Mid-infrared gas sensor based on 3D printing metamaterial and preparation method thereof

Abstract

The application discloses a kind of based on 3D printing metamaterial mid-infrared gas sensor and preparation method thereof.The application is printed on the periodic arrangement of column arm unit on substrate using 3D printing technology, and metal film is deposited on its surface, to realize the narrow-band resonance absorption of specific wavelength mid-infrared light.The application can be adjusted by the geometric parameter and arrangement mode of column arm unit, and the absorption characteristics of sensor in mid-infrared wave band are optimized, so that it can produce resonance response to the characteristic absorption peak of target gas, thereby significantly improving the sensitivity and selectivity of gas detection.Compared with traditional planar nanostructure, the optical performance of the sensor structure design of the application is greatly improved, and it has the advantages of miniaturization, rapid response, high sensitivity and excellent gas selectivity, and can be widely used in environmental monitoring, industrial emission monitoring and safety detection and other fields.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photonics and gas detection technology, and in particular, to a mid-infrared gas sensor based on 3D-printed metamaterial and a preparation method thereof. BACKGROUND

[0002] The mid-infrared waveband (3-10 μm) covers the characteristic absorption peaks of most gas molecules, and has important application value in the fields of environmental monitoring, industrial emission control, public safety and health. Although there are many types of existing mid-infrared gas sensors, they still generally face the following problems: insufficient sensitivity, poor selectivity, insufficient response speed, large device size, and complex manufacturing process, high cost, etc. These problems seriously restrict the promotion and application of mid-infrared gas sensors in practical scenarios. For example, patent application publication number CN118130416A proposes a real-time monitoring system based on a mid-infrared sensor, which combines signal analysis and environmental feature evaluation to improve the real-time performance of gas monitoring to a certain extent. However, its core device still uses a traditional mid-infrared sensor, and the structure design is limited, so the sensitivity and miniaturization level are still insufficient.

[0003] In order to break through the limitations of traditional materials, metamaterial technology has been gradually introduced into the field of gas sensing. Metamaterials can achieve narrow-band absorption or resonance effects in specific wavebands by precisely designing periodic structures at sub-wavelength scales. Patent application publication number CN116735532A discloses a gas sensor based on a two-dimensional Fano resonance super surface, which uses a two-dimensional super surface coupled with graphene to improve sensitivity and response speed. Although this technology shows certain advantages in two-dimensional planar structures, its resonance mode is single, making it difficult to cover different absorption peaks of multiple gas molecules, and it still relies on traditional planar processes such as photolithography, which lacks manufacturing flexibility.

[0004] On the other hand, 3D printing technology, especially two-photon polymerization micro-nano printing, provides a new manufacturing method for preparing complex three-dimensional microstructures. Patent application publication number CN119253285A proposes using 3D printing technology to manufacture a multi-layer metal-dielectric metamaterial structure to improve electromagnetic wave absorption performance. This scheme proves the potential of 3D printing in the field of metamaterials, but its application is mainly concentrated in the field of electromagnetic wave shielding or stealth, and it does not design for mid-infrared gas sensing, so it cannot meet the demand for selective enhancement of gas characteristic absorption peaks.

[0005] In summary, existing technologies have the following shortcomings: limitations of two-dimensional metasurfaces, making it difficult for two-dimensional structures to form multimodal coupling, resulting in limited resonant response and an inability to achieve high-sensitivity detection of various gases; limitations in manufacturing processes, with traditional processes such as photolithography having bottlenecks in the fabrication of complex three-dimensional structures, lacking low-cost, large-scale fabrication capabilities; and insufficient application of 3D printing, with existing 3D printing metamaterial research mainly focusing on the field of electromagnetic wave absorption, while three-dimensional metamaterial solutions for mid-infrared gas detection have not yet been reported. Summary of the Invention

[0006] The purpose of this invention is to address the problems of low sensitivity, slow response time, poor selectivity, and high manufacturing cost in existing gas sensors, and to provide a mid-infrared gas sensor based on 3D-printed metamaterials and its fabrication method. This invention utilizes 3D printing technology to precisely manufacture metamaterial arrays with high sensitivity and selectivity, enabling low-cost, efficient, and rapid gas detection with broad application prospects, particularly in environmental monitoring, industrial gas emission control, and indoor air quality monitoring.

[0007] The specific technical solution adopted in this invention is as follows:

[0008] In a first aspect, the present invention provides a mid-infrared gas sensor based on 3D-printed metamaterials, which includes a metamaterial array, a light source unit, a detection unit and a signal processing unit;

[0009] The metamaterial array includes a substrate and a column arm unit array formed by 3D printing. The column arm unit array is arranged periodically on the front side of the substrate in groups of three column arm units. Each column arm unit consists of a support column supported on the substrate and a cantilever mounted on top of the support column. The cantilevered sides of the three column arm units in each periodic unit all face the center of the periodic unit. The column arm unit array and the front side of the substrate are completely covered with a metal thin film.

[0010] The light source unit is used to emit incident light in the mid-infrared band to the metamaterial array;

[0011] The detection unit is used to receive the reflected light signal generated by the interaction between the metamaterial array and gas molecules, and to obtain the reflection spectrum.

[0012] The signal processing unit is used to extract the characteristic absorption peak intensity of the gas to be detected from the reflection spectrum detected by the detection unit, and to calculate the gas concentration on the surface of the metamaterial array through conversion.

[0013] As a preferred embodiment of the first aspect, in the metamaterial array, each periodic unit has a side length of 3-4 μm, each column arm unit has a support column and a cantilever with a cross-sectional radius of 0.1-0.5 μm, the support column has a height of 1-1.8 μm, and the cantilever has a length of 0.5-1.5 μm; the substrate has a thickness of 1-2 μm; and the metal film has a thickness of 50-200 nm.

[0014] As a preferred embodiment of the first aspect, the substrate is made of silicon (Si) or silicon dioxide (SiO2).

[0015] As a preferred embodiment of the first aspect, the column arm unit is made by printing a 3D printable photopolymer material using a two-photon polymerization 3D printing technology.

[0016] As a preferred embodiment of the first aspect, the metal film is made of gold, silver, aluminum, nickel, or an alloy of one or more of them.

[0017] As a preferred embodiment of the first aspect, the metamaterial array has multiple sub-arrays, the column arm units in the same sub-array have the same structure size parameters, and the column arm units in different sub-arrays have different overall scaling ratios.

[0018] As a preferred embodiment of the first aspect, the light source unit is a quantum cascade laser (QCL) capable of emitting mid-infrared light.

[0019] As a preferred embodiment of the first aspect, the detection unit is a mercury cadmium telluride (MCT) detector or a pyroelectric detector.

[0020] In a second aspect, the present application provides a preparation method of a metamaterial array for a mid-infrared gas sensor, which comprises:

[0021] S1, according to a pre-designed three-dimensional geometric structure model of the metamaterial array, printing a photopolymer material on a substrate by a two-photon polymerization 3D printing technology to form a combination of the substrate and a column arm unit array;

[0022] S2, depositing a metal film on the column arm unit array surface and the substrate front surface of the combination by a chemical plating method, and obtaining the metamaterial array after cleaning and drying.

[0023] In a third aspect, the present application provides a method for detecting the concentration of a gas using the 3D-printed metamaterial-based mid-infrared gas sensor according to any one of the first aspect described above, which specifically comprises the following steps: placing the metamaterial array in the gas atmosphere to be detected, emitting incident light in the mid-infrared band to the metamaterial array through the light source unit, receiving the reflected light signal generated after the interaction between the metamaterial array and the gas molecules through the detection unit, and obtaining the reflectance spectrum; finally, extracting the characteristic absorption peak intensity of the gas to be detected from the reflectance spectrum by the signal processing unit, calling the pre-fitted mapping relationship between the characteristic absorption peak intensity and the gas concentration, and calculating the concentration of the gas to be detected on the surface of the metamaterial array.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] The present application uses 3D printing technology to print a periodic array of column arm units on a substrate and deposits a metal film on the surface thereof to achieve narrow-band resonant absorption of specific wavelength mid-infrared light; at the same time, by precisely adjusting the geometric parameters and arrangement of the column arm units, the absorption characteristics of the sensor in the 3-10 μm mid-infrared band can be optimized, so that it can produce a resonant response to the characteristic absorption peak of the target gas, thereby significantly improving the sensitivity and selectivity of gas detection.

[0026] The present application uses 3D printing technology to manufacture the metamaterial array, which reduces the high cost in the traditional manufacturing process and has a high cost performance. At the same time, by precisely designing the geometric structure of the metamaterial array, the present application can effectively adsorb gas molecules and achieve high-sensitivity detection of multiple gases. In addition, the present application has strong adaptability and can simultaneously detect multiple gases, which has a wide application prospect, especially for gas monitoring in complex environments.

[0027] In summary, through the technical scheme of the present application, the gas sensor can be applied in multiple fields with low cost, high sensitivity and fast response, and provides a more accurate and efficient gas monitoring solution. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 FIG. 1 is a schematic diagram of a 3D-printed metamaterial-based mid-infrared gas sensor according to the present application;

[0029] Figure 2 FIG. 3 is a schematic diagram of a metamaterial array in a mid-infrared gas sensor according to the present application;

[0030] Figure 3 FIG. 4 shows a structural schematic diagram (a) containing a single column arm unit in a single period and simulation results (b) of the reflectivity-wavelength relationship;

[0031] Figure 4Structure schematic (a) and simulation results of reflectivity versus wavelength (b) of a structure containing two post-arm units in a single period are shown.

[0032] Figure 5 Structure schematic (a) and simulation results of reflectivity versus wavelength (b) of a structure containing three post-arm units in a single period are shown.

[0033] Figure 6 Structure schematic (a) and simulation results of reflectivity versus wavelength (b) of a structure containing four post-arm units in a single period are shown.

[0034] Figure 7 The effect of arm length d in the post-arm unit on the reflection spectrum is shown.

[0035] Figure 8 An exemplary metamaterial array (3x3) schematic is shown.

[0036] Figure 9 Simulation results of reflectivity versus wavelength of an exemplary metamaterial array (3x3) are shown, scaled by 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15 and 1.2, respectively.

[0037] Figure 10 A system schematic of an exemplary mid-infrared gas sensor is shown. DETAILED DESCRIPTION

[0038] In order to make the above objectives, features and advantages of the present application more clear and comprehensible, the specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. In the following description, a lot of specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be implemented in many different ways other than those described herein, and one of ordinary skill in the art can make similar improvements without departing from the spirit of the present application, and therefore the present application is not limited to the specific embodiments disclosed below. The technical features in each embodiment of the present application can be combined accordingly without conflict, provided that there is no conflict.

[0039] In the description of the present application, it should be understood that when an element is considered to be "connected" to another element, it can be directly connected to the other element or indirectly connected to the other element with an intermediate element. In contrast, when an element is referred to as being "directly" connected to another element, there is no intermediate element.

[0040] As Figure 1As shown in a preferred embodiment of the present application, a 3D printing metamaterial-based mid-infrared gas sensor is provided, the core component units of which include a metamaterial array, a light source unit, a detection unit and a signal processing unit. The present application uses two-photon polymerization 3D printing technology to construct a three-dimensional metamaterial array composed of periodic column arm units on a substrate, and combines with metal film deposition to achieve narrow-band resonant absorption of mid-infrared light. The three-dimensional column arm unit structure of the present application can form multiple local resonance modes in a single periodic unit, thereby producing a multi-peak absorption characteristic, effectively covering the characteristic absorption band of multiple gas molecules, and greatly improving the sensitivity and selectivity of gas detection. At the same time, the 3D printing process breaks through the limitations of traditional photolithography, realizing precise controllable and low-cost preparation of complex structures. The specific structure and cooperation of each component unit of the mid-infrared gas sensor will be described in detail below.

[0041] As shown in Figure 2 The metamaterial array includes a substrate and a column arm unit array formed by 3D printing, and the column arm unit array is arranged periodically on the front surface of the substrate in groups of three column arm units. The three column arm units in each periodic unit have the same monomer structure, and the only difference is that they are arranged at different angles on the substrate. Each column arm unit is composed of a support column supported on the substrate and a cantilever erected on the top of the support column. The cantilever overhang side of the three column arm units in each periodic unit (the two ends of the cantilever structure are respectively referred to as the fixed side and the overhang side, and the overhang side refers to the end that is not fixed) all face the center of the periodic unit, and the center lines of the cantilevers of the three column arm units intersect at an angle of 120°. In addition, for ease of description, the surface of the substrate used to support the column arm unit array is referred to as the front surface. Both the column arm unit array and the front surface of the substrate are completely covered with a metal film, which is used to enhance the absorption and response characteristics of mid-infrared light.

[0042] The metamaterial array uses two-photon polymerization technology to print periodically arranged column arm units on the substrate, and deposits a metal film on the surface, thereby achieving narrow-band resonant absorption of specific wavelength mid-infrared light. By accurately adjusting the period, geometric parameters and arrangement of the column arm units, the absorption characteristics of the sensor in the 3-10 μm mid-infrared band can be optimized, so that it can produce a resonant response to the characteristic absorption peak of the target gas, thereby significantly improving the sensitivity and selectivity of gas detection

[0043] By designing specific periods, geometric shapes and sizes, the present application can achieve strong absorption and narrow-band optical response in the mid-infrared band, so the specific parameters need to be optimized according to the actual detection requirements.

[0044] In the embodiment of the present application, the column arm unit adopts resin or other photopolymerization materials capable of 3D printing as the base material, and is processed and formed by the two-photon polymerization 3D printing technology. The specific photopolymerization material can be selected according to actual needs, for example, a negative photoresist material can be used. The side length of each periodic unit in the metamaterial array is 3-4 μm, so as to adapt to the mid-infrared absorption and response characteristics in the 3-10 μm wave band. The support column and cantilever of each column arm unit are both cylindrical with a cross-sectional radius of 0.1-0.5 μm, the height (i.e. the length in the direction of the cylindrical generatrix) of the support column is 1-1.8 μm, and the length (i.e. the length in the direction of the cylindrical generatrix) of the cantilever is 0.5-1.5 μm. It should be noted that there is a certain overlapping area at the junction of the two cylinders during actual processing, but since the column arm unit is made of 3D printing technology, it can be directly integrated and processed, without the need for prior processing of two cylinders and assembly. In addition, the thickness of the substrate below the metamaterial array is 1-2 μm, and the substrate can be made of silicon (Si) or silicon dioxide (SiO2) and the like. The surface of each column arm unit in the column arm unit array and the metal film covering the front surface of the substrate need to have a thickness of 50-200 nm, and the metal film is made of one of gold, silver, aluminum, nickel or an alloy of multiple thereof. The covering metal film can ensure that the mid-infrared light cannot be transmitted, thereby enhancing the absorption of light and optimizing the response to mid-infrared light.

[0045] The column arm unit of the present application is preferably manufactured by the two-photon polymerization 3D printing technology, and specifically, the resin or other photopolymerization materials suitable for 3D printing can be compounded and stacked on the substrate, and then 3D processed to form the corresponding metamaterial array surface structure.

[0046] In the embodiment of the present application, a preparation method of the above-mentioned metamaterial array is also provided, and the steps are as follows:

[0047] S1, according to the three-dimensional geometric structure model of the pre-designed metamaterial array, the photopolymerization material is printed on the substrate by the two-photon polymerization 3D printing technology to form a combination composed of the substrate and the column arm unit array.

[0048] S2, a layer of metal film is deposited on the column arm unit array surface and the front surface of the substrate by using the chemical plating method, and the metamaterial array is obtained after cleaning and drying.

[0049] The above-mentioned metamaterial array is a core component of the entire mid-infrared sensor, but in addition to this component, the overall gas concentration detection still needs the cooperation of a light source unit, a detection unit and a signal processing unit. The light source unit is used to emit incident light in the mid-infrared band to the metamaterial array; the detection unit is used to receive the reflected light signal generated after the metamaterial array interacts with gas molecules, and obtain the reflection spectrum; and the signal processing unit is used to extract the characteristic absorption peak intensity of the gas to be detected from the reflection spectrum detected by the detection unit, and calculate the gas concentration on the surface of the metamaterial array through conversion.

[0050] In the embodiment of the present application, the above-mentioned light source unit preferably adopts a quantum cascade laser (QCL) capable of emitting mid-infrared light, which can emit precise mid-infrared light to excite the absorption characteristics of the metamaterial array.

[0051] In the embodiment of the present application, the above-mentioned detection unit preferably adopts a mercury cadmium telluride (MCT) detector, which can accurately detect the reflection signal and output spectrum data related to the gas concentration. Of course, other mid-infrared detectors such as pyroelectric detectors can also be used.

[0052] In the embodiment of the present application, the above-mentioned signal processing unit can adopt a microprocessor or a digital signal processor (DSP) for data processing of the received reflection signal, so as to accurately calculate the gas concentration.

[0053] On the basis of the above-mentioned mid-infrared gas sensor based on 3D printed metamaterial, the present application further provides a gas concentration detection method, which specifically comprises the following steps: placing the metamaterial array in a gas atmosphere to be detected, emitting incident light in the mid-infrared band to the metamaterial array through the light source unit, receiving the reflected light signal generated after the metamaterial array interacts with gas molecules through the detection unit, and obtaining the reflection spectrum; and finally extracting the characteristic absorption peak intensity of the gas to be detected from the reflection spectrum by the signal processing unit, calling the pre-fitted mapping relationship between the characteristic absorption peak intensity and the gas concentration, and calculating the concentration of the gas to be detected on the surface of the metamaterial array.

[0054] It should be noted that the mapping relationship between the characteristic absorption peak intensity and the gas concentration needs to be fitted separately for each kind of gas during the sensor calibration stage. When calibrating, the absorption peak wavelength corresponding to the target gas can be found from the reflection spectrum, then the metamaterial array is placed in an atmosphere of the gas with different concentrations, the corresponding absorption peak intensity is found from the absorption peak wavelength of the reflection spectrum, and the different absorption peak intensities and gas concentrations are fitted to obtain a fitting formula, which represents the mapping relationship between the characteristic absorption peak intensity and the gas concentration.

[0055] Embodiment 1: Preparation and application of a mid-infrared gas sensor based on a 3D printed metamaterial array

[0056] (1) Design and printing of metamaterial array

[0057] First, a three-dimensional geometric structure of the metamaterial array is designed by using computer-aided design (CAD) software. In order to verify the influence of different numbers of column arm units in the periodic unit inside the column arm unit array in the metamaterial array of the present application on the performance of the final device, the present application takes one, two, three and four column arm units as one period respectively, and verifies the relationship between the reflectivity of the metamaterial array and the wavelength under different numbers of column arm units through simulation. The material and structure size of the metamaterial array are as follows: the side length of each periodic unit p = 3.5 μm; the support column and cantilever of each column arm unit are both cylindrical with a cross-sectional radius r = 0.3 μm, the height of the support column h3 = 1.4 μm, and the length of the cantilever d = 0.975 μm; the thickness of the substrate h1 = 1.45 μm; the thickness of the metal film h2 = 50 nm. The distance from the center of the bottom surface of the support column of the column arm unit to the center point of the periodic unit is 0.975 μm. The substrate is silicon dioxide (SiO2), the material of the metal film is nickel, and the material of the column arm unit array is IP-Dip photopolymer resin. In order to facilitate subsequent description, the material and structure size of the above metamaterial array are referred to as the basic parameter scheme.

[0058] Finally, the simulation results of each period containing one, two, three and four column arm units are shown in Figure 3 , Figure 4 , Figure 5 and Figure 6 respectively. As can be seen, the metamaterial array with three column arm units has three obvious absorption peaks, the metamaterial array with one and two column arm units has only two obvious absorption peaks, and the metamaterial array with four column arm units has only one obvious absorption peak. Therefore, the metamaterial array with three column arm units in each periodic unit can produce multiple local resonance modes through coupling, and different modes exhibit three absorption peaks in the spectrum. This "multi-peak characteristic" can cover more gas absorption spectra, increase the types of gas detection, and be more suitable for gas sensing.

[0059] In addition, based on the metamaterial array containing three column arm units in each period, the present application further optimizes the arm length in the column arm unit based on the above basic parameter scheme. Figure 7 The influence of the arm length d on the reflection spectrum is shown, and when the arm length d changes, the intensity and wavelength of the two peaks in the reflection spectrum also change, which indicates the necessity of the 3D column arm unit structure.

[0060] In addition, based on the metamaterial array containing three column arm units in each period, the present application further explores the influence of different sizes of column arm units on the performance of the final device on the basis of the above basic parameter scheme. Figure 8 A schematic diagram of a metamaterial array composed of 3x3 subarrays is shown, which contains a total of 9 9x10 subarrays, each of which contains three column arm units (the center lines of the cantilever arms of the three column arm units intersect at an angle of 120°), and the structure size parameters of the column arm units in the same subarray are the same, but the overall size of the column arm units in different arrays is scaled by different proportions on the basis of the above basic parameter scheme, wherein the nine scaling ratios are 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15 and 1.2, so that the structure size parameters of the column arm units between different subarrays have different overall scaling ratios. Thus, the array with a scaling ratio of 1 corresponds to the aforementioned basic parameter scheme. Figure 9 The simulation results of the reflectivity of the 3x3 metamaterial array versus wavelength are shown, and it can be seen from the simulation results that different scaling ratios will cause different shifts of the absorption peaks in the reflected spectrum. Therefore, different subarrays in the above metamaterial array have different characteristic absorption peaks, which can be used to detect the concentration of different gases.

[0061] Thus, the geometric structure and arrangement of the metamaterial array are precisely designed, which can optimize the adsorption capacity of gas molecules, especially the light absorption performance in the mid-infrared band (3-10 μm).

[0062] After the design is completed, based on the metamaterial array design scheme shown in Figure 8 A Nanoscribe Photonic Professional GT 3D micro-printer is used to print the design by using two-photon polymerization 3D printing technology. During printing, silica (SiO2) with a thickness of 1.45 μm is used as the substrate, and negative photoresist resin material (IP-Dip photopolymerization resin) is laid on the substrate to print the column arm unit array, and the printing accuracy reaches the nanometer level, ensuring accurate reproduction of the geometric structure of the metamaterial array.

[0063] (2) Deposition of metal coating

[0064] After the metamaterial array is printed, a metal coating process is performed to optimize its optical performance. Because the three-dimensional metamaterial structure can be blocked, resulting in the structure of the blocked part being unable to be plated with a metal film, the traditional sputtering technology cannot be used. The present application uses a chemical plating method to perform film plating. First, the sample is immersed in an acetone solution and gently stirred for cleaning. Then, the sample is rinsed in deionized water (DI water), and then immersed in a NaOH solution, and then rinsed with DI water for 1 minute. Next, the surface of the sample is sensitized by immersing it in an aqueous solution containing SnCl2·2H2O and HCl, and then rinsing with DI water. After sensitization, the surface of the sample is activated by immersing it in an aqueous solution containing PdCl and HCl, and then rinsing with DI water. After activation, the surface of the sample is metallized by immersing it in a nickel plating bath mixed from equal volumes of nickel plating chemical A and B. The metallization process is performed at 80°C with vigorous stirring, and the plating thickness is controlled by adjusting the metallization time. In this embodiment, the thickness of the deposited nickel film is controlled to be 50 nm. After this step is completed, the sample is removed and rinsed in DI water, and then allowed to air dry. The metal coating can significantly enhance the light absorption performance of the metamaterial array in the mid-infrared waveband and improve its adsorption capacity for gas molecules.

[0065] (3) Connection and assembly of the signal processing module

[0066] The metamaterial array after coating is assembled with a light source unit, a detection unit, and a signal processing unit to form a complete mid-infrared gas sensor system. The light source unit is used to emit incident light in the mid-infrared waveband to the metamaterial array; the detection unit is used to receive the reflected light signal generated after the metamaterial array interacts with gas molecules, and obtain the reflection spectrum; the signal processing unit is used to extract the characteristic absorption peak intensity of the gas to be detected from the reflection spectrum detected by the detection unit, and calculate the gas concentration on the surface of the metamaterial array through conversion.

[0067] However, it should be noted that in the above-mentioned mid-infrared gas sensor system, auxiliary elements need to be introduced according to the specific layout when necessary due to the involvement of the optical path. In this embodiment, as shown in Figure 10As shown, an exemplary mid-infrared gas sensor system with optical path is shown, which includes a metamaterial array 1, a low numerical aperture (NA) objective lens 4, a beam splitter 5, a light source unit 6, a detection unit 7, a gas chamber 8, and in addition, the detection unit 7 also needs to be connected to an external signal processing unit. The light source unit 6 uses a quantum cascade laser (QCL) capable of emitting mid-infrared light, the detection unit 7 uses a mercury cadmium telluride (MCT) detector, and the signal processing unit uses a digital signal processor (DSP). The gas chamber 8 is provided with a gas inlet 801 and a gas outlet 802, and the inside is kept airtight. A light-transmitting window is provided on the top surface, and the gas to be detected is continuously introduced into the inside of the gas chamber 8 through the gas inlet 801, and discharged from the gas outlet 802. Figure 8 The metamaterial array 1 is built into the gas chamber 8, and has one side of the column arm unit array facing the light-transmitting window. After the gas to be detected is introduced, the column arm unit array is exposed to the atmosphere of the gas to be detected. The low numerical aperture (NA) objective lens 4 and the beam splitter 5 are located directly above the light-transmitting window of the gas chamber 8. The mid-infrared incident light generated by the light source unit 6 is first reflected by the beam splitter 5 and focused by the low numerical aperture objective lens 4, and then irradiates the metamaterial array 1 after passing through the light-transmitting window of the gas chamber 8. The reflected light signal generated after the interaction between the metamaterial array and the gas molecules continues to return along the optical path, and is received by the detection unit 7 after passing through the low numerical aperture objective lens 4 and the beam splitter 5. The detection unit 7 obtains the reflection spectrum according to the received reflected light signal. Subsequently, the signal processing unit can extract the characteristic absorption peak intensity of the gas to be detected from the reflection spectrum, call the pre-fitted mapping relationship between the characteristic absorption peak intensity and the gas concentration, and calculate the concentration of the gas to be detected on the surface of the metamaterial array.

[0068] It should be noted that since the metamaterial array has multiple sub-arrays, and the structural size parameters of the column arm units in different sub-arrays have different overall scaling ratios, according to the performance comparison described above, it can be seen that the absorption peaks of sub-arrays with different scaling ratios are different. Therefore, different gas types may actually need to focus the incident light onto the corresponding sub-array through the low numerical aperture objective lens 4 according to the wavelength of the absorption peak, in order to accurately obtain the concentration of the gas to be detected on the surface of the metamaterial array.

[0069] (4) Performance test and calibration

[0070] The assembled mid-infrared gas sensor system is tested for performance and calibrated. First, expose the metamaterial array 1 to different concentrations of gas environments (such as CO2, CH4, NO2, etc.), and use a gas concentration analyzer for comparison to ensure the correspondence between the sensor output signal and the actual gas concentration is accurate. By adjusting the mapping relationship and other necessary parameters built into the signal processing unit, optimize the sensitivity and response time of the sensor, complete the sensor calibration.

[0071] (5) Gas detection and real-time monitoring

[0072] The calibrated mid-infrared gas sensor system can be applied to environmental monitoring, industrial gas emission control, indoor air quality detection, etc. In practical applications, the sensor detects the mid-infrared spectral changes of the gas in real time, quickly responds to fluctuations in gas concentration, and provides accurate concentration data through the signal processing module. Through connection with the monitoring system, users can obtain real-time gas monitoring data and adjust equipment operating parameters as needed.

[0073] (6) Application scenarios of the sensor

[0074] This mid-infrared gas sensor system is particularly suitable for occasions requiring high sensitivity, fast response, and long-term stability. For example, in industrial emission monitoring, it can monitor the emission concentration of harmful gases in real time; in indoor air quality detection, it can quickly respond to changes in carbon dioxide concentration; in environmental monitoring, it can detect changes in the concentration of greenhouse gases such as methane.

[0075] Example 2: Application of mid-infrared gas sensor in multi-gas detection

[0076] To verify the multi-gas detection capability of the mid-infrared gas sensor system assembled and calibrated in Example 1 of the present application, CO2, CH4 and NO2 were selected for the experiment. The experimental steps are as follows:

[0077] (1) Use the above-mentioned assembled and calibrated mid-infrared gas sensor system to expose it to known concentrations of CO2 (concentration range: 100 ppm to 2000 ppm), CH4 (concentration range: 50 ppm to 1000 ppm) and NO2 (concentration range: 20 ppm to 500 ppm) gas environments.

[0078] (2) Record the reflected spectral signals generated by the interaction between gas molecules and the sensor metamaterial array in real time through the detection unit 7.

[0079] (3) According to the characteristic absorption peak wavelength of each gas, extract the corresponding absorption peak intensity from the reflected spectral signals, analyze and output the gas concentration data in real time through the signal processing unit, and verify the detection sensitivity and accuracy of the sensor for different gases.

[0080] The experimental results show that the sensor of the present application can accurately detect the concentrations of CO2, CH4 and NO2 gases simultaneously and respond quickly to different concentration changes, verifying the high sensitivity and selectivity of the gas sensor.

[0081] Example 3: Application of mid-infrared gas sensor in industrial emission monitoring

[0082] In industrial emission monitoring, the mid-infrared gas sensor system assembled and calibrated in Example 1 of the present application can effectively monitor the concentration changes of emitted gases and timely detect over-standard emission situations. The sensor is installed at the emission port to monitor the mid-infrared absorption characteristics of the gas in real time. When the gas concentration exceeds the set safety threshold, the signal processing module immediately sends an alarm signal to inform the staff to take appropriate measures. This function can effectively ensure industrial safety and reduce harmful gas emissions. For example, in the emission port of a chemical plant, the concentration changes of methane, carbon dioxide and hydrogen sulfide are detected using the present sensor. The results show that the sensor can quickly detect any abnormal changes in the concentration of emitted gases and accurately provide real-time monitoring data.

[0083] Example 4: Application of mid-infrared gas sensor in indoor air quality detection

[0084] To verify the effectiveness of the mid-infrared gas sensor system assembled and calibrated in Example 1 of the present application in indoor air quality detection, this example tests the performance of the gas sensor in a standardized indoor environment. The indoor environment includes common indoor pollution gases such as CO2, methane, ammonia and TVOC (total volatile organic compounds). In this example, the gas sensor is tested in a standardized indoor environment (volume of 30 m³) at different concentrations (CO2 concentration of 1000 ppm, methane concentration of 150 ppm, ammonia concentration of 50 ppm). The experimental results show that the present sensor can quickly respond and accurately measure the concentrations of various gases, making it suitable for indoor air quality monitoring and enabling timely detection of air quality decline and giving early warning.

[0085] Example 5: Application of portable gas detection equipment

[0086] This embodiment demonstrates how to apply the mid-infrared gas sensor of the present application to a portable gas detection device. The device is small, light, suitable for emergency response and on-site detection occasions. Specifically, the gas sensor of the present application is used and integrated into a portable device, the device is powered by a built-in battery and can run for a long time on site. The device sends real-time data to the cloud through wireless communication, and users can view gas concentration data in real time through mobile devices. Such portable gas detection devices can be quickly deployed and provide real-time gas detection data, widely used in industrial safety, environmental monitoring and emergency response scenarios.

[0087] In summary, through the verification of the above multiple embodiments, the mid-infrared gas sensor based on 3D printed metamaterial array of the present application has high sensitivity, fast response, low cost and multi-gas detection capability, and can be widely used in environmental monitoring, industrial gas emission control, indoor air quality detection and other fields. The flexible design of the sensor can adapt to various detection needs, providing more efficient and accurate gas monitoring solutions.

[0088] However, it should be noted that the above-mentioned embodiments are only some of the preferred implementation schemes of the present application, but not to limit the present application. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the scope of the present application.

Claims

1. A 3D-printed metamaterial-based mid-infrared gas sensor, characterized in that, The application relates to a material array, a light source unit, a detection unit and a signal processing unit. The material array comprises a substrate and a column arm unit array formed by 3D printing, the column arm unit array is arranged on the front surface of the substrate in groups of three column arm units and is periodically arranged on the front surface of the substrate, each column arm unit is composed of a supporting column supported on the substrate and a cantilever arranged on the top of the supporting column, the cantilevers of the three column arm units in each periodic unit are all directed towards the center of the periodic unit, and the center lines of the cantilevers of the three column arm units are intersected at an angle of 120 DEG; the column arm unit array and the front surface of the substrate are both completely covered with a metal film; the length of each periodic unit in the material array is 3-4 microns, the supporting column and the cantilever of each column arm unit are both cylindrical with a cross-section radius of 0.1-0.5 microns, the height of the supporting column is 1-1.8 microns, and the length of the cantilever is 0.5-1.5 microns; the two ends of the cantilever are a fixed end and a cantilever end respectively, and the cantilever end is the unfixed end of the cantilever; the material array can generate multiple local resonance modes through coupling, and different modes show three absorption peaks in the spectrum; The light source unit is used for emitting incident light in the middle infrared wave band to the material array. The detection unit is used for receiving reflected light signals generated after the material array interacts with gas molecules and obtaining a reflection spectrum. The signal processing unit is used for extracting the characteristic absorption peak intensity of the detected gas from the reflection spectrum detected by the detection unit and calculating the gas concentration on the surface of the material array through conversion.

2. The 3D-printed metamaterial-based mid-infrared gas sensor of claim 1, wherein, The thickness of the substrate is 1-2 microns, and the thickness of the metal film is 50-200 nm.

3. The 3D-printed metamaterial-based mid-infrared gas sensor of claim 1, wherein, The substrate is made of silicon (Si) or silicon dioxide (SiO2).

4. The 3D-printed metamaterial-based mid-infrared gas sensor of claim 1, wherein, The column arm unit is made of a photopolymer material capable of being 3D printed by using a two-photon polymerization 3D printing technology.

5. The 3D-printed metamaterial-based mid-infrared gas sensor of claim 1, wherein, The material of the metal film is one of gold, silver, aluminum and nickel or an alloy of multiple materials.

6. The 3D-printed metamaterial-based mid-infrared gas sensor of claim 1, wherein, The material array has multiple sub-arrays, the structure size parameters of the column arm units in the same sub-array are the same, and the structure size parameters of the column arm units in different sub-arrays have different overall scaling ratios.

7. The 3D-printed metamaterial-based mid-infrared gas sensor of claim 1, wherein, The light source unit is a quantum cascade laser (QCL) capable of emitting middle infrared light.

8. The 3D-printed metamaterial-based mid-infrared gas sensor of claim 1, wherein, The detection unit is a mercury cadmium telluride (MCT) detector or a pyroelectric detector.

9. A method of fabricating a metamaterial array in a mid-infrared gas sensor as claimed in claim 1, wherein, The application further relates to a method for manufacturing the material array. S1: printing a photopolymer material on a substrate by using a two-photon polymerization 3D printing technology according to a three-dimensional geometric structure model of a pre-designed material array to form a combination composed of the substrate and a column arm unit array; S2: depositing a metal film on the column arm unit array surface and the front surface of the substrate by using a chemical plating method, and obtaining the material array after cleaning and drying.

10. A method for detecting a gas concentration using the mid-infrared gas sensor based on 3D printing metamaterial according to claim 1, characterized in that, The metamaterial array is placed in a gas atmosphere to be detected, the light source unit emits incident light in the middle infrared band to the metamaterial array, the detection unit receives reflected light signals generated after the metamaterial array interacts with gas molecules, and a reflectance spectrum is obtained; finally, the signal processing unit extracts the characteristic absorption peak intensity of the gas to be detected from the reflectance spectrum, calls a pre-fitted mapping relationship between the characteristic absorption peak intensity and the gas concentration, and calculates the concentration of the gas to be detected on the surface of the metamaterial array.

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