A cantilever beam type VOC gas sensor based on polyethylene film and its manufacturing method
Through the cantilever beam VOC gas sensor based on polyethylene film, the problem of expensive equipment and poor portable sensor performance in the prior art is solved, and the ability to detect VOCs is achieved at low cost, portable, and real-time. It has high sensitivity and humidity resistance, and is suitable for air quality monitoring and personal harmful gas evaluation.
Patent Information
- Application Number
- CN202310034723.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-01-10
- Publication Date
- 2025-09-02
- Estimated Expiration
- 2043-01-10
AI Technical Summary
The existing VOC detection technology equipment is expensive, bulky, requires professional places and personnel operation, and cannot achieve portable real-time detection. The existing portable sensors are expensive, have poor selectivity, and require frequent corrections, which cannot meet the needs of low-cost, portable and real-time detection.
A cantilever beam VOC gas sensor based on polyethylene film is used. Through a simple production method, traditional equipment such as laser cutting machines, roller presses and ordinary cameras are used to build low-cost, portable sensors, combined with Matlab software for data processing, achieving high sensitivity and humidity resistance.
It realizes the ability to detect VOCs in low-cost, portable, real-time VOCs, has high sensitivity and good humidity resistance, reduces maintenance costs, is easy to mass production, and has a lower detection limit of 2ppm, comparable to existing PID detectors. It is suitable for indoor and outdoor air quality monitoring and personal harmful gas exposure evaluation.
Smart Images
Figure CN116297443B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of sensor chip processing, and in particular relates to a cantilever beam type VOC gas sensor based on a polyethylene film and a manufacturing method thereof. Background Art
[0002] With the development of society and the demands of people's daily lives, volatile organic compounds (VOCs) emitted by both human and natural processes have become a major source of environmental pollution. For example, the processing and use of petroleum energy and various chemical materials emit large amounts of VOCs. Indoor and outdoor VOC pollution seriously impacts the environment, ecological security, and human health. Benzene series (BTEX), a collective term for benzene, ethylbenzene, toluene, and xylene, are among the most hazardous VOCs. For example, benzene is a carcinogen designated by the World Health Organization (WHO). Therefore, real-time monitoring of indoor and outdoor VOC and BTEX concentrations is crucial for monitoring air pollution, promoting air pollution control, and protecting people's lives and health. This also aligns with the national requirement for "focusing on people's lives and health" among the four aspects of scientific research. Therefore, the development of sensors for VOC and BTEX detection is crucial. The current gold standard for detecting individual VOC gases is gas chromatography coupled with mass spectrometry (GC-MS). However, this method is expensive, bulky, time-consuming, and requires specialized equipment and facilities for professional use, preventing real-time on-site detection. This significantly limits its widespread application.
[0003] Among various portable VOC detectors, photoionization detectors (PIDs) are widely accepted in the market. However, they remain expensive, costing at least 20,000 yuan (RAE PGM series, such as the 7300 and 7400), and are dominated by foreign technology. They provide broad-spectrum detection and lack selectivity, requiring regular calibration. PIDs have a lifespan of approximately two years, and replacement costs are high. Due to the complex composition and varying levels of harmfulness found in VOCs, greater selectivity is required. While inexpensive, electrochemical and semiconductor sensors suffer from poor performance and reliability, making them difficult to gain market acceptance. They are generally used only for qualitative reference. Summary of the Invention
[0004] The main purpose of the present invention is to use a simple and low-cost fabrication method to obtain a low-cost, portable, moisture-resistant, and highly sensitive polyethylene film-based cantilever beam VOC gas sensor.
[0005] To achieve the above objectives, the present invention provides a method for manufacturing a cantilever beam VOC gas sensor based on a polyethylene film, comprising the following steps:
[0006] Step 1: manufacturing a cantilever beam, wherein the cantilever beam comprises a supporting layer, a bonding layer and a functional layer;
[0007] Step 2: Make a sensor chamber;
[0008] Step 3: Adjust the laser and the fixed-focus camera to establish the detection optical path of the cantilever beam;
[0009] Step 4: Connect the gas line and use a micro air pump to pump the gas to be tested out of the sample bag and into the sensor chamber; and
[0010] Step 5: Build a sensor detection circuit for detection. The detection circuit is connected to the humidity sensor, power supply, data transmission line, gas sampling bag, air pump, computer, etc., and is uniformly controlled, read and processed by a self-written program code based on Matlab.
[0011] A further improvement of the present invention is that, in the step one, one end of the cantilever beam is used as a fixed end, and the protruding end is used as a free end; the supporting layer is made of 6μm copper foil as the raw material; the adhesive layer is made of 5μm double-sided tape as the raw material; the functional layer is made of 10μm polyethylene film (PE) as the raw material; the supporting layer and the functional layer are respectively located on the upper surface and the lower surface, and the middle layer is the adhesive layer, which bonds the functional layer and the supporting layer together; first apply the copper foil to one side of the double-sided tape, and then apply the PE film to the other side of the double-sided tape, and then sandwich it between multiple layers of A4 paper or weighing paper, and send it into a roller press for multiple rolling, so that the three layers of material are tightly fitted together; then use small scissors to cut it into a cantilever beam of 10mm long and 1mm wide; send the cut cantilever beam into the roller press for multiple rolling as described above, so that the three layers of the cantilever beam are tightly fitted, kept horizontal and without obvious bending.
[0012] A further improvement of the present invention is that in step 2, a laser cutting machine is used to process the sensor chamber and the sensor chamber is assembled using screws and elastic stainless steel sheets. The sensor chamber is divided into a cantilever beam fixing platform and a T-shaped gas chamber with a gas inlet and outlet. The cantilever beam in step 1 is horizontally fixed on the fixing platform of the cantilever beam chamber.
[0013] A further improvement of the present invention is that in step three, a small laser pointer-type laser is fixed to an optical breadboard using a universal shaft, and its position and angle are adjusted so that its smallest light spot is directed toward the top position of the free end of the cantilever beam at an angle of 45 degrees, and the laser brightness is adjusted so that it presents a relatively regular light spot with appropriate brightness on the copper substrate; the fixed-focus camera at the other end of the cantilever beam is adjusted with the universal shaft to clearly image the laser spot on the copper substrate in a 45-degree direction, and the laser brightness is adjusted again so that the laser spot presented at the camera end presents a regular and as small as possible light spot; the imaging of the fixed-focus camera is presented on the computer end, and the laser spot is displayed in real time.
[0014] A further improvement of the present invention is that in step five, the sensor is connected to the computer via a USB port, wherein the hygrometer and flowmeter use 485 signal transmission to present the gas humidity in real time, and the electronic flowmeter is used to detect the gas flow rate; the gas sampling bag is mainly used to load the target gas and the control gas; the air pump is used to introduce the target gas from the gas sampling bag into the gas path; the computer uses Matlab software and self-compiled program code to process the data obtained by the camera, hygrometer, and flowmeter.
[0015] A further improvement of the present invention is that a sensor box is used in step three, a T-shaped air path is present inside the sensor box, a fixing clip is located inside the sensor for fixing one end of the cantilever beam, and a transparent glass window is provided on the top of the sensor box.
[0016] A further improvement of the present invention is that the laser spot imaging optical path formed by the semiconductor laser, the fixed-focus camera and the sensor chip are kept on the same straight line, forming a detection optical path.
[0017] A further improvement of the present invention is that the sensor box has a size of 50 mm*50 mm*20 mm.
[0018] In order to achieve the above object of the invention, the present invention also provides a cantilever beam VOC gas sensor based on polyethylene film, which is manufactured according to the above method.
[0019] Compared with existing technologies, the present invention offers the following advantages: It uses a simple manufacturing method, eliminating the need for microfabrication techniques such as photolithography and etching, and eliminating the need for large, expensive, and bulky processing equipment, thus reducing costs. It also offers easy replacement, low cost, and high selectivity; high sensitivity, comparable to existing PID detectors; and excellent humidity resistance, eliminating the need for the dehumidifier CaCl2 and frequent replacement, reducing costs, improving usability, and eliminating maintenance. Furthermore, it eliminates the need for expensive PSDs, opting for a simpler, lower-cost, and more portable displacement detection algorithm based on cameras and image processing. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 It is a schematic diagram of the cantilever beam structure of the present invention.
[0021] Figure 2 1 is a diagram of the sensor chamber of the present invention.
[0022] Figure 3 It is a diagram of the detection principle of the present invention.
[0023] Figure 4 It is a schematic diagram of the detection mechanism of the present invention.
[0024] Figure 5Schematic diagram of the detection platform of the present invention.
[0025] Figure 6 This is the online image processing APP page designed by the present invention.
[0026] Figure 7 The gas sensor designed by the present invention displays a change curve of xylene.
[0027] Figure 8 The gas sensor designed by the present invention shows a change curve of xylene with different concentrations.
[0028] Figure 9 Different concentrations of xylene vs. signal calibration curve.
[0029] Figure 10 Schematic diagram of humidity influence: 30ppm under 0.5% humidity difference, at this time the humidity is 42% for indoor air RH.
[0030] Figure 11 Test curve of low concentration xylene 5ppm.
[0031] Figure 12 Responses to different VOC gases. DETAILED DESCRIPTION
[0032] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.
[0033] It should be emphasized that, in the process of describing the present invention, various formulas and constraints are distinguished by using consistent labels, but it is not excluded that different labels are used to mark the same formulas and / or constraints. The purpose of this setting is to more clearly illustrate the characteristics of the present invention.
[0034] Please combine Figures 1-12 As shown, the present invention proposes a method for manufacturing a cantilever beam type VOC gas sensor based on a polyethylene film, comprising the following steps:
[0035] Step 1: Fabrication of cantilever beam.
[0036] See also Figure 1As shown, the cantilever beam structure primarily consists of a base layer, an adhesive layer, and a functional layer. One end of the cantilever beam serves as the fixed end, while the protruding end serves as the free end. The support layer is primarily made of 6μm copper foil, the adhesive layer is primarily made of 5μm double-sided tape, and the functional layer is primarily made of 10μm polyethylene film (PE). The support and functional layers are located on the upper and lower surfaces, respectively, with the adhesive layer serving as the middle layer, bonding the functional and support layers together. First, apply the copper foil to one side of the double-sided tape, then apply the PE film to the other side, taking care to avoid wrinkles and bubbles. The cantilever beam is then sandwiched between multiple layers (approximately two layers above and below) of A4 paper or weighing paper and fed into a roller press for multiple rolls to tightly adhere the three layers. Using small scissors, the beam is then cut into cantilever beams 10mm long and 1mm wide. The cut cantilever beams are then fed into a roller press and rolled multiple times, as described above, to ensure the three layers are tightly adhered and level without noticeable bending. Fix it horizontally on the fixing table of the cantilever beam chamber processed in step 2.
[0037] Step 2: Fabrication of the sensor chamber.
[0038] See also Figure 2 As shown, the sensor chamber shown in the figure is processed by a laser cutting machine and assembled using screws and elastic stainless steel sheets: it is mainly divided into a cantilever beam fixing platform and a T-shaped gas chamber with a gas inlet and outlet.
[0039] Step 3: Adjust the laser and fixed-focus camera to establish the detection light path.
[0040] See also Figure 3 and Figure 4 As shown, a small laser pointer-style laser is secured to an optical breadboard using a universal joint. Adjust its position and angle so that its smallest spot is directed at the top of the free end of the cantilever at an angle of approximately 45 degrees. Adjust the laser brightness to produce a relatively regular, appropriately bright spot on the copper substrate. Use the universal joint to adjust the fixed-focus camera (webcam) at the other end of the cantilever to clearly image the laser spot on the copper substrate at approximately a 45-degree angle. Adjust the laser brightness again to maintain a regular, minimal laser spot on the camera. The webcam (fixed-focus camera) image is displayed on a computer, providing a real-time image of the laser spot.
[0041] The sensor box has a T-shaped air passage inside. A fixing clip is located inside the sensor, securing one end of the cantilever beam. A transparent glass window is located on the top of the sensor box. The prototype dimensions of this sensor box are approximately 50mm*50mm*20mm.
[0042] The laser spot imaging optical path formed by the semiconductor laser, the fixed-focus camera and the sensor chip is kept on the same straight line as much as possible to achieve a better detection optical path.
[0043] Step 4: Connect the gas line. Use a micro air pump to pump the gas to be tested out of the sample bag and into the sensor chamber.
[0044] Step 5: Build the sensor detection circuit and connect the reference sensor, power supply, data transmission line, etc.
[0045] See also Figure 5 As shown, the power supply is used to power a reference sensor and a laser. Humidity sensor, the humidity sensor is automatically connected to the computer via the USB port, wherein the hygrometer and flow meter use 485 signal transmission to present the gas humidity in real time. The electronic flow meter is used to detect the gas flow rate. Gas sampling bag, the gas sampling bag is mainly used to load the target gas and the reference gas. Air pump, the air pump is used to introduce the target gas from the gas sampling bag into the gas path. The entire gas testing platform and gas path are shown as follows. Figure 5 A computer is provided, wherein the computer uses Matlab software and self-written program codes to process the data obtained by the camera, the hygrometer, and the flow meter.
[0046] This invention achieves an easy-to-process, low-cost, portable, online VOC sensor. The prototype detection box measures just 50mm*50mm*20mm, and the cantilever beam measures 8mm (length)*1mm (width)*20μm (thickness). The entire manufacturing process requires only traditional lamination (by hand), rolling (using a 200-yuan Deli roller press), and mechanical cutting (using scissors), eliminating the need for expensive processing equipment and facilitating mass production.
[0047] The materials used are 6μm-thick copper foil, 5μm-thick double-sided tape, and 10μm-thick PE film, and the cost of a single cantilever beam is less than 0.1 yuan. The total cost of the pump, air circuit, and detection box is less than 50 yuan. The laser is a standard laser pointer type, measuring 10mm in diameter and 60mm in length, with a power consumption of 5mW and a price of 100 yuan. The camera costs 200 yuan. Furthermore, there are no special requirements for the camera; an ordinary webcam will suffice, as will the cameras found in most mobile phones on the market. The supporting circuit board only needs to provide a 5V regulated power supply, resulting in a total cost of approximately 20 yuan. Therefore, the hardware cost of the entire detector is less than 400 yuan, and the most expensive camera component can be replaced by a mobile phone, thus reducing the hardware cost to less than 200 yuan. The hygrometer and flowmeter in this embodiment are used to study the factors affecting the sensor's signal and are not essential components of the sensor in this embodiment. Although Matlab is currently used as software, this image processing process can also be implemented using the open source Python + OpenCV. Image processing can also be performed using a mobile phone.
[0048] In summary, the present invention offers the advantages of low cost, small size, and portability. It can be used for online monitoring of outdoor air quality and indoor air pollution, enabling more comprehensive, rapid, and detailed monitoring of indoor and outdoor air quality. It can also be used for personal exposure assessment of hazardous gases, providing hazardous gas warnings, rapidly identifying the cause of disease, and establishing cumulative exposure relationships between disease and hazardous gases, thereby protecting people's health.
[0049] The present invention has good humidity resistance. Due to the use of copper substrate, it is more resistant to humidity interference than paper substrate. The sensor does not use dehumidifiers and directly uses ambient air as the base gas. The additional humidity sensor shows that when the humidity difference between the sample gas and the base gas is less than 0.5%, the humidity effect can be ignored ( Figure 10 Furthermore, even when exposed to air, it will not bend due to changes in ambient humidity, making it convenient to use and store.
[0050] The present invention has good sensitivity, consistency, and low detection limit. The copper substrate has good support and strong resistance to airflow disturbance, so the noise is low, which is conducive to improving sensitivity and data consistency. The reflective properties of the copper substrate make it easy for the laser spot on the substrate to have high brightness, regular spot shape, high edge contrast, easy imaging, and conducive to image processing, and also improve sensitivity. A detection limit of 2ppm xylene can be achieved (based on Figure 11 The sensor achieves a signal-to-noise ratio (S / N) of 3, matching the lower detection limit of commercial PID detectors (~1 ppm). In this experiment, xylene was systematically tested as a representative gas sample for both BTEX and VOCs. However, given the swelling properties of the PE polymer film, the sensor will respond to other VOCs, particularly hydrocarbons within the VOC family, with varying sensitivity, generally positively correlated with molecular size. Therefore, this sensor can be used as a sensor for both BTEX and VOCs. Figure 12 The response signals of different gases with the same concentration are also given.
[0051] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention.
Claims
1. A method for manufacturing a cantilever beam VOC gas sensor based on polyethylene film, characterized in that: The following steps are involved: Step 1: manufacturing a cantilever beam, wherein the cantilever beam comprises a supporting layer, a bonding layer and a functional layer; Step 2: Make a sensor chamber; Step 3: Adjust the laser and fixed-focus camera to establish the detection light path; Step 4: Connect the gas line and use a micro air pump to pump the gas to be tested out of the sample bag and into the sensor chamber; as well as Step 5: Build a sensor detection circuit for detection. The detection circuit is connected to the humidity sensor, power supply, data transmission line, gas sampling bag, air pump, and computer, and is uniformly controlled, read, and processed by a self-written program code based on Matlab; In the step 1, one end of the cantilever beam is used as a fixed end, and the extended end is used as a free end; the support layer is made of 6 μm copper foil as a raw material; the adhesive layer is made of 5 μm double-sided tape as a raw material; the functional layer is made of 10 μm polyethylene film (PE) as a raw material; the support layer and the functional layer are respectively located on the upper surface and the lower surface, and the middle layer is the adhesive layer, which bonds the functional layer and the support layer together; first, the copper foil is applied to one side of the double-sided tape, and then the PE film is applied to the other side of the double-sided tape, and then it is sandwiched between multiple layers of A4 paper or weighing paper, and sent to a roller press for multiple rolling, so that the three layers of material are tightly fitted together; then, small scissors are used to cut it into a cantilever beam of 10 mm long and 1 mm wide; the cut cantilever beam is sent to the roller press for multiple rolling as described above, so that the three layers of the cantilever beam are tightly fitted, kept horizontal and without obvious bending; In the step 2, a sensor chamber is processed using a laser cutting machine and assembled using screws and elastic stainless steel sheets. The sensor chamber is divided into a cantilever beam fixing platform and a T-shaped gas chamber with a gas inlet and outlet. The cantilever beam in the step 1 is horizontally fixed on the fixing platform of the cantilever beam chamber.
2. The method for manufacturing a polyethylene film-based cantilever beam VOC gas sensor according to claim 1, characterized in that: In step three, the laser is fixed to an optical breadboard using a universal joint, and its position and angle are adjusted so that its smallest light spot is projected toward the top position of the free end of the cantilever at an angle of 45 degrees, and the laser brightness is adjusted so that it presents a relatively regular light spot with appropriate brightness on the copper substrate; the fixed-focus camera at the other end of the cantilever is adjusted using the universal joint to clearly image the laser spot on the copper substrate in a 45-degree direction, and the laser brightness is adjusted again so that the laser spot at the camera end presents a regular and as small as possible light spot; the imaging of the fixed-focus camera is presented on the computer end, and the laser spot is displayed in real time.
3. The method for manufacturing a polyethylene film-based cantilever beam VOC gas sensor according to claim 1, characterized in that: In step five, the sensor is connected to a computer via a USB port, wherein the hygrometer and flowmeter use 485 signal transmission to present gas humidity in real time, and the electronic flowmeter is used to detect the gas flow rate; the gas sampling bag is mainly used to load the target gas and the control gas; the air pump is used to introduce the target gas from the gas sampling bag into the gas path; the computer uses Matlab software and self-compiled program code to process the data obtained by the camera, hygrometer, and flowmeter.
4. The method for manufacturing a polyethylene film-based cantilever beam VOC gas sensor according to claim 2, characterized in that: In step three, a sensor box is used. A T-shaped air passage is provided inside the sensor box. A fixing clip is located inside the sensor to fix one end of the cantilever beam. A transparent glass window is provided on the top of the sensor box.
5. The method for manufacturing a polyethylene film-based cantilever beam VOC gas sensor according to claim 4, characterized in that: The laser spot imaging optical path formed by the laser, the fixed-focus camera and the sensor chip is kept in a straight line.
6. The method for manufacturing a polyethylene film-based cantilever beam VOC gas sensor according to claim 4, characterized in that: The sensor box has a size of 50 mm*50 mm*20 mm.
7. A cantilever beam VOC gas sensor based on polyethylene film, characterized in that: Prepared according to the method according to any one of claims 1 to 6.