US2238381A - Image analyzer - Google Patents

Description

April 1941- J. c. BATCHELOR 2,238,381

' IMAGE ANALYZER" Filed March 12, 1938 v L INVENTOR Patented Apr. 15, 1941 UNITED STATES PATENT OFFICE 6 Claims.

My invention relates to improvements in television scanning devices of the electronic type, and particularly to those having a mosaic-type screen structure.

One form of scanning device for television transmission comprises a tube provided with a mosaic screen, means for developing a ray of electrons and directing the ray at the screen, and means for deflecting the ray to cause it to scan a given area of one surface of the screen, upon which surface an image of the View or object to be transmitted is projected. Various forms of screens for such a cathode ray scanning device have been proposed, but all of these screens have the same general character as the typical example which is described in United States Patent 2,065,570. This particular form of screen comprises, essentially, an insulating base member provided on one surface or side thereof with individual, minute, photosensitive, metallic elements insulated from each other and spaced substantially uniformly apart. On the opposite surface or side of the insulating base member, and often integrally affixed to the member, is an electrode from which the picture signals are taken by a suitable connection thereto, and which is common with respect to and constitutes with each of the photosensitive elements a capacitor.

In operation, when the object to be transmitted is illuminated and an image thereof is projected individual elements, which action manifests itself by the assumption of corresponding electrostatic charges by these elements. The ray of electrons is rhythmically deflected to cause it to scan a given, usually rectangular area of the photosensitive surface, during which action the electrostatic charges previously assumed by the individual, photosensitive elements are discharged to develop the picture signals. The ability of the scanning device to develop picture signals in faithful correspondence to the light image of the object, depends to a large extent upon the capability of the minute, individual elements to accumulate the electrostatic charges, and to retain those electrostatic charges until the elements are struck by the electron ray. Furthermore, the amplitude of the picture signals developed at the mosaic screen of the cathode ray scanning tube is a function of the capacitance of the individual capacitors over the mosaic surface. In the various constructions of screens proposed heretofore for cathode ray scanning tubes, the capacitance of the individual capacitors has been more or less limited on account of the characteristic of the construction. That is, between the individual, photosensitive elements and the electrode common thereto, there has been a relatively large amount of the dielectric material of the supporting base member, and in the prior constructions it is not feasible to increase the capacitance of the individual capacitors on account of the practical constructional difficulties which are encountered. Although the value of the capacitance has been increased somewhat in certain types of construction of which that described in United States Patent 2,045,984 is typical, the difficulty of constructing and of producing this type of mosaic renders it considerably less than satisfactory.

A further disadvantage in the early mosaic screens is the relatively high ratio of the mutual capacitance between adjacent elements to the capacitance between any given element and the electrode on the backsurface of the base member. This stray capacitance has the eifect of reducing the effective sensitivity of each element of the mosaic.

With the foregoing in mind, it is one of the objects of my invention to provide an improved cathode ray scanning device of the general type referred to, in which the construction is such as to provide that the capacitance of the individual capacitors over the mosaic, photosensitive surface of the screen is substantially greater than such capacitances in the various scanning tubes used heretofore, with the result that the magnitude or strength of the picture signals developed at the screen is substantially greater than that in the prior constructions operating under similar conditions.

A further object of my invention is to provide an improved mosaic element for use in a scanning device of this type and includes, as an essential feature, the method of producing such a mosaic member.

Other objects and advantages will be evident from the description which follows.

In accordance with my invention, the mosaic photosensitive screen of the cathode ray scanning tube is made in the form of a base part of insulating material provided, on the surface which is scanned by the cathode ray and upon which the optical image of the object is projected, with a grid which is common with respect to the individual capacitors and which constitutes one of the plates of each capacitor. Also, disposed on this same surface or side of the screen, and in the interstices of the grid, are discrete, photosensitive elements or particles constituting, respectively, the other plates of the capacitors. Since the photosensitive particles are on the same side of the screen as the grid or common electrode, and are spaced only relatively minute distances from the adjacent edges of the grid, the capacitance of the individual capacitors formed is substantially greater than the capacitance of the corresponding capacitors in the various constructions proposed heretofore for this same purpose.

For the purpose of illustrating my invention, an embodiment thereof is shown in the drawing, in which- Figure 1 is a simplified, diagrammatic view of a television transmitting system constructed and operating in accordance wth my'invention;

Figure 2 is an enlarged, fragmentary, detail view of the mosaic screen, looking toward the right in Figure 1;

' Figure 3 is a section-a1 view, the section being taken on the line 33 in Figure 2;

Figure 4 is a view similar to Figure 3, showing a modification; and

Figure 5 is a schematic View of certain apparatus useful in the production of the mosaic screen.

In the drawing, the reference numeral I0 designates an evacuated tube provided with a screen l2 of my improved construction, and with means in the form of an electron gun l4 for developing a ray it of electrons and directing the ray at the screen. In operation, the ray I6 is simul taneously deflected horizontally and vertically by the coils I8 and 20 to cause it to scan a given rectangular area of the surface or side 22 of the screen, upon which surface an optical image of the object for transmission, such as a motion picture film 24, is projected.

The picture signals developed are taken from the screen by way of a lead-in wire 26 and fed to a suitable transmitter 28.

With reference now to Figures 2 and 3, the screen I2 comprises a base part 30 of insulating material provided on its surface 22 with a grid 32 of electrically-conductive material and with 1 particles 34 disposed in the interstices of the grid and spaced as shown from the adjacent edges of the latter and from each other. The base part 30 is made of mica or other suitable insulating material provided on the surface 22 with a coating of silver which may be engraved or scratched to form the pattern as shown in Figure 2, resulting in the grid 32 and the associated particles 34.

After the screen I2 is mounted in the tube It], the particles 34 are photosensitized in the well known manner, to provide each with a top coating or layer 36 or photosensitive material. It is seen that, during this operation photosensitive material may collect also on the exposed surfaces of the grid 32. If, for any reason, the presence of this material on the grid 32 is-undesirable it may be eliminated by the application to the lead-in wire 25 of a voltage which will prevent the oxidation of the surface of the grid 32 during the time when the photosensitive particles 34 are being oxidized for the purpose of accepting, for example, an alkali metal coating in acocrdance with the well known method of producing photoelectrically sensitive surfaces.

The screen construction just described providesa multitude ofdiscrete capacitors 38 disposed over the surface 22. The grid 32 is common with respect to the capacitors and constitutes one of the plates of each capacitor. The photosensitive particles 34 constitute, respectively, the other plates of the capacitors, and the capacitance of any capacitor is determined by the intervening space between the respective photosensitive particles 34 and the adjacent edge of the common grid 32. From this it will be seen that the capacitance of the individual capacitors 38 is substantially greater than would be the capacitance of the capacitors in the prior construction referred to in which the common electrode or common plate of the capacitors is on the surface or side of the insulating base member opposite to the surface or side on which the individual, photosensitive elements are disposed.

For the purpose of improving the electrical contact between the extensions 46 on the leadin wire 26 and the grid 32, I have found it convenient to apply one or more strips, or even a complete margin, of metal film such as platinum on the support screen I2, and such strips may be seen more clearly in Figure 5, in the electrodes 4| and 42.

For the purposes of still further increasing the capacitance of the individual capacitors when this is desirable, the spaces between the photosensitive particles 34 and the adjacent edges of the grid 32 are filled with a suitable insulating or dielectric material such as, for example, calcium fluoride. This may be done by evaporating the material to cause its application in the interstices of the grid 32 and to the surface 22 of the screen, after which the exposed surface of the grid 32 and the particles 34 is polished off with a mild abrasive so that the insulating material 40, remaining between the particles 34 and the adjacent edges of the grid 32, is flush with the surface thereof, as shown in Figure 4. The individual capacitors, therefore, will-have a greater capacitance than is the case in the embodiment shown in Figures 2 and 3, this being caused by the fact that the interstitial material has a dielectric constant substantially greater than would the vacuum which would otherwise exist in that space.

Having now described one embodiment of my invention, I shall proceed to a description of a method of producing my improved mosaic structure which I have found to have particular advantages,

In a manner similar to that described in considerable detail in United States Patent 2,065,570 previously referred to, I deposit on the surface 22 of the screen l2 a substantially uniformly distributed layer of a metallic compound, for example silver oxide, by permitting the powder to settle from a substantially suspended condition in the air over the horizontally disposed surface 22 of the screen I2, all in Figure 5; I

then connect between the electrodes 4| and 42 an external electrical circuit as shown including the battery 43 and the current indicating device 44 in a manner such that the continuity in the electrical circuit across'the screen 12, through the powder 45, or its product, will be indicated by the current indicating device 44.

With the circuit so connected, I subject the screen l2 carrying thepowder 45 to an atmosphere whose temperature may be of the order of 800 degrees centrigrade for a period of, for example, 20 seconds. During the period of exposure to the high temperature atmosphere, I prefer to observe the current indicating device 44 continuously. At the moment of application of high temperature, no indication will exist on the indicating device 44 but after'a short exposure to the reducing'influence of the heat, a relatively large reading will appear signifying the existence of a substantiallycontinuous electrical circuit between the electrodes M and 42. I continue the application of heat until the reading of the current indicating device decreases to a point which indicates an increase of electrical resistance between the electrodes 41 and 42 to a value which may be, for example, twice the minimum value of resistance, whereupon the screen I2 is quickly removed fromthe influence of the heat. 1

' During the application of this process, I believe that the preliminary exposure and the high temperature atmosphereoperates to reduce the compound to a metallic state, and the resulting.

metal tends to form a uniform film over the surface 22. The continued application of heat causes the film to break up into a multiplicity of discrete globules, and, because of the fact that this breaking up is not an instantaneous phenomenon, it may be interrupted at a point where it has been only partially completed, with the result that a metallic film grid corresponding to the grid 32 in whose interstices is a multiplicity of discrete particles corresponding to the particles 34, is produced.

The mosaic element thus produced is utilized in the tube l and is likewise treated by any of the known processes to render the discrete particles of metal photoelectrically sensitive.

It will be recognized that the process just described will be correct only when the surface tension of the metal with respect to the surface 22 of the screen I2 is such that the metal tends to become a multiplicity of globules rather than to wet the surface 22 to form a continuous film. If, on the other hand, the metal tends to become a thin film on the surface 22, the preferred procedure will be to heat the screen [-2 carrying the powder 45 to a temperature sufficient to reduce the compound to a metallic state and to continue or increase the heat until a portion of the discrete particles which are first formed have fused together to form a grid having interstices containing the particles which at that point remain unaffected by the greater heat. In this instance, it will be recognized that the current indicating device 44 will continue to give no indication until such time as particles form a continuous electrical circuit between the electrodes 4| and 42. Experimentally, the minimum resistance as reflected by the maximum indication of the device 44 may be determined after which the intermediate reading of the indicating device 44 at which the application of heat should be stopped may be deduced for use in producing my improved mosaic structure.

It may be seen that the optimum amount of decrease in electrical conductivity in the first instance, and increase in the second instance, between the electrodes 4| and 42 may best be determined experimentally by producing a number of mosaic elements in accordance with my process with successively diiferent amounts of resistance change, and observing microscopically the quality of the resulting mosaic.

As a modification of this process just described, I have found certain advantages to exist in a method of mosaic production which involves the use of a rarefied atmosphere to assist the reduction of the metal compound to a metallic state. As an example of this process, I have found it convenient to apply a layer of metallic compound on the screen l2, whereupon, the member carrying the powder is inserted in a vacuum bell jar and the member is preferably placed upon a platform adapted to be heated, for example, by radio frequency induction. By an appropriate combination of the proper degree of exhaustion of the bell jar and of heating of the screen [2, I have found that it is possible to control with great accuracy the proportion of the metallic powder which, upon reduction, becomes a portion of the grid, and the portion which contributes to the production of discrete globules which form, in cooperation with the grid member, the individual capacitor units. It is believed that the optimum relation of the quantity of metal in the grid to the quantity in the discrete particles will approach that which exists in the device disclosed in the United States Patent 2,045,984 between the volume of metal in the mesh and the volume of the metal filling the interstices of the mesh. It may be seen that in many instances, departures in one direction or the other from this relation will be indicated, however.

Still further, in many instances, I have found it desirable to replace the vacuum in the bell jar just discussed with a reducing atmosphere such as, for example, hydrogen which materially assists the reduction of the compound and, when the pressure of the gas is properly controlled, materially assists in producing a mosaic having a desirable distribution of the metal between the grid and the particles.

It will be recognized that the method of increasing the values of the capacitors 38 which comprises filling the interstices between the photosensitive particles 34 and the grid 32 with a material of relatively high dielectric constant is equally applicable to the mosaic element produced in accordance with the method described in reference to Figure 5, and similar advantages will result from the introduction of this feature.

I claim:

1. A mosaic electrode structure which comprises a plane 'imperforate insulating base, an electrically conductive grid formed upon said insulating base and supported exclusively by said base, and a multiplicity of isolated metallic particles microscopic in size formed upon said base and in the interstices of said grid and supported by said base coplanar with but independently of said grid.

2. A mosaic photosensitive electrode structure which comprises a plane imperforate insulating base, an electrically conductive grid formed upon said insulating base and supported exclusively by said base, a multiplicity of isolated metallic particles microscopic in size formed upon said base in the interstices of said grid and supported by said base coplanar with but independently of said grid and a photoelectrically sensitive surface layer on the exposed surface of said metallic particles.

3. An electronic scanning tube comprising an envelope, an electron gun and an image screen within said envelope; said screen comprising a plane imperforate insulating base, an electrically conductive grid formed upon said insulating base and supported exclusively by said base, a multiplicity of isolated metallic particles microscopic in size formed upon said base in the interstices of said grid and supported by said base coplanar with but independently of said grid, and a photoelectrically sensitive surface layer on the exposed surface of said metallic particles presented toward said electron gun.

4. A mosaic electrode structure which com- Within said envelope, said screen comprising a plane imperforate insulating base, an electrically conductive grid formed upon said insulating base and supported exclusively thereby, a multiplicty of isolated metallic particles formed upon said base in the interstices of said grid but smaller than said interstices, said particles being supported by said base coplanar with but independently of said grid, dielectric material in the remaining space in said interstices between said particles and said grid, and a photoelectrically sensitive surface layer on the exposed surface of said metallic particles presented toward said electron gun,

6. A scanning device comprising a tube provided with an image screen; means within said tube for developing a ray of electrons and directing said ray at said screen; and means for defleeting the ray to cause it to scan a given area of one surface of said screen, said screen comprising a plane imperforate insulating base, an electrically conductive grid formed upon said insulating base and supported exclusively thereby,

' a multiplicity of isolated metallic particles formed upon said base in the interstices of said grid but smaller than said interstices, and a photoelectrically sensitive surface layer on the exposed surface of said metallic particles presented toward said electron gun.

JOHN C. BATCHELOR.

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