therefore, every time we grind all the metal off the top of one of these pyramids, we have reduced the capacity of the condenser b a definite amount, and since we are grinding the ceramic on edge, as it were, a sharp line of demarcation is left with no zone of uncertainty. A long leakage path between the two plates of the condenser is assured by the provision of rims 246.

Experience has shown that, if we attempt to grind away a thin flat condenser by rindin away its edge, due to the small cross-section of the condenser and its consequent thinness a very small leakage path is left, and in addition streaks of silver may be deposited across the small area of ceramic to form partial or complete short circuits. The rims 2 obviate these difiiculties.

It will be noted that the capacity is removed.

I have described what I believe to be the best embodiment of my invention.- I do not wish, however, to be confined to the embodiment shown, but what I desire to cover by Letters Patcut is set forth in the appended claims.

I claim:

1. A condenser adapted to be adjusted substantially to a desired capacity by unit amounts through grinding, comprising a dielectric base having integral therewith a multiplicity of duplicate spaced, abruptlyrising, island projections on a face thereof, the projections being of equal predetermined height and of equal predetermined cross-section a conductive, metallic body accessible for grinding and covering said face to a depth sumcient to cover the projections, and a further conductive metallic m covering the opposite face of said base and disposed equidistantly from the tops of a plurality of the projections.

2. A condenser-adapted to be adjusted substantially to a desired capacity by unit amounts through grinding, comprising a dielectric base having integral therewith a multiplicity of spaced, abruptly rising, flat-topped, island projections of uniform, predeined area and uniform, preof the projections.

3. A condenser adapted to be adjusted substantially to a'desired capacity by unit amounts through grinding, comprising a dielectric base' having integral therewith a continuous peripheral flange of uniform height, and having integral therewith a multiplicity of spaced, abruptly rising, flat-topped, island projections disposed within the area surrounded by the flange the "projections being of equal predete w :1 height and of equal predetermined cross-section, a conductive metallic body accessible for grinding and covering the areaof the base surrounded by the flange to a depth sufficient to cover the projections, and a further conductive metallic body covering the opposite face of said base and disposed equidistantly from the tops of a plurality of the projections.

SIDNEY Y. WHITE.

REFERENCES @ETED The following references are of record in the file of this patent:

, UNITED STATES PATENTS Number Name Date 1,517,370 Marbury 2, 1924 2,303,391 Rosenthal Dec. 1, 1942 FOREIGN PATENTS Number Country I Date 6,575 Great Britain 1914 615,146 Germany June 28, 1935. 660,890 Germany June 4, 1938

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