US2426494A

US2426494A - Heat detection device

Info

Publication number: US2426494A
Application number: US515058A
Authority: US
Inventors: Evans John
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1943-12-20
Filing date: 1943-12-20
Publication date: 1947-08-26
Anticipated expiration: 1964-08-26
Also published as: GB601070A

Description

Aug. 26, 1947, J. EVANS HEAT DBTECTION DEVICE Fii'ed nec. 2o, 1943 Zmnentor Cittomeg- Patented Aug. 26, 1947 26,494 f- I l FICE naar DE'rac'noN DEVICE John Evans, Kingston, N. J., aasignor to'Radlo Corporation of America, a corporation of Dela- Appllcatlon December 20, 1943, Serial No. 515,058

Claims.. (Cl. 201-63) This invention relates to heat detecting devices and especially to a heat detecting device including a plurality of separately responsive units .adapted to respond to a plurality of heat sources at'the same or at different temperatures.

Numerous heat detecting devices have been disclosed in the prior art. Many of these devices are in the form of cells which are notespecially sensitive. Some cells vmay have the required sensitivity but their response is sluggish and they are not suitable when rapid response is required. In many systems sluggish response may be tolerated but in systems for forming an image of a scene by scanning the radiations there from, a rapid response is required if the image is to be formed rapidly. Moreover, if good resolution is required, the image must be made up of a large number of elements, and a large number of elements correspond to a large number of heat responsive cells, which would be grouped to form a mosaic. While a large number of the prior art devices may be combined to form a mosaic, the design andmanufacturing difculties become more apparent by assuming that a suitable image would include not less than say`100 lines or 10,000 elements.

'According to an object of the present invention there is provided an improved heat responsive cell in which rapid response and increased sensitivity are secured. Another object is to provide an improved heat responsive device including a plurality of separate heat responsive units. An additional object is 4to provide an improved method for manufacturing multi-unit heat responsive devices suitablefor scanning systems. A further object is to provide an improved heat responsive device in which a plurality `of heat responsive elements .are linearly arranged.

The invention will be described by referring to the accompanying drawings in which Figure 1 is an elevational view of an assembled heat response device according to a preferred embodiment of the invention; Figure 2 is a sectional view Y 2 porting plate includes an aperture 1. which may be surrounded by a grommet I. The grommet may include a heat transparent window (not shown). suitably disposed behind the aperture 1 is membrane I I which is hereinafter described. The membrane is stretched tightly over an insulated support I3. The support may be made of Ya synthetic resinous material, such as Lucite.

The insulated support I3 may include a metal backing plate I5. The insulated support I3 is spaced `from the metal support I by insulated spacing strips I'I, I9. One of these spacing strips I'I includes a common conductor 2|; the other spacing strip I9 includes a plurality of conductors 23 which engage conductors connected to the separate units 25 of the heat responsive means 5.

The membrane I I may be composed of cellulose acetate with suitable plasticizer and hardening agents. By way of example, a liquid of the following ingredlents may be composed of the approximate amounts as indicated:

Pear oil cc-- 50 Pure cellulose gram 1 Formaldehyde cc-- .01 Chrome alum .,ngram 1 Synthetic camphor (Dupont) do .25 Glycerine cc-.. .01

The ingredients are dissolved in the above sequence. A few drops of the thus prepared liqquid may be poured upon water and left to solidify to form a membrane having a thickness of several taken along the line IIfII of Figure 1; Figure 3 r microns, for example, 3X 10-8 centimeters. Since the membrane is very delicate, it may be best lifted from the water by inserting a hollow rectangular frame under the membrane. Instead of lifting the membrane from the water, the support I3 may be inserted in th'e water before the liquid is poured on the surface ofthe water and after the membrane has formed the water level is low-1 ered until the membrane rests on the support I3. If the frame method is employed and if the frame encloses an area appreciably larger than the support I3, the membrane may be deposited upon the support and will be secured thereto by molecular bonding, provided the surface of the support I3 has been,polish'ed. After the membrane is fastened securely the surplus may be trimmed by tearing or by dissolving the excess. The membrane'after drying exhibits a very low thermal storage capacity, which is necessary if rapid respouse is desired.

The next step in preparing the heat responsive units is to cover the membrane with a mask.

lating support I3. The mask is rst disposed in one position, say to the left of the center of the membrane and then the assembly is inserted in `to a suitable bell'jar. 'I'he bell jar includes tungsten baskets, which are provided with heaters and gold to be evaporated. The bell jar is then evacuated to a hard vacuum, l. e., -5 to 10 millimeters oi pressure. Thereafter the baskets are heated and the gold is evaporated and is deposited on the portions of the membrane exposed by the apertures in the mask to form a row of gold contacts.

The assembly is then removed from the bell jar, and the mask positioned to the right of the center of the membrane. .Che gold evaporating process as previously described is repeated thereby to deposit a second row of gold contacts. The assembly is again removed from the bell jar and the mask is centrally disposed vwith respect to the membrane.

The assembly with the mask centrally disposed is inserted in the bell jar in which tungsten baskets containing metallic tellurium have been placed. 'I'he bell jar is exhausted until a hard vacuum is obtained. A small amount of oxygen is permitted to enter the bell jar by heating a side tube which contains mercuric oxide. The heated mercurio oxide gives up oxygen .to establish an oxygen atmosphere within the bell jar. When the tellurium is evaporated in the oxygen atmosphere, the tellurium molecules combine with the oxygen molecules. The combination is deposited on the membrane through the apertured portions of the mask, forming a semiconductox'" between each oi the gold contacts. The semi-conductor. tellurium oxide which forms the heat responsive unit 25, has a negative thermal coeillcient of resistance of large magnitude as compared with pure metals.

The gold contacts to the left of the heat responsive tellurium oxide elements 2l are connected to a common conductor 2l as described previously. The contacts to the right of the heat responsive elements are connected to separate external conductors by means of a multielement contact bar which may be made as follows: An insulating strip 28 (see Fig. 5) oi the required length and of suitable cross section is wound with wire Il of a diameter preferably slightly smaller than the gold contacts. The turns of the wire may be spaced by a notched plate. The several turns are made oi the desired length by a jig which positions the notched plate and the insulating strip. The strip, after the wires are in place, is wetted by means oi a solvent. The wetted strip is clamped so that the wires are embedded in the wetted strip. The solvent on the strip is then allowed to harden Aso that the wires are securely positioned. 'Ihe turns 23 may be cut along one edge o! the strip to form e. plurality of wires each having ends embedded in the strip. The embedded ends are then sandpapered or otherwise scraped to remove the insulation whereby good electrical contacts will be made when the strip is positioned as shown in Fig, 5. Thus the heat responsive units are connected to a common lead and to separate leads.

One suitable circuit including the heat responsive unit is shown in Figure 6. A battery 38 is connected through a series resistor It to a heat esQ sponsive element to scan or to'interrupt the heat from a source not shown.

The modes of operation are as follows: First,

-ii the capacitor is short clrcuitedand the disk or shutter is not used to interrupt the heat, theheat falling on the heat responsive element `I1 decreases the electrical resistance of the element because o! its negative coeillcient. If the resistance is lowered. more current will dow from the battery and hence a greater voltage drop will be indicated by the meter 32. Second, if the capacitor 4l is not short circuitedand if the shutter is used to interrupt the heat which is applied to the heat responsive unit, the resistance of the unit 31 will increase and decrease at the rate of the interruptions. Thus. the current ilowins through the unit 31 will increase and decrease and the voltage across the unit will vary. The magnitude ot the varying voltage will be indicated on the meter 39. The magnitude o1 the varying voltage will be a measure of the temperature of the applied heat. Third. if the scanning disc is used with a plurality of units, heat may be applied separately to the several units o! a multiunit heat detector. Those units may be connected to separate indicators or the output may be used to form an image of the heat source as disclosed and claimed in copendlng application Serial No. 515,879, filed December 28, 1943, entitled Systems ior forming images ot heat radiating objects, Patent No. 2,403,066, and assigned to the same assignee as the instant application.

Thus the invention has been described as an improved heat responsive unit consisting of a very y Iductors or alloys oi materials may be used. auch as tellurium silver alloy composed oi the order oi 10 percent silver and 90 percent tellurium. A

simple method has been described ior forming a plurality of separate heat responsive umts which are deposited on a common membrane. 'I'he heat responsive devices may be used to indicate heat which is applied steadily or intermittently to one or to more than one unit.

I claimas my invention: y

1. A heat detector including a stretched membrane oi low thermal capacity, a semi-conductor having a high coelcient of resistance attached to one side oi said membrane, and a pair of conductors connected to said semi-conductor.

2. A heat detector including an electrically insulated stretched membrane, a semi-conductor having a high coeilicient of resistance deposited on one side of said membrane, and a D011' of conductors engaging said semi-conductor.

3. A heat detector including in combination an electrically insulated stretched membrane of low thermal capacity. a semi-conductive material havupon one side of said membrane, and a. semiconductor having a negative coeicient of resistance connected between said pair of conductors. l

5. A heat detector-including a cellulose acetate membrane, a, pair of electrical conductors deposited thereon, anda semi-conductor of tellurium oxide connected between said conductors.

6. A heat detector including a cellulose acetate membrane, a pair of electrical conductors deposited thereon, and a semi-conductor of tellurium oxide deposited upon said membrane and connected between said conductors.

7. A heat detector including a flexible plastic membrane a supporting member for said membrane, at least a pair of conductors deposited on said membrane, and tellurium oxide heat respon sive units connected between said conductors.

8. 'Ihe'method of forming a heat responsive detector on a stretched membrane of low thermal capacity having a thickness of the order oi 3 108 cm. which includes the steps of depositing on .one side of said membrane a pair of conductors, and depositing between said conductors a semi-conductor having a negative coeilicient of resistance.

9. The method of forming heat responsive units on a membrane which consists in masking portions of said membrane, placing said masked membrane within a vacuum, disposing within said vacuum a conductor, heating said conductor to deposit conductive portions on the unmasked portions oi said membrane, arranging said mask to expose portions of said membrane between said conductive portions, placing the thus masked membrane within a vacuum, and heating tellurium within said vacuum to deposit tellurium on the exposed portions of said membrane.

12. A heat detector including a stretched membrane of low thermal capacity, and a negative thermal coefficient semi-conductor deposited cn one side of said membrane.

13. A heat detector including a stretched membrane of low thermal capacity, a pair of conducinsulating support, a membrane stretched over 10. The method set forth in claim 9 plus the n additional step of supplying oxygen to said vacuum so that the tellurium deposit is oxidized.

11. A heat detector including a stretched membrane of low thermal capacity, and a semi-conductor deposited on one side of said membrane, said semi-conductor consisting of a material having a negative coeiiicient of resistance as a function of temperature.

said support and supported so as to have a suspended central portion, a thin layer of a metallic oxide having a relatively high coeiiicient of resistance deposited on said membrane and means for establishing electrical connections to spaced portions of said layer. v

JOHN EVANS.

REFERENCES CITED The following references are of record in the ille of this patent:

l UNITED STATES PATENTS Number Name Date 1,697,451 Baird Jan. 1, 1929 1,997,973 Moore Apr. 16, 1935 1,997,479 Burg Apr. 9, 1935 1,827,016 Joffe Oct. 13, 1931 1,647,652 Murray Nov. 1, 1927 FOREIGN PATENTS Number Country Date 188,030 Great Britain Oct. 23, 1922 383,990 Great Britain- Dec. 1, 1932 OTHER REFERENCES Harris et al., Review of Scientic Instruments, vol. 5, 1934, page 157.

Strong, Procedures in Experimental Physics 1942, pages 329-331 (copyright `1938).