US2547638A - Image storage tube - Google Patents

Description

April 3, 1951 B. c. GARDNER 2,547,638

IMAGE STORAGE TUBE Filed Dec. 18, 1948 3 Sheets-Sheet 1 April 3, 1951 B. c. GARDNER 2,547,638

IMAGE STORAGE TUBE Filed Dec. 18; 1948 3 Sheets-Sheet 2 AT V April 3, 1951 c, GARDNER 2,547,638

IMAGE STORAGE. TUBE Filed Dec. 18, 1948 3 Sheets-Sheet 3 80 T ELECTRON MIRROR A ELECTRON GUN CATHOD E //v VENTOI? BERNARD C. GARDNER A TTORNEY Patented Apr. 3, 1951 IMAGE STORAGE TUBE Bernard C. Gardner, Waltham, Mass., assignor to Raytheon Manufacturing Company,

Newton,

Mass., a corporation of Delaware Application December 18, 1948, Serial No. 66,083

22 Claims.

This invention relates to electron tubes of the kind wherein an image can be stored in the form of an electrical charge pattern, and in particular to a tube having great flexibility of use.

It is an object of the invention to provide an image storage tube wherein an image can be recorded at any desired rate of speed within wide limits, stored for a great length of time and examined repeatedly without appreciable loss of definition.

It is another object of the invention to provide such a storage tube wherein the stored image can be removed rapidly when desired.

It is another object of the invention to provide such a tube which has high resolving power, and can consequently record and store an image having a great many elements of information.

It is still another object of the invention to provide an image storage tube wherein the stored image has a large dynamic range of intensities.

The foregoing and other objects and features of the invention will be appreciated from the detailed discussion of certain embodiments thereof that follows, reference being had to the accompanying drawings wherein:

Fig. 1 illustrates, partly in vertical section, a tube in accordance with the invention in a circuit which is shown schematically;

Fig. 2 illustrates the storage element of the tube of Fig. 1 in cross-section, greatly enlarged, cooperating with an electron beam;

Fig. 3 illustrates, partly in vertical section, another tube constructed in accordance with the invention;

Fig. 4 illustrates schematically an erasing circuit for-the tube of Fig. 3;

Fig. 5 illustrates schematically a writing circuit for the tube of Fig. 3;

Fig. 6 illustrates schematically a reading circuit for the tube of Fig. 3;

Fig. 7 is a diagrammatic view, greatly enlarged, illustrating the operation of the tube of Fig. 3;

Fig. 8 illustrates, partly in vertical section, a third tube in accordance with the invention;

Fig. 9 illustrates schematically a writing and/or erasing circuit for the tube of Fig. 8;

Fig. 10 illustrates a reading circuit for the tube of Fig. 8; and,

Fig. 11 illustrates a modification of the tube of Fig. 8. r

In general, the present invention contemplates the employment of a perforated conducting screen electrode which is coated on one side with a nonconductive material functioning as a storage element, writing being accomplished by scanning the dielectric coated side of the screen, and reading being accomplished by scanning the uncoated side of the screen. Such a screen electrode, as employed herein, may also be termed a target. The charge pattern on the coated side of the screen determines the current that flows to a collector electrode which is suitably positioned with relation to the storage screen. The charge pattern controls the passage to the collector electrode of secondary electrons formed when a high voltage reading beam strikes the uncoated side of the screen, or of a low voltage reading beam directly.

Referring now to Fig. 1, the tube there shown comprises an envelope it of glass,.or the like, having at the right hand end a first electron gun I l which is employed for writing and erasing purposes, and at the left hand end a second electron gun IZ, which is employed for reading purposes. The first gun H includes a cathode 13, a. control grid l4 and a focusing and accelerating anode I5. A deflection coil system It is suitably placed around the neck of the tube at the right hand end to cooperate with the first gun II. A high voltage accelerating and scavenging electrode I! is coated on the inside of the envelope ID in front of the first gun II. This high voltage electrode may be made of a suspension of colloidal carbon known as Aquadag.

The second electron gun I2 includes a cathode 2 l a control grid 22, and a focusing and accelerating anode 23. A second set of deflection coils 24 is suitably disposed around the left hand end of the tube to cooperate with the second gun I? for the purpose of deflecting the beam produced thereby. A second high voltage and scavenging electrode 25 is coated on the inside of the envelope l 0, covering substantially all the left hand half of the envelope in front of the second gun l2. The second high voltage electrode 25 is constructed similarly to the first high voltage electrode I1.

A storage screen 26 is disposed transversely in the envelope ID, at about the center portion thereof. This screen, which is shown greatly enlarged in Fig. 2, comprises essentially a thin sheet of metal 21, which may, for example, be a nickel plate of a thickness 0.0005 inch, coated on one side with a dielectric 28 of similar thickness. The composition of the dielectric will be discussed in detail below. The plate 21 is provided with square holes 30, of which there are about 400 to the inch along the surface of the plate. Each hole 30 is initially about 0.0015 inch square, so that the uncoated screen is about 36 per cent storage screen, will simultaneously coverfapproxi-' mately six of the holes 30, when the beam has a diameter of approximately 0.020 inch. Such a beam is termed a "six-element beamfif As-will; become apparent below, beams as narrow lash 0.010 inch in diameter are suitabIe and' desirable for use in tubes of the invention; Thelbeamgthat is illustrated in Fig. 2-i'sgfs'oidisposcd 'with relation to the storage screen26 that it may be considered to be a reading beam.

Referring again to Fig. 1, a collector electrode 35 is 'coated on the inside of the envelope III in the form of an annulus disposed between the storage screen 26 and the high voltage anode I! of the first gun II. The arrangement or elements is such that a charge pattern can be placed upon the dielectric coating 28 of the storage screen 28 by a beam from the first gun II, and this storage pattern can influence the passage of electrons either primary or secondary originating from the reading beam of the second gun I2 to the collector electrode 35. Circuits for accomplishing the various desired functions of the tube will now be discussed.

Erasing Erasing of any prior stored information or any prior stored charge pattern on the dielectric 28 is accomplished by flooding the screen 26 with slow electrons from the first gun I I of a potential so low that the number of secondary electrons leaving the screen is fewer than the number of primary electrons arriving thereat. As is well known, when electrons strike a body, be it conductive or non-conductive, secondary electrons are caused to be emitted from the body. Depending upon the velocity with which the striking electrons, known as primary electrons, im-

pinge upon the body, the secondary electrons will be either fewer or greater in number than the primary electrons, being greater in number when the velocity is high. There is a critical velocity connected at its positive side to the two anodes I5 and I! of the first gun II. The. cathode I3 of this gun is connected to the movable element M of a three-position, single pole switch 42 of which one terminal 43 is the erase terminal. The erase terminal is connected to a movable tap 44 on the battery 40, which tap is adjusted to choose the required accelerating potential for the erase beam. Erasure is effected by operating the switch 42 to the erase position and scanning the beam from the first gun II repeatedly over the dielectric 28 of the storage screen 28 until a sufficiently uniform nzgative charge is placed thereon. The negative charge that results will approach that of the cathode I3 with respect to the applied potential accelerating the erase beam.

It is desirable to charge the dielectric side 28 or the storage screen to a uniform negative potential of approximately 50 volts with respect to the collector electrode 35.

' Writing It will be assumed that the dielectric side of the storage screen '26 is charged to a uniform f negative potential of the order of 50 volts with respect to the collector 35. Writing is accomplished by scanning the dielectric side or the screen 26 with a moderately high velocity electron beam, the velocity of which is sufllcient so that the beam, when striking the dielectric 28, generates secondary electrons greater in number than the primary electrons. With such a velocity, the number of secondary electrons leaving an area under the beam will be greater than the number arriving, so that the area will become chargcd in a positive direction in proportion to the number of primary electrons striking the area. The secondary electrons will go to the collector 35 and anode coating I1 of the tube. Primary electrons passing through the screen 28 will be collected by the anode coating 25 of the second gun I2. The storage screen 26 is maintained positive in potential with respect to the anode coatings I1 and 25, and the collector 35 is maintained positive with respect to the screen. By the action of scanning and modulation of the writing beam intensity, 2. charge pattern is placed upon the dielectric surface 28 varying in intensity in accordance with the modulation. When the writing beam is cut off, the charge pattern remains, as there is no source of electrons to remove the charge.

The various required potentials can be furnished by any suitable means, for example, the battery 40 furnishes the accelerating potential for the writing beam when the full voltage thereof is applied between the cathode I3 and the high voltage anode I1. To this end the switch 42 is provided with a second selection terminal 46 which is connected to the negative end of the battery 40, and is employed as the write" terminal of the switch. For writing, the switch 42 is operated to the write position. The screen 26 is made more positive than the anode coating I! by a second battery 41, and the collector 35 is made more positive than the screen 26 by a third battery 48. Modulation of the intensity of the beam of the first gun II during writing is accomplished by means of a write input circuit 50, shown in block form, connected between the cathode I3 and the control grid I4 of the gun. A bias battery 5| provides an initial negative bias which is overcome or aided by the write input circuit to modulate the beam.

' Reading Once a charge pattern is placed upon thedielectric 28 of the screen 28, it can be read by scanning the uninsulatcd side 21 of the screen with an electron beam. The reading beam is furnished by the second gun I2 and can be arranged to provide a high voltage or low voltage beam, either above or below the critical velocity potential for the metal 21, as desired. It a high voltage beam is employed, those electrons which pass through the screen, shown more clearly in Fig. 2, travel at sufliciently high velocity to be collected by the coating anode I! of the first gun ll, while those which impinge upon the metal 21 cause the emissionof secondary electrons. The metal 21 is connected in a circuit with the l2,,so that no change in potential of the metal occurs thereby. The metal 21 of the screen 26 ismaiiitained positive with relation to the anode coating .25 of the second gun l2, and the collector electrode 35 is maintained positive with respect to the "metal 21 of the screen 26. Accordingly, the secondary. electrons are attracted to the collector electrode ,35 rather than to the anode coating of theisecond gun l2. The charge existing around each, of .the holes by virtue of the charge pattern" DQ533113 dielectric 28 governs the number of sccondarfy and calcium tungstate.

coated on the metal plate 21 by evaporation in a vacuum, calcium tungstate cataphoretically,

and magnesium oxide by smoke precipitation inelectrons that pass through each hole 30 to the collector electrode 35. Recalling that the dielectric 28 was originally charged to a potential approximately 50 volts negative with respect to the collector 35, it will be appreciated that with properly selectcd potential diiferences between the anode coating 25, the metal 21, and the collector 35, this charge in itself can be suflicient to prevent the passage of any secondary elec-- trons through the holes 30. Thus the presence of positive charges in varying numbers around the various holes 30 governs the passage of secondary electrons through the holes 30 to the collector in accordance with the amount of such charge. This, in turn, is in accordance with the modulation placed upon the writing beam by the write input circuit 50. The current that flows in this manner to the collector 35 flows also through a load resistor 53, across which the output signal is taken. The reading beam is scanned by the deflection coil system 24 of the second gun I2.

A suitable potential for accelerating the reading beam is provided by a battery 55 which is connected between the cathode 2| and the anodes 23 and 25 of the second gun l2 by a read switch .53 of the single-pole, double-throw variety. A

suitable bias potential for the control grid 22 is furnished by a bias battery 51. The screen metal 21 is made positive with respect to the anode 25 of the second gun I 2 by means of a suitable battery 58. The battery 48 which is connected between the screen metal 21 and the collector 35, which is used in the write circuit, is also used in the read circuit. The read switch 53 has an off position at which it is operated during writing and erasing. The write switch 42 has a third terminal at which it is operated to store an image, which is then available to be read when desired.

By lowering the potential of the battery 55 below the value required to provide the electrons in the beam of the second gun I2 with critical velocity or above, a slow beam is provided. With this beam, those electrons which strike the metal 21 are absorbed by the screen 26 and returned to the cathode 2|. Those electrons which tend to side an enclosed chimney. These procedures have been found to yield uniform coatings without tooseriously reducing the hole' size.

Performance tests made with storage screens constructed as set forth above have yielded the following information. If a stored image be read at the rate of 30 frames per second, the scanning thereof being performed as in television, an image stored on a magnesium oxide screen will be found to persist for a time greater than ten minutes which corresponds to the retention of a stored signal for more than 18,000 readings. The same stored signal is retained for more than sixteen hours with the reading beam turned off. Under similar reading circumstances,

- a calcium fluoride screen was found to have a pass through the holes 30 are influenced at each a hole by the charge pattern existing around the hole on the dielectric 28, so that the number of holding time greater than fifteen minutes, a lithium fluoride screen not more than fifteen minutes, and a barium fluoride screen less than one-tenth of a second.

The resolving power of the foregoing screens in a tube of the present invention is found to be substantially higher than that of prior known storage tubes. The resolving power of tubes of the invention was measured by writing an image made up of a series or group of dot elements on the storage surface and reading out the stored image on a monitor. The number of dots per inch placed upon the storage screen by the writing beam was made initially few, and increased for successive writings until further increase showed a noticeable deterioration of the monitor image. With the magnesium oxide dielectric coating, the resolving power for read-out was measured in this way to be forty dots per inch on the storage screen. Using a writing beam which is 0.020 inch in diameter, it is possible to' write fifty dots per inch on the storage screen; that is, the electron spot size is fifty dots per inch. Therefore, the resolving power for readout with the magnesium oxide screen is per cent of the theoretical maximum permitted by the reading electron gun.' Similar tests showed that the calcium fluoride screen was 58 per cent efficient in this manner and the lithium fluoride screen 74 per cent eflicient.

The writing speed that can be obtained with storage screens constructed as set forth above was measured by means of a sine wave oscillator applied to deflect the writing beamin one direction and a single synchronized pulse to defleet the writing beam at right angles thereto. The resulting trace was then examined by reading out on the monitor. The oscillation frequency or amplitude, or both, were increased between successive writings (with erasure between writings) until the trace showed indications of thinning at the center. The writing speed at the center of the trace for this condition is taken as the maximum or saturation writing speedfor-the tube. Increase in writing speed beyond this point causes a dimmer trace rather than adisappearance of the trace, for the reason that in the tubes terminal I8 of the storage screen ring 81.

,of this invention the stored image has a continuous dynamic range. In this manner a saturationwriting speed of 0.78 kilometer per sec-' ond' was measured fora 3.2 mioroampere beam current, using a magnesium.oxide screen. The critical potential for this screen was estimated to be 75 volts. The writing speed of calcium fluoride and lithium fluoride screens was found to be less than this value. I

Referring now to Fig. 3, another tube constructed in accordance with theinvention is there shown, wherein reading and writing are accomplished with one and the same electron gun.-

while .erasure is accomplished by a second flood gun, .the beam of which does not have to be scanned. This tube comprises an envelope 88, of glass or the like, having in the right-hand end a reading and writing gun-8|, and in the left-hand end an erasing gun 62. The reading and writing gun 8| is provided .with deflection coil means 63 and a-coated anode 64 inside the envelope 68 in the right-hand portion thereof. The coated anode 84 is provided with a terminal 65 imbedded inthe glass of the envelope and in electrical contact with the anode 84. This terminal 65 is conveniently termed a "button terminal because ofits button-like appearance. The storage screen (not shown) is mounted in a ring ol'which is supported upon- studs 68 and 68,

-of which the latter is electrically connected to a button terminal 18,. which is, in turn, mounted in and through the envelope 68; The stud 68 has fastened thereto an insulation bead I2, while the other stud 68 has fastened thereto a second insulating bead I3. A second ring I4, having two mounting studs I and I8, is supported in the beads I2 and 13 by these studs in parallel relation to the first ring 61. The second stud I6 makes electrical contact with a button terminal 18 mounted in and through the envelope 88 in approximately diametric opposition to the button A metallic screen 88 of the order of 108 mesh, 85 per cent open, is stretched tightly across the opening in the second ring 14, nearest the first ring 61. The storage screen which is mounted'in the first ring 61 has its dielectric surface facing toward the metallic screen 88. v

The flood gun 62 includes a cathode 82, a control grid 83, and an accelerating anode 84, having terminals 85, 86 and 81 passing through the left-hand wall 88 of the tube for the purpose of its positive terminal to the coated anode 88, the collector electrode 82, and the metallic screen 88 together. A variable tap 88 on the battery 85 is connected to the metallic screen 21 of the storage screen 26. The potential furnished by the battery88 is sumcient to accelerate electrons 'toward the storage surface 28 with a-somewhat high voltage, which is reduced to a voltage below the critical value by the potential furnished to themetal 21 of the storage screen 28 via the tap 86 on the battery 85, whereby the metal 21 is made, negative with respect to the metallic screen 88, collector electrode 82, and coated anode "'88. The beam from .the electron gun 82 is a broad beam covering the entire storage surface 28, and imparts electrons to the storage surface until the' charge thereonclosely approaches the .potential of the cathode 82.. This action is similar to the erasing action described above in connection with Fig. 1.'-

Writing The circuit shown in Fig. 5 is suitable for use 4 in writing. A battery 81 is connected at its negalic screen 88 and the collector electrode 82 are making electrical connections thereto. This gun may be of the kind shown and described in copendingapplication, Serial No. 775,291, filed September 20, 1947. A coated anode 88 is provided for-this gun on the inside of the envelope 68 in the left-hand portion thereof, this anode having a button terminal 8| mounted on, the wall of the envelope A collector electrode 82, annular .in form like the collector electrode 35 in Fig. 1.

is coated inside the envelope 68 between the erasing gun, coated anode 88, and the metallic screen 88. This-collector electrode is likewise provided,

'. For erasing the storage surface of the screen I 26, the circuit shown in Fig. 4 is suitable. ,A battery 85 is connected at its negative terminal to thecathode 82 of the erasing gun 62, and at made negative with respect to the cathode 88 by means of an auxiliary battery III. A bias battery I82 is connected between the cathode 88 and the control grid 88 of the reading and writing gun 8|, via the write input circuit 58. Deflection coil means I83 serve to deflect the beam I84 furnished by the gun GI, and thereby scan it over the storage screen28. No connections are made to the erase gun or its coated anode 88 in Fig. 5. The metallic screen 88 is sufliciently negative with respect to the metal2l of the storage screen 28 so that electrons of the beam I84, which pass through apertures 38 in the storage screen '28, are turned back and strike the dielectric material 28. For this reason. the metallic screen 88 is termed an electron mirror.

Referring now to Fig. '7, the operation of the electron mirror will be explained in detail. In Fig. 7, only those parts which ar necessary to explain the action of the electron mirror are shown, and these are shown greatly enlarged and in simplified form. However, the parts .shown bear the same reference characters as the corresponding parts in Fig. 5. The path of a single electron passing from the cathcde 88 through a hole 38 in the storage screen 25 is shown by a dashed line I88. The electron passes through a hole 38 and is carried by its momentum toward the electron mirror 88, .which, however, exerts. a retarding force upon the moving electron. Located between the storage screen 28 and the electron mirror 88 there is a plane of zero potential, represented by a dashed line AA, at which the moving electron is stopped and turned about, and accelerated back towards the storage screen 26. The path of the electron, after entering the region between the storage screen 28 and the electron mirror 88, is very much like the trajectory of a projectile being hurled through the earths atmosphere from one point on the earth to another with constant horizontal velocity and an initial upward velocity Vo which is thereafter reduced to zero and reversed by the constant force of :beam H2 at the storage screen 26.

9 gravity. The electron then strikes the dielectric 28 at a point B with a velocity above critical for the dielectric, and causes secondary electrons to emerge. Sinc the velocity of the primary electron upon striking is greater than the critical velocity, two secondary electron paths are shown to indicate more secondary electrons than primary electrons as a result 'of the striking. One secondary electron path I6! is shown in dotted line, while the other, I08, is a dot-dashed line. The secondary electrons are repelled by the electron mirror 80 and attracted by the metal 21 of the storage screen 26 and by the coated anode 64 of the read-write gun 6|. As a result, th point B at which the primary electron struckthe dielectric material 28 becomes more positive, as happens in the operation described above in connection with Fig. 1. It will be appreciated that writing has been accomplished by scanning the dielectric side of the storage screen 26 with a writing beam, just as is done in Fig. 1. However,

the writing gun is located on the conductive side of the storage screen 26, and the beam is caused toreach the dielectric side by means of an electron mirror 80. Secondary electrons, which are emitted from the conductive side 21 of the storage screen 26, are captured by either the conductive metal 21 or the coated anode 64. By this construction, the same gun 6| can be used for writ ing as well as for reading.

Reading The reading function of the tube of Fig. 3 can be performed with the circuit shown in Fig. 6. This circuit closely resembles that of Fig. 1 for reading. 'A battery I I I is connected at its negative end to the cathode 98 of the read-write gun SI, and at its positive end to the electron mirror 80 and the two coated anodes 64 and 90 to thereby produce a beam I I2 of any velocity desired, the velocity being governed by the voltage of the battery. The metal 2'! of the storage screen 26 is made more positive than the electron mirror 86-and the two coated anodes 90 and 64 by means of a battery H3, while the collector electrode 92 is made still more positive by means of still another battery H4. The last battery H4 is connected at its negative terminal to the metal 21 of the screen electrode 26 and at its positive terminal to the collector electrode 92 via a resistor H5. The output signal upon reading is taken across this resistor.

As has been mentioned above, reading of the either by direct modulation of the electron beam H2 with the charge pattern, or by modulation of a cloud of secondary electrons created by the Primary electrons which strike the conductive metal 21 cause the emission of secondary electrons therefrom, which are now attracted to the collector electrode 92. The flow of secondary electrons to the collector electrode 92 through the holes 30 is governed by the potential of the electron mirror 60, which is not sufiiciently great to cut off their flow, and by the charge on the dielectric 28 at the hole 36 through which a particular electron seeks to pass. The more positive the stored charge is, the greater will be the flow of secondary electrons through a particular hole 30 to the collector electrode 92. Thus, as in Fig. l, with a reading beam of constant intensity and under the action of scanning, controlled by the deflection coil means I03, a current flows in the resistor I I in accordancewith the charge pattern on the storage screen 26.

When electrons of the beam H2 approach the screen 26 at suificiently low velocity so that the charge pattern can have a modulating efiect on them, primary electrons passing through the holes 30 in the storage screen 26 are modulated or governed in. quantity in the same manner'as are secondary electrons as described immediately above. 1

Referring now to Fig. 8, an embodiment of the invention is there shown wherein a single gun I I7 is employed for reading, writing, and erasing. This tub employs a storage screen and metallic screen assembly similar in many respects to that shown in Fig. 3. Accordingly, like parts of this assembly have like reference characters in both Figs. 3 and 8. However, the metallic screen is nearer to the gun HI than is the ring 6'! of the storage screen 26. The dielectric side of the storage screen 25 faces away from the gun III, as is indicated in Figs. 9 and 10. A coated anode H9 is provided inside the envelope I 20, being disposed between th metallic screen 80 and the gun H1. Deflection coil means H8 are provided for the gun. As will be explained below, the metallic screen 80 is employed as an element of the anode H9 in the present embodiment, and not as an electron mirror. In its place, a coated electron mirror I2I is provided on the interior of the wall of the tube opposite the end of the gun I I1. Button terminals I22 and I23 are provided for the coated electron mirror I2I and the coated anode H9, respectively.

Erasing Erasing in the embodiment of Fig. 8 is accomplished in the following manner. As shown in Fig. 9, a battery I26 is connected at its negative terminal to the cathode I21 of the gun H1, and at its positive terminal to the metallic screen 80 and the coated anode H9 together. A movable tap I25 on the battery I26 is connected to the metal 21 of the storage screen 26. A second battery I24 is connected at its positive terminal to the cathode I21 and a its negative terminal to the electron mirror I2I. The beam furnished by the gun H1 is provided with an initial potential by the battery I26, which is above critical for the dielectric material 28, but which is reduced below critical by setting the movable tap I25 sufliciently close to the negative terminal of the battery I26. With the proper setting, electrons, traveling at below the critical velocity for the dielectric material 28, enter the region between the storage screen 26 and the electron mirror I2I, are turned about, and strike the dielectric material 28 at a voltage below critical, thereby imparting a negative charge to the dielectric material. By suitable scanning, this negative charge is made uniform throughout, and the storage screen 26 is thereby erased to a uniform negative potential level.

Writing Writing is accomplished with the circuit of Fig. 9, with the sole change that the tap I25 is moved suiliciently near the positive terminal of the battery I26, so that electrons which enter the region between the storage screen 26 and the electron mirror I2I are turned about and strike the dielectric material 28 with a voltage greater than critical. Secondary electrons,

11 which are thereby emitted, are attracted by the metallic screen 80 and the coated anode H9. The function of the metallic screen 80 in this case is to provide a uniform attracting field parallel to the storage screen 26, which is not provided by the coated anode II9, alone. Secondary electrons which are emitted by the striking of the beam against the metal 21 are likewise attracted by the metallic screen 8|! and the coated anode H9. In this manner, writing produces a pattern of positive charges as in the other embodiments of the invention.

Readinil Reading is accomplished with a circuit like that shown in Fig. 10. A battery I30 is connected at its-negative terminal to the cathode I21, and at its positive terminal to the electron mirror I2I, via a load resistor I35, the electron mirror in this case functioning as a collector electrode. The metallic screen 80 and the coated anode II9 are together connected to a movable tap I32 on the battery I30. The metal 21 of the storage screen 26 is connected to a second movable tap I3I on the battery I30, which is maintained nearer the negative end of the battery than the first tap I32. The potential for accelerating the reading beam is determined by the setting of the first tap I32. The setting of the second tap 'I3I determines a deceleration potential to be applied to the beam. It is preferable to employ a fast beam initially in the interests of good resolving power, and to decelerate this beam at the storage screen in order that the charge pattern on the storage screen may control the flow therethrough of slow electrons to the collector I2I. The current in the; collector I2I flows through the resistor I35 across which the output is taken. I

The foregoing considerations of the operation of the various embodiments of the invention have been confined toierasure of the type which produces negative charge, and writing of the type which produces positive charge. It is possible, by sufilciently accelerating the erasing beam to provide erasure which produces a positive charge. trons produced by the first gun II from the dielectric material 28 would be collected by the coated anode I1 and by the collector anode 35. Thereafter, writing with a beam of lower velocity than critical would add charges to the screen and produce a negative charge pattern. The charge pattern on the storage screen 261 would then operate upon a reading beam in the same manner as described above, producing, however, an image which is photographically negative with respect to the image produced when writing is positive on a negative screen.

It will be appreciated by those skilled in the art that similar operation of the other embodiments of the invention can be had. For example, in Fig. 4, if the electrons from the gun 62 are sufficiently fast, secondary electrons will emerge from the dielectric 28 and will be collected at the positive terminal of the battery 95, thereby charging the dielectric 28 positively for erasure purposes. Then in Fig. 5, if writing is with a sufiiciently slow beam, the electrons which are turned about by the electron mirror 80 will accumulate on the dielectric 28 and produce a In this case in Fig. 1, secondary elec- 12 the recorded charge pattern, for the same gun is used in each embodiment to provide both the writing and reading electron beams. With tracking of this kind, it is further possible to return to a particular portion of the recorded charge pattern on the screen 26 to sample the information stored therein, without the necessity of ex- 7 amining the entire charge pattern.

- If it is desired to enable an observer to view a charge pattern that is being read, the coated electrode I2I in the embodiment of Fig. 8 may be made in two layers, as shown in Fig. 11. One layer is a thin film III of platinum in contact with the envelope I20 and the other layer 2 is a fluorescent material. The platinum film Ill is normally evaporated onto the envelope end wall and is maintained sufliciently thin so that it is only about 20 per cent opaque, while the fluorescent material I42 is deposited on the platinum. The reading beam impinging on the fluorescent material will then cause visible emission therefrom, which will be visible through the platinum film. Electrons will penetrate the fluorescent film and arrive at the platinum film which then functions as a collector electrode. The platinum film also functions as an electron mirror in the circuit of Fig. 9.

Many other variations .and modifications will occur to those skilled in the art, and it is therefore intended that the claims that follow shall not be limited by the details of any of the embodiments shown and described herein, but only by the prior art.

What is claimed is: w

1. In an electronic charge storage device, a perforated storage target having an electrically conductive side and a dielectric side, means providing an electron beam for scanning said dielectric side, to produce a charge pattern thereon, and means providing an electron beam to scan said conductive side.

2. In an electronic charge storage device, a

perforated storage target having an electrically conductive side and a dielectric side, means providing an electron beam for scanning said dielectric side, means for modulating said beam during scanning, and means providing an electron beam to scan said conductive side, I

3. In an electronic charge storage device, a charge storage target having an electrically conductive side and a dielectric side, a plurality of formly distributed over the surface thereof,-

means providing an electron beam for scanning said dielectric side, said beam being of sufllcient width simultaneously to include several of said apertures, and means providing an electron beam having a width of the same order of magnitude as the first-mentioned beam to scan said conductive side.

5. In an electronic charge storage device, a perforated storage target having an electrically conductive side and a dielectric side, means providing an electron beam for scanning said conductive side, and means to cause an electron- 13 of said beam which passes through said target to alter its course and impinge upon said dielectric side.

6. In an electronic charge storage device, a perforated storage target having an electrically conductive side and a dielectric side, means providing an electron beam for scanning said conductive side, and means to cause an electron of said beam which passes through said target substantially to reverse its course and impinge upon said dielectric side near the region of passing through.

7. In an electronic charge storage device, a perforated storage target having an electrically conductive side and a dielectric side, means providing an electron beam for scanning said dielectric side, to produce a charge pattern thereon, means providing an electron beam to scan said conductive side, and means for providing a uniform charge of a desired polarity to said dielectric side.

8. In an electronic charge storage device, a perforated storage target having an electrically conductive side and a dielectric side, means providing an electron beam for scanning said dielectric side, to produce a charge pattern thereon, means providing an electron beam to scan said conductive side, and means for scanning said dielectric side with an electron beam substantially uniformly over the entire area thereof.

9. In an electronic charge storage device, a perforated storage target having an electrically conductive side and a dielectric side, means pro viding an electron beam for scanning said dielectric side, to produce a charge pattern thereon, means providing an electron beam to scan said conductive side, and means providing a beam of electrons of sufficient width to cover substantially the entire area of said dielectric side.

10. In an electronic charge storage device, a perforated storage target having an electrically conductive side and a dielectric side, means for causing electrons to impinge on said dielectric side substantially uniformly throughout the area thereof, means providing an electron beam for scanning said dielectric side, and means providing an electron beam to scan said conductive side.

11. In an electronic charge storage device, a perforated storage target having an electrically conductive side and a dielectric side, means for causing electrons to impinge on said dielectric side substantially uniformly throughout the area thereof and with a velocity below the critical velocity for the dielectric material, means providing an electron beam with a velocity above said critical velocity for scanning said dielectric side, and means providing an electron beam to scan said conductive side.

12. In an electronic charge storage device, a perforated storage target having an electrically conductive side and a dielectric side, means for causing electrons to impinge on said dielectric side substantially uniformly throughout the area thereof and with a velocity on one side of the critical velocity for the dielectric material, means providing an electron beam with a velocity on the other side of said critical velocity for scanning said dielectric side, and means providing an electron beam to scan said conductive side.

13. An electronic charge storag device comprising a perforated storage target having an electrically conductive side and a dielectric side,

iii.

a first electron gun disposed to said conductive electrically conductive side and a dielectric side,

an electron gun disposed to said conductive side, and an electron mirror disposed to said dielectric side.

15. An electronic charge storage device comprising a perforated storage target having an electrically conductive side and a dielectric side, an electron gun disposed to said conductive side. and a conductive plate lying in a plane parallel to that of said target to said dielectric side.

16. An electronic charge storage device comprising a perforated storage target having a conductive side and a dielectric side, a first electron gun disposed to said conductive side, a second electron gun disposed to said dielectric side, and a conductiv screen interposed between said dielectric side and said second gun.

1'7. In an electronic charge storage device, a perforated'storage target having an electrically conductive side and a dielectric side, means providing an electron beam for scanning said dielectric side, to produce a charge pattern thereon, means providing an electron beam to scan said conductive side, and output signal collector means disposed to said dielectric side.

18. An electronic charge storage device comprising a perforated storage target having an electrically conductive side and a dielectric side, an electron gun disposed to said conductiv side, a planar conductive element disposed to said dielectric side parallel to said screen and of similar extent, and an annular electrode disposed between said conductive element and said target circumscribing but out of a direct path from said element to said target.

19. An electronic charge storage device comprising a perforated storage target having an electrically conductive side and a dielectric side, an electron gun disposed to said conductive side, and a conductive element disposed to said dielectric side, said conductive element including a fluorescent material.

20. An electronic charge storage device comprising a perforated storage target having an electrically conductive side and a dielectric side, an electron gun disposed to said conductive side, and a conductive element disposed to said dielectric side, said conductive element being in the form of a layer of conductive material and a layer of fluorescent material.

21. In an electronic charge storage device, a perforated storage target having an electrically conductive side and a dielectric side, means providing an electron beam adapted to scan said conductive side, means to cause an electron of said beam which passes through said target to alter its course and impinge upon said dielectric side, and means on said dielectric side adapted to provide a second beam of electrons of suflicient width to cover substantially the entire area of said dielectric side.

22. An electronic charge storage device com- 'prising a perforated storage target having a conductive side and a dielectric side, a first electron gun disposed to said conductive side and arranged to provide a narrow electron beam, means for scanning said beam over said con- 15 ductive side, a second electron gun disposed to said dielectric side and arranged to provide a beam of breadth suflicient to cover all elements of said dielectric side simultaneously with electrons, and an electrically conductive screen interposed between said second gun and said dielectric side.

' I BERNARD C. GARDNER.

' REFERENCES CITED Number 16 UNITED STATES PATENTS Name Date Steudel Sept. 17, 1940 Riez et a1. June 10, 1941 Hengem'other Apr. 21, 1942 Law Jan. 25, 1949 Sziklai Feb. 22, 1949 Snyder Mar. 15, 1949 Snyder Mar. 21, 1950 Jensen Apr. 11, 1950 Rose Ma 9, 1950 Cassman May 16, 1950

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