Infrared radiation device

Abstract

The present invention relates to an infrared radiation device (1), said infrared radiation device (1) comprising: an infrared-emitting film (10) having a first surface (11) and a second surface (12), the second surface (12) being opposite the first surface (11), the infrared-emitting film (10) being configured to be heated to an infrared radiation temperature such that the first surface (11) and the second surface (12) emit infrared light at the infrared radiation temperature, and the emissivity of the first surface (11) and the second surface (12) is less than 0.7; a mirror (20, 20') facing one of the first surface (11) or the second surface (12) of the infrared-emitting film (10), the mirror (20, 20') having a plurality of holes (40) passing through at least a portion of the infrared-emitting film (10), any cross-section of the plurality of holes (40) in a plane parallel to one of the first surface (11) or the second surface (12) of the infrared-emitting film having a maximum dimension greater than the longest wavelength of a given region of the electromagnetic spectrum for which the infrared-emitting device (1) is designed; Equipped with. The infrared radiation device (1) according to the invention has an improved emissivity.

Description

[Technical field]

[0001] The present invention relates to an infrared (IR) radiating device made of refractory material, capable of emitting broadband infrared radiation at temperatures above 2000K. [Background technology]

[0002] In this context, infrared light has a wavelength that falls within the range of 0.8 μm to 12 μm.

[0003] Infrared emitters are known for a variety of applications, including, but not limited to, infrared spectroscopy, illumination for gas detection, hot plates in chemical platforms, and hot plate inserts in transmission electron microscopes (TEMs) and scanning electron microscopes (SEMs).

[0004] Examples of known infrared emitters are described in the applicant's patent document 1 (WO2020012042), patent document 2 (WO2021144463), or patent document 3 (WO2021144464).

[0005] Infrared emitters emit according to the blackbody theory of radiation, which gives detailed information about how the radiation intensity varies with temperature and wavelength.

[0006] However, because real materials are not truly black, the blackbody emissivity must be adjusted by a variable called emissivity ε, which is a function of wavelength and temperature.

[0007] Most thermal infrared emitters are based on materials that are as black as possible, i.e., materials with an ε in the wavelength range close to 1.0. The problem is that there are very few materials with high emissivity, and most materials can generally only withstand relatively low temperatures, i.e., temperatures below 2000K.

[0008] Most IR heat radiators are made of refractory materials. Refractory materials are materials with a melting point above 2000°C. Examples of refractory materials are tungsten, titanium, hafnium, zirconium, tantalum, molybdenum and their nitrides, oxides and carbides. Refractory metals are materials with a melting point above 2000°C.

[0009] At infrared wavelengths, refractory metals are highly reflective (reflectance ranges from 30% to over 99%) with corresponding emissivities ranging from 0.7 to 0.01. The advantage of refractory metals is that they are stable at high temperatures, but the problem is their low intrinsic emissivity.

[0010] In order to obtain high efficiency, it is interesting to improve the emissivity of infrared emitting devices by surface structuring. It is well known that rough structures have a higher emissivity than smooth surfaces.

[0011] It is known that subwavelength structures can significantly enhance the emissivity of metal surfaces. There are two main methods: the first is to configure the surface to couple light into surface waves known as surface plasmons. The surface structures are generally periodic structures that act like a diffraction grating and couple light from normal incidence into the surface wave. The most important problem is that this technique is very sensitive to both the wavelength of the light and the angle of incidence of the light. Averaged over all angles, such structures increase the emissivity by only a few percent at most.

[0012] The second method is to use very small features in metals to enhance absorption through a mixture of diffraction and scattering. The problem with such structures is that they are difficult to fabricate because the feature size is so small. Furthermore, the very large surface area makes the structures unstable when heated. For such small features in the range of 0.8 μm to 2 μm, the emissivity of tungsten, for example, is between 0.2 and 0.4.

[0013] There are hybrid approaches that combine these two ideas, but in both cases the metals are structured at the submicron level and are therefore susceptible to defects that arise during fabrication or use.

[0014] Therefore, many known solutions to enhance emissivity are based either on very small structures relative to the active area and / or on resonant structures that depend on the exact dimensions of the structures, either in size, type or periodicity. On the other hand, it is well known that at high temperatures, materials undergo processes such as electromigration and the Soret effect. These processes lead to the movement of atoms on the surface of the material and after a while the surface becomes rough. The smaller the feature size, the more likely it is to be deformed, losing the benefit of emissivity enhancement. This is problematic for implementations at high temperatures.

[0015] In summary, current prior art uses periodic structures that operate at a single wavelength and / or sub-wavelength structures that are difficult to fabricate, have limited lifetimes, and either lose emissivity enhancement at high temperatures or do not age well at high temperatures.

[0016] DE102018101974 describes a monolithic radiating element for infrared spectroscopy, which is arranged in a cantilevered manner in a sealed housing. The infrared radiating surface is composed of a nanostructure with nanorods fixed perpendicularly on the infrared radiating surface. The emissivity of the radiating element can be adjusted by the size of the nanorod structures. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] International Publication No. 2020 / 012042 [Patent Document 2] International Publication No. 2021 / 144463 [Patent Document 3] International Publication No. 2021 / 144464 [Patent Document 4] DE 102018101974 Summary of the Invention [Problem to be solved by the invention]

[0018] Therefore, there is a need for an infrared emitting device that has improved emissivity and overcomes the shortcomings and limitations of current prior art.

[0019] SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to provide an infrared emitting device having improved emissivity and overcoming the shortcomings and limitations of current prior art.

[0020] Another object of the invention is to provide an infrared emitting device that has improved emissivity and is easier to manufacture and / or has a longer lifetime than known solutions.

[0021] Another object of the present invention is to provide an infrared radiation device which does not lose its enhanced emissivity even at high temperatures.

[0022] Another object of the present invention is to provide an infrared emitting device which has improved emissivity and less wavelength and / or angle sensitivity than known solutions. [Means for solving the problem]

[0023] According to the invention, these objects are achieved by the subject matter of the claims, in particular by an infrared radiation device as claimed in claim 1.

[0024] An infrared emitting device according to the present invention comprises an infrared emitting film including a first surface and a second surface, the second surface being opposite the first surface, the infrared emitting film being arranged to be heated to an infrared radiation temperature such that the first surface and the second surface emit infrared light at the infrared radiation temperature. In one embodiment, the infrared radiation temperature is greater than 2000K.

[0025] In this context, the term "membrane" refers to an element whose thickness value is smaller than its other two dimensions. In a preferred embodiment, the membrane is substantially planar. In a preferred embodiment, the membrane is self-supporting, i.e., structurally independent. In another embodiment, the membrane is not self-supporting unless attached on all sides.

[0026] In the present invention, the emissivity of the first and second surfaces is lower than 0.7. In fact, the present invention aims at improving the emissivity of the infrared emitting device, and this improvement is useful for low emissivity materials, i.e. materials with emissivity lower than 0.7. In other words, there is little interest in increasing the emissivity of good emitting materials, i.e. materials with emissivity of 0.7 or higher.

[0027] In the present invention, the apparatus also includes a mirror facing one of the first surface or the second surface of the infrared-emitting film.

[0028] In the present invention, at least a portion of the infrared-emitting film comprises a plurality of holes (openings) passing therethrough, the maximum dimension of any cross section of said holes in a plane parallel to one of the first or second surfaces of the infrared-emitting film being greater than the longest wavelength of the given region of the electromagnetic spectrum in which the infrared-emitting device is designed to operate. Due to this condition, the emitted infrared light may pass freely through the plurality of holes without being reflected at the openings of the holes belonging to the (external) surface of the film. In other words, the cut-off wavelength of the light propagating in the holes is longer than the maximum wavelength used in the application of the device. In other words, due to this condition, the infrared-emitting device may act as a sieve or colander for the infrared-emitted light passing freely through the plurality of holes of the infrared-emitting device.

[0029] An infrared emitting device according to the invention is designed for, i.e. designed to operate in, a given region of the electromagnetic spectrum.

[0030] In one embodiment, this predetermined region of the electromagnetic spectrum is the shortwave infrared region (SWIR) ranging from 0.9 μm to 3 μm. In this region, the infrared emitting device according to the invention can be used for spectroscopic applications or thermal radiation for material analysis. Such spectroscopy is useful for identifying materials such as plastics, organic solids and liquids, skin, plant properties, and is used in industries such as recycling, healthcare, pharmaceuticals, and agriculture. In this embodiment, the maximum dimension of any cross section in a plane parallel to one of the first or second surfaces of the infrared emitting membrane of the through hole of the infrared emitting device of the invention is greater than 3 μm.

[0031] In one embodiment, this predetermined region of the electromagnetic spectrum is the mid-infrared region (MIR) in the range of 3 μm to 5 μm. In this region, the infrared emitting device of the present invention can be used as a non-dispersive gas sensor for detecting non-dispersive gases such as carbon dioxide. The infrared emitting device of the present invention used as a non-dispersive gas sensor can be tracked with a spectral filter. In this embodiment, the maximum dimension of any cross-section in a plane parallel to one of the first surface or second surface of the infrared emitting membrane of the plurality of through holes of the infrared emitting device of the present invention is greater than 5 μm.

[0032] In one embodiment, the predetermined region of the electromagnetic spectrum is the long wavelength infrared or thermal infrared region (LIR) in the range of 8 μm to 12 μm, where the infrared emitting device according to the invention can be used for distributed gas sensing, or glucose detection, or thermal imaging, etc. In this embodiment, the maximum dimension of any cross-section in a plane parallel to one of the first surface or the second surface of the infrared emitting membrane of the plurality of through holes of the infrared emitting device of the invention is greater than 12 μm.

[0033] In the various regions, the operating temperature (or infrared radiation temperature) is selected to maximize the spectral overlap with the given region of interest, for example according to Stefan's displacement law. In other words, an infrared radiation device configured to operate in a given region of interest is an infrared radiation device configured to be heated at an infrared radiation temperature that can emit infrared light having a maximum spectral overlap with the given region of interest or having a peak emission in this given region of interest, for example in the center of this given region of interest.

[0034] For example, if the peak radiation is to be at 1.05 μm or 1.5 μm (SWIR applications), the infrared radiation temperature should be about 2000 K. If the peak radiation is to be at 4 μm (MIR applications), the infrared radiation temperature should be about 700 K. If the peak radiation is to be at 10 μm (LIR applications), the infrared radiation temperature should be about 300 K. However, these are generally minimum operating temperatures. In practice, the higher the temperature, the more light there is at the wavelength of interest. As a result, the operating temperature for thermal radiation, for example for LIR, is closer to 1000 K. This generally encourages the use of emitters with higher temperatures. The disadvantage of most materials that can withstand high temperatures is their low emissivity, which is why there is an interest in improving the emissivity with the device according to the invention.

[0035] According to the present invention, the sum of the areas of the holes is at least 10% of the area of ​​the first surface or the second surface of the infrared-emitting film, respectively. In other words, the infrared-emitting film needs to be sufficiently perforated.

[0036] The present invention uses membranes and mirrors with holes extending therethrough to increase the emissivity of infrared emitting devices made from materials with emissivity less than 0.7.

[0037] Due to the presence of the mirror, the emitted infrared wavelengths may be reflected at least once before exiting the multiple holes, and this reflection may increase the emissivity of the device. In other words, the present invention may reflect a portion of the light emitted from the infrared emitting film off the same surface, thereby increasing the effective emissivity.

[0038] The infrared emitting device of the present invention is simple to manufacture and, moreover, has a lower wavelength and / or angle sensitivity than known solutions.

[0039] The holes do not need to be uniform in size or periodic, which is an advantage for fabrication and wavelength sensitivity.

[0040] Another important advantage associated with the present invention is that due to the presence of multiple holes, less mass is heated, which makes the infrared radiation device of the present invention more efficient than known solutions.

[0041] The infrared emitting device of the present invention does not utilize any interference between the (directly) emitted light and the light reflected and emitted by the mirror, which makes the infrared emitting device of the present invention independent of the wavelength of the emitted light and the distance between the film and the mirror.

[0042] Finally, the infrared radiation device of the present invention does not lose its enhanced emissivity even at high temperatures because the sieve or sieve effect provided by the multiple holes through it is not affected by high temperatures.

[0043] In one embodiment, the infrared emissive membrane is made of (or includes) a refractory material, such as a refractory metal and / or an alloy of a refractory metal.

[0044] In one embodiment, the surface of the mirror facing the infrared-emitting film is an infrared-emitting surface, in which case the mirror may be referred to as a "hot mirror."

[0045] In one embodiment, the surface of the hot mirror facing the infrared-emitting film, the first surface of the infrared-emitting film, and the second surface of the infrared-emitting film are made of the same material.

[0046] In one embodiment, the infrared radiation device is a single block device.

[0047] In one embodiment, the surface of the mirror facing the infrared-emitting film is not an infrared-emitting surface and the mirror has a reflectivity greater than 80% (i.e., is a highly reflective mirror), in which case the mirror may be referred to as a "cold mirror."

[0048] In one embodiment, the thickness of the infrared-emitting film is greater than 0.1 times the average distance between the holes, in which case the film may be referred to as a "thick film." In this embodiment, emissivity may be further improved by utilizing reflections from the walls inside the holes.

[0049] In one embodiment, the ratio of the area of ​​the holes to the area of ​​the sidewalls of the holes is less than 1. This embodiment further exploits reflections on the internal (side)walls of the holes, which may further improve the emissivity.

[0050] In this context, the term "area of ​​a hole" refers to the area of ​​the hole on the outer surface of the radiating membrane that contains the hole, i.e. the first surface or the second surface. In one embodiment, the area of ​​the hole on the first surface is equal to the area of ​​the hole on the second surface (in other words, the hole is substantially cylindrical).

[0051] In one embodiment, the thickness of the infrared-emitting film is less than or equal to 0.1 times the average distance between the plurality of holes, and the sum of the areas of the plurality of holes is less than 50% of the area of ​​each of the first surface or the second surface of the infrared-emitting film, in which case the film may be referred to as a "thin film."

[0052] In one embodiment, the mirror is planar and the distance of the mirror to the membrane is a multiple of the average distance between two adjacent holes or a multiple of the spacing between the holes.

[0053] In one embodiment, at least some of the holes are square holes.

[0054] In one embodiment, at least some of the holes are cross-shaped holes.

[0055] In one embodiment, the infrared emissive membrane is a one-piece membrane.

[0056] In one embodiment, the infrared emissive film is a multi-layer film.

[0057] In one embodiment, the arrangement of the holes is not periodic (e.g., randomly arranged) and / or the holes have different sizes and / or different shapes. Indeed, the infrared radiation device according to the present invention does not utilize any "coherent" effects due to diffraction and surface plasmon effects, which require a periodic arrangement of sub-wavelength structures and / or sub-wavelength structures having equal sizes and / or shapes.

[0058] In one embodiment, the infrared emitting device (membrane) comprises a plurality of resistive arms connected to the infrared emitting membrane, the infrared emitting membrane being suspended by the resistive arms, and the infrared emitting membrane being heated to an infrared emitting temperature via the resistive arms. In one embodiment, the infrared emitting device also comprises the features described in U.S. Pat. No. 5,399,433, U.S. Pat. No. 5,499,433 or U.S. Pat. No. 5,499,433 filed by the applicant and incorporated herein by reference.

[0059] In one embodiment, the infrared-emitting device according to the present invention is used in an InGaAs detector, wherein any cross-section of the through holes in a plane parallel to one of the first surface or the second surface of the infrared-emitting film has a maximum dimension greater than 1.6 μm.

[0060] In one embodiment, the infrared emitting device according to the present invention is used for detecting CO. In this embodiment, any cross-section of the through holes in a plane parallel to one of the first surface or the second surface of the infrared emitting membrane has a maximum dimension greater than 4.2 μm.

[0061] In one embodiment, the infrared emitting device according to the present invention is heated to an infrared emitting temperature of 4000 K. In this embodiment, any cross-section in a plane parallel to one of the first surface or the second surface of the infrared emitting film of the plurality of through holes has a maximum dimension greater than 1 μm.

[0062] In one embodiment, the distance between the (first or second) surface of the infrared-emitting film facing the mirror and the mirror is zero. In other words, the first or second surface of the infrared-emitting film facing the mirror and the surface of the mirror are in direct contact. In other words, since the surface of the mirror is in direct contact with one of the first or second surfaces of the infrared-emitting film, the entire plurality of holes of the (weighted) infrared-emitting device are blocked by the mirror, resulting in blocked plurality of holes.

[0063] In this embodiment, the mirror may be a "hot mirror". In this embodiment, the holes may be relatively deep, e.g., the membrane is a "thick membrane" in order to take advantage of reflections on the inner walls of the holes. In this embodiment, the ratio of the area of ​​at least one hole to the area of ​​its sidewalls may be less than 1 in order to further take advantage of reflections on the inner (side) walls of the holes.

[0064] Exemplary embodiments of the invention are disclosed in the description and illustrated in the drawings. [Brief description of the drawings]

[0065] [Figure 1] FIG. 1 shows a schematic of an infrared radiation system for illustrating the Lagrangian invariant. [Diagram 2] FIG. 2 shows a cross-section of a portion of an infrared radiation device in one embodiment of the present invention. [Diagram 3] FIG. 3 shows a cross-section of a portion of an infrared radiation device in accordance with another embodiment of the present invention. [Figure 4] FIG. 4 shows a cross-section of an embodiment of a portion of an infrared emitting film of an infrared emitting device according to the present invention. [Figure 5A] FIG. 5A shows a cross-section of an embodiment of a portion of a (thick) infrared-emitting film of an infrared-emitting device according to the invention. [Figure 5B] FIG. 5B shows a cross-section of a portion of an infrared-emitting device according to one embodiment of the present invention, which includes a (thick) infrared-emitting film including a surface with a distance from the mirror equal to zero. [Figure 6A]FIG. 6A shows a top view on a possible embodiment of a plurality of holes in an infrared-emitting membrane of an emitting device according to the invention. [Figure 6B] FIG. 6B shows a top view of a possible embodiment of a plurality of holes in the infrared-emitting membrane of an emitting device according to the invention. [Figure 6C] FIG. 6C shows a top view on a possible embodiment of a plurality of holes in the infrared-emitting membrane of an emitting device according to the invention. [Figure 6D] FIG. 6D shows a top view of a possible embodiment of a plurality of holes in the infrared-emitting membrane of an emitting device according to the invention. [Figure 6E] FIG. 6E shows a top view of a possible embodiment of a plurality of holes in the infrared-emitting membrane of an emitting device according to the invention. [Figure 7] Figure 7 shows the emissivity enhancement as a function of the film fill factor and material emissivity for a cold mirror with a thin film and 95% reflectivity. [Figure 8] Figure 8 shows the emissivity as a function of the film fill factor and material emissivity for a thin film and a cold mirror with 95% reflectivity. [Figure 9] Figure 9 shows the emissivity enhancement as a function of the filling factor and film thickness (normalized to the period of the holes) for a thick film and a 100% reflective cold mirror with an infrared emitting film with emissivity equal to 0.4. [Figure 10] Figure 10 shows the emissivity enhancement as a function of the filling factor and film thickness (normalized to the period of the holes) for a thick film and a 100% reflective cold mirror with an infrared emitting film with emissivity equal to 0.1. [Figure 11] FIG. 11 shows the emissivity enhancement as a function of the fill factor and film thickness (normalized to the period of the holes) for a thick film without a cold mirror, for an infrared emitting film with emissivity equal to 0.4. [Figure 12] FIG. 12 shows the emissivity enhancement as a function of the fill factor and film thickness (normalized to the period of the holes) for a thick film without a cold mirror, for an infrared emitting film with emissivity equal to 0.1. [Figure 13]FIG. 13 shows the emissivity enhancement as a function of the square size / period ratio and film thickness (normalized to the period of the holes) for an infrared emitting film with emissivity equal to 0.1 and square holes, for a thick film with a hot mirror. [Figure 14] FIG. 14 shows an example of an infrared emitting device according to the present invention, in which the infrared emitting membrane comprises a number of resistive arms connected to the infrared emitting membrane. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0066] FIG. 1 shows a schematic of an infrared radiation system 1000 for illustrating the Lagrangian invariant. The system comprises a first infrared radiation device 100, an (optional) optical system 300, and a second infrared radiation device 400. According to this invariant, the etendue is always conserved. The simplest formulation of this invariant is that the product of the area of ​​the infrared radiation device and the corresponding solid angle is conserved. In other words, if the area of ​​the first infrared radiation device 100 is dA1 with a corresponding solid angle Ω1 and the area of ​​the second infrared radiation device 400 is dA2 with a corresponding solid angle Ω2, then:

number

[0067] Let the emissivity of the area dA1 be ε. By definition, ε is less than 1, so the emissivity cannot be increased by external optical systems. For this reason, a great deal of effort is expended on increasing the emissivity of materials.

[0068] According to the invention, the emissivity is increased by using a special infrared radiation device, namely an infrared radiation device comprising a membrane with multiple holes and a mirror as described in claim 1.

[0069] For absorbing materials, ε=1-R m , where R m is the reflectivity of the material. By reflecting some of the light emitted from a material back off the same surface, the effective emissivity can be increased.

[0070] Figure 2 shows a cross section of a part of an infrared emitting device 1 according to an embodiment of the invention. In this embodiment, the infrared emitting device 1 comprises an infrared emitting membrane 10 including a first surface 11 and a second surface 12, the second surface 12 being opposite the first surface 11, the infrared emitting membrane 1 being arranged to be heated to an infrared radiation temperature such that the first surface 11 and the second surface 12 emit infrared light at the infrared radiation temperature. The sizes and proportions of the different elements shown in Figure 2 are only approximate and do not necessarily correspond to the actual sizes and proportions. The same applies to the inclinations of the depicted arrows.

[0071] According to the present invention, the emissivity ε of the first surface 11 and the second surface 12 is less than 0.7. In one embodiment, the first surface 11 and the second surface 12 are made of the same material. In another embodiment, the first surface 11 and the second surface 12 are made of different materials, but both have emissivities less than 0.7. Non-limiting examples of materials with emissivities less than 0.7 in the infrared (IR) include refractory materials, such as refractory metals and their alloys. Examples of refractory metals are tungsten, titanium, hafnium, zirconium, tantalum, molybdenum, and their nitrides, oxides, and carbides.

[0072] Although the first surface 11 and the second surface 12 are depicted as being parallel, this is not required by the invention. Although the first surface 11 and the second surface 12 are depicted as being substantially plate-like, this is also not required by the invention.

[0073] In the illustrated embodiment, the infrared-emitting film 10 is a single piece film. In another embodiment, shown in Figure 4, the infrared-emitting film 10 is a multi-layer film, i.e., it comprises at least one layer 13 (of a different material) between the first surface 11 and the second surface 12.

[0074] According to the invention, at least a portion of the infrared-emitting film 10 comprises a plurality of through holes 40, the cross section of which in any plane parallel to one of the first or second surfaces of the infrared-emitting film has a maximum dimension greater than the longest wavelength of the infrared radiation emitted in a given region of the electromagnetic spectrum. This last condition allows the emitted infrared radiation to pass freely through the plurality of holes 40 without being reflected at the opening of the holes belonging to the (external) surface of the film. In a preferred embodiment, the infrared-emitting device is designed to operate only up to a certain maximum wavelength, which is determined by the application. In a preferred embodiment, the infrared-emitting device is designed so that the emitted infrared radiation belongs to the range of 0.9 μm to 3 μm, the range of 3 μm to 5 μm or the range of 8 μm to 12 μm.

[0075] According to the present invention, the sum of the areas of the multiple holes 40 is at least 10% of the area of ​​each of the first surface 11 or the second surface 12 of the infrared-emitting film 10. In other words, the "fill factor" of the infrared-emitting film 10 is at least 10%. In fact, in the present invention, if the infrared-emitting film 10 is sufficiently perforated, the emissivity of the infrared radiation device can be sufficiently increased.

[0076] The shape and arrangement of the plurality of holes 40 is not important to the operation of the present invention, as long as the "fill factor" of the infrared-emitting film 10 is at least 10%. This means that the plurality of holes 40 do not necessarily have to be periodic on the infrared-emitting film 10, but can be of any shape. The through holes 40 can also have different sizes, as long as the maximum dimension of any cross-section of said through holes 40 in a plane parallel to one of the first or second surfaces of the infrared-emitting film is greater than the longest wavelength of the infrared radiation emitted.

[0077] 6A-6E show top views of possible embodiments of a plurality of holes 40 in an infrared emitting film 10 according to the present invention.

[0078] In one embodiment, at least some of the holes 40 are cross-shaped holes. A cross-shaped structure has approximately 40% more (side) walls than a similar disk of the same total surface area. A cross-shaped structure also allows wavelengths longer than the width of the arms of the cross to be incident (for both polarizations) as long as the perimeter is at least twice the wavelength.

[0079] According to the invention, the infrared emitting device 1 of Fig. 2 also comprises a mirror 20. In the embodiment shown, the mirror 20 faces the second surface 12 of the infrared emitting film 10. In one embodiment, as shown in Fig. 2, there is a distance D different from zero between the surface 21 of the mirror 20 facing the surface of the infrared emitting film (e.g. the second surface 12 in Fig. 2) and the surface of the infrared emitting film 10. In another embodiment, this distance D is equal to zero. In the embodiment shown in Fig. 2, the mirror 20 is a cold mirror, i.e. the surface 21 of the mirror 20 facing the infrared emitting film 20 is not an infrared emitting surface. In this particular case, the reflectivity of the mirror 20 is higher than 80%, so as to provide a sufficient reflection.

[0080] In the embodiment shown, the mirror 20 is planar, in which case the distance of the mirror to the membrane should be a multiple of the average distance between two adjacent holes 40, or a multiple of the spacing between the holes if multiple holes are present.

[0081] However, the mirror 20 does not necessarily have to be planar, but may have other shapes, for example curved shapes.

[0082] Power P1 is emitted by the infrared-emitting film 10 towards the cold mirror 20 (as in the example). This power is reflected by the cold mirror 20 as P2. There may be any number of reflections, and the power is P i The number of reflections illustrated in FIG. 2 is by way of example and should not be considered limiting.

[0083] Due to the presence of the mirror 20, the emitted wavelengths of infrared light are reflected at least once before exiting the multiple holes 40, and this reflection can increase the emissivity of the device 1. In other words, the present invention allows a portion of the light emitted from the infrared emitting film to be reflected by the same surface, thereby increasing the effective emissivity.

[0084] Furthermore, due to the presence of multiple holes 40, less mass is heated, which makes the infrared radiation device 1 of the invention more efficient than known solutions.

[0085] Figure 3 shows a cross-section of a part of an infrared radiation device 1 according to another embodiment of the invention. The difference with respect to figure 2 is that the mirror in figure 3 is a hot mirror 20'. In a preferred embodiment it is made (at least in part) of the same material as the material of one of the first surface 11 or the second surface 12.

[0086] In one embodiment, the temperature of the hot mirror 20 ′ is assumed to be similar to that of the infrared emissive film 10 .

[0087] The hot mirror 20' also emits, further improving the emissivity of the infrared-emitting device 1. In other words, the hot mirror 20' provides a better emissivity of the device than the cold mirror 20. In the illustrated embodiment, the distance D between the surface 21 of the mirror 20 facing the surface of the infrared-emitting film (e.g., the second surface in FIG. 3) and that surface of the infrared-emitting film 10 is different from zero, but in other embodiments this distance D can be equal to zero, for example as shown in FIG. 5B.

[0088] In one embodiment, the surface 21 of the mirror 20' facing the infrared-emitting film 10, the first surface 11 and the second surface 12 of the infrared-emitting film 10 are made of the same material. In this embodiment, the infrared-emitting device may be a single block device.

[0089] In one embodiment, as illustrated in Figure 5A, the thickness t of the infrared-emissive film is greater than 0.1 times the average distance d between the holes 40. In this case, the infrared-emissive film 10 is considered to be "thick."

[0090] In the case of a thick infrared-emitting film 10, light is also emitted from the walls 44 of the holes in the film 10. Furthermore, as illustrated diagrammatically in FIG. 5A, the light may be multiple-reflected from the (side) walls 44. This further improves the emissivity of the device compared to "thin" films, i.e., films having a thickness of 0.1 times the average distance between the holes 40 or less.

[0091] In a preferred embodiment, the ratio of the area of ​​the hole to the area of ​​the walls 44 of the hole 40 is less than one.

[0092] In one embodiment, which can be combined with other embodiments of the present invention, as illustrated for example in FIG. 5B, the distance D between the (first or second) surface of the infrared-emitting film facing the mirror 20, 20' and the mirror is zero. In other words, in this embodiment, the first or second surface of the infrared-emitting film facing the mirror and the surface of the mirror are in direct contact. In other words, since the surface of the mirror is in direct contact with one of the first or second surfaces of the infrared-emitting film, the plurality of holes 40 of the entire infrared-emitting device are blocked by the mirror and therefore are blocked holes.

[0093] In this embodiment, the mirror may be a "hot mirror", as shown in FIG. 5B. In this embodiment, the holes may be relatively deep, e.g. the membrane is a "thick membrane" so as to reflect off the inner walls 44 of the holes. In this embodiment, the ratio of the area of ​​at least one hole to the area of ​​the hole's side walls may be less than 1, so that reflection off the inner (side) walls of the holes can be further exploited. This embodiment with D=0 is more efficient with a "thick membrane" and a hot mirror, but can also be used with a "thin membrane" and / or a cold mirror.

[0094] In an embodiment where D=0, the infrared emitting device may be a single block device.

[0095] For a thin film 10, the applicant has found that the sum of the areas of the holes should be less than 50% of the area of ​​each of the first surface or the second surface of the infrared-emitting film in order to improve the emissivity of the device 1. Preferably, the sum of the areas of the holes should be in the range of 5% to 25%, particularly in the range of 10% to 20%.

[0096] In one embodiment, the infrared emitting device comprises a plurality of resistive arms connected to the infrared emitting film, the infrared emitting film being suspended by the plurality of resistive arms, and the infrared emitting film being heated to an infrared emitting temperature via the plurality of resistive arms. In one embodiment, the infrared emitting device also comprises the features described in U.S. Pat. No. 5,399,633, U.S. Pat. No. 5,499,633 or U.S. Pat. No. 5,499,633 filed by the applicant.

[0097] Below we present a detailed mathematical analysis of some embodiments of the present invention.

[0098] First embodiment: thin film and cold mirror

[0099] In the following, the effect of the membrane thickness is neglected, i.e. the side walls of the pores are neglected. The periodic boundary condition is used to include the effect of the (semi-infinite) array of pores. The array of pores can be in any configuration as long as the average distance between the pores is maximized. The pores can be of any shape. The only important parameter is the ratio of the area of ​​the pores to the area of ​​the usable device, i.e. the filling factor of the pores, F, which ranges from 0 to 1.

[0100] Let e0 be the emissivity of the emitting device and R be the reflectivity of the cold mirror. Applicant has found that the emitted power is given by the following equation (2):

number

[0101] Applicant has found that the improvement of the multiple holes and rearview mirror is given by the following formula (3):

number

[0102] FIG. 7 shows the emissivity enhancement as a function of the film fill factor and the emissivity of the film material for a thin film and a cold mirror with 95% reflectivity.

[0103] FIG. 8 shows the emissivity as a function of the film fill factor and the emissivity of the film material for a thin film and a cold mirror with 95% reflectivity.

[0104] From Figures 7 and 8, it can be seen that the film with holes and the back reflector has a higher emissivity than the film alone without holes.

[0105] Second embodiment: thick membrane and cold mirror

[0106] In this embodiment, the effect of light being emitted from multiple (side) walls of multiple holes in the film and the light being multiple reflected from the multiple walls is taken into account.

[0107] In this embodiment, the holes are considered to be cylindrical with radius r and height h.

[0108] Light in the hole leaks out the ends or is absorbed by the walls. Applicants have found that the effective transmission in a particular direction is equal to Equation (4) below.

number

[0109] The pores are similarly emitted. The applicant has found that the pores are emitted to the front as the following formula (5):

number

number

[0110] Because the pores are thick, the escape routes to the outside are reduced, and this follows the formulas (7) to (9) found by the applicant.

number

[0111]

number

[0112]

number

[0113] In general, the following formula (10):

number

[0114] This equation (10) can be rewritten as the following equation (11).

number

[0115] The enhancement factor due to the shape of the hole is given by the following formula (12).

number

[0116] For round holes the enhancement factor is 1.7726 and for square holes it is 2.

[0117] Figure 9 shows the emissivity enhancement as a function of filling fraction and film thickness (normalized to the period of the holes) for a thick film and a 100% reflective cold mirror, with an infrared emitting film with emissivity of 0.4.

[0118] Figure 10 shows the emissivity enhancement as a function of filling fraction and film thickness (normalized to the period of the holes) for a thick film and a cold mirror with 100% reflectivity, and for an infrared emitting film with emissivity of 0.1.

[0119] Figure 11 shows the emissivity enhancement as a function of the filling fraction and the film thickness (normalized to the period of the holes) for an infrared emitting film with emissivity equal to 0.4 for a thick film without a cold mirror.

[0120] Figure 12 shows the emissivity enhancement as a function of the filling fraction and the film thickness (normalized to the period of the holes) for an infrared emitting film with emissivity equal to 0.1 for a thick film without a cold mirror.

[0121] From Figures 9-10, the optimal hole size to thickness ratio can be found.

[0122] To resume, thicker films are significantly better than thinner ones. Rearview mirrors add significant enhancement for film thicknesses up to twice the period (or average hole spacing). There are clear design rules for maximizing the emissivity of a device for a given material emissivity.

[0123] Third embodiment: thick membrane and hot mirror

[0124] Light is emitted from the rearview mirror. The equation is the same as in the second embodiment, except that in addition to the reflection term, there is also a radiation term from the rearview mirror.

[0125] Figure 13 shows the emissivity enhancement as a function of the square size / period ratio and film thickness (normalized to the period of the holes) for a thick film without a hot mirror and an infrared emitting film containing multiple square holes with emissivity equal to 0.1.

[0126] FIG. 14 shows an example of an infrared emitting device 1 according to the invention, in which an infrared emitting film 10 comprises a number of resistive arms 4 connected to the infrared emitting film 10, the infrared emitting film 10 being suspended by the resistive arms, and the infrared emitting film 10 being heated to an infrared emitting temperature via the resistive arms 4. Each arm 4 in the illustrated example of FIG. 14 has a length 5, a width 6 and a thickness 7, and its cross-sectional area is much smaller than that of the film 10. The multiple connection pads 3 are designed to provide a mechanical connection to the substrate, such that the film 10 is supported relative to the substrate only by the multiple arms 4 and the multiple pads 3. The multiple connection pads 3 provide an electrical connection to the multiple arms 4 and thereby to the film 10. The film 10, the multiple pads 3 and the multiple arms 4 are preferably made from one continuous piece of material. Other features and other embodiments of this infrared emitting device 1 and / or this emitting film 10 are described in US Pat. No. 5,399,433, US Pat. No. 5,499,463, filed by the applicant and enclosed herein by reference. [Explanation of symbols]

[0127] 1. Infrared radiation device 3 Connection Pads 4 Arm 5 Arm Length 6 Arm Width 7 Arm Thickness 10 Infrared radiation film 11 First Surface 12 The Second Surface 20 Cold Mirror 20' Hot Mirror 21 Mirror Surface 40 holes 44 Hole (side) wall 100 First infrared radiation device 200 Cold Mirror 200' Hot Mirror 300 Optical system 400 Second infrared radiation device 1000 Infrared Radiation System d Distance between multiple holes D Distance between the surface of the mirror facing the surface of the infrared emitting film and the surface of the infrared emitting film P1, P j Power t Thickness Ω1, Ω2 solid angle

Claims

1. An infrared radiation device (1) for a given region of the electromagnetic spectrum, comprising: The infrared radiation device (1) comprises: an infrared-emitting film (10) having a first surface (11) and a second surface (12), the second surface (12) being opposite the first surface (11), the infrared-emitting film (10) being configured to be heated to an infrared radiation temperature, such that the first surface (11) and the second surface (12) emit infrared light belonging to said region at the infrared radiation temperature; a mirror (20, 20') facing one of the first surface (11) or the second surface (12) of the infrared emitting film (10); Equipped with The infrared emitting film (10) has a plurality of holes (40) penetrating at least a portion of the infrared emitting film (10). In the infrared radiation device (1), The emissivity of the first surface (11) and the second surface (12) is less than 0.7; and In order to improve the emissivity of the infrared radiation device, Any cross section of the plurality of holes (40) in a plane parallel to one of the first surface and the second surface of the infrared emitting film has a maximum dimension greater than the longest wavelength of the predetermined region; the total area of ​​the plurality of holes (40) is at least 10% of the area of ​​each of the first surface (11) and the second surface (12) of the infrared emitting film (10); An infrared radiation device (1), characterized in that

2. The infrared emitting film (10) is made of refractory materials, such as refractory metals and / or alloys of refractory metals, or Refractory materials, including refractory metals and / or alloys of refractory metals; Infrared radiation device (1) according to claim 1.

3. 3. Infrared radiation device (1) according to claim 1 or 2, wherein the surface (21) of the mirror (20') facing the infrared emitting film (10) is an infrared emitting surface.

4. 4. The infrared radiation device (1) according to claim 3, wherein the surface (21) of the mirror (20') facing the infrared radiation film (10), the first surface (11) of the infrared radiation film (10), and the second surface (12) of the infrared radiation film (10) are made of the same material.

5. Infrared radiation device (1) according to claim 3 or 4, wherein the infrared radiation device is a single block device.

6. The surface (21) of the mirror (20) facing the infrared emitting film (10) is not an infrared emitting surface, 3. Infrared radiation device (1) according to claim 1 or 2, wherein the reflectivity of the mirror (20) is higher than 80%.

7. Infrared radiation device (1) according to any one of the preceding claims, wherein the thickness of the infrared radiation film (10) is greater than 0.1 times the average distance between the holes (40).

8. 8. Infrared radiation device (1) according to claim 7, wherein the ratio between the area of ​​the hole and the area of ​​its side walls is lower than 1.

9. The thickness (t) of the infrared radiation film is 0.1 times or less than the average distance (d) between the plurality of holes; The total area of ​​the plurality of holes is less than 50% of the area of ​​each of the first surface (11) or the second surface (12) of the infrared emitting film. Infrared radiation device (1) according to any one of the preceding claims.

10. The mirrors (20, 20') are planar, the distance of the mirror to the membrane (10) is a multiple of the average distance between two adjacent holes (40) or a multiple of the spacing between the holes; Infrared radiation device (1) according to any one of the preceding claims.

11. Infrared radiation device (1) according to any one of the preceding claims, wherein at least some of the plurality of holes (40) are square holes or cross-shaped holes.

12. The arrangement of the plurality of holes is not periodic, and / or The holes have different sizes and / or shapes. Infrared radiation device (1) according to any one of the preceding claims.

13. a plurality of resistive arms connected to an infrared emitting membrane; an infrared emitting membrane suspended by said resistive arm; The infrared emitting film is heated to an infrared emitting temperature via the resistive arm. Infrared radiation device (1) according to any one of the preceding claims.

14. Infrared radiation device (1) according to any one of the preceding claims, wherein the predetermined area is in the range of 0.9 μm to 3 μm, 3 μm to 5 μm, or 8 μm to 12 μm.

15. Infrared radiation device (1) according to any one of claims 1 to 14, wherein the first surface (11) or the second surface (12) of the infrared emitting film (10) facing the mirror (20, 20') is in direct contact with a surface (21) of the mirror (20, 20').

Images