Compact gas sensor with a simple design

Abstract

gas sensor (1) comprising a housing (2), the sensor also comprising: a light source (10), configured to emit a light wave (11) propagating in the housing, forming, from the light source, a first cone of light (Ω1); a measurement photodetector (20) capable of detecting a light wave (14) emitted by the light source (10) and having propagated through the housing; the light source and the measurement photodetector being supported by a printed circuit board (7); a first-order reflective surface, forming part of an ellipsoid of revolution, having a first focus (P1-1) and a second focus (P1-2), the first-order reflective surface being disposed opposite the light source (10), so as to reflect the first cone of light towards the second focus, the first reflective surface forming part of an ellipsoid of revolution.

Description

Title of the invention: Compact gas sensor of simple design Technical field

[0001] The technical field of the invention is an optical gas sensor, and more particularly a non-dispersive infrared sensor. PREVIOUS ART

[0002] The use of optical methods for gas analysis is quite common. Devices make it possible to determine the composition of a gas based on the fact that the species composing a gas have different absorption spectral properties from each other. Thus, knowing an absorption spectral band of a gaseous species, its concentration can be determined by an estimation of the absorption of light passing through the gas, using Beer Lambert's law. This principle allows an estimation of the concentration of a gaseous species present in the medium.

[0003] The light source is usually a source emitting in the infrared, the method used being usually designated by the Anglo-Saxon term "NDIR detection", the acronym NDIR meaning Non Dispersive Infra-Red. Such a principle has been frequently implemented, and is for example described in numerous documents, for example in US5026992 or WO2007064370.

[0004] According to the most common methods, the gas analyzed extends between a light source and a photodetector, called a measuring photodetector, the latter being intended to measure a light wave, emitted by the source, transmitted through the gas to be analyzed, and partially absorbed by the latter. The methods generally comprise a measurement of a light wave, called a reference light wave, emitted by the source, and not absorbed by the gas analyzed.

[0005] The comparison between light radiation in the presence of gas and light radiation without gas makes it possible to characterize the gas. This involves, for example, determining a quantity of a gaseous species in the gas, according to the technology designated by the term "NDIR by absorption". It can also involve estimating a quantity of particles in the gas, by detecting light scattered by the latter according to a predetermined angular scattering range.

[0006] The reference light wave is measured by a reference photodetector. This may be a reference photodetector different from the measuring photodetector, and arranged so as to be placed facing the light source, the reference photodetector being associated with a reference optical filter. The reference optical filter defines a reference spectral band, in which the gas to be analyzed does not present significant absorption.

[0007] Documents EP2711687 and EP2891876 describe gas sensors comprising enclosures, in which one or more mirrors are arranged. The mirrors make it possible to maximize the path of light in the enclosure, and to focus the light rays having passed through the gas onto the photodetector(s). This makes it possible to increase the detection sensitivity while using compact devices.

[0008] US2022 / 0214267 describes a compact configuration of a gas sensor, compatible with a so-called “4R” format, which is a common standard in the field of gas detection.

[0009] The applicant has designed a particularly compact gas sensor, compatible with the 4R format, the manufacture of which is simpler and less expensive than that of the sensor described in US2022 / 0214267. This results in a gas sensor with optimized performance, particularly favoring compactness and cost. Statement of the invention

[0010] A first object of the invention is a gas sensor comprising an enclosure, configured to receive a gas, the sensor also comprising: - a light source, configured to emit a light wave propagating in the enclosure by forming, from the light source, a first cone of light; - a measuring photodetector configured to detect a light wave emitted by the light source and having propagated through the enclosure; - the light source and the measuring photodetector being supported by a printed circuit; - a reflective surface of rank 1, forming part of an ellipsoid of revolution, having a first focus and a second focus, the reflective surface of rank 1 being arranged facing the light source, so as to reflect the first cone of light towards the second focus, the first reflective surface forming part of an ellipsoid of revolution; - the device being characterized in that: • the printed circuit comprises a plane mirror, forming a reflective surface of rank 2, the second focus of the reflective surface of rank 1 being located on the plane mirror or at a distance of less than 1 mm from the latter; • the device comprises a final reflecting surface, of rank N, N being greater than or equal to 3, comprising a first focus, located at the level of a plane mirror, arranged on the circuit printed, forming a reflective surface of rank AM, the last reflective surface comprising a second focus;

[0011] such that the light background emitted by the light source is successively reflected by the N reflecting surfaces, according to their respective ranks, before converging towards the second focus of the last reflecting surface, forming a last cone of light, the measuring photodetector being arranged so as to extend into the last cone of light.

[0012] According to one possibility, the light source is arranged at the level of the first focus of the reflective surface of rank 1, or at a distance of less than 1 mm from the latter.

[0013] According to one possibility, the measuring photodetector is arranged at the level of the second focus of the last reflecting surface, or at a distance of less than 1 mm from the latter.

[0014] According to one possibility: the device comprises several even-ranked reflective surfaces, each even-ranked reflective surface being a plane mirror arranged on the printed circuit; the device comprises several reflective surfaces of odd rank, each reflective surface of even rank forming part of an ellipsoid of revolution and extending opposite the printed circuit.

[0015] According to one possibility: each reflective surface of rank n is configured to reflect the light it receives by forming a light cone of rank n+1, the latter extending around a propagation axis of rank n+1; when n <N, l'axe de propagation de rang n+1 s'étend entre la surface réfléchissante de rang n jusqu'à la surface réfléchissante de rang n+1 ; when n is odd, and n < AM, each reflecting surface extends along a part of an ellipsoid of revolution, the propagation axis of rank n+1 passing through the second focus of the surface of rank n, the latter being merged with the first focus of the surface of rank n+2; when n = N, the propagation axis of rank AM extends between the surface of rank ^ to the measuring photodetector;

[0016] such that the light background emitted by the light source undergoes a number of reflections corresponding to the number of reflective surfaces before reaching the measuring photodetector.

[0017] According to one possibility, in which when n <N etn est impair, chaque cône de lumière de rang n+1 converge vers le deuxième foyer de la surface de rang n à partir de laquelle il se propage.

[0018] The odd-numbered reflective surfaces may be provided on an internal face of the same wall, forming a sensor cover. The enclosure may be formed by assembling the sensor cover above a base, the printed circuit being arranged on the base.

[0019] The or each plane mirror may be formed by a thin layer of a reflective material deposited on the printed circuit.

[0020] The number of reflective surfaces extending between the light source and the measuring photodetector is preferably odd. The number of reflective surfaces extending between the light source and the measuring photodetector may be 3 or 5.

[0021] According to one possibility, the sensor comprises a reference photodetector, configured to detect a light wave considered to be not attenuated by the gas.

[0022] The sensor may comprise a reference reflecting surface, forming an ellipsoid of revolution, the reference surface comprising: - a first focus, arranged at the level of a flat reflective surface, of even rank, or at a distance less than 1 mm from the latter; - a second focus, arranged at the level of the reference photodetector, or at a distance less than 1 mm from the latter.

[0023] A second subject of the invention is a method for analyzing a gas using a sensor according to the first subject of the invention, the method comprising the following steps: a. introduction of gas into the sensor enclosure; b. illumination of the gas using the light source; c. measurement of a light intensity of a light wave, emitted by the light source, and having propagated through the enclosure by the measuring photodetector; d. determination of a quantity of a gaseous species in the gas, from the measured light intensity.

[0024] Step d) can be implemented by a processing unit from a signal generated by the measuring photodetector.

[0025] The method may comprise detection, by a reference photodetector, of a reference light wave, considered as not absorbed, or negligible, by the gas. Step d) is then implemented by the processing unit from a reference signal generated by the reference photodetector.

[0026] The invention will be better understood upon reading the description of the exemplary embodiments presented in the remainder of the description, in conjunction with the figures listed below. FIGURES

[0027] Figures 1A and 1B are sections of the gas sensor, respectively in a transverse plane XZ and in a principal plane XY, the principal plane being perpendicular to the transverse plane.

[0028] [Fig.2A] shows schematically the base and the cover of the sensor and shows the location of the main components of the sensor, i.e. a light source, a measuring photodetector, as well as three reflective surfaces. In this figure, the axis Di corresponds to a circular generator shown in [Fig.1B]. This representation amounts to unrolling the sensor enclosure along this generator.

[0029] [Fig.2B] represents a variant of the embodiment shown schematically in [Fig.2A], implementing a reference photodetector.

[0030] [Fig.3A] shows an embodiment implementing 5 successive reflective surfaces.

[0031] [Fig.3B] represents a variant of the embodiment shown schematically in [Fig.3A], implementing a reference photodetector.

[0032] [Fig.4] shows an experimental test bench for determining the reflectivity of different thin layers. PRESENTATION OF SPECIAL EMBODIMENTS

[0033] Figures 1A and 1B diagram a gas sensor 1 according to the invention. The gas sensor 1 comprises an enclosure 2 delimited by a base 4, a cover 5 and a transverse wall 6. The transverse wall 6 extends parallel to a transverse axis Z. The transverse wall 6 is an annular wall, around the transverse axis Z. It extends between the base 4 and the cover 5. The transverse axis Z extends perpendicular to a main plane XY. The enclosure 2 forms a cylindrical housing, obtained by placing the cover 5 on the base 4.

[0034] The base 4 has an external face 4e and an internal face 4;. The cover 5 has an external face 5e and an internal face 5;. The respective external faces 4e, 5e of the base 4 and the cover 5 are flat, parallel to the main plane XY. They are perpendicular to the transverse axis Z around which the annular wall 6 extends. The respective internal faces 4;, 5; of the base 4 and the cover 5 are oriented towards the inside of the enclosure 2. The enclosure 2 is connected to connection pins 3, parallel to the transverse axis Z.

[0035] The shape and dimensions of the sensor 1 conform to a standard format in the field of gas detection, known as 4R format. The diameter <e>of enclosure 2, in the XY plane, is 20 mm, and its height h (along the Z axis) is 16.6 mm. Taking into account the thickness of the transverse wall 6, the internal diameter <e>' of enclosure 2 is 17 mm. A positive direction of rotation around the transverse axis Z is defined, which is arbitrarily considered to be similar to the direction of rotation of the hands of a clock.

[0036] An advantage of the 4R format is that it is widely used in the field of electronics. Thus, a gas sensor 1 complying with this format can easily be connected to existing electronic circuits. Compliance with this format facilitates the maintenance of measurement systems, by facilitating the replacement of sensors.

[0037] The enclosure 2 is intended to be occupied by a gas G to be analyzed. The gas to be analyzed comprises a gaseous species Gx for which a concentration C is to be determined, in the gas. The gaseous species Gx absorbs light, and in particular infrared light, in an absorption spectral band AXx. The sensor 1 also comprises: • a light source 10, configured to emit a light wave 11 in an emission spectral band AX. The emission spectral band can extend between the near ultraviolet and the mid-infrared, for example between 200 nm and 20 pm, and most often in the infrared, the emission spectral band AX being for example between 1 pm and 20 pm. • a measurement photodetector 20, configured to detect a light wave 14, called a transmitted light wave, in the absorption spectral band AXx. The transmitted light wave is a light wave emitted by the light source 10, and having propagated through the enclosure, gradually attenuating during its journey through the gas. The measurement photodetector 20 may be associated with a bandpass filter, defining a detection spectral band AXd included in the absorption spectral band AXx. • a reference photodetector 20ref, configured to detect a reference light wave. The reference light wave detected by the reference photodetector 20ref is considered to be unattenuated by the gas G present in the enclosure. In this example, the reference photodetector detects the reference light wave 20ref in a reference spectral band AXref, in which the attenuation of the light wave emitted by the source is considered to be negligible, or due to a variation in environmental conditions, for example temperature or humidity. The reference photodetector may be associated with a reference bandpass filter, defining the reference spectral band AXref. For example, the reference spectral band AXref is centered around the wavelength 3.91 pm. The use of a reference photodetector is optional but is advantageous.Alternatively, the reference photodetector is not arranged in the enclosure 2 comprising the gas, in which case the reference spectral band may be similar to the measurement spectral band.

[0038] Preferably, the light source 10, the measurement photodetector 20 and the reference photodetector 20ref are connected to the same flat support. This may in particular be an electronic card forming the first wall 4 of the enclosure 2. Such a dis- position simplifies the manufacturing of the sensor.

[0039] The light source may be pulsed, and emit light pulses whose duration is generally between 50 ms and 1 s. It may in particular be an infrared light source of the filament type formed on a suspended membrane, the filament being traversed by an electric current. In this way, the suspended membrane is heated to a temperature between 400°C and 800°C, so as to emit infrared light.

[0040] The measurement photodetector 20 and the reference photodetector 20ref may be thermopiles or pyrodetectors or photodiodes. Each photodetector is configured to generate a detection signal, the amplitude A of which corresponds to an intensity I of the detected light background.

[0041] The intensity 1 of the light background detected by the measuring photodetector 20 depends on the concentration Cx of the gaseous species of interest Gx according to the Beer Lambert relationship:

[0042] a^ — L — g-rfcy

[0043] where: - qfCx) is an attenuation coefficient, dependent on the concentration C, re sought; - I is the thickness of gas crossed by the luminous flux in the enclosure; - l0 corresponds to the background intensity which is or would be detected by the photo measuring detector 20 in the absence of absorbing gas in the enclosure.

[0044] The comparison between 1 and 10 taking the form of a ratio 1 / 10, corresponds to an attenuation att caused by the gaseous species Gx considered. During each pulse of the light source 10, it is thus possible to determine n(Cx), which makes it possible to estimate the quantity Cx knowing that the relationship between Cx and Cx) is known.

[0045] The intensity l0 can be predetermined, for example during a calibration, or measured in the absence of gas in the enclosure 20. When the sensor comprises a reference photodetector 20ref, the reference intensity / ^measured by the reference photodetector makes it possible to measure variations in A).

[0046] The sensor comprises a processing unit 30, receiving the signals measured respectively by the measurement photodetector 20 and the possible reference photodetector 20ref. The processing unit 30 makes it possible to carry out, from the latter, the calculations for estimating the concentration of the gaseous species sought. The processing unit 30 comprises for example a microprocessor.

[0047] The dimensions of the enclosure 2 in which the gas extends are particularly small. However, it is preferable for the light background detected by the measuring photodetector 20 to be sufficiently attenuated so that the attenuation att is more easily quantifiable, taking into account the different noises of the measuring chain. It is therefore preferable that the length l traveled by the rays reaching the measuring photodetector is sufficiently high. The applicant considers that the attenuation att must be greater than 0.2.

[0048] In application US2022 / 0214267, a particularly compact configuration of a gas sensor is described, in which the rays are reflected by ellipsoidal reflective surfaces. By ellipsoidal surface is meant a surface following a part of an ellipsoid of revolution. The reflective surfaces allow the light emitted by the light source to carry out multiple reflections before reaching the measuring photodetector. This results in a sufficient length l traveled, in the enclosure 2, by the rays reaching the measuring photodetector 20. However, such a configuration assumes the production of a large number of ellipsoidal surfaces, which must be precisely arranged relative to each other. In addition, this assumes the production of two different parts having complex shapes.

[0049] [Fig.2A] shows the interior of the enclosure 2. In [Fig.2A], the interior of the enclosure 2 is represented by following a circular generator Di shown in dotted lines in [Fig.1B]. This representation amounts to unrolling the enclosure along the circular generator Db along which extend reflective surfaces S„ of rank n. The index n is a natural integer such that 1 < n < N, N being the number of reflective surfaces located on the optical path of the light background emitted by the light source 10 and propagating towards the measurement photodetector 20.

[0050] In this device, depending on whether n is even or odd, the reflecting surface Sn of rank n is respectively flat or ellipsoidal. Thus, the sensor is formed from an alternation of ellipsoidal (rank n odd) or flat (n even) reflecting surfaces. The use of flat reflecting surfaces simplifies the manufacture of the sensor.

[0051] The term ellipsoidal surface Sn denotes an ellipsoidal surface of revolution, obtained by a rotation in space of an ellipse En around one of its axes. In the example described, each ellipsoidal surface Sn, n being odd, is associated with an ellipse En having a major axis and a minor axis. By ellipsoidal surface associated with an ellipse, we mean an ellipsoidal surface formed by a rotation of the ellipse around one of its axes. In the example shown, each ellipsoidal surface Sn is obtained by a rotation of ellipse En, to which it is associated, around its major axis. Such an ellipsoidal surface is said to be elongated, which corresponds to the Anglo-Saxon designation "prolate spheroid" or "prolate ellipsoid".

[0052] By reflective surface is meant a surface whose reflection coefficient, in all or part of the AX emission spectral band, is greater than 40%, or even 50%, and preferably greater than 80%. In the infrared spectral range, a reflective wall can be formed using a reflective material such as a metal, for example gold.

[0053] In the configurations shown in Figures 2A and 2B, N = 3. In the configurations shown in Figures 3A and 3B, N = 5. A can be between 3 and 10, but the applicant considers that A = 5 corresponds to an optimum.

[0054] Whatever the configuration, each reflecting surface S„, n being odd, is ellipsoidal. It comprises a first focus Pi „ and a second focus P2 „, the two foci being distinct from each other. When 3 4 n < N, the first focus PL„ coincides with the second focus P2.f„.2) of an ellipsoidal reflecting surface S^ of rank n-2. When n = 1 (first reflecting surface Sj), the second focus P24 coincides with the first focus Pi 3 of the second reflecting surface ^ When n = N (last surface), the first focus Pi coincides with the second focus P2tN2l of the ellipsoidal surface S^ of rank N-2. The first reflecting surface S, allows a reflection of incident light background 11 emitted by the light source 10, while the last reflecting surface SN allows a reflection of incident light background light, having passed through the enclosure 10, towards the measuring photodetector 20.

[0055] Each reflecting surface Sn, n being even, is a plane mirror. Each reflecting surface Sn, n being even, is located at: - of the second focus P2>ni of the ellipsoidal reflecting surface S, . / of immediately lower rank; - of the first focus Pi>n+i of the ellipsoidal reflecting surface of immediately higher rank Sn+].

[0056] The light source 10 and the measurement photodetector 20 are carried by a printed circuit 7, the printed circuit being designated by the English term Printed Circuit Board (PCB). Preferably, the light source and the measurement photodetector are carried by the same printed circuit. Preferably, each plane mirror, forming a reflective surface Sn of even rank, is formed by a thin layer of a reflective material, such as gold or nickel, directly on the PCB. The thickness of the thin layer may be a few 100 nanometers, for example between 50 nm and 1 pm, or between 300 nm and 1 pm. Thus, advantageously, each mirror results from a deposition of the reflective material directly on the PCB. This simplifies the detector manufacturing process. The plane thin layer is arranged so as to be located in the axis An_i of the light cone Qn i emitted by the ellipsoidal reflective surface Sn, of previous rank.As previously indicated, each reflecting surface Sn, n being even, extends to the level of the second focus P2>n of the ellipsoidal reflecting surface Sn.i of the previous rank, as well as to the level of the first focus Pi>n+ of the ellipsoidal reflecting surface Sn+] of the next rank.

[0057] One of the advantages of the invention is that only the odd-rank reflective surfaces are ellipsoidal. The latter are arranged on the cover 5, and more precisely precisely form the inner face 5; of the cover. Unlike the configuration described in US2022 / 0214267, the ellipsoidal reflective surfaces are formed on a single part, intended to be arranged facing the printed circuit 7. This limits the number of complex parts to be produced. Furthermore, the formation of plane mirrors on the printed circuit is particularly simple and inexpensive, which reduces the price of the sensor. It is possible either to deposit a thin reflective layer or to arrange a prefabricated plane mirror.

[0058] The light wave 11 emitted by the light source is successively reflected by the different reflecting surfaces Sn, according to their respective ranks, taken in ascending order. In other words, the reflecting surfaces S}... SN extend successively between the light source 10 and the measuring photodetector 20. The term extend successively is to be interpreted by considering the propagation of the light between the light source 10 and the measuring photodetector 20. The light background path, projected onto the base 4 or the cover 5, describes an arc of a circle.

[0059] The light source 10 is configured to emit light emission beam 11 according to a light cone Qb called the first cone, extending around a first axis Ab to the first ellipsoidal reflecting surface S}. The light source 10 is arranged at a vertex of the first light cone. The light source 10 is preferably coincident with the first focus Pu of the first reflecting surface S}.

[0060] The terms "confused" or "at the level of" are to be interpreted with a certain tolerance, and can mean "being located in the vicinity of", the vicinity corresponding to an area extending at a short distance from a point. By short distance, it is understood a distance of less than 1 mm, or even less than 0.5 mm.

[0061] In the configuration shown in [Fig.2A], the first ellipsoidal reflecting surface S} is configured to reflect the first light cone Qi to form a second light cone Q2, extending around a second axis A2. The second light cone converges towards the second focus P24 of the first reflecting surface Sj, the latter being located at the plane mirror S2, which forms the second reflecting surface.

[0062] The sensor comprises a third ellipsoidal reflecting surface S3, the first focus Pi 3 of which extends at the level of the second reflecting surface S2. The second reflecting surface S2 is configured to reflect the second light cone Q2 to form a third light cone Q3, extending around a third axis A3. The third light cone Q3 diverges to the third ellipsoidal reflecting surface S3.

[0063] The third ellipsoidal reflecting surface S3 is configured to reflect the third light cone Q3 to form a fourth light cone Q4, extending around a fourth axis A4. The fourth light cone Q4 converges towards the measuring photodetector 20, the latter being located at the level of the second focus P2 3 of the third reflector St.

[0064] Thus, light wave 11 emitted by the light source 10 propagates between the different reflecting surfaces S}... SN, alternately ellipsoidal and planar, before reaching the measurement photodetector. In this example, N = 3. N can be equal to 5, or to another odd integer greater than or equal to 3. Between the light source 10 and the measurement photodetector 20, light wave emitted by the light source undergoes N successive reflections, that is to say as many reflections as there are reflecting surfaces extending between the light source 10 and the measurement photodetector 20. This makes it possible to minimize signal losses during each reflection. Between two reflecting surfaces of successive rank n, 7 / +1, the light wave 11 does not undergo reflection by another reflecting surface. The reflecting surfaces of odd rank are ellipsoidal. The rank 2 reflective surface is a plane mirror arranged on the printed circuit 7.

[0065] [Fig.2B] shows a configuration in which the sensor 1 comprises a reference photodetector 20ref, the latter being arranged on the same printed circuit 7 as the light source 10 and the measuring photodetector 20. The sensor comprises a reference reflective ellipsoidal surface Supposed to the reference photodetector 20ref. The reference reflective surface comprises a first focus Pi_ref and a second focus P2 ref, the foci being distinct from each other. The first focus Pi_ref of the reference reflective surface Sre / - is located on the reflective surface S 2. The second focus P2 ref of the reference reflective surface is located at the reference photodetector 20ref.Like the odd-ranked reflective surfaces, the reference reflective surface Sre / - is preferably carried by the wall opposite that carrying the light source, the measuring photodetector 20 and the reference photodetector 20ref. In [Fig.2B], the reference cones Qref>i and Qref>2 respectively incident on the reference reflective surface Sref and reflected by the latter have been delimited by mixed dashes.

[0066] In Figure 3A, a configuration is shown in which the number N of reflecting surfaces is equal to 5. In [Fig.3B], a configuration is shown with 5 reflecting surfaces, and a reference reflecting surface which directs a reference light cone towards the reference photodetector 20ref. In [Fig.3B], the reference cones Qref,i and Qref>2 respectively incident on the reference reflecting surface and reflected by the latter are delimited by mixed dashes.

[0067] The ability of a simple thin layer, deposited on a printed circuit, to reflect a light wave has been experimentally verified. [Fig.4] represents the experimental device implemented.

[0068] A light source L emits filament-type light, collimated by a first lens L1, towards a flat reflective surface S. The light reflected by the thin layer is focused by a second lens L2 towards a thermopile-type photodetector D. The reflective surface was either a mirror or a gold layer, deposited on a PCB, on a 5 μm nickel bonding layer. Two different PCB boards were used: on a first PCB1, the thickness of the gold layer was 66 nm. On a second bonding layer, the thickness was 744 nm. The light collected by the detector made it possible to estimate the reflectivity of the reflective surface, the reflectivity corresponding to the percentage of light emitted by the light source and collected by the photodetector D. The angle 0 shown in [Fig.4] was 30°. The distances dl and d2 were 33.5 mm and 52.9 mm respectively.

[0069] Two PCBs were used, each with different finishing qualities. PCB1 had a coarse surface finish, treated in a standard manner by an electrochemical finish. The second PCB had a smoother surface finish, following an electrolytic finish.

[0070] On PCB 1, four identical plane mirrors, referenced M1 to M4, were formed. The same applies to PCB2, on which four identical plane mirrors M6 to M10 were formed.

[0071] The table below shows the reflectivities respectively determined for each plane mirror.

[0072] [Tables 1] Reference Mirror Type Reflectivity PCB1 Ml 41 M2 42 M3 39 M4 38 PCB2 M6 62 M7 50 M8 64 M9 49 M10 46 Reference Mirror 97

[0073] The last line of the table corresponds to a reference mirror, considered perfect.

[0074] It is observed that improving the surface condition of the PCB makes it possible to significantly improve the reflectivity.

[0075] The invention may be applied for gas detection in environmental monitoring, or in industrial gas control applications, particularly in the food industry, the oil industry, or gas distribution.< / e> < / e>

Claims

Claims

1. Gas sensor (1) comprising an enclosure (2), configured to receive a gas (G), the sensor also comprising: a light source (10), configured to emit a light wave (11) propagating in the enclosure by forming, from the light source, a first light cone (Qi); a measuring photodetector (20) configured to detect a light wave (14) emitted by the light source (10) and having propagated through the enclosure; the light source and the measuring photodetector being supported by a printed circuit (7); - a reflective surface of rank 1, forming part of an ellipsoid of revolution, having a first focus (PI-1) and a second focus (P 1-2), the reflective surface of rank 1 being arranged facing the light source (10), so as to reflect the first cone of light towards the second focus, the first reflective surface forming part of an ellipsoid of revolution; - the device being characterized in that: • the printed circuit comprises a plane mirror, forming a reflective surface of rank 2, the second focus of the reflective surface of rank 1 being located on the plane mirror or at a distance of less than 1 mm from the latter; the device comprises a last reflecting surface (SN) of rank N, N being greater than or equal to 3.1a last reflecting surface comprising a first focus (PI- AO, located at the level of a plane mirror, arranged on the printed circuit, the plane mirror forming a reflecting surface of rank N -1, the last reflecting surface comprising a second focus (P2- AO; such that the light wave (11) emitted by the light source is successively reflected by the N reflecting surfaces, according to their respective ranks, before converging towards the second focus (P2- N ) of the last reflecting surface (SN), forming a last cone of light (42^), the measuring photodetector being arranged so as to extend into the last cone of light.

2. Sensor according to claim 1, wherein the light source (10) is arranged at the first focus (Pl-1) of the rank 1 reflective surface (Sj), or at a distance less than 1 mm from the latter.

3. Sensor according to any one of the preceding claims, in which the measuring photodetector (20) is arranged at the second focus (P2-A0 of the last reflecting surface (SN), or at a distance of less than 1 mm from the latter.

4. Sensor according to any one of the preceding claims, in which: - the device comprises several reflective surfaces of even rank, each reflective surface of even rank being a plane mirror arranged on the printed circuit; - the device comprises several reflective surfaces of odd rank, each reflective surface of even rank forming a part of an ellipsoid of revolution and extending opposite the printed circuit.

5. Sensor according to claim 4, in which: - each reflective surface of rank n is configured to reflect the light background that it receives by forming a light cone (Q„+i) of rank n+1, the latter extending around a propagation axis (A„+;) of rank n+1; - when n <N, l'axe de propagation (A„+;) de rang n+1 s'étend entre la surface réfléchissante (S„) de rang n jusqu'à la surface (Sn+]) de rang n+1 ; - lorsque n est impair, etn < N-2, chaque surface réfléchissante (Sn) s’étend selon une partie d’une ellipsoïde de révolution, l’axe de propagation de rang n+l passant par le deuxième foyer (P2- n) de la surface (S„) de rang n, ce dernier étant confondu avec le premier foyer (PI- n+2) de la surface (S„+2) of rank n +2; - when n = N, the propagation axis (A^+y) of rank A+l extends between the surface (SN) of rank A up to the measuring photodetector (20); such that the light wave emitted by the light source (10) undergoes a number of reflections corresponding to the number (AO of reflecting surfaces before reaching the measuring photodetector (20).

6. A sensor according to claim 5, wherein when n <N etn est impair, chaque cône de lumière (Q„+i) de rang n+1 converge vers le deuxième foyer (P2- n) de la surface (Sn) de rang n à partir de laquelle il se propage.

7. Sensor according to any one of the preceding claims, in which the reflective surfaces of odd rank are provided on an internal face (50) of the same wall (5), forming a cover of the sensor.

8. Sensor according to claim 7, in which the enclosure (2) is formed by assembling the cover (5) of the sensor above a base (4), the printed circuit (7) being arranged on the base.

9. A sensor according to any preceding claim, wherein the or each plane mirror is formed by a thin layer of reflective material deposited on the printed circuit.

10. A sensor according to any preceding claim, wherein the number (N) of reflective surfaces extending between the light source (10) and the measuring photodetector (20) is odd.

11. A sensor according to claim 10, wherein the number of reflective surfaces extending between the light source and the measuring photodetector is 3 or 5.

12. Sensor according to any one of the preceding claims, comprising a reference photodetector (20ref), configured to detect a light wave considered as not attenuated by the gas (G).

13. Sensor according to claim 12, comprising a reference reflecting surface (Sref), forming an ellipsoid of revolution, the reference surface comprising: - a first focus (Pi _ref) arranged at the level of a plane reflecting surface, of even rank, or at a distance less than 1 mm from the latter; - a second focus, (P2 - ref) arranged at the level of the reference photodetector, or at a distance less than 1 mm from the latter.

14. A method of analyzing a gas (G) using a sensor (1) according to any one of the preceding claims, the method comprising the following steps: a. introduction of the gas into the enclosure (2) of the sensor (1); b. illumination of the gas using the light source (10); c. measurement of a light intensity of a light wave, emitted by the light source, and having propagated through the enclosure (2) by the measuring photodetector (20); d. determination of a quantity of a gaseous species in the gas (G.). from the measured light intensity.

15. Method according to claim 14, in which step d) is implemented by a processing unit (30) from a signal generated by the measuring photodetector (20).

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