US2813998A - Method of storing, maintaining, and reproducing electrical signals, and means therefor - Google Patents

Description

Nov. 19, 1957 A. v. HAEFF 2,813,998

METHOD OF STORING, MAINTAINING. AND REPRODUCING ELECTRICAL SIGNALS, AND MEANS THEREFOR Filed Aug. 15, 1947 2 Sheets-Sheet l 6 SIGNAL sweep 7 =5 SOURCE 72 CIRCUIT A A 4 4 a 4/ -T VARIABLE 4 VOLTAGE 3 I SUPPLY m i I 8 A a! VARIABLE I 5% l 3 VOLTAGE 20 SUPPLY 8 1 #3 I VARIABLE i VOLTAGE 3 a SUPPLY L I sweep HIGH VOLTAGE s fi cmcun' SUPPLY 30 0 VIDEO Y AMPLIFIIIER 3 6 4 0 grww vfw ANDREW b. HAE'FF Nov. 19, 1957 A. v. HAEFF 2,813,998

- METHOD OF STORING, MAINTAINING, AND REPRODUCING ELECTRICAL SIGNALS, AND MEANS THEREFOR Filed Aug. 15, 1947 2 Sheets-Sheet 2 Potential SURFACE DIMENSION so I a/ a2 WAVE m 53583538; m STORAGE TUBE souRcE NETWORK NETWORK OF FIG.I

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84 DEMODULATION FILTER ANDRE M HAEFF ate METHOD OF STORING, MAINTAINING, AND REPRODUCING ELECTRICAL SIGNALS, AND MEANS THEREFOR Andrew V. Haeff, Washington, D. C.

This invention is directed to the storing and reproduction of electrical signals, and primarily relates to storage devices for establishing, storing, reading, and re-reading electrical charge patterns for such purposes.

The electrical signal may correspond to speech waves, television or radar signals, or any other informationbearing electrical variation. Such signal is stored for future reproduction in the form of a surface charge variation pattern. The charge patterns referred to may be placed on a linear or a plane surface. Such surfaces may consist of insulating material, or discrete particles of conductive material supported on an insulator. The charge pattern is normally applied to such surface by means of an electron beam generated by a conventional electron gun such as is employed in a cathode ray tube, but may be established optically or otherwise.

Due to leakage of the supporting surfaces carrying such a charge pattern, serious time limitations have existed with regard to the duration of such charge distributions. Further, in order to scan or read the charge pattern the same is swept with an electron beam to obtain an output signal. This output signal was obtained by neutralizing the charge at least in part so that in very few cases could multiple readings be obtained. Where they were obtained, they were few in number.

This has constituted a most important limitation on the utility of previously known charge storage devices.

' For visual presentation, or for use as a memory component in computing circuits and related devices, neither the time of storage nor the number of readings and rereadings can be limited.

*It is the object of this invention to provide an electrical memory device which can record information presented in the form of an electrical signal; preserve the same without degradation for an unlimited period, or for such shorter time as may be desired; and which will supply the stored information at will at any time, and as many times as may be desired.

-It is further the object of the invention to provide a new method of preserving and repeating information.

It is a further object of the invention to provide a novel cathode ray device, and components thereof.

It is another object of this invention to provide a charge storage system in which an image may be preserved for an indefinite period of time, and re-read as often as is desired.

In the instant invention a surface charge pattern is established on a semi-conductive material capable of substantial secondary emission. The surface charge pattern is distinguished from that of the basic surface background charge. Thus, if operation is started with a positively charged plate, the portions of the plate defining the pattern will carry a negative charge of a substantial value relative to the background potential.

Such image or pattern may be caused by action of an electron beam, by photo-emission from an optically active surface, or otherwise.

The characteristics of a distributed charge pattern are ice known. Such patterns become progressively less defined by the acquisition of charges from the surrounding space, and by current flow along the charged surfaces between adjacent areas of different potentials. Due'to the very low capacity of the surface carrying such a distributed charge pattern, very small charges acquired or lost will cause very substantial changes in the potential at any point of such a surface. Relatively substantial changes therefore take place in comparatively short time.

The charge pattern is then maintained by introducing relatively low speed electrons which enter the field of the surface charge distribution and are controlled thereby. Negatively charged areas of the patterns will decelerate the approaching electrons and will only receive the same until the negative charge acquired thereby is sufficient to repel them. Such negative surfaces will therefore approach, and under a continual supply maintain, an equilibrium potential which is near the potential of the electron source. The repelled electrons may be conveniently collected by various means.

Electrons approaching a positive portion of the charged surface, however, will have an entirely different effect. These electrons, entering the field of the surface charge, are accelerated by the positive charge. The terminal velocity at a positively charged surface is sufficient to give excess secondary emission beyond unit response, so that such electrons may cause the emission of several times their number from such charged surfaces. Such action causes the positively charged surface to acquire a more positive charge. Under continued application of such electrons, the surface will approach a positive equilibrium potential determined by the applied field.

It will thus be seen that through the process described the charge distribution pattern may be maintained by the application of low speed electrons to areas of low potential, without secondary emissions on such areas, and the application of high speed electrons to surface areas carrying more positive potentials with resulting heavy secondary emission.

The electrons for maintaining the charge distribution pattern may be obtained by projecting a wide, diffused beam onto the entire active surface area. Such beam if of sufficient current density and proper velocity will maintain the charge pattern as long as desired. To erase the charge pattern, the beam may be diminished in intensity or cut off. If the beam velocity is increased so as to generate an excess of secondary emission all over the plate regardless of the surface potential, the plate will be charged uniformly positive. The beam velocity may also be reduced so that it does not cause excess secondary emission even in positive areas, and thus charge the plate negatively to erase the pattern.

Instead of a broad uniform beam, a narrow beam may be progressively swept over the surface to maintain the pattern. The narrow beam maybe somewhat defocused to provide a large spot, or it may be confined to a narrow pencil.

When the beam traces over a positive area element, it leaves it at the positive equilibrium potential. In tracing the adjacent areas it may, however, give rise to secondary emission, and the electrons will in part be collected by the positive area element. Consequently, before the area element is retraced by the beam, its potential will have decreased during the sweep period, and will be again restored.

This restoration of its potential may be taken off as a reading signal at the same time that the potential is restored. Manifestly, the positively charged areas will have drifted negatively of the equilibrium potential and will under restoration supply a positive output signal. Similarly, the negatively charged areas, in case they have changed potential, will have shifted positive and will supply a negative output signal. Thus, the output signal is determined by the direction of potential shift and on restoring the area to its equilibrium, will be characteristic of the charge existing at that point.

Such take-off signals may be obtained from collector elements in the tube adjacent the surface. As is well known, the shift in potential over a surface may also be taken off from a conducting plate capacitatively coupled thereto. The latter procedure is notpreferred in the instant invention, however, due to the increased capacity resulting therefrom at the target surface.

The signal may be taken off from a capacitatively coupled element or from a collector electrode.

For the highest stability and resolution, a broad diffused holding beam and a separate reading beam are preferable. Under this type of operation, the surface is normally at one or the other equilibrium potentials. The

reading beam is preferably of sufficiently high velocity to.

induce excess secondary emission in all areas.

As the reading beam sweeps a positive area, however, such area is not driven more positive due to recapture of the secondary electrons, since it was already practically at collector potential. Negative areas, however, shift positive under the reading beam and give an output signal at the collector.

Conversely, a low velocity reading beam may be used, insufficient to induce excess secondary emission even in positive surface areas. Such a beam will reduce the potential at positive portions of the screen but will not reach negative areas already at the potential of the holding beam cathode. The signal may be taken off from the collector or by capacitative coupling.

In each case the holding beam restores an area to its former equilibrium potential after the passage of the reading beam.

A number of factors in connection with these phenomena may be mentioned. For some applications, as in television and radar, changing conditions may be represented. For this purpose, unlimited persistence may be undesirable. .By cutting down the holding beam velocity, a point may be reached where the image is maintained only the desired amount of time. This controlled persistence of the pattern is of wide utility.

Where the holding beam is diffused over the plate, the collector screen carries currents additional to that generated by the reading beam. Electrostatic pick-off may be desirable under these circumstances. The reading beam may be intensity modulated at an intermediate or low radio frequency and the output current due thereto may be selectively taken off by a parallel resonant load circuit, the direct current and low frequency components being passed to ground through the inductor.

If a fluorescent storage surface is employed with a diffused holding beam, the positively charged areas may be visible for observation. I

The invention will be further described in connection with the embodiment shown in the drawings, in which:

Figure 1 shows diagrammatically a tube of the present invention and operating circuits therefor,

Figure 2 shows the collector and active surface of the tube of Figure l,

Figures 3 through 7 show secondary emission ratios of a target surface,

Figure 8 is a diagram showing a mode of operation of the device,

Figure 9 shows a system employing the invention, and

Figure 10 illustrates a further type of operation.

Figure 1 shows an embodiment of the invention. An insulator plate is shown at 1. This plate may carry on its surface at 2 a substance having the desired secondary emission characteristics. In a specific embodiment, the plate 1 may be of glass, and transparent. The active surface2 may be composed of distributed willemite particles such as is employed for phosphors. The

4 phosphor P-S (calcium tungstate with tungsten activator) may also be employed.

The use of a phosphor is convenient for monitoring purposes but fluorescence is manifestly immaterial in many applications of the instant charge storage device. In case the plate 1 itself has the desired characteristics, manifestly no coating 2 would be necessary. Glass, for instance, has the necessary insulating and secondary emission characteristics. Material 2, if self-supporting, would not inherently require any backing plate whatever.

The initial charge distribution pattern may be established on active surface 2 by an electron gun including cathode 3. The beam of this gun may be controlled by grid 4 and deflection-means 5 under signal supplied from signal source 6 and sweep circuit 7 respectively. The beam is focused by a conventional lens electrode system shown diagrammatically at 8, for which a high voltage supply 13 is provided. The main tube anode 17 coated on the interior of the envelope, is also energized by 13. Sweep source 7 is operative to establish a sweep over the plate and the beam intensity during the sweep is modulated by the signal source 6. Television type sweeps and generators may be employed, or radial sweeps of the plan position indicator type used in radar. The intensity modulation signal applied to grid 4 may be derived from a black and white television type signal, or it may be a chopped signal such as from a continuous wave code transmission circuit, one derived from scanning a half-tone, or radar echo signals.

The charge distribution pattern established over the plate may be as shown in Figure 2, an X 10 defined in positive charges on a negative background 11 which itself comprises the entire sweep area.

Due to charges available within envelope 12, which may deposit on the target surface, the pattern 10 will progressively become less well defined. This action may be accelerated by loss of definition at the edges of the pattern through conductivity along the plate itself.

In order to maintain the charge pattern as described above, it is therefore necessary to introduce, to the field of charges on active surface 2, low velocity electrons. While as understood from normal operating procedure, electron gun 3 would be supplied with a negative potential at its cathode of a high value relative to active surface 2 and the field in its region; to supply a low velocity beam another electron gun within tube 12, having cathode 15, may be used. The cathode 3 may be supplied from a high negative adjustable voltage supply 16, and cathode 15 from a considerably lower negative adjustable voltage supply, 14. The voltage supply 13 may supply suitable voltages to the lens elements 8 for cathode 15 to establish a highly diffused beam and substantially uniform distribution of electrons of low velocity across the entire area of active surface 2. The main tube anode 17 is supplied from 13 to obtain the desired current density.

A collector screen 20 is placed adjacent active surface 2. The spacing between collector and target is preferably small in order to obtain high resolution. This screen may be of fine mesh such as 200 to the inch. With a relatively large beam, in which the cross section includes a number of screen cells,collector 20 will have little effect on the diameter of the writing beam obtained from cathode 3. If the screen wires have the same order of size as the writing beam, this will become a factor directly affecting the resolution which the system may attain. At the present time, the smallest beam size is much larger than screen apertures easily available.

The spacing between the sensitive surface and the screen is important. Where large spacing is used, the time of electron transit from the screen to the surface may give time for deflection by surface charges on surface areas not intersectedby the projected electron path. Consequently, resolution would be adversely affected.

The higher beam velocity employed the less will be the loss in resolution.

Since the limitation on resolution rests ultimately on the size of the writing beam cross section, primarily the screen position will be such as not to degrade this resolution particularly. For such purposes, the screen spacing will be of the order of the diameter of the writing beam.

Very close spacing, while advantageous to high resolution, is deleterious to writing speed because the proximity of the conducting screen increases the capacity of the surface and requires more charge to effect the desired potential shifts.

The collector screen 20 functions in connection with the writing beam from cathode 3 to collect the secondary electrons emitted from points of positive charge on the surface distribution pattern in a fashion similar with that of other types of collectors such as conductive coating on envelope 12 adjacent the active surface. In connection with the low velocity beam from cathode 15, however, the function of the collector screen is more critical. It establishes a definite potential at a predetermined distance from the active surface 2. The low velocity electrons therefore pass through the screen with a velocity determined by the potential ditference between the cathode 15 and screen 20. They then enter a space in which the field is defined not by the potential relations between cathode 15 and screen 20, but by the potential differences existing between the equipotential surface at screen 20 and active surface 2. Thus, an electron penetrating a screen aperture may see a high positive charge carried on the active surface 2 such as part of cross mark 10. Under this field the electron, which enters the area between the screen and the active surface with a relatively small velocity, is accelerated towards the highly positively charged area and at the end of its path causes the emission of a multiplicity of secondary electrons. These secondary electrons will be collected by collector 20.

The low velocity electrons which when passing through an aperture in the active surface 2 see a negatively charged active surface area, and on being repelled, lose velocity. If the area is at the negative equilibrium potential near that of cathode 15 they do not reach it, but drift to the collector 20 or to a nearby positive area. If, however, the negative surface area has drifted to a more positive potential or has been charged somewhat positive by a high velocity reading beam, the low velocity electrons will reach that area and restore it to its negative equilibrium voltage.

It will therefore be understood that through the operation of the beam from cathode 3 a surface charge distribution has been established on active surface 2 and that by the diffused beam from cathode 15 the surface distribution pattern may be maintained on the plate as long as desired.

For maintaining the image an indefinite period, the holding beam will be operated as above. Other effects, however, are possible and may have useful application. If the holding beam is given a higher velocity, the positive areas grow and encroach on the negative areas. This effect is produced by an increased production of secondaries in the negative areas combining at the edges thereof with surface leakage of the positive charge, it is believed.

A lower velocity holding beam has the reverse effect and enlarges the negative areas.

For controlled persistence of the image, these conditions are used to cause the pattern to fade into the background after the desired duration of time. Adjustment of voltage supplies 14 and 16 to obtain these results is easily made.

In order to read the charge distribution pattern, the charged area 11 may be swept progressively by means of a beam from a third cathode 25, energized by an adjustable voltage supply 26. Manifestly, the reading beam,

if it is not to destroy the image completely, must not have the high electron velocity and high density present in the writing beam if the writing and reading speeds are the same. If that were the case, the entire picture area 11 would be raised to the positive equilibrium potential defined in the cross area 10. On the other hand, the reading beam may actually have a velocity as low as that of the diffused beam supplied from cathode 15. This is because, as described above, the output signal obtained from collector 20 or a capacitatively coupled conductor 27 backing the active surface, depends on the charge variation at the point under the beam.

The use of so low a velocity in the reading beam, is however, an extreme example. Considerations of stability and signal output magnitude render an intermediate reading beam velocity desirable. However, the electron velocity of the reading beam is not at all critical and satisfactory output signal is obtained over an electron velocity range of 4 to 1 or even greater.

Suitable velocity for the reading beam may be easily determined by variation of the cathode voltage supply 26.

The sweep circuit of the reading beam supplied by cathode 25 is shown at 28. Such sweep may generate the usual television sweep signals to scan area 11 in the same fashion in which the signal pattern was established by signal source 6. If the output signal is to be employed for visual presentation of a visual pattern, the signal may be taken through switch 30 and through a video amplifier 31 to a control grid 32 of a remote indicator tube 33. Similar television sweeps may be generated at 34 which together with blanking voltages may be applied to grid 32 and to sweep means 35 of tube 33. A synchronization channel may lead from sweep generator circuit 28 to the sweep circuit generator 34 for the purpose of obtaining proper television type presentation of the active surface pattern 11.

Erasure of the image in Figure 1 may be accomplished in a variety of ways. The method consists of raising the low voltage areas to the positive equilibrium value by secondary emission, or lowering the potential of the positive areas, whichever is desired.

To generate a positive background, a high velocity beam is used. For this purpose variable voltage supply 14 of holding gun cathode 15 may be set to a higher potential difference with respect to screen collector 20 so that negative areas of plate 2 are charged positively by secondary emission. Alternately collector screen 20 may be connected to a source of positive potential 36 by switch 37.

If, during the use of a high velocity reading beam, the holding beam is turned off, the image may be extinguished in a few cycles of the reading sweep.

For negative charging, the holding beam may be used alone under lowered potential dilference with respect to screen 20, so that even postive areas receive a net negative charge. Alternately, screen 20 may be connected to a low voltage source 40 so that secondary emission from positive areas is not collected thereby until the potential drops to that imposed on the collector. If at portions of the screen reaching the reduced collector potential, excess secondary emission does not occur, then the potential will drop further, to that of the electron source.

In a specific example the following voltages were employed, collector screen 20 being regarded as ground potential. The potential of maintaining gun cathode 15 Was 3OO volts, and the potential of reading gun cathode 25 was 400 volts. The cathode of the writing gun was 500 volts. The backing plate 1 was a transparent sheet of glass, the active surface 2 was a calcium tungstate phosphor applied over the glass surface in an amount substantially that used in a normal cathode ray tube screen for visual observation purposes, and collector screen 20 was spaced from the active surface 2 by a peripheral mica spacer 41 one-tenth of a millimeter thick. The screen mesh was x 165 to the inch.

As will be understood, three electron guns have been illustrated for present-purposes in Figure 1. It is apparcut, however, that such guns are not of necessity'employed simultaneously. As explained above,- it .is not obligatory to apply a continuous maintaining beam constantly on the surface of the pattern but such beams may be a recurrent low electron velocity trace. Nor is it necessary that the writing and takeoff gun be used at the same time. It is therefore, quite possible that a fewer number of guns may be employed, such as two or one.

Thus, the circuit of Figure 1 may be employed with the use of only two guns, permitting the elimination of the gun including cathode 15. The reading and holding functions are both effected in the manner described above in connection with a recurrently swept beam tracing over the entire recording area.

In such an application, sweep circuit 28 is continuously operative, and output signals are available at all times on channels 29 and 38. Voltage supply 26 will furnish cathode potential of a value similar to that of supply 14 in the operation of Figure l as first described.

The pattern may be erased by variation of supply 14 or 26, Whichever is controlling the holding beam, to vary the beam velocity impinging on the recording surface. Very low beam velocity will charge the plate uniformly negative while high beam velocity will effect excess secondary emission in all areas.

It will be apparent that the tube as shown in Figure 1 is a device of broad possibilities, capable of many modes of operation. The holding gun may also be operated to effectuate the purposes of the reading gun. The writing gun may be used to establish either positive or negative areas. The erasure may be accomplished by variations of either gun or screen potentials. The system comprises both method and apparatus aspects, as exemplified in the specification and defined in the appended claims.

The operation of the present invention may be further understood by reference to secondary emission effects on the net current to a target area under the beam.

In the operation of an electron beam on the target, two important factors namely, electron velocity and current density, must be taken into account. The velocity, by its efifect on secondary emission ratio, determines the polarity of the charge left on the surface. The current density determines the rapidity of the voltage change. For instance, where a high velocity beam is used for reading, the sweep velocity and current must be correlated to avoid charging the negative areas to above the critical voltage from which the holding beam would raise the potential to the positive equilibrium value. Should the sweep trace velocity be increased, the beam current may be increased to maintain the same operation.

With reference to Figure 3, the current is plotted against the target potential, assuming an arbitrary incident beam current density. At the point a the target is at zero potential with respect to the electron source (the cathode of the holding beam). No current reaches the target. As the potential of the target increases the electrons reach the target at an increasing velocity. Point c is the critical potential at which the secondary emission current equals the primary current due to incident electrons. Beyond this value the net current to the surface is positive due to the excess loss of electrons by secondary emission. The current increases until the collector potential is approached. V is the critical voltage and depends on the sensitive surface.

From the maximum value at d the current falls to zero when the target is sufficiently positive to recapture secondary electrons which are otherwise received by the collector.

In the operation of the tube, with relation to the holding gun cathode which may be operated at potential a, the positive areas lie above c, and the negative areas lie below c. Consequently, the net current due to the holding beam is of a sign to reinforce the charge existing at that point.

A high velocity writing beam could be operated as' 8 shown in Figure 4. The writing cathode potential is at g which is further to the left in the figure because of the higher potential difference between this cathode and the collector.

Assuming a diffused holding beam operative as shown in Figure 3, it may be seen from Figure 4 that under suitable beam current densities the writing beam will override the holding beam and create positive areas wherever desired. The net current flow to the target under bombardment by the holding and writing beam simultaneously is shown by the curve g-hia,-b,c,-d,-e of Fig.- ure 4.

Under normal operation for the purposes of the circuit of Figure 1, all the target potentials will lie between the values a and e of Figures 3 and 4.

In order to obtain electrical output the cathode of the reading beam may be adjusted to a potential m as shown in Fig. 5 which may lie either between the values a and g as shown in Figure 4, or outside that interval. Under simultaneous bombardment by the holding and reading beams the net current to the target will be as shown by the curve mn0a -a' b -c d -e of Fig. 5. Thus with the particular primary currents shown the potential of the target elements normally at a level a would change their potential to the stable level a',.

On the other hand, the reading beam cathode may have a potential between 0 and a'. This is shown in Figure 6 at q. The net current to the target due to bombardment by electrons of this low velocity will be negative. Therefore positive areas of the target will be reduced in potential when traced by the reading beam to generate output signals. The reduction in potential, will not be sufficient to lower the voltage'below the value 0, however, so that under subsequent operation of the holding beam the voltage will be restored to the positive equilibrium near e.

Negative areas of the target lying between a and q will not receive the reading beam.

Erasure of the target image is easily visualized from Figure 3, for instance. If the screen collector potential is shifted from its value e to one below 0, primaries in positive areas will generate secondary electrons, but these will immediately be recaptured until the area falls below the new collector potential. Therefore the positive areas Will be reduced in potential to a value below that causing excess secondary emission, and thence will fall to the holding gun potential a.

The-screen potential e may then be restored and a new image established by a writing gun operated as in Figure 4.

If a positive background is desired, an erasure gun may be operated as in Figure 4, to sweep the entire target. Sufficient current can be employed to override the action of the holding beam. Therefore the target will charge uniformly to collector potential.

The writing gun can then be operated under low velocity. For this purpose, conditions as in Figure 7 may be employed. Current densities of .the beam and the tracing velocity will be selected as sufficient to override the action of the holding beam. Therefore the negative current as shown in Figure 7 will lower the target potential where desired to a value below 0 so that under the holding beam these areas will be reduced to the negative equilibrium potential as at a. a

Reference will be made to exemplary methods of employing the tube and modifications thereof. In Figure 8 the reinforcement of an image is shown. The base line 70 indicates the background charge of the sensitive area. This has been established as slightly above the critical potential for the holding beam when generated. A negative pattern is put on the plate by a low velocity writing beam as shown at 72, establishing areas at potentials below 71. The holding beam is then passed over the area, the screen potential being raised, and the voltage differentials of the pattern amplified to the values shown at 73.

One method of recording a speech wave is shown at Figure 9. The wave source 80 is coupled into a frequency modulation network 81 to supply an output carrier of higher frequency which is frequency modulated with the speech signal. This FM signal is applied to the storage tube circuit of Figure 1, shown diagrammatically at 82. The signal waveform is shifted to square Wave of the same frequency on the storage surface by the action of the holding beam. The output circuit may include a low pass filter 83 to eliminate harmonics and supply a sine wave FM output similar to the input signal for such use as may be desired.

A second method of recording a signal is shown in Figure 10. A pair of adjacent sweep line areas of the target surface are shown at 90 and 91. The writing beam spot is shown at 92. This beam may be taken as writing with positive charge on a negative plate background. The beam is under focus control of the input signal being recorded. Its quiescent width may be half the sweep line areas, and the spot size is enlarged or diminished in accordance with the input signal so that the positive area of the trace line zone is proportional to the input signal. The quiescent width may also approach zero width in which case the input signal will enlarge the line width in proportion to signal amplitude. For this purpose the input signal may be applied to the focusing electrode of the writing beam gun lens system. It may also be applied simultaneously to the intensity grid, as the beam should be of suflicient density to saturate the plate to an equilibrium potential at all points thereunder during the recording operation. Signal take-ofi is effected with a reading beam shown at 93, covering the full line width. The output current will be a function of the proportion of the line width carrying the positive signal potential.

As was pointed out above, the sensitive target surface requires certain secondary emission characteristics which may be obtained either from non-conductive or metallic materials. If such a metallic surface is divided into small discrete elements supported on an insulator, the surface will support a charge distribution pattern. Such mosaic surfaces are well known. The non-conductive surface referred to in the claims comprehends such mosaics, since such surface as a whole is non-conductive.

As will be understood the subject of invention is capable of many embodiments and applications. The specific embodiments disclosed in this application are exemplary only and are not submitted for the purpose of defining the limits of the invention.

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.

What is claimed is:

1. The method of operating a cathode ray tube with an electron target having a secondary emission ratio characteristic varying with incident electron velocity from less than unity at lower velocities through unity at a critical velocity to greater than unity at higher velocities, comprising projecting an electron beam for establishing on the target at least two charged areas of substantially different potential, projecting electrons toward the target at a speed effecting greater than critical incident velocity on the relatively positive target charge area and less than critical incident velocity on the relatively negative charge area, and collecting the excess secondary electrons emitted from the relatively positive area to raise the collector potential to a more positive value.

2. In a charge pattern storage device, a storage member, a first electron beam source for emitting a relatively high velocity electron beam for establishing potential areas on the storage member both positive and negative of a critical voltage, a second electron beam source for emitting a relatively low velocity electron beam for bombarding said storage member to apply primary electrons to potential areas negative of the critical voltage and to withdraw secondary electrons from potential areas positive of the critical voltage, and means including an electron beam having a distinct velocity from said relatively low velocity beam for reading the information stored on said storage member.

3. An information storage device comprising a storage member, a first electron beam source for emitting relatively high velocity electrons for charging an area of said storage member, a second electron beam source for emitting relatively low velocity electrons for bombarding said storage member to retain the charge thereon, a third electron beam source for emitting relatively high velocity electrons for scanning the storage member surface and producing appreciable secondary emission current from said storage member and a collector operative to collect said secondary emission and to produce current flow variations to an external control circuit.

4. An electron tube comprising a charge pattern sustaining electron target having a secondary emission ratio characteristic varying with incident electron velocity from less than unity at lower velocities through unity at a critical velocity to greater than unity at higher velocities, target charge pattern forming means operative to set up relatively positive and negative areas on the target, cathode means operative to project electrons into the immediate field of the charge pattern at a uniform velocity differing from the critical velocity by less than the maximum charge pattern voltage range to effect greater than unity secondary emission ratios in relatively positive target charge pattern areas and less than unity secondary emission ratios inrelatively negative target charge pattern areas, collector electrode means near the target at a potential relative to the cathode means substantially greater than the critical velocity potential operative to collect secondary electrons emitted from target areas at lower potentials, whereby the cathode potential establishes a stable limiting equilibrium potential for relatively negative target charge pattern areas and the collector potential establishes a stable limiting equilibrium potential for relatively positive target charge pattern areas, the target equilibrium potentials, relative to the cathode, being respectively below and above the critical potential for unity secondary emission ratio, and an electron beam source for producing an electron beam having a velocity higher than said uniform velocity operative sequentially on adjacent target charge areas to vary their potential an amount dependent upon their charge, and output circuit means operatively responsive to change in potential of a target charge area.

References Cited in the file of this patent UNITED STATES PATENTS 2,147,760 Vance Feb. 21, 1939 2,231,960 Smith Feb. 18, 1941 2,233,037 Smith Feb. 25, 1941 2,276,359 Von Ardenne Mar. 17, 1942 2,280,191 Hergenrother Apr. 21, 1942 2,339,662 Teal Jan. 18, 1944 2,407,000 Evans Sept. 3, 1946 2,464,420 Snyder Mar. 15, 1949 2,508,408 Liebson May 23, 1950 2,532,339 Schlesinger Dec. 5, 1950 2,547,638 Gardner Apr. 3, 1951 2,548,789 Hergenrother Apr. 10, 1951 2,639,425 Russell May 19, 1953 OTHER REFERENCES M. I. T. Radiation Laboratory Report 562, A Moving Target Selector Using Deflection Modulation on a Storage Mosaic (14 pp.; 5 sheets).

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