Gas detection device

Abstract

To provide a small-sized gas detector capable of performing measurement with high accuracy.SOLUTION: A gas detection device includes: a light emitting part (10); a light receiving part (20); and a light guide part (30) for guiding light from the light emitting part (10) to the light receiving part (20). The light guide part (30) includes a mirror (50) and has a shape of a part of one or more spheroids. The mirror (50) is provided at a position of a first focal point of the spheroid or in the vicinity of the first focal point. Each of the light emitting part (10) and the light receiving part (20) is provided at the position of a focal point which is not the first focal point of the spheroid or in the vicinity of the focal point which is not the first focal point. The light emitting part (10) and the light receiving part (20) are arranged in parallel to the long axis direction of the spheroid.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a gas detection device.

Background Art

[0002] Gas detection devices for detecting gases are used in various fields. For example, Patent Document 1 discloses a device provided with a light source that emits infrared rays and a detector that detects infrared rays of a specific wavelength inside a case having an inner surface of an ellipsoid (ellipsoidal mirror), and configured such that the gas to be detected is introduced into the case.

Prior Art Documents

Patent Documents

[0003] <00000!17>

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, FIG. 9 is a diagram for explaining the problem that the image formed in a gas detection device having an ellipsoidal mirror is blurred. The light source (light emitting unit 110) and the light receiving unit 120 are provided at the positions of the foci of the ellipsoid inside the case. The light emitted from the light emitting unit 110 of the gas detection device is reflected at a plurality of positions on the inner surface of the ellipsoid, and a plurality of light rays are collected by the light receiving unit 120. At this time, as shown in FIG. 9, in one optical path, the distance to the reflection point is a, and the distance from the reflection to the light receiving unit 120 is b. In another optical path, the distance to the reflection point is a', and the distance from the reflection to the light receiving unit 120 is b'. The magnification of the image on the light receiving surface of the light receiving unit 120 is (b / a) and (b' / a') respectively with respect to these optical paths. When the light guiding unit is composed of one ellipsoidal mirror, since images of a plurality of magnifications are formed in the light receiving unit 120, the image may be blurred.

[0005] For example, Patent Document 2 discloses an optical system having a double elliptic prism mirror. A line passing through three foci is used as the optical axis, and a light source (emitting unit) and a detector (receiving unit) are positioned outside the double elliptic prism mirror on the optical axis. A sample is placed at the common focus of the double ellipse, and an incident beam switching mirror and an exit beam switching mirror are positioned at the remaining two foci. By controlling the orientation of these beam switching mirrors, an optical configuration can be obtained in which light is incident on the sample at any incident angle, and the emitted light from the sample at any angle is detected by the detector. In the optical system of Patent Document 2, the optical path can be controlled, but the beam switching mirrors must be located inside the double elliptic prism mirror. Therefore, if such an optical system is adopted, it is not possible to miniaturize the gas detection device. Furthermore, it is assumed that the emitting unit and the receiving unit are outside the double elliptic prism mirror, so such an optical system cannot be directly adopted in a small gas detection device that has the emitting unit and the receiving unit inside a case.

[0006] In view of these points, the purpose of this disclosure is to provide a gas detection device that is small and capable of accurate measurement. [Means for solving the problem]

[0007] A gas detection device according to one embodiment of the present disclosure, It comprises a light-emitting section, a light-receiving section, and a light-guiding section that guides light from the light-emitting section to the light-receiving section. The light guide portion includes a mirror and has the shape of a part of one or more ellipsoids. The mirror is provided at the position of the first focal point of the ellipsoid or in the vicinity of the first focal point. Each of the light-emitting unit and the light-receiving unit is provided at the position of a focal point other than the first focal point of the ellipsoid, or in the vicinity of a focal point other than the first focal point. The light-emitting unit and the light-receiving unit are arranged parallel to the major axis of the ellipsoid. [Effects of the Invention]

[0008] According to this disclosure, it is possible to provide a gas detection device that is small and capable of accurate measurement. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 shows an example of the configuration of a gas detection device according to one embodiment of the present disclosure. [Figure 2] Figure 2 is a diagram illustrating an example of the arrangement of the components of the gas detection device shown in Figure 1. [Figure 3] Figure 3 shows an example configuration of a gas detection device according to another embodiment of the present disclosure. [Figure 4] Figure 4 is a diagram illustrating an example of the arrangement of the components of the gas detection device shown in Figure 3. [Figure 5] Figure 5 is a diagram illustrating the tilt and shape of the mirror of the gas detection device shown in Figure 3. [Figure 6] Figure 6 is a diagram illustrating an example of the arrangement of the light-emitting and light-receiving sections of the gas detection device shown in Figure 3. [Figure 7] Figure 7 illustrates another example of the arrangement of the light-emitting and light-receiving units of the gas detection device shown in Figure 3. [Figure 8] Figure 8 shows the simulation results of the gas detection device shown in Figure 3. [Figure 9] Figure 9 illustrates the problem of blurred images in a gas detection device with an ellipsoidal mirror. [Figure 10] Figure 10 illustrates another tilt of the mirror in the gas detection device shown in Figure 3. [Figure 11] Figure 11 is a diagram illustrating the parallel arrangement. [Modes for carrying out the invention]

[0010] Hereinafter, a gas detection device according to an embodiment of the present disclosure will be described with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals. In the description of this embodiment, the description of the same or corresponding parts will be omitted or simplified as appropriate.

[0011] [First Embodiment] FIG. 1 is a block diagram of a gas detection device according to the first embodiment. The gas detection device is a device that measures the concentration of a detected gas in a gas. In the present embodiment, the gas detection device is an NDIR (Non Dispersive InfraRed) type device that measures the concentration of the detected gas based on infrared light transmitted through the introduced gas. The detected gas can be, for example, carbon dioxide, water vapor, carbon monoxide, nitric oxide, ammonia, sulfur dioxide, alcohol, formaldehyde, methane, propane, etc. The gas detection device is, as an example, a small device with a vertical × horizontal × height of 7 mm × 9 mm × 3 mm, and is also referred to as a gas sensor.

[0012] The gas detection device includes a light emitting unit 10, a light receiving unit 20, and a light guiding unit 30 that guides light from the light emitting unit 10 to the light receiving unit 20. The light guiding unit 30 includes a mirror 50 and has the shape of a part of one or more ellipsoids of revolution. In the present embodiment, the ellipsoid of revolution is an ellipsoid (oblate ellipsoid) formed by rotating an ellipse around its major axis. The gas detection device may further include a gas port 31. Further, the gas detection device may further include a holding unit 40. Further, the gas detection device may additionally include a control unit that controls at least one of the light emitting unit 10 and the light receiving unit 20.

[0013] Here, in FIG. 1 and the drawings referred to below, orthogonal coordinates corresponding to the orientation of the gas detection device are set. The x-axis direction is a direction parallel to the major axis direction of the ellipsoid of revolution that the light guiding unit 30 has a part of the shape. The z-axis direction is the height direction of the gas detection device. The y-axis direction corresponds to the minor axis direction of the ellipsoid of revolution that is orthogonal to the x-axis direction and the z-axis direction. In the following, the positional relationship may be described using the axes of this orthogonal coordinate system.

[0014] FIG. 2 is a diagram for explaining an arrangement example of the components of the gas detection device of FIG. 1. As shown in FIGS. 1 and 2, the gas detection device according to the present embodiment includes a light emitting unit 10, a light receiving unit 20, and a light guiding unit 30 held by a holding unit 40. The gas detection device may further include a control unit held by the holding unit 40.

[0015] The light-emitting surface of the light-emitting unit 10 and the light-receiving surface of the light-receiving unit 20 are in contact with the space (detection space) between the inner surface of the light-guiding unit 30 and the upper surface of the holding unit 40. The light-guiding unit 30 is also equipped with a gas port 31 to allow the introduction and exit of gas into and out of the detection space.

[0016] Light emitted from the light-emitting unit 10 is reflected at least once by the inner surface of the light-guiding unit 30, which includes the reflective surface of the mirror 50, before reaching the light-receiving unit 20.

[0017] As shown in Figure 2, in this embodiment, the mirror 50 is provided at the position of the first focal point F1 of the ellipsoid. Here, in this disclosure, the mirror 50 may be provided at or near the first focal point F1. A preferred range near the focal point will be described later. In this embodiment, the light-emitting unit 10 and the light-receiving unit 20 are each provided at a focal point other than the first focal point F1 of the ellipsoid. The light-emitting unit 10 and the light-receiving unit 20 are also arranged parallel to the major axis of the ellipsoid. In this disclosure, the light-emitting unit 10 and the light-receiving unit 20 may be provided at or near the focal point of the ellipsoid. Referring in detail to the example in Figure 2, the light guide unit 30 has the shape of a part of two ellipsoids S1 and S2 that share the first focal point F1. The two ellipsoids S1 and S2 share a major axis. Furthermore, when the focal point other than the first focal point F1 of one of the two ellipsoids (ellipsoid S1) is designated as the second focal point F2, and the focal point other than the first focal point F1 of the other ellipsoid (ellipsoid S2) is designated as the third focal point F3, the light-emitting unit 10 is provided at the position of the second focal point F2, and the light-receiving unit 20 is provided at the position of the third focal point F3.

[0018] The details of the components of the gas detection device according to this embodiment are described below.

[0019] <Light-emitting part> The light-emitting unit 10 is a component that emits light used to detect the gas to be detected. The light-emitting unit 10 is not particularly limited as long as it outputs light that includes wavelengths absorbed by the gas to be detected. In this embodiment, the light emitted by the light-emitting unit 10 is infrared, but is not limited to this.

[0020] The light-emitting unit 10 is composed of a light-emitting element. In this embodiment, the light-emitting element is an LED (light-emitting diode). As an alternative example, the light-emitting element may be a lamp, a laser (light amplification by stimulated emission of radiation), an organic light-emitting element, or a MEMS (micro-electro-mechanical systems) heater. Furthermore, the light-emitting unit 10 may be composed not only of a light-emitting element but also of a passive element that passively emits light in response to light emitted by the light-emitting element. Examples of passive elements include a reflector, an optical filter, a phosphor, an optical image, an optical fiber, an optical waveguide, a lens, a diffraction grating, etc. From the viewpoint of miniaturization, it is preferable that the light-emitting unit 10 includes a semiconductor light-emitting element (for example, an LED). Furthermore, it is preferable that the light-emitting element is a planar surface light source.

[0021] <Light receiving section> The light-receiving unit 20 is a component that receives light transmitted through a gas introduced into the detection space. The light-receiving unit 20 is not particularly limited as long as it has sensitivity to a band of light that includes wavelengths absorbed by the gas being detected. In this embodiment, the light received by the light-receiving unit 20 is infrared, but is not limited to this.

[0022] The light-receiving unit 20 is configured to include a light-receiving element. In this embodiment, the light-receiving element is a photodiode. As an alternative example, the light-receiving element may be a phototransistor, thermopile, pyroelectric sensor, bolometer, or photoacoustic detector. Furthermore, the light-receiving unit 20 may be configured to include not only a light-receiving element but also an indirect element that guides light to the light-receiving element. Examples of indirect elements include a reflector, optical filter, phosphor, lens, diffraction grating, optical fiber, and optical waveguide. From the viewpoint of miniaturization, it is preferable that the light-receiving unit 20 includes a semiconductor light-receiving element (a photodiode as an example).

[0023] <Light guide section> The light guide 30 is a component that guides the light emitted from the light-emitting unit 10 to the light-receiving unit 20, and is part of the optical system of the gas detection device. As described above, the light from the light-emitting unit 10 is reflected at least once on the inner surface of the light guide 30, which includes the reflective surface of the mirror 50, before reaching the light-receiving unit 20. As shown in Figure 2, in this embodiment, the mirror 50 is arranged such that its reflective surface is parallel to the major axis of the ellipsoid (parallel to the x-axis).

[0024] In this embodiment, the inner surface of the light guide section 30 is a reflective surface. Furthermore, as described above, the inner surface of the light guide section 30 has the shape of a part of one or more ellipsoids. In addition to the mirror 50, the light guide section 30 may further include auxiliary reflectors, lenses, diffraction gratings, optical filters, etc. The mirror 50 may be equipped with a wavelength-selective reflective filter.

[0025] Here, the materials constituting the inner surface of the light guide section 30 and the reflective surface of the mirror 50 may be, for example, metal, glass, ceramics, stainless steel, etc., but are not limited to these. From the viewpoint of improving detection sensitivity, it is preferable that the materials constituting these reflective surfaces are made of materials with a low light absorption coefficient and high reflectivity. Specifically, a resin housing coated with an alloy containing aluminum, gold, or silver, a dielectric, or a laminate thereof is preferred. Examples of resin housing materials include LCP (liquid crystal polymer), PP (polypropylene), PEEK (polyether ether ketone), PA (polyamide), PPE (polyphenylene ether), PC (polycarbonate) or PPS (polyphenylene sulfide), PMMA (polymethyl methacrylate resin), PAR (polyarylate resin), and hard resins made by mixing two or more of these. Furthermore, from the viewpoint of reliability and changes over time, a resin housing coated with a gold or gold-containing alloy layer is preferred. In addition, it is preferable to form a dielectric laminate on the surface of the metal layer to increase reflectivity. When the inner surface of the light guide portion 30 is formed on a resin housing by vapor deposition or plating, compared to when it is formed from a metal material, productivity and weight reduction can be improved. Furthermore, the difference in thermal expansion coefficient with respect to the holding portion 40 becomes smaller, suppressing thermal deformation and reducing fluctuations in sensitivity.

[0026] Furthermore, the light guide portion 30 may be formed by machining, but from the viewpoint of productivity, it is more preferable that it be formed by injection molding.

[0027] <Holding part> The holding portion 40 is a member that holds the light-emitting portion 10, the light-receiving portion 20, and the light-guiding portion 30. Holding means maintaining the relative positional relationship of each member with respect to external forces. The form of holding is not particularly limited. If the gas detection device includes a control unit, the holding portion 40 may further hold the control unit.

[0028] The holding part 40 is not limited to a specific material as long as it can hold the light-emitting part 10, the light-receiving part 20, and the light-guiding part 30. In this embodiment, the holding part 40 is a resin package. In this embodiment, a lead frame is included inside the resin package, and the light-emitting part 10 and the light-receiving part 20 are electrically connected to the lead frame by wires or the like. If the gas detection device includes a control unit, the light-emitting part 10, the light-receiving part 20, and the control unit may be electrically connected via the lead frame. As another example, the holding part 40 may be a semiconductor substrate, a printed circuit board, or a ceramic package. For example, if the holding part 40 is a semiconductor substrate, the light-emitting part 10 and the light-receiving part 20 may be formed on the semiconductor substrate. For example, if the holding part 40 is a printed circuit board, the light-emitting part 10 and the light-receiving part 20 may be electrically and mechanically joined by solder. The light-guiding part 30 is mechanically held to the holding part 40 by adhesive, screws, claws, fits, grommets, or welding. The holding portion 40 may have connection terminals for making an electrical connection to an external device of the gas detection device.

[0029] <Department Head> The control unit is a component that controls at least one of the light-emitting unit 10 and the light-receiving unit 20. The control unit may have an analog-to-digital conversion circuit that converts the analog electrical signal output from the light-receiving unit 20 into a digital electrical signal. Furthermore, the control unit may have a calculation unit that calculates the concentration of the detected gas based on the converted digital electrical signal. The control unit may be included in the gas detection device or may be provided as an external device electrically connected to the gas detection device.

[0030] The control unit may have at least one general-purpose processor that performs functions according to the program to be loaded, and a dedicated processor specialized for specific processing. The dedicated processor may include an Application Specific Integrated Circuit (ASIC). The processor may include a Programmable Logic Device (PLD).

[0031] <Explanation of the principle> As explained with reference to Figure 9, in conventional gas detection devices with an ellipsoidal mirror, images of multiple magnifications are formed on the light-receiving surface, which can cause the image to become blurred. In the light guide unit 30 of the gas detection device according to this embodiment, as shown in Figure 2, it has the shape of two ellipsoids S1 and a part of an ellipsoid S2 that share a first focal point F1. The light-emitting unit 10 is provided at the position of the second focal point F2 (a focal point of ellipsoid S1 that is not the first focal point F1), and the light-receiving unit 20 is provided at the position of the third focal point F3 (a focal point of ellipsoid S2 that is not the first focal point F1). Light emitted from the light-emitting unit 10 is reflected at the reflection point (first reflection point) of ellipsoid S1, reflected at the reflective surface of the mirror 50, reflected at the reflection point (second reflection point) of ellipsoid S2, and reaches the light-receiving unit 20.

[0032] In the gas detection device according to this embodiment, the distance from the light-emitting unit 10 to the first reflection point is a, and the distance from the first reflection point to the reflective surface of the mirror 50 is b. Also, the distance from the reflective surface of the mirror 50 to the second reflection point is b, and the distance from the second reflection point to the light-receiving unit 20 is a. At this time, the magnification of the image on the mirror 50 is (b / a), and this image is multiplied by (a / b) in the optical path from the mirror 50 to the light-receiving unit 20. In other words, in the gas detection device according to this embodiment, a 1x magnification image is formed on the light-receiving unit 20 regardless of the position of the reflection point (regardless of the optical path), so blurring of the image can be suppressed. Not blurring the image means that light with high intensity can be received within a certain range of the light-receiving surface, reducing light intensity fluctuations in response to fluctuations in the measurement environment. Therefore, highly accurate measurement becomes possible when measuring the concentration of the gas to be detected.

[0033] Furthermore, the light-emitting unit 10 and the light-receiving unit 20 can each be configured to include semiconductor elements, enabling the realization of a compact gas detection device equipped with the light-emitting unit 10 and the light-receiving unit 20 within a case. Thus, the gas detection device according to this embodiment is compact and can accurately measure the gas to be detected.

[0034] In the example shown in Figure 2, the light guide unit 30 was configured to have the shape of a portion of two ellipsoids S1 and S2 that share a first focal point F1. However, the number of ellipsoids is not limited to two; any even number is acceptable. In other words, the light guide unit 30 only needs to have the shape of a portion of multiple ellipsoids, each having an even number of adjacent ellipsoids that share one focal point. Multiple ellipsoids share a major axis. A mirror 50 is placed at the focal point shared by adjacent ellipsoids. A light-emitting unit 10 is placed at one of the non-shared focal points (the focal points at both ends along the major axis of the ellipsoid), and a light-receiving unit 20 is placed at the other. If the number of ellipsoids is even, as in the example shown in Figure 2, a 1x image is formed in the light-receiving unit 20, and image blurring can be suppressed.

[0035] [Second Embodiment] Figure 3 shows an example of the configuration of a gas detection device according to the second embodiment. In the gas detection device according to this embodiment, the mirror 50 is arranged so that its reflective surface intersects with the major axis direction of the ellipsoid. Specifically, the mirror 50 includes not only a portion arranged parallel to the major axis direction of the ellipsoid (hereinafter referred to as "mirror 50a") as in the first embodiment, but also a portion arranged to intersect with the major axis direction of the ellipsoid (hereinafter referred to as "mirror 50b"). Furthermore, in the gas detection device according to this embodiment, the light-emitting unit 10 and the light-receiving unit 20 are each provided near a focal point other than the first focal point F1 of the ellipsoid. To avoid redundant explanation, the configurations that differ from the first embodiment are described below.

[0036] Figure 4 is a diagram illustrating an example of the arrangement of the components of the gas detection device shown in Figure 3. As shown in Figures 3 and 4, in the gas detection device according to this embodiment, the light guide unit 30 has the shape of a part of a spheroid S1, with the second focal point F2 being a focal point other than the first focal point F1. In the example in Figures 3 and 4, the mirror 50b is positioned so that its reflective surface intersects perpendicularly with the major axis of the spheroid. The reflected image of the spheroid S1 by the mirror 50b can be treated as a virtual spheroid S2 (see Figure 2). Therefore, in this embodiment, the light guide unit 30 has the shape of a part of multiple spheroids, the sum of the actual spheroids and the virtual spheroids being an even number. The actual size of the gas detection device according to this embodiment is half that of the first embodiment in terms of the major axis of the ellipsoid. The gas detection device according to this embodiment can be further miniaturized by including the mirror 50b.

[0037] In the examples shown in Figures 3 and 4, a mirror 50 is positioned at the first focal point F1, and the light-emitting unit 10 and the light-receiving unit 20 are each located near the second focal point F2. Similar to the first embodiment, the light-emitting unit 10 and the light-receiving unit 20 are positioned parallel to the major axis of the ellipsoid S1. The second focal point F2 may be located between the light-emitting unit 10 and the light-receiving unit 20. Also, as shown in Figure 4, if the distance between the light-emitting unit 10 and the light-receiving unit 20 is d, then d must be 0 or greater. In other words, the light-emitting unit 10 and the light-receiving unit 20 may be separated or positioned adjacent to each other. When the light-emitting unit 10 and the light-receiving unit 20 are adjacent, the portion where the light-emitting unit 10 and the light-receiving unit 20 touch may coincide with the position of the second focal point F2 when viewed in a direction parallel to the major axis of the ellipsoid S1.

[0038] In this embodiment, light emitted from the light-emitting unit 10 is reflected at the reflection point (first reflection point) of the ellipsoid S1, reflected at the reflective surface of the mirror 50, reflected at the reflection point (second reflection point) of the ellipsoid S1, and reaches the light-receiving unit 20. Here, as shown in Figure 4, the reflection at the reflective surface of the mirror 50 includes reflection at mirror 50b and reflection at mirror 50a. The optical path is substantially the same before and after reflection at the reflective surface of the mirror 50. Therefore, in the gas detection device according to this embodiment, an image of approximately 1x magnification is formed at the light-receiving unit 20 regardless of the position of the reflection point (regardless of the optical path), thus suppressing image blurring.

[0039] Here, the mirror 50b is a planar mirror or a conical surface with a large radius of curvature that is close to a plane, as will be described later. The mirror 50b is not limited to an arrangement where the reflective surface intersects perpendicularly with the major axis of the ellipsoid, but can have an inclination. Figure 5 is a diagram illustrating the inclination and shape of the mirror 50b. For example, as shown in Figure 5, when the heights of the light-emitting unit 10 and the light-receiving unit 20 are different (in other words, the positions of the light-emitting surface of the light-emitting unit 10 and the light-receiving surface of the light-receiving unit 20 in the z-axis direction), the inclination or translation of the mirror 50b can be adjusted so that an image is formed within a desired range on the light-receiving surface of the light-receiving unit 20. The difference in height between the light-emitting unit 10 and the light-receiving unit 20 may occur, for example, when only one of the light-emitting unit 10 or the light-receiving unit 20 has an optical filter.

[0040] As shown in Figure 5, the mirror 50b can be tilted such that it is contained within a space divided by a width w along the major axis of the ellipsoid, with the first focal point F1 as the starting point, and can be rotated and translated (although not shown, this also includes the combination of rotations around the z axis). w is not particularly limited, but it must be determined such that the paraxial approximation holds with respect to the ellipsoid S1, aberrations are suppressed, and an optical image is formed on the ray path. If the maximum diameter of the ellipsoid S1 is Lmax, it is on the order of approximately twice the radius of curvature Rtyp that represents the ellipsoid S1, so the distance between the optical image and its focal point must be sufficiently smaller than Rtyp, that is, it is preferable that w is 1 / 10 or less of Lmax. In other words, the mirror 50b may be positioned so that it is contained within a space divided by a width of 1 / 10 or less of Lmax along the major axis of the ellipsoid, with the first focal point F1 as the starting point. Furthermore, if the mirror 50b is a cone, it may move within the range w in the direction of the major axis around the first focal point F1 at a position b away from the major axis in the z-axis direction, so the radius of curvature is b 2 It may be greater than / W. Here, the light guide portion 30 has a configuration that has the shape of a part of the ellipsoid S1, and the maximum diameter is not included within the light guide portion 30. However, it is possible to calculate the maximum diameter from the part of the ellipsoid S1 that the light guide portion 30 contains, and the above Lmax is a calculated value. Also, the tilt of the mirror 50b is not limited to a configuration in which it is tilted around the first focal point F1. As long as the mirror 50b is included in the above space, it may be accompanied by translation in the x-axis direction, for example, the mirror 50b can be tilted as shown in Figure 10.

[0041] Figures 6 and 7 are diagrams illustrating examples of the arrangement of the light-emitting unit 10 and the light-receiving unit 20. As described above, the light-emitting unit 10 and the light-receiving unit 20 are arranged parallel to the major axis direction (parallel to the x-axis) of the ellipsoid so that light emitted from the light-emitting unit 10 is reflected off the inner surface of the light-guiding unit 30 and reaches the light-receiving unit 20. However, the positions of the light-emitting unit 10 and the light-receiving unit 20 in the y-axis direction are not limited. Furthermore, when the light-emitting unit 10 and the light-receiving unit 20 are not the same size, the arrangement of the light-emitting unit 10 and the light-receiving unit 20 parallel to the major axis direction of the ellipsoid includes the following case. As shown in Figure 11, the sizes of the light-emitting unit 10 and the light-receiving unit 20 are compared by an overhead view from the z-axis direction, and the larger figure is designated as figure A, and the smaller figure as figure B. In addition, a figure Aex is defined, which has an outer perimeter that extends from the outer perimeter of figure A by a distance of half the maximum length La of figure A. If, when figure B is moved parallel to the major axis of the ellipsoid, figure B is included in figure Aex, then the light-emitting unit 10 and the light-receiving unit 20 are arranged parallel to the major axis of the ellipsoid. As shown in the example in Figure 6, the light-emitting unit 10 and the light-receiving unit 20 may be arranged so that they are located on the major axis of the ellipsoid. Also, as shown in the example in Figure 7, even if the light-emitting unit 10 and the light-receiving unit 20 are not located on the major axis of the ellipsoid, this is still included in the arrangement near the second focal point F2. Furthermore, regardless of the y-axis positions of the light-emitting unit 10 and the light-receiving unit 20, the distance d between the light-emitting unit 10 and the light-receiving unit 20 can be set to 0. In other words, the light-emitting unit 10 and the light-receiving unit 20 can be arranged adjacent to each other. Also, as long as an image is formed within a desired range on the light-receiving surface of the light-receiving unit 20, the second focal point F2 does not need to be between the light-emitting unit 10 and the light-receiving unit 20; for example, the second focal point F2 may overlap with the light-emitting unit 10, or it may overlap with the light-receiving unit 20. Thus, when we say that the light-emitting unit 10 and the light-receiving unit 20 are located near the focal point, it means that the light-emitting unit 10 and the light-receiving unit 20 are positioned close to the focal point so that an image is formed on a desired range of the light-receiving surface of the light-receiving unit 20. Furthermore, the light-emitting unit 10 and the light-receiving unit 20 are positioned within the range v in the direction of the major axis, centered on the x-axis coordinate of the second focal point F2 (see Figure 7). While v is not particularly limited, it needs to be determined such that a paraxial approximation holds with respect to the ellipsoid S1, aberrations are suppressed, and an optical image is formed on the light ray path.If Lmax is the maximum diameter of the ellipsoid S1, then it is on the order of approximately twice the radius of curvature Rtyp that represents the ellipsoid S1. Therefore, the distance between the optical image and its focal point must be sufficiently smaller than Rtyp, meaning that v is preferably 1 / 10 or less of Lmax. The light-emitting center of the light-emitting unit 10 and the light-receiving center of the light-receiving unit 20 should each be positioned within the range of v in the direction of the major axis, with the x-axis coordinate of the second focal point F2 as the starting point.

[0042] Figure 8 shows the simulation results of the gas detection device according to this embodiment. In the gas detection device configured as shown in Figure 3, a simulation was performed to calculate the intensity of light emitted from the light-emitting unit 10 and received by the light-receiving unit 20. The distance between the centers of the light-emitting unit 10 and the light-receiving unit 20 was set to 700 μm. The size of the light-emitting surface of the light-emitting unit 10 was set to 154 μm in the x-axis direction and 194 μm in the y-axis direction. The size of the light-receiving surface of the light-receiving unit 20 was set to 390 μm in both the x-axis and y-axis directions. The major axis of the ellipsoid S1 included in the light-guiding unit 30 is 18.00 mm, and the minor axis is 14.94 mm. The mirror 50 is a planar mirror and is positioned perpendicular to the major axis of the ellipsoid at the position of the first focal point F1. As shown in Figure 8, the simulation results showed that light with high intensity can be received in the central part of the light-receiving surface. Here, the darker the color (the blacker the color), the greater the light intensity. Furthermore, the light intensity was calculated in the region enclosed by the dashed line including the light-receiving section 20 in Figure 8. The energy efficiency was 96.3% when the reflectance of the light guide section 30 was set to 100%, and 81.8% even when the reflectance of the light guide section 30 was set to 96%. The simulation showed that the gas detection device according to this embodiment can receive light of high intensity within a certain range of the light-receiving surface, and also exhibits high energy efficiency.

[0043] Here, several more simulations were performed by changing the arrangement of the light-emitting unit 10 and the light-receiving unit 20 of the gas detection device. As a result, it was found that in order to improve energy efficiency, it is preferable to position the light-emitting unit 10 closer to the first focal point F1 than the light-receiving unit 20. For example, when the light-emitting unit 10 and the light-receiving unit 20 are arranged with the second focal point F2 in between, it is preferable to position the light-emitting unit 10 towards the center (closer to the first focal point F1) as shown in Figure 4, rather than on the outer circumference of the ellipsoid.

[0044] In this embodiment, the gas detection device forms an image at approximately 1x magnification in the light-receiving unit 20, thus suppressing image blurring. Furthermore, by including the mirror 50b, the gas detection device according to this embodiment can be made smaller than that of the first embodiment. Therefore, the gas detection device according to this embodiment can measure the gas to be detected with small size and accuracy, making it particularly useful in applications where miniaturization is required.

[0045] In the example shown in Figure 4, the light guide unit 30 was configured to have the shape of a part of a single ellipsoid S1. However, the number of ellipsoids is not limited to one. In the first embodiment, the total number of ellipsoids had to be even. In this embodiment, the number of ellipsoids, including virtual ones, becomes even due to the reflected image from the mirror 50b. Therefore, in this embodiment, there is no restriction on the number of ellipsoids, and they do not have to be even. In this embodiment as well, the major axis is shared when there are multiple ellipsoids.

[0046] While embodiments of this disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art will find it easy to make various modifications or alterations based on this disclosure. Therefore, it should be noted that these modifications or alterations are within the scope of this disclosure. For example, the functions included in each component can be rearranged in a logically consistent manner, and multiple components can be combined into one or separated. [Explanation of Symbols]

[0047] 10 Light-emitting part 20 Light receiving section 30 Light guide section 31 Gasport 40 Holding part 50, 50a, 50b mirrors 110 Light-emitting part 120 Light receiving part

Claims

1. It comprises a light-emitting section, a light-receiving section, and a light-guiding section that guides light from the light-emitting section to the light-receiving section. The light guide portion includes a mirror and has the shape of a part of one or more ellipsoids. The mirror is provided at or near the position of the first focal point of the ellipsoid, Each of the light-emitting unit and the light-receiving unit is provided at the position of a focal point other than the first focal point of the ellipsoid or in the vicinity of a focal point other than the first focal point. The light-emitting unit and the light-receiving unit are arranged parallel to the major axis of the ellipsoid in a gas detection device.

2. The mirror includes a portion in which the reflective surface is positioned such that it intersects with the major axis of the ellipsoid, and the maximum diameter of the ellipsoid is Lmax. The gas detection device according to claim 1, wherein the portion of the mirror is arranged to be contained within a space delimited by a width of one-tenth of Lmax in the front-to-back direction along the major axis of the ellipsoid, with the first focal point as the starting point.

3. The gas detection device according to claim 2, wherein the portion of the mirror is arranged such that its reflective surface intersects perpendicularly with the major axis of the ellipsoid.

4. The light guide portion has the shape of a part of a spheroid that has a second focal point other than the first focal point. The gas detection device according to claim 2 or 3, wherein the light-emitting unit and the light-receiving unit are each provided near the second focal point.

5. The gas detection device according to claim 4, wherein the second focal point is located between the light-emitting unit and the light-receiving unit.

6. The gas detection device according to claim 4, wherein the light-emitting unit and the light-receiving unit are arranged adjacent to each other.

7. The gas detection device according to claim 2 or 3, wherein the light-emitting unit is provided at a position closer to the first focal point than the light-receiving unit.

8. The gas detection device according to claim 1, wherein the mirror is arranged such that its reflective surface is parallel to the major axis of the ellipsoid.

9. The light guide portion has the shape of a part of two ellipsoids that share the first focal point, The gas detection device according to claim 8, wherein, when the focal point of one of the two ellipsoids that is not the first focal point is designated as the second focal point, and the focal point of the other that is not the first focal point is designated as the third focal point, the light-emitting unit is provided at the position of the second focal point, and the light-receiving unit is provided at the position of the third focal point.

10. The gas detection device according to claim 1, 2, 3, 8, or 9, wherein the light-emitting portion includes a semiconductor light-emitting element, and the light-receiving portion includes a semiconductor photodetector.

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