RADIOMETRIC PERFORMANCE ENHANCEMENT OF EXTENDED AREA BLACKBODIES

Abstract

An extended area cavity type blackbody for use as a radiometric reference for imaging systems may have a well in the form of a cube having four sidewalls and a back wall, and open at the front. The temperature of the back wall may be controlled independently of the temperature(s) of the sidewalls. This system may produce infrared radiance closer to an ideal radiator than typical extended area sources. A simple blackbody is disclosed, having a source plate with a front emitting surface; a ledge element disposed in front of and below the source plate for heating air in front of the source plate; and (optionally) another ledge element disposed in front of and above the source plate for cooling air in front of the source plate. A housing may support the source plate and ledge element, and a vent may be provided in front of and above the source plate. A resistive heater may be associated with the ledge element; and (optionally) TECs may be associated with the other (cooling) ledge element. Angles of the ledges may be adjustable to optimize the best uniformity for a particular implementation. Temperature control of the ledges may be in unison with or independent from the source plate.

Claims

1. Improved extended area blackbody comprising: an enclosure having a number (n) of sidewalls and a rear wall, wherein the sidewalls and rear wall are formed of a thermally conductive material, and a front of the enclosure is open or has an opening for infrared radiation to exit the cavity; a coating with a high emissivity material disposed on an interior surface of the sidewalls; and a coating with a high emissivity material disposed on the interior surface of the back wall; wherein the thermally conductive material is selected from the group consisting of copper and aluminum, wherein the high emissivity material is selected from the group consisting of carbon nanotubes (CNT) and paint.

2. The blackbody of claim 1, wherein: the number (n) of sidewalls is at least (n>=3).

3. The blackbody of claim 1, wherein: the number (n) of sidewalls is four (n=4).

4. The blackbody of claim 1, wherein: the number (n) of sidewalls is greater than four (n>4).

5. The blackbody of claim 1, wherein: the sidewalls are flat.

6. The blackbody of claim 1, further comprising: thermoelectric modules (TEM) mounted to at least some of the sidewalls, and to the rear wall.

7. The blackbody of claim 1, further comprising: resistive heaters mounted to at least some of the sidewalls, and to the rear wall.

8. The blackbody of claim 1, wherein: the enclosure is in the form of a cube, with the four sidewalls and the back wall having substantially the same dimension as each other.

9. The blackbody of claim 1, wherein: the enclosure has the form of a rectangular prism

10. The blackbody of claim 1, wherein: in a non-cube geometry, the sidewalls have substantially the same dimension as each other, and the back wall is larger than the sidewalls.

11. The blackbody of claim 1, further comprising: thermoelectric modules (TEMs) or resistive heaters associated with the sidewalls and the back wall; wherein the temperature of the side walls are controlled separately controlled from the temperature of the back wall.

12. Improved extended area blackbody comprising: a source plate having a front emitting surface; and a bottom ledge element disposed in front of and below the source plate for heating air in front of the source plate.

13. The blackbody of claim 12, further comprising: a TEC or a resistive heater associated with the bottom ledge element.

14. The simple blackbody of claim 12, further comprising: a top ledge element disposed in front of and above the source plate for cooling air in front of the source plate.

15. The simple blackbody of claim 14, further comprising: a TEC associated with the top ledge element.

16. The simple blackbody of claim 14, wherein: an angle of the top (cooler) ledge element is adjustable to optimize the best uniformity for a particular implementation.

17. The blackbody of claim 12, wherein: an angle of the bottom (heater) ledge element is adjustable to optimize the best uniformity for a particular implementation.

18. The blackbody of claim 12, wherein: the bottom (heater) ledge element heater is not separately controlled from the source plate.

19. The blackbody of claim 12, wherein: for very large temperature ranges, the ledges have independent temperature control from the emissive surface (source plate).

20. The blackbody of claim 12, further comprising: a housing supporting the source plate and bottom ledge element; and a vent disposed in the housing at the top of the source plate to prevent hot air from pooling there.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Reference will be made in detail to embodiments of the disclosure, non-limiting examples of which may be illustrated in the accompanying drawing figures (FIGs). The figures may generally be in the form of diagrams. Some elements in the figures may be stylized, simplified or exaggerated, others may be omitted, for illustrative clarity.

[0047] Although the invention is generally described in the context of various exemplary embodiments, it should be understood that it is not intended to limit the invention to these particular embodiments, and individual features of various embodiments may be combined with one another. Any text (legends, notes, reference numerals and the like) appearing on the drawings are incorporated by reference herein.

[0048] Some elements may be referred to with letters (AS, CBR, CF, MA, MT, TCM, etc.) rather than or in addition to numerals. Some similar (including substantially identical) elements in various embodiments may be similarly numbered, with a given numeral such as 310, followed by different letters such as A, B, C, etc. (resulting in 310A, 310B, 310C), and may collectively (all of them at once) referred to simply by the numeral (310).

[0049] The following figures may be referred to and/or described in the text.

[0050] FIG. 1 is a perspective view of an improved extended area blackbody (BB), in the form of an open-ended cube, according to an exemplary embodiment of the invention.

[0051] FIG. 2 is a cross-sectional view of an exemplary sidewall or back wall of the cavity blackbody (BB) of FIG. 1.

[0052] FIG. 3 is a diagram of an improved extended area blackbody using a ledge heater in front of the source plate, and optionally a top ledge for cooling, according to an exemplary embodiment of the invention.

[0053] FIG. 4 is a diagram of an improved extended area blackbody using a ledge heater in front of the source plate, and with a vent above the source plate, according to an exemplary embodiment of the invention.

DESCRIPTION

[0054] Various embodiments (or examples) may be described to illustrate teachings of the invention(s), and should be construed as illustrative rather than limiting. It should be understood that it is not intended to limit the invention(s) to these particular embodiments. It should be understood that some individual features of various embodiments may be combined in different ways than shown, with one another. Reference herein to one embodiment, an embodiment, or similar formulations, may mean that a particular feature, structure, operation, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Some embodiments may not be explicitly designated as such (an embodiment).

[0055] The embodiments and aspects thereof may be described and illustrated in conjunction with systems, devices and methods which are meant to be exemplary and illustrative, not limiting in scope. Specific configurations and details may be set forth in order to provide an understanding of the invention(s). However, it should be apparent to one skilled in the art that the invention(s) may be practiced without some of the specific details being presented herein.

[0056] Furthermore, some well-known steps or components may be described only generally, or even omitted, for the sake of illustrative clarity. Elements referred to in the singular (e.g., a widget) may be interpreted to include the possibility of plural instances of the element (e.g., at least one widget), unless explicitly otherwise stated (e.g., one and only one widget).

[0057] In the following descriptions, some specific details may be set forth in order to provide an understanding of the invention(s) disclosed herein. It should be apparent to those skilled in the art that these invention(s) may be practiced without these specific details. Any dimensions and materials or processes set forth herein should be considered to be approximate and exemplary, unless otherwise indicated. Headings (typically underlined) may be provided as an aid to the reader, and should not be construed as limiting.

[0058] Reference may be made to disclosures of prior patents, publications and applications. Some text and drawings from those sources may be presented herein, but may be modified, edited or commented to blend more smoothly with the disclosure of the present application.

[0059] FIG. 1 illustrates a box-like enclosure 100, forming a cavity or well. The enclosure may be in the form of a cube, or another rectangular solid having straight walls, for example rectangular prismatic, cuboid, or hexagonal prismatic.

[0060] The exemplary enclosure has four (4) side walls (left, right, top, bottom), and a rear (back) wall. A front of the enclosure may be open, or may be partially enclosed, with an opening. The enclosure thus resembles an open box.

[0061] The front is open so that an IR Camera or other sensor is able to stare into the open end and view the back plate (rear wall). Since the surface temperature is so close to the well temperature and the emissivity is nearly 1 (should be well over 99% with CNTs), then the thermal emission should closely follow the ideal Planck function.

[0062] Source plate assemblies may be mounted to the four (for example) side walls, and to the back (rear) wall. A source plate assembly may comprise a source plate, thermoelectric modules, or other temperature control device, such as a resistive heater, and a heatsink. See, for example, a typical single-plate extended area blackbody source, such as the SBIR Infinity line: (https://sbir.com/blackbodies/)

[0063] The thermally conductive walls, with thermoelectric modules and heat sinks in place thus become, in effect, source plates.

[0064] An interior surface of the side walls may be coated with a high-emissivity material, such as black paint, or may be coated with carbon nanotubes (CNT). The interior surface of the back (rear) wall may be coated with carbon nanotubes, or may also be coated with paint.

[0065] The side walls and back (rear) wall may preferably be flat, to accommodate mounting thermoelectric modules (TEM) to the exterior surface thereof. Thermoelectric modules (TEM) may be mounted to the sidewalls and to the back wall to heat and cool the enclosure to a controlled temperature. The individual sidewalls and back wall may be individually controlled with control electronics (not shown, well known). [0066] Note: Thermoelectric, or Peltier Cooling Modules (also known as a TEC or a TEM) come in a wide variety of types and sizes. While typically used for cooling, they can also be used for heating (by reversing the electric current flow) and even for power generation.

[0067] Alternatively, the back wall may be curved, or conical, and may not have thermoelectric modules (TEM) mounted to its exterior surface.

[0068] The back plate (wall) interior surface may be modified to geometrically increase its effective emissivity, through the use of grooves, microcavities and the like. Such geometries reduce reflectance, but usually look worse than a flat plate due to variations in the surface temperature of the grooves, etc. The air-heating effect of the cavity may make those surface geometries more attractive.

[0069] Note that although shown as a cube in FIG. 1, the embodiment does not have to be in the shape of a regular prism. The side walls may be smaller than the back wall may be rectangular or some other shape as dictated by use-case requirements. For example, circular and rounded-rectangle blackbodies are in use and such shapes of the back wall can be used in conjunction with the inventions described herein to improve their radiometric performance.

[0070] FIG. 2 illustrates, in cross-section, an exemplary side wall, or back wall, showing (in order, from exterior to interior), [0071] a heat sink, [0072] thermoelectric modules (TEM's, or TEC's), alternatively, resistive heaters may be used instead of thermoelectric heaters [0073] the exemplary wall (which functions as a source plate), and [0074] a coating of carbon nanotubes (CNT) or paint on the interior surface thereof.

[0075] The temperature of the sidewalls may be maintained (e.g., by the TEM's or resistive heaters) to be the same as one another. The temperature of the back wall may be maintained (e.g., by the TEM's or resistive heaters) to be the same as, or different than the temperature of the sidewalls.

Another Embodiment

[0076] Many blackbodies have their uniformity limited by convective losses from their front surface. This is particularly true for inexpensive blackbodies with thin source plates.

[0077] According to an embodiment of the invention, losses can be limited by heating the air below (and in front of) the source place such that it is comparable (substantially equal) to the plate temperature as it rises (increases), thus limiting heat exchange between the air and the surface.

[0078] FIG. 3 is a diagram of an extended area blackbody 300 using a ledge heater disposed in front of a source plate, according to an exemplary embodiment of the invention.

[0079] A temperature-controlled source plate 302, comparable to the back wall of the black body shown in FIG. 1, has an emitting surface (left, as shown), and may be comparable to the source plate arrangement shown in FIG. 2.

[0080] A ledge heater 304, which is another heated plate, may be disposed in front of (to the left, as shown) and generally below the temperature-controlled source plate 302, and may be comparable to the source plate arrangement shown in FIG. 2.

[0081] The ledge heater 304 does not need to be separately controlled. It can be connected and controlled in series with the heater in the source plate.

[0082] The ledge heater 304 area, power and angle may be adjusted to provide good uniformity over a range of temperatures.

[0083] By using the ledge heater 304 in conjunction with the source plate 302, as shown, nonuniformity (NU) may be reduced significantly, such as by a value of 3 or more!

[0084] Resistive heaters may be used to control the temperature of the ledge heater.

[0085] Another ledge plate (top ledge) 306 may be used for cooling, in conjunction with thermoelectric modules (TEM's, or TEC's; not shown), and may be disposed in front of and generally above the temperature-controlled source plate 302.

[0086] Using the ledge heater 304 in conjunction with the source plate, as shown, may be considered to be a simple, and lower-cost step towards the concept disclosed in FIG. 1, both of which may be concerned with reducing errors due to convection.

[0087] A noticeable difference between the simple blackbody 300 of FIG. 3 and the cavity-like extended area blackbody 100 of FIG. 1 is that the simple blackbody 300 does not have four sidewalls. In fact, it may have essentially no sidewalls, only the aforementioned lower ledge heater 304 and upper ledge plate 306. More particularly, the simple blackbody illustrated in FIG. 3 may only have a source plate (comparable to the rear wall of the blackbody in FIG. 1) and a small bottom sidewall (in the form of a ledge), without having a left, right or top sidewall (compare FIG. 1), and may be implemented as a heat-only blackbody with a resistive heater instead of TECs.

[0088] Optionally, the top ledge (comparable to the top wall of the blackbody in FIG. 1), may be incorporated (with TECs) for cooling, or ledges at both the top and bottom may be used for implementations where it is desirable to have a source that can be controlled both above and below the ambient air temperature.

[0089] In other words, for a heat-only blackbody, an upward-tilted ramp or ledge is provided at the bottom of the source plate (back wall) to heat the air in front of the source plate in order to reduce nonuniformity from convection. Convection will still be there, but the air at the bottom is heated so that it is at approximately the same temperature as the source plate as it (the heated air) flows up the surface. As shown, the heating ledge 304 is tilted (inclined) upward from its right (as viewed) side, adjacent the source plate/emitting surface 302 towards the front of the simple blackbody 300. The upper ledge plate 306 may similarly be tilted from its right (as viewed) side, adjacent the source plate/emitting surface 302 towards the front of the simple blackbody 300, and may (or may not) be parallel to the lower heating ledge 304.

[0090] Many blackbodies have their source plates recessed to help reduce the effects of external air currents. When using a lower ledge heater, a passage can be created at the top of the source plate in order to prevent hot air from pooling at the top of the source plate. This passage can be made slightly convoluted such that air currents near the exit do not have a direct path to the source plate, and thus help improve the stability and uniformity of the blackbody.

[0091] FIG. 4 is a diagram of simple blackbody 400, comparable to the simple blackbody 300 of FIG. 3, and similarly uses a ledge heater 404 (compare 304) disposed in front of the source plate 402 (compare 302).

[0092] In this embodiment, the blackbody 400 is shown having a housing 410 supporting the source plate 402 and ledge heater 404. There is no top ledge (compare 306) for cooling. Rather, a vent 412 is provided in the housing, in front of and at the top of the source plate/emitting surface 402 to prevent hot air from pooling in the housing at the top of the source plate 402in other words, to allow air heated by the lower ledge heater 404 and passing by the front of the emitting surface to escape the housing 410.

[0093] Note that the housing 410 is shown as having only a top wall 410a and a bottom wall 410b. It should be understood that the housing 400 may additionally have two (left and right) sidewalls, in a manner similar to that of the cavity blackbody 100 shown in FIG. 1, though the sidewalls are not always required.

APPENDIX

[0094] Enclosed herewith, and forming part of the disclosure hereof is a document entitled Nightingale Body Temperature Reference. As disclosed therein: [0095] Santa Barbara Infrared's Nightingale Body Temperature Reference (BTR) blackbody systems provide a stable, uniform, low cost and simple to operate thermal source for human body temperature detection. Nightingale sources are primarily designed to be incorporated into thermal imaging body temperature screening systems. They work by providing a viewable thermal reference area for Infrared camera systems. The Nightingale BTR source features set and forget configuration. An operator simply configures the reference source through the USB interface and stores the set point into non-volatile memory. After configuration, the blackbody will automatically control to the set point upon each power up. A status LED visually indicates when the reference is stable and ready for use as a calibration source. The Nightingale's performance has been optimized for a range of absolute temperature set points and ambient conditions that are required by most body temperature screening systems.

[0096] Various technical specifications for the Nightingale Body Temperature Reference are set forth therein.

[0097] While the invention(s) may have been described with respect to a limited number of embodiments, these should not be construed as limitations on the scope of the invention(s), but rather as examples of some of the embodiments of the invention(s). Those skilled in the art may envision other possible variations, modifications, and implementations that are also within the scope of the invention(s), and claims, based on the disclosure(s) set forth herein.