Manufactured controllable cold background for passive biomimetic sensor

Abstract

A target-detection apparatus includes a passive biomimetic sensor for detecting a target in an ambient environment. The passive biomimetic sensor includes a field o f view. The ambient environment comprising ambient thermal radiation. The apparatus includes at least one plate comprising a surface located directly or indirectly in the field of view. The surface includes a surface emissivity, a surface temperature, and a surface thermal radiation. The surface emissivity and the surface temperature contribute to the surface thermal radiation. The surface thermal radiation is distinguishable from the ambient thermal radiation by the passive biomimetic sensor.

Description

IN THE UNITED STATES PATENT AND TRADEMARK OFFICEAPPLICATION FOR LETTERS PATENTTitle:MANUFACTURED CONTROLLABLE COLD BACKGROUND FOR PASSIVE BIOMIMETIC SENSORInventors:Cobey L. McGinnisJason D. MyersKenneth J. EwingJesse A. FrantzJasbinder S. SangheraMANUFACTURED CONTROLLABLE COLD BACKGROUND FOR PASSIVE BIOMIMETIC SENSORCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims the benefit of U. S. Provisional Application Serial No.63 / 734,308 filed on 16 December 2024, the entirety of which is incorporated herein by reference.FEDERALLY-SPONSORED RESEARCH AND DEVELOPMEN T

[0002] The United States Government has ownership rights in this invention. Licensing inquiries may be directed to Office of Technology Transfer, US Naval Research Laboratory, Code 1004, Washington, DC 20375, USA; +1.202.767.7230; techtran@nrl.navy.mil, referencing NC 212.498-US2.BACKGROUND OF THE INVENTIONField of the Invention

[0003] This invention relates in general to an apparatus for discriminating between chemical targets and ambient interferents, and in particular to an apparatus for discriminating between chemical targets and ambient interferents using an infrared detector with a manufactured controllable cold background.Description of the Related Art

[0004] Infrared spectroscopy is a well-known technique that can be used to measure the presence of materials, chemicals, and chemical vapors based on their unique absorption bands in theinfrared portion of the electromagnetic spectrum. This technique relies on measuring the intensity of transmitted or reflected light from a well-controlled and characterized infrared source, typically with the use of a detector cooled either thermoelectrically or with liquid nitrogen. This technique has been used for outdoor and indoor measurement of airborne chemicals.

[0005] U. S. Patent Nos. 11,029,247 and 9,857,295, incorporated herein by reference, disclose systems, which detects infrared chemical signatures either as a solid / liquid on a surface or as a vapor in the atmosphere as well as a methodology to discriminate these chemical signatures using the Infrared C1E methodology, which is an infrared analog of the visible color space defined by the International Commission on Illumination. These systems utilize an unadulterated view' of the clear sky as a cold, stable background.SUMMARY OF THE INVENTION

[0006] An embodiment of the invention includes a target-detection apparatus. The apparatus includes a standard, passive biomimetic sensor for detecting a target in an ambient environment. The passive biomimetic sensor includes a field of view. The ambient environment comprising ambient thermal radiation. The apparatus includes at least one plate comprising a surface located one of directly and indirectly in the field of view. The surface includes a surface emissivity, a surface temperature, and a surface thermal radiation. The surface emissivity and the surface temperature contribute to the surface thermal radiation. The surface thermal radiation is distinguishable from the ambient thermal radiation by the passive biomimetic sensor.

[0007] An embodiment of the invention includes an apparatus having a manufactured, controlled background. The manufactured, controlled background provides an adequate thermal contrast to discriminate chemical vapors from other airborne interferents circumventing the need foran unadul terated view of the clear sky. A thin, thermally conductive material is placed within the field of view of the apparatus’ sensor. The surface of this material is roughened to increase the surface emissivity decreasing reflected ambient infrared spectral signatures. The temperature of this surface is regulated and maintained using a thermoelectric Peltier cooler. Airborne chemicals pass between the detector and this material within the field of view. This embodiment of the invention allows for the discrimination of chemical vapors from background interferents without the reliance on the cold sky as a stable background.

[0008] An embodiment of the invention allows for the detection / discrimination of chemical vapors from background interferents (i.e. water vapor, and carbon dioxide).

[0009] An embodiment of the invention allows for operation of a passive biomimetic sensor without the reliance on the clear cold sky as a background.

[0010] An embodiment of the invention allows for generation of a cold IR background that minimizes, or rejects, condensation of water vapor, present as ambient humidity in the atmosphere, on the cold stop.

[0011] An embodiment of the invention allows for measurements in multiple environments including but not limited to indoor, outdoor, urban, industrial, and clinical.

[0012] An embodiment of the invention allows for continuous monitoring of or for chemical vapors.

[0013] An embodiment of the invention allows for detection and / or discrimination of multiple different chemical vapors simultaneously.

[0014] An embodiment of the invention allows for acquisition of information regarding concentration of chemical vapors in real time.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is an illustrative block diagram of an embodiment of the invention.

[0016] FIG. 2 is an illustrative block diagram of a target in an ambient environment according to an embodiment of the invention.

[0017] FIG. 3 A is an illustrative block diagram of a passive biomimetic sensor according to an embodiment of the invention.

[0018] FIG. 3B is an illustrative block diagram of another passive biomimetic sensor according to an embodiment of the invention.

[0019] FIG. 3C is an illustrative block diagram of another passive biomimetic sensor according to an embodiment of the invention.

[0020] FIG. 4 is an illustrative block diagram of a passive biomimetic sensor cooperating with a mechanical shutter according to an embodiment of the invention.

[0021] FIG. 5 A is an illustrative block diagram of a plate according to an embodiment of the invention.

[0022] FIG. 5B is an illustrative block diagram of another plate according to an embodiment of the invention.

[0023] FIG. 5C is an illustrative block diagram of another plate according to an embodiment of the invention.

[0024] FIG. 5D is an illustrative block diagram of another plate according to an embodiment of the invention.

[0025] FIG. 5D is an illustrative block diagram of another plate according to an embodiment of the invention.

[0026] FIG. 5F is an illustrative block diagram of another plate according to an embodiment of the invention.

[0027] FIG. 6A is an illustrative block diagram of a metal for a plate according to an embodiment of the invention.

[0028] FIG. 6B is an illustrative block diagram of another metal for a plate according to an embodiment of the invention.

[0029] FIG. 6C is an illustrative block diagram of another metal for a plate according to an embodiment of the invention.

[0030] FIG. 7A is an illustrative block diagram of a coating for a plate according to an embodiment of the invention.

[0031] FIG. 7B is an illustrative block diagram of another coating for a plate according to an embodiment of the invention.

[0032] FIG. 8A is an illustrative block diagram of a metamaterial emitter structure for a plate according to an embodiment of the invention.

[0033] FIG. 8B is an illustrative block diagram of another metamaterial emitter structure for a plate according to an embodiment of the invention.

[0034] FIG. 8C is an illustrative block diagram of another metamaterial emitter structure for a plate according to an embodiment of the invention.

[0035] FIG. 9 is an illustrative block diagram of a temperature regulator for a plate according to another embodiment of the invention.

[0036] FIG. 10 is an illustrative block diagram of an embodiment of the invention including a pair of plates.

[0037] FIG. 11 is an illustrative block diagram of an embodiment of the invention including a reflective telescope.

[0038] FIG. 12 is an illustrative block diagram of an embodiment of the invention including an airtight enclosure.

[0039] FIG. 13A is an illustrative block diagram of a window of the airtight enclosure according to an embodiment of the invention.

[0040] FIG. 13B is an illustrative block diagram of another window of the airtight enclosure according to an embodiment of the invention.

[0041] FIG. 13C is an illustrative block diagram of another window of the airtight enclosure according to an embodiment of the invention.

[0042] FIG. 14A is an illustrative block diagram of an airtight enclosure having a gas according to an embodiment of the invention.

[0043] FIG. 14B is an illustrative block diagram of an airtight enclosure having another gas according to an embodiment of the invention.DETAILED DESCRIPTION OF THE INVENTION

[0044] An embodiment of the invention includes a target-detection apparatus 10 and is described as follows with reference, by way of non-limiting examples, to FIGs. 1 and 2. The apparatus 10 includes a standard, passive biomimetic sensor 20 for detecting a target 30 in an ambient environment 40. For the purpose of this patent application, ‘'passive biomimetic sensor” is a term of art and means an infrared detector cooperating with overlapping spectral filters over each pixel of the infrared detector so as to detect infrared chemical signatures of a solid, liquid, or gas, using an Infrared CIE methodology. For example, the target 30 includes a solid, liquid, and / or gas.For the purpose of this patent application, the terms “gas” and “vapor” are understood to be interchangeable. The passive biomimetic sensor 20 includes a field of view 25. Optionally, in an embodiment of the invention, standard optical elements, e.g., at least one standard lens and / or at least one standard mirror, intermediate an optical path between the passive biomimetic sensor 20 and the target 30. The ambient environment 40 includes ambient thermal radiation 45. Ambient temperature is a measure of the kinetic energy of air molecules. Ambient thermal radiation 45 includes the aggregate electromagnetic energy radiated by all objects in the ambient environment. An object's temperature and surface properties (e.g., its emissivity) determine the amount of thermal radiation it emits. The apparatus 10 includes at least one plate 50 comprising a surface 52 located directly or indirectly in the field of view 25. Optionally, the plate 50 is situated a distance away from the passive biomimetic sensor 20 such that the surface 52 fills the field of view 25 of the passive biomimetic sensor. The surface 52 includes a surface emissivity 54, a surface temperature 56, and a surface thermal radiation 58. The surface emissivity 54 and the surface temperature 56 contribute to the surface thermal radiation 58. The target 30 includes a target infrared signature 32. The target infrared signature 32 is different from the surface thermal radiation 58 and from the ambient thermal radiation 45. The passive biomimetic sensor 20 detects the target infrared signature 32.

[0045] Optionally, as shown by way of non-limiting examples in FIGs. 3A-3C, the infrared detector includes a standard, pyroelectric detector 22; a standard, uncooled bolometer 24; or a standard, cooled semiconductor (e.g., a standard InSb, strained layer superlattice, or a standard HgCdTe) detector 26. For example, the HgCdTe (“MCT”) detector includes a standard, amplified MCT detector. Examples of the pyroelectric detector 22 are found in U. S. Patent Nos. 9,857,295 and 11,029,247. Optionally, as shown by way of non-limiting example in FIG. 4, the passivebiomimetic sensor 20 includes a standard mechanical shutter 60 located between the infrared detector, e.g., at least one pyroelectric detector 22, and the at least one plate 50.

[0046] Optionally, the surface thermal radiation 58 is different from the ambient thermal radiation 45.

[0047] Optionally, as shown by way of non-limiting examples in FIGs. 5A-5F, the plate 50 includes a standard ceramic 80; a standard glass 90; a standard polymer 100; a standard metal 110; a standard coating 120; or a standard metamaterial emitter structure 130. An example of the ceramic 80 includes aluminum oxide. An example of the glass 90 includes fused silica. Examples of the polymer 100 includes Acrylonitrile Butadiene Styrene, polytetrafluoroethylene, polypropylene, and a polyimide. Examples of the metal 110 include copper, gold, stainless steel, and aluminum.Examples of the coating 120 include standard paint, carbon dust, and soot blackening.Examples of the paint include a standard, alkyd paint and a standard, acrylic-based paint. Examples of the plate 50 includes a surface layer, wherein the surface layer includes the ceramic, the polymer, the metal, or the metamaterial emitter structure. Optionally, as shown by way of non-limiting example in FIG. 6A, the metal 110 includes a standard, sufficiently high-emissivity metal 112 cooled such that the surface thermal radiation 58 is distinguishable from the ambient thermal radiation 45 by the passive biomimetic sensor 20. Optionally, the high-emissivity metal 112 includes a standard, anodized metal 114. Optionally, as shown by way of non-limiting examples in FIGs. 6B and 6C, the metal 110 includes a standard, sufficiently low-emissivity metal 116 cooled such that the surface thermal radiation 58 is distinguishable from the ambient thermal radiation 45 by the passive biomimetic sensor 20. Optionally, the low-emissivity metal 116 includes a standard, smooth metal 118 and a standard, polished metal 119. One of ordinary skill in the art will readily appreciate that a smooth metal need not be a polished metal. For example, a smooth metal having astandard "mill finish" has a dull, smooth surface fabricated using a standard machining process, e.g., using at least one standard cutter with a large nose radius or at least one wiper insert. Polished metal, by contrast, has a highly reflective and / or shiny finish fabricated using a standard, abrasive process (e.g., polishing, buffing, burnishing, and / or electropolishing). Optionally, as shown by way of non- limiting examples in FIGs. 7A and 7B, the coating 120 includes a sufficiently high- emissivity material 122 such that the surface thermal radiation 58 is distinguishable from the ambient thermal radiation 45 by the passive biomimetic sensor 20. Optionally, the coating 120 includes a sufficiently low-emissivity material 124 such that the surface thermal radiation 58 is distinguishable from the ambient thermal radiation 45 by the passive biomimetic sensor 20.Optionally, as shown by way of non-limiting examples in FIGs. 8A-8C, the metamaterial emitter structure 130 includes a standard, dielectric resonator 132; a standard, metallic resonator 134; or a standard, metal-insulator-metal resonator 136, wherein these examples are fabricated to have a known infrared emission profile. Optionally, the surface thermal radiation 58 includes a surface spectrum 59. The target infrared signature 32 includes a target spectrum 34, and the surface spectrum 59 is inverse of the target spectrum. For the purpose of this patent application, the surface spectrum being inverse of the target spectrum means a surface spectrum having high emission at wavelengths for which the target infrared signature has low emission.

[0048] Optionally, as shown by way of non-limiting example in FIG. 9, the apparatus 10 further includes a standard, thermoelectric cooler 140 operably connected to the plate 50 and regulating the surface temperature 56 such that the surface emissivity 54 and the surface temperature cooperate to distinguish the surface thermal radiation 58 from the ambient thermal radiation 45. Optionally, the apparatus 10 further includes a standard heatsink 150 operably connected to the thermoelectric cooler 140; and a first fan 160 operably connected to the heatsink.

[0049] Optionally, as shown by way of non-limiting example in FIG. 10, the at least one plate includes a pair of plates 50, 52. The passive biomimetic sensor 20 is located between the pair of plates 50, 52. The apparatus further includes a second fan 162 operably located to blow the target 30 between the pair of plates 50, 52, and to blow the target against or past the passive biomimetic sensor 20. The dotted lines in FIG. 10 represent a direction of airflow from the second fan 162 toward the target 30 and toward the passive biomimetic sensor 20.

[0050] Optionally, as shown by way of non-limiting example in FIG. 11, the apparatus 10 further includes a standard, reflective telescope 170 optically located between the passive biomimetic sensor 20 and the target 30. Examples of the reflective telescope 170 include a standard modified Cassegrain telescope and a standard modified Newtonian telescope.

[0051] Optionally, the target infrared signature 32 includes a target spectrum 34. The passive biomimetic sensor 20 includes at least one spectral filter 180 respectively corresponding to the at least one pyroelectric detector 22. The at least one spectral filter 180 operably passes the target spectrum 34.

[0052] Optionally, as shown by way of non-limiting example in FIG. 12, the apparatus 10 further includes a standard, airtight enclosure 190 enclosing the plate 50. The enclosure 190 includes a standard window 200 located optically between the passive biomimetic sensor 20 and the plate 50. The window' 200 is transparent to the wavelengths of interest in the target spectrum 34. Optionally, as shown by way of non-limiting examples in FIGs. 13A-13C, the window' 200 includes a CaF2 material 202; a sapphire material 204; or a ZnSe material 206. Optionally, the airtight enclosure 190 includes nitrogen 210; or a non-IR-active gas 212. For the purpose of this patent application, “non-IR-active” is a term of art and means a vibrational mode in a molecule that does not change its dipole moment, and therefore does not absorb infrared (“IR”) radiation. In practiceof an embodiment of the invention, the non-IR-active gas has absorption bands within the IR that do not overlap those exhibited by the chemical of interest. Examples of non-IR-active gases include carbon dioxide, and dicholordilluoromethane.[0053 j Alternative embodiments of the invention are described as follows. One or more embodiments include a roughened, flat surface; standard means of regulating a temperature (e.g., via heating or cooling) of the flat surface, and / or at least one standard, multi-pixel, infrared detector with a field of view, and a broad overlapping filters over each pixel. For example, a chemical vapor passes between the detector and a cold roughened surface within the field of view of the detector. The roughened surface is cooled either to maintain ambient temperature or below the ambient temperature to provide an adequate thermal contrast between the chemical vapor of interest and the background surface.

[0054] For example, another embodiment of the inventi on includes a roughened polymer (e.g., ABS) surface mounted to a standard thermoelectric Peltier cooler with a standard heatsink and a standard, electric fan, which together comprise a controllable, cooled background. For example, the polymer surface is 3D-printed in a standard manner. This embodiment of the invention includes a passive biomimetic sensor system containing a standard mechanical shutter and multiple standard pyroelectric detectors with spectral filters. The controllable cooled background is mounted a distance away such that the surface completely fills the field of view of the passive biomimetic sensor system and samples an appropriate volume to detect any chemical vapors passing between the passive biomimetic sensor and the controllable cold background. The thermoelectric Peltier cooler allows for the temperature of the polymer surface to be controlled and maintained at or below ambient temperature. The pyroelectric detector measures the summation of the emitted blackbody radiation from the polymer surface and the chemical vapor passing within the area between thepolymer surface and the detector. Therefore, the polymer surface temperature is controlled to create a uniform temperature distribution within the field of view of the pyroelectric detector that is either at the same temperature as the chemical vapor or below. As the temperature difference between the polymer surface and the chemical vapor increases, the emitted blackbody radiation from the chemical vapor will dominate the signal measured by the pyroelectric detector. The greater the temperature difference between the chemical vapor and cold stop, the greater the detection / discrimination ability of the passive biomimetic sensor.

[0055] In another embodiment of the invention, multiple pyroelectric detectors are oriented such that their fields of view overlap or otherwise observe the polymer surface. Each pyroelectric has 4 channels / pixels with each channel / pixel having a different, standard thin film filter. This allows combination of multiple different filter sets, for analysis with the CIE-IR methodology, increasing the number of chemical vapors that can be detected / discriminated and for optimization to specific chemical vapor agents.

[0056] In another embodiment of the invention, the controllable cooled background is effected, using a metallic surface. In this embodiment of the invention, replacing the polymer with metal allows for the surface to reach lower temperatures and to have a more uniform temperature distribution along the surface than would be possible using the polymer. For example, because the very smooth surface of metal has an inherently low emissivity, the metal is anodized or otherwise coated with a high-emissivity material to increase the emissivity.

[0057] In another embodiment of the invention, the 3D-printed polymer (or anodized metal) surface is enclosed in a standard airtight enclosure. The enclosure includes a window facing the pyroelectric detector, and the window is transparent at the wavelengths covered by the filters on the channels / pixels of the detector; the window is made from, for example, CaF2, sapphire, ZnSe, orother standard material that transmits in the infrared spectral region of interest. This enclosure, for example, filled with nitrogen or other non-IR active gas, ensures that there is no condensation of water vapor on the surface of the cooled polymer / anodized metal, thereby minimizing the interference from water IR absorption bands. To enable semi-quanti tati ve measurement of the concentration of the target chemical vapor, the enclosure is, for example, filled with (1) a gas of known concentration or (2) the surface of the polymer / anodized metal is coated with a thin film of material at a known thickness and density. The gas or deposited film is chosen based on the presence of a strong absorption band outside of the absorption bands of interest for likely chemical vapors. One of the filters on the pyroelectric detector exhibits an IR window that encompasses all or a portion of this absorption band. Semi-quantitative data on the concentration of a given target chemical vapor is then generated by referencing the signal measured by the pyroelectric detector at the absorption band of the gas or thin fi lm on the detector surface to the signal measured by one, two, or three of the pyroelectric detectors at the absorption bands of the chemical vapors of interest.

[0058] In another embodiment of the invention, the high-emissive surface is replaced with a low' emissive surface (e.g., gold or non-anodized aluminum). In this embodiment of the invention, a smaller cooled area is projected and magnified through a series of optical lenses so that the thermal radiation from this cooled area covers the entire low' emissive surface at an off angle from normal to the low7emissive surface. The passive biomimetic sensor is placed at the conjugate to that off angle and collects only the thermal radiation from the smaller cooled area.

[0059] In another embodiment of the invention, the high emissive surface is placed behind the passive biomimetic sensor. A series of standard mirrors, e.g., a reflective telescope, focuses the thermal radiation from the cold surface onto the surface of the pyroelectric detector. The thermal radiation from a chemical vapor of interest uses the same series of mirrors to be focused on thesurface of the pyroelectric detector as well. This embodiment reduces a need to orient the passive biomimetic sensor such that its field of view is completely filled by the cold sky and allows the passive biomimetic sensor to scan down range from the apparatus with less reliance on the sky background.

[0060] In other embodiments of the invention, the surface of the controllable background is neither a polymer nor a metal. Rather, the background plate has a high surface emissivity so that the reflection of ambient thermal radiation onto a pyroelectric detector is minimized.

[0061] In another embodiment of the invention, the chemical vapor of interest passes, within the field of view of the pyroelectric detector, between the open aperture of the passive biomimetic sensor system and a high emissivity surface. The temperature of the high emissivity surface, which is at or below ambient, is controlled in such a way as to ensure uniformity along the surface facing the pyroelectric detector, and to provide an adequate temperature difference between the surface and the chemical vapor of interest.

[0062] In another embodiment of the invention, the apparatus includes a standard mechanical shutter aligned with a standard IR-transmitting lens such that the emitted thermal radiation is modulated by the shutter, collected by the lens and projected onto a pyroelectric detector. The pyroelectric detector has multiple pixels / channels. Each pixel / channel is outfitted with a different broadband filter. A minimum of three broadband filters exhibit band passes which overlap, enabling the pyroelectric detector to measure light over each wavelength range as determined by the broadband filters.

[0063] In another embodiment of the invention, a pixel / channel of the passive biomimetic sensor has a broadband filter chosen such that its band pass sits at the center of or on the shoulder ofan absorption band from the background or a known concentration reference within the system known as the reference filter.

[0064] Although a particular feature of the disclosure may have been illustrated and / or described with respect to only one of several implementations, such features may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Also, to the extent that the terms "including”, "includes", "having", "has", "with", or variants thereof are used in the detailed description and / or in the claims, such terms are intended to be inclusive in a manner similar to the term "comprising".

[0065] As used herein, the singular forms “a”, “an,” and “the” do not preclude plural referents, unless the content clearly dictates otherwise.

[0066] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0067] As used herein, the term “about” when used in conjunction with a stated numerical value or range denotes somewhat more or somewhat less than the stated value or range, to within a range of ±10% of that stated.

[0068] All documents mentioned herein are hereby incorporated by reference for the purpose of disclosing and describing the particular materials and methodologies for which the document was cited.

[0069] Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departing from the spirit and scope of the invention. Terminology used herein should not be construed as being “meansplus-function” language unless the term “means” is expressly used in association therewith.

[0070] This writen description sets forth the best mode of the invention and provides examples to describe the invention and to enable a person of ordinary skill in the art to make and use the invention. This written description does not limit the invention to the precise terms set forth. Thus, while the invention has been described in detail with reference to the examples set forth above, those of ordinary skill in the art may effect alterations, modifications and variations to the exampl es without departing from the scope of the invention.

[0071] These and other implementations are within the scope of the following claims.

Claims

CLAIMSWhat is claimed as new and desired to be protected by Letters Patent of the United States is:

1. An apparatus comprising:a passive biomimetic sensor for detecting a target in an ambient environment,said passive biomimetic sensor comprising a field of view,the ambient environment comprising ambient thermal radiation;at least one plate comprising a surface located one of directly and indirectly in the field of view,the surface comprising a surface emissivity, a surface temperature, and a surface thermal radiation,the surface emissivity and the surface temperature contributing to the surface thermal radiation,wherein the target comprises a target infrared signature, the target infrared signature being different from the surface thermal radiation and from the ambient thermal radiation, wherein said passive biomimetic sensor detects the target infrared signature.

2. The apparatus according to claim 1, wherein said passive biomimetic sensor comprises one of:at least one pyroelectric detector;at least one uncooled bolometer; andat least one semiconductor detector.

3. The apparatus according to claim 2, wherein said passive biomimetic sensor comprises; a mechanical shutter located between said at least one pyroelectric detector and said at least one plate.

4. The apparatus according to claim 1, wherein the surface thermal radiation is different from the ambient thermal radiation.

5. The apparatus according to claim 1, wherein said plate comprises one of;a ceramic;a glass;a polymer;a metal;a coating; anda metamaterial emitter structure.

6. The apparatus according to claim 5, wherein said metal comprises a high-emissivity metal cooled such that the surface thermal radiation is distinguishable from the ambient thermal radiation by the passive biomimetic sensor.

7. The apparatus according to claim 6, wherein said high-emissivity metal comprises an anodized metal.

8. The apparatus according to claim 5, wherein said coating comprises a sufficiently high- emissivity material so that the surface thermal radiation is distinguishable from the ambient thermal radiation by the passive biomimetic sensor.

9. The apparatus according to claim 5, wherein said metal comprises a low-emissivity metal cooled such that the surface thermal radiation is distinguishable from the ambient thermal radiation by the passive biomimetic sensor.

10. The apparatus according to claim 9, wherein said low-emissivity metal comprises one of a smooth metal and a polished metal.

11. 'Hie apparatus according to claim 5, wherein said coating comprises a sufficiently low- emissivity material so that the surface thermal radiation is distinguishable from the ambient thermal radiation by the passive biomimetic sensor.

12. The apparatus according to claim 5, wherein said metamaterial emitter structure comprises one of:a dielectric resonator;a metallic resonator; anda metal-insulator-metal resonator.

13. The apparatus according to claim 4, wherein the surface thermal radiation comprises a surface spectrum,wherein the target infrared signature comprises a target spectrum, the surface spectrum being inverse of the target spectrum.

14. The apparatus according to claim 1, further comprising:a thermoelectric cooler operably connected to the plate and regulating the surface temperature such that the surface emissivity and the surface temperature cooperate to distinguish the surface thermal radiation from the ambient thermal radiation.

15. The apparatus according to claim 14, further comprising:a heatsink operably connected said thermoelectric cooler; anda first fan operably connected to said heatsink.

16. The apparatus according to claim 1, wherein said at least one plate comprises a pair of plates, said passive biomimetic sensor being located between said pair of plates,wherein the apparatus further comprises:a second fan operably located to blow the target between said pair of plates and one of against and past said passive biomimetic sensor.

17. The apparatus according to claim 1, further comprising:a reflective telescope optically located between said passive biomimetic sensor and the target.

18. The apparatus according to claim 2, wherein said target infrared signature comprises a target spectrum,wherein said passive biomimetic sensor comprises at least one spectral filter respectively corresponding to said at least one pyroelectric detector, said at least one spectral filters operably passing the target spectrum,wherein the apparatus further comprises:an airtight enclosure enclosing said plate, said enclosure comprising:a window located optically between said passive biomimetic sensor and said plate, said window being transparent to the target spectrum,19. The apparatus according to claim 18, wherein said window comprises one of:CaF2;sapphire; andZnSe,20. The apparatus according to claim 18, said airtight enclosure comprises one of:nitrogen; anda non-IR-active gas.

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