US2061113A - Control system for electron emission - Google Patents

Description

Nov. 17, 1936. T. w. SUKUMLYN CONTROL SYSTEM FOR ELECTRON EMISSION Filed May 20, 1931 2 Shets-Sheet 1 W Z w A W5; fla W a my 6/ 18 jqiim Nov. 17, 1936. w, SUKUMLYN 2,061,113

CONTROL SYSTEM FOR ELECTRON EMISSION Filed May 20, 1951 2 Sheets-Sheet 2 Mill illlil .57 45 1 J 1 J 1 1/ 9 g g f5 f9 60 i ,4,. I 5% E V 55 g i 5/ r? imgas 2 1.1M 1'1 ,Z'nyanfar 64 MEL mamas M wum/ yn Patented Nov. 17, 1936 PATENT OFFICE CONTROL SYSTEM FOR. ELECTRON EMISS ION Thomas W. Sukumlyn, Los Angeles, Calif.

Application May 20, 1931, Serial No. 538,723

I Claim.

This invention relates to a system for controlling electron emission.

There are numerous applications now known for electron emission devices. Among others may be mentioned the scheme for electrically scanning an image to be transmitted for television. In such schemes, an image is focussed on a photoelectric surface, as for example, may be formed by a. layer of sodium, potassium or other suitable compounds. Electrons are emitted from each element of this surface in accordance with the intensity of illumination reaching it. The whole area of this surface thus projects a beam of the same cross sectional dimensions as the surface, formed of electrons. The scanning is obtained by causing relative movement across the beam, of a target or anode which is maintained positive with respect to the photoelectric surface or cathode. The number of electrons reaching the target at 20 any instant thus depends upon the intensity of electron discharge from that elemental area of the surface which is at that instant active to send electrons to the target.

The relative movement of the beam and target must be cyclic and so rapid that the whole area is scanned during the period that is within the period of the persistence of vision; that is, so that the complete scannings occur at such a frequency as to give the impression of continuity. 30 This speed is of the order of one-tenth or onefifteenth of a second, which represents the time' for one complete scanning of the beam, whereby ten or fifteen images are produced every second. The varying electron flow to the target is made 5. use of for varying the current flowing in an output circuit, which can be reproduced synchronously at a distant point for translating the currents into light impulses reassembled to form the image.

It is apparent that since each image must be subdivided into a large number of elements, the scanning must be extremely rapid, and appropriate amplifiers must be used to provide sufficient variations in current to be eiiectively transmitted. To secure the rapid scanning, it has been proposed to secure the relative motion of the electron beam and the target by moving the beam cyclically and leaving the target stationary. This permits the use of electricity for the movement of the beam, as by appropriate magnetic or electric forces. For example, across one direction of the beam, an electromagnetic force can be applied, alternating at a high rate and of suflicient intensity to swing the beam clear across the target; and across another transverse direction, an-

other electromotive force can be provided, alternating at a lower rate and of sufficient intensity to swing the beam along this direction clear across the target. The resultant motion of the beam is compound, and can be described as a 5 series of back and forth movements successively at different levels until the whole beam is scanned, when the cycle is repeated.

Definite difficulties arise in such scanning systems. For example, a high driving potential must 10 be used, as by the aid of a positive screen, for impelling the electrons across the evacuated space between the emitter and the target. However it has been found that emission from the photoelectric surface is complex in response to the 15 energizing light. Some of the electrons proceed at such slow 'rate as never to reach the target; and others instead of proceeding in a direction normal to the surface, are oblique. These cause distortion of the reproduced image.

It is one of the objects of my invention to make it possible to reduce this cause of distortion very materially; and more particularly by a definite structure of the positive screen which acts either to straighten the elemental beam from the eleas mental area, or to reduce the diverging component thereof.

It is a further object of this invention to make it tpossible to reduce the size of the transmitter tu e.

In the prior schemes of this general character, the whole beam of electrons is influenced by a common set of electrical influencing devices, such as coils or condenser plates. It is apparent that the edges of the beam, nearest these devices, is influenced most, so that a further cause of distortion is introduced. It is another object of my invention to obviate this distortion by influencing elements of the beam separately.

My invention possesses many other advantages, 40 and has other objects which may be made more easily apparent from a consideration of several embodiments of my invention. For this purpose I have shown a few forms in the drawings accompanying and forming part of the present specification. I shall now proceed to describe these forms in detail, which illustrate the general principles of my invention; but it is to be understood that this detailed description is not to be so taken in a limiting sense, since the scope of my invention is best defined by the appended claims.

Referring to the drawings:

Figure 1 is a diagram of a system embodying one form of the invention;

system;

Figs. 6 and? are greatly enlarged detail fragmentary views of the screen used in connection with the form of the invention shown in Fig. and

tion.

In Fig. 1 there is shown an envelope or tube II which is highly evacuated and which encloses the elements of the electronic transmitter. Thus there is a cathode l2 having a suitable photo-sensitive surface facing an illuminated object l3 exterior of the tube II. This object has an image focussed on cathode i2. as by a lens system 4. The electron beam emanating from cathode I2 is accelerated by a screen l5 (Fig. 2) which is kept at a suitable high positive potential, such as 500 volts, with respect to cathode 12. A battery l6 isindicated as supplying this suitable potential.

A target or anode I I is disposed at the opposite end of tube II, and is kept at a suitable positive potential with respect to cathode l2, as by a battery I8. The circuit connecting anode l1 with cathode |2 also can be connected to appropriate amplifiers l9' and to a transmission line. This target I! has an area corresponding-to an elemental portion of the beam. In order to ensure that only one element of the beam is active at one time to pass electrons to target use can be made of an electric shutter or shield 2| of mesh form, and held at a suitable positive potential with respect to cathode I2, as by a battery 22. This shield can pass the light from object I3, and has a central aperture exposing target Thus this shield captures all electrons except those that pass directly to the target, and acts as an electric shutter.

The movement of the electron beam relatively to target can be effected either by capacity action or by electromagnetic action. In the present instance, there is shown apair of coils 23, 24, to affect the beam magnetically, and arranged on opposite sides of tube II, and energized by an oscillator 25 for causing the beam to swing in a vertical direction, say at the rate of fifteen times a second. Horizontal oscillation of the beam is similarly effected, but at a much higher rate, say five thousand times a second, by the aid of horizontally arranged coils, energized from oscillator 26. Only one of the pair of coils so energized is shown at 21; but it is to be understood that'on the other side of tube H, a similar coil energized similarly to coil 21, is provided.

Some of the electrons in the beam have a tendency to diverge from the straight normal path; and some are emitted from cathode l2 at a low velocity. To keep the electrons normal and to absorb those at low velocity, the screen If: is made deep, as by the use of side interconnecting plates forming elemental areas 29, Due to the positive charge on screen l5, and to its depth these low velocity electrons are readily attracted thereto; and the high speed electrons are given a greater impetus inthe direction intended for them. The elemental areas or open spaces 29 of the screen are merely illustrated diagrammatically; ordi-- Fig. 8 is a diagram of a still further modificaformed by thin intersecting or honeycombed plates in an obvious manner.

Shield or shutter 2| can be also made deep, to eliminate as much as possible, any charges on the back wall of tube The angled beam of electrons are thus more apt to be caught thereon instead of passing through the shield. The light beams from lens I4 can, however, pass because they are substantially in line with the shield openings.

A thin metal deposit 28 inside tube H and kept at a positive potential, serves as a plate extending shield 2| to return the electrons to the oathode when the beam is angled to reach the sides of the tube.

W Furthermore, for effective operation, the tube II should be very highly evacuated, and the potentials of elements l5, 2|, and I1 should be high, of the order of five hundred to a thousand volts, to provide the desired acceleration of the electrons. Y

Fig. 3 illustrate a form of the invention in which the length of the transmitter tube can be reduced.

Thus in the evacuated vessel or tube 30; the cathode or photosensitive device 3| as well as the wide screen 32 are concave toward the target 33, producing'a converging electron beam. The illuminated object 33 has its image focused as by lens 34 onto the concave surface of cathode 3|. The beam being more restricted, can also be more readily controlled by the devices 23, 24; 21. The shield 20'can be also deep and concave.

The idea of concentrating or straightening the electron beam by appropriate design of the screen can be carried out in other ways. For example, in Fig. 4, the cathode 35 emits electrons through a pair of sets of plates 36, 31 which together form the screen. The set 36 is arranged horizontally, and set 31 is arranged vertically. Both sets are in general kept at a high positive potential with respect to cathode 35, as by the aid of battery 38. However, each set of plates includes alternate plates that are maintained positive with respect to the other plates of the set. In other words, the plates form alternate positive and negative elements, which can be kept at constant potenials as by batteries 39, 39'.

As an elemental stream of electrons passes between the plates 36, the positive plates pull the stream away from the negative plates, causing the elemental stream to be flattened as indicated by the dotted lines 40, in a horizontal direction. The angularities of these dotted lines are exaggerated for clarity, it being understood that these lines converge on the shield 2|. Each of these fiat streams, is split up into a series of elements by the plates 31, which act on each of the split up elements to concentrate them in a vertical direction. Thus by the action of the two sets of plates, the electron stream is divided and again subdivided into the desired small elements which are concentrated in both directions, and keep them moving in a straight line. As in the prior forms described, the depth of the entire screen structure 36-31 is sufficient to capture the very slow moving electrons and the greatly deviating electrons, and ensure distortionless transmission. However, most of the electrons will here be concentrated into ,straight beams without absorption. r

Of course, no attempt is made to indicate a practical separation of the plates in elements 36, 31; as preferably a much larger number can be used in each set, to provide smaller elemental beams.

The successive compression of the elemental beam in two transverse directions to obtain concentrated beam elements, can also be produced by a compound shield structure, such as is illustrated in Figs. 5, 6 and 7. In this instance the cathode 4 l, shutter 42, and target 43 are arranged substantially as before; as well as the scanning elements 23, 24, 21. The screen 44, however, has two series of plates of definite arrangement, which are kept positive and negative with respect to each other.

One set of plates 45 (Fig. 6) is convoluted to form a series of bends. These plates are so arranged that the bends come opposite each other, the series of bends thus forming a series of cellular spaces or honeycombs 41. All of these plates are kept at a potential negative with respect to another set of plates to be described, as by a battery 46. It is through the spaces 41 that the elemental beams of electrons travel.

Another set of plates 48 is used, which intersect the spaces 41, as by being spaced between adjacent plates 45. These plates are, however, insulated from plates 45, as by very thin pieces of insulation 49. This insulation can be formed by a thin film of enamel, or a thin plate of mica, or the like. All of the plates 48 are connected together, and maintained positive with respect to plates 45, as bybattery 50. Furthermore, at the center of each space 41 formed between plates 45, the plates 48 are provided with projections 5|.

It is now possible to explain the action of the screen 44 as the electrons progress through spaces 41 (in Fig. 6, in a direction normal to the plane of the drawings). Since plates 48 and accordingly projections 5| are positive With respect to plates 45, these projections attract the electrons, while the sides of the spaces 41, being negative, repel the electrons. The net result is that the electrons cluster near the projections 5| as indicated diagrammatically by the dots 52. Many electrons deviating from the straight normal, as well as the slow moving electrons, will be straightened out and accelerated. Because the width of plates 45, 48 is quite substantial, as illustrated in Figs. 5 and 7, the very slow moving electrons and those greatly deviating from normal will be captured by plates 48.

In this form of the invention, the scanning is effected as before by the coils 23, 24, 21, or equivalent devices. Such devices, however, influence those elemental electron beams most strongly which are adjacent the edges of the tube. In the form of my invention illustrated in Fig. 8, the elemental beams are not so discriminated against.

In this form, the evacuated tube 53 encloses the usual photoelectric cathode 54, the positive concentrating and accelerating shield 55 (constructed in any of the ways heretofore described), the positive shutter 56, and anode or target 51. The circuit connecting target 51 with cathode 54 can include the appropriate amplifiers 58. The deflecting of the elemental beams from cathode 54 to produce the scanning effect is provided by a pair of sets of plates 59, 50. The set 59 is arranged horizontally inside tube 53 and is used for swinging the elemental beams in a vertical direction. The set 60 is arranged vertically inside tube 53 and is used for swinging the elemental beams horizontally.

Since both sets of plates are similarly constructed, set 59 only, need be described in detail. This set includes a series of paired plates, the number shown being diagrammatic and it being understood that many more could be used in an actual embodiment, to secure a fine subdivision of the whole beam. The plates are alternately of opposite polarities. In the instance shown, the top plate and every other plate is negative, while the remaining plates are positive. The plates are in closely adjacent pairs, providing spaces such as SI for the elemental beams to pass between a pair of opposite polarity plates. The plates can be held separated in any desired manner as by insulation layers. 1

At the instant shown, the beams are swun downwardly in these spaces 6| as indicated by the dotted lines 62, because the top plate of each space is negative nd repels the electrons, while the bottom plate is positive and attracts the electrons. However, the relative polarities change, say at the rate of fifteen times a second, so that the beams are oscillated at that frequency in a vertical direction. This change in polarity is accomplished by connecting the alternate plates to opposite terminals of a source of alternating current, such as transformer 63, fed by oscillator 6 The horizontal oscillation of the elemental beams is accomplished at a much faster rate, as by providing the oscillator 55 of 5,000 cycles, feeding transformer 66. The opposite terminals of this transformer are connected to alternate plates of the set 60. This set operates in a manner similar to set 59.

I claim:

1. In a system for electric scanning, a photoelectric cathode, an anode, means for causing relative movement between the beam of electrons emitted from the cathode, and the anode, and means in the path of the beam for dividing the beam into concentrated elemental beams, said dividing means comprising a series of electrical plates that are alternately negative and positive with respect to each other.

2. In a system of electrical scanning, a photoelectric cathode, an anode, means for causing relative movement between the beam of electrons emitted from the cathode, and the anode, and a positive screen in the path of the beam, said screen having deep cellular spaces, the cathode and screen being concave toward the anode.

3. In a system of electrical scanning, a photoelectric cathode, an anode, means for causing relative movement between the beam of electrons emitted from the cathode, and the anode, a series of spaced plates in the electron stream and having alternately opposite polarities, another series of similar plates but transverse to the first series, and means for maintaining said two series of plates positive with respect to the cathode.

4. In an electronic emission device, a cathode, an anode, and a positive screen in the path of the electrons, and between the anode and cathode, the cathode and screen being concave toward the anode, and the screen having deep cellular spaces.

5. In an electronic emission device, a cathode, an anode, a series of spaced plates in the path of the electrons and having alternately opposite polarities, another series of similar plates but transverse to the first series, and means for maintaining said two series of plates positive with respect to the cathode.

6. In a system of electric scanning, a photoelectric cathode, an anode, an evacuated vessel enclosing the anode and cathode, a series of plates defining elemental spaces and located in the vessel, and means for varying the potentials of the plates on opposite sides of each space to swing the electron beam passing through the space.

7. In a system of electric scanning, a photoelectric cathode, an anode, an evacuated vessel enclosing the anode and cathode, a pair of series of plates inside the vessel, one series being transverse to the other and defining elemental spaces for the passage of electrons, and means for varying the potentials of the plates on opposite sides of each space to swing the electron beam passing through the space.

THOMAS W. SUKUMLYN.

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