INTEGRATED DETECTOR DEWAR CRYOENGINE

Abstract: The integrated detector dewar cryoengine (10) includes a detector (12) for detecting received electromagnetic radiation. The integrated detector dewar cryoengine (10) further comprises expander end cap (18) for removing thermal energy from said detector (12) which is in mechanical communication with said detector (12).

Description: IQ^GRA ED DEEICTOR DEWAR CRYOENGINE BACKGROUND OF THE JSIVENTION 1. Field of the Invention This invention relates to the field of infrared sensing, and more particularly to an integrated detector dewar cryoengine. 2. Description of Related Art Infrared detectors are often used in conjunction with missiles and night vision systems to sense the presence of electr πagnetic radiation having a wavelength of 1-15 urn. Because they are often most sensitive when operating at approximately 77 K, infrared detectors such as those fabricated from rfercury-cacijTάurtt-tell'uride often require a cryoengine assembly to produce and maintain the required operating temperature. Such cryoengine assemblies are typically used in conjunction with an evacuated dewar in which the infrared detector is placed. The dewar is evacuated to remove thermally conductive gases which would otherwise occupy the region surrounding the detector. The dewar is cooled by placing an indented region ("coldwell") of the dewar in contact with an expansion chamber ("expander") of the cryoengine assembly which is supplied with a cooling fluid such as helium. The coldwell and the expander are separated by a gap to allow for variation in the dimensional characteristics of the dewar and expander, as well as to accαrtπodate for differences in their thermal expansion characteristics. To supply the expander with the cooling fluid, the cryoengine assembly often includes a compressor which delivers the fluid to the expander through a transfer line. As the fluid expands in the expander, it absorbs thermal energy frcm both the expander and the dewar causing 1 the detector to cool- Because the temperature of the expander is related to the amount of" fluid delivered by the compressor, the temperature of the detector may be controlled by varying the compressor speed. ' -5- ' While the infrared detector assemblies described above were able to produce and ir intain the t-_mperature levels required for sensitive operation of the ιιjercurγ-cac_miuiur-telluride detectors, they often had several disadvantages in terms of thermal conduction between the expander and the environment. Because the dewar and expander are 0 structurally independent, the gap between the expander and the dewar acted as an insulator to prevent optimal conduction between the expander and the detector. In addition, the cross-sectional area through which cold loss occurred not only included the cross-sectional area of expander, but also included the walls of the dewar which were adjacent 5 to the expander. These two features necessarily meant that the capacity of the cryoengine had to be scmewhat larger than would otherwise be required. SUMMARY OF THE INVENTION An apparatus for detecting elect_romagnetic radiation is disclosed. The apparatus comprises a detector for detecting electromagnetic radiation. Thέ apparatus also comprises an expander end cap for removing thermal energy frcm said detector. The device for removing thermal energy frcm said detector mechanically ccmrπunicates with the detector. . BRIEF DESCRIPTION OF THE DRAWINGS Various advantages of the present invention will tjecome apparent to one skilled in the art upon reading the following specification and by reference to the drawings in which: FIG. 1 is a cross-sectional view of the integrated detector dewar cryoengine by the present invention; and FIG. 2 is an exploded perspective view of the integrated detector cryoengine shown in FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED JSMBODIMENT With reference to the drawings, an integrated detector dewar cryoengine 10 according to the present invention is shown. The integrated detector dewar cryoengine 10 includes an infrared detector 12 for receiving infrared radiation and generating responsive electrical signals. While the detector 12 may be made from a layer of on a sapphire substrate material, other suitable materials such as CdTe and CdSe may also be used. The detector 12 is secured on a detector platform 14 by a thermally conductive adhesive, which rermits thermal energy to flow from the detector 12. While the detector platform 14 may be fabricated from beryllium, other suitable materials may be used. To remove thermal energy from the detector 12 so as to pe mit optimum detector performance, the integrated detector dewar cryoengine 10 further comprises an expander assembly 16 (see FIG. 2) . The expander assembly 16 includes an expander end cap 18 which mechanically cc-rrittunicates with the detector platform 14 so that thermal energy can flow from the detector platform 14 to the expander end cap 18. The detector platform 14 is disposed between two of four castellations located on the expander end cap 18 and is secured to the expander end cap 18 by means of a thermally conductive adhesive. The expander end cap 18 is disc shaped so as to have a low thermal mass and a high thermal conductivity. The expander end cap 18 is preferably fabricated frcm beryllium so as to provide a relatively high degree of thermal conductivity, though it is to be understood that other suitable materials may be used. . The expander assembly 16 also includes an expander tube 20 which is-brazed to the expander end cap 18. The expander tube 20 houses the refrigeration mechanism Tϊor cooling the detector 12 and receives cooling fluid such as helium from a σ_mpressor (not shown) . By expansion of the fluid inside the expander tube 20, thermal energy is drawn frcm the expander end cap 18 thereby cooling the detector 12. The ' expander tube 20 is preferably fabricated frcm Inconel so as to have low tiermal conductivity while being sufficiently rigid to minimize detector movement during operation. To support the expander tube 20, an expander housing 22 is provided. The expander housing 22 is brazed to the expander tube 20 and is connected to the cryoengine compressor (not shown) . The expander assembly 16 also includes a cable support 24 which is used to support the flex cables described below. To monitor the temperature of the infrared detector array, two thermal sensors 26 are located adjacent to the detector 12 on the flex cables described below. The outputs from the thermal sensors 26 are used to control the compressor speed which in turn controls the temperature of the expander assembly 16. Each of the thermal sensors 26 may be a 2N2222 switching diode, though it is to be understood that other suitable temperature sensors which are sensitive to temperature variation in the requisite ranges may be used. To mount the thermal sensors 26 on the expander end cap 18, a thermal sensor mount 28 is provided. The thermal sensors 26 are secured to the thermal sensor mount 28 by means of a i±._rmally conductive adhesive. The thermal sensor mount 28 may be fabricated from a ceramic, though other suitable materials may be used. To permit electrical ccmmunication between the detector 12 and external electronics, two flex cables 30 are provided. The flex cables 30 permit signals generated by the detector 12 to be delivered to a distribution board 32. The flex cables 30 are attached at one end to the conductive pads of the detector 12 through gold lead wires. The other end of the flex cables 30 connect to a distribution board 32. For purposes of clarity, the flex'cables shown in FIG. 1 have been rotated by 45°. The flex cables 30 comprise a flexible etched circuit having metallic conductors disposed between layers of rxolymide base dielectric material attached by means of an acrylic adhesive. The distribution board 32 includes a plurality of internal conductors oriented to permit access to the electrical signals delivered to one side of the distribution board by the flex cables 30 to the opposing side of the distribution board 32. A plurality of load springs 34 and screws 36 are provided to clamp the flex cables 30 to the distribution board 32. To permit access to the electrical signals delivered to the distribution board 32 by the flex cables 30, a connector 38 is provided. The connector 38 receives the electrical signals frcm the distribution board 32 through a plurality of conductive pins 40. The conductive pins 40 extend frcm the distribution board 32 through the connector 38 to a position above the connector 38 where they can be accessed. A shroud 39 is provided to protect the distribution board 32 from the environment. To appropriately bias to the detectors 12, the bias resistor board 42 is provided which electrically communicates with the connector 38. The bias resistor board 42 functions as a voltage divider so that the appropriate voltages are delivered to the detector 12 to ensure proper operation. To provide structural integrity to the integrated detector dewar cryoengine 10, the integrated detector dewar cryoengine 10 further comprises an assembly housing 44 and a mount plate 46. The assembly housing 44 is used to provide structural support to the ccmponents of the integrated detector dewar cryoengine 10, and may be fabricated from a low expansion alloy. It is to be understood, however, that other suitable materials may be used. The mount plate 46 is used to secure the integrated detector dewar cryoengine 10 in its appropriate position. The mount plate 46 mechanically cciriπunicates with a base adjustment nut 48, which permits rotation of the mount plate 46 independent of the expander housing 22. An 0-ring 50 is disposed between expander housing 22 and the mount plate 46 to provide friction upon rotation of the mount plate 46. To environmentally isolate the detector 12 and the expander end cap 18, the integrated' detector dewar cryoengine 10 further comprises a bulkhead 52 and a .-shield 54. The bulkhead 52 is welded to the assembly housing 44 and mechanically cc-raπurϊάcates with an evacuation tube 56. The evacuation tube. 56 is used to withdraw gases frcm the integrated detector dewar cryoengine 10 to m__dmize the thermal isolation. The bulkhead 52 also cccιm__Lcates with two getter feedthrus 58 which ccrrmunicate with two getters 60. The getters 60 are used during the evacuation process to further eliminate gases inside the integrated detector dewar cryoengine 10. The bulkhead 52 mechanically cc-Tirainicates with shield 54 and a frame 64 to form the sides of the vacuum chamber. A window 66 and a window housing 68 are provided to form the top of the vacuum chamber. The window 66 is fabricated from germanium or zinc selenide to produce the desired transmission band, and is used to transmit incoming infrared radiation on the detector 12. The window housing 68 is used to support the window 66 and to pe it the integrated detector dewar cryoengine 10 to be evacuated. To minimize the amount of thermal radiation delivered to the detector 12 from sources other than the scene, a coldshield 70 is provided which is centrally located over the detector 12. The coldshield 70 is connected to two of four castellations on the expander end cap 18 and has an aperture which provides an unobstructed path for infrared radiation from the environment to be received by the detector 12. The coldshield 70 has a thin wall and is fabricated frcm a high conductivity material so as to have a relatively low thermal mass which reduces cooldown time. While the coldshield may be fabricated frcm 6061-T6 alι_minum, it is to be understood that other suitable materials may be used. Because the detector 12 is in direct thermal corππunication with the expander end cap 18, the detector 12 may be cooled more rapidly than would otherwise be possible. In addition, because the dewar and the expander form an integrated unit, the cross-sectional area through which cold loss can occur is reduced. It should therefore be understood that this invention was described in connection with a particular example thereof. Other modifications will become apparent to those skilled in the art after a' study of the specification, drawings, and following claims.

Claims: CLAIMS What is Claimed is: I 1 1. An apparatus for detecting electromagnetic radiation comprising: detector means for detecting electromagnetic radiation; and means for removing thermal energy from said detector means, 5 said means for removing thermal energy frcm said detectormeans being in mechanical ccrrmunication with said detector means. 1 2. The apparatus of Claim 1, wherein said means for removing thermal energy frcm said detector means comprises an expander. 1 3. The apparatus of Claim 2, wherein said expander includes an expander end cap. ■1 . 4. The apparatus of Claim 3, wherein said expander end cap is disc shaped. ,1 5. The apparatus of Claim 4, wherein said expander end cap is fabricated from beryllium. 6. The apparatus of Claim 1, wherein said means for removing thermal energy from said detector means further comprises a detector mount, said detector mount mechanically communicating with said detector means. 1 7. An apparatus for detecting electromagnetic radiation comprising: detector means for detecting electromagnetic radiation; means for removing thermal energy frcm said detector means; 5 and means for environmentally isolating said detector means and said means for removing thermal energy frcm said detector means. 8. The apparatus of Claim 7, wherein said means for removing thermal energy from said detector means comprising an expander, said means for environmentally isolating said detector means and said means for removing thermal energy 'from said detector means comprises an expander housing operably to mechanically support said expander. 9. The apparatus .of Claim 8, wherein said means for environmentally isolating said detector means and said means for removing thermal energy frcm said detector means further comprises an assembly housing. 10. The apparatus of Claim 9, wherein said means for environmentally isolating said detector means and said means for removing thermal energy from said detector means further comprises a bulkhead mechanically ccmmunicating with said assembly housing. 11. The apparatus of Claim 10, wherein said means for environmentally isolating said detector means and said means for removing thermal energy from said detector means further comprises a shield mechanically ccximunicating with said bulkhead. 12. The apparatus of Claim 11, wherein said means for environmentally isolating said detector means and said means for removing thermal energy from said detector means further comprises a frame mechanically ccmmunicating with said shield. 13. The apparatus of Claim 12, wherein said means for environmentally isolating said detector means and said means for removing thermal energy from said detector means further comprises a distribution board mechanically ccmmunicating with said frame. 14. The apparatus of Claim 13, wherein said means for environmentally isolating said detector means and said means for removing thermal energy from said detector means further comprises a window housing mechanically communicating with said assembly housing. 15. The apparatus of Claim 14, wherein said means for eαivironrtientally isolating 'said detector means and said means for removing thermal energy frcm said detector means further comprises a window mechanically cctr-fliinicating with said window housing. 16. The apparatus of Claim 7, wherein said means for removing thermal energy frcm said detector means comprises a detector mount disposed on an expander end cap, said detector means rrechanically ccπi αnicating with said detector mount. 17. A method for removing theαrnal energy frcm a detector in an electromagnetic detection apparatus using an expander, said method ccmprising the steps of: - evacuating a region of said apparatus surrounding said detector and said expander; and permitting thermal energy frcm said detector to be drawn from said detector_to said expander. 18. The method of Claim 17, wherein said expander comprises a disc shaped ' expander end cap. 19. The method of Claim 18, wherein said detector mount is fabricated from beryllium. 20. The rrethod of Claim 17, wherein said step of r^rmitting thermal energy to flow from said detector to said expander includes the step of permitting thermal energy to flow through a detector mount mechanically craimunicating with said detector and said expander.

Inventors: NEITZEL FRED J, PECK LEONARD E JR, RALL RICHARD M, NEITZEL, FRED, J., PECK, LEONARD, E., JR., RALL, RICHARD, M.
Applicants: SANTA BARBARA RES CENTER, SANTA BARBARA RESEARCH CENTER
Application year: 1987
Main classification: G01J5
IPC codes: F25D19, G01J5