JP2023027408A - Gas sensor and gas detection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor and a gas detection system that can accurately detect a gas.

SOLUTION: The gas sensor has a plurality of detection elements. The detection elements are arranged in a gas passage through which a detection target gas passes. The detection elements includes a sensitive film having a metal organic structure with fine holes for absorbing gases. The detection elements are arranged so that the fine holes become larger from an upstream side to a downstream side along a direction of flow of the detection target gas.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present invention relates to gas sensors and gas detection systems.

For example, Patent Literature 1 discloses an olfactory system using a sensor array provided with a plurality of QCM elements. With this sensor array, it is possible to determine the number of sensors that act specifically on a specific substance molecule, their arrangement, and the types of sensors after arbitrarily designing the reaction pattern in the entire array when they act. be. By storing the reaction pattern in advance in the information storage unit, it is possible to identify an aggregate of a plurality of odor-causing substances by comparing it with the reaction of the sensor array to the odor factor.

WO2016/031080

Gas sensors that detect such gases are desired to detect gases with high sensitivity.

In view of the circumstances as described above, an object of the present invention is to provide a gas sensor and a gas detection system capable of detecting gas with high sensitivity.

In order to achieve the above object, a gas sensor according to one aspect of the present invention comprises a plurality of detection elements.
The detection element is arranged in a gas passage through which a gas to be detected passes.
The detection element includes a sensitive film made of a metal organic structure having pores that adsorb gas.
The plurality of detection elements are arranged in the gas passage so that the pores become larger from the upstream side to the downstream side along the flow direction of the detection target gas.

According to such a configuration of the present invention, since a plurality of detection elements are arranged so that the pores become larger in order from upstream to downstream, gas is detected while molecular sieving is performed according to the pore size. It is possible to detect gas with high sensitivity.

A molecular size of the gas selectively adsorbed by the sensitive film of each of the plurality of detection elements may increase from the upstream side to the downstream side of the gas passage.

A gas detection system according to one aspect of the present invention includes the gas sensor described above and an arithmetic device.
The sensing element causes a resonance frequency change due to adsorption of the gas.
The computing device detects the detection target gas of the detection element based on the change in the resonance frequency of the detection element.

The computing device may determine whether the detection target gas of the detection element is detected or not, depending on whether or not the amount of change in resonance frequency of the detection element is equal to or greater than a set value.

As described above, according to the present invention, gas can be detected with high sensitivity.

1 is a schematic diagram showing the configuration of a gas sensor according to an embodiment of the present invention; FIG. It is a front view of a detection element included in the gas sensor. It is a simulation result using the said gas sensor. It is a flowchart explaining the gas detection method in an arithmetic unit. It is a schematic diagram showing a partial configuration of a gas sensor as a comparative example. It is a simulation result using the gas sensor of a comparative example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1 , the gas detection system 1 includes a gas sensor 2 , an arithmetic device 4 and a display device 5 .

The gas sensor 2 includes an accommodation chamber 20, a first QCM sensor element (hereinafter referred to as first QCM) 10a as a first detection element, and a second QCM sensor element (hereinafter referred to as a second detection element). , referred to as a second QCM) 10b, a third QCM sensor element (hereinafter referred to as a third QCM) 10c as a third detection element, and a fourth QCM sensor element as a fourth detection element (hereinafter referred to as a fourth QCM) 10d, a temperature/humidity sensor 30, a first frequency counter circuit 31a, a second frequency counter circuit 31b, a third frequency counter circuit 31c, and a fourth frequency A counter circuit 31d is provided.

The housing chamber 20 houses the first QCM 10 a , the second QCM 10 b , the third QCM 10 c , the fourth QCM 10 d and the temperature/humidity sensor 30 .
The storage chamber 20 has an intake port 21 for sucking the detection target gas 23 from the outside, and an exhaust port 22 for exhausting the detection target gas 23 introduced into the storage chamber 20 from the storage chamber 20 to the outside. .
The intake port 21, the storage chamber 20, and the exhaust port 22 form a gas passage through which the detection target gas 23 passes. The detection target gas 23 flows from the intake port 21 toward the exhaust port 22 . A plurality of QCMs (first QCM 10a, second QCM 10b, third QCM 10c, and fourth QCM 10d in this embodiment) are arranged along the flow direction of the gas 23 to be detected.

The temperature/humidity sensor 30 detects the temperature and humidity of the atmosphere inside the accommodation room 20 . Temperature and humidity information detected by the temperature/humidity sensor 30 is output to the computing device 4 . Depending on the type of the sensitive film, the detected resonance frequency varies greatly due to changes in ambient temperature or humidity.
Based on the temperature detected by the temperature/humidity sensor 30, the resonance frequency detected by each of the QCMs 10a to 10d may be corrected by the computing device 4 so as to cancel changes in resonance frequency due to temperature and humidity. As a result, it is possible to detect only the resonance frequency change due to adsorption of the gas to be detected, which is not affected by temperature and humidity.
For the temperature/humidity sensor 30, for example, a digital temperature/humidity sensor (model number: SHT21) manufactured by Sensirion can be used.

Each of the first QCM 10a, the second QCM 10b, the third QCM 10c, and the fourth QCM 10d adsorbs a crystal oscillator as an oscillator and a specific gas provided on the crystal oscillator. It has a structure provided with a sensitive film, and the basic structure is the same except that the type of the sensitive film is different. Hereinafter, the first QCM 10a, the second QCM 10b, the third QCM 10c, and the fourth QCM 10d may be referred to as the QCM 10 when there is no particular need to distinguish them.
Similarly, if there is no particular need to distinguish between the first frequency counter circuit 31a, the second frequency counter circuit 31b, the third frequency counter circuit 31c, and the fourth frequency counter circuit 31d, the frequency counter circuit 31 may be described as

As shown in FIG. 2, the QCM 10 includes a crystal oscillator 13, an electrode 11, a sensitive film 12, a lead land 16A, a lead land 16B, a lead 14A, a lead 14B, a pin terminal 19A, and a pin terminal 19B and a holder 18. The crystal oscillator 13 is an AT-cut crystal plate.

Since the resonance frequency of the crystal oscillator 13 of the QCM 10 decreases in proportion to the weight of the gas adsorbed on the sensitive film 12, the amount of change in the resonance frequency is calculated for each crystal oscillator. It is possible to detect whether or not the gas contains a gas that serves as a detection target.

In this embodiment, a crystal oscillator having a resonance frequency of 9 MHz is used as the detection element, but the present invention is not limited to this. For example, ceramic oscillators, surface acoustic wave devices, cantilevers, diaphragms, etc. can be used in addition to crystal oscillators, and detect physical changes such as weight increase and expansion stress increase due to gas adsorption of the sensitive film, and convert them into electrical signals. Applicable wherever possible.

Hereinafter, the sensitive film provided in the first QCM 10a is referred to as the first sensitive film 12a, the sensitive film provided in the second QCM 10b is referred to as the second sensitive film 12b, and the sensitive film provided in the third QCM 10c is referred to as the third The sensitive film provided in the fourth QCM 10d is called the fourth sensitive film 12d.

The electrodes 11 are formed on both surfaces of the crystal oscillator 13 , and the sensitive film 12 is formed on the electrode 11 formed on one surface of the crystal oscillator 13 . The lead land 16A is integrally formed with the electrode 11 formed on one surface, and the lead land 16B is integrally formed with the electrode 11 formed on the other surface.

The leads 14A and 14B are made of a metal spring material and arranged parallel to each other.
One end of the lead 14A is electrically connected to the electrode 11 formed on one surface through the lead land 16A, and the other end is connected to the pin terminal 19A. One end of the lead 14B is electrically connected to the electrode 11 formed on the other surface through the lead land 16B, and the other end is connected to the pin terminal 19B.

The pin terminals 19A and 19B are supported by a holder 18 provided on the substrate, and the crystal oscillator 13 is supported by the holder 18 so as to freely vibrate.

Pin terminals 19A and 19B of the QCM 10a (10b, 10c, 10d) are connected to an oscillation circuit (not shown), and a driving voltage is applied to the QCM 10a (10b, 10c, 10d). When the drive voltage is applied to the QCM 10a (10b, 10c, 10d), the crystal oscillator 13 oscillates at its own resonance frequency (9 MHz in this example).

As the sensitive film 12 adsorbs gas, the mass changes, and the oscillation frequency of the crystal oscillator 13 decreases according to the amount of gas adsorbed. In this manner, the QCM 10 performs gas detection using weight changes due to gas adsorption as frequency changes. Also, the gas concentration can be quantified according to the amount of change in frequency.
The first QCM 10a, the second QCM 10b, the third QCM 10c, and the fourth QCM 10d are respectively a first frequency counter circuit 31a, a second frequency counter circuit 31b, and a third frequency counter, which are resonance frequency measurement units. The circuit 31c is connected to the fourth frequency counter circuit 31d.

The first frequency counter circuit 31a (the second frequency counter circuit 31b, the third frequency counter circuit 31c, the fourth frequency counter circuit 31d) operates on the first QCM 10a (the second QCM 10b, the third QCM 10c, the 4 QCM 10d), the resonance frequency of the first sensitive film 12a (second sensitive film 12b, third sensitive film 12c, fourth sensitive film 12d) is measured. The electrical signals of the resonance frequencies measured by the frequency counter circuits 31a to 31d are output to the computing device 4. FIG.

The sensitive film 12 is made of a porous metal organic framework (MOF). A metal-organic framework has a three-dimensional structure formed by bonding an organic ligand and a metal ion, and has a plurality of pores.
The metal-organic framework captures the gas to be detected through physical bonding.
The pore diameter (pore size) and polarity of the sensitive film composed of the metal-organic structure can be set arbitrarily depending on the types of the constituent metal ions and organic ligands and the functional groups to be modified. By using the metal-organic structure as the sensitive film in this way, the design range of the sensitive film is widened.

In this embodiment, the type of gas that is selectively adsorbed on the sensitive film 12 is controlled by the type of metal organic structure, and the molecular size of the gas that is adsorbed on the sensitive film 12 is adjusted by adjusting the pore size. controlled.

The sensitive film 12 is coated on the electrode 11 by a known coating method such as dipping, spinning, or spraying.

The first sensitive film 12a, the second sensitive film 12b, the third sensitive film 12c, and the fourth sensitive film 12d are each made of a different kind of metal organic structure, and the pore size of each sensitive film is is different.

In this embodiment, the first sensitive film 12a is a sensitive film containing Ti ⁴⁺ as a metal ion and 1,4-benzenedicarboxylic acid as an organic ligand, and has a pore diameter of 60 nm.
The second sensitive film 12b is a sensitive film containing Zr ⁴⁺ as the metal ion and 1,4-benzenedicarboxylic acid as the organic ligand, and has a pore diameter of 75 nm.
The third sensitive film 12c is a sensitive film containing Ni ²⁺ as metal ions and 1,4-benzenedicarboxylic acid as an organic ligand, and has a pore diameter of 100 nm.
The fourth sensitive film 12d has Zr ⁴⁺ as the metal ion and biphenyl-4,4′-dicarboxylic acid as the organic ligand, and has a pore diameter of 120 nm.
The four QCMs 10a to 10d are arranged in the gas passage so that the pores gradually become larger from the upstream side to the downstream side along the flow direction of the gas 23 to be detected.
The specific material and pore size of the sensitive membrane of each QCM are not limited to these, and each sensitive membrane may be configured so that the pore size gradually increases from the upstream side to the downstream side in the gas passage. .

The first QCM 10a includes a first sensitive membrane 12a having a plurality of pores with a pore diameter of 60 nm, and detects gas with a molecular diameter of 60 nm or less.
In this embodiment, the first QCM 10a has, for example, ammonia as a first gas as a detection target, and has a first sensitive film 12a that more selectively adsorbs ammonia. Ammonia has a molecular diameter of 38 nm.

The second QCM 10b includes a second sensitive membrane 12b having a plurality of pores with a pore diameter of 75 nm, and detects gas with a molecular diameter of 60 nm or less.
The second QCM 10b has, for example, toluene as a second gas as a detection target, and has a second sensitive film 12b that more selectively adsorbs toluene. The molecular diameter of toluene is 70 nm.
Since the second QCM 10b is located downstream of the first QCM 10a, among the detection target gases introduced into the storage chamber 20, the gas that is not adsorbed by the first sensitive film 12a, It adsorbs gases with a molecular diameter of 60 nm or less.

The third QCM 10c includes a third sensitive membrane 12c having a plurality of pores with a pore diameter of 100 nm, and detects gas with a molecular diameter of 100 nm or less.
The third QCM 10c uses, for example, tributylamine as a third gas as a detection target, and has a third sensitive film 12c that more selectively adsorbs tributylamine. The molecular diameter of tributylamine is 81 nm.
Since the third QCM 10c is located downstream of the first QCM 10a and the second QCM 10b, the first sensitive film 12a and the second sensitive It adsorbs gas that is not adsorbed by the film 12b and has a molecular diameter of 100 nm or less.

The fourth QCM 10d includes a fourth sensitive membrane 12d having a plurality of pores with a pore diameter of 120 nm, and detects gas with a molecular diameter of 120 nm or less.
The fourth QCM 10d uses, for example, trifluorobutylamine as a fourth gas as a detection target, and has a fourth sensitive film 12d that more selectively adsorbs trifluorobutylamine. The molecular diameter of tributylamine is 100 nm.
Since the fourth QCM 10d is located downstream of the first QCM 10a, the second QCM 10b, and the third QCM 10c, the first sensitive film 12a , which are not adsorbed by the second sensitive film 12b and the third sensitive film 12c and have a molecular diameter of 120 nm or less.
Thus, the molecular size of the detection target gas of each QCM increases in order from the upstream side to the downstream side in the flow direction of the gas to be detected.

In this embodiment, since a plurality of QCMs are arranged so that the pores become larger in order from the upstream side to the downstream side in the flow direction of the detection target gas, the gas is detected while applying molecular sieving according to the pore size It is possible to detect gas with high sensitivity.

FIG. 3 shows a simulation result of detection of gas by the gas sensor 2 of the present embodiment shown in FIG. 1, using a mixed gas of ammonia, toluene, tributylamine, and trifluorobutylamine as the gas to be detected.

FIG. 5 is a schematic diagram showing a partial configuration of a gas sensor 102 as a comparative example. FIG. 6 shows a simulation result of using a mixed gas of ammonia, toluene, tributylamine, and trifluorobutylamine as the gas to be detected and detecting the gas with the gas sensor 102 shown in FIG. In addition, in FIG. 5, the same symbols are attached to the same configurations as those of the gas sensor 2,
Description is omitted.

As shown in FIG. 5, in the gas sensor 102 of the comparative example, a plurality of QCMs 10a to 10d and a temperature/humidity sensor 30 are arranged in the housing chamber 120, like the gas sensor 2. FIG. The gas sensor 102 differs from the gas sensor 2 in that the positions of the intake port 121 and the exhaust port 122 are different.
Accordingly, in the gas sensor 102 of the comparative example, as shown in FIG. 5, a plurality of QCMs 10 are arranged in parallel with respect to the flow direction of the detected gas. On the other hand, in the gas sensor 2 of this embodiment, as shown in FIG. 1, a plurality of QCMs 10 are arranged in series along the flow direction of the gas to be detected.

As shown in FIG. 5, in the gas sensor 102 of the comparative example, since a plurality of QCMs 10a to 10d are arranged in parallel with respect to the flow direction of the gas to be detected, the gas to be detected similarly reaches all of the QCMs 10.
Therefore, as shown in FIG. 6, any QCM 10 detects four kinds of gases: ammonia, toluene, tributylamine, and trifluorobutylamine. For example, the first QCM 10a detects more ammonia than the other QCMs, but the difference is not large. Similarly, the second QCM 10b detects more toluene than the other QCMs, but the difference is not large. The third QCM 10c detects more tributylamine than the other QCMs, but the difference is not large. The fourth QCM 10d detects more trifluorobutylamine than the other QCMs, but the difference is not large.
As described above, in the gas sensor 102 in which a plurality of QCMs 10a to 10d are arranged in parallel, the gas to be detected reaches each QCM without molecular sieving, resulting in decreased detection sensitivity and gas identification accuracy.

On the other hand, in the gas sensor 2 of the present embodiment, the QCMs 10a to 10d are arranged in series so that the pore size of the sensitive membrane 12 gradually increases from the upstream side to the downstream side along the flow direction of the detection target gas. is placed. As a result, among the gases to be detected, molecules are adsorbed by the respective sensitive membranes 12 in ascending order of size. be adsorbed. In this manner, the gas sensor 2 separates gas molecules in order from the smallest size while passing through the molecular sieve, and can detect the gas molecules in order from the smallest size. In this way, by detecting the gas while applying the molecular sieve, the gas that is the detection target of each QCM efficiently reaches the corresponding QCM, so that the gas can be detected with high sensitivity. , the accuracy of gas identification is improved.

For example, as shown in FIG. 3, the first QCM 10a detects ammonia with approximately four times more sensitivity than the other QCMs. Similarly, the second QCM 10b detects toluene approximately three times more sensitive than the other QCMs. A third QCM 10c detects tributylamine approximately three times more sensitive than the other QCMs. A fourth QCM 10d detects trifluorobutylamine approximately four times more sensitive than the other QCMs.
In this way, the gas sensor 2 in which a plurality of QCMs 10a to 10d are arranged in series has improved detection sensitivity and odor discrimination accuracy.

Arithmetic device 4 includes acquisition unit 41 , determination unit 42 , and output unit 43 .

The acquisition unit 41 obtains the electric signal of the resonance frequency of the first QCM 10a, the electric signal of the resonance frequency of the second QCM 10b, the electric signal of the resonance frequency of the third QCM 10d, the electric signal of the resonance frequency of the third QCM 10d, and the electric signal of the resonance frequency of the third QCM 10d. 4, and the temperature and humidity information detected by the temperature and humidity sensor 30 are acquired.

The determination unit 42 calculates the frequency change amount of each QCM 10a to 10d based on the electric signal of the resonance frequency of each QCM 10a to 10d and the information on temperature and humidity acquired by the acquisition unit 41, ammonia, toluene, tributylamine , trifluorobutylamine, and each gas is detected or not detected. Gas detection and identification are thereby performed. Also, the determination unit 42 can perform quantitative analysis of the gas based on the amount of frequency change.

The output unit 43 outputs the resonance frequencies of the QCMs 10 a to 10 d acquired by the acquisition unit 41 and the identification result and quantitative analysis result of the detected gas determined by the determination unit 42 to the display device 5 .
In this manner, the arithmetic device 4 identifies the detected gas and measures the gas concentration.

The display device 5 has a display section, and displays the identification result of the detected gas, the gas concentration, etc. output from the arithmetic device 4 on the display section. The user can grasp the gas detection result by checking the display unit.

Next, the gas detection method performed by the arithmetic device 4 will be described with reference to the flowchart of FIG.

As shown in FIG. 4, the obtaining unit 41 obtains electric signals of resonance frequencies of the QCMs 10a to 10d detected by the frequency counter circuits 31a to 31d (St1).

Next, the determination unit 42 calculates the frequency change amount of each of the QCMs 10a to 10d based on the electrical signal acquired by the acquisition unit 41, and the frequency change amount is equal to or greater than a preset value for each of the QCMs 10a to 10d. It is determined whether or not (St2).

Next, the determination unit 42 determines that the gas of the detection target of the QCM 10 is detected when the frequency change amount is equal to or greater than the set value (St3), and determines that the gas is not detected when the amount is less than the set value. (St4).
This determination is made individually for each of the QCMs 10a-10d.

For example, when the frequency change amount in the first QCM 10a is greater than or equal to the set value, it is determined that ammonia, which is the detection target gas of the first QCM 10a, is detected in the detection target gas 23, and is less than the set value. In this case, ammonia is determined to be undetected.
Similarly, when the amount of frequency change in the second QCM 10b is equal to or greater than the set value, it is determined that ammonia toluene, which is the detection target gas of the second QCM 10b, has been detected in the detection target gas 23, and less than the set value. , toluene is determined to be undetected.
If the amount of frequency change in the third QCM 10c is greater than or equal to the set value, it is determined that tributylamine, which is the detection target gas of the third QCM 10c, is detected in the detection target gas 23, and if it is less than the set value , tributylamine was determined to be undetected.
When the amount of frequency change in the fourth QCM 10d is equal to or greater than the set value, it is determined that trifluorobutylamine, which is the detection target gas of the fourth QCM 10d, is detected in the detection target gas 23, and is less than the set value. trifluorobutylamine is determined not to be detected.

The adsorption mechanism of each QCM 10 is based on physical adsorption, and calibration can be performed by flowing clean air into the storage chamber 20 after the detection process is completed. Alternatively, calibration may be performed by heating.

As described above, in this embodiment, it is possible to detect gas with high sensitivity.

Of course, the present invention is not limited to the above-described embodiments, and can be modified in various ways.
For example, in the above-described embodiments, the case where four QCMs are used as a plurality of detection elements has been described, but the number of detection elements may be two or more. Also, by increasing the number of detection elements, more types of gases can be identified.

Further, in the above-described embodiment, an example is given in which whether or not gas is detected is determined based on whether or not the amount of change in frequency of each QCM is equal to or greater than a set value, but the present invention is not limited to this. For example, the detection data in each QCM for each type of gas is stored in advance in a database, and the detection data stored in advance and the detection data actually acquired by the gas sensor 2 are collated to determine the type and concentration of the detected gas. may be determined.

In the above-described embodiments, the QCM that detects the frequency change due to gas adsorption was described as an example of the detection element, but it is not limited to this. It may be a semiconductor system that detects changes in electrical characteristics by means of a sensor.

2... Gas sensor 4... Computing device 10a... First QCM (detection element)
10b... Second QCM (detection element)
10c... Third QCM (detection element)
10d... Fourth QCM (detection element)
12a... First sensitive film (sensitive film)
12b... Second sensitive film (sensitive film)
12c... Third sensitive film (sensitive film)
12d... Fourth sensitive film (sensitive film)
13a... First oscillator (oscillator)
13b... Second oscillator (oscillator)
13c... Third oscillator (oscillator)
13d... Fourth oscillator (oscillator)

Claims (4)

comprising a plurality of detection elements arranged in a gas passage through which the gas to be detected passes;
The detection element includes a sensitive film having a metal organic structure having pores that adsorb gas,
The plurality of detection elements are arranged in the gas passage so that the pores become larger from the upstream side to the downstream side along the flow direction of the gas to be detected. The gas sensor according to claim 1,
The gas sensor, wherein the molecular size of the gas selectively adsorbed by the sensitive film of each of the plurality of detection elements increases from the upstream side to the downstream side of the gas passage. a gas sensor according to claim 1 or claim 2;
A gas detection system comprising: a computing device for detecting a detection target gas of the detection element based on the resonance frequency change of the detection element, the detection element generating a resonance frequency change due to adsorption of the gas. The gas detection system of claim 3, wherein
The arithmetic unit determines whether the detection target gas of the detection element is detected or not, depending on whether or not the amount of change in resonance frequency of the detection element is equal to or greater than a set value.

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