Gas sensor system

Abstract

To provide a gas sensor system capable of detecting a target substance restraining an influence of humidity.SOLUTION: A gas sensor system includes: first piping for conveying a specimen atmosphere; second piping for conveying humidified air that is at a higher temperature and a higher humidity than a specimen atmosphere and at a lower steam pressure than a saturated steam pressure; a mixing device that is connected to the first piping and the second piping and mixes a specimen atmosphere and humidified air such that a steam pressure of mixed air between a specimen atmosphere and humidified air becomes lower than a saturated steam pressure; third piping that is connected to the mixing device and conveys mixed air; a cooling device that cools mixed air conveyed through the third piping and sets a steam pressure of the mixed air to a saturated steam pressure; and a chemical sensor device that is connected to the third piping and has a sensor surface to which mixed air cooled by the cooling device is supplied.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a gas sensor system.

Background Art

[0002] For example, when a sensor element using graphene is used as a gas sensor, the electrical or chemical response in the sensor element tends to vary greatly due to the influence of the humidity in the sample atmosphere. This affects the detection accuracy of the target substance in the sample atmosphere.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Embodiments of the present invention aim to provide a gas sensor system capable of detecting a target substance while suppressing the influence of humidity.

Means for Solving the Problems

[0005] According to an embodiment of the present invention, a gas sensor system includes: a first pipe through which a sample atmosphere is conveyed; a second pipe through which humidified air that is at a higher temperature and higher humidity than the sample atmosphere and has a vapor pressure lower than the saturated vapor pressure is conveyed; a mixing device connected to the first pipe and the second pipe, the mixing device mixing the sample atmosphere and the humidified air such that the vapor pressure of the mixed air of the sample atmosphere and the humidified air is lower than the saturated vapor pressure; a third pipe connected to the mixing device through which the mixed air is conveyed; a cooling device that cools the mixed air conveyed through the third pipe and makes the vapor pressure of the mixed air the saturated vapor pressure; and a chemical sensor device connected to the third pipe, the chemical sensor device having a sensor surface to which the mixed air cooled by the cooling device is supplied.

Brief Description of the Drawings

[0006]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0007] Hereinafter, each embodiment will be described with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the ratio of the sizes between parts, etc. are not necessarily the same as the actual ones. Even when representing the same part, the dimensions and ratios may be represented differently in the drawings. Also, the same or similar elements are denoted by the same reference numerals.

[0008] As shown in FIG. 1, the gas sensor system 1 of the embodiment includes at least a first pipe 11, a second pipe 12, a third pipe 13, a mixing device 20, a cooling device 40, and a chemical sensor device 30.

[0009] The first pipe 11 has a first collection port 11a. The sample atmosphere is taken into the first pipe 11 from the first collection port 11a. The sample atmosphere is, for example, air.

[0010] The second pipe 12 is connected to the humidifying device 90. Humidified air is supplied to the second pipe 12 from the humidifying device 90. The humidified air is at a higher temperature and higher humidity than the sample atmosphere and has a water vapor pressure lower than the saturated water vapor pressure. As the humidifying device 90, for example, a bubbling device or a spraying device can be used. The humidifying device 90 can be provided with a heater that heats the humidified air or maintains the humidified air at a predetermined temperature.

[0011] The first pipe 11 and the second pipe 12 are connected to the mixing device 20. The gas sensor system 1 further includes a control device 50. The mixing device 20 mixes the sample atmosphere conveyed through the first pipe 11 and the humidified air conveyed through the second pipe 12 at a predetermined mixing ratio under the control of the control device 50 so that the water vapor pressure of the mixed air of the sample atmosphere and the humidified air is lower than the saturated water vapor pressure.

[0012] The mixed air of the sample atmosphere and the humidified air is conveyed through the third pipe 13 connected to the mixing device 20.

[0013] The third pipe 13 is connected to the chemical sensor device 30. A cooling device 40 is provided near the connection portion with the chemical sensor device 30 in the third pipe 13. The first distance along the third pipe 13 between the cooling device 40 and the chemical sensor device 30 is smaller than the second distance along the third pipe 13 between the cooling device 40 and the mixing device 20. The cooling device 40 cools the mixed air immediately before the mixed air conveyed through the third pipe 13 is supplied to the chemical sensor device 30 and makes the water vapor pressure of the mixed air the saturated water vapor pressure. As the cooling device 40, for example, a Peltier element can be used. Also, as the cooling device 40, a pipe through which a liquid such as water flows may be wound around the third pipe 13.

[0014] The chemical sensor device 30 has a sensor element 31. Further, the chemical sensor device 30 has an enclosure 34 that houses the sensor element 31. The mixed air that is cooled by the cooling device 40 and has a water vapor pressure below the saturated water vapor pressure is supplied to the sensor surface 31a of the sensor element 31 through a third pipe 13 that leads to the inside of the enclosure 34.

[0015] The sensor element 31 is, for example, a graphene FET (field effect transistor) sensor, and the sensor surface 31a contains graphene. As shown in FIG. 2(a), the sensor element 31 has a substrate 37, graphene 32 supported on the substrate 37, a first electrode 35, and a second electrode 36.

[0016] The substrate 37 is, for example, a silicon substrate. The graphene 32 is provided, for example, on the substrate 37 via an underlayer film 38. As the underlayer film 38, for example, a silicon oxide film can be used. Also, the underlayer film 38 can be given the function of a chemical catalyst for forming the graphene 32.

[0017] One of the first electrode 35 and the second electrode 36 functions as a drain electrode, and the other functions as a source electrode. The first electrode 35 and the second electrode 36 are in electrical contact with the graphene 32. A current flows between the first electrode 35 and the second electrode 36 through the graphene 32.

[0018] As shown in FIG. 2(b), the sensor surface 31a can further include probe molecules 33 formed on the graphene 32. Due to chemical, charge-based attraction, hydrophobic interaction, etc., the probe molecules 33 are bound to, adsorbed on, or in proximity to the graphene 32, and the probe molecules 33 are constrained on the surface of the graphene 32. As the probe molecules 33, for example, any substance that shows binding properties to a target substance, such as a protein, peptide, antibody, DNA aptamer, or derivatives thereof, can be used.

[0019] When the probe molecule 33 recognizes or captures the target substance, the target substance approaches the surface of the graphene 32. Therefore, the electronic state of the graphene 32 changes due to the charge of the target substance or the structural change of the probe molecule 33 caused by capturing the target substance. By detecting this as a change in the current flowing between the first electrode 35 and the second electrode 36, the presence and concentration of the target substance in the sample atmosphere can be known. Also, by applying an appropriate bias voltage to the substrate 37, the sensor element 31 can be operated at an operating point with a large current change rate.

[0020] An exhaust pipe 15 is connected to the chemical sensor device 30. The exhaust pipe 15 communicates with the inside of the outer container 34. For example, by driving a vacuum pump connected to the exhaust pipe 15, a gas flow is formed from the first pipe 11 and the second pipe 12, through the inside of the third pipe 13 and the outer container 34, to the exhaust pipe 15. Since the gas flow is formed, even if the mixed air cooled by the cooling device 40 contains minute condensed water, dew condensation is unlikely to occur inside the chemical sensor device 30. Dew condensation means that water vapor becomes water droplets on the surface of a solid substance. The sensor element 31 is located inside the outer container 34, in a portion between the connection part of the chemical sensor device 30 with the exhaust pipe 15 and the connection part of the chemical sensor device 30 with the third pipe 13.

[0021] The sample atmosphere taken into the first pipe 11 is mixed with the humidified air conveyed through the second pipe 12 in the mixing device 20. This mixed air flows through the third pipe 13 toward the chemical sensor device 30 and is cooled by the cooling device 40 immediately before being supplied to the chemical sensor device 30. The cooled mixed air is supplied to the sensor surface 31a of the chemical sensor device 30. When the sample atmosphere contains a target substance, the target substance can be detected by changes in the electrical characteristics of the sensor element 31 or the like. The mixed air supplied to the chemical sensor device 30 is exhausted from the exhaust pipe 15.

[0022] The sample atmosphere is mixed with humidified air that is at a higher temperature and higher humidity than the sample atmosphere and has a water vapor pressure lower than the saturated water vapor pressure. The mixing device 20 mixes the sample atmosphere and the humidified air at a predetermined mixing ratio such that the water vapor pressure of the mixed air of the sample atmosphere and the humidified air is lower than the saturated water vapor pressure.

[0023] As an example, when the temperature of the sample atmosphere is 20°C, the humidity of the sample atmosphere is 0%RH, the water vapor pressure of the sample atmosphere is 0 hPa, the temperature of the humidified air is 70°C, the humidity of the humidified air is 61%RH, and the water vapor pressure of the humidified air is 190 hPa (the saturated water vapor pressure at 70°C is 312 hPa), 1 L of humidified air is mixed with 4 L of the sample atmosphere to obtain mixed air with a temperature of 29°C and a water vapor pressure of 38 hPa. The saturated water vapor pressure at 29°C is 40 hPa, and the water vapor pressure of the above mixed air is slightly lower than the saturated water vapor pressure.

[0024] The above mixed air is conveyed through the third pipe 13 toward the chemical sensor device 30 and then cooled by the cooling device 40 so that the water vapor pressure of the mixed air becomes the saturated water vapor pressure. For example, the temperature of the mixed air illustrated above is cooled from 29°C to 25°C. The saturated water vapor pressure of the mixed air at 25°C is 32 hPa. That is, in the case of the above example, 6 hPa of water vapor condenses after cooling, and the water vapor pressure of the mixed air after cooling becomes saturated. Therefore, even if the sample atmosphere taken into the first pipe 11 is dry, it is supplied to the sensor surface 31a in a state where the humidity is almost constant (relative humidity 100% at the temperature after cooling), so the influence of humidity is suppressed, and a response such as the electrical characteristics of the sensor element 31 depending on the presence or concentration of the target substance can be obtained.

[0025] Also, until it is cooled immediately before the sensor element 31, the state where the water vapor pressure of the mixed air is lower than the saturated water vapor pressure is maintained, so the mixed air containing the sample atmosphere can be conveyed close to the sensor element 31 while preventing condensation. Thereby, it is possible to suppress the target substance from coming into contact with water and being taken in. As a result, the detection sensitivity of the target substance by the sensor element 31 can be increased.

[0026] The water vapor pressure of the mixed air depends on the temperature and humidity of the specimen atmosphere to be introduced. It is easier to control the water vapor pressure of the mixed air by adjusting the mixing ratio of the specimen atmosphere and the humidified air than by adjusting the temperature and humidity of the humidified air according to the temperature and humidity of the specimen atmosphere. Therefore, it is preferable to provide a first temperature and humidity sensor 71 for measuring the temperature and humidity of the specimen atmosphere, and the control device 50 controls the mixing ratio of the specimen atmosphere and the humidified air in the mixing device 20 based on the measurement values of the first temperature and humidity sensor 71. For example, the control device 50 includes a storage device that stores data on the temperature and humidity of the specimen atmosphere and the corresponding mixing ratio, and can control the mixing ratio obtained by referring to the measurement results of the temperature and humidity in the data.

[0027] Furthermore, by providing a second temperature and humidity sensor 72 for measuring the temperature and humidity of the humidified air, and the control device 50 controlling the mixing ratio of the specimen atmosphere and the humidified air based on the measurement values of the first temperature and humidity sensor 71 and the second temperature and humidity sensor 72, the control accuracy of the water vapor pressure of the mixed air can be improved.

[0028] Furthermore, by further providing a third temperature and humidity sensor 73 for measuring the temperature and humidity of the mixed air before being cooled by the cooling device 40, and the control device 50 feeding back the measurement value of the third temperature and humidity sensor 73 to the control of the mixing ratio of the specimen atmosphere and the humidified air, the control accuracy of the water vapor pressure of the mixed air can be further improved.

[0029] In addition, in order to prevent dew condensation inside the outer container 34, it is preferable to further provide a heating device 80 for heating the chemical sensor device 30. By heating with the heating device 80, the temperature of the chemical sensor device 30 is set to be about 30°C, for example. The heating device 80 heats the chemical sensor device 30 to be higher than the temperature (25°C) of the mixed air cooled by the cooling device 40. Thereby, it is possible to suppress water from adhering to the sensor surface 31a and the sensor element 31 from responding to water.

[0030] Even if condensation occurs inside the outer enclosure 34, as shown in FIG. 1, by arranging the sensor element 31 so that the sensor surface 31a faces the gravitational direction (downward), it is possible to prevent water from adhering to the sensor surface 31a. As shown in FIG. 1, by providing the heating device 80 in the gravitational direction (downward) of the outer enclosure 34, the water generated by condensation can be efficiently evaporated. Further, the heating device 80 may be provided on the side of the outer enclosure 34 where the sensor element 31 is arranged. It is possible to prevent condensation from occurring on the sensor surface 31a.

[0031] When a graphene sensor is used as the sensor element 31, it is preferable to include a fourth pipe 14 through which reference air is conveyed and a switching device 60. Air near the sample atmosphere is taken into the fourth pipe 14 from the second collection port 14a. The first pipe 11, the fourth pipe 14, and the mixing device 20 are connected to the switching device 60. As the switching device 60, for example, a three-way valve can be used. The switching device 60 can switch between a reference phase in which the connection between the first pipe 11 and the mixing device 20 is blocked and the connection between the fourth pipe 14 and the mixing device 20 is established, and a detection phase in which the connection between the fourth pipe 14 and the mixing device 20 is blocked and the connection between the first pipe 11 and the mixing device 20 is established.

[0032] Detection of the target substance in the sample atmosphere becomes possible from the relative change in the electrical characteristics (e.g., current) of the sensor element 31 in the detection phase with respect to the electrical characteristics (e.g., current) of the sensor element 31 in the reference phase.

[0033] When a sensor element that can easily determine the presence or absence of the target substance from the absolute value of electrical characteristics or the like is used as the sensor element, the fourth pipe 14 and the switching device 60 may not be provided. For example, when a sensor element including a metal oxide film on the sensor surface is used, the target substance can be detected from the resistance value or the like of the metal oxide film.

[0034] Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

Explanation of Reference Numerals

[0035] 1…Gas sensor system, 11…First pipe, 12…Second pipe, 13…Third pipe, 14…Fourth pipe, 15…Exhaust pipe, 20…Mixing device, 30…Chemical sensor device, 31…Sensor element, 31a…Sensor surface, 32…Graphene, 33…Probe molecule, 40…Cooling device, 50…Control device, 71…First temperature and humidity sensor, 72…Second temperature and humidity sensor, 73…Third temperature and humidity sensor, 80…Heating device, 90…Humidifying device

Claims

1. A first pipe through which a sample atmosphere is conveyed; A second pipe through which humidified air that is at a higher temperature and higher humidity than the sample atmosphere and has a water vapor pressure lower than the saturated water vapor pressure is conveyed; A mixing device connected to the first pipe and the second pipe, the mixing device mixing the sample atmosphere and the humidified air such that the water vapor pressure of the mixed air of the sample atmosphere and the humidified air is lower than the saturated water vapor pressure; A third pipe connected to the mixing device through which the mixed air is conveyed; A cooling device that cools the mixed air conveyed through the third pipe and makes the water vapor pressure of the mixed air equal to the saturated water vapor pressure; A chemical sensor device connected to the third pipe, the chemical sensor device having a sensor surface to which the mixed air cooled by the cooling device is supplied; A gas sensor system comprising the above.

2. The gas sensor system according to claim 1, wherein the sensor surface contains graphene.

3. The gas sensor system according to claim 2, wherein the sensor surface further contains probe molecules formed on the graphene.

4. A fourth pipe through which reference air is conveyed; A switching device capable of switching between a reference phase that blocks between the first pipe and the mixing device and connects between the fourth pipe and the mixing device, and a detection phase that blocks between the fourth pipe and the mixing device and connects between the first pipe and the mixing device; The gas sensor system according to claim 2, further comprising the above.

5. A first temperature and humidity sensor that measures the temperature and humidity of the sample atmosphere; A control device that controls the mixing ratio of the sample atmosphere and the humidified air in the mixing device based on the measurement value of the first temperature and humidity sensor; The gas sensor system according to any one of claims 1 to 4, further comprising the above.

6. Further comprising a second temperature and humidity sensor that measures the temperature and humidity of the humidified air, The control device controls the mixing ratio based on the measurement value of the second temperature and humidity sensor. The gas sensor system according to claim 5.

7. Further comprising a third temperature and humidity sensor that measures the temperature and humidity of the mixed air before being cooled by the cooling device, The control device controls the mixing ratio based on the measurement value of the third temperature and humidity sensor. The gas sensor system according to claim 5.

8. The gas sensor system according to any one of claims 1 to 4, further comprising a heating device that heats the chemical sensor device.

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