SENSOR FOR DETECTION OF GAS AND METHODS FOR MANUFACTURING

Abstract

The invention concerns sensors (1) for detection of gas, in particular sensors for detection of transcutaneous gas such as CO.sub.2, and methods for manufacturing a sensor (1). The sensor (1) comprises at least one radiation source (3) for emitting radiation, at least one detector (4) for detection of radiation emitted by the radiation source (3), and at least one measurement chamber (6) for receiving the sample gas. The radiation source (3), the detector (4), and the measurement chamber (6) are arranged such that at least a part of the radiation propagates along a path passing through the measurement chamber (6). The sensor (1) further comprises a casing (7), wherein the radiation source (3), the detector (4), the measurement chamber (6) are arranged. The sensor (1) has a contact face (8) which is directable towards a measuring site and the sensor (1) has at least one gas-access channel (9) enabling gas to migrate from the contact face (8) into the measurement chamber (6). The casing (7) comprises a, preferably metallic, material having a high thermal conductivity, preferably more than 10 W/m/K.

Claims

1.-33. (canceled)

34. A sensor for detection of transcutaneous gas, comprising: at least one radiation source for emitting radiation; at least one detector for detection of radiation emitted by the radiation source; and at least one measurement chamber for receiving the gas to be measured, the radiation source, the detector, and the measurement chamber being arranged, such that at least a part of the radiation propagates along a path passing through the measurement chamber, the sensor further comprising a casing, wherein the radiation source, the detector and the measurement chamber are arranged within the casing, the sensor having a contact face which is directable towards a measuring site, wherein the casing comprises a material having a thermal conductivity exceeding 10 W/m/K.

35. The sensor for detection of gas according to claim 34, wherein the radiation source, the detector, and the measurement chamber are arranged on or in an optical module support.

36. The sensor for detection of gas according to claim 34, wherein the sensor has at least one gas-access channel enabling the gas to be measured to migrate from the contact face into the measurement chamber.

37. The sensor for detection of gas according to claim 34, wherein the sensor comprises a mirror for reflecting radiation emitted by the radiation source, the mirror being arranged such that at least a part of the radiation propagates along a path involving a reflection at the mirror.

38. A sensor for detection of transcutaneous gas, comprising: at least one radiation source for emitting radiation; at least one detector for detection of radiation emitted by the source; and at least one measurement chamber for receiving the gas to be measured, the radiation source, the detector, and the measurement chamber being arranged such that at least a part of the radiation propagates along a path passing through the measurement chamber, the sensor further comprising a casing, wherein the radiation source, the detector and the measurement chamber are arranged within the casing, the sensor having a contact face which is directable towards a measuring site and wherein the radiation source is placed in a source compartment and the sensor comprises at least one venting channel leading from the source compartment to the environment.

39. The sensor for detection of gas according to claim 38, wherein the sensor has at least one gas-access channel, enabling the gas to be measured to migrate from the contact face into the measurement chamber.

40. The sensor for detection of gas according to claim 38, wherein the sensor comprises a mirror for reflecting radiation emitted by the radiation source, the mirror being arranged such that at least a part of the radiation propagates along a path involving a reflection at the mirror.

41. The sensor according to claim 38, wherein the sensor comprises a liquid tight venting channel seal for sealing the venting channel.

42. The sensor according to claim 41, wherein the venting channel seal comprises a material selected from at least one of: a material which is applicable as a liquid or a paste and that cures to a solid, gas-permeable material, a non-porous but gas-permeable material, a porous material, and a supporting material having pores, voids, or holes and a further a gas-permeable layer.

43. A sensor for detection of transcutaneous gas, comprising: at least one radiation source for emitting radiation; at least one detector for detection of radiation emitted by the source; at least one mirror for reflecting the radiation; at least one measurement chamber for receiving the gas to be measured, the radiation source, the detector, the mirror, and the measurement chamber being arranged such that at least a part of the radiation propagates along a path involving a reflection at the mirror and passing through the measurement chamber, the sensor having a contact face which is directable towards a measuring site, wherein the mirror is arranged at a distance from the contact face, and/or the sensor further comprises a casing, wherein the mirror is arranged at a distance from the casing, and the mirror is thermally decoupled from the casing.

44. The sensor according to claim 43, wherein a thermally insulating layer is arranged between the mirror and the casing, the thermally insulating layer comprising a material having a thermal conductivity less than 10 W/m/K.

45. A sensor for detection of transcutaneous gas, comprising at least one radiation source for emitting radiation; at least one detector for detection of radiation emitted by the source; at least one mirror for reflecting the radiation; and at least one measurement chamber for receiving the gas to be measured, the radiation source, the detector, the mirror, and the measurement chamber being arranged such that at least a part of the radiation propagates along a path involving a reflection at the mirror and passing through the measurement chamber, the sensor having a contact face which is directable towards a measuring site and the sensor having at least one gas-access channel enabling the gas to be measured to migrate from the contact face into the measurement chamber, wherein the walls of the at least one gas-access channel are arranged distant from the mirror's edge and such that they do not lead through the mirror.

46. The sensor according to claim 45, wherein the gas-access channel is arranged to run along a portion of an inner face of the mirror.

47. A sensor for detection of transcutaneous gas, comprising: at least one radiation source for emitting radiation; at least one detector for detection of radiation emitted by the source; at least one mirror for reflecting the radiation; and at least one measurement chamber for receiving the gas to be measured, the radiation source, the detector, the mirror and the measurement chamber being arranged such that at least a part of the radiation propagates along a path involving a reflection at the mirror and passing through the measurement chamber, the sensor having a contact face which is directable towards a measuring site wherein the mirror comprises a deformable material.

48. The sensor according to claim 47, wherein the deformable material is at least one of inert, non-porous, thermally well conducting, and highly reflective for measurement radiation.

49. The sensor according to claim 47, wherein the mirror is attached by inelastic deformation of the mirror without adhesives or other fixation members.

50. A sensor for detection of transcutaneous gas, comprising: at least one radiation source for emitting radiation; at least one detector for detection of radiation emitted by the source; and at least one measurement chamber for receiving the gas to be measured, the radiation source, the detector, and the measurement chamber being arranged such that at least a part of the radiation propagates along a path passing through the measurement chamber, the sensor having a contact face which is directable towards a measuring site and the sensor having at least one gas-access channel enabling the gas to be measured to migrate from the contact face into the measurement chamber wherein the gas-access channel comprises an access opening, wherein the access opening is covered by an access-opening seal, which is permeable for the gas to be measured, but liquid tight or liquid repellent, wherein the access opening is located near the contact face of the sensor such that the surface of the access-opening seal does not stand above or lie below the contact face by more than 0.3 mm.

51. The sensor according to claim 50, wherein the access-opening seal comprises a substrate having holes or being porous and a gas-permeable coating or filling.

52. The sensor according to claim 51, wherein the substrate of the access-opening seal comprises protrusions, and wherein the permeable coating or filling is arranged at least in between the protrusions, wherein the material of the protrusions is more resistive to abrasion than the material of the permeable coating.

53. The sensor according to claim 50, wherein the access-opening seal contains at least one anchor that is mechanically fixed.

54. The sensor according to claim 50, wherein a liquid-tight membrane is placed between the access-opening seal and the access opening of the gas-access channel.

55. The sensor according to claim 50, wherein the cross-sectional area of a gas-access channel has an at least local maximum at said access opening.

56. The sensor according to claim 55, wherein the cross-sectional area of a gas-access channel at a location next to its access opening is smaller than the cross-sectional area of said access opening.

57. The sensor according to claim 50, wherein the access-opening comprises shallow cavities leading away from the gas-access channel.

58. The sensor according to claim 50, wherein the access-opening seal comprises shallow cavities running towards the gas-access channel.

59. A sensor for detection of transcutaneous gas, the sensor comprising: at least one radiation source for emitting radiation; at least one detector for detection of radiation emitted by the source; and at least one measurement chamber for receiving the gas to be measured, the radiation source, the detector, and the measurement chamber being arranged such that at least a part of the radiation propagates along a path passing through the measurement chamber, wherein the sensor comprises an optical module support, wherein that optical module support forms a part of the measurement chamber and comprises an opening.

60. The sensor according to claim 59, wherein the opening allows the deposition of a reflective coating onto at least a part of the measurement chamber surfaces.

61. The sensor according to claim 59, wherein the sensor comprises a closure component with which the opening can be closed after deposition of a reflective coating.

62. The sensor according to claim 59, wherein the optical module support comprises a material having a thermal conductivity of at least 30 W/m/K.

63. The sensor according to claim 59, wherein the optical module support comprises at least a part of at least one gas-access channel, enabling the gas to be measured to migrate through the gas-access channel into the measurement chamber.

64. The sensor according to claim 59, wherein the optical module support comprises an attachment and sealing zone near said opening, enabling mechanical attachment of the closure component to the optical module support with good thermal contact.

65. The sensor according to claim 59, wherein the optical module support comprises an undercut, in which a lateral volume of the closure component can be arranged.

66. The sensor according to claim 59, wherein the optical module support is formed from a material selected from the group consisting of brass, bronze, stainless steel, pure aluminum, alloyed aluminum, copper, titanium, silver, gold, aluminum oxide, zirconium oxide, aluminum nitride, epoxy, PEEK, LCP, POM, and ABS.

67. The sensor according to claim 59, wherein the sensor has a contact face and wherein the optical module support is arranged within a casing, such that no part of the optical module support forms a part of the contact face.

68. The sensor according to claim 34, wherein the measurement chamber is confined by surfaces of which at least some have high reflectivity for measurement radiation.

69. A method for manufacturing a sensor, comprising the steps of: providing an optical module support with an opening revealing at least a part of a measurement chamber; coating at least a part of the optical module support with at least one reflective coating through that opening; closing said opening with a mirror after application of the reflective coating, such that a part of the mirror's inner face forms a part of the measurement chamber's surfaces; and arranging at least one radiation source for emitting radiation such that at least a part of that radiation is reflected by the mirror.

70. The method according to claim 69, wherein for attachment of the mirror is deformed.

71. The method according to claim 70, wherein the mirror is inelastically deformed.

72. The method according to claim 69, comprising the further step of arranging on or in the optical module support at least one detector for detecting radiation emitted by the radiation source, the detector being arranged such that at least a part of the radiation emitted by the radiation source propagates through the measurement chamber and impinges on a detection surface of the detector.

73. The method according to claim 69, comprising the further step of providing at least a major part of at least one gas-access channel within the optical module support, the gas-access channel leading into the measurement chamber.

74. The method according to claim 73, comprising the further step of covering an access opening of the gas-access channel with an access-opening seal, which is permeable for the gas to be measured, but liquid tight or liquid repellent.

75. The method according to claim 69, comprising the further steps of providing a casing with a contact face which is directable towards a measuring site, arranging the optical module support within the casing.

76. The method according to claim 75, comprising the further steps of providing at least one gas-access channel, with an access-opening seal, such that the access-opening seal forms a smooth contact face with the surface of the casing.

Description

[0191] The invention is further explained with reference to preferred embodiments and the following drawings which show:

[0192] FIG. 1: A schematic cross-sectional view of a first example of a sensor according to the invention;

[0193] FIG. 2: a schematic cross-sectional view of a further example of a sensor according to the invention;

[0194] FIG. 3: a schematic cross-sectional view of a part of an optical module support before assembly;

[0195] FIG. 4: a schematic cross-sectional view of a part of an optical module support illustrating mirror assembly;

[0196] FIG. 5: a schematic cross-sectional view of a part of an optical module after mirror assembly;

[0197] FIG. 6: a schematic cross-sectional view of a part of a further example of a sensor according to the invention;

[0198] FIG. 7: a schematic cross-sectional view of a part of a further example of a sensor according to the invention;

[0199] FIG. 8: a schematic cross-sectional view of a part of a further example of a sensor according to the invention;

[0200] FIG. 9: a schematic cross-sectional view of a part of a further example of a sensor according to the invention;

[0201] FIG. 10: a schematic cross-sectional view of a part of a further example of a sensor according to the invention;

[0202] FIG. 11: a schematic view of a part of an optical module illustrating an example of a gas-access channel's access opening;

[0203] FIG. 12: a schematic view of a part of an optical module illustrating a further example of a gas-access channel's access opening;

[0204] FIG. 13: a schematic cross-sectional view of a part of a further example of a sensor according to the invention;

[0205] FIG. 14: a schematic cross-sectional view of an example of an access-opening seal;

[0206] FIG. 15: a schematic cross-sectional view of a further example of an access-opening seal;

[0207] FIG. 16: a schematic cross-sectional view of a further example of an access-opening seal;

[0208] FIG. 17: a schematic cross-sectional view of a further example of an access-opening seal;

[0209] FIG. 18: a schematic cross-sectional view of a further example of an access-opening seal;

[0210] FIG. 19: a schematic cross-sectional view of an example of an optical module.

[0211] Identical parts or parts with the same function have the same reference numbers in all figures.

[0212] FIG. 1 shows a schematic cross-sectional view of a sensor 1 for detection of gas, in particular a sensor 1 for detection of transcutaneous CO.sub.2. The sensor 1 comprises an optical module 2. The optical module 2 comprises an optical module support 19, a radiation source 3 in the form of a thermal radiator or an LED for emitting radiation, a detector 4 in the form of an infrared photovoltaic or photoconductive detector for detection of radiation emitted by the source 3 and a wavelength-sensitive element 41 formed by an interference filter, a mirror 5 for reflecting the radiation, a measurement chamber 6 for receiving the sample gas, a radiation entrance window 20, and a radiation exit window 21.

[0213] The optical module support 19 is for example made of a copper alloy, i.e. of a material having a thermal conductivity of 100 W/m/K or higher. The optical module support 19 does not extend to the contact face 8.

[0214] The mirror 5 is for example formed of gold, which is a highly reflecting, deformable, inert, non-porous and/or thermally well conducting material. It is attached to the optical module support 19 by plastic deformation, such that it closes an opening in the optical module support 19 and such that a good thermal contact is established between mirror 5 and optical module support 19.

[0215] The radiation source 3, the detector 4, the mirror 5 and the measurement chamber 6 are arranged such that at least a part of the radiation propagates through the measurement chamber 6 along paths involving a reflection at the mirror 5.

[0216] The measurement chamber 6 possesses surfaces that are highly reflective for measurement radiation. In this embodiment the high reflectivity is for example achieved by a high-reflectivity coating of gold on these surfaces. The coating may be applied through the opening in the optical module support 19 prior to attachment of the mirror 5.

[0217] The sensor 1 further comprises a casing 7, in which the optical module 2 is arranged. The casing 7 is formed of a metallic material (in particular a copper alloy, an aluminum alloy, or a titanium alloy) having a high thermal conductivity of preferably more than 10 W/m/K.

[0218] The sensor 1 has a contact face 8 which is directable towards a measuring site and which is intended to be in close contact with the skin of a patient during a transcutaneous measurement.

[0219] The sensor 1 has gas-access channels 9 enabling gas to migrate from the contact face 8 into the measurement chamber 6. The gas-access channels 9 are arranged such that they lead neither through nor directly around the mirror 5. The gas-access channels 9 lead from near the contact face 8 into the measurement chamber 6 and are arranged to run along a portion of an inner face 24 (see FIG. 4) of the mirror 5. The portion is chosen such that the gas-access channel 9 does not reach the edge 25 of the mirror 5 (see also FIG. 4). The gas-access channel 9 predominantly is arranged within the optical module support 19.

[0220] The radiation source 3 is placed in a source compartment 10. The sensor 1 comprises at least one venting channel 11 leading from the source compartment 10 to the environment 22.

[0221] The sensor 1 comprises a liquid tight but gas permeable venting-channel seal 12 for protecting the venting channel 11 from liquids or particles while allowing gas trapped in the source compartment 10 to escape to the environment 22. The seal 12 is for example made of a polymer such as silicone.

[0222] The detector 4 is placed in a detector compartment 27.

[0223] The mirror 5 is arranged at a distance 13 from the contact face 8 and covered by a part 14 of a casing 7.

[0224] The mirror 5 is thermally decoupled from the casing 7. A thermally insulating layer 15 for example made of epoxy is arranged between the mirror 5 and the part 14 of the casing 7.

[0225] The gas-access channel 9 ends in an access opening 17 arranged close to the contact face 8 of the sensor 1. The access opening 17 is covered by an access-opening seal 18, which is permeable to gas but liquid tight or liquid repellent. The seal for example is formed by a substrate made of titanium, steel, or glass and a polymeric coating such as a fluoropolymer, a silicone, or a polyolefin. Otherwise empty space between an access-opening seal 18 and casing 7 is filled with a potting material 37, such as epoxy. The access-opening seal 18 and the potting material 37 are formed and arranged such that they form a rather smooth contact face 8 with a part of the casing 7.

[0226] Empty space within the sensor's interior, such as between optical module 19 and casing 7, is potted with a potting material 16, in particular with epoxy.

[0227] The sensor 1 may comprise an additional membrane 26, at least during use, such that sensor reliability is improved in a wet or in a humid environment. The additional membrane 26 is be attached to a casing 7 of the sensor 1 and exchangeable.

[0228] The sensor may furthermore contain a cover or cap 35, preferably made from a polymer, which closes and protects the top part of the sensor.

[0229] FIG. 2 shows a schematic cross-section of a further example of a sensor 1. In addition, the optical module 2 comprises radiation-window seals 34 along at least a part of the radiation entrance window 20 and the radiation exit window 21 in order to hinder gas exchange between measurement chamber 6 and source compartment 10 or detector compartment 27.

[0230] The sensor 1 further comprises a venting channel 11 leading through the optical module support 19. The venting channel 11 originates in the source compartment. A venting-channel seal 12 allows unwanted gas present in the source compartment 10 to diffuse out of the source compartment 10 and into the sensor's environment 22. The venting channel 11 may extend into the venting-channel seal 12 to some extent.

[0231] FIG. 3 shows a schematic cross-sectional view of a part of an optical module support 19 before assembly. The optical module support 19 comprises a major part of a gas-access channel 9 (see FIG. 1). The optical module support 19 comprises an opening 28, which allows the application of a reflective coating 29 onto surfaces defining an important part of the measurement chamber 6 surfaces (see FIG. 1).

[0232] The reflective coating 29 is for example made of gold or of a combination of silver with a protective coating. It is highly reflective for measurement radiation.

[0233] An attachment and sealing zone 30 is provided on the optical module support 19 on a surface that is to be covered by the mirror 5 (see FIGS. 4 and 5) and that is located between a part of a gas-access channel 9 and an undercut 33 in the optical module support 19.

[0234] FIG. 4 shows a schematic cross-sectional view of a part of an optical module support 19 illustrating a method to assemble a mirror 5, where the opening 28 is closed with the mirror 5.

[0235] The mirror 5 is placed on the optical module support 19 such that the edge 25 of the mirror 5 will be situated close to the undercut 33 and such that an inner face 24 of the mirror covers a part of the gas-access channel 9. Plastic deformation of the mirror 5 is then achieved by pressing onto the mirror 5 with a stamp die 31, such that material from a lateral volume 32 of the mirror is displaced into the undercut 33 (see FIG. 5).

[0236] FIG. 5 shows a schematic cross-sectional view of a part of an optical module 2 after assembly of a mirror 5 onto the optical module support 19 by crimping.

[0237] A lateral volume 32 of the mirror 5 is displaced into an undercut 33 in the optical module support 19, such that said mirror 5 is anchored in the undercut 33 and such that a good thermal contact to the optical module support 19 is achieved.

[0238] A part of the gas-access channel 9 leads along the mirror's inner face 24 and into the measurement chamber 6.

[0239] FIG. 6 shows a schematic cross-sectional view of a part of a further example of a sensor 1.

[0240] An optical module 2, comprising at least the optical module support 19 and the mirror 5, is arranged within the casing 7. A thermally insulating layer 15 is provided in between the optical module 2 and casing 7, particularly also between mirror 5 and part 14 of the casing 7.

[0241] A gas-access channel 9 runs from the measurement chamber 6 along a part of the inner face 24 of the mirror 5, then through the optical module support 19, not directly around the edge of the mirror 5, to near the contact face 8 of the sensor 1. Gaps between optical module support 19 and casing 7 are filled with potting material 37, which may be different from or the same as the material used as a thermally insulating layer 15. The access opening 17 of the gas-access channel 9 widens near the end of the gas-access channel.

[0242] An additional membrane 26 is present near the contact face of the sensor at least during use, which protects the gas-access channel from becoming clogged with contamination such as liquids, pastes, or particles.

[0243] FIG. 7 shows a schematic cross-sectional view of a part of a further example of a sensor 1.

[0244] In this embodiment, the access opening 17 of the gas access channel 9 is covered by an access-opening seal 18. Any voids between access-opening seal 18 and casing 7 are potted with a potting material 37. Casing 7, potting material 37, and access-opening seal 18 are arranged such that a smooth contact face 8 is formed.

[0245] A thermally insulating epoxy layer 15 is arranged between mirror 5 and access-opening seal 18, such that the mirror is thermally decoupled from the contact face 8.

[0246] The access-opening seal 18 is much wider than the access opening 17 of the gas-access channel 9. If the sensor possesses one or more further gas-access channels with their individual access openings, the access-opening seal 18 may be used to cover and protect also such further access openings.

[0247] FIG. 8 shows a schematic cross-sectional view of a part of a further example of a sensor 1.

[0248] The gas-access channel 9 running mostly through the optical module support 19 ends near the contact face 8. The access opening 17 of the gas-access channel 9 widens towards the access-opening seal 18 with which the access opening 17 is covered. The widening of the access opening 17 helps sample gas to migrate into the gas-access channel 9 after having diffused through the access-opening seal 18.

[0249] The access-opening seal 18 contains anchors 36. The anchors 36 are embedded in a potting material 37, preferably in epoxy, such that they are mechanically fixed.

[0250] FIG. 9 shows a schematic cross-sectional view of a part of a further example of a sensor 1.

[0251] The access opening 17 of the gas-access channel 9 is covered with a liquid-tight membrane 42 for example made of a fluoropolymer, a silicone, or a polyolefin, which in turn is covered by an access-opening seal 18 for example made of a metallic, glassy, or ceramic substrate and a polymeric coating.

[0252] FIG. 10 shows a schematic cross-sectional view of a part of a further example of a sensor 1.

[0253] The access opening 17 is wider than the gas-access channel 9 and comprises a shallow cavity 43 extending along the interface to the access-opening seal 18. This shallow cavity 43 helps sample gas to migrate into the gas-access channel 9 after having diffused through the access-opening seal 18. The shallow cavity 43 or access opening 17 may be formed such that it is present underneath a major part of the access-opening seal 18.

[0254] FIG. 11 shows a schematic top view of an example of a part of an optical module support 19, specifically of a gas-access channel's 9 access opening 17. The access opening 17 comprises shallow cavities 43 spreading away from the end of the gas-access channel 9 in a star-like pattern.

[0255] Such a star-like shallow cavity 43 is advantageous over a simple shallow cylindrical cavity, because the access-opening seal 18 is mechanically supported over most of its area, while with a cylindrical cavity it is not. This is particularly relevant if the shallow cavity spreads over a large area.

[0256] FIG. 12 shows a schematic top view of a further example of a part of an optical module support 19, specifically of a gas-access channel's 9 access opening 17. The access opening 17 comprises shallow cavities 43 arranged in the vicinity of the end of the gas-access channel 9 in a grid-like pattern.

[0257] The grid-like arrangement of the shallow cavities 43 supports gas migration towards the gas-access channel 9 also for large areas, i.e., also for large access-opening seals, while the additional gas-accessible volume formed by the shallow cavities 43 remains small. In addition, also large access-opening seals remains mechanically well supported by the optical module support 19.

[0258] FIG. 13 shows a schematic cross-sectional view of a part of a further example of a sensor 1.

[0259] The access opening 17 of the gas-access channel 9 is not significantly wider than the adjacent part of the gas-access channel 9.

[0260] The access-opening seal 18 comprises a shallow cavity 44 extending along a part of the interface to the access-opening seal 18. This shallow cavity 44 helps sample gas to migrate into the gas-access channel 9 after having diffused through the access-opening seal 18 in the same way as the shallow cavities in the access opening 17 as described above (FIGS. 10-12). The shallow cavity 44 may be formed in a major part of the access-opening seal 18 in a star- or grid-like or in any other pattern leading towards the gas-access channel 9.

[0261] FIG. 14 shows a schematic cross-sectional view of an example of an access-opening seal 18.

[0262] The access-opening seal 18 comprises a substrate 38, which contains holes leading from the upper to the lower face of the substrate. The substrate 38 comprises protrusions 39.

[0263] A gas-permeable coating 40 is arranged at least in between the protrusions 39. The material of the protrusions 39 for example is titanium, steel, glass, or a ceramic which is more resistive to abrasion than the material of the permeable coating 40.

[0264] Preferably, the gas-permeable coating 40 also covers the protrusions. This is particularly advantageous when the coating 40 for example is a fluoropolymer which possesses non-stick or easy-clean properties.

[0265] FIG. 15 shows a schematic cross-sectional view of a further example of an access-opening seal 18.

[0266] Here, the gas-permeable coating 40 is arranged at least in between the protrusions 39 and also to some extent or fully within the holes.

[0267] FIG. 16 shows a schematic cross-sectional view of a further example of an access-opening seal 18.

[0268] The substrate 38 contains larger holes in the upper part of the access-opening seal 18 and smaller holes leading from the bottom of the larger holes to the lower face of the access-opening seal 18. There may be one or several smaller holes in each larger hole. The larger holes may be formed in a conical form such that an undercut is generated. In between the larger holes, the substrate 38 comprises protrusions 39.

[0269] A gas-permeable coating 40 is arranged at least in between the protrusions 39 within the larger holes. Hence, the gas-permeable coating 40 in the larger holes is protected from abrasion and at the same time kept in place due to the conical form of the larger holes. The smaller holes may be so small in diameter that the gas-permeable coating 40 does not easily penetrate into them during the coating process. This may enable lower thicknesses of the gas-permeable coating 40, which in turn reduces the diffusion time of sample gas from the measurement site into a gas-access channel.

[0270] The access-opening seal 18 additionally comprises shallow cavities 43 in the bottom face, which connect the small holes and lead towards the access opening of a gas-access channel in a fully assembled sensor. The shape of the shallow cavities 43 may be cylindrical, star-like, grid-like, or have any other shape.

[0271] FIG. 17 shows a schematic cross-sectional view of a further example of an access-opening seal 18.

[0272] The access-opening seal 18 comprises a porous substrate 38, formed by fused particles. There is no direct channel extending from the top to the bottom face of the substrate, or there are only few such channels. Instead, many voids between the constituents of the porous substrate 38 are interconnected and form an arbitrary shaped diffusion channel. The irregular structure of substrate 38 results in protrusions 39.

[0273] A gas-permeable coating 40 is arranged at least in between the protrusions 39. The material of the protrusions 39 is more resistive to abrasion than the material of the permeable coating 40. The gas-permeable coating 40 may extend partly or completely into the voids of the substrate.

[0274] FIG. 18 shows a schematic cross-sectional view of a further example of an access-opening seal 18.

[0275] A gas-permeable coating 40 made of a material as described above is arranged within the holes of the substrate 38, or at least within a part of these holes. The material of the substrate 38 is more resistive to abrasion than the material of the permeable coating 40, hence the substrate protects the coating from damage.

[0276] FIG. 19 shows a schematic cross-sectional view of an example of an optical module 2. The optical module 2 comprises an optical module support 19, which preferably is made from a copper alloy which is a thermally well-conducting material. A mirror 5 is attached to the optical module support 19 as described above. Gas-access channels 9 run through the optical module support 19 and between the optical module support 19 and the inner face 24 of the mirror 5. Sample gas present at the access opening 17 of the gas-access channel 9 is able to diffuse into the measurement chamber 6 on a path not directly leading around the edge of the mirror 5.

[0277] The optical module 2 further comprises a radiation entrance window 20 and a radiation exit window 21. Radiation-window seals 34 separate measurement chamber 6 from the source compartment 10 and from the detector compartment 27, which both are essentially worked into the optical module support 19, such that gas exchange between measurement chamber 6 and source compartment 10 or detector compartment 27 is strongly limited. Measurement radiation emitted by the radiation source 3 may propagate through the radiation entrance window 20 into the measurement chamber 6, where it will undergo reflection at the mirror 5 and/or the measurement chamber 6 surfaces. Measurement radiation may further propagate through the radiation exit window 21 and through the wavelength-sensitive element 41; thereafter it may be absorbed by a detection surface of a detector 4. The radiation may propagate in a non-imaging way.

[0278] The optical module 2 further comprises at least a part of a venting channel 11, through which unwanted gas present in the source chamber 10 may escape.