US2957140A - Cathode ray signal storage device - Google Patents

Description

Oct. 18, 1960 F. H. HARRIS 2,957,140

CATHODB RAY SIGNAL STQRAGE DEVICE 3 Sheets-sheaf 1 Filed May 1, 1957 INVENIOR FRANKLIN H. HARRIS BY W W ATTORNEY) Oct. 18, 1960 F. H. HARRIS 2,957,140

CATHODE RAY SIGNAL STORAGE DEVICE Filed May 1, 1957 s Sheets-Sheet 2 INVENTOR FRANKLIN H. HARRIS BY WW 7/! MM ATTORNEY Oct. 18, 1960 F. H. HARRIS CATHODE RAY SIGNAL STORAGE DEVICE Filed May '1. 1957 3 Sheets-Sheet 3 mmljusz OmQ INVENTOR Amatimtnowzo 235 mQOOmOZOE t 7 53mm NEE; $2 5002 i623;

FRANKLIN H. HARRIS BY V fiW/ ATTORNEYS United States atent 2,957,149 Patented Oct. 18, 1960 CATHODE RAY SIGNAL STORAGE DEVICE Franklin H. Harris, Accokeek, Md., assignor to the United States of America as represented by the Secretaryof the Navy The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates generally to cathode ray signal storage devices, and more specifically to a cathode ray signal storage system capable of recording, storing and reproducing information signals for an indefinite number of repetitions. This invention also specifically relates to atwo-sided mosaic.

Cathode ray tubes are well known in the prior art which will perform the sequential functions of an information device, namely recording, storage, reproduction and erasure of an information signal. These electron discharge tubes operate upon the principle of translating received information into charges and coincident potentials upon the surface of an insulating material and subsequently recovering this information by exploring the surface with a focussed electron beam. As a result of the extremely high impedance offered by an insulator to the flow of current to and from a charged area, in the absence of a reproduction operation the charges and coincident potentials initially impressed upon the dielectric will persist without substantial deterioration over a period of time during which the information which they represent may be made available. -When elicitation of the information stored is accomplished, however, by scansion of the insulating surface with an electron reading beam, the information being recovered either as a secondary emission current from the dielectric or as capacitively induced current due to a shift in potential of the initially impressed potentials, in the prior art the information bearing charges and potentials are progressively destroyed with .successive repetitions of the reading operation. Thus in most of the prior art devices information reproduction can only be efiected by destructive reading.

'In my copending application Serial No. 288,365, filed May 16, 1952, there is disclosed a half-tone memory tube comprising three electron guns namely, a writing, a reading and a holding gun positioned in a triangular mount, and a storage surface or target capable of storing a signal for long periods of time. The storage target has a faceconsisting of an electrically conducting membet and an indefinitely large number of separated dielectric masses dispersed throughout the surface of the conducting member in suificient concentration so that a considerable number of these dielectric masses appear within an area approximating in dimension the spot of a focussed electron beam.

Thepresent invention is an improvement over my copending application and provides a two-sided mosaic consisting of a thinfilm of dielectric formed on an electroformed nickel screen. The new type of mosaic permits greater writing speeds and also provides a storage surface on which the information is written on one side of the screen and the information is read from the opposite side. This requires a rearrangement of the electron guns such that the read and write guns are directly opposite each other and on opposite sides of the storage surface.

The present invention also provides an improvement over the prior art tubes which have read and write guns on opposite sides of the storage screen. In the prior art devices a collector is associated with the screen in the form of a coating on the tube surface or a charged screen adjacent to the storage screen surface. The new mosaic tube of the present invention does away with the usual collector through the use of an improved storage screen which serves to carry out proper storage and also acts as the collector.

It is therefore an object of the present invention to provide an improved signal-storage device capable of half-tone storage and reproduction.

A further object is to provide a signal-storage device capable of storing and reproducing half-tone signals with substantially zero decay.

Still another object is to provide a signal-storage de vice which has good control, is simple in operation and relatively inexpensive to manufacture.

Yet another object is to provide an improved two-sided mosaic which is simply and cheaply manufactured and yet provides good control without any deterioration of the original stored pattern.

Other and more specific objects of this invention will become apparent upon a more careful consideration of the following detailed description when taken together with the accompanying drawings, in which:

Fig. .1 illustrates a cathode ray storage tube according to the present invention having a write gun on one end and a gun on the opposite end for both holding and reading. c

Fig. 2 illustrates the relative parts of the storage screen assembly shown in spaced relationship for simplification.

Fig. 3 is a schematic of the signal storage device illus trated in Fig. 1.

Fig. 4 is a block diagram of the storage tube of Fig. 1 and associated equipment simulating scan converter op eration.

Fig. 5 is a greatly enlarged cross section of the storage surface which illustrates the relationship between the metal screen and the dielectric.

Fig. 6 is an enlarged View of the mosaic screen structure.

In accordance to the present invention a cathode ray storage tube is provided which is capable of capturing a single frame of a television picture which has good tone quality. The storage tube can be used for scan conversion, signal integration, for capturing single transients, and for temporary storage of different patterns such as maps for radar display purposes.

The storage tube device is intended for storing electrical charges and comprises a storage surface including a conductive fine metal screen grid-like structure having a plurality of interstices to which a dielectric material is attached and which bridges the interstices. An electrode system is provided for projecting a recording or write cathode-ray beam onto the storage surface during writing intervals and for projecting a holding and reproducing or reading cathode-ray beam on the opposite side of the storage surface during reading. In writing, the write beam produces electric charges on the write side of the dielectric. The charges are stored as potential energy in an electrostatic field which exists partly within the dielectric, and partly in the space between the dielectric and the metal screen. The mechanisms of holding and reading utilize only the electrostatic field in the space near the screen and the field within the dielectric is of no value and therefore should be minimized. For this reason, the dielectric is formed as thin as possible.

Referring now to the drawings wherein like reference characters represent like parts, throughout, the device shown by illustration .in Fig. ,,1 comprises an evacuted glass envelope 11 which encloses a storage electrode or 'mosaic 12 and two conventionalcathode-ray guns .13

and 14. The cathode ray guns arepositioned respec: tively in opposite ends of the tube on opposite sides of the storage electrode and are magnetically focussed and deflected in the conventional manner as used in television picture tubes. Conductive coatings 15 and 16of silver paint are respectively provided on the inside and the outside of each end ofihe envelope, to shield the storage mosaichfrom. the electrostatic 'fields of the .deflection coil and yet does not interfere with the. magnetic fields. Theinner coatings 15 merge with transparent conductive coatings 17, such as, a metallic oxide, which serves as the second anodesand are transparent to facili tate inspection of ,the inside of the tube if desired. A cylinder 18 positioned within the envelope on the readbeam side of the storage mosaic serves to collimate the read-beam electrons inorder to' obtain equal values of forward electron'velocity over the surface of the mosaic. The collimating cylinder is provided with av ridge 19 a about the outer surface thereof'for the purpose of securing ,thecylinder ,within the envelope; for purpose of illustration, three. glass holders 21 are provided for securing the collimating cylinder in position. .The inner surface-of the collimating cylinder has three equally spaced tabs or lugs 22, attached thereto along one end about the inner circumference to provide meansfor securing the mosaic-surface, in'positionwith respect to the electron. guns. andvthe collimating cylinder. The tube is providedwith argetterj27 to keep the residual gas pressure low duringoperation. 7

Fig. 2 illustrates the relationship of the collimating cylinder and the mosaic surface. The mosaic surface is formed between two hoops or rings 23 and 24, one fitted into the other to hold the mosaic surface therebetween and then assembled between a metal disc 25 through which electrical connections are made tothe 4 limating cylinder and preferably positioned to receive the write beam on the dielectric side of the wire screen.

Fig. 3 is a schematic of the tube illustrating the operating voltages for the various elements and in operation of an assembled tube, magnetic focussing and electron acceleration is carried out by "conventional television type scan circuits 37 illustrated in block form by Fig. 4 in which the accelerating and focussingassernblies' are maintained at a positive potential with respect to'ground; The write cathode 41 is maintained at an 'ope'r'ating'negative voltage of about 1000 volts by any suitable grounded voltage source'not shown and has connected thereto a variable write beam current control 42 of 100 volts for controlling the period'duiing which writing proceeds. Electrons emitted, by thecathode are resolv ed inthe usual manner by the accelerating and focussing mechanism into a writing beam of small cross sectional diameter and high intensity, the intensity; pf whichmaybe modulated byinformation signals originating with an information signal source 43' and impressed upon the write control grid 44;in the-form of'varying voltages. The bias of the'control grid relative to the cathodemay be adjusted as desired by a variable'tap- 45 on the current control42 and has-a decoupling resistor 46 connected between the grid and the tap. The first anode 47 is placed at a relatively high potential such as positive 1.5 kv. with respect to the cathode and a second anode .48 is placed ata potentialstill-higher than the firstanode such as a positive 3 kv. with respect to thecathode. The second anode is the same as the inner .coating-17 and. has an'additional purpose of collecting secondary elec-. trons which escape from the mosaic. Between the first anode'and the write grid a'second grid 49 with a nega tive voltage of about 500 volts is placed. :The electrons from the write gun strikes the insulation 'with suflicient energy to generate secondary electrons inexcess of. the. primary electrons on the insulator; The. mosaicf is maintained at'zero potential and is brought out through an.

external load resistor 51 to ground. The video output from the mosaic is taken off'by a terminal between the resistor and the. mosaic and connected to the inputv circuitof a video' amplifier. 52 whichisthenconne'cted 'tol metaltscreen of the, storage surfaceand mica disc .26

made of several layers of mica by three bolts 28 .and nuts 29. .Any suitable insulators 31 such as glass, are provided to insulate the metal disc from the bolts and also to provide space between the metal disc 25 and mica disc 26 in which space the mosaic is positioned. Mica disc 26 has a metal disc 32 secured thereto by tabs 33 which are bent over along the surfaces of the metal disc 32 and connected to a few of the mica layers of the mica disc 26. Metal disc 32 iscut away in the vicinity of the bolts 28 and therefore does not have to be insulated therefrom. The end of bolts 28 are inserted through lugs 22 and connected thereto by nuts 34 and the'mica disc and the metal disc 25 is connected to the bolts by nuts 29 screwed on the ends of the bolt, the collimating cylinder and mosaic surface is now ready for assembly in the envelope and connected to the-proper lead lines from suitable pins in the connector 30.

The mosaic is made of a very thin metal screen 35 having a thickness from about 0.00005 to 0.0006 inch and with from about 300 to 1000 mesh per inch. The thin metal screen 'is covered with bentonite clay by a method to be described later to form a very, very thin dielectric surface 36 which fills the openings or interthe control grid of a monitoring cathode-ray picturev tube 53. I

The read beam and holding electron gun assembly 13 is located-on the opposite side. of the mosaic from the Write gun 14 and focuses the read beam -current' onto the metallic screen and insulatorcellsof the storage} mesh with a constantbeam current. The read cathode 54 has a negative potential of about 40 volts for holding without any decay. The cathode has connected thereto a read beam current control '55, which is connected to. a

" control grid 56 by a variable tap 57.. I A second control grid 58 having a positive potential of 400 volts relative to the cathode is positioned about. the cathode between control grid 56 and a first anode 61 which has a positivepotential of 1.5 kv. with respect to the cathode; A sec-.

- ond anode connection-'62 connects with the, inner coatstices of the screens and also covers the screen surfaces, 7

screen is negligible since it is so thin; therefore, in effect, the dielectric film in each of the interstices form individual isolated cells separated by the conducting portions of the screen. The mosaic is securedto the col-- ing 15 and the transparentcoating which forms the sec-. ond anode and has'an additional purpose of collecting stray electrons and to help protect the mosaic from elec-- trostatic forces. Collimating cylinder 18 having a positive potential of 350 ,v. is positioned on thereadrbeam side of the tube adjacent to mosaic 12 and serves to collimateat right angles'the read beam electrons with ref spect to the mosaic surface- -Metal disc 32 connected to' the mica plate 27 is electrically connected toan outside terminal and adapted to be vprovidedhwith a positive po-' tential, if additional, electron correcting features are re, quired for collimation. a f l In the preferred operation of the device, the insulator-'1 cells of the mosaic are erased and, prepared for writing by I priming to the black by. means of apriming cycle,

is done by scanning the insulator-cellswith a read bearn whose cathode voltage is nearly atzero, then dime about second, thecathode voltage is returned to a'holding voltage :value, V of about 40 volts. During the priming .cycle the insulator will accumulate electrons, negative charges and thus its coincident potential will take on a negative value similar to the instantaneous potential of the read-cathode voltage, and .thus maintain a low-velocity .of arriving read electrons, consequently, wery few secondary electrons are released by the surface. The e'flt'ect'iof priming .the. mosaic .is to .cause negative charges to appear on:the write side :of the insulator wherein during the writing period, electrons .Wlth about 1000- .volts energy :strike :the insulator "with ample velocity to generate-secondary electrons inexcesszof'the primary electrons from .the write cathode. The escaping secondary =electrons in excess of the number of beam electrons -'strik- .ing the insulator results in 'arnet .pos'itive charging of the insulator and results in writing on the mosaic. The esraping secondary electrons are collected by the positive coating of :the second :anode on the surface of the envelope.

'Inrreading the stored signal, the electrons from the read electron gun 13 providing the read 'beam are focused by suitable circuitry to scan the metallic screen mesh and insulator .cells of the mosaic with a constant beam cur- .rent. The read beam causes secondary electrons to escape from the metallic mesh at points where the insulating cells are charged positively While secondaries from the metallic mesh are supressed by grid action at the points where :the insulating cells are charged negatively. The .secondaries are emitted with very low velocities (approximately ,2 volts or less) and are therefore easily controlled by the nearby electric fields of the insulator :cells. The variations in secondary escape current from the conductive metallic mesh, owing to charges in the insulator cells, register as variations in the current through the load resistor 51 connected externally to the conductive mesh and constitute the output reading current. The load resistor 51 has negligible DC. voltage drop as a consequence of the read or write beam currents. Simultane bus with reading, the read beam regenerates original Writ- .ten charges Within each insulator cell by its holding action. The bombarding velocity has the same value of all parts :of the :mosaic because the deflection angles are cancelled out by the lens produced by the eollimating cylinder. At read-beam bombarding energies less than the critical potential V :(the potential of the bombarded dielectric portion with respect to the electron source, where the total number of secondary electrons escaping from the surface ofthe dielectric equals the total number of primary electrons absorbed by it) the insulator cells accumulate electrons and charge negatively to apotential V At readbeam bombarding energies higher than V the insulator cells lose electrons and charge positively to an equilibrium potential V where the potential of the insulator cells equals the potential of the conducting member. The holding action of the read-beam overcomes electrical leakage and other deleterious effects, and thus the charge pattern established by the write beam is maintained within :each storage cell at either the positive equilibrium potential V (white) or the negative equilibrium potential V (black).

A more complete and detailed discussion of the electrical operation of the mosaic due to the incident beam from the writing and reading gum is set forth in my copending application Serial No. 288,365, filed May 16, .1952.

It is to be understood that the new mosaic of the present invention can be used with a three gun tube wherein the read and write guns are on opposite sides of the mosaic and the holding gun is set off to one side on the read side of the mosaic. The operation of the holding gun is substantially the same as described in my referred to copending application and the holding beam is properly focussed onto the mosaic by the collirnating cylinder.

In operation of the two gun storage tube for long time storage the mosaic is primed to charge the insulator cells negatively in order to maintain low velocity of arriving read electrons, during priming negative charges are caused to appear on the write side of the insulator. Write electrons with 1000 volts energy strikes the insulator with ample velocity to generate secondary electrons in excess of the primary electrons. The excess secondary electrons escape to result in a net positive charge on the insulator which corresponds to writing white. The net positive charge remains on the insulator surface, then the read eam of a negative 40 volts is focused on the read side of the screen. The read beam .scans the metallic screen and insulator cells of the storage surface to provide secondary electrons. Due to the charge of the screen and Iinsulator,"thesecondaries are emitted with very low velocities and are easily controlled by the nearby electric fields of the insulator cells. The variation in secondary escape :current from the metallic screen mesh due to the charges in the insulator cells, register as variations in the current through the load resistor connected 'to the screen mesh and constitute the output signal (reading current) to'the cathode ray tube circuitry where the signal is reproduced on the screen of the cathode ray tube.

The mosaic comprises a thin dielectric film having a thickness of from about .02 micron to about 1.3 microns which bridge the openings of a fine mesh nickel screen having a thickness of about 0.00005 to about 0.0006 inch and from 300 to 1000 mesh per inch and formed according to the following method. The screen is placed over a nickel-plated steel ring 'or hoop 23, stretched taut and then held in position by placingring 23 into a second like ring 24 of larger diameter. In order to position ring 23 with the fine mesh over it into ring 24, ring 23 is cooled to shrink the ring and ring 24 is heated to expand it. The screen covered ring is then slid into ring 24 and therings are allowedto return to their normal temperatures whereby the screen and ring is held tightly in ring 24. The assembly is then cleaned by washing it in water with a detergent and then in acetone to remove any foreign solids, salts or oils. Then the assembly is placed on a level surface and water is applied to the screen surface for wetting purposes.

The dielectric film is formed from a preparation of bentonite clay hydrosol made from bentonite clay (montmorillonite) which is a natural mineral classed as an aluminosilicate Al (Si O -xH O. A refined form of bentonite clay hydrosol containing 2.3% solids by weight is diluted with distilled water to form a fluid which contains a much lower concentration of solids about 28x10" parts by weight. In percentage concentrations of 1% or more, the hydrosol has the property of being a thixotropic gel (the property of becoming fluid when agitated and returning to a gel when left undisturbed). The dilute 2.8 10 parts solid hydrosol appears to have the properties of viscosity and surface tension identical to those of distilled water and can be applied to the screen in liquid form.

The screen is prepared for coating as described above and the surface thereof wet with a pool of distilled water one to two millimeters deep for approximately twenty minutes. The small mesh of the screen and the surface tension of the water serves to prevent the water from going through the screen; however, if the screen is extremely clean the water will run through. In order to obviate this, the screen is purposely contaminated with any suitable solution, for example by immersing the screen momentarily in a solution of amyl acetate and l0-- parts by volume of collodion. This is allowed to dry and then the distilled water is placed on the surface as described above.

After the distilled water has been on the screen surface approximately 20 minutes, most of the water is drained off with the aid of an aspirator or any other convenient means. The removed distilled water is :immediately replaced with the 2.8 X 10* parts solid'bentonite The water evaporates from the solution and the surface of'tlie screen, to leave a' uniform film ofbentonite clay which weighs approximately 1.1 milligrams and having a thickness of 0.1 micron (4X 10" inches). The average thickness 'of the film is determined by'the formula (1 I (S.G.)A a

where d is the thickness in microns, w is'the weightin grams of the formed film, S.G.-the specific. gravity, and 'A is the area (cm?) of the covered screen. The above values for. forming the dielectric film .are typical values fora preferred dielectric film and other concentration of solidsmziy be used 'to form films having difierent thickness. Hydrosols containing 8.25 X l0 to 2.0)(- solids by weight will form suitable dielectric films having a t-hickness' of from about 0.02 micron to about 1.3 microns, the thickness of the dielectric film is limited by the thickness and strength of the screen surface. "If the hydrosol placed on the screen is too heavy the screen will tear away and films cannot be formed; therefore, the thickness of the film is limited to the strength of the screen. V

It is highly important that 'dustparticles do not settle on' the-screen during forming and that the film have uniform thickness. For this purpose the screen is placed ona stationary level stand or fiat surface'and a glass cover is placed over the screen as soon as the hydrosol has been placed on it. Since the screen is covered, drying'proceeds slowly wherein the water is forced to evaporate primarily from the underside throughthe openings in the screen. Since the hydrosol has approximately the properties 'of viscosity and surface'tension of distilled water, the fluid is pulled by gravity into the interstices of the screen wherein the fluid clings to the screen surface 'due to surface tension, this forms a uniform film within the interstices which is thicker than the film over the screen surface. When the water has evaporated and the film formed onto the screen, the screen is removed from the glass cover. The screen in this state can be used as a storage surface; however, the film does not demonstrate as low an electrical conductivity as mica and has slight electrical leakage therefore it is necessary to further treat the film to obtain the desired dielectric qualities. The bentonite clay film can be converted to a lowconductivity material similar to mica by either of the following two methods. In one method, the storage screen is removed from under the glass cover and placed in a container such as'a stainless steel vented container and heated at approximately 1000 degrees for minutes in hydrogen. The stainless steel vented container serves to shield the screen from the heating flame'of the'hydrogen furnace and also provides thermal lag which pre:

vents rupture of the storage surface when the container is removed from the furnace. The screen being thin would shrink more rapidly than the mounting rings and therefore would rupture if allowed to cool too rapidly. The storage surface is removed from the hydrogen atmosphere while it is hot (approximately 400 degrees centigrade) and cooled within the container in air. It has been determined that removal from the hydrogen at a temperature below y400 degrees centigrade makes the bentonit'efilm slightly conductive and when removed at temperatures greater than 400 degrees centigrade, a slight I 7 oxidation of the nickel screen occurs. Oxidation is not significantly harmful for operation in the tube of the present invention.

In another method of converting of the bentonite clay film to a low-conductivity material, the film is treated with lead. 'Bentonite clay dispersed in water is neces- 8 sa-rily sodium bentonite, therefore 'the dried film onthe screen is sodium -bentonite clay; 'The: assembly'bfzthe screen with the dri'edfilm' thereon is immersed in a concentrated lead-nitrate solution. :Atbase'exchange reaction occurs iniwhich the's'odiumi'of 'theffilrn is replaced by lead' After' about a five minute inimersio'nfin the leadnitrate solution,the assembly is r'emoved from'the solution, 'rinsedflwi'th. distilled water and then dried; The films are nonconductive and have the properties 'ofmic'a. Filnis'as thin as 20 millimicrons 'have'beenformed by this method, wherein such thin'films formed by the'firs't' method would disintegrate due to the higlrheat intensity. 'In'either method described above, the conductivity of the films is comparable to that of mica, and this, :com-

-bined .with their thinness results iii/negligible conductance along their planej Even though .the films are very thin, they can withstand the high bake tem'perature*(400 C.) required to outgas the tube; In addition sodium-'bentonite films have excellent mechanicalladherence tothen'ickel screens in order to form the thin films in the interstices of the screen and in which that portion of thefilm covering the conducting portions of the screen are thinner than that within the interstices." V

A mosaic formed according to the'above method combines'a metal screen and a very thin insulator in which the insulator is formed in. the interstices such that'the cells of the insulator are electrically. guarded one from the other by the conductor'screen. 'The read'beam bombards both the conductor and insulator. to fulfill read and hold functions, and the write beam can charge the insulator and control the field on the read sidef The Y iator surface in which it is essential that one face surface of the screen be in contact with the insulator material. For such tubes, the storage electrode made according to the above method'can be used wherein the dielectric film side of the storage electrode is used' as a substrate and an insulating material added theretoby any well known method such as the evaporation technique,'or the water dispersed'colloid suspension method. For example quartz, silicon dioxide or aluminum oxide'can be added to the bentonite clay film to increase 'thethickn'ess of the insulating'surfacei The application 'of the additional insulating surface'by the colloid suspension method is preferred since the liquid would flow into the interstices, fill the interstices and then provide a smooth outer-surface." In the evaporation method the insulation would build up over the screen surface as well as in the interstic'es. The method used depends on the outer surface desired. 7

The present invention is concerned with the use of thin dielectric films for the mosaic of a storage tube, however, it would be obvious to anyone'skilled in the art to use thin'dielectric films for other uses; therefore, it is to be understood, that within the scope" of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1; A signal storage device comprising incombination an information storage electrode said storage electrode comprising a conductive grid-like structure having a plurality of interstices and a secondary electron-emissive dielectricfilm distributed on a single surface of said structure and across said interstices in a plane midway between the outer surfaces of said grid-like structure said film portion across said interstices having a greater thickness than the thickness of said film covering the surfaces of said grid-like structure, a write electron beam source, means for intensity modulating said write beam, inaccordance with an electrical input signal representing an 9 image to be stored on said storage electrode, a read-hold electron beam source, means for focussing and deflecting said write and read-hold electron beams, collimating means for directing said read-hold electron beam onto one surface of said storage electrode, and means connected to said conductive structure for deriving an electrical output signal from said conductive structure which corresponds to an image stored on said storage electrode.

2. A signal storage device as claimed in claim 1 wherein said dielectric film is formed from a form of bentonite clay hydrosol having a concentration of solids from about 8.2 l to about 2.0 parts by weight.

3. A signal storage device as claimed in claim 2 wherein said conductive grid-like structure is a screen having a thickness of from about 0.00005 to about 0.0006 inch having from about 300 to 1000 mesh per inch.

4. A signal storage device as claimed in claim 2 wherein said conductive grid-like structure is a screen having a thickness of from about 0.00005 to about 0.0006 inch having from about 300 to 1000 mesh per inch and the dielectric film across the interstices having a thickness of from about 0.02 micron to about 1.3 microns.

5. A storage electrode for a signal storage device comprising a conductive grid-like structure having a plurality of interstices, a dielectric film distributed on a single surface of said grid-like structure, said film extending into and across said interstices in a plane midway between the outer surfaces of said grid-like structure, said film extending into and across said interstices having a thickness greater than the thickness of said film over said gn'dlike structure.

6. A storage electrode for a signal storage device comprising a conductive grid-like structure having a plurality of interstices, a secondary electron-emissive dielectric film of substantially uniform thickness distributed on one surface of said grid-like structure said film extending into and across said interstices in a plane midway between the outer surfaces of said grid-like structure said film across said interstices having a thickness greater than the thickness of said film covering the surfaces of said grid-like structure.

7. A storage electrode for a signal storage device as claimed inclaim 6 wherein the dielectric film is formed from a thixatropic gel.

ture has a thickness of from about 0.02 micron to about 1.3 microns.

11. A storage electrode for a signal storage device as claimed in claim 6 wherein said grid-like structure has a thickness of from about 0.00005 to about 0.0006 inch.

12. A storage electrode for a signal storage device as claimed in claim 6 wherein said grid-like structure has a thickness of from about 0.00005 to about 0.0006 inch and said dielectric film extending into and across the interstices of said grid-like structure has a thickness of from about 0.02 micron to about 1.3 microns.

13. A storage electrode for a signal storage device as claimed in claim 6 wherein said grid-like structure is a screen having from about 300 to 1000 mesh per inch and a thickness of from about 0.00005 to 0.0006 inch.

References Cited in the file of this patent UNITED STATES PATENTS 2,237,681 McGee et al. Apr. 8, 1941 2,373,752 Flory Apr. 17, 1945 2,395,744 Kent Feb. 26, 1946 2,493,539 Law Jan. 3, 1950 2,540,635 Steier Feb. 6, 1951 2,547,638 Gardner Apr. 3, 1951 2,687,492 Szegho et al. Aug. 24, 1954 2,730,640 Koller Jan. 10, 1956 2,745,772 Cassman May 15, 1956 2,777,060 Waters Jan. 8, 1957 2,804,403 Clemens et al. Aug. 27, 1957 2,830,225 Moore Apr. 8, 1958 2,864,031 Smith Dec. 9, 1958

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