A waveguide gas sensor based on a porous gas-sensitive carrier

Abstract

The present invention discloses a waveguide gas sensor based on a porous gas-sensitive carrier, comprising: a first housing having an axially penetrating waveguide cavity; a second housing having an axially penetrating waveguide cavity, the second housing being coaxially arranged with the first housing; wherein, an air inlet hole is formed in the second housing, and the air inlet hole communicates with the waveguide cavity of the second housing; an air inlet pipe is connected to the air inlet hole; a resonance chip, which is clamped between the first housing and the second housing, and the edge of the resonance chip is fixedly connected to one end of the first housing and one end of the second housing at the same time; wherein, a long strip-shaped through hole is formed in the center of the resonance chip; a porous gas-sensitive carrier, which is fixedly arranged in the long strip-shaped through hole; wherein, the porous gas-sensitive carrier has a three-dimensional interactive pore structure and can adsorb gas; two wave-to-same converters, which are respectively fixedly connected to the other end of the first housing and the other end of the second housing; ports are respectively arranged on the two wave-to-same converters for connecting a vector network analyzer.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave gas sensors, and particularly relates to a waveguide gas sensor based on a porous gas-sensitive carrier. Background Art

[0002] Currently, most microwave gas sensors use planar circuits, which have the advantages of small size, simple processing, and low cost. However, in planar circuits, powdered sensitive materials are usually coated on sensitive areas, and an air chamber needs to be built during the testing process of planar circuit microwave gas sensing, making the testing process relatively complex. Moreover, the electric and magnetic fields in planar circuits often intertwine, and most measure the change in dielectric properties after the material adsorbs gas. The quality factor and electromagnetic field strength are restricted by the planar circuit structure.

[0003] Currently, waveguide structure sensors are mainly used for non-destructive testing and imaging of objects, surface crack detection, thickness detection, humidity detection, and dielectric constant detection. In the field of gas sensors, there are relatively many related studies on optical waveguide gas sensors. Although the currently used optical waveguide gas sensing has high sensitivity and rapid response, the optical waveguide testing system is relatively complex, the instrument price and processing cost are relatively expensive, and it is easily affected in an environment where light propagation is restricted. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the prior art and provide a waveguide gas sensor based on a porous gas-sensitive carrier, which places the porous gas-sensitive carrier in a waveguide cavity and can realize the detection of different gases, with the characteristics of high sensitivity, low detection limit, and wide detection range.

[0005] The technical solution provided by the present invention is as follows:

[0006] A waveguide gas sensor based on a porous gas-sensitive carrier, comprising:

[0007] A first housing having an axially through waveguide cavity;

[0008] A second housing having an axially through waveguide cavity, and the second housing is coaxially arranged with the first housing;

[0009] Wherein, an air inlet hole is opened on the second housing, and the air inlet hole is communicated with the waveguide cavity of the second housing; an air inlet pipe is connected to the air inlet hole;

[0010] A resonant chip, which is clamped between the first housing and the second housing, and the edge of the resonant chip is fixedly connected to one end of the first housing and one end of the second housing at the same time;

[0011] Wherein, a long strip through hole is opened at the center of the resonant chip;

[0012] A porous gas-sensing carrier, which is fixedly arranged in the long strip-shaped through hole;

[0013] Wherein, the porous gas-sensing carrier has a three-dimensional interactive pore structure and can adsorb gas;

[0014] Two wave converters, which are respectively fixedly connected to the other end of the first housing and the other end of the second housing;

[0015] Wherein, ports are respectively arranged on the two wave converters for connecting a vector network analyzer.

[0016] Preferably, the shapes and sizes of the first housing and the second housing are the same.

[0017] Preferably, the center of the porous gas-sensing carrier coincides with the center position of the long strip-shaped through hole.

[0018] Preferably, the porous gas-sensing carrier is a cylinder, and the porous gas-sensing carrier is fixed in the long strip-shaped through hole by an interference fit method.

[0019] Preferably, the porous gas-sensing carrier is a cylinder, and the maximum cross-sectional size of the porous gas-sensing carrier is smaller than the size of the long strip-shaped through hole, and the porous gas-sensing carrier is fixed in the long strip-shaped through hole by an adhesive method.

[0020] Preferably, the porous gas-sensing carrier is made of zeolite material, organic polymer material, organic-inorganic hybrid material or gel material.

[0021] Preferably, the materials of the first housing and the second housing are aluminum.

[0022] Preferably, the material of the resonant chip is copper.

[0023] Preferably, when the detected gas is ammonia, the porous gas carrier is an In2O3 / Al2O3 cylinder.

[0024] Preferably, the preparation method of the porous gas carrier being an In2O3 / Al2O3 cylinder is as follows:

[0025] Under ice bath conditions, dissolve PEO in ethanol, and then sequentially add deionized water and AlCl3·6H2O and stir to dissolve to obtain a first solution;

[0026] Keep the ice bath conditions unchanged, add PO to the first solution to make the solution layer; stir to make the layering phenomenon disappear to obtain a uniform and transparent sol;

[0027] Pour the sol into a centrifuge tube and seal it, and then place the centrifuge tube in a 40°C water bath to convert the sol into a gel;

[0028] After aging and drying the gel, it is calcined at 800 °C for 2 h to obtain an Al2O3 monolithic material;

[0029] InCl3·4H2O, sodium dodecyl sulfate and urea are added to deionized water, and then the Al2O3 monolithic material is added. After stirring, the mixture is transferred to a reaction kettle and heated at 120 °C for 12 h. The obtained sample is calcined at 500 °C to obtain an In2O3 / Al2O3 bulk;

[0030] The In2O3 / Al2O3 bulk is cut to obtain an In2O3 / Al2O3 cylinder.

[0031] The beneficial effects of the present invention are as follows:

[0032] The waveguide gas sensor based on a porous gas-sensitive carrier provided by the present invention has a simple structure, and has the characteristics of high sensitivity, low detection limit and wide detection range, and can be used for gas sensing instead of an optical waveguide with a complex system and high price.

[0033] For the waveguide gas sensor based on a porous gas-sensitive carrier provided by the present invention, the porous gas-sensitive carrier is placed in the waveguide cavity, and there is no need to coat the sensitive material by means of deposition such as coating, which greatly improves the reconfigurability of the sensor; the three-dimensional structure of the waveguide cavity itself can provide a closed atmosphere environment, and there is no need to build a gas chamber during the test process, further simplifying the test system; for different target gases, only the specific sensitive material needs to be replaced to realize the detection of different gases. Brief Description of the Drawings

[0034] Figure 1 It is a schematic diagram of the overall structure of the waveguide gas sensor based on a porous gas-sensitive carrier according to the present invention.

[0035] Figure 2 It is a top view of the waveguide gas sensor based on a porous gas-sensitive carrier according to the present invention.

[0036] Figure 3 It is a front view of the waveguide gas sensor based on a porous gas-sensitive carrier according to the present invention.

[0037] Figure 4 It is a left view of the waveguide gas sensor based on a porous gas-sensitive carrier according to the present invention.

[0038] Figure 5 It is a schematic diagram of the combined structure of the resonator plate and the porous gas-sensitive carrier according to the present invention.

[0039] Figure 6 It is an XRD pattern of the Al2O3 monolithic material and the In2O3 / Al2O3 monolithic composite material prepared in the embodiment of the present invention.

[0040] Figure 7 This is the elemental distribution map of the In2O3 / Al2O3 monolithic composite material prepared in the embodiment of the present invention.

[0041] Figure 8 This is the SEM image of the In2O3 / Al2O3 monolithic composite material prepared in the embodiment of the present invention.

[0042] Figure 9 This is the gas sensing performance graph of ammonia by the gas sensor in the embodiment of the present invention. Detailed implementation manners

[0043] The following further elaborates on the present invention in conjunction with the accompanying drawings, enabling those skilled in the art to implement it with reference to the text of the specification.

[0044] As Figures 1-5 shown, the present invention provides a waveguide gas sensor based on a porous gas sensing carrier, which includes: a first housing 110, a second housing 120, a resonator chip 130, a waveguide-to-coaxial converter 140, and a porous gas sensing carrier 150.

[0045] The first housing 110 has an axially penetrating waveguide cavity; the second housing 120 has an axially penetrating waveguide cavity 121, and the second housing 120 is coaxially arranged with the first housing 110. Among them, an air inlet hole 122 is opened on the second housing 120, and the air inlet hole 122 communicates with the waveguide cavity 121 of the second housing 120; an air inlet pipe 123 is connected to the air inlet hole 122. The resonator chip 130 is clamped between the first housing 110 and the second housing 120, and the edge of the resonator chip 130 is fixedly connected to one end of the first housing 110 and one end of the second housing 120 (the end opposite to the first housing 110) at the same time. A long strip-shaped through hole 131 is opened at the center of the resonator chip 130; the porous gas sensing carrier 150 is fixedly arranged in the long strip-shaped through hole 131. When the porous gas sensing carrier 150 is not installed, the second housing 120 communicates with the first housing 110 through the long strip-shaped through hole 131. Among them, the porous gas sensing carrier 150 has a three-dimensional interactive pore structure and can adsorb gas. Two waveguide-to-coaxial converters 140 are respectively fixedly connected to the other end of the first housing 110 and the other end of the second housing 120, blocking the ports of the first housing 110 and the second housing 120, so as to form a closed cavity inside the whole device. Among them, ports 141 are respectively arranged on the two waveguide-to-coaxial converters 140 for connecting a vector network analyzer. The vector network analyzer collects the dielectric constant and connects to a computer to save data, and the waveguide-to-coaxial converters at both ends are the transitions of coaxial waveguides.

[0046] In one embodiment, the cross-sections of the waveguide cavities of the first housing 110 and the second housing 120 are both rectangular. In other embodiments, a cylindrical waveguide cavity or a waveguide cavity of other shapes can also be used.

[0047] As a preference, the shapes and dimensions of the first housing 110 and the second housing 120 are the same to ensure that the long rectangular through-hole 131 on the resonance chip 130 is located at the center of the entire waveguide cavity formed by the connection of the first housing 110 and the second housing 120.

[0048] In one embodiment, the materials of the first housing 110 and the second housing 120 are both aluminum without coating. The conductive metal housing does not absorb electromagnetic waves but only reflects them. At the air inlet hole 122, hot melt adhesive is used to connect with the air inlet pipe 123 to ensure its airtightness. The air inlet pipe 123 is a glass tube, and a rubber hose is connected to the end of the air inlet pipe 123. The material of the resonance chip 130 is copper. The ports 141 of the waveguide-to-coaxial converter 140 are respectively connected to a vector network analyzer through coaxial cables to perform real-time testing on the microwave signals transmitted in the waveguide cavity. Among them, both ends of the first housing 110 and the second housing 120 have flange structures, and the waveguide-to-coaxial converter 140 is also provided with a flange structure. The flange of the first housing 110, the flange of the second housing 120 are respectively connected to the flange of the waveguide-to-coaxial converter 140 through bolts; at the same time, through-holes corresponding to the flanges of the first housing 110 and the second housing 120 are provided near the periphery of the resonance chip 130, and the connection between the flanges of the first housing 110 and the second housing 120 and the resonance chip 130 is realized through bolts.

[0049] In one embodiment, the porous gas-sensing carrier 150 is a column, which can be a prism or a cylinder; and the porous gas-sensing carrier is fixed in the long rectangular through-hole 131 by an interference fit method.

[0050] In another embodiment, the porous gas-sensing carrier 150 is a column, which can be a prism or a cylinder; and the maximum cross-sectional dimension of the porous gas-sensing carrier 150 is smaller than the dimension of the long rectangular through-hole, and the porous gas-sensing carrier is fixed in the long rectangular through-hole 131 by an adhesive method.

[0051] As a preference, the center of the porous gas-sensing carrier 150 coincides with the center position of the long rectangular through-hole 131 to ensure that the porous gas-sensing carrier 150 is located at the center of the entire waveguide cavity. Since the sensitive area of the waveguide cavity is concentrated at the center of the cavity, setting the porous gas-sensing carrier at the center of the entire waveguide cavity can further improve the sensitivity of gas detection.

[0052] Such as Figure 5As shown, in one embodiment, the porous gas-sensitive carrier 150 is a cylinder. The height of the cylinder is the same as the height of the elongated through-hole 131. The axis of the porous gas-sensitive carrier 150 is perpendicular to the axis direction of the elongated through-hole 131, and the center of the porous gas-sensitive carrier 150 coincides with the center position of the elongated through-hole 131. At this time, the porous gas-sensitive carrier 150 is fixed and clamped in the elongated through-hole 131 because its upper and lower ends abut against the frame of the elongated through-hole 131.

[0053] The porous gas-sensitive carrier 150 can be made of zeolite monolithic materials such as silica zeolite monolithic columns, Fe-ZSM-5 monolithic materials, MFI zeolite monolithic materials; organic polymer monolithic columns such as polyacrylamide monolithic columns, polystyrene monolithic columns, polymethacrylate monolithic columns, etc.; organic-inorganic hybrid monolithic columns such as carbon nanotube organic polymer monolithic columns, graphene oxide organic polymer monolithic columns, etc.; gel monolithic materials such as In2O3, SiO2, WO3, CuFe2O4, etc.; carbon monoliths, metal oxide monoliths, molecular sieve monolithic materials prepared based on 3D printing technology, etc.

[0054] In actual use, for different target gases, only the specific sensitive material needs to be replaced to achieve the detection of different gases.

[0055] The waveguide gas sensor provided by the present invention, with a three-dimensional structure having a waveguide cavity inside, can transmit TE mode and TM mode, can well separate the electric field concentration region and the magnetic field concentration region, making the quality factor of the circuit much higher than that of a planar circuit, and greatly improving the sensitivity of the microwave sensor. The three-dimensional structure of the waveguide cavity in the present invention itself can provide a closed atmosphere environment. Only the porous gas-sensitive carrier needs to be placed in the waveguide cavity, and there is no need to build a gas chamber during the test process, further simplifying the test system. The hierarchical porous structure of the porous gas-sensitive carrier is beneficial to gas adsorption, can broaden the detection range of the sensor. At the same time, the hierarchical porous structure of the porous gas-sensitive carrier is beneficial to the deposition of metal oxides, avoiding the aggregation of metal oxide nanoparticles. The deposited metal oxides increase the active sites for gas reaction, and can further improve the sensitivity of the sensor.

[0056] Embodiment

[0057] In this embodiment, the gas to be detected is ammonia, and the volume of the waveguide cavity in the device is 1.3L; the porous gas carrier is an In2O3 / Al2O3 column.

[0058] The preparation method of the porous gas carrier being an In2O3 / Al2O3 column is as follows:

[0059] (1) Preparation of the Al2O3 monolithic column

[0060] Under ice bath conditions, 0.9 g of PEO (polyethylene oxide) was continuously stirred and dissolved in 43.5 g of ethanol, and then 40 g of deionized water was added to the above solution under stirring; 43.2 g of AlCl3·6H2O was dissolved in the above mixed solution; while keeping the ice bath unchanged, 31.3 g of PO (propylene oxide) was added to the above solution to cause the solution to layer; after increasing the stirring intensity, the layering phenomenon disappeared, and the system presented a uniform and transparent sol; the sol was poured into a 10 ml centrifuge tube and sealed; the centrifuge tube was placed in a 40 °C water bath, and after 15 min, the sol turned into a gel; after aging for 24 h, the gel became a wet gel, and the wet gel was dried at 40 °C for 7 days; calcined at 800 °C for 2 h to obtain an Al2O3 monolith column.

[0061] (2) Preparation of In2O3 / Al2O3 monolith column

[0062] 0.9 mmol of InCl3·4H2O (0.2639 g), 2.8 mmol of sodium dodecyl sulfate, and 4.7 mmol of urea were added to 80 mL of deionized water, and then 0.1 g of the Al2O3 monolith column was added. After strong magnetic stirring for 1 h, the mixture was transferred to a 100 ml autoclave and heated at 120 °C for 12 h. After cooling to room temperature, it was washed alternately with deionized water and absolute ethanol for several times. The obtained product was dried at 60 °C for 12 h to obtain the In(OH)3 / Al2O3 monolith column precursor. The obtained sample was calcined at 500 °C for 2 h with a heating rate of 2 °C / min, and In(OH)3 was converted to In2O3 to obtain the In2O3 / Al2O3 monolith column. By cutting, an In2O3 / Al2O3 column with a suitable size was obtained.

[0063] Figure 6 The XRD patterns of the pure Al2O3 monolith column and the In2O3 / Al2O3 monolith column are shown. The absence of characteristic crystalline peaks in the XRD pattern indicates its amorphous structure. The increase in the peak intensity of the In2O3 / Al2O3 monolith column after calcination at 500 °C indicates an increase in crystallinity. The absence of the In2O3 peak was observed because the content of In2O3 was low. Figure 7 The energy-dispersive X-ray spectroscopy (EDS) images of the hierarchical porous In2O3 / Al2O3 monolithic material are given in. Elemental mapping shows that the signals of In, Al, and O elements are evenly covered on the entire microstructure of the Al2O3 3 / monolithic material, indicating that In2O3 is uniformly decorated in the hierarchical porous Al2O3 monolithic material structure. It can also be seen from this that the content of In element is low, which is consistent with the XRD analysis results.

[0064] SEM was used to characterize the morphology and structure of the samples, as Figure 8As shown, the In2O3 / Al2O3 monolithic column forms a mutually connected hierarchical porous structure, which can enhance gas adsorption sites, accelerate the diffusion of gas molecules inside the sensing material, and improve the gas-sensing performance of the sensor.

[0065] Place the porous gas carrier 150 (In2O3 / Al2O3 column) in the long strip through-hole 131 of the resonator chip (as Figure 5 shown), assemble the waveguide gas sensor, and test the response to ammonia. Figure 9 Figure shows the response curve of the In2O3 / Al2O3 monolithic column sensor to 0 - 10 ppm NH3 at room temperature. As Figure 9 shown, the response increases with the increase in ammonia concentration. As the adsorption amount of gas molecules by the monolithic column with the hierarchical porous structure increases, the response of the sensor increases rapidly when exposed to low-concentration ammonia, while at high concentrations, the response curve changes slowly and tends to saturate due to the accumulation of gas molecules. It can be seen from the test results that the In2O3 / Al2O3 monolithic column has a lower detection limit (10 ppb) and a higher sensitivity (0.1206 dB / ppb).

[0066] Compare the test results of the ammonia sensor prepared in this embodiment with those of the planar circuit ammonia sensor in the prior art. The results are shown in Table 1.

[0067] Table 1 Comparison between the sensor in this embodiment and the planar circuit ammonia sensor

[0068]

[0069]

[0070] It can be seen from the comparison results in Table 1 that the ammonia sensor adopted in this embodiment has significantly lower detection limits and higher sensitivities compared to the planar circuit coated with the sensitive material. Due to the saturation of the porous gas-sensing carrier (sensitive material) in this embodiment, the detection ability at high concentrations is limited. If the amount of the porous gas-sensing carrier (sensitive material) is increased (only 0.1 g in this embodiment), high-concentration detection can also be achieved. This shows that the microwave gas sensor using the waveguide resonator structure and the hierarchical porous monolithic material provided by the present invention has great advantages.

[0071] Although the embodiments of the present invention have been disclosed as above, they are not limited to only the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details and the examples shown and described herein.

Claims

1. A waveguide gas sensor based on a porous gas-sensitive carrier, characterized in that, Comprising: A first housing having an axially penetrating waveguide cavity; A second housing having an axially penetrating waveguide cavity, the second housing being coaxially arranged with the first housing; Wherein, an air inlet hole is provided on the second housing, and the air inlet hole communicates with the waveguide cavity of the second housing; an air inlet pipe is connected to the air inlet hole; A resonant chip, which is clamped between the first housing and the second housing, and the edge of the resonant chip is fixedly connected to one end of the first housing and one end of the second housing at the same time; Wherein, a long strip-shaped through hole is provided at the center of the resonant chip; A porous gas-sensitive carrier, which is fixedly arranged in the long strip-shaped through hole; Wherein, the porous gas-sensitive carrier has a three-dimensional interactive pore structure and can adsorb gas; Two wave-to-common converters, which are respectively fixedly connected to the other ends of the first housing and the second housing; Wherein, ports are respectively provided on the two wave-to-common converters for connecting a vector network analyzer.

2. The waveguide gas sensor based on a porous gas-sensitive support according to claim 1, characterized in that, The shapes and sizes of the first housing and the second housing are the same.

3. The waveguide gas sensor based on a porous gas-sensitive support according to claim 2, wherein The center of the porous gas-sensitive carrier coincides with the center position of the long strip-shaped through hole.

4. The waveguide gas sensor based on a porous gas-sensitive support according to claim 3, characterized in that, The porous gas-sensitive carrier is a cylinder, and the porous gas-sensitive carrier is fixed in the long strip-shaped through hole by an interference fit method.

5. The waveguide gas sensor based on a porous gas-sensitive carrier according to claim 3, characterized in that, The porous gas-sensitive carrier is a cylinder, and the maximum cross-sectional dimension of the porous gas-sensitive carrier is smaller than the dimension of the long strip-shaped through hole, and the porous gas-sensitive carrier is fixed in the long strip-shaped through hole by an adhesive method.

6. The waveguide gas sensor based on a porous gas-sensitive support according to claim 3, 4 or 5, characterized in that The porous gas-sensitive carrier is made of zeolite material, organic polymer material, organic-inorganic hybrid material or gel material.

7. The waveguide gas sensor based on a porous gas-sensitive carrier according to claim 6, characterized in that, The materials of the first housing and the second housing are aluminum.

8. The waveguide gas sensor based on a porous gas-sensitive support according to claim 7, characterized in that, The material of the resonant chip is copper.

9. The waveguide gas sensor based on a porous gas-sensitive carrier according to claim 8, wherein When the gas to be detected is ammonia, the porous gas-sensitive carrier is an In2O3 / Al2O3 cylinder.

10. The waveguide gas sensor based on a porous gas-sensitive carrier according to claim 9, characterized in that, The preparation method of the porous gas-sensitive carrier being an In2O3 / Al2O3 cylinder is as follows: Under an ice bath condition, dissolve PEO in ethanol, then sequentially add deionized water and AlCl3·6H2O and stir to dissolve to obtain a first solution; Keep the ice bath condition unchanged, add PO to the first solution to make the solution layer; Stir to make the layering phenomenon disappear to obtain a uniform and transparent sol; Pour the sol into a centrifuge tube and seal it, then place the centrifuge tube in a 40°C water bath to convert the sol into a gel; After aging and drying the gel; calcine it at 800°C for 2 h to obtain an Al2O3 bulk material; Add InCl3·4H2O, sodium dodecyl sulfate and urea to deionized water, then add the Al2O3 bulk material, stir, transfer the mixture to a reaction kettle, heat it at 120°C for 12 h, and calcine the obtained sample at 500°C to obtain an In2O3 / Al2O3 block; Cut the In2O3 / Al2O3 block to obtain an In2O3 / Al2O3 cylinder.

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