A gas sensing system and a method for detecting concentration of volatile organic compounds

Abstract

The application discloses a gas sensing system and a volatile organic compound concentration detection method. The gas sensing system comprises a laser light source, a liquid crystal-polymer composite material film, and an image acquisition device and a processor which are electrically connected with each other. The liquid crystal-polymer composite material film is exposed in an environment without volatile organic compounds and an environment with volatile organic compounds in sequence, so that the arrangement mode of liquid crystal molecules of the liquid crystal-polymer composite material film changes, and the scattering state of laser light changes. The image acquisition device acquires the image of a speckle light field formed by scattering of laser light by the liquid crystal-polymer composite material film. Due to the change of the arrangement mode of the liquid crystal molecules, the image also changes. The processor obtains the gas concentration of the volatile organic compounds by comparing the correlation coefficients of the images. The gas sensing system of the scheme realizes VOC detection by using the change of the image, and has a relatively simple overall structure and low cost.

Description

Technical Field

[0001] This application relates to the field of gas sensing technology, and in particular to a gas sensing system and a method for detecting the concentration of volatile organic compounds. Background Technology

[0002] Volatile organic compounds (VOCs) are chemical substances with relatively high vapor pressures at room temperature and atmospheric pressure. VOCs are primarily emitted in a gaseous state, thus posing a threat to the atmospheric environment and human life. VOC emission sources are widespread, including both natural elements and human activities.

[0003] VOCs can be detected using gas sensors, which are generally applied in various fields such as health management, environmental monitoring, public safety, agriculture, and food production, where there is a high demand for VOC detection. Currently reported methods for VOC detection mainly include mass spectrometry and gas chromatography. These methods require sample collection and laboratory analysis, making the detection process relatively complex. Furthermore, the detection equipment is mostly bulky, complex in structure, expensive, and energy-intensive, requiring highly trained professionals for operation, making them unsuitable for on-site real-time detection and widespread application. Summary of the Invention

[0004] To address the aforementioned issues, this application provides a gas sensing system and a method for detecting the concentration of volatile organic compounds, with the aim of providing a simple and low-cost gas sensing system for VOC detection.

[0005] The embodiments of this application disclose the following technical solutions:

[0006] The first aspect of this application provides a gas sensing system, which includes: a laser light source, a liquid crystal-polymer composite film, and an image acquisition device and a processor electrically connected to each other;

[0007] The laser source is used to emit laser light toward the liquid crystal-polymer composite film;

[0008] When the liquid crystal-polymer composite film is exposed to an environment free of volatile organic compounds and an environment containing volatile organic compounds, the arrangement of the liquid crystal molecules in the liquid crystal-polymer composite film changes.

[0009] The image acquisition device is used to acquire a first image of the speckle light field formed by the laser scattering of the liquid crystal-polymer composite film when the liquid crystal-polymer composite film is exposed to an environment without volatile organic compounds, and to acquire a second image of the speckle light field formed by the laser scattering of the liquid crystal-polymer composite film when the liquid crystal-polymer composite film is exposed to an environment containing volatile organic compounds.

[0010] The processor is used to obtain the gas concentration of the volatile organic compound when the image acquisition device acquires the second image by comparing the correlation coefficients of the first image and the second image.

[0011] In one alternative implementation, the liquid crystal-polymer composite film is disposed between the laser light source and the image acquisition device.

[0012] In one optional implementation, the system includes a gas chamber, on which the liquid crystal-polymer composite film is disposed on the sample stage inside the gas chamber; a first transparent optical window is provided at the top of the gas chamber, and a second transparent optical window is provided at the bottom of the gas chamber; the first transparent optical window is located between the liquid crystal-polymer composite film and the image acquisition device, and the second transparent optical window is located between the liquid crystal-polymer composite film and the laser source.

[0013] In one optional implementation, the air chamber is provided with an air inlet and an air outlet;

[0014] In the first stage after the laser source emits a laser to the liquid crystal-polymer composite film, air is first introduced into the air inlet of the gas chamber so that the image acquisition device can capture the first image;

[0015] In the second stage after the laser source emits a laser beam onto the liquid crystal-polymer composite film, a volatile organic compound is introduced into the air inlet of the gas chamber, and the air introduced into the gas chamber in the first stage is discharged from the air outlet, so that the image acquisition device can capture the second image.

[0016] In one alternative implementation, the liquid crystal-polymer composite film is one or more of the following combinations:

[0017] Liquid crystal gel film, polymer-dispersed liquid crystal PDLC film, or polymer-stabilized liquid crystal PSLC film.

[0018] In one alternative implementation, the liquid crystal-polymer composite film includes a polymer network and liquid crystal droplets dispersed within the polymer network. Before the liquid crystal-polymer composite film is exposed to an environment containing volatile organic compounds, the liquid crystal molecules within the liquid crystal droplets are nematic phases, and the long axes of the liquid crystal molecules have an orientation sequence.

[0019] In one alternative implementation, the liquid crystal-polymer composite film is successively exposed to an environment containing volatile organic compounds. The gaseous volatile organic compounds are adsorbed into the liquid crystal droplets, causing a phase transition in the liquid crystal molecules. This results in a change in the arrangement of the liquid crystal molecules, which in turn causes a change in the scattering state of the liquid crystal-polymer composite film to the laser, thus altering the image captured by the image acquisition device for the speckle light field.

[0020] In one alternative implementation, the liquid crystal-polymer composite film is positioned directly above the laser light source, and the image acquisition device is positioned directly above the liquid crystal-polymer composite film; the distance between the image acquisition device and the liquid crystal-polymer composite film is set based on the clarity requirement of the image acquisition device in capturing speckle particles in the speckle light field.

[0021] In one optional implementation, the gas sensing system further includes an alarm device, wherein the processor is further configured to compare the detected gas concentration of the volatile organic compound with a preset concentration threshold, and if the detected gas concentration exceeds the preset concentration threshold, send an alarm command to the alarm device.

[0022] The alarm device is used to activate the alarm mechanism to indicate that the gas concentration exceeds the preset concentration threshold according to the alarm command sent by the processor.

[0023] In one alternative implementation, the gas sensing system further includes a display device, wherein the processor is further configured to generate a concentration display instruction based on the detected gas concentration of the volatile organic compound;

[0024] The display device is used to display the gas concentration according to the concentration display command.

[0025] A second aspect of this application provides a method for detecting the concentration of volatile organic compounds, which is applied to a gas sensing system provided in any implementation of the first aspect. The method for detecting the concentration of volatile organic compounds includes:

[0026] Laser light is emitted from a laser source toward a liquid crystal-polymer composite film.

[0027] The liquid crystal-polymer composite film is exposed to an environment free of volatile organic compounds and an environment containing volatile organic compounds, respectively, to change the arrangement of liquid crystal molecules in the liquid crystal-polymer composite film. A first image of the speckle light field formed by laser scattering of the liquid crystal-polymer composite film when the film is exposed to an environment free of volatile organic compounds is acquired using an image acquisition device, and a second image of the speckle light field formed by laser scattering of the liquid crystal-polymer composite film when the film is exposed to an environment containing volatile organic compounds is acquired.

[0028] The processor compares the correlation coefficients of the first image and the second image to obtain the gas concentration of the volatile organic compound when the image acquisition device acquires the second image.

[0029] Compared with the prior art, this application has the following advantages:

[0030] The gas sensing system provided in this application includes a laser source, a liquid crystal-polymer composite film, and an image acquisition device and a processor electrically connected to each other. The laser source primarily emits laser light towards the liquid crystal-polymer composite film, which scatters the laser light to form a speckle light field. The image acquisition device captures images of this speckle light field. During VOC detection, the liquid crystal-polymer composite film is exposed sequentially to an environment free of volatile organic compounds and an environment containing volatile organic compounds. This alters the arrangement of the liquid crystal molecules in the film, thereby changing its scattering state towards the laser. The image acquisition device acquires a first image of the speckle light field formed by the laser scattering from the liquid crystal-polymer composite film when exposed to an environment free of volatile organic compounds, and a second image of the speckle light field formed by the laser scattering from the liquid crystal-polymer composite film when exposed to an environment containing volatile organic compounds. Due to the change in the arrangement of the liquid crystal molecules, the image of the speckle light field also changes; that is, the second image differs from the first image. The processor obtains the gas concentration of volatile organic compounds (VOCs) when the image acquisition device acquires the second image by comparing the correlation coefficients of the first and second images. The gas sensing system provided in this solution utilizes image changes to achieve VOC detection. Its overall structure is relatively simple, its cost is low, and it does not require highly specialized skills from operators, making it suitable for on-site detection and facilitating widespread VOC detection applications. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1A This application provides a schematic diagram of the basic structure of a gas sensing system.

[0033] Figure 1B This is a schematic diagram of an example structure of a gas sensing system provided in an embodiment of this application;

[0034] Figure 2 This is a schematic diagram of the internal structural transformation of a liquid crystal-polymer composite film;

[0035] Figure 3 This is a schematic diagram of the structure of a single liquid crystal droplet when a liquid crystal-polymer composite film is exposed to an environment containing volatile organic compounds.

[0036] Figure 4 This is a schematic diagram illustrating the calculation of volatile organic compound gas concentrations based on the correlation coefficients between images in an image sequence.

[0037] Figure 5 This is a schematic diagram illustrating the change in the correlation coefficient of the image as volatile organic compounds are introduced and removed.

[0038] Figure 6 This is a flowchart illustrating a method for detecting the concentration of volatile organic compounds provided in an embodiment of this application. Detailed Implementation

[0039] As described above, current equipment for VOC detection using mass spectrometry and gas chromatography generally suffers from complex detection processes, large and complex structures, high prices and high energy consumption, and requires a high level of professional skills from the operators.

[0040] Liquid crystals, as a special functional material between solids and liquids, possess properties of both liquids and crystals, making them an ideal signal transduction material. They readily respond to external stimuli, such as electric fields, magnetic fields, light, pressure, temperature, and chemical analytes. Certain types of volatile organic compounds (VOCs) can diffuse or even dissolve into liquid crystal materials, altering their orientation or phase characteristics. This changes the optical or electrical properties of the liquid crystal material. Past research using micrometer-thick, low-molecular-weight liquid crystal films has shown poor stability, and the micropores or micropillar arrays filling the liquid crystal involve complex microfabrication processes. VOC gas sensors based on liquid crystal materials require characterizing the detection results through changes in the brightness of the liquid crystal in the field of view of a polarizing microscope. Polarizing microscopes typically include polarizers, analyzers, and other components, resulting in complex structures, large sizes, and high manufacturing costs. Furthermore, relying solely on human visual brightness resolution often fails to accurately identify the concentration of VOCs.

[0041] To address the above problems, the inventors have proposed a technology for VOC concentration detection based on the changes in images before and after speckle light fields and the correlation coefficients between images. This technology is mainly implemented through a novel gas sensing system. This system solves the problems of complex structure, large size, and high cost of previous detection equipment. It does not require visual inspection, reduces reliance on human expertise, and can automatically calculate and obtain the detection results of VOC gas concentration.

[0042] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0043] See Figure 1A This figure is a schematic diagram of the basic structure of a gas sensing system provided in an embodiment of this application. Figure 1A The gas sensing system shown includes: a laser light source 1, a liquid crystal-polymer composite film 3, and an image acquisition device 5 and a processor 6 that are electrically connected to each other.

[0044] The laser source 1 can be a laser with a wavelength of 520nm, and the image acquisition device can be a small complementary metal-oxide-semiconductor (CMOS) camera.

[0045] Laser source 1 emits laser light onto liquid crystal-polymer composite film 3. The liquid crystal-polymer composite film 3 is exposed to environments without volatile organic compounds and environments containing volatile organic compounds, causing a change in the arrangement of liquid crystal molecules. In one optional implementation, the liquid crystal-polymer composite film 3 is positioned between laser source 1 and image acquisition device 5. For example, laser source 1 is positioned directly above the liquid crystal-polymer composite film 3, and image acquisition device 5 is positioned directly below the liquid crystal-polymer composite film 3. Alternatively, the laser source 1 is positioned directly below the liquid crystal-polymer composite film 3, and image acquisition device 5 is positioned directly above the liquid crystal-polymer composite film 3, with the relative positions as follows: Figure 1A As shown. It should be noted that in the gas sensing system provided in this application embodiment, the distance between the image acquisition device 5 and the liquid crystal-polymer composite film 3 is set based on the clarity requirements for the image acquisition device 3 to capture speckle particles in the speckle light field. In one example, the image acquisition device 5 and the liquid crystal-polymer composite film 3 are 18 cm apart to ensure that the image acquisition device 5 can accurately capture speckle particles of suitable size. In other implementations, the distance can be set with reference to the parameters of the optical components of the image acquisition device 5, such as the object distance and focal length of the optical components.

[0046] When the laser emitted by the laser source 1 is scattered by the liquid crystal-polymer composite film 3, a speckle light field is formed. Based on the distance between the image acquisition device 5 and the liquid crystal-polymer composite film 3, the speckle light field can be imaged, and the resulting image can be called a speckle image. The correlation between the speckle images acquired by the image acquisition device 5 under different gas environment conditions reflects the degree of environmental change. This scheme utilizes this characteristic to analyze VOC gas concentration.

[0047] When used for detection, the gas sensing system can be directly placed in the environment where the concentration of the VOC gas to be detected is located. During experimental verification, a gas chamber can also be set up in the gas sensing system to construct a specific gas environment within it. In other words, the gas chamber is a non-essential component in the gas sensing system provided in this application embodiment. The following is in conjunction with... Figure 1B An exemplary description is provided for a gas sensing system having a gas chamber.

[0048] Figure 1B This application provides an example structural schematic diagram of a gas sensing system according to an embodiment. Distinguished from... Figure 1A The basic structure of the gas sensing system shown is as follows: Figure 1BIn the diagram, the dashed box represents the gas chamber 7, and the liquid crystal-polymer composite film 3 is disposed on the sample stage 8 inside the gas chamber 7; the top of the gas chamber 7 is provided with a first transparent optical window 9, and the bottom of the gas chamber 7 is provided with a second transparent optical window 10. The first transparent optical window 9 is located between the liquid crystal-polymer composite film 3 and the image acquisition device 5, and the second transparent optical window 10 is located between the liquid crystal-polymer composite film 3 and the laser source 1.

[0049] In one alternative implementation, the gas chamber 7 is provided with an inlet 7-1 and an outlet 7-2. Gas enters the gas chamber 7 through the inlet 7-1, and when it is necessary to expel the current gas in the gas chamber 7, the gas is discharged through the outlet 7-2. In one example, the gas in the gas chamber 7 is air. Then, the inlet 7-1 and the outlet 7-2 are opened, and VOCs are introduced through the inlet 7-1, increasing the concentration of VOCs in the gas chamber 7. During this period, the liquid crystal-polymer composite film 3 can continuously respond to the VOCs. Then, air continues to be introduced through the inlet 7-1, so that the VOCs in the gas chamber 7 are continuously discharged through the outlet 7-2, and the concentration of VOCs in the gas chamber 7 decreases until the gas chamber 7 is filled with air, at which point the liquid crystal-polymer composite film 3 ends its response to the VOCs.

[0050] To detect VOC concentration, the image acquisition device 5 acquires a first image of the speckle light field formed by laser scattering from the liquid crystal-polymer composite film 3 when the film is exposed to an environment free of volatile organic compounds, and a second image of the speckle light field formed by laser scattering from the liquid crystal-polymer composite film 3 when the film is exposed to an environment containing volatile organic compounds. In the first stage after the laser source 1 emits laser light onto the liquid crystal-polymer composite film 3, air is first introduced into the air inlet 7-1 of the gas chamber 7 to allow the image acquisition device 5 to capture the first image. In the second stage after the laser source 1 emits laser light onto the liquid crystal-polymer composite film 3, volatile organic compounds (VOCs) are introduced into the air inlet 7-1 of the gas chamber 7, and the air introduced into the gas chamber 7 in the first stage is discharged from the air outlet 7-2 to allow the image acquisition device 5 to capture the second image.

[0051] Because the gas environment of the liquid crystal-polymer composite film 3 is drastically different in the two stages (note that this does not refer to the change in the position of the liquid crystal-polymer composite film 3), the arrangement of the liquid crystal molecules in the liquid crystal-polymer composite film 3 changes, leading to a change in the scattering state of the liquid crystal-polymer composite film 3 to the laser, resulting in a change in the image captured by the image acquisition device 5 for the speckle light field. Therefore, a comparison can be formed between the first image and the second image, both reflecting the change in the gas environment.

[0052] In the gas sensing system provided in this application embodiment, the image acquisition device 5 completes the conversion of optical signals to electrical signals, transforming the acquired optical signals into electrical signals corresponding to the image. The image acquisition device can send the image to the processor 6 via an electrical connection, whereby the processor 6 performs computational processing based on the speckle image. The processor 6 is used to obtain the gas concentration of volatile organic compounds when the image acquisition device 5 acquires the second image by comparing the correlation coefficients of the first and second images.

[0053] Figure 1A and Figure 1B In the process, laser 2 is emitted by laser source 1 and incident on liquid crystal-polymer composite film 3. After passing through liquid crystal-polymer composite film 3, scattered light 4 is formed and acquired by image acquisition device 5 to obtain the image of the corresponding speckle light field.

[0054] Figure 2 This is a schematic diagram illustrating the internal structural transformation of a liquid crystal-polymer composite film, showing the structural changes after VOC adsorption and desorption. Figure 2 As shown, the liquid crystal-polymer composite film includes a polymer network 3.1 and liquid crystal droplets 3.2, wherein the liquid crystal droplets 3.2 are dispersed within the polymer network 3.1. The liquid crystal droplets 3.2 contain... Figure 3 The liquid crystal molecule 3.2.1 is shown. Before the liquid crystal-polymer composite film is exposed to an environment containing volatile organic compounds, the liquid crystal molecules 3.2.1 within the liquid crystal droplets 3.2 are nematic phases, and the long axes of the liquid crystal molecules 3.2.1 have an orientation sequence.

[0055] Figure 3 This is a schematic diagram of the structure of a single liquid crystal droplet when a liquid crystal-polymer composite film is exposed to an environment containing volatile organic compounds. (Combined with...) Figure 3 It is not difficult to observe that when the liquid crystal-polymer composite film is exposed to an environment containing volatile organic compounds (VOCs), the gaseous molecules 3.2.2 of the VOCs are adsorbed into the liquid crystal droplets 3.2, causing a phase transition of the liquid crystal molecules 3.2.1 within the droplets 3.2. This leads to a change in the arrangement of the liquid crystal molecules 3.2.1 within the droplets 3.2, and consequently, a change in the refractive index of each droplet 3.2. Throughout this process, the refractive index of the polymer network 3.1 remains unaffected. When the gaseous molecules 3.2.2 of the VOCs are desorbed from the liquid crystal droplets 3.2, the arrangement of the liquid crystal molecules 3.2.1 gradually returns to its initial state. The transition between these two states can be found in [reference needed]. Figure 2 As shown.

[0056] In one alternative implementation, Figure 1A and Figure 1B The liquid crystal-polymer composite film 3 shown is one or a combination of the following: liquid crystal gel film, polymer dispersed liquid crystal (PDLC) film, or polymer stabilized liquid crystal (PSLC) film. Several example preparation methods for the liquid crystal-polymer composite film 3 are provided below.

[0057] Preparation Example 1:

[0058] The liquid crystal-polymer composite film 3 is a liquid crystal gel film. The liquid crystal gel film is composed of 5CB liquid crystal and a polystyrene microsphere network, wherein the ordinary and extraordinary refractive indices of the 5CB liquid crystal are respectively: n o =1.53, n e =1.71; the polystyrene microspheres have a particle size of 500 nm and a refractive index of 1.59–1.60. An example of the preparation method for the liquid crystal gel film is as follows:

[0059] (1) Preparation of polystyrene microspheres by soap-free emulsion polymerization

[0060] First, styrene containing the polymerization inhibitor was washed four times with a 10wt% sodium hydroxide solution, then washed with deionized water until neutral, and then dried with a small amount of anhydrous magnesium sulfate for later use. 0.1g of potassium persulfate solid was dissolved in 20ml of deionized water to prepare the initiator solution. 10g of styrene and 100g of deionized water were added to a 250ml four-necked flask in a reflux condenser. The mixture was stirred continuously at 350r / min for 15min at room temperature, while nitrogen (N2) was introduced. Then, the temperature was raised to 70℃, the initiator solution was added, and the stirring speed was set to 250r / min, and the reaction was continued for 24h. After the reaction was complete, the reaction product was centrifuged at 9000r / min for 10min in a high-speed centrifuge. The supernatant was discarded, and the remaining solid was washed three times by centrifugation in deionized water. Finally, the solid was ultrasonically dispersed again in deionized water to prepare a microsphere suspension. The microsphere suspension was dried at room temperature for three days to obtain polystyrene microsphere powder.

[0061] (2) Preparation of liquid crystal gel

[0062] At room temperature, 5CB liquid crystal was mixed with the polystyrene microsphere powder prepared in step (1) above at a certain mass fraction ratio to form a mixture of liquid crystal and polystyrene microsphere powder. The mixture was ultrasonically dispersed at 60°C for 6 hours to form a homogeneous solution. The homogeneous solution was placed in a muffle furnace and the cooling rate was set to 0.2°C / min to cool the homogeneous solution to room temperature, forming a liquid crystal gel.

[0063] (3) The liquid crystal gel is pressed into a film. The operation procedure is as follows:

[0064] A small amount of the liquid crystal gel prepared in step (2) was placed on a substrate glass slide. A polyethylene terephthalate (PET) film of a certain thickness was placed around the liquid crystal gel on the substrate glass slide. The substrate glass slide was placed on a heating stage and heated to 60°C to make the liquid crystal gel transparent and suspended. A hydrophobic top glass slide was placed on the substrate glass slide to form an assembly. The assembly was clamped and quickly transferred to a muffle furnace and cooled to room temperature at a cooling rate of 0.2°C / min. The top glass slide was removed to obtain the liquid crystal gel film.

[0065] Preparation Example 2:

[0066] Liquid crystal-polymer composite film 3 is a polymer-dispersed liquid crystal PDLC film. The polymer-dispersed liquid crystal film is composed of E7 liquid crystal and NOA65 UV-curable polymer, wherein the ordinary light refractive index and extraordinary light refractive index of the E7 liquid crystal are respectively: n o =1.52, n e =1.75; the refractive index of NOA65 UV-cured polymer after curing is 1.52. The preparation method of PDLC film is as follows:

[0067] (1) Weigh E7 liquid crystal and NOA65 UV-curable polymer solution according to a certain mass fraction ratio. After mixing E7 liquid crystal and NOA65 UV-curable polymer, use an ultrasonic machine at 60°C for 90 minutes under light-shielding conditions to make E7 liquid crystal and NOA65 polymer evenly mixed. Let the mixture stand to obtain PDLC solution.

[0068] (2) Spin-coat the PDLC solution onto the glass substrate.

[0069] (3) The PDLC solution spin-coated on the glass substrate is cured by ultraviolet exposure to obtain a PDLC film.

[0070] It should be noted that in the above two embodiments for preparing liquid crystal gel films and PDLC films, the settings of parameters such as temperature, processing time, and cooling rate used in the preparation process are only examples, and the vessels and vessel shapes used are also examples, and are not intended to limit the method of preparing liquid crystal-polymer composite films. In actual applications, the selection of parameters and vessels can be determined specifically according to the preparation requirements.

[0071] In one example, acetone gas was used as the volatile organic compound to describe the changes in the liquid crystal gel film. The liquid crystal gel film was placed... Figure 1B On the sample stage 8 inside the gas chamber 7. Acetone gas enters the gas chamber 7 through the inlet 7-1 and exits the gas chamber 7 through the outlet 7-2.

[0072] Because the refractive index of the polystyrene microsphere network in the liquid crystal gel film is mismatched with that of the 5CB liquid crystal droplets, a scattered field is formed when the incident laser 2 propagates through the polystyrene microsphere network and the 5CB liquid crystal droplets. The scattered light 4 exits from the first transparent optical window 9 at the top of the gas chamber 7. Since the incident laser 2 has good coherence, the scattered light 4 in the scattered field will undergo random interference in space, exhibiting a laser speckle pattern with uneven light intensity distribution and alternating bright and dark areas.

[0073] When acetone gas is introduced into the gas chamber 7, acetone gas molecules are adsorbed into the liquid crystal droplets of the liquid crystal gel film, changing the arrangement of the liquid crystal molecules within the droplets. When the acetone gas introduced into the gas chamber 7 is replaced with air, the acetone gas molecules in the liquid crystal droplets are purged and escape, restoring the initial arrangement of the liquid crystal molecules. During this change in the arrangement of liquid crystal molecules, the scattering state of the liquid crystal gel film changes accordingly, leading to a change in laser speckle. The image captured by the image acquisition device 5 also changes.

[0074] The image acquisition device 5 can perform the shooting action according to a preset time interval. For example, it may capture one image every 5 seconds. In an optional embodiment, clean and dry air is introduced into the air chamber 7 before the timing begins. When t = 0s, the image acquisition device 5 captures the first speckle image; subsequently, speckle images are continuously captured. When t = 300s, the air supply is stopped while the acetone gas is continuously introduced into the air chamber 7. When t = 1200s, the acetone gas supply is stopped, and air is introduced into the air chamber again for purging. When t = 1800s, the image acquisition device 5 captures the last speckle image and then stops shooting.

[0075] Figure 4This diagram illustrates the calculation of volatile organic compound (VOC) gas concentrations based on the correlation coefficients between images in an image sequence. In an optional embodiment, the captured speckle images form an image sequence, which can be represented as: [speckle image 1, speckle image 2, ..., speckle image m, ..., speckle image n] according to the chronological order of image capture (acquisition). Speckle image 1 is the first speckle image, and speckle image n is the last speckle image. The introduction of VOC gas occurs between capturing speckle image 2 and capturing speckle image m, and the removal of VOC gas occurs between capturing speckle image m and capturing speckle image n. Each speckle image captured after speckle image 1 can have its correlation coefficient calculated with speckle image 1. Figure 4 In the middle, ρ 1,1 , ρ 1,2 , ρ 1,m , ρ 1,n Let represent the correlation coefficients of speckle image 1, speckle image 2, speckle image m, and speckle image n with speckle image 1, respectively.

[0076] Figure 5 This is a schematic diagram illustrating the change in the correlation coefficient of the image as volatile organic compounds are introduced and removed. (Combined with...) Figure 5 It is evident that before the introduction of VOC gas (i.e., during the stage when the liquid crystal-polymer composite film is exposed to a VOC-free environment), the correlation coefficient remains stable at a high level, indicating that the arrangement of liquid crystal molecules in the film has not changed significantly, resulting in a high correlation between the image and the earliest captured image. From the introduction of VOC gas, the correlation coefficient between the captured speckle image and the earliest captured speckle image continuously decreases, indicating that the gas sensing system responds to the introduced VOC gas. When the correlation coefficient decreases to a point where it gradually becomes constant, it indicates that the adsorption capacity of the liquid crystal-polymer composite film for VOC gas molecules is approaching saturation. When the gas sensing system removes the VOC gas and reintroduces air, the calculated correlation coefficient rebounds, indicating that the VOC gas molecules dissolved in the liquid crystal-polymer composite film gradually escape from the film, and the arrangement of liquid crystal molecules gradually returns to its initial state, until the calculated image correlation coefficient approaches the highest correlation coefficient level calculated earlier. At this point, the gas sensing system's response to VOC gas ends. Figure 5 It can be seen that by comparing the correlation coefficients between each image in the image sequence captured by the image acquisition device 5 before and after the introduction of VOC gas and the first speckle image, the concentration of the introduced VOC gas can be reflected.

[0077] In this application, the second image mentioned in the gas sensing system described above can specifically be a speckle image captured between the introduction of VOC gas and the complete escape (complete elimination) of the VOC gas from the gas chamber. The first image can specifically be a speckle image captured before the introduction of VOC gas; in the example, it can be the first speckle image captured before the introduction of VOC gas, such as... Figure 4 The speckle image shown is 1.

[0078] Each speckle image captured by the image acquisition device 5 consists of several pixels. In an optional implementation, to calculate the correlation coefficient between the captured speckle images, the images can be converted into a matrix, and the gray value of each pixel is stored in the converted matrix. The correlation coefficient between any two speckle images can be calculated using the following formula (1):

[0079]

[0080] In formula (1), I i and I j Let i represent the light intensity of the i-th speckle image and j represent the light intensity of the j-th speckle image. Let σ represent the average light intensity of the i-th speckle image and the j-th speckle image, respectively. i , σ j Let represent the standard deviation of light intensity for the i-th speckle image and the standard deviation of light intensity for the j-th speckle image, respectively.

[0081] In specific applications of the gas sensing system provided in this application, the strength or weakness of VOC gas concentration can be analyzed by combining the changes in image correlation coefficients during the introduction and removal of VOC gas. Alternatively, by pre-calibrating the mapping relationship between gas concentration and correlation coefficient, when using the gas sensing system for VOC concentration detection, only the correlation coefficient needs to be calculated, and the numerical information of VOC gas concentration can be obtained by combining the calibrated mapping relationship.

[0082] In an optional implementation, to further improve the sensitivity of the gas sensing system in detecting VOC gas concentration, this embodiment proposes to enhance the scattering degree of the liquid crystal-polymer composite film to the incident laser by setting the position or angle of the film, or by changing its shape or surface state. This makes the changes in scattered light more dramatic, resulting in more pronounced changes in the speckle image and further improving the detection sensitivity of the gas sensing system.

[0083] The gas sensing system provided in this solution detects VOCs by utilizing image changes. Its overall structure is relatively simple and low-cost, requiring minimal operator skill, making it suitable for on-site testing and facilitating widespread VOC detection applications. Compared to existing solutions, it eliminates the need for a polarizing microscope, reducing structural complexity and size. Furthermore, it eliminates the need for visually interpreting changes in liquid crystal brightness, enabling intelligent and automated calculation of gas concentration, thus making it more convenient to use and reducing the professional requirements for operators. It is suitable for on-site testing and facilitates widespread VOC detection applications.

[0084] To better inform users of specific VOC concentration levels or to provide warnings about VOC gas concentrations, the gas sensing system in this solution may further include an alarm device. A preset concentration threshold is set as the alarm's critical standard. The processor compares the detected volatile organic compound gas concentration with the preset threshold. If the detected gas concentration exceeds the preset threshold, an alarm command is sent to the alarm device. The alarm device activates the alarm mechanism based on the alarm command sent by the processor, indicating that the gas concentration has exceeded the preset threshold. Through the alarm device's alerts, users can be promptly informed of the hazards of VOC gas concentrations, providing more convenient safety and health protection for industrial production and people's lives.

[0085] In an alternative implementation, the gas sensing system also includes a display device. The display device can be a display panel, primarily used to present the detection results in conjunction with the detection mechanism. The processor also generates a concentration display command based on the detected concentration of volatile organic compounds. The display device displays the gas concentration according to the concentration display command. The display can show specific concentration values ​​or indicate concentration levels, such as high, medium, or low. The display device facilitates a more intuitive understanding of the detection results for the user, enhancing the user experience.

[0086] Based on the gas sensing system described in the foregoing embodiments, this application further provides a method for detecting the concentration of volatile organic compounds. The method is described below. Figure 6 This is a flowchart illustrating a method for detecting the concentration of volatile organic compounds provided in an embodiment of this application. Figure 6 As shown, the method includes:

[0087] S601, laser light is emitted onto the liquid crystal-polymer composite film through a laser light source.

[0088] The laser source can be manually activated or activated under the instruction of a controller to emit laser light. Referring to the previous example, the laser source can be positioned directly beneath the liquid crystal-polymer composite film, such as... Figure 1B As shown.

[0089] S602. The liquid crystal-polymer composite film is exposed to an environment without volatile organic compounds and an environment with volatile organic compounds in turn to change the arrangement of liquid crystal molecules in the liquid crystal-polymer composite film. A first image of the speckle light field formed by laser scattering of the liquid crystal-polymer composite film when the liquid crystal-polymer composite film is exposed to an environment without volatile organic compounds is acquired by an image acquisition device, and a second image of the speckle light field formed by laser scattering of the liquid crystal-polymer composite film when the liquid crystal-polymer composite film is exposed to an environment with volatile organic compounds is acquired.

[0090] Environmental adjustments for liquid crystal-polymer composite films can be achieved by introducing a specific gas into the environment surrounding the film. For example, introducing air exposes the film to a VOC-free environment; introducing VOC gas allows VOC molecules to dissolve into the film, altering the arrangement of the liquid crystal molecules, changing the scattering state of the laser, and thus altering the scattered light field, consequently affecting the image captured by the image acquisition device. Based on this, the processor can analyze the correlation coefficients between images and determine the VOC gas concentration accordingly.

[0091] S603. The processor compares the correlation coefficients of the first image and the second image to obtain the gas concentration of volatile organic compounds when the image acquisition device acquires the second image.

[0092] It should be noted that in the embodiments of this application, after VOC gas is introduced to expose the liquid crystal-polymer composite film to the VOC gas environment, air can be further introduced to allow the VOC gas to escape from the gas chamber, thereby restoring the correlation coefficient to the high value state before the introduction of VOC gas.

[0093] The proposed method for detecting the concentration of volatile organic compounds (VOCs) utilizes a gas sensing system that detects VOCs by observing changes in the image. The overall structure is relatively simple and the cost is low. It does not require highly specialized skills from operators and is suitable for on-site testing, which is conducive to the widespread application of VOC detection.

[0094] It should be noted that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for the method embodiments, since they are basically similar to the system embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the system embodiments. The system embodiments described above are merely illustrative, and the units described as separate components may or may not be physically separate. The components indicated as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of the solution in this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0095] The above description is merely one specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A gas sensing system, characterized in that, Includes: a laser light source, a liquid crystal-polymer composite film, and an image acquisition device and processor electrically connected to each other; The laser source is used to emit laser light toward the liquid crystal-polymer composite film; When the liquid crystal-polymer composite film is exposed to an environment free of volatile organic compounds and an environment containing volatile organic compounds, the arrangement of the liquid crystal molecules in the liquid crystal-polymer composite film changes. The image acquisition device is used to acquire a first image of the speckle light field formed by the laser scattering of the liquid crystal-polymer composite film when the liquid crystal-polymer composite film is exposed to an environment without volatile organic compounds, and to acquire a second image of the speckle light field formed by the laser scattering of the liquid crystal-polymer composite film when the liquid crystal-polymer composite film is exposed to an environment containing volatile organic compounds. The processor is used to obtain the gas concentration of the volatile organic compound when the image acquisition device acquires the second image by comparing the correlation coefficients of the first image and the second image.

2. The system according to claim 1, characterized in that, The liquid crystal-polymer composite film is disposed between the laser light source and the image acquisition device.

3. The system according to claim 2, characterized in that, The system includes a gas chamber, on which the liquid crystal-polymer composite film is placed on the sample stage inside the gas chamber. A first transparent optical window is provided at the top of the gas chamber, and a second transparent optical window is provided at the bottom of the gas chamber. The first transparent optical window is located between the liquid crystal-polymer composite film and the image acquisition device, and the second transparent optical window is located between the liquid crystal-polymer composite film and the laser source.

4. The system according to claim 3, characterized in that, The air chamber is provided with an air inlet and an air outlet; In the first stage after the laser source emits a laser to the liquid crystal-polymer composite film, air is first introduced into the air inlet of the gas chamber so that the image acquisition device can capture the first image; In the second stage after the laser source emits a laser beam onto the liquid crystal-polymer composite film, a volatile organic compound is introduced into the air inlet of the gas chamber, and the air introduced into the gas chamber in the first stage is discharged from the air outlet, so that the image acquisition device can capture the second image.

5. The system according to any one of claims 1-4, characterized in that, The liquid crystal-polymer composite film is one or more of the following combinations: Liquid crystal gel film, polymer-dispersed liquid crystal PDLC film, or polymer-stabilized liquid crystal PSLC film.

6. The system according to any one of claims 1-4, characterized in that, The liquid crystal-polymer composite film includes a polymer network and liquid crystal droplets, the liquid crystal droplets being dispersed within the polymer network. Before the liquid crystal-polymer composite film is exposed to an environment containing volatile organic compounds, the liquid crystal molecules within the liquid crystal droplets are nematic phases, and the long axes of the liquid crystal molecules have an orientation sequence.

7. The system according to claim 6, characterized in that, The liquid crystal-polymer composite film is exposed to an environment containing volatile organic compounds. The gaseous volatile organic compounds are adsorbed into the liquid crystal droplets, causing a phase transition of the liquid crystal molecules. This changes the arrangement of the liquid crystal molecules and leads to a change in the scattering state of the liquid crystal-polymer composite film to the laser, resulting in a change in the image captured by the image acquisition device for the speckle light field.

8. The system according to claim 2, characterized in that, The liquid crystal-polymer composite film is positioned directly above the laser light source, and the image acquisition device is positioned directly above the liquid crystal-polymer composite film. The distance between the image acquisition device and the liquid crystal-polymer composite film is set based on the clarity requirements of the image acquisition device in capturing speckle particles in the speckle light field.

9. The system according to any one of claims 1-4, characterized in that, Also includes: The alarm device, wherein the processor is further configured to compare the detected gas concentration of the volatile organic compound with a preset concentration threshold, and if the detected gas concentration exceeds the preset concentration threshold, send an alarm command to the alarm device; The alarm device is used to activate the alarm mechanism to indicate that the gas concentration exceeds the preset concentration threshold according to the alarm command sent by the processor.

10. The system according to any one of claims 1-4, characterized in that, Also includes: The display device, wherein the processor is further configured to generate a concentration display instruction based on the detected gaseous concentration of the volatile organic compound; The display device is used to display the gas concentration according to the concentration display command.

11. A method for detecting the concentration of volatile organic compounds, characterized in that, The method, applied to the gas sensing system according to any one of claims 1-10, comprises: Laser light is emitted from a laser source toward a liquid crystal-polymer composite film. The liquid crystal-polymer composite film is exposed to an environment free of volatile organic compounds and an environment containing volatile organic compounds, respectively, to change the arrangement of liquid crystal molecules in the liquid crystal-polymer composite film. A first image of the speckle light field formed by laser scattering of the liquid crystal-polymer composite film when the film is exposed to an environment free of volatile organic compounds is acquired using an image acquisition device, and a second image of the speckle light field formed by laser scattering of the liquid crystal-polymer composite film when the film is exposed to an environment containing volatile organic compounds is acquired. The processor compares the correlation coefficients of the first image and the second image to obtain the gas concentration of the volatile organic compound when the image acquisition device acquires the second image.

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