JP7621216B2 - Gas detection equipment - Google Patents

Description

This disclosure relates to a gas detection device.

Gas detection devices that detect gases are used in a variety of fields. For example, Patent Document 1 discloses a device that includes a light source that emits infrared rays and a detector that detects infrared rays of a specific wavelength, housed in a case that has an ellipsoidal inner surface (ellipsoidal mirror), and that is configured so that the gas to be detected is introduced into the case.

US Patent Application Publication No. 2018/0348121

Figures 1 and 2 are examples of ray tracing in an optical path design in which the centers of the light emitting unit and the light receiving unit are located at the focal position of an ellipsoidal mirror as in Patent Document 1. When the ellipsoidal mirror is sufficiently large compared to the size of the light emitting unit as in Figure 1, the light rays emitted from the light emitting unit placed at the focal position can be collected at the light receiving unit placed at the other focal position. In other words, since the light emitting unit can be approximately regarded as a point light source, the light rays emitted from one focal position are collected at the other focal position in accordance with the general properties of an ellipsoid.

On the other hand, if the ellipsoidal mirror is not large enough compared to the size of the light-emitting part, as shown in Figure 2, the light emitted from the light-emitting part scatters over the entire ellipsoidal mirror and cannot be collected at the light-receiving part of the light-receiving element. This is because the physical image of the light-emitting part approximately behaving as a point source breaks down, and the aberration of the ellipsoidal mirror due to the size of the light-emitting part has a strong effect.

With the recent trend towards miniaturization of gas detection devices, the ratio of the size of the light-emitting part to the size of the ellipsoidal mirror is becoming smaller.

In view of these circumstances, the objective of this disclosure is to provide a small, highly accurate gas detection device that uses an ellipsoidal mirror.

A gas detection device according to an embodiment includes:
The light emitting device includes a light receiving section, and a light guiding section that guides light from the light emitting section to the light receiving section.
At least a part of the shape of the inner surface of the light guiding section is composed of all or part of n (n: a natural number of 1 or more) ellipsoids,
The n ellipsoids are denoted as ellipsoids E ₁ , E ₂ , . . . , E _(n-1) , and E _n ;
Let Ec _i be the ellipse that has the largest area in the cross section of the ellipsoid E _i (i: a natural number satisfying 1≦i≦n), and let E si be the ellipse that has the smallest volume that passes through the two foci F _ai and F _bi of the ellipse E c _i and has a scaling relationship with the ellipsoid E _i without _rotation , then
A region inside the ellipsoid _Ei but not including the ellipsoid _Esi is defined as a region _Ri .
The ellipsoid _Ei including the light source region of the light emitting unit is defined as an ellipsoid _Es ,
The ellipsoid E _i including the light receiving area of the light receiving unit is defined as an ellipsoid E _d ,
The region R _i of the ellipsoid E _s is defined as region R _in ,
When the region R _i of the ellipsoid E _d is defined as the region R _out ,
60% or more of the light source area exists in the area _Rin , and 60% or more of the light receiving area exists in the area _Rout .

A gas detection device according to an embodiment includes:
The light emitting device includes a light receiving section, and a light guiding section that guides light from the light emitting section to the light receiving section.
At least a part of the shape of the inner surface of the light guiding section is composed of all or part of n (n: a natural number of 1 or more) ellipsoids,
The n ellipsoids are denoted as ellipsoids E ₁ , E ₂ , . . . , E _(n-1) , and E _n ;
Let Ec _i be the ellipse that has the largest area in the cross section of the ellipsoid E _i (i: a natural number satisfying 1≦i≦n), and let E si be the ellipse that has the smallest volume that passes through the two foci F _ai and F _bi of the ellipse E c _i and has a scaling relationship with the ellipsoid E _i without _rotation , then
A region inside the ellipsoid _Ei but not including the ellipsoid _Esi is defined as a region _Ri .
The ellipsoid _Ei including the light source region of the light emitting unit is defined as an ellipsoid _Es ,
The ellipsoid E _i including the light receiving area of the light receiving unit is defined as an ellipsoid E _d ,
The region R _i of the ellipsoid E _s is defined as region R _in ,
When the region R _i of the ellipsoid E _d is defined as the region R _out ,
The center of gravity of the light source area or the peak point of brightness is designated as point G _in , and the center of gravity of the light receiving area is designated as point G _out ,
A point G _in exists in the region R _in , and a point G _out exists in the region R _out .

According to an embodiment of the present disclosure, it is possible to provide a small, highly accurate gas detection device using an ellipsoidal mirror.

FIG. 1 is a diagram showing an example of ray tracing in an ellipsoidal mirror. FIG. 2 is a diagram showing another example of ray tracing in an ellipsoidal mirror. FIG. 3 is a partially see-through perspective view of the gas detection device according to the embodiment. FIG. 4 is a diagram showing the results of a ray tracing simulation for a spheroidal mirror. FIG. 5 is a diagram for explaining the region R _i . FIG. 6 is a diagram showing an example of the configuration of the gas detection device according to this embodiment. FIG. 7 is a diagram showing a modified example of the gas detection device according to the present embodiment. FIG. 8 is a diagram showing the results of a light ray simulation for a general ellipsoid. FIG. 9 is a diagram showing an example of the configuration of a light-emitting section including a passive element and a light-receiving section including an indirect element. FIG. 10 is a diagram showing another example of the configuration of a light-emitting section including a passive element and a light-receiving section including an indirect element.

<Gas detection device of this embodiment>
The gas detection device of this embodiment includes 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 shape of at least a portion of the inner surface of the light guide is composed of the whole or partial figures of n (n: natural number equal to or greater than 1) ellipsoids.

The n number of ellipsoids are defined as ellipsoids E ₁ , E ₂ , ..., E _(n-1) , E _n . An ellipsoid that passes through two foci F _ai and F _bi of the ellipsoid E _i (i: a natural number satisfying 1≦i≦n), has the same rotational symmetry axis as the rotational symmetry axis of the ellipsoid E _i , and has a homothetic contraction relationship with the ellipsoid E _i is defined as an ellipsoid E _si . A region inside the ellipsoid E _i that does not include the ellipsoid E _si is defined as a region R _i . The ellipsoid E _i that includes the light source region of the light emitting unit is defined as an ellipsoid E _s . The ellipsoid E _i that includes the light receiving region of the light receiving unit is defined as an ellipsoid E _d (when there is one ellipsoid, that is, when n=1, E _s =E _d ). The region R _i of the ellipsoid E _s is defined as a region R _in . The region R _i of the ellipsoid E _d is defined as the region R _out .

In the gas detection device of this embodiment, 60% or more of the area of the light source region is in region _Rin , and 60% or more of the area of the light receiving region is in region _Rout .

The detailed principle will be described later, but by using this configuration, it is possible to provide a small, highly accurate gas detection device that uses an ellipsoidal mirror.

<An example of a specific configuration of the gas detection device according to the present embodiment>
3 is a partially transparent perspective view of a gas detection device according to an embodiment of the present disclosure. The gas detection device is, for example, a small device having dimensions of 7 mm x 5 mm x 3 mm in length x width x height, and is also called a gas sensor.

In this embodiment, the gas detection device is an NDIR (Non Dispersive InfraRed) type device that measures the concentration of the detected gas based on infrared rays that pass through the introduced gas.

The gases to be detected are, for example, carbon dioxide, water vapor, carbon monoxide, nitric oxide, ammonia, sulfur dioxide, or hydrocarbon gases such as alcohol, formaldehyde, methane, and propane.

<Architecture (interrelationships between components)>
The gas detection device includes a light emitting section, a light receiving section, and a light guiding section. The gas detection device may further include a holding section. The gas detection device may additionally include a control section. The gas detection device according to an embodiment of the present disclosure shown in FIG. 3 includes a light receiving section 20 and a light emitting section 10 held by a holding section 40, and a light guiding section 30 held by the holding section 40. Although not shown, a control section that controls at least one of the light emitting section 10 and the light receiving section 20 may be provided within the holding section 40.

The surfaces of the light-emitting unit 10 and the light-receiving unit 20 are in contact with the space (detection space) between the inner wall of the light-guiding unit 30 and the upper surface of the holding unit 40. The light-guiding unit 30 also has a gas port 31 that can introduce and extract gas into and from the detection space.

The light emitted from the light-emitting unit 10 is reflected at least once on the inner surface of the light-guiding unit 30 and reaches the light-receiving unit 20.

Next, we will provide a detailed explanation of the components of the gas detection device of this embodiment.

<Light emitting part>
The light emitting unit 10 is a component that emits light used to detect the detection target gas. The light emitting unit 10 is not particularly limited as long as it outputs light that includes a wavelength that is absorbed by the detection target gas. In this embodiment, the light emitted by the light emitting unit 10 is infrared light, but is not limited thereto.

The light-emitting unit 10 has a light-emitting element 10A. In this embodiment, the light-emitting element 10A is an LED (light emitting diode), but as another example, it 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. The light-emitting unit 10 may also include not only the light-emitting element 10A, but also a passive element that passively emits light upon receiving light emitted by the light-emitting element 10A. Specifically, the passive element is a mirror, an optical filter, a phosphor, an optical image, an optical fiber, an optical waveguide, a lens, or a diffraction grating.

In this embodiment, the light-emitting unit 10 only has the light-emitting element 10A, so the light-emitting unit 10 and the light-emitting element 10A are synonymous.

The light-emitting unit 10 has a light source region. The light source region is the region where photons of the light-emitting element 10A are generated when light is guided directly from the light-emitting element 10A to the light-guiding unit 30 without passing through a passive element, as in this embodiment. Specifically, if the light-emitting element 10A is a quantum type, it is the active region, and if it is a thermal light source, it is the high-temperature region. For example, in the case of a lamp, it is the filament.

In addition, when the light-emitting unit 10 includes a passive element and the light emitted by the light-emitting element 10A is guided to the light-guiding unit 30 via the passive element, the light source region is a collection of the light-emitting ends of the passive elements. Specifically, when the passive element is a mirror, the light source region is the region that reflects the light.

In addition, if the passive element is an optical filter with wavelength selection function, the area through which the light ray passes on the surface of the optical filter that is in contact with the space may be considered as the light source area.In addition, if the passive element is an optical fiber, optical waveguide, or lens, the exit surface through which the light ray passes on the surface that is in contact with the space may be considered as the light source area.

In addition, when an optical image is formed as the light-emitting unit 10 by a lens or mirror, the formed image may be regarded as the light source area.

Here, the light-emitting element 10A is preferably a planar surface light source such as an LED, a MEMS heater, or a VCSEL (Vertical Cavity Surface Emitting LASER).

<Light receiving section>
The light receiving unit 20 is a component that receives light that has passed through the introduced gas. The light receiving unit 20 is not particularly limited as long as it has sensitivity to a band of light that includes a wavelength that is absorbed by the gas to be detected. In this embodiment, the light received by the light receiving unit 20 is infrared light, but is not limited thereto.

The light receiving unit 20 has a light receiving element 20A. In this embodiment, the light receiving element 20A is a photodiode, but as another example, it may be a phototransistor, a thermopile, a pyroelectric sensor, a bolometer, or a photoacoustic detector. The light receiving unit 20 may also include not only the light receiving element 20A, but also an indirect element that guides light to the light receiving element 20A. Specifically, the indirect element is a mirror, an optical filter, a phosphor, a lens, a diffraction grating, an optical fiber, or an optical waveguide.

In this embodiment, the light receiving unit 20 only has the light receiving element 20A, so the light receiving unit 20 and the light receiving element 20A are synonymous.

The light receiving unit 20 has a light receiving area. When the light receiving element 20A receives light directly without an indirect element as in this embodiment, the light receiving area is an area of the light receiving element 20A that has the function of converting the received light into a signal. Specifically, when the light receiving element 20A is a photodiode, the light receiving area is the active layer, and when it is a thermopile, it is the thermoelectric conversion section.

In addition, when the light receiving unit 20 receives light through an indirect element to the light receiving element 20A, the light receiving area is an area of the indirect element that has an optical function for directing the received light to the light receiving element 20A and through which the light rays pass. Specifically, when the indirect element is an optical filter with a wavelength selection function, the area through which the light rays pass on the surface of the optical filter that contacts the space may be considered as the light receiving area. In addition, when the indirect element is an optical fiber, optical waveguide, or lens, the incident surface through which the light rays pass on the surface that contacts the space may be considered as the light receiving area. In addition, when the indirect element is a mirror, the light receiving area is an area that reflects the light rays.

<Light guide section>
The light guiding section 30 is a member that guides the light emitted by the light emitting section 10 to the light receiving section 20, and is an optical system of the gas detection device. The light emitted from the light emitting section 10 is reflected by the light guiding section 30 and reaches the light receiving section 20. In other words, the light guiding section 30 optically connects the light emitting section 10 and the light receiving section 20.

In this embodiment, the inner surface of the light guide unit 30 is a mirror (reflective surface). The shape of at least a portion of the inner surface is a figure of all or part of an ellipsoid. The light guide unit 30 may further include a plane mirror, a concave mirror or a convex mirror, a lens, and a diffraction grating as auxiliary components.

The material that constitutes the mirror may be, for example, metal, glass, ceramics, stainless steel, etc., but is not limited to these.

From the viewpoint of improving the detection sensitivity, it is preferable that the material constituting these mirrors is composed of a material with a small light absorption coefficient and a high reflectance. Specifically, a resin housing coated with an alloy containing aluminum, gold, or silver, a dielectric, or a laminate of these is preferable. Examples of materials for the resin housing 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), etc., and hard resins in which two or more of these are mixed. In addition, from the viewpoint of reliability and change over time, a resin housing coated with gold or an alloy layer containing gold is preferable. Furthermore, it is preferable to form a dielectric laminate film on the surface of the metal layer to increase the reflectance. When the inner surface of the light guide unit 30 is formed on the resin housing by deposition or plating, it is possible to improve productivity and weight reduction compared to when it is formed from a metal material. Furthermore, the difference in thermal expansion coefficient with the holding part 40 is reduced, thermal deformation is suppressed, and sensitivity is less likely to fluctuate.

In addition, the light guide section 30 may be formed by cutting, and from the viewpoint of productivity, it is more preferable that it be formed by injection molding.

<Holding part>
The holding section 40 is a member that holds the light receiving section 20, the light emitting section 10, and the light guiding section 30. Holding means maintaining the relative positional relationship of each member against external forces. There are no particular limitations on the form of holding, but mechanical holding is preferable. The form of holding may be electromagnetic or chemical.

If the gas detection device of this embodiment has a control unit, the control unit may be held by the holding unit 40.

The holding unit 40 is not particularly limited as long as it can hold the light receiving unit 20, the light emitting unit 10, and the light guiding unit 30. In this embodiment, the holding unit 40 is a resin package, but as another example, it may be a printed circuit board or a ceramic package. Alternatively, the holding unit 40 may be a semiconductor substrate, and the light receiving unit 20 and the light emitting unit 10 may be formed on the same semiconductor substrate. When the holding unit 40 is a resin package, a lead frame may be built in, and the lead frame may be electrically connected to the light emitting unit 10, the light receiving unit 20, and the control unit by wires or the like. When the holding unit 40 is a printed circuit board, the printed circuit board may be electrically and mechanically joined to the light receiving unit 20 and the light emitting unit 10 by solder. Furthermore, the holding unit 40 and the light guiding unit 30 are mechanically held by adhesive, screws, claws, fittings, grommets, welding, or the like. The holding unit 40 may also have a connection terminal for electrically connecting to the outside.

<Control Unit>
The control unit is a member 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 an 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 executes gas concentration calculation based on the converted digital electrical signal.

The control unit may have at least one of a general-purpose processor that executes functions according to the loaded program 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).

<Gas detector size>
1(a) and 1(b), when the ellipsoid mirror is sufficiently large with respect to the size of the light emitting unit 10, the light beam emitted from the light emitting unit 10 can be collected at the light receiving unit 20. Here, as the size of the light guiding unit 30, the shape of a part of the light guiding unit 30 is configured as an ellipsoid, and the maximum length of the ellipsoid containing the light emitting unit 10 is defined as Lms, and the maximum length of the light source region is defined as Ls. Here, when the condition Ls<Lms/50 is satisfied, the size of the light emitting unit 10 is sufficiently small with respect to the ellipsoid mirror, and it can be approximately regarded as a point light source. Therefore, the light beam emitted from one focal position is collected at the other focal position. On the other hand, as shown in FIG. 2(a) and FIG. 2(b), when the ellipsoid mirror is not sufficiently large with respect to the size of the light emitting unit 10 (Ls≧Lms/50), the light beam emitted from the light emitting unit 10 is scattered throughout the ellipsoid mirror and cannot be collected at the light receiving unit 20.

Although not particularly limited, the gas detection device of this embodiment has a particularly significant effect when Ls ≧ Lms/50.

Similarly, although not particularly limited, the gas detection device of this embodiment has a particularly significant effect when Ld ≧ Lmd/50, where Lmd is the maximum length of the ellipsoid that contains the light receiving unit 20 and Ld is the maximum length of the light receiving unit 20.

Next, the principle of the gas detection device of this embodiment will be explained in detail with reference to the drawings.

<Explanation of the principle>
Fig. 4 is a diagram for explaining the basic principle of this embodiment, and shows the results of a ray tracing simulation in a plane passing through the rotation axis of a spheroid mirror. As described above, the gas detection device may be composed of a plurality of spheroids, but the basic principle will be explained using one spheroid. When n spheroids (n: a natural number of 1 or more) constituting the gas detection device are spheroids _E1 , ..., _Ei , ..., _En (i: a natural number satisfying 1 ≤ i ≤ n), the spheroids in Figs. 4(a), 4(b) and 5 correspond to one spheroid _Ei (i = n = 1).

4A shows the simulation results of a ray emitted from a point in region R _i , which is an area outside the focal points F _ai and F _bi of the ellipsoid. At this time, the ray is repeatedly reflected on the mirror surface. However, the ray does not enter region R _INTER, which is an area connecting the foci near the center of the ellipsoid.

4B shows the results of a simulation of a ray emitted from a point in the region R _INTER . The ray does not enter the region R _EDGE, which is the region on both ends outside the focal points F _ai and F _bi of the ellipsoid.

The phenomenon of separation of the light ray's entry area in the region R _i and the region R _INTER (hereinafter referred to as the region separation phenomenon) can be explained by considering the trajectory of the light ray as the trajectory of the hard sphere that repeatedly elastically collides with the wall of the same shape as the mirror surface as the same. For the motion of the hard sphere in free space that is elastically reflected by the ellipsoidal wall, the generalized angular momentum J = L _Fai · L _Fbi , which is the inner product of the angular momentum L _Fai centered on the focal point F _ai and the angular momentum L _Fbi centered on the focal point _{F bi,} is preserved. At this time, in the trajectory of the hard sphere emitted from the point of the region R _i , the angular momentum L _Fai and L _Fbi are in the same direction as seen from each focal point, so the generalized angular momentum J is positive (J>0). On the other hand, in the case of the trajectory that passes through the region R _INTER , the rotation direction as seen from each focal point is opposite, so the generalized angular momentum J is negative (J<0).

That is, according to the conservation law of the generalized angular momentum J, the trajectory (ray) of the hard ball first emitted from the region R _i has a positive generalized angular momentum J, and no matter how many times it is reflected by the wall of the mirror, it will not become the trajectory (ray) of the hard ball passing through the region R _INTER with a negative generalized angular momentum J. Conversely, the trajectory (ray) of the hard ball emitted from the region R _INTER with a negative generalized angular momentum J will not become the trajectory (ray) of the hard ball passing through the region R _i with a positive generalized angular momentum J, no matter how many times it is reflected by the wall of the mirror. In this way, the region separation phenomenon occurs. Here, when the generalized angular momentum J=0, it corresponds to a trajectory emitted from a focal point and reaching the other focal point, and the phase space of the motion of the hard ball is separated.

Here, when the ellipse Ec _i is the ellipse with the largest area in the cross section of the ellipsoid E _i (i: a natural number satisfying 1≦i≦n), if it is a rotating ellipsoid, the focal point is uniquely determined, and the largest area is the cross section passing through the two foci. Also, when the ellipse _E si is the ellipse that has the smallest volume that passes through the two foci F _ai and F _bi of the ellipse Ec _{i and} has a relationship of expansion and contraction with the ellipsoid E _i without rotation, if it is a rotating ellipsoid, the focal point is uniquely determined. Therefore, the above principle generally holds true when "the ellipse Ec _i is the ellipse with the largest area in the cross section of the ellipsoid E _i (i: a natural number satisfying 1≦i≦n), and the ellipse E si is the ellipse that passes through the two foci F _ai and F _bi of the ellipse Ec _i and has the smallest volume that has a relationship of expansion and contraction with the ellipsoid E _i without _rotation ."

Next, we will explain the configuration of the gas detection device of this embodiment, taking into account the separation phenomenon of the light penetration area described above.

5 is a diagram illustrating the present embodiment in which the region separation phenomenon is applied to the inner surface of the light guide unit 30 including one spheroidal shape. By arranging at least a part of the light source region in the region R _i due to the region separation phenomenon, the light beam emitted from the light source at this position always exists in the region R _i even if it is repeatedly reflected by the mirror. In this case, by arranging the light receiving region in the same region R _i , the light beam stays in the region R _i without scattering in the region R _INTER , so that the light can be efficiently collected in the light receiving region.

This can improve the gas sensitivity of the detection device. Even if the light source region and the light receiving region are partially present in the region R _i , the effect of this embodiment is exerted in the partial region. Therefore, the effect is realized when 60% or more of the light source region is present in the region R _i . Also, although it is a complementary and identical expression, the effect is realized when less than 40% of the light source region and the light receiving region are present in the region R _INTER . From the viewpoint of improving gas sensitivity, it is preferable that 70% or more of the light source region is present in the region R _i , more preferably that 80% or more of the light source region is present in the region R _i, and it is preferable that all of the light source region is present in the region R _i . Similarly, from the viewpoint of improving gas sensitivity, it is preferable that 70% or more of the light receiving region is present in the region R _i , more preferably that 80% or more of the light receiving region is present in the region R _i , and it is preferable that all of the light receiving region is present in the region R _i .

That is, when an ellipsoid _{E si} is defined as an ellipsoid having a shape of at least a part of the inner surface of the light guide unit 30 passing through two focal points F _ai and F _bi of the ellipsoid E _{i ,} having the same rotational symmetry axis as the rotational symmetry _axis of the ellipsoid E i, and being in a homothetic contraction relationship with the ellipsoid E i, a region inside the ellipsoid E _i that does not include the ellipsoid E _si is defined as region R _i , and 60% or more of the area of the light source region of the light emitter 10 and the light receiving region of the light receiving unit 20 is present in region R _i , a small-sized and highly accurate gas detection device using an ellipsoid mirror is realized. This effect is remarkable when the two focal points of the ellipsoid are sufficiently apart from each other and a region R _INTER is formed. Specifically, this effect is remarkable when the ratio "a/b" of the minor axis b to the major axis a of the ellipsoid is 1.2 or more.

Here, it is assumed that 60% or more of the light source region exists in region _Rin , and 60% or more of the light receiving region exists in region _Rout , but when focusing on the center of gravity or the peak point of brightness, the following holds true. That is, the center of gravity or the peak point of brightness of the light source region is point _Gin , and the center of gravity of the light receiving region is point _Gout . In this case, point _Gin exists in region _Rin , and point _Gout exists in region _Rout .

<Arrangement on multiple ellipsoids>
Although an embodiment in which there is one spheroid mirror (i=1) has been described above, the gas detection device of this embodiment also exhibits the same effects when it is provided with a light-guiding section 30 having a plurality of spheroid mirrors.

Figure 6 is a diagram illustrating a gas detection device according to this embodiment when three light guides 30 having spheroid-shaped inner surfaces (reflecting surfaces) are used. Figure 6(a) is a schematic diagram. Figure 6(b) shows the results of a ray tracing simulation.

In FIG. 6(a), the region _R1 of the ellipsoid _E1 that includes the light source region is defined as region _Rin . The adjacent ellipsoid _E2 includes region _R2 . When the light source region is in region _Rin , the light beam is transported to region _Rin on the other end side of the ellipsoid _Es1 without scattering. By regarding the region to which this light is transported as the light source of the ellipsoid _E2 again, the light beam can move through region _R2 without scattering. In order to realize this efficiently, it is preferable to further have an auxiliary reflecting unit 50 as shown in FIG. 6(a) and FIG. 6(b) as a light guide unit 30 to the adjacent ellipsoid for turning back the light beam. The form of the auxiliary reflecting unit 50 is not particularly limited, and examples thereof include a plane mirror, a concave mirror, and a convex mirror. The auxiliary reflecting unit 50 may be configured with a shape different from that of the ellipsoid. From the viewpoint of simplicity and efficiency, the auxiliary reflecting unit 50 is preferably a plane mirror. In addition, the auxiliary reflecting unit 50 may have a wavelength selection function. The auxiliary reflecting portion 50 is preferably disposed within the region R _i of the spheroid.

By repeating this process sequentially, the light can travel without scattering, as shown in the ray tracing simulation results in Figure 6 (b). Finally, by placing the light receiving area in area _Rout , which is area _R3 of ellipsoid _E3 , the light can be collected efficiently in the same way as in the case of a single ellipsoid mirror.

That is, by having 60% or more of the area of the light source region of the light emitter 10 exist in region _Rin and 60% or more of the area of the light receiving region of the light receiving unit 20 exist in region _Rout , a small-sized, highly accurate gas detection device using an ellipsoidal mirror can be realized. Compared to the case where one ellipsoidal mirror is used, it is possible to design the optical path length to be longer, which may be preferable from the viewpoint of detection accuracy.

Fig. 7 shows a modified example in which there are two spheroids. The light guide section 30 is made up of a mirror combining two spheroids and one plane mirror, and the major axes of the two spheroids intersect at a right angle. In this case, by providing an auxiliary reflecting section 50 in the region _Ri , a small-sized, highly accurate gas detection device using an ellipsoid mirror can be realized, as in the case of Fig. 6.

Although the light guide unit 30 has been described above as a spheroid, it may be a general ellipse, that is, one that does not have rotational symmetry and has three different diameters. This is because a system of hard spheres that elastically reflect inside the ellipsoid wall (the so-called billiard problem) is also an integrable system, so there is a conserved quantity similar to the general angular momentum J, and a similar region separation phenomenon follows. FIG. 8 shows a simulation result of a light ray emitted from a point in a region R _i that is an area outside the foci F _ai and F _bi of a general ellipsoid. The foci F _ai and F _bi shown in FIG. 8 are the foci of a planar ellipse that has the largest area when the ellipsoid is cut by a plane, and a light ray emitted from the region R _i outside the ellipsoid continues to stay in the region R _i even after repeated reflections. This can also be understood from the fact that when the smallest diameter of the ellipse becomes 0 in the limit, it becomes the same as the region separation phenomenon due to the focus when a light ray is emitted inside a planar ellipse, and a general ellipse is positioned in the middle between the spheroids described so far and this planar ellipse.

Although the embodiment has been described above based on the drawings and examples, it should be noted that a person skilled in the art would easily be able to make various modifications and corrections based on this disclosure. It should be noted, therefore, that these modifications and corrections are included in the scope of this disclosure. For example, the functions included in each component, each means, etc. can be rearranged so as not to cause logical inconsistencies, and multiple means, etc. can be combined into one or divided.

Figures 9 and 10 are diagrams showing an example of the configuration of a light-emitting unit 10 including a passive element and a light-receiving unit 20 including an indirect element in another embodiment. In the example of Figure 9, the light-emitting unit 10 is configured to include a light-emitting element 10A and a passive element that is a 45° mirror. Also, in the example of Figure 9, the light-receiving unit 20 is configured to include a light-receiving element 20A and an indirect element that is a 45° mirror. In the example of Figure 10, the light-emitting unit 10 is configured to include a light-emitting element 10A and a passive element that is a lens. Also, in the example of Figure 10, the light-receiving unit 20 is configured to include a light-receiving element 20A and an indirect element that is a concave mirror.

(Additional Note)
A gas detection device according to an embodiment includes:
The light emitting device includes a light receiving section, and a light guiding section that guides light from the light emitting section to the light receiving section.
At least a part of the shape of the inner surface of the light guiding section is formed of all or part of n (n: a natural number of 1 or more) spheroids,
The n number of spheroids are denoted as ellipsoids E ₁ , E ₂ , . . . , E _(n−1) , and E _n ,
When an ellipsoid E _{si is} an ellipsoid that passes through two foci F _ai and F _bi of an ellipsoid E _{i (i: a natural number satisfying 1≦i≦n), has the same axis of rotational symmetry as the axis of rotational symmetry of the ellipsoid E i ,} and is in a homothetic contraction relationship with the ellipsoid E _i ,
A region inside the ellipsoid _Ei but not including the ellipsoid _Esi is defined as a region _Ri .
The ellipsoid _Ei including the light emitting surface of the light emitting unit is defined as an ellipsoid _Es ,
The ellipsoid E _i including the light receiving surface of the light receiving unit is defined as an ellipsoid E _d ,
The region R _i of the ellipsoid E _s is defined as region R _in ,
When the region R _i of the ellipsoid E _d is defined as the region R _out ,
60% or more of the area of the light emitting surface may be present in region _Rin , and 60% or more of the area of the light receiving surface may be present in region _Rout .

REFERENCE SIGNS LIST 10 Light emitting section 20 Light receiving section 30 Light guiding section 31 Gas port 40 Holding section 50 Auxiliary reflecting section

Claims (12)

The light emitting device includes a light receiving section, and a light guiding section that guides light from the light emitting section to the light receiving section.
At least a part of the shape of the inner surface of the light guiding section is composed of all or part of n (n: a natural number of 1 or more) ellipsoids,
The n ellipsoids are denoted as ellipsoids E ₁ , E ₂ , . . . , E _(n-1) , and E _n ;
Let Ec _i be the ellipse that has the largest area in the cross section of the ellipsoid E _i (i: a natural number satisfying 1≦i≦n), and let E si be the ellipse that has the smallest volume that passes through the two foci F _ai and F _bi of the ellipse E c _i and has a scaling relationship with the ellipsoid E _i without _rotation , then
A region inside the ellipsoid _Ei but not including the ellipsoid _Esi is defined as a region _Ri .
The ellipsoid _Ei including the light source region of the light emitting unit is defined as an ellipsoid _Es ,
The ellipsoid E _i including the light receiving area of the light receiving unit is defined as an ellipsoid E _d ,
The region R _i of the ellipsoid E _s is defined as region R _in ,
When the region R _i of the ellipsoid E _d is defined as the region R _out ,
A gas detection device, wherein 60% or more of the light source area exists in an area _Rin , and 60% or more of the light receiving area exists in an area _Rout . 2. The gas detection device according to claim 1, wherein a ratio a/b of the major axis a to the minor axis b of each of the ellipsoids _Es and _Ed is 1.2 or more. 3. The gas detection device according to claim 1, wherein Ls is a maximum length of the light source region and Lms is a maximum length of the ellipsoid _Es , and Ls is greater than or equal to Lms/50. 4. The gas detection device according to claim 1, wherein Ld≧Lmd/50 is satisfied, where Ld is a maximum length of the light receiving portion and Lmd is a maximum length of the ellipsoid _Ed . The gas detection device according to any one of claims 1 to 4, wherein the same holder holds the light emitting unit and the light receiving unit. The gas detection device according to claim 5, wherein the same holding unit also holds a control unit. The gas detection device according to any one of claims 1 to 6, wherein at least one of the light receiving section and the light emitting section is provided with an optical filter. The gas detection device according to any one of claims 1 to 7, further comprising an auxiliary reflector configured with a shape different from the n ellipsoids. The gas detection device according to claim 8 , wherein the auxiliary reflecting portion is present within the region _Ri . The gas detection device according to any one of claims 1 to 9, wherein the light-emitting portion is a surface light source. The gas detection device according to any one of claims 1 to 10, wherein the n ellipsoids are ellipsoids of revolution. The light emitting device includes a light receiving section, and a light guiding section that guides light from the light emitting section to the light receiving section.
At least a part of the shape of the inner surface of the light guiding section is composed of all or part of n (n: a natural number of 1 or more) ellipsoids,
The n ellipsoids are denoted as ellipsoids E ₁ , E ₂ , . . . , E _(n-1) , and E _n ;
Let Ec _i be the ellipse that has the largest area in the cross section of the ellipsoid E _i (i: a natural number satisfying 1≦i≦n), and let E si be the ellipse that has the smallest volume that passes through the two foci F _ai and F _bi of the ellipse E c _i and has a scaling relationship with the ellipsoid E _i without _rotation , then
A region inside the ellipsoid _Ei but not including the ellipsoid _Esi is defined as a region _Ri .
The ellipsoid _Ei including the light source region of the light emitting unit is defined as an ellipsoid _Es ,
The ellipsoid E _i including the light receiving area of the light receiving unit is defined as an ellipsoid E _d ,
The region R _i of the ellipsoid E _s is defined as region R _in ,
When the region R _i of the ellipsoid E _d is defined as the region R _out ,
The center of gravity of the light source area or the peak point of brightness is designated as point G _in , and the center of gravity of the light receiving area is designated as point G _out ,
A gas detection device, wherein a point G _in exists in an area R _in and a point G _out exists in an area R _out .

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