US2156392A - Television transmitting apparatus - Google Patents

Description

H. A. IAMS TELEVISION TRANSMITTING APPARATUS May 2, 1939.

Filed Dec. 30, 1936 IIIIII AAAAAAAA VVIVVVVVV INVENTOR HARLEY A. [AMS (Patented May 2, 1939*, I

' "UNITED STATES PATENT .OFFICE l TELEVISION TRANSMITTING APPARATUS Harley A. Iams, Berkeley Heights, N. J., assignor, by mesne assignments, to Radio Corporation oi America, a corporation of Delaware Application December 30, 1936, Serial No. 118.194 6 Claims. (Cl. Z50-153) My invention relates to picture or television invention will appear from the followingdescriptransmitting apparatus and particularly to tion taken in connection with the accompanying cathode ray tubes for transmission of infra-red drawing, in which I U light images of objects, such as are obtained when Figure 1 is a diagrammatic view illustrating one objects are viewed through fog and haze. form of my television device; and

The transmission of images of objects viewed Figure 2 is a diagrammatic .view partially in through fog and haze is diilicult and unsatisfacsection showing in enlarged detail a portion of f tory with the usual form of cathode ray transthe structure shown in Figure 1. y n mitter tube in which an optical image of an ob- Referring to Figure l the tube comprises a 10 ject of which a picture is to be transmitted is highly evacuated envelope `o`r bulb I with a tubu- 10 -fmed upon the front surface of a target or lar arm or neck section enclosing aconventional mosaic electrode consisting in general of an intype electron gun and a spherical section enclossulating sheet with a great number of discrete ing a flat screen or target 2 so positioned that photo-electrically sensitive elements on the front its front surface may-be scanned by a beam of l5 surface and a conductive coating on the other electrons from the electron gun, and also may 15 surface, the front or illuminated surface being have projected `upon it the image to be transscannedby a cathode ray beam to generate picmitted. Since the image vis produced principally ture signals. The eiectiveness of such a transby infra-red light or radiation having a wavemitter with infra-redlight or radiation is `limlength of at least ten lmicrons and the usual ited by the photoelectric properties of available glasses do not transmit Aas well asdesired wave- 20 materials. Furthermore, all wavelengthsin the lengths greater than three microns, Iv prefer to infra-red spectrum are not equally effective in provide in the wall of the bulb I in registry passing through fog and haze. Much depends with the target 2 a window' 3 with transmission on the particle size of the material in the air characteristics such that infra-red rays of the which causes absorption or scattering of the light desired wavelength may pass through the window 25 from the object. For light transmission with yto the target 2. The window may be made of slight dispersion or attenuation the wave-length material such as a crystal of potassium chloride, of the incident light or radiation from' thev object which 'is capable of transmitting light or `energy viewed must be large in comparison with the of the desired wavelength. Othermaterialsl, such particle size. Since much of the attenuation of vas quartz, or crystals of rock 'salt rof fluoride 30 the light is due to scattering it has been found may' be used for this purpose, depending "on' the necessary to use a wavelength on which the transmission characteristics desired. The image, light transmission is near unity in order to get if desired, may be focused onthe target 2 by a sharpness of detail, hence for dense fog the light lens system l made oi similar materials and Waves must be at least ten microns long. This mounted in front ofthe window. 35 wavelength is far outside the range of photo- The electron gun assembly of the conventional electric sensitivity of even such. a1 material as type comprises a cathode 5, a control electrode caesium. 1 y 6 connected to the usual biasing battery, and a It is an object of my invention to provide a first anode 1 maintained positive with respect 40 television device which will produce satisfactory to the cathode 5. 'Ihe electron stream leaving 40 picture signals from Vinfra-red light images, and the rst anode 1 is accelerated and is also concenespecially from images of objects viewed through vtrated into an electron 'scanning beam focused on fog and haze;v To this end I project an infrathe front surface of the target 2 by a second red light optical image on a screen consisting of a anode 8, preferably a conductive coating on the thin continuous lfilm of a conductor having. high surface of the envelope i near the neck of fthe 45 thermo-electric "power, and deposited on a sup'- bulb. The' first anode l and second anode 8.are port having low specific heat and low heat transmaintained at the desired positive potentials with mission, and scan theV film witha cathode ray respect to the cathode 5 by batteries 9 and 9'. lbeam-to generate picture signals, which are elec- Conventional deflection means,` such as deflection trical impulses representative of the light values coils i0 and Il may be used to sweep the beam 50 of elemental areasv of Athe image. The picture in a horizontal and verticalplane, respectively, to signals may be amplified and applied toa cathode scan the target. It is obvious that conventional ray type of receiving tube to produce a visible electrostatic deflection plates may be substituted reproduction of theimage on the film. for the deflection coils if desired. :..p

Other objects, features, and advantages of my Inaccordance with my invention, the target or -material having low heat capacity and low heat conductivity, such as a thin sheet of mica, preferably about two one thousandths of an inch thick, with the front surface coated with the thin iilm I of germanium which I have found gives good results. Other metals having similar thermo-electric properties, such as antimony, and bismuth may be used for this purpose. These metals have a thermoelectric power greater than 50 with reference to platinum at normal .room temperature (20 C.), this value being computed in the generally accepted manner as shown in Table 1 on page 214 of the International Critical Tables, i'lrst edition, Volume VI (McGraw Hill, New York city, 1929) To facilitate the electrical connection of the iilm of germanium on the target electrode to the output circuit the mica base I1 preferably has a strip or border I9 of metal of good electrical conductivity extending around its periphery and over the surface of the base for approximately one quarter inch to electrically engage the iilm I5 and a metal frame 2| extending around the edge of the mica base and in electrical connection with the strip I9. A lead 23 extending from the frame 2| through the wall of the envelope I connects the germanium film I5 through an impedance 25 to the second anode 8.

In making the target electrode, I prefer as the first step to apply the metal border or strip I9 to the edge of the mica sheet I1, which may conveniently be done by painting a border on the mica sheet with liquid compounds of platinum or of silver followed by baking to remove any binder or volatile substances.

The next step in preparing the target electrode is to mask a portion of the metallized border on one side of the electrode, and then coat this side of the mica with the vthin film I5 of metal such as germanium having high thermo-electric power. The iilm should be thin enough to have low heat conductivity, and has a surface in which the change of secondary electron emission with change in film voltage is high. 'This coating process may conveniently be done in a vacuum chamber containing a tungsten filament coated with aluminum oxide and carrying some of the metal with which the mica sheet is to be coated. By heating the filament the metal is evaporated, and it deposits on the mica as a thin uniform iilm. The metal iilm on the mica should be thin enough to have low heat conduction along the surface of the iilm yet, thick enough to produce apprecisf able variations in voltage in response to sudden changes in temperature. For example, in a tube made and exhausted by conventional methods of cathode ray tube manufacture, I have used a germanium iilm which on clear mica was translucent and had a light transmission of about 1% of incident light produced by a tungsten filament at incandescene.

I do not desire to be restricted to any particular theory of operation, but it seems probable that when there is an image or light pattern on the screen each elemental area of the metallic film reaches a temperatur r dependent on the incident energy on that area thereby forming a thermal pattern which is a replica of the image or light pattern, and that the ability of an elemental area to emit secondary electrons upon bombardment by a cathode ray depends on the temperature of that area. Under different values of incident energy the elemental areas of the metallic iilm will reach different temperatures, the rapidity of the" change in temperature being determined by the thermal conduction and radiation of the iilm. In this way different elemental areas of the film become secondary electron emitting to dierent degrees, determined by the temperature each area attained by reason of the incident energy from the image. The film does not emit photoelectrons and is not photoemissive to any perceptible degree, the electrons which are emitted being secondary electrons emitted only under the influence of the cathode ray beam and controlled in inten-A sity by the thermal pattern generated on the film by the image or light pattern focused or formed thereon. The emitted secondary electrons are collected by the second anode 8, and variations in the secondary electron iiow from the iilm as it is scanned by the cathode ray beam provide the utilization current lfor the device which flows through the impedance 25 to ground and the second anode 8. The voltage drop produced by the current flow in the impedance corresponds to the picture signals, and may be impressed across the input of the translating device 26, further amplified, and applied to a transmitting network in a manner well known in the art.

From the foregoing description it will be apparent that various other modifications may be made in my invention without departing from the spirit and scope thereof and I desire, therefore, that only such limitations shall be placed thereon as are necessitated by the prior art and set forth in the appended claims.

I claim:

1. An image forming screen for a cathode ray television transmitting tube comprising a thin sheet of material having low specific heat and low heat transmission, and a film of germanium forming a coating on one surface of said sheet.

2. An image forming screen for a cathode ray television transmitting tube comprising a thin sheet of mica, and a translucent iilm of germanium on one surface of said sheet.

3. An image forming screen for a cathode ray television transmitting tube comprising a sheet of mica approximately two thousandths of an inch in thickness, a translucent film of germanium on one surface of said sheet and a frame for maintaining said sheet coplanar.

4. A cathode ray television transmitting tube comprising an envelope having a light transmitting portion, a sheet of material having low specic heat and low heat transmission, a continuous film of metal having negligible photosensitivity having a thermoelectric power greater than 50 at 20 C. with respect to platinum on one surface of said sheet to produce a thermal pattern in response tcla light pattern projected on said film, a lead electrically connected to said film, mean's for generating a cathode ray beam and scanning said film with said beam, and an anode adjacent said film.

5. A cathode ray television transmitting tube comprising an envelope having a light transmitting portion, a non-photosensitive secondary electron emitting screen of a continuous iilm of metal selected from the group consisting of germanium, bismuth, and antimony, and exposed to said envelope portion to produce a thermal pattern in response to alight pattern projected on said film, a lead extending outside the tube and electrically connected to said iilm, means for generating a cathode ray beam, means for scanning said lm with said beam, and an anode adjacent said screen to collect secondary electrons emitted by said screen. v

6. A cathode ray television transmitting tube having a light transmitting portion, a sheet o! material having low specic heat and low heat transmission exposed to said portion, a film of germanium on one surface of said sheet to produce a, thermal pattern in response to alight pattern projected on said film, a lead electrically connected to said lm, an electron gun directed to said film and including an anode adjacent said lm for generating a cathode ray beam, and means for scanning said lm with said cathode `ray beam.

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