JP6213906B2 - Gas sensor - Google Patents

Description

The present invention relates to a gas sensor and a gas sensing method for detecting a gas such as carbon dioxide (CO ₂ ) or ammonia (NH ₃ ).

  In recent years, for example, a gas sensor for detecting carbon dioxide has been researched in response to a request for environmental monitoring. As this type of gas sensor, an infrared light absorption type gas sensor (NDIR: Non dispersive infrared detector) is known (for example, see Non-Patent Document 1). As another gas sensor, a gas sensor using surface plasmon resonance (SPR) is also known (see, for example, Non-Patent Document 2).

S.Neethirajan, D.S.Jayas, and S.Sadistap, “Carbon dioxide (CO2) sensors for the agri-food industry-areview,” Food Bioprocess Technol., Vol.2, pp.115-121,2009. Shozo Miwa, and Tsuyoshi Arakawa, “Selective gas detection by means of surface plasmon resonancesensors,” Thin Solid Films, vol.281, pp.466-468, 1996.

  However, the infrared light absorption type gas sensor shown in the former has a problem that an optical system becomes large because it is necessary to provide a light absorption path.

  Further, the latter gas sensor using surface plasmon resonance does not require a light absorption path and can be reduced in size accordingly. However, since the refractive index to be measured is approximately proportional to the molecular weight, for example, carbon dioxide It is practically difficult to measure such a low molecular weight gas.

  Therefore, the present invention has been made in view of the above-described conventional problems, and the object thereof is to realize downsizing, detection of even a gas having a low molecular weight, and low power consumption. Another object of the present invention is to provide a highly versatile gas sensor and gas sensing method.

  The inventors of the present application have completed the present invention by paying attention to a gas absorber whose characteristics change by absorbing the gas to be detected.

That is, in order to achieve the above object, the gas sensor according to the present invention includes:
An anode and a cathode;
A gas that covers at least a part of the anode and at least a part of the cathode, and is disposed so as to be in contact with the gas to be detected, and whose conductivity is changed by absorbing the gas. An absorber,
A detection unit for detecting the gas based on an impedance value between the anode and the cathode via the gas absorber;
It is characterized by having.

  According to the said structure, the gas of the detection target contained in air | atmosphere is absorbed by the gas absorber by making a gas absorber contact the air | atmosphere, for example. The conductivity of the gas absorber changes by absorbing the gas to be detected. Therefore, the gas to be detected can be detected based on the impedance value between the anode and the cathode by interposing the gas absorber between the anode and the cathode.

  According to this configuration, it is not necessary to ensure a long optical path length unlike a conventional infrared light absorption type gas sensor, so that the apparatus (gas sensor) can be downsized.

  Further, according to the above configuration, since gas detection is performed using a gas absorber whose conductivity is changed by absorbing the gas to be detected, even a gas having a low molecular weight such as carbon dioxide can be measured. Is possible.

  Further, since no light source is required as compared with an infrared light absorption type gas sensor, power consumption can be reduced. In addition, since the conventional infrared light absorption type gas sensor uses a light source, it takes time until the light source becomes measurable. On the other hand, since the gas sensor of this embodiment does not require a light source, the measurement time can be shortened compared with the conventional infrared light absorption type gas sensor.

  Moreover, according to said structure, since gas can be detected structurally by providing an electrode pair and a gas absorber, a comparatively cheap gas sensor can be provided.

Moreover, in addition to said structure, one form of the gas sensor which concerns on this invention is
Further comprising a base provided with a recess,
The gas absorber is filled in the recess,
It is preferable that at least a part of the anode and at least a part of the cathode are arranged at positions separated from each other in the recess.

  According to the above configuration, at least a portion of the anode and at least a portion of the cathode are placed in the liquid droplet in a state where the gas absorber is present in a liquid droplet state using the surface tension on the surface of the flat base. Even when configured to be arranged, the function as the gas sensor according to the present invention can be realized. However, there is a possibility that the sensor function cannot be maintained normally due to an external impact or the like if the liquid droplets remain. On the other hand, by filling the recess provided in the base with the gas absorber as in the above configuration, the gas absorber can be prevented from protruding from the surface of the base, and the impact resistance is relatively low. It is possible to provide a reliable gas sensor that can be enhanced. In addition, the droplets do not protrude from the surface of the base portion, and the flatness of the surface on the side in contact with the gas of the gas sensor can be maintained.

Moreover, in addition to said structure, one form of the gas sensor which concerns on this invention is
An input unit for inputting a signal having a certain frequency to the anode and the cathode;
The detection unit may be configured to detect gas based on the impedance value based on the signal of the certain frequency.

Moreover, instead of the above configuration, one form of the gas sensor according to the present invention is
An input unit for inputting signals having at least two frequencies to the anode and the cathode;
It is preferable that the detection unit be configured to detect gas based on the impedance value based on the signal of each frequency.

  According to the above configuration, for example, by inputting two types of frequency signals and detecting the gas based on the impedance value based on the signals of the respective frequencies, detection is performed as compared with the case of using only one type of frequency. An improvement in accuracy can be realized. Specifically, as described later, for example, a difference between impedance values based on signals of respective frequencies is taken, a method for detecting the presence / absence and concentration of gas from the difference, and a presence / absence and concentration of gas are detected from the increase / decrease ratio of impedance There is a method and a method for detecting the presence and concentration of gas by obtaining impedance from two frequencies. be able to. Even when one type of frequency is used, detection is possible by using data in which the impedance value is associated with the presence / absence of gas and / or the concentration of gas, but a plurality of impedance values are obtained. More accurate detection can be performed by deriving the result based on these.

Moreover, in addition to said structure, one form of the gas sensor which concerns on this invention is
The detection unit has a first impedance value when a signal having a first frequency, which is a certain frequency, is input to the anode and the cathode, and a second frequency different from the first frequency. It is preferable that the gas is detected based on a difference from a second impedance value or an increase / decrease rate when a signal having the same is input to the anode and the cathode.

  According to the above configuration, detection accuracy can be improved as compared with the case where impedance is measured using one type of frequency.

Moreover, in addition to said structure, one form of the gas sensor which concerns on this invention is
There are a plurality of pairs consisting of the anode and the cathode,
It is preferable that the input unit is configured to input signals having different frequencies from each other to the plurality of pairs.

  According to the above configuration, for example, gas detection based on signals of each frequency can be realized by inputting signals of a plurality of frequencies such as two types of frequencies.

Moreover, in addition to said structure, one form of the gas sensor which concerns on this invention is
It is preferable that the gas absorber further includes holding means for covering the side in contact with the gas and holding the gas absorber on the base.

  According to the above configuration, the gas absorber can be stably held at the base by covering the side of the gas absorber in contact with the gas by the holding means. The gas sensor according to the invention can be attached to a ceiling portion of the room, and the gas sensor can be installed in a desired direction while holding the gas absorber.

Moreover, in addition to said structure, one form of the gas sensor which concerns on this invention is
The gas absorber is a liquid or a gel,
The concave portion is provided with an opening portion that opens toward the ground side, and a ceiling surface disposed on the top side,
A holding means for covering the opening and holding the gas absorber in the recess;
The ceiling surface has a raised portion that is partially raised toward the opening,
It is preferable that the anode and the cathode are disposed on the raised portion.

  According to the above configuration, even if the liquid level of the gas absorber (liquid) filled in the recesses is reduced for some reason and the liquid level is lower than the ceiling surface where the recesses are disposed, Since the anode and the cathode are disposed at a position lower than the ceiling surface of the recess toward the opening, the anode and the cathode are not immediately exposed from the gas absorber inside the recess.

  Moreover, according to the said structure, an anode and a cathode exist in the position near the opening part side rather than the ceiling surface of a recessed part. This makes the distance between the gas contact surface of the gas absorber and the anode and cathode shorter than when the anode and cathode are disposed at the same position (the same height) as the ceiling surface of the recess. can do. Therefore, the reaction rate (that is, the detection rate) can be increased while a relatively large amount of the gas absorber is filled and held in the recess.

Moreover, in addition to said structure, one form of the gas sensor which concerns on this invention is
The anode and the cathode may be arranged such that the end of the anode and the end of the cathode are opposed to each other.

Moreover, in addition to said structure, one form of the gas sensor which concerns on this invention is
Each of the anode and the cathode is a comb electrode having a plurality of comb teeth,
The plurality of comb teeth of each of the anode and the cathode mesh with each other, or are arranged so as to be nested,
It is preferable that the gas absorber covers a region where the plurality of comb teeth portions mesh with each other or are nested.

  According to the invention described above, since the gas absorber covers a plurality of comb tooth portions of the anode and the cathode which are engaged with each other or nested, it is possible to increase the amount of impedance change due to gas absorption. And the resolution can be improved.

Moreover, in addition to said structure, one form of the gas sensor which concerns on this invention is
It is preferable that the said recessed part has a shape where the diameter is gradually reduced toward the bottom part of the said recessed part prescribed | regulated on the opposite side to the said opening part from the opening part of the said recessed part.

  According to the above invention, since the opening portion of the recess is configured most widely among the recesses, it is possible to ensure a wide gas contact surface even with a relatively small amount of gas absorber filling, Gas can be absorbed effectively and the reaction rate can be improved.

  Further, in one embodiment of the gas sensor according to the present invention, specifically, an ionic liquid can be used as the gas absorber.

In order to achieve the above object, the gas sensing method according to the present invention provides:
Using the gas sensor in which at least a part of the anode and at least a part of the cathode are covered with a gas absorber whose conductivity is changed by absorbing the gas to be detected, the anode and the cathode through the gas absorber And a detection step of detecting the gas based on the impedance value between the two.

  According to the said structure, the gas of the detection target contained in air | atmosphere is absorbed by the gas absorber by making a gas absorber contact the air | atmosphere, for example. The gas absorber changes its conductivity by absorbing the gas to be detected. Therefore, by measuring the impedance between the anode and the cathode by interposing the gas absorber between the anode and the cathode, it is possible to detect the change in impedance and detect the gas to be detected.

  According to this configuration, it is not necessary to ensure a long optical path length unlike a conventional infrared light absorption type gas sensor, so that the apparatus (gas sensor) can be downsized.

  Further, according to the above configuration, since gas detection is performed using a gas absorber whose conductivity is changed by absorbing the gas to be detected, even a gas having a low molecular weight such as carbon dioxide can be measured. Is possible.

  Moreover, since it is a sensing method that does not require a light source as compared with an infrared light absorption type gas sensor, a reduction in power consumption can be realized. In addition, since the conventional infrared light absorption type gas sensor uses a light source, it takes time until the light source becomes measurable. On the other hand, since the gas sensor of this embodiment does not require a light source, the measurement time can be shortened compared with the conventional infrared light absorption type gas sensor.

Further, the gas sensing method according to the present invention, in addition to the above configuration,
In the detection step, the gas can be detected based on the impedance value when a signal having a certain frequency is input to the anode and the cathode.

In addition, the gas sensing method according to the present invention, instead of the above configuration,
In the detection step, the gas is preferably detected based on the impedance value for each frequency when signals having at least two types of frequencies are input to the anode and the cathode.

  According to the above configuration, for example, by inputting signals of two types of frequencies and measuring the impedance based on the signals of each frequency, the detection accuracy is higher than when impedance is measured using one type of frequency. Improvements can be realized.

  Specifically, for example, as described later, the difference between the impedance values based on the signals of the respective frequencies can be taken, and the presence and concentration of the gas can be detected from the difference. Even when one type of frequency is used, detection is possible by using data in which the impedance value is associated with the presence / absence of gas and / or the concentration of gas, but a plurality of impedance values are obtained. It is more accurate to derive the results based on these.

Moreover, in addition to said structure, one form of the gas sensor which concerns on this invention is
In the detection step, a first impedance value when a signal having a first frequency which is a certain frequency is input to the anode and the cathode, and a second frequency different from the first frequency are obtained. It is preferable to detect the gas based on the second impedance value when a signal having the same is input to the anode and the cathode.

  According to the above configuration, for example, a difference in impedance value based on a signal for each frequency can be taken, and the presence and concentration of gas can be detected from the difference. Thereby, improvement in detection accuracy can be realized as compared with the case where only one type of frequency is used.

  According to the present invention, it is possible to provide a highly versatile gas sensor and gas sensing method capable of downsizing and detecting even a gas having a low molecular weight, and having few consumption electrodes.

It is a figure which shows the structure of the gas sensor of 1st Embodiment which is one Embodiment of the gas sensor which concerns on this invention. It is arrow sectional drawing which showed the state which cut | disconnected the sensor part of the gas sensor of FIG. 1 by the cutting line AA 'shown in FIG. It is a figure explaining the gas sensing principle of the gas sensor which concerns on this invention. FIG. 2 is a perspective view of a sensor unit of the gas sensor of FIG. 1 and a diagram illustrating a configuration of a test apparatus for performing a verification test of the sensor unit. It is a figure of the graph which shows the verification test result of the gas sensor of FIG. It is a figure of the graph which shows the verification test result of the gas sensor of FIG. It is a figure of the graph which shows the verification test result of the gas sensor of FIG. It is a figure of the graph which shows the verification test result of the gas sensor of FIG. It is a figure of the graph which shows the verification test result of the gas sensor of FIG. It is a figure of the flowchart of the gas sensing method using the gas sensor of FIG. It is a figure which shows the modification of the gas sensor of FIG. It is a figure which shows the modification of the gas sensor of FIG. It is a figure which shows the modification of the gas sensor of FIG. It is a figure which shows the modification of the gas sensor of FIG. It is a figure which shows the modification of the gas sensor of FIG. It is a figure which shows the structure of the gas sensor of 2nd Embodiment which is other embodiment of the gas sensor which concerns on this invention. It is a figure of the flowchart of the gas sensing method using the gas sensor of FIG. It is a figure which shows the modification of the gas sensor of FIG.

  As a result of intensive studies to solve various problems of conventional gas sensors, the present inventors have found gas sensing by a gas absorber, and until reaching the present invention, the dielectric constant of the gas absorber is due to gas absorption. Using this change, we have developed a gas sensor that performs gas detection using a surface plasmon resonance phenomenon in which a change in dielectric constant of a gas absorber disposed on the surface of the metal layer occurs in the metal layer. In addition, a gas nanotube based on a change in the source / drain current is obtained by using a carbon nanotube disposed between the electrodes and a gas absorber serving as a gate insulating layer, and utilizing the fact that the state of the gate insulating layer changes due to gas absorption. We are also developing a gas sensor that detects this. These developed gas sensors are small and can measure gases with low molecular weight such as carbon dioxide, but they are superior to conventional gas sensors. However, the gas sensors using the former surface plasmon resonance phenomenon Uses a light source and consumes a large amount of power. The gas sensor with carbon nanotubes arranged between the latter electrodes has a small detection current of nA order and does not use a light source, but considering the cost of carbon nanotubes, it is practical. There is a problem. Therefore, the inventors of the present application have further studied the gas sensor provided with the gas absorber and completed the present invention.

  That is, the gas sensor according to the present invention covers a base having an anode and a cathode, at least a part of the anode and at least a part of the cathode, and can come into contact with a gas to be detected. A gas absorber whose conductivity is changed by absorbing the gas, and a detector that detects the gas based on the impedance value between the anode and the cathode via the gas absorber. And.

  Hereinafter, the gas sensor according to the present invention will be described with some embodiments and modifications. However, the configuration of the gas sensor shown in these embodiments is merely an example, and the present invention is limited to these configurations. It is not a thing.

[First Embodiment]
(1) Configuration of Gas Sensor of First Embodiment An embodiment (first embodiment) of a gas sensor according to the present invention will be described with reference to FIGS.

  FIG. 1A is a perspective view of a gas sensor according to a first embodiment of the present invention, and FIG. 1B is an exploded view thereof. 2 is a cross-sectional view of the gas sensor of FIG.

  The gas sensor 100 of 1st Embodiment is provided with the sensor part 10 and the detection part 7, as shown to (a) of FIG.

  As shown in FIG. 1B, the sensor unit 10 includes a base 1 on which an anode 2 and a cathode 3 are formed, an ionic liquid 4 (gas absorber), and a liquid sealing organic polymer film 5 ( Holding means) and a protective mesh member 6 (holding means).

  As shown in FIG. 1 and FIG. 2, the base 1 is provided with a recess 1 a on one side. The concave portion 1a is constituted by a side surface and a bottom surface, and the side surface may be perpendicular to one side of the base 1 but may be inclined with respect to one side of the base 1 as shown in FIG. . Although the concave portion 1a shown in FIG. 1B is circular, the shape of the concave portion 1a is not limited in the present invention.

  In FIG. 2, the diameter of the concave portion 1a is the largest at the opening portion (that is, the boundary portion between the side surface of the concave portion 1a and the edge surface that forms the periphery of the concave portion 1a), and extends from the opening portion toward the bottom surface of the concave portion 1a. The opening diameter is continuously reduced. The base 1 can be composed of, for example, silicon or glass.

  Anode 2 and cathode for performing impedance measurement, which will be described later, along the side surface and the bottom surface of the recess 1a from the edge surface adjacent to the opening of the recess 1a on the surface of the base 1 where the recess 1a is provided A metal layer 3 is formed.

  Each of the anode 2 and the cathode 3 has first end portions 2a and 3a on the edge surface adjacent to the opening portion of the recess 1a, and second ends 2b and 3b on the bottom surface side of the recess 1a. ing. A wiring is connected to the first ends 2 a and 3 a, and the wiring is connected to the detection unit 7. The second ends 2b and 3b of the anode 2 and the cathode 3 are opposed to each other with a predetermined distance on the bottom surface of the recess 1a. In the first embodiment, as shown in FIG. 1 (b), the anode 2 and the cathode 3 are disposed at positions facing each other across the center point of the opening portion of the recess 1a. However, the present invention is not limited to this arrangement. As described later, a signal having a predetermined frequency is input from the detection unit to the first end portions 2a and 3a connected to the detection unit 7 via the wiring. That is, the detection unit 7 also serves as an input unit for the signal.

  Examples of a method for forming the anode 2 and the cathode 3 include, but are not limited to, pattern formation using a mask. The anode 2 and the cathode 3 can be made of, for example, a titanium-aluminum alloy (Ti-Al alloy).

  In this way, the recess 1a of the base 1 where the anode 2 and the cathode 3 are formed is filled with the ionic liquid 4, and at least a part of the anode 2 and at least a part of the cathode 3, that is, the side and bottom surfaces of the recess 1a, The part arranged along the line is covered with the ionic liquid 4.

  As the ionic liquid 4, a liquid amount that completely fills the concave portion 1a, that is, a liquid amount that reaches the opening of the concave portion 1a is used. However, when the sensor unit 10 of the gas sensor 100 of the first embodiment is configured to perform gas sensing in a state where the lower side of FIG. 2 is the ground side and the upper side of the paper is the top side, It is not necessary for the ionic liquid 4 to completely fill the recess 1a. However, when the location where the sensor unit 10 of the gas sensor 100 is installed is an inclined surface or an installation surface that is inclined after being installed, either the anode 2 or the cathode 3 is exposed from the ionic liquid 4. In order to avoid this, it is preferable that the ionic liquid 4 completely fills the concave portion 1a as in the first embodiment.

Here, the ionic liquid 4 as a gas absorber is, for example, [EMIM] [BF ₄ ] (1-ethyl-3-methylimidazolium tetrafluoroborate) or [BMIM] [BF ₄ ] (1-butyl- 3-methylimidazolium tetrafluoroborate), [BMIM] [PF ₆ ] (1-butyl-3-methylimidazolium hexafluorophosphate), [OMIM] [Br] (1-n-octyl-3-methyl Imidazolium bromide), [Hmpy] [Tf ₂ N], [Hmim] [Tf ₂ N], [Bmim] [Tf ₂ N], [C ₆ H ₄ F ₉ mim] [Tf ₂ N], [Tf ₂ N] Amim] [BF ₄ ], [Pabim] [BF ₄ ], [Am-im] [DCA], [Am-im] [BF ₄ ], [BMIM] [BF ₄ ] + PVDF, [C ₃ NH ₂ mim ] [CF ₆ SO ₃ ] + PTFE, [C ₃ NH ₂ mim] [Tf ₂ N] + PTFE, [H ₂ NC ₃ H ₆ mim] [Tf ₂ N] + cross-linked Nylon66, P [VBBI] [ BF ₄ ], P [MABI] [BF ₄ ], P [VBBI] [Tf ₂ N], P [VBTMA] [BF ₄ ], P [MATMA] [BF ₄ ], etc. Ionic liquid that can absorb the gas depending on the type It may be appropriately selected.

In particular, for example, when the gas sensor 100 capable of detecting carbon dioxide is used, [EMIM] [BF ₄ ], [EMIM] [BF ₄ ], [BMIM] [BF ₄ ], [BMIM] capable of absorbing carbon dioxide. ] [PF ₆ ], [Hmpy] [Tf ₂ N], [Hmim] [Tf ₂ N], [Bmim] [Tf ₂ N], [C ₆ H ₄ F ₉ mim] [Tf ₂ N], [Amim ] [BF ₄ ], [Pabim] [BF ₄ ], [Am-im] [DCA], [Am-im] [BF ₄ ], [BMIM] [BF ₄ ] + PVDF, [C ₃ NH ₂ mim] [CF ₆ SO ₃ ] + PTFE, [C ₃ NH ₂ mim] [Tf ₂ N] + PTFE, [H ₂ NC ₃ H ₆ mim] [Tf ₂ N] + cross-linked Nylon 66, P [VBBI] [BF ₄ ], P [MABI] [BF ₄ ], P [VBBI] [Tf ₂ N], P [VBTMA] [BF ₄ ], P [MATMA] [BF ₄ ] and the like are used as the ionic liquid 4.

Further, when the gas sensor 100 capable of detecting ammonia is used, an ionic liquid in general that absorbs water, such as [EMIM] [BF ₄ ] that can absorb ammonia, is used as the ionic liquid 4.

  Note that PEI (polyethyleneimine) may be added to the ionic liquid 4.

  In the first embodiment, the case where the ionic liquid 4 is applied as the gas absorber has been described. However, the present invention is not limited to this, and various other types such as hydroxide solutions of alkali metals and alkaline earth metals can be used. The gas absorber may be applied. Note that when an alkali metal and alkaline earth metal hydroxide aqueous solution is used as the gas absorber, carbon dioxide can be absorbed, so that a gas sensor using carbon dioxide as a detection target can be realized.

  Furthermore, the gas sensor according to the present invention can also detect moisture. That is, it can be used as a hygrometer.

  As shown in FIG. 2, the liquid-sealing organic polymer film 5 is disposed on one side of the base 1 in a state where the recess 1 a is filled with the ionic liquid 4. The liquid-sealing organic polymer film 5 is a film that does not transmit the ionic liquid 4 but transmits gas, and can be specifically constituted by a parylene film. Even when the base 1 (sensor part 10 of the gas sensor 100) is vibrated or inclined by being covered with the liquid-sealing organic polymer film 5, the ionic liquid 4 is stably stabilized in the recess 1a of the base 1. Can continue to hold. The liquid sealing organic polymer film 5 may be formed after the ionic liquid 4 is filled in the recess 1a, or the recess 1a is covered with the liquid sealing organic polymer film 5 before the ionic liquid 4 is filled. Then, the ionic liquid 4 may be injected into the recess 1a after the coating. When the organic polymer film 5 for liquid sealing is formed after the ionic liquid 4 is filled, the material used for the organic polymer film 5 for liquid sealing can be formed by, for example, a CVD (Chemical Vapor Deposition) method. is there.

  The protective mesh member 6 is a lid member that covers the base 1 on which the anode 2 and the cathode 3 are formed, the ionic liquid 4, and the organic polymer film 5 for liquid sealing. The protective mesh member 6 is subjected to external force. In some cases, it has a function of protecting the base 1, the ionic liquid 4, and the organic polymer film 5 for liquid sealing. In the protective mesh member 6, the region facing the recess 1 a has a mesh structure, and the region where the mesh structure is provided is a region through which gas can pass between the ionic liquid 4 arrangement side and the outside air side. . The protective mesh member 6 has a diameter slightly larger than that of the base 1, for example, and is along the deposition direction of the base 1, the metal layer (the anode 2 and the cathode 3), the ionic liquid 4, and the liquid sealing organic polymer film 5. May have side surfaces. The base 1 on which the anode 2 and the cathode 3 are formed to hold the ionic liquid 4, the organic polymer film 5 for liquid sealing, and the protective mesh member 6 are shown in FIG. Or may be screwed.

  Note that the liquid sealing organic polymer film 5 and the protective mesh member 6 are not essential components for realizing the gas sensing function of the gas sensor according to the present invention. That is, even if the liquid sealing organic polymer film 5 and the protective mesh member 6 are not provided, the gas sensing function can be realized. However, it is preferably provided for the purpose of securely holding the ionic liquid 4 on the base 1, for the purpose of avoiding foreign matters from entering the ionic liquid 4 from the outside, and for the purpose of enhancing the external impact of the gas sensor. Further, at least one of the liquid sealing organic polymer film 5 and the protective mesh member 6 may be sufficient. By adjusting the shape or opening diameter of the mesh hole of the protective mesh member 6, the ionic liquid 4 can be reliably held on the base 1 only by the protective mesh member 6 without the organic polymer film 5 for liquid sealing. There are cases where it is possible. Specifically, if the opening diameter of the mesh hole of the protective mesh member 6 is 100 μm or less, the ionic liquid 4 does not flow out of the mesh hole and flows into the base 1 due to the interaction between the mesh hole and the surface tension of the ionic liquid 4. Holds securely.

  The detection unit 7 is connected to the first ends 2a and 3a of the anode 2 and the cathode 3 via wirings, and inputs signals to the anode 2 and the cathode 3 during sensing, via the ionic liquid 4 The impedance between the anode 2 and the cathode 3 is measured, and the presence / absence of the detection target gas and the concentration of the detection target gas are detected. The principle of the gas sensor according to the present invention will be described below.

(2) Principle of Gas Sensor According to the Present Invention FIG. 3 is a diagram for explaining the principle of the gas sensor according to the present invention. The sensor unit 10 of the gas sensor 100 shown in FIG. 3 has a simplified configuration for explaining the principle, but the gas sensor according to the present invention functions as a gas sensor even in the configuration shown in FIG. Fulfill. In FIG. 3, droplets of ionic liquid 4 are formed on the surface of the base 1 of the flat plate on which the anode 2 and the cathode 3 are formed. In the configuration shown in FIG. 3, the liquid sealing organic polymer film 5 shown in FIGS. 1 and 2 is not provided.

  The ionic liquid 4 has a predetermined conductivity. And this conductivity changes by absorbing the gas (for example, carbon dioxide) absorbed by the ionic liquid. In the present invention, by measuring the impedance of the change in conductivity, the amount of gas absorbed in the ionic liquid, that is, the gas concentration value in the space to be measured is obtained from the impedance value. FIG. 3 shows a gas sensor for detecting carbon dioxide, the left side of FIG. 3 shows the state of the ionic liquid of the gas sensor installed in the space where the carbon dioxide concentration is low, and the right side of FIG. The state of the ionic liquid of the gas sensor installed in the high space is shown. A large amount of carbon dioxide is absorbed in the ionic liquid of the right gas sensor. The viscosity of the ionic liquid decreases according to the amount of carbon dioxide absorbed, and when the viscosity decreases, the ion mobility increases and the conductivity increases. Therefore, the detection unit 7 captures a change in the conductivity of the ionic liquid by applying a voltage between the anode and the cathode and passing an electric current (alternating current) to measure the impedance value. The detection unit stores data in which an impedance value and a gas concentration value are associated in advance. Therefore, the gas concentration value can be calculated by obtaining the impedance value.

(3) Verification Test Using one embodiment of the gas sensor according to the present invention, it was verified whether gas detection based on the above-described principle (gas presence / absence and gas concentration specification) was possible.

The gas sensor used in the verification test will be described with reference to FIG. 4 and is basically based on the configuration shown in FIGS. FIG. 4A is a perspective view of the gas sensor 100 used for the verification test, and FIG. 4B is a diagram showing the configuration of the entire test apparatus used for the verification test. For convenience of explanation, in FIG. 4B, the gas sensor 100 is a cross-sectional view taken along the line AA ′ of the gas sensor 100 in FIG. The gas sensor 100 shown in FIG. 4 is a CO ₂ (carbon dioxide) sensor.

The test apparatus 50 shown in FIG. 4B includes a chamber 30 in which the gas sensor 100 can be disposed, a CO ₂ (carbon dioxide) gas storage unit 20 for changing the carbon dioxide concentration inside the chamber 30, and And a valve 21 and an intake / exhaust valve 40 for air (outside air) that does not actively contain the gas to be detected. The gas sensor 100 includes a base 1 made of a liquid cell electrode, an ionic liquid 4 made of [EMIM] [BF ₄ ], an organic polymer film 5 for liquid sealing made of a parylene film, and a protective mesh member 6 described above. In addition, a detection unit 7 is provided to which wirings extending from an anode 2 made of a Ti—Al alloy and a cathode 3 made of a Ti—Al alloy are connected.

The base 1 used is a recess 1a having a depth of about 11 mm from the opening portion to the bottom surface, a diameter of the opening portion of about 25 mm and a diameter of the bottom surface of about 15 mm, and is open to an intermediate position of the depth of the recess portion 1a. diameter continuously becomes narrower from the portion, from the intermediate position to the bottom has a diameter equal shape, the volume of the recesses 1a in 1943Mm ^3, ionic liquids 4 about 2cc satisfies the complete recess 1a gas sensor 100 was used.

  Using the test apparatus 50 shown in FIG. 4 (b), the anode 2 and the cathode via the ionic liquid 4 are detected by the detection unit 7 connected to the anode 2 and the cathode 3 via wiring while changing the carbon dioxide concentration. The impedance between 3 was measured.

  The measurement was performed by inputting a signal having a frequency of 0.01 Hz from the detection unit 7 to the anode 2 and the cathode 3. The measurement is performed while the gas sensor 100 is left in the chamber 30 and the carbon dioxide concentration in the chamber 30 is changed from 0 ppm to 4000 ppm in steps of about 500 ppm so that the carbon dioxide concentration is changed from low to high. It was. In addition, the impedance was measured by the detection unit 7 when 1 minute had passed after the concentration in the chamber 30 reached a predetermined concentration.

  The measurement results are shown in FIG. As shown in FIG. 5, when a signal having a frequency of 0.01 Hz is input to the anode 2 and the cathode 3, the impedance value of the ionic liquid 4 decreases as the carbon dioxide concentration in the chamber 30 increases. It was. That is, it can be said that as the carbon dioxide concentration in the chamber 30 becomes higher, the conductivity of the ionic liquid 4 has increased, that is, the viscosity of the ionic liquid 4 has decreased. This is because the ionic liquid 4 adsorbs a large amount of carbon dioxide as the carbon dioxide concentration in the chamber 30 increases.

  Similarly to the above method, the case where a signal with a frequency of 0.1 Hz is input to the anode 2 and the cathode 3 and the case where a signal with a frequency of 1 Hz is input to the anode 2 and the cathode 3 are also classified according to the carbon dioxide concentration. Impedance characteristics were tested. FIG. 6 shows the result when a signal having a frequency of 0.1 Hz is input, and FIG. 7 shows the result when a signal having a frequency of 1 Hz is input. 5 to 7 show that the impedance value of the ionic liquid 4 decreases as the carbon dioxide concentration increases. Further, as can be seen from FIG. 8 in which the results of the frequencies 0.01 Hz, 0.1 Hz, and 1 Hz are combined into one, each result shows a linear impedance characteristic, and the change in the Z value is lower at the lower frequency. The difference was shown to be clear.

  Next, the carbon dioxide concentration (carbon dioxide concentration: 0 ppm, 400 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm) is fixed using the test apparatus shown in FIG. The impedance characteristics at each carbon dioxide concentration were measured. The measurement was performed by applying a direct current (DC) bias (1.8 volts) to the anode 2 and the cathode 3. The result is shown in FIG. FIG. 9 shows that impedance values at a certain frequency are different from each other depending on the carbon dioxide concentration, and that the Z value is different depending on the carbon dioxide concentration.

  From the above verification test, if the gas sensor of this embodiment is used, the presence or absence of the gas to be detected can be determined by measuring the impedance using a gas absorber whose conductivity changes by absorbing the gas to be detected. It can be seen that the concentration can be detected.

  In addition to the method of measuring impedance, for example, gas detection can be performed by obtaining the amount of change in impedance before and after the detection operation. That is, the present invention is to perform gas detection based on an impedance value (using a gas absorber) regardless of whether impedance is measured.

The gas absorber is not limited to a liquid, and may be a gel or a solid. For example, an ionic liquid [BMIM] [BF ₄ ] (67% wt) mixed with polymer PVdF (HFP) (33% wt) can be used as the gas absorber.

(4) Gas Sensing Method FIG. 10 is a flowchart of a gas sensing method using the gas sensor 100 of the first embodiment.

  In a state where the gas sensor 100 of the first embodiment is installed at a predetermined location, a signal having a predetermined frequency is transmitted from the detection unit 7 connected to the anode 2 and the cathode 3 of the sensor unit 10 via wiring. Input to the cathode 3 (step S1).

  Subsequently, the impedance between the anode 2 and the cathode 3 through the ionic liquid 4 is measured (step S2: detection step).

  Subsequently, the impedance value measured in step S2 is collated with corresponding data in which the concentration of the detection target gas and the impedance value are associated in advance to detect the gas concentration (step S3: detection step). Here, as the correspondence data, for example, data stored in advance in a memory provided in the detection unit 7 can be used. However, the present invention is not limited to this, and the correspondence data may be created by acquiring the impedance value using the sensor unit 10.

(5) Effects of First Embodiment From the above, when the gas sensor of this embodiment is used, impedance is measured using a gas absorber whose conductivity changes by absorbing the gas to be detected. The presence and concentration of the detection target gas can be detected by a relatively simple method.

  According to the configuration of the first embodiment, it is not necessary to ensure a long optical path length unlike a conventional infrared light absorption type gas sensor, so that the apparatus (gas sensor) can be downsized, and carbon dioxide It is possible to measure a gas having a small molecular weight.

  Further, since no light source is required as compared with an infrared light absorption type gas sensor, power consumption can be reduced. Since the conventional infrared light absorption type gas sensor uses a light source, it takes time until the light source becomes measurable. On the other hand, since the gas sensor of the first embodiment does not require a light source, the measurement time can be shortened compared with the conventional infrared light absorption type gas sensor.

  Moreover, the gas sensor of 1st Embodiment is filled with the ionic liquid which is a gas absorber in the recessed part provided in the base. Here, it is assumed that the base is a flat member provided with an anode and a cathode, and that the ionic liquid is applied to the flat surface so as to cover the anode and the cathode in the form of droplets using the surface tension. Even if it is formed, the function as the gas sensor according to the present invention can be realized (see FIG. 3). However, there is a possibility that the sensor function cannot be maintained normally due to an external impact or the like if the liquid droplets remain. On the other hand, if the ionic liquid is filled in the recess as in the first embodiment, the ionic liquid can be prevented from protruding from the surface of the base, and the impact resistance can be relatively improved. A reliable gas sensor can be provided. Further, the ionic liquid droplets do not protrude from the surface of the base, and the flatness of the surface of the gas sensor that comes into contact with the gas can be maintained.

(6) Modifications Modification 1 (electrode pattern)
In the above-described first embodiment, as shown in FIG. 1B, the anode 2 and the cathode 3 have substantially the same width between the first end 2a, 3a and the second end 2b, 3b. It has a belt-like shape. That is, the second end portions 2 b and 3 b are configured to have the same width as the other portions of the strip-like anode 2 and cathode 3. However, the present invention is not limited to this. For example, the second ends 2b and 3b may have a shape as shown in FIG.

  FIG. 11 is a partial top view showing the formation positions of the second end portions 2 b and 3 b of the anode 2 and the cathode 3 and the ionic liquid 4 of the first modification. The second end portions 2b and 3b shown in FIG. 11 are configured to be wider than portions other than the second end portions 2b and 3b in the anode 2 and the cathode 3, and are shaped like a T-shaped head. I am doing. The second end portion 2b and the second end portion 3b are formed with their T-shaped heads facing each other, and the second end portion 2b and the second end portion 3b of the T-shape are made into an ionic liquid. 4 is configured to cover. Thereby, compared with the case of the shape of the second end portions 2b and 3b shown in FIG. 1B, the area of the electrode itself is increased, thereby reducing the impedance. It is possible to measure in a low impedance region with little.

・ Modification 2 (electrode pattern)
In the above-described first embodiment, as shown in FIG. 1B, the anode 2 and the cathode 3 have substantially the same width between the first end 2a, 3a and the second end 2b, 3b. It has a single strip shape. However, the present invention is not limited to this. For example, the second ends 2b and 3b may have the shape shown in FIG.

  FIG. 12 is a partial top view showing the formation positions of the second end portions 2b and 3b of the anode 2 and the cathode 3 and the ionic liquid 4 of the second modification. The second ends 2b and 3b shown in FIG. 12 have a plurality of comb teeth 2bb and 3bb, respectively, and the plurality of comb teeth 2bb at the second end 2b of the anode 2 and the cathode 3 The plurality of comb teeth 3bb of the second end 3b mesh with each other or are nested. Then, the ionic liquid 4 covers a region where a plurality of comb teeth portions mesh with each other or are nested. Thereby, compared with the case of the shape of the second end 2b and the second end 3b shown in FIG. 1B, the area of the electrode itself is increased, thereby reducing the impedance. Accordingly, measurement can be performed in a low impedance region with little noise in the measurement system.

・ Modification 3 (electrode pattern)
In the first embodiment described above, impedance is measured using a single strip-like anode 2 and cathode 3 as shown in FIG. However, the present invention is not limited to this. For example, the impedance measurement electrode may have the configuration shown in FIG.

  FIG. 13 is a partial top view showing the impedance measurement electrodes and the formation positions of the ionic liquid 4 of the third modification. The electrode for impedance measurement of Modification 3 is composed of a plurality of conductive wires 9 arranged in parallel, and one of the conductive wires is the anode 2 and the other conductive wire is the cathode 3. As shown in FIG. 13, the plurality of conductive wires 9 are connected in series by the ionic liquid. The plurality of conductive wires can be made of a Ti—Al alloy.

  Thereby, the amount of impedance change can be increased, and the detection (decomposition) ability can be improved.

Modification 4 (recessed shape)
In the first embodiment described above, as shown in FIG. 2, the shape of the recess 1a provided in the base 1 is such that the diameter of the opening is slightly larger than the diameter of the bottom surface, and the anode 2 and the cathode 3 The two end portions 2b and 3b are arranged along the bottom surface of the concave portion 1a. However, this invention is not limited to this, For example, it is good also as a structure shown in FIG.

  FIG. 14 is a cross-sectional view of the gas sensor 100 of the fourth modification. In the present modification 4, a groove 1b is formed by deeply digging the bottom surface of the base 1 recess 1a, and the anode 2 and the cathode 3 are disposed on the side surface of the groove 1b. Although the depth from the opening portion to the bottom surface of the recess 1a is shallow, the diameter of the opening portion is wide and there is a sufficient area to come into contact with air during gas detection. On the other hand, the depth of the groove 1b provided on the bottom surface of the groove 1b is small, and the diameter from the opening portion to the bottom surface is deep, but the diameter of the opening portion is small. That is, the ratio (aspect ratio) between the width and the depth of the groove 1b is larger than the ratio (aspect ratio) between the width and the depth of the recess 1a.

  With the configuration shown in FIG. 14, the anode 2 and the cathode 3 are located relatively shallow from the opening of the recess 1 a, and a large facing area between the anode 2 and the cathode 3 can be secured, and the anode 2 and the cathode 3 can be secured. Therefore, the reaction rate can be increased while the amount of the ionic liquid 4 can be increased. As another advantage, integration is easy by digging a plurality of grooves.

Modification 5 (recessed shape and electrode position)
In the first embodiment described above, as shown in FIG. 2, the shape of the recess 1a provided in the base 1 is configured such that the diameter of the opening is slightly larger than the diameter of the bottom surface, and the bottom surface is flat. However, the present invention is not limited to this. For example, the configuration shown in FIG.

  FIG. 15 is a cross-sectional view of the gas sensor 100 of the fifth modification. The gas sensor 100 according to the fifth modification is configured to assume a mode in which the concave portion 1a provided in the base portion 1 is installed such that the opening portion opens toward the ground side and the bottom surface becomes the top side. In the fifth modification, the bottom surface of the recess 1a is described as the ceiling surface of the recess 1a.

  A feature of the present modification 5 is that a part of the ceiling surface of the concave portion 1a has a raised portion raised toward the opening portion, and the anode 2 and the cathode 3 are disposed in the raised end region of the raised portion. There is in point. A liquid sealing organic polymer film 5 is provided at the opening of the recess 1a so that the ionic liquid 4 filled in the recess 1a does not flow out.

  In the configuration of the fifth modification, as shown in FIG. 15, the gas sensor 100 is installed such that the opening of the recess 1a is on the ground side and the ceiling surface of the recess 1a is on the top side. When the amount of the filled ionic liquid 4 is reduced, the liquid level is lowered and the ceiling surface of the recess 1a is exposed from the liquid surface of the ionic liquid 4 (for example, the liquid surface is at the position indicated by the arrow in FIG. 15). . However, according to the configuration of the fifth modification, the anode 2 and the cathode 3 are disposed at a position lower than the ceiling surface of the recess 1 a, so that the anode 2 and the cathode 3 are exposed from the liquid surface of the ionic liquid 4. Never do. By adopting such a configuration, the sensing function can be maintained even if the amount of the ionic liquid 4 is somewhat reduced, so that the life of the gas sensor can be extended.

[Second Embodiment]
Another embodiment (second embodiment) of the gas sensor according to the present invention will be described with reference to FIGS. In the present embodiment, in order to explain differences from the first embodiment, members having the same functions as those described in the first embodiment are denoted by the same member numbers for convenience of explanation. The description is omitted.

(1) Configuration of Gas Sensor of Second Embodiment FIG. 16 is an exploded view of the configuration of the sensor unit 10 ′ of the gas sensor 100 according to the second embodiment of the present invention.

  In the first embodiment described above, the sensor unit 10 (see FIG. 1B) is provided with a pair of electrodes (anode 2 and cathode 3). On the other hand, in the second embodiment, as shown in FIG. 16, in addition to the anode 2 and the cathode 3, another pair of electrodes (the anode 22 and the cathode 33) is provided in the sensor unit 10 ′. Yes.

  In the first embodiment, a signal having a certain frequency is input to the anode 2 and the cathode 3 to measure impedance. On the other hand, in the second embodiment, detection is performed so that a gas concentration is detected by inputting a signal of a different frequency to each electrode pair, performing impedance measurement based on the signal of each frequency, and obtaining the difference. Part 7 'is configured.

(2) Gas Sensing Method FIG. 17 is a flowchart of a gas sensing method using the gas sensor 100 according to the second embodiment. The principle of gas sensing is the same as that already described in the first embodiment.

  In a state where the gas sensor 100 of the second embodiment is installed at a predetermined location, a first frequency (for example, 0.01 Hz) which is a certain frequency is supplied from the detection unit 7 ′ to the anode 2 and the cathode 3 through the wiring. A signal having a second frequency (for example, 1 Hz) different from the first frequency is input from the detection unit 7 ′ to the anode 22 and the cathode 33 via the wiring (step S1 ′). .

  Subsequently, the impedance between the anode 2 and the cathode 3 via the ionic liquid 4 is measured, and the impedance between the anode 22 and the cathode 33 via the ionic liquid 4 is measured (step S2: detection step). .

  Subsequently, a difference between the first impedance value based on the first frequency measured in step S2 and the second impedance value based on the second frequency is obtained (step S3 ′: detection step).

  Subsequently, the difference value calculated in step S3 ′ is collated with corresponding data in which the concentration of the detection target gas and the difference value are associated in advance to detect the gas concentration (step 4: detection process).

(3) Effects of the Second Embodiment According to the above configuration, the impedance based on the signals of each frequency is measured by inputting signals of two types of frequencies and measuring the impedance based on the signals of each frequency. Thus, the presence or concentration of gas is detected from the difference. Thereby, compared with the case where gas detection is performed using one type of frequency (configuration of the first embodiment), detection accuracy can be improved.

  In the second embodiment, the difference between the impedance values based on the signals of the respective frequencies is taken. However, the present invention is not limited to the difference, and a plurality of impedance values such as a ratio,%, and an increase / decrease rate are set. Gas detection can be performed using any method of comparison.

(4) Modifications Modification 1 (electrode pattern)
The present invention is not limited to the formation positions of the anodes 2 and 22 and the cathodes 3 and 33 in the second embodiment described above, and may have a shape as shown in FIG.

  FIG. 18 is a partial top view showing the arrangement positions of the pair of electrodes and another pair of electrodes and the formation position of the ionic liquid 4 in the first modification. As shown in FIG. 18, the anode 2, the cathode 3, the anode 22, and the cathode 33 are formed in parallel in the coating region of the ionic liquid 4. In such an electrode structure, measurement can be performed by the four-terminal method. By using this method, the contact resistance between the ionic liquid and the metal electrode can be removed.

-Modification 2 (impedance measurement method)
In the second embodiment described above, a signal having the first frequency is input to one electrode pair, and a signal having the second frequency is input to another electrode pair. That is, it is the structure which inputs into a different electrode for every frequency. However, the present invention is not limited to this.

  For example, a signal combining the first frequency and the second frequency is input to one electrode pair, and the signal output from the one electrode pair is subjected to Fourier analysis to extract only the signal of one frequency, By obtaining the impedance value of the frequency, it is possible to perform gas detection by the same method as in the first embodiment described above. Further, gas detection can be performed in the same manner as in the second embodiment described above by separately extracting signals of respective frequencies.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and technical means disclosed in different embodiments or examples are appropriately combined. Embodiments or examples obtained in this manner are also included in the technical scope of the present invention.

  According to the present invention, it is possible to provide a gas sensor that can be miniaturized and can detect even a gas having a low molecular weight and has high versatility. Therefore, the present invention can be applied to an environmental monitoring device equipped with a gas sensor. is there.

DESCRIPTION OF SYMBOLS 1 Base 1a Recessed part 1b Groove part 2, 22 Anode 2a 1st edge part 2b 2nd edge part 2bb Comb tooth part 3, 33 Cathode 3a 1st edge part 3b 2nd edge part 3bb Comb tooth part 4 Ionic liquid ( Gas absorber)
5 Liquid polymer organic polymer film (holding means)
6 Protective mesh member (holding means)
7, 7 'detector 9 conductive wire 10, 10' sensor 20 gas reservoir 21 valve 30 chamber 40 intake / exhaust valve 50 test device 100 gas sensor

Claims (9)

An anode and a cathode;
A gas that covers at least a part of the anode and at least a part of the cathode, and is disposed so as to be in contact with the gas to be detected, and whose conductivity is changed by absorbing the gas. An absorber,
A detection unit for detecting the gas based on an impedance value between the anode and the cathode via the gas absorber;
A base provided with a recess,
The recess has a shape in which the length of the minimum inner dimension in the opening in the direction perpendicular to the depth direction is longer than the length in the depth direction which is the distance from the opening to the bottom surface,
The gas absorber is filled in the recess,
At least a portion of the anode and at least a portion of the cathode are disposed at positions spaced apart in the recess,
Each of the anode and the cathode has a first end disposed on an edge surface adjacent to the opening of the recess and a second end disposed in the recess ,
A gas sensor , wherein two sets of the anode and the cathode are provided, and the two sets of the anode and the cathode are formed in parallel for measurement by a four-terminal method . An input unit for inputting a signal having a certain frequency to the anode and the cathode;
The gas sensor according to claim 1, wherein the detection unit is configured to detect gas based on the impedance value based on the signal having the certain frequency. An input unit for inputting signals having at least two frequencies to the anode and the cathode;
The gas sensor according to claim 1, wherein the detection unit is configured to detect gas based on the impedance value based on a signal of each frequency.   The detection unit has a first impedance value when a signal having a first frequency, which is a certain frequency, is input to the anode and the cathode, and a second frequency different from the first frequency. 4. The gas detection apparatus according to claim 3, wherein the gas is detected based on a difference or a rate of increase / decrease with respect to the second impedance value when a signal having the same is input to the anode and the cathode. Gas sensor.   The gas sensor according to claim 1, further comprising holding means for covering the side of the gas absorber that contacts the gas and holding the gas absorber on the base. The concave portion is provided with an opening portion that opens toward the ground side, and a ceiling surface disposed on the top side,
A holding means for covering the opening and holding the gas absorber in the recess;
The ceiling surface has a raised portion that is partially raised toward the opening,
The gas sensor according to claim 1, wherein the anode and the cathode are disposed on the raised portion.   The gas sensor according to claim 2, wherein the anode and the cathode are disposed so that an end portion of the anode and an end portion of the cathode face each other. The concave portion has a shape in which an inner dimension is gradually reduced from an opening portion of the concave portion toward a bottom portion of the concave portion defined on the opposite side to the opening portion. The gas sensor according to claim 1. The gas sensor according to any one of claims 1 to 8 , wherein the gas absorber is an ionic liquid.

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