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

Abstract

The invention discloses an intermediate infrared gas sensor based on a 3D printing metamaterial and a preparation method of the intermediate infrared gas sensor. The periodically arranged column arm units are printed on the substrate by adopting a 3D printing technology, and the metal film is deposited on the surface of the column arm units, so that narrow-band resonance absorption of mid-infrared light with a specific wavelength is realized. According to the invention, the absorption characteristic of the sensor in the middle-infrared band can be optimized by accurately adjusting the geometric parameters and the arrangement mode of the column arm units, so that the sensor can generate resonance response to the characteristic absorption peak of the target gas, thereby obviously improving the sensitivity and selectivity of gas detection. Compared with a traditional planar nano structure, the sensor structure design greatly improves optical performance, has the advantages of miniaturization, quick response, high sensitivity, excellent gas selectivity and the like, and can be widely applied to the fields of environmental monitoring, industrial emission monitoring, safety detection and the like.

Description

Technical Field

[0001] This invention relates to the fields of photonics and gas detection technology, and more specifically, to a mid-infrared gas sensor based on 3D-printed metamaterials and its fabrication method. Background Technology

[0002] The mid-infrared band (3-10 μm) covers the characteristic absorption peaks of most gas molecules and has significant application value in environmental monitoring, industrial emission control, public safety and health, and other fields. While there are many types of existing mid-infrared gas sensors, they generally face the following problems: insufficient sensitivity, poor selectivity, slow response speed, large device size, complex manufacturing processes, and high cost. These problems severely 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. This scheme combines signal analysis and environmental characteristic assessment, which can improve the real-time performance of gas monitoring to a certain extent. However, its core component still uses a traditional mid-infrared sensor, and the structural design is limited, resulting in insufficient sensitivity and miniaturization.

[0003] To overcome the limitations of traditional materials, metamaterials technology has been gradually introduced into the field of gas sensing. Metamaterials, through the precise design of subwavelength-scale periodic structures, can achieve narrowband absorption or resonance effects in specific wavelength ranges. Patent application publication number CN116735532A discloses a gas sensor based on a two-dimensional Fano resonant metasurface, which utilizes the coupling of the two-dimensional metasurface with graphene to improve sensitivity and response speed. Although this technology shows certain advantages in two-dimensional planar structures, its resonance mode is singular, making it difficult to cover the different absorption peaks of multiple gas molecules. Furthermore, it still relies on traditional planar processes such as photolithography, resulting in insufficient manufacturing flexibility.

[0004] On the other hand, 3D printing technology, especially two-photon polymerization micro / nano printing, provides a novel manufacturing method for preparing complex three-dimensional microstructures. Patent application publication number CN119253285A proposes using 3D printing technology to fabricate multilayer metallic dielectric metamaterial structures to improve electromagnetic wave absorption performance. This approach demonstrates the potential of 3D printing in the field of metamaterials, but its applications are mainly concentrated in electromagnetic wave shielding or stealth applications, and it does not address mid-infrared gas sensing design, thus failing to meet the need 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 above, in the metamaterial array, the side length of each periodic unit is 3-4 μm, the support column and cantilever of each columnar arm unit are both cylindrical with a cross-sectional radius of 0.1-0.5 μm, the height of the support column is 1-1.8 μm, and the length of the cantilever is 0.5-1.5 μm; the thickness of the substrate is 1-2 μm; and the thickness of the metal thin film is 50-200 nm.

[0014] As a preferred embodiment of the first aspect above, 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 manufactured by printing a photopolymer material capable of 3D printing using two-photon polymerization 3D printing technology.

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

[0017] As a preferred embodiment of the first aspect, the metamaterial array has multiple subarrays, the structural dimension parameters of the column arm units in the same subarray are the same, and the structural dimension parameters of the column arm units in different subarrays have different overall scaling ratios.

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

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

[0020] Secondly, the present invention provides a method for fabricating a metamaterial array for a mid-infrared gas sensor, comprising:

[0021] S1. Based on the pre-designed three-dimensional geometric model of the metamaterial array, the photopolymer material is printed on the substrate using two-photon polymerization 3D printing technology to form a combination of the substrate and the column arm unit array.

[0022] S2. A metal thin film is deposited on the surface of the column arm unit array of the assembly and the front side of the substrate using chemical plating. After cleaning and drying, a metamaterial array is obtained.

[0023] Thirdly, the present invention provides a gas concentration detection method using a mid-infrared gas sensor based on 3D-printed metamaterials as described in any of the first aspects above. Specifically, the method involves placing the metamaterial array in a gas atmosphere to be detected, emitting mid-infrared incident light to the metamaterial array through the light source unit, receiving the reflected light signal generated by the interaction between the metamaterial array and gas molecules through the detection unit, and obtaining the reflection spectrum. Finally, the signal processing unit extracts the characteristic absorption peak intensity of the gas to be detected from the reflection spectrum, calls the 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.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] This invention employs 3D printing technology to print a periodically arranged array of columnar arm units on a substrate and deposits a thin metal film on its surface to achieve narrowband resonant absorption of mid-infrared light at a specific wavelength. Simultaneously, by precisely adjusting the geometric parameters and arrangement of the columnar arm units, the absorption characteristics of the sensor in the 3-10 μm mid-infrared band can be optimized, enabling it to generate a resonant response to the characteristic absorption peaks of the target gas, thereby significantly improving the sensitivity and selectivity of gas detection.

[0026] This invention utilizes 3D printing technology to fabricate metamaterial arrays, reducing the high costs associated with traditional manufacturing processes and offering high cost-effectiveness. Furthermore, by precisely designing the geometry of the metamaterial array, this invention can effectively adsorb gas molecules and achieve highly sensitive detection of multiple gases. In addition, this invention exhibits strong adaptability, capable of simultaneously detecting multiple gases, and has broad application prospects, particularly suitable for gas monitoring in complex environments.

[0027] In summary, through the technical solution of this invention, the gas sensor can be applied in multiple fields with its characteristics of low cost, high sensitivity, and fast response, providing a more accurate and efficient gas monitoring solution. Attached Figure Description

[0028] Figure 1 A schematic diagram of a mid-infrared gas sensor based on 3D-printed metamaterials;

[0029] Figure 2 A schematic diagram of a metamaterial array in a mid-infrared gas sensor is shown.

[0030] Figure 3 A schematic diagram of a structure containing a single column arm unit within a single cycle is shown (a), along with simulation results of the relationship between reflectivity and wavelength (b).

[0031] Figure 4The diagram shows a structural schematic (a) containing two columnar arm units within a single cycle, and the simulation results (b) show the relationship between reflectivity and wavelength.

[0032] Figure 5 The diagram shows a structural schematic of three columnar arm units within a single cycle (a) and the simulation results of the relationship between reflectivity and wavelength (b).

[0033] Figure 6 A schematic diagram of a structure containing four columnar arm units within a single cycle is shown (a), along with simulation results of the relationship between reflectivity and wavelength (b).

[0034] Figure 7 This demonstrates the effect of the arm length d in the column arm unit on the reflection spectrum;

[0035] Figure 8 A schematic diagram of an exemplary metamaterial array (3×3) is shown;

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

[0037] Figure 10 A schematic diagram of an exemplary mid-infrared gas sensor system is shown. Detailed Implementation

[0038] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Technical features in various embodiments of the present invention can be combined accordingly without mutual conflict.

[0039] In the description of this invention, it should be understood that when an element is considered to be "connected" to another element, it can be a direct connection to the other element or an indirect connection, i.e., there is an intermediate element. Conversely, when an element is said to be "directly" connected to another element, there is no intermediate element.

[0040] like Figure 1As shown, in a preferred embodiment of the present invention, a mid-infrared gas sensor based on 3D-printed metamaterials is provided. Its core components include a metamaterial array, a light source unit, a detection unit, and a signal processing unit. The present invention utilizes two-photon polymerization 3D printing technology to construct a three-dimensional metamaterial array composed of periodic columnar arm units on a substrate, and combines this with metal thin film deposition to achieve narrowband resonant absorption of mid-infrared light. The three-dimensional columnar arm unit structure of the present invention can form multiple local resonant modes within a single periodic unit, thereby generating multi-peak absorption characteristics, effectively covering the characteristic absorption bands of various gas molecules, and significantly improving the sensitivity and selectivity of gas detection. Simultaneously, the 3D printing process overcomes the limitations of traditional photolithography, achieving precise control and low-cost fabrication of complex structures. The specific structure and cooperative operation of each component unit in this mid-infrared gas sensor are described in detail below.

[0041] like Figure 2 As shown, the metamaterial array includes a substrate and a columnar arm unit array formed by 3D printing. The columnar arm unit array consists of groups of three columnar arm units arranged periodically on the front side of the substrate. The three columnar arm units within each periodic unit have identical monolithic structures, differing only in their arrangement angle on the substrate. Each columnar arm unit comprises a support column on the substrate and a cantilever mounted on top of the support column. The cantilevered sides of the three columnar arm units within each periodic unit (the two ends of the cantilever structure are referred to as the fixed side and the cantilevered side, respectively; the cantilevered side refers to the unfixed end) all face the center of the periodic unit, and the center lines of the three cantilever units intersect each other at a 120° angle. For ease of description, the surface on the substrate used to support the columnar arm unit array is referred to as the front side. Both the columnar arm unit array and the front side of the substrate are completely covered with a thin metal film, which enhances the absorption and response characteristics to mid-infrared light.

[0042] This metamaterial array employs two-photon polymerization to print periodically arranged columnar arm units on a substrate, and then deposits a thin metal film on their surface, thereby achieving narrowband resonant absorption of mid-infrared light at a specific wavelength. By precisely adjusting the period, geometric parameters, and arrangement of the columnar arm units, the absorption characteristics of the sensor in the 3-10 μm mid-infrared band can be optimized, enabling it to resonate with the characteristic absorption peaks of the target gas, thus significantly improving the sensitivity and selectivity of gas detection.

[0043] This invention achieves strong absorption and narrow-band optical response in the mid-infrared band by designing specific periods, geometries and sizes. Therefore, the specific parameters need to be optimized according to actual detection requirements.

[0044] In embodiments of the present invention, the column arm unit uses 3D-printable resin or other photopolymer materials as the substrate and is formed by two-photon polymerization 3D printing technology. The specific photopolymer material can be selected according to actual needs; for example, a negative photolithography resin material can be used. The side length of each periodic unit in the metamaterial array is 3-4 μm to adapt to the mid-infrared absorption and response characteristics in the 3-10 μm wavelength 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 of the support column (i.e., the length along the generatrix of the cylinder) is 1-1.8 μm, and the length of the cantilever (i.e., the length along the generatrix of the cylinder) is 0.5-1.5 μm. However, it should be noted that during actual processing, there is a certain overlap area between the support column and the cantilever at their junction. But since the column arm unit is made using 3D printing technology, it can be directly integrated and formed without first processing the two cylinders and then assembling them. Furthermore, the substrate beneath the metamaterial array has a thickness of 1-2 μm and can be made of materials such as silicon (Si) or silicon dioxide (SiO2). The surface of each pillar unit in the pillar unit array and the front side of the substrate need to be covered with a metal thin film with a thickness of 50-200 nm. The metal thin film is made of one or an alloy of gold, silver, aluminum, and nickel. Covering with the metal thin film ensures that mid-infrared light cannot pass through, thereby enhancing light absorption and optimizing the response to mid-infrared light.

[0045] The column arm unit of the present invention is preferably manufactured using two-photon polymerization 3D printing technology. Specifically, resin or other photopolymer materials suitable for 3D printing can be composited and superimposed on a substrate, and then 3D processed to form a corresponding metamaterial array surface structure.

[0046] In an embodiment of the present invention, a method for preparing the above-mentioned metamaterial array is also provided, the steps of which are as follows:

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

[0048] S2. A metal thin film is deposited on the surface of the column arm unit array of the assembly and the front side of the substrate using chemical plating. After cleaning and drying, a metamaterial array is obtained.

[0049] The aforementioned metamaterial array is the core component of the entire mid-infrared sensor. However, in addition to this component, the overall gas concentration detection still requires the cooperation of a light source unit, a detection unit, and a signal processing unit. Specifically, the light source unit emits mid-infrared incident light into the metamaterial array; the detection unit receives the reflected light signal generated by the interaction between the metamaterial array and gas molecules, obtaining the reflection spectrum; and the signal processing unit extracts the characteristic absorption peak intensity of the gas to be detected from the reflection spectrum detected by the detection unit and calculates the gas concentration on the surface of the metamaterial array through conversion.

[0050] In embodiments of the present invention, the light source unit is preferably a quantum cascade laser (QCL) capable of emitting mid-infrared light, which can emit precise mid-infrared light to excite the absorption properties of the metamaterial array.

[0051] In embodiments of the present invention, the detection unit preferably employs a mercury cadmium telluride (MCT) detector, which is capable of accurately detecting reflected signals and outputting spectral data related to gas concentration. Of course, other mid-infrared detectors, such as pyroelectric detectors, can also be used.

[0052] In embodiments of the present invention, the signal processing unit described above may employ a microprocessor or a digital signal processor (DSP) to perform data processing on the received reflected signal, thereby accurately calculating the gas concentration.

[0053] Based on the aforementioned mid-infrared gas sensor based on 3D-printed metamaterials, this invention also provides a gas concentration detection method. Specifically, the metamaterial array is placed in the gas atmosphere to be detected. Mid-infrared incident light is emitted to the metamaterial array through the light source unit. The reflected light signal generated by the interaction between the metamaterial array and gas molecules is received by the detection unit to obtain the reflection spectrum. Finally, the signal processing unit extracts the characteristic absorption peak intensity of the gas to be detected from the reflection spectrum, calls the 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.

[0054] It should be noted that the mapping relationship between the characteristic absorption peak intensity and the gas concentration mentioned above needs to be fitted individually for each gas during the sensor calibration phase. During calibration, 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 that gas with different concentrations, and the corresponding absorption peak intensity is found from the absorption peak wavelength of the reflection spectrum. The different absorption peak intensities are fitted with the gas concentration, and the resulting fitted formula can represent the mapping relationship between the characteristic absorption peak intensity and the gas concentration.

[0055] Example 1: Fabrication and Application of a Mid-Infrared Gas Sensor Based on a 3D-Printed Metamaterial Array

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

[0057] First, the three-dimensional geometry of the metamaterial array was designed using computer-aided design (CAD) software. To verify the impact of different numbers of pillar arm units within the periodic cells of the pillar arm unit array on the final device performance, simulations were conducted using single, two, three, and four pillar arm units as a period to verify the relationship between the reflectivity and wavelength of the metamaterial array under different numbers of pillar arm units. The material and structural dimensions of the metamaterial array are as follows: the side length of each periodic cell is p = 3.5 μm; the supporting pillar and cantilever of each pillar arm unit are both cylindrical with a cross-sectional radius r = 0.3 μm, the height of the supporting pillar is h3 = 1.4 μm, and the length of the cantilever is d = 0.975 μm; the substrate thickness is h1 = 1.45 μm; and the metal thin film thickness is h2 = 50 nm. The distance from the center of the bottom surface of the supporting pillar of the pillar arm unit to the center point of the periodic cell is 0.975 μm. The substrate is silicon dioxide (SiO2), the metal thin film is nickel, and the pillar arm unit array is made of IP-Dip photopolymer resin. For ease of subsequent description, the material and structural dimensions of the above metamaterial array will be referred to as the basic parameter scheme.

[0058] Finally, the simulation results for each cycle containing one, two, three, and four columnar arm elements are as follows: Figure 3 , Figure 4 , Figure 5 and Figure 6 As shown, the metamaterial array with three columnar units exhibits three distinct absorption peaks, while the metamaterial arrays with one and two columnar units have only two distinct absorption peaks, and the metamaterial array with four columnar units has only one distinct absorption peak. Therefore, a metamaterial array with three columnar units per periodic unit can generate multiple localized resonant modes through coupling, with each mode exhibiting three absorption peaks in the spectrum. This "multi-peak characteristic" can cover a wider range of gas absorption spectra, increasing the variety of gases detected and making it more suitable for gas sensing.

[0059] In addition, based on the metamaterial array containing three columnar arm units in each cycle, this invention further optimizes the arm length of the columnar arm units on the basis of the above-mentioned basic parameter scheme. Figure 7 The effect of arm length d on the reflection spectrum is shown. When the arm length d changes, the intensity and wavelength of two peaks in the reflection spectrum also change, thus demonstrating the necessity of the 3D column arm unit structure.

[0060] Furthermore, based on a metamaterial array containing three columnar arm units in each cycle, this invention further explores the influence of different columnar arm unit sizes on the final device performance, building upon the aforementioned basic parameter scheme. Figure 8 A schematic diagram of a metamaterial array composed of 3×3 subarrays is shown, containing a total of nine 9×10 subarrays. Each periodic cell in each 9×10 subarray contains three columnar arm elements (the cantilever centerlines of the three columnar arm elements intersect each other at a 120° angle). The structural dimensions of the columnar arm elements within the same subarray are identical. However, the overall dimensions of the columnar arm elements in different arrays are scaled down by different ratios from the aforementioned basic parameter scheme. The nine scaling ratios are 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, and 1.2, resulting in different overall scaling ratios for the structural dimensions of the columnar arm elements between different subarrays. Thus, the array with a scaling ratio of 1 corresponds exactly to the aforementioned basic parameter scheme. Figure 9 Simulation results show the relationship between reflectivity and wavelength for a 3×3 metamaterial array. The simulation results demonstrate that different scaling ratios cause different shifts in the absorption peaks of the reflection spectrum. Therefore, different subarrays within the aforementioned metamaterial array possess different characteristic absorption peaks, which can be used to detect the concentrations of different gases.

[0061] Therefore, the geometry and arrangement of metamaterial arrays can be precisely designed to 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 Figure 8 The metamaterial array design shown was printed using two-photon polymerization 3D printing technology via a Nanoscribe Photonic Professional GT 3D micro-printer. During printing, a 1.45μm thick silicon dioxide (SiO2) substrate was used as the base. A negative photolithography resin material (IP-Dip photopolymer resin) was then deposited on the substrate to print the column arm unit array. The printing precision reached the nanometer level, ensuring accurate reproduction of the metamaterial array's geometry.

[0063] (2) Deposition of metal coatings

[0064] After the metamaterial array is printed, a metal coating is applied to optimize its optical properties. Because the three-dimensional metamaterial structure can cause occlusion, preventing the metal film from being deposited on the obscured parts, traditional sputtering techniques are not feasible. This invention employs a chemical plating method for film deposition. First, the sample is cleaned by immersing it in an acetone solution with gentle agitation. Then, the sample is rinsed in deionized water (DI water), then immersed in NaOH solution, and rinsed with DI water for 1 minute. Next, the sample surface is sensitized by immersion in an aqueous solution containing SnCl₂·2H₂O and HCl, followed by rinsing with DI water. After sensitization, the sample surface is activated by immersion in an aqueous solution containing PdCl and HCl, followed by rinsing with DI water. After activation, the sample surface is metallized by immersion in a nickel plating bath containing equal volumes of electroless nickel plating kits A and B. The metallization process is performed at 80°C with vigorous stirring, and the coating 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 completing this step, remove the sample and rinse it in DI water, then allow it to air dry. The metallic coating significantly enhances the light absorption performance of the metamaterial array in the mid-infrared band and improves its adsorption capacity for gas molecules.

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

[0066] The coated metamaterial array 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 emits mid-infrared incident light into the metamaterial array; the detection unit receives the reflected light signal generated by the interaction between the metamaterial array and gas molecules, obtaining the reflection spectrum; and the signal processing unit extracts the characteristic absorption peak intensity of the gas to be detected from the reflection spectrum detected by the detection unit and calculates the gas concentration on the surface of the metamaterial array through conversion.

[0067] However, it should be noted that the aforementioned mid-infrared gas sensor system involves an optical path, therefore auxiliary components may need to be introduced depending on the specific layout. In this embodiment, such as... Figure 10The diagram illustrates an exemplary mid-infrared gas sensor system with an optical path, comprising 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, and a gas chamber 8. The detection unit 7 is also connected to an external signal processing unit. The light source unit 6 employs 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 employs a digital signal processor (DSP). The gas chamber 8 has an inlet 801 and an outlet 802, maintaining an airtight interior. A light-transmitting window is located on the top surface, allowing the gas to be detected to be continuously introduced into the gas chamber 8 through the inlet 801 and discharged through the outlet 802. Figure 8 The metamaterial array 1 shown is embedded in the gas chamber 8, with the side having the columnar arm unit array facing the light-transmitting window. After the gas to be detected is introduced, the columnar 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 NA objective lens 4, and then shines on the metamaterial array 1 after passing through the light-transmitting window of the gas chamber 8. The reflected light signal is generated after the metamaterial array interacts with the gas molecules. The reflected light signal continues to return along the optical path, and is received by the detection unit 7 after passing through the NA objective lens 4 and the beam splitter 5. The detection unit 7 obtains the reflection spectrum based on 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 contains multiple subarrays, and the structural dimensions of the columnar arm units between different subarrays have different overall scaling ratios, as shown in the aforementioned performance comparison, the absorption peaks of subarrays with different scaling ratios are different. Therefore, for different gas types, it may be necessary to focus the incident light onto the corresponding subarray using a low numerical aperture objective lens 4 according to the wavelength of its 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 testing and calibration

[0070] The assembled mid-infrared gas sensor system underwent performance testing and calibration. First, the metamaterial array 1 was exposed to gas environments of varying concentrations (e.g., CO2, CH4, NO2), and the results were compared using a gas concentration analyzer to ensure accurate correspondence between the sensor output signal and the actual gas concentration. By adjusting the mapping relationship built into the signal processing unit and other necessary parameters, the sensor's sensitivity and response time were optimized, completing the sensor calibration.

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

[0072] A calibrated mid-infrared gas sensor system can be applied to environmental monitoring, industrial gas emission control, and indoor air quality detection. In practical applications, the sensor rapidly responds to fluctuations in gas concentration by detecting changes in the mid-infrared spectrum of the gas in real time, and provides accurate concentration data through a signal processing module. By connecting to a monitoring system, users can obtain gas monitoring data in real time and adjust the equipment operating parameters as needed.

[0073] (6) Application scenarios of sensors

[0074] This mid-infrared gas sensor system is particularly suitable for applications requiring high sensitivity, rapid 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; and 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 Embodiment 1 of this invention, three gases—CO2, CH4, and NO2—were selected for the experiment. The experimental steps are as follows:

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

[0078] (2) The reflection spectrum signal generated by the interaction between gas molecules and sensor metamaterial array is recorded in real time by the detection unit 7.

[0079] (3) Based on the characteristic absorption peak wavelength of each gas, the corresponding absorption peak intensity is extracted from the reflection spectrum signal, and the gas concentration data is analyzed and output in real time through the signal processing unit to verify the sensor’s detection sensitivity and accuracy for different gases.

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

[0081] Example 3: Application of Mid-Infrared Gas Sensors in Industrial Emission Monitoring

[0082] In industrial emission monitoring, the mid-infrared gas sensor system assembled and calibrated in Embodiment 1 of this invention can effectively monitor changes in the concentration of emitted gases and promptly detect excessive emissions. The sensor is installed at the emission outlet and monitors the mid-infrared absorption characteristics of the gas in real time. When the gas concentration exceeds a set safety threshold, the signal processing module immediately issues an alarm signal, notifying personnel to take appropriate measures. This function effectively ensures industrial safety and reduces the emission of harmful gases. For example, at the emission outlet of a chemical plant, this sensor is used to detect changes in the concentrations of methane, carbon dioxide, and hydrogen sulfide. 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 sensors in indoor air quality detection

[0084] To verify the effectiveness of the mid-infrared gas sensor system assembled and calibrated in Embodiment 1 of this invention in indoor air quality detection, this embodiment tested the performance of the gas sensor in a standardized indoor environment. The indoor environment included common indoor pollutants such as CO2, methane, ammonia, and TVOC (total volatile organic compounds). This embodiment tested the gas sensor in a standardized indoor environment (volume 30 m³) at different concentrations (CO2 1000 ppm, methane 150 ppm, ammonia 50 ppm). Experimental results show that this sensor can respond quickly and accurately measure the concentration of various gases, making it suitable for indoor air quality monitoring and capable of promptly detecting air quality declines and providing early warnings.

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

[0086] This embodiment demonstrates how to apply the mid-infrared gas sensor of the present invention to a portable gas detection device. This device is compact and lightweight, suitable for emergency response and on-site detection applications. Specifically, by employing the gas sensor of the present invention and integrating it into a portable device powered by a built-in battery, the device can operate for extended periods in the field. The device transmits real-time data to the cloud via wireless communication, allowing users to view gas concentration data in real time via mobile devices. Such portable gas detection devices can be rapidly deployed and provide real-time gas detection data, making them widely applicable to scenarios such as industrial safety, environmental monitoring, and emergency response.

[0087] In summary, through the verification of the above embodiments, the mid-infrared gas sensor based on a 3D-printed metamaterial array of the present invention possesses high sensitivity, fast response, low cost, and multi-gas detection capabilities, and can be widely applied in fields such as environmental monitoring, industrial gas emission control, and indoor air quality detection. The sensor's flexible design allows it to adapt to various detection needs, providing a more efficient and accurate gas monitoring solution.

[0088] However, it should be noted that the embodiments described above are only some preferred implementations of the present invention, and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A mid-infrared gas sensor based on 3D-printed metamaterials, characterized in that, It includes a metamaterial array, a light source unit, a detection unit, and a signal processing unit; 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 cantilever 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. 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 by the interaction between the metamaterial array and gas molecules, and to 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 to calculate the gas concentration on the surface of the metamaterial array through conversion.

2. The mid-infrared gas sensor based on 3D-printed metamaterials as described in claim 1, characterized in that, In the metamaterial array, the side length of each periodic unit is 3-4 μm, and the support column and cantilever of each columnar arm unit are both cylindrical with a cross-sectional radius of 0.1-0.5 μm. The height of the support column is 1-1.8 μm, and the length of the cantilever is 0.5-1.5 μm. The thickness of the substrate is 1-2 μm, and the thickness of the metal thin film is 50-200 nm.

3. The mid-infrared gas sensor based on 3D-printed metamaterials as described in claim 1, characterized in that, The substrate is made of silicon or silicon dioxide.

4. The mid-infrared gas sensor based on 3D-printed metamaterials as described in claim 1, characterized in that, The column arm unit is manufactured by printing photopolymer materials that can be 3D printed using two-photon polymerization 3D printing technology.

5. The mid-infrared gas sensor based on 3D-printed metamaterials as described in claim 1, characterized in that, The material of the metal film is one or an alloy of gold, silver, aluminum, and nickel.

6. The mid-infrared gas sensor based on 3D-printed metamaterials as described in claim 1, characterized in that, The metamaterial array has multiple subarrays. The structural dimensions of the column arm units in the same subarray are the same, while the structural dimensions of the column arm units in different subarrays have different overall scaling ratios.

7. The mid-infrared gas sensor based on 3D-printed metamaterials as described in claim 1, characterized in that, The light source unit employs a quantum cascade laser capable of emitting mid-infrared light.

8. The mid-infrared gas sensor based on 3D-printed metamaterials as described in claim 1, characterized in that, The detection unit employs a mercury cadmium telluride detector or a pyroelectric detector.

9. A method for fabricating a metamaterial array for a mid-infrared gas sensor, characterized in that, include: S1. Based on the pre-designed three-dimensional geometric model of the metamaterial array, the photopolymer material is printed on the substrate using two-photon polymerization 3D printing technology to form a combination of the substrate and the column arm unit array. S2. A metal thin film is deposited on the surface of the column arm unit array of the assembly and the front side of the substrate using chemical plating. After cleaning and drying, a metamaterial array is obtained.

10. A method for detecting gas concentration using a mid-infrared gas sensor based on 3D-printed metamaterials as described in claim 1, characterized in that, The metamaterial array is placed in the gas atmosphere to be detected. The light source unit emits mid-infrared incident light into the metamaterial array, and the detection unit receives the reflected light signal generated by the interaction between the metamaterial array and gas molecules to obtain the reflection spectrum. Finally, the signal processing unit extracts the characteristic absorption peak intensity of the gas to be detected from the reflection spectrum, calls the 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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