FR3053783A1 - INFRARED SPECTROSCOPY DEVICE - Google Patents

Abstract

The invention relates to an infrared spectroscopy device (10) comprising: - a light source (20) which comprises a metal network, and means for heating the metal network, the metal network comprising a set of metal tracks parallel to a X direction, and arranged in a period P in a direction Y perpendicular to the direction X, the light source (20) being intended to emit directional infra-red radiation in a range of wavelengths determined by a temperature T imposed on the metal network by the heating means, - a thermo-detector (50) at a distance d from the light source, and which comprises at least one thermosensitive cell (51) intended to collect at least part of the directional infra-red radiation capable of to be emitted by the light source.

Description

INFRA-RED SPECTROSCOPY DEVICE DESCRIPTION

TECHNICAL AREA

The present invention relates to a compact and lightweight infra-red spectroscopy device for detecting one or more gases.

PRIOR ART

Gas detection and identification is a major issue in industrial and domestic environments. Indeed, for safety reasons for example, it may be necessary to detect the presence of a gas, and if necessary to determine the concentration. In this respect, hydrocarbons, some of which present a high degree of danger, must be detectable and above all correctly identified. This is particularly the case of methane and ethane which are explosive gases, and whose concentration can be particularly high in hydrocarbon and gas plants, but also in domestic environments, as soon as a leak of gas is observed. Thus, in order to effectively detect these gases, a multitude of gas detection and identification systems must be distributed in the gas and hydrocarbon plants. This constraint therefore requires these gas detection systems to have a low cost, and also a small footprint.

In addition, portable or mobile solutions may also be required.

Infrared spectroscopy is a particularly effective method for the detection and identification of gases.

However, current devices, including equipment operating on the principle of infrared spectroscopy Fourier transform, are extremely expensive and bulky.

Furthermore, the implementation of these devices must meet requirements in terms of vibration level and temperature variations that make them incompatible with the aforementioned applications.

An object of the present invention is then to provide a device for detecting and identifying gas having a bulk and a reduced cost compared to infra-red spectroscopy systems known from the state of the art.

Another object of the present invention is also to provide a device for detecting and identifying light gas.

STATEMENT OF THE INVENTION

The aims of the invention are at least partly achieved by an infrared spectroscopy device comprising: a light source which comprises a metal network and means for heating the metal network, the metal network comprising a set of parallel metal tracks to a direction X, and arranged in a period P in a direction Y perpendicular to the direction X, the light source being intended to emit an infra-red radiation in a range of wavelengths λ \ determined by a temperature T imposed on the network metal by the heating means, the infra-red radiation being directional so that each wavelength λΙ is emitted according to a plane Pi of its own, the plane Pi is at an angle θi with a symmetry plane Ps of the metal network , the plane Ps comprises the direction X and is normal to the metal network, a thermo-detector at a distance d from the light source, and which comprises at least one thermosensitive cell intended to collect at least partly the directional infra-red radiation likely to be emitted by the light source.

Thus, the device according to the invention is light and compact.

Moreover, its arrangement allows a wavelength selective collection of light radiation, and thus reconstruct the absorption spectrum of a gaseous species.

In addition, the device according to the invention is not sensitive to environmental conditions and vibrations, and its use in mobile applications can be envisaged.

According to one embodiment, the heating means comprise a heating membrane on which the metal network rests, the heating membrane comprising a heating element interposed between a first layer and a second layer made of at least one dielectric material.

According to one embodiment, the range of wavelengths is between a minimum wavelength λmin and a maximum wavelength λmax, the period P of the metal network being equal to the minimum wavelength λmin.

According to one embodiment, the metal tracks have a thickness greater than one-fiftieth of the minimum wavelength λmin.

According to one embodiment, the metal tracks have a width, measured along the Y direction, equal to half of the period P.

According to one embodiment, each wavelength λϊ and the corresponding angle φi are linked by the relation: λ \ = P (l + sin (0i)).

According to one embodiment, the metal tracks comprise at least one selected from the following materials: tungsten. Aluminum, Copper, Gold, Silver, Tantalum, Titanium, Palladium, Molybdenum, Platinum.

According to one embodiment, the at least one thermosensitive cell comprises a bolometer.

According to one embodiment, the thermo-detector comprises a plurality of photosensitive cells arranged in a column parallel to the direction X.

According to one embodiment, the infrared spectroscopy device further comprises rotation means for rotating the light source about an axis parallel to the X direction.

According to one embodiment, the thermo-detector comprises a plurality of photosensitive cells arranged in the form of a matrix parallel to a plane comprising the X and Y directions.

According to one embodiment, the light source is arranged parallel to the thermo-detector.

According to one embodiment, the assembly formed by the thermo-detector and the light source is symmetrical with respect to a plane parallel to the metal tracks.

According to one embodiment, the light source extends over a length I in the direction Y, the ratio of the length I over the distance d being greater than one hundredth.

According to one embodiment, the length I is between 10 μm and 1 mm, for example 250 μm.

According to one embodiment, the distance d is between 1 mm and 10 cm, for example 1 cm.

According to one embodiment, the thermo-detector comprises 320 columns of thermosensitive cells parallel to the direction X, the heat-sensitive cells having a square shape of 25 μm side.

According to one embodiment, the infrared spectroscopy device further comprises a data processing module that can be collected by the thermo-detector. The invention also relates to a method of using the infra-red spectroscopy device for the detection and identification of hydrocarbons, the hydrocarbons advantageously comprising methane and ethane.

According to one embodiment, the heating means heat the metal network to a temperature adapted for the light source to emit infrared radiation in a range of wavelengths ranging from 3 μm to 4.69 μm.

BRIEF DESCRIPTION OF THE DRAWINGS Other characteristics and advantages will appear in the following description of the embodiments of the infrared spectroscopy device, given by way of non-limiting examples, with reference to the appended drawings in which: FIG. 1 is a schematic representation of the light source in a plane comprising the X and Y directions, according to the invention. FIG. 2a is a schematic representation of the heating membrane in a plane comprising the X and Y directions; FIG. 2b is a schematic representation of the heating membrane in a sectional plane AA '(indicated in FIG. 2a); FIG. 3 is a schematic representation of the light source along a sectional plane comprising the plane H, FIG. 3 further illustrating the directional character of the light source according to the invention, FIGS. 4a and 4b are graphical representations of the light source. directional emissivity of two light sources according to the invention, more particularly, the graphical representations give, in gray scale, the light intensity at a given wavelength (along the vertical axis) as a function of the angle d emissivity Θ (along the horizontal axis), - Figure 5a is a schematic representation of the infrared spectroscopy device according to a first embodiment of the invention, - the figure 5b is a schematic representation of the thermo-detector according to a sectional plane BB 'indicated in FIG. 5a, and relating to the first embodiment of the invention; FIG. 6a is a schematic representation of the infrared spectroscopy device according to FIG. a second embodiment of the invention, - Figure 6b is a schematic representation of the thermo-detector according to a sectional plane CC 'shown in Figure 6a, and relating to the second embodiment of the invention, - the figure 7 is a schematic representation of the infrared spectroscopy device according to the second embodiment of the invention, the thermodetector comprising only one line of thermosensitive cells, parallel to the direction Y, and further comprising the focusing means, FIG. 8 is a graphical representation of the variation of the luminous flux collected (on the vertical axis) by the acquisition channel Ci associated with the wavelength 4.26 pm depending on the the concentration of CO2 in ppm (on the horizontal axis), according to the second embodiment of the invention. FIG. 9 illustrates the spectral width actually collected by a series of adjacent acquisition channels for a distance d of 1 cm, and a matrix pitch Pm of 25 μm according to the invention, the vertical axis represents the luminous intensity in arbitrary units, and the horizontal axis the wavelength, - Figure 10 illustrates the differences in light intensities collected by the series of adjacent acquisition channels of Figure 9, the vertical axis representing the light intensities and the horizontal axis representing the wavelength, - Figure 11 shows the absorption spectra of methane M and ethane E superimposed with the differences in light intensities emitted by the light source, and collected by the series of channels d Figure 12a shows the superimposition of the infrared absorption spectra of methane (M) and ethane (E) as a function of the wavenumber in cm '. horiz axis ontal), - figures 12b (for methane), 12c (for ethane) and 12d (for a methane / ethane mixture) represent, in grayscale, the infra-red intensity collected by acquisition channels (numbered from 1 to 10).

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

For the different modes of implementation, the same references will be used for identical elements or ensuring the same function, for the sake of simplification of the description.

The present invention uses a compact and lightweight infrared spectroscopy device. The infrared spectroscopy device comprises a suspended membrane light source adapted to emit directional infra-red radiation (hereinafter referred to as "directional"), and a thermo-detector including at least one line of cells heat sensitive. The arrangement of the at least one temperature-sensitive cell line with respect to the light source makes it possible to implement infrared spectroscopy measurements.

In FIGS. 5a and 6b, schematic representations of the infrared spectroscopy device 10 according to the invention can be seen.

The device comprises a light source 20 represented in FIG. 1. The light source is adapted to emit light radiation in the infra-red domain (hereinafter "infra-red").

The light source 20 comprises a metal network 30 formed by a set of metal tracks 31 and a metal layer 32.

Advantageously, the metal tracks 31 are in direct contact with the metal layer 32. The thickness of the metal layer 32 is advantageously greater than 50 nm, still more advantageously greater than 100 nm.

The metal tracks 31 are arranged parallel to a direction X.

In the context of the present invention, we consider that the metal network 30 is plane.

The metal tracks 31 are also periodically arranged with a period P in a direction Y perpendicular to the direction X.

Advantageously, the light source 20 extends over a length I in the direction Y. More particularly, the length I is between 10 μm and 1 mm, for example 250 μm.

The metal tracks 31 may comprise at least one of the following metals: tungsten. Aluminum, Copper, Gold, Silver, Tantalum, Titanium, Palladium, Molybdenum, Platinum.

The metal layer 32 may comprise at least one of the following metals: tungsten. Aluminum, Copper, Gold, Silver, Tantalum, Titanium, Palladium, Molybdenum, Platinum.

The light source 20 also comprises heating means 40 of the metal network 30. It is thus understood, without it being necessary to specify, that the heating means 40 are adapted to impose a temperature rise to the metal network 30.

The light source 20 can advantageously be evacuated (encapsulated) in order to limit the losses by conduction in the air, and thus improve its efficiency. The encapsulation techniques of the light sources are known to those skilled in the art and are therefore not described in the present invention.

It is known that a body, for example a metal body, emits radiation whose spectral extent depends on its temperature. More particularly, this radiation, also known as dark body radiation, is governed by Planck's law.

Thus, for example, tungsten heated to 500 ° C emits a major portion of its light radiation in the wavelength range 3 μm to 4.69 μm.

The heating means 40 may comprise a membrane, for example a heating membrane 41, on which metal lattice 30 rests (shown in a view from above in FIG. 2a, and along a sectional plane AA 'in FIG. 2b). The heating membrane 41 may have a circular or square or rectangular shape.

The heating membrane 41 may comprise a heating element 42, interposed between a first layer 43 and a second layer 44 each made of at least one dielectric material. The heating element 42 may comprise a metal, for example platinum. The at least one dielectric material forming the first layer 43 and the second layer 44 may comprise at least one of the following materials: silicon nitride, silicon oxide.

The heating membrane 41 may be sized and manufactured according to the method described in document [1] cited at the end of the description. Thus, according to an advantageous embodiment, the first layer 43 may comprise a layer of silicon nitride (Si3N4) of 100 nm thick. The second layer 44 may comprise a layer of silicon oxide (SiO 2) 100 nm thick on which a layer of silicon nitride of 100 nm thick rests. The heating element 42 may comprise a TiN / Pt / TiN stack of 10 nm, 30 nm and 10 nm, respectively. The heating membrane 40 may be circular in shape with a diameter of between 50 μm and 150 μm, for example 50 μm or 100 μm or 150 μm.

The formation of the metal network 30 on the heating membrane 40 uses techniques known to those skilled in the art and is therefore not described in detail in the present application.

The light source 20 according to the invention is thus adapted to emit directional light radiation.

By directional light radiation, it is meant that each wavelength λ forming the light radiation is emitted in a plane of its own. More particularly, in the context of the present invention, when it is heated to a temperature T, the metal network 30 emits a set of wavelengths λϊ. Each wavelength λΙ is emitted along a plane Pi. The plane Pi is at an angle φ with a plane Ps of symmetry of the metal network 30. The plane Ps comprises the direction X, and is normal to the plane of the metal network 30. is also understood, without it being necessary to specify it, that each plane Pi and the plane of symmetry Ps intersect at the level of the plane of the metal network 30. The inventors have demonstrated that the wavelength λϊ and the angle 0i corresponding satisfy the relation (1). λi = P (l + sin (0i)) (1)

Thus, and advantageously, the range of wavelengths X 1 lies between a minimum wavelength λmin and a maximum wavelength λmax, the period P of the metal network being equal to the minimum wavelength λmin.

For example, the metal network 30 may be heated by the heating element 42 at a temperature of 500 ° C, so as to emit most of its light radiation in the wavelength range 3 μm - 4.69 μm.

An increase in the temperature imposed by the heating element 42 makes it possible to increase the light radiation emitted by the metal network 30.

However, increasing said temperature also increases the power consumption of the heater 42, and can also degrade it. It can thus be advantageous to limit the temperature imposed by the heating element 42 to 700 ° C.

Advantageously, the metal tracks 31 have a thickness E greater than one fiftieth of the minimum wavelength λmin, advantageously the thickness E is between one fiftieth and one tenth of the minimum wavelength λmin. The thickness E of the metal tracks 31 is for example between 50 nm and 300 nm, for example 175 nm.

By thickness of a metal track 31 is meant the dimension of said metal track in a direction perpendicular to the plane of the metal network 30.

Advantageously, the width of the metal tracks 31 is between 0.5 μm and 2.5 μm, for example 1.5 μm.

More particularly, the width of the metal tracks 31 may be equal to half the period P of the metal network 30.

By width of the metal tracks 31 is meant the dimension of said metal tracks 31 in the Y direction.

The length of the metal tracks 31 can be between lOpm and 1mm.

The inventors have thus made optical simulations of a light source according to the present invention in order to determine the emissivity spectrum of said source as a function of the angel 0i. In these simulations, the inventors have considered metal tracks 31 made of tungsten, with a period P of 3 μm.

FIG. 4a is a graphical representation of an optical simulation in a first configuration, the thickness E is 175 nm, and the width is 1.5 μm.

The metal tracks also rest on a metal layer 32 of 100 nm of tungsten. In FIG. 4a, the vertical axis represents the length of the wave λ, and the horizontal axis represents the emissivity angle Θ. The luminous intensity emitted for each wavelength is given in gray levels.

FIG. 4b is a graphical representation of an optical simulation in a first configuration, the thickness E is 100 nm, and the width is 2.5 μm. In FIG. 4b, the vertical axis represents the length of the wave λ, and the horizontal axis represents the emissivity angle Θ. The luminous intensity emitted for each wavelength is given in gray levels.

These simulations can be used for sizing the light source 20 and / or a thermo-detector 50.

The infrared spectroscopy device 10 further comprises a thermo detector 50.

The thermo-detector 50 comprises at least one thermosensitive cell 51.

By thermosensitive cell 51, we mean a cell capable of detecting heat incident on its surface.

Also, when infra-red radiation is incident on the surface of a thermosensitive cell, the latter undergoes an increase in temperature which is a function of the light energy of the infra-red radiation incident. Moreover, as soon as infrared light radiation incident on a heat-sensitive cell 51 causes the latter to heat up, we consider that the infrared radiation is collected by said thermosensitive cell. The at least one thermosensitive cell 51 may comprise bolometers.

A bolometer is a cell capable of collecting infrared radiation.

The bolometer generally comprises a suspended membrane made of a material having a temperature coefficient of resistance ("TCR" or "Temperature Coefficient of Resistance" according to the terminology Anglo-Saxon).

In other words, the temperature variation of the bolometer by absorption of infra-red radiation induces a variation of electrical resistance of said bolometer. Thus, the measurement and / or detection of infra-red radiation is based on a measurement of the electrical resistance variation by the diaphragm suspended membrane. Bolometers are known to those skilled in the art, and described for example in the patent application [2] cited at the end of the description.

Advantageously, the thermo-detector 50 and the light source 20 are facing and at a distance from one another. Thus, the at least one heat-sensitive cell 51 can collect a portion of the infra-red radiation emitted by the light source 20. More particularly, since the light source 20 is directional. the at least one thermosensitive cell 51 is exposed only to a restricted range of wavelengths.

The distance d can be between 1mm and 10cm, for example 1 cm.

Advantageously, the ratio of the length I to the distance d being greater than one hundredth.

Advantageously, the infrared spectroscopy device 10 may further comprise a data processing module 60 capable of being collected by the thermo-detector 50. The data processing module 60 may be a computer or a computer equipped with a computer program adapted to process the data collected by the thermo-detector 50.

According to a first particularly advantageous embodiment illustrated in FIG. 5a, the thermo-detector 50 comprises only one column of heat-sensitive cells 51 arranged parallel to the X direction (FIG. 5b).

Thus, the column of heat-sensitive cells 51 is exposed only to a restricted range of wavelengths.

For example, a column of thermosensitive cells 51 with a width of 25 μm, and disposed one centimeter from the light source 20 of period P = 3 μm, will be theoretically exposed to a radiation with a spectral width of 80 μm. nm (also called spectral resolution).

The column of heat-sensitive cells 51 may comprise 320 heat-sensitive cells 51.

Advantageously, and in the context of the first embodiment, the light source 20 may be provided with a rotation means 21, for example a stepping motor. Thus, the thermo-detector 50 can collect and sample all the infra-red radiation emitted by the light source 20.

According to a second embodiment, illustrated in FIG. 6a, the thermodetector 50 comprises a plurality of photosensitive cells 51 arranged in the form of a matrix (FIG. 6b).

By matrix, we mean a regular and periodic arrangement of photosensitive cells according to the X and Y directions. The periodicity in the Y direction is noted as a matrix pitch Pm.

Thus, we define the expression line of heat-sensitive cells by an arrangement of thermosensitive cells aligned in direction Y.

Equivalently, a column of heat-sensitive cells is a set of cells aligned along the X direction.

It is understood that the matrix may comprise only one line of heat-sensitive cells 51. In this particular case, the infrared spectroscopy device 10 may comprise means 70 for focusing the infra-red radiation on the line of heat-sensitive cells 51 ( illustrated in Figure 7).

The focusing means 70 may comprise a lens, for example a convergent lens. The choice or the dimensioning of the focusing means 70 are part of the general knowledge of those skilled in the art and are therefore not described in more detail in the present description.

Advantageously, the light source 20 may be arranged parallel to the thermo-detector 50.

Still advantageously, the assembly formed by the thermodetector 50 and the light source 20 is symmetrical with respect to a plane parallel to the metal tracks 31, and perpendicular to the Y direction.

Each column of heat-sensitive cells 51 corresponds to an acquisition channel Ci of a spectral band of the infra-red radiation emitted by the light source 20.

The spectral power detected by an acquisition channel Ci can be determined in order to determine the sensitivity of the infra-red spectroscopy device 10 according to the invention. Sensitivity means the ability of the infrared spectroscopy device to detect a variation in light intensity at a given wavelength due to the presence of a chemical species between the light source and the thermodetector 50. for example, we consider the wavelength 4.26 pm (which is a line of carbon dioxide CO2 absorption).

The light source considered in this example has the characteristics given in Table 1:

Each acquisition channel Ci of the thermo-detector comprises 480 bolometers of NEP type 10 pW of 25 μm side. The flux then collected by the acquisition channel Ci associated with the length λΙ of 4.26 μm is of the order of 165 nW, and is similar to the flux collected by a pyroelectric sensor illuminated by a black body (non-directional light source within the meaning of the invention). The device according to the invention has a detection noise of the order of 205 pW (the determination of the detection noise is part of the general knowledge of those skilled in the art and is therefore not described in the present description). FIG. 8 then shows the variation of the light flux collected (on the vertical axis) by the acquisition channel Ci associated with the wavelength 4.26 μm as a function of the CO2 concentration in ppm (on the axis horizontal). It can be deduced from this graph that a variation of 1000 ppm in CO2 equates to a flux variation of 30 nW (100 times greater than the detection noise). It is thus possible to detect a few tens of ppm of gas (CO2) with the infra-red spectroscopy device according to the invention.

The spectral resolution of the infrared spectroscopy device according to the invention is given by the width of the spectral band Bsi effectively collected by each acquisition channel Ci.

The determination of the spectral resolution must take into account the divergence of the beam, of wavelength λΙ (the wavelength λΙ being the central wavelength of the spectral band Bsi collected by the acquisition channel Ci) emitted in each direction di, and given by the following relation:

where w (z) is the size (area) of the beam, in a given direction and at the distance z from the light source, wo is the area of the light source actually seen by an acquisition channel, and Zr is given by the relationship :

FIG. 9 illustrates the spectral width actually collected by a series of adjacent acquisition channels for a distance d of 1 cm, and a matrix pitch Pm of 25 μm. We thus observe a spectral resolution of the device 10 of 80 nm in FIG. 7. FIG. 8 illustrates, for the same device, the successive differences between the intensities collected by neighboring acquisition channels Ci and Ci + 1. The resolution thus obtained is of the order of 40 nm.

The infrared spectroscopy device 10 may advantageously be used for the detection and identification of hydrocarbons, the hydrocarbons advantageously comprising methane and ethane.

It is understood, without it being necessary to specify, that the detection and identification of hydrocarbons requires that the latter be present between the light source 20 and the thermo-detector 50.

Furthermore, the heating means can heat the metal network 31 to a temperature adapted for the light source 20 to emit infrared radiation in a range of wavelengths ranging from 3 pm to 4.69 pm. By way of illustration, Figure 11 shows the absorption spectra of methane and ethane superimposed with differences in light intensities emitted by the light source, and collected by the series of adjacent acquisition channels.

Figure 12a shows the superposition of the infrared absorption spectra of methane (M) and ethane (E) as a function of the wavenumber in cm 2 (on the horizontal axis).

FIGS. 12b (for methane), 12c (for ethane) and 12d (for a methane / ethane mixture) represent, in grayscale, the infra-red intensity collected by acquisition channels (numbered 1 to 10). The acquisition channels 1 to 10 each collect a 40 nm spectral band, each acquisition channel being "spectrally" 8 nm apart from the nearest acquisition channels. More particularly, all of the acquisition channels make it possible to collect infra-red radiation extending from 2945 cm -1 to 3025 cm -1. A pronounced gray reveals a strong absorption of radiation before it reaches the acquisition channel, while a light gray reveals a very weak absorption of infra-red radiation. Figure 12b shows that acquisition channels 1 to 3 and 10 are essentially sensitive to the presence of methane, while channels 4 to 8 may reveal the presence of ethane.

Thus, the device according to the invention allows the detection but also the discrimination of hydrocarbons, and more particularly of ethane and methane. The analysis of the gray levels of the signal collected by each of the channels also makes it possible, by using the Beer-Lambert law, to determine the concentration of the detected gases.

The infra-red spectroscopy device 10 according to the invention is thus a compact device, and has a relatively low cost. It can therefore be used as a gas detector, more particularly as a methane and ethane detector. The device 10 also makes it possible to determine the concentration in the air of the detected gas.

Moreover, unlike conventional spectroscopic devices, such as Fourier transform devices, the infrared spectroscopy device according to the invention is not sensitive to vibrations, and is stable. It can therefore also be used as portable equipment, and / or mobile applications, embedded on drones, for example.

REFERENCES

[1] P. Barritault et al., "Mid-IR source based on a free-standing micro-sensor for independent CO2 sensing in indoor applications," Sensors and Actuators A, 172, p. 379-385, (2011), [2] FR 2 977 937.

Claims (20)

An infrared spectroscopy device (10) comprising: - a light source (20) which comprises a metal network (30) and heating means (40) of the metal network (30), the metal network (30) comprising a set of metal tracks (31) parallel to a direction X, and arranged in a period P in a direction Y perpendicular to the direction X, the light source (20) being intended to emit infrared radiation in a range of lengths of waves λΙ determined by a temperature T imposed on the metal network by the heating means, the infra-red radiation being directional so that each wavelength λΙ is emitted according to a plane Pi which is specific to it, the plane Pi is an angle φ with a plane Ps of symmetry of the metal network (30), the plane Ps comprises the direction X and is normal to the metal network (30), - a thermo-detector (50) at a distance d from the light source, and who understands at least one thermosensitive cell (51) intended to collect, at least in part, the directional infra-red radiation that can be emitted by the light source (20). 2. Device according to claim 1, wherein the heating means (40) comprises a heating membrane (41) on which the metal network (30) rests, the heating membrane (41) comprising a heating element (42) interposed between a first layer (43) and a second layer (44) made of at least one dielectric material. 3. Device according to claim 1 or 2, in whichthe wavelength range is between a minimum wavelength λmin and a maximum wavelength λmax, the period P of the metal grating being equal to the length of wavelength. minimum wave Xmin. 4. Device according to claim 3, wherein in the metal tracks have a thickness greater than one fiftieth of the minimum wavelength λmin. 5. Device according to one of claims 1 to 4, wherein the metal tracks have a width, measured in the direction Y, equal to half of the period P. 6. Device according to one of claims 1 to 5, wherein each wavelength λΙ and the corresponding angle θi are linked by the relationship: λi = P (l + sin (0i)). 7. Device according to one of claims 1 to 6, wherein the metal tracks comprise at least one of the materials selected from: tungsten. Aluminum, Copper, Gold, Silver, Tantalum, Titanium, Palladium, Molybdenum, Platinum. 8. Device according to one of claims 1 to 7, wherein the at least one heat-sensitive cell comprises a bolometer. 9. Device according to one of claims 1 to 8, wherein the thermo-detector comprises a plurality of photosensitive cells (51) arranged in a column parallel to the direction X. 10. Device according to claim 9, wherein the infrared spectroscopy device (10) further comprises rotation means (21) for rotating the light source (20) about an axis parallel to the X direction . 11. Device according to one of claims 1 to 10, wherein the thermo-detector (50) comprises a plurality of photosensitive cells (51) arranged in the form of a matrix parallel to a plane comprising the directions X and Y. 12. Device according to claim 11, wherein the light source is disposed parallel to the thermo-detector (50). 13. Device according to claim 12, wherein the assembly formed by the thermo-detector (50) and the light source (20) is symmetrical with respect to a plane parallel to the metal tracks (31). 14. Device according to one of claims 1 to 13, wherein the light source extends over a length I in the direction Y, the ratio of the length I over the distance d being greater than one hundredth. 15. Device according to claim 14, wherein the length I is between 10 pm and 1 mm, for example 250 pm. 16. Device according to claim 15, wherein the distance d is between 1mm and 10 cm, for example 1 cm. 17. Device according to claim 16, the thermo-detector comprises 320 columns of heat-sensitive cells parallel to the direction X, the heat-sensitive cells having a square shape of 25 pm side. 18. Device according to one of claims 1 to 17, wherein the infrared spectroscopy device further comprises a module (60) for processing data that can be collected by the thermo-detector. 19. A method of using the infrared spectroscopy device according to one of claims 1 to 18 for the detection and identification of hydrocarbons, the hydrocarbons advantageously comprising methane and ethane. 20. The method of claim 19, wherein the heating means heat the metal network to a temperature adapted for the light source to emit infrared radiation in a wavelength range extending from 3 μm to 4, 69 μm.