PM2.5 monitoring device based on optical fiber sensing technology and monitoring method thereof

Abstract

The invention provides a PM2.5 monitoring device based on an optical fiber sensing technology and a monitoring method thereof, and belongs to the technical field of optical fiber sensing and air quality monitoring. The monitoring device comprises a fiber bragg grating micro-cantilever module, a PTFE hydrophobic dustproof film layer, a sensing module, a signal acquisition and processing output module and a shell and airflow guide structure, the fiber bragg grating micro-cantilever module, the sensing module and the signal acquisition and processing output module are fixedly arranged in the shell and the airflow guide structure, and the PTFE hydrophobic dustproof film layer is arranged on the fiber bragg grating micro-cantilever module. The monitoring method comprises the following steps of S1, device deployment and system initialization; s2, capturing PM2.5 and acquiring an optical signal; s3, signal processing and interference separation; and S4, carrying out concentration conversion and data output. The device is good in stability, low in cost and convenient to install and carry; the safety is high, and the anti-interference capability is strong; the micro-cantilever structure is sensitive in response to tiny mass change and is superior to a traditional light scattering method.

Description

Technical Field

[0001] This invention relates to a PM2.5 monitoring device and method based on fiber optic sensing technology, belonging to the field of fiber optic sensing and air quality monitoring technology. Background Technology

[0002] PM2.5 refers to fine particulate matter in the atmosphere with a diameter of ≤2.5 micrometers, also known as respirable particulate matter. Its particle size is only 1 / 20 to 1 / 30 the diameter of a human hair. It is mostly in solid or liquid form, and its core components include sulfates, nitrates, ammonium salts, organic carbon, elemental carbon, and heavy metals. Sources include both natural and anthropogenic emissions, with industrial production, vehicle exhaust, coal combustion, and dust being the main sources. Large amounts of uncontrolled PM2.5 directly emitted into the atmosphere can cause serious environmental and health hazards. PM2.5 is now included in the key air pollutant control indicators, and its concentration reduction is listed as a core assessment target, demonstrating its central role in air pollution prevention and control. The effectiveness of control directly affects the achievement of air quality improvement goals. In the industrial and agricultural sectors, PM2.5 emission control is related to production quality and green development. Industries such as steel and chemicals control emissions through technological upgrades and the installation of waste gas treatment facilities, balancing environmental protection and energy efficiency improvement. In the environmental protection field, PM2.5 is a core monitoring indicator, providing data for pollution source tracing and governance decisions. In laboratory experiments, it is also necessary to monitor PM2.5 concentration in real time, so as to adjust experimental conditions and finally optimize the experimental process.

[0003] Existing PM2.5 monitoring technologies mainly include: beta-ray absorption, light scattering, and traditional fiber optic sensing. Beta-ray absorption utilizes beta rays emitted by radioactive isotopes; by comparing the intensity difference after passing through a blank filter membrane and a filter membrane adsorbing PM2.5, the concentration of particulate matter is indirectly calculated based on relevant laws. Light scattering utilizes the scattering effect produced when PM2.5 is irradiated by a light source; a photodetector receives the scattered light and converts it into an electrical signal, which is then converted into a concentration using a calibration curve (requiring correction for environmental interference factors). Traditional fiber optic sensing relies on the sensitivity of optical fibers, such as transmittance and refractive index, to particulate matter; by detecting changes in the optical signal output by the fiber after PM2.5 adsorption, the particulate matter concentration is inferred. The limitations of these existing technologies are as follows:

[0004] 1. Beta-ray absorption method: It requires a radioactive source (such as C-14), which poses risks to safe storage and disposal. In addition, the detector surface is prone to dust accumulation, requiring weekly disassembly and cleaning maintenance, resulting in high maintenance costs.

[0005] 2. Light scattering method: The concentration is calculated by the intensity of the light scattered by the particles to the laser. However, it is easily affected by the ambient humidity (interference from water vapor scattering) and dust accumulation (lens contamination). In high humidity (RH≥80%) or high dust scenarios, the measurement error can reach more than ±15%, resulting in low detection accuracy.

[0006] 3. Traditional fiber optic sensing method: This method often uses ordinary fiber optic gratings that directly contact the air. The sensing surface has no protective structure, making it easy to adsorb water vapor and dust, which leads to wavelength drift (interference shift not caused by PM2.5). Furthermore, it is not sensitive enough to minute changes in mass (the mass of a single PM2.5 particle is only 0.001 to 0.1 μg), and the concentration resolution can only reach 1 to 2 μg / m³, which cannot meet the accurate monitoring needs of low concentration (e.g., ≤10 μg / m³) scenarios.

[0007] None of the above technologies have solved the problem of synergistic effect between "contamination protection of sensing surface" and "high-sensitivity detection of minute mass changes", resulting in a difficulty in achieving both long-term stability and detection accuracy of the device. Summary of the Invention

[0008] The purpose of this invention is to solve the problems existing in the prior art and to provide a PM2.5 monitoring device and monitoring method based on fiber optic sensing technology.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A PM2.5 monitoring device based on fiber optic sensing technology includes:

[0011] It includes: a fiber Bragg grating micro cantilever beam module, a PTFE hydrophobic and dustproof film layer, a sensing module, a signal acquisition and processing output module, and a housing; the fiber Bragg grating micro cantilever beam module, the sensing module, and the signal acquisition and processing output module are all fixedly installed inside the housing, and the PTFE hydrophobic and dustproof film layer is installed on the fiber Bragg grating micro cantilever beam module;

[0012] The fiber optic grating microcantilever beam module includes: a microcantilever beam substrate, a sensing grating, a mounting frame, and a base; one end of the microcantilever beam substrate is a fixed end along its length, and the other end is a free end; the lower surface of the fixed end of the microcantilever beam substrate is fixedly connected to the top of the mounting frame; the free end of the microcantilever beam substrate is suspended and a sensing grating is provided on its upper surface; the bottom end of the mounting frame is rigidly connected to the upper surface of the base, and the base is rigidly connected to the outer shell;

[0013] The PTFE hydrophobic and dustproof membrane layer is disposed on the upper and lower surfaces of the free end of the microcantilever beam substrate;

[0014] The sensing module includes: a broadband light source, a 2×2 fiber coupler, and a reference grating; the broadband light source is connected to the signal input end of the 2×2 fiber coupler, and the signal input and output ends of the 2×2 fiber coupler are respectively connected to the reference grating and the sensing grating.

[0015] The signal acquisition and processing output module includes: a photodetector, a data processor, and a display; the signal input terminal of the photodetector is connected to the signal output terminal of a 2×2 fiber optic coupler, the signal output terminal of the photodetector is connected to the signal input terminal of the data processor, and the signal output terminal of the data processor is connected to the signal input terminal of the display.

[0016] The outer shell has an airflow inlet on one side and an airflow outlet on the other side, thus forming an airflow guiding structure; the free end of the micro-cantilever beam base is positioned facing the airflow inlet.

[0017] Preferably, the PTFE hydrophobic and dustproof film layer is coated on the upper and lower surfaces of the free end of the microcantilever beam substrate by a low-temperature spraying process. The PTFE hydrophobic and dustproof film layer uniformly covers the sensing grating area and has a bonding strength with the microcantilever beam substrate of ≥5MPa.

[0018] Preferably, the outer shell is made of ABS engineering plastic.

[0019] Preferably, a 5μm filter screen is provided in the airflow inlet to filter PM10 and larger particles; a miniature fan is provided in the airflow outlet.

[0020] A PM2.5 monitoring method based on fiber optic sensing technology includes the following steps:

[0021] Step S1: Device Deployment and System Initialization

[0022] The PM2.5 monitoring device based on fiber optic sensing technology is horizontally fixed in the scene to be measured. The monitoring device is started and initialized, and the data processor records the initial wavelength of the sensing grating. Initial wavelength of the reference grating and photodetector baseline voltage Three sets of core baseline parameters are stored; the data processor loads the core parameters calibrated by standard traceability equipment before shipment: quality-wavelength sensitivity coefficient. Wavelength-concentration conversion factor and temperature compensation coefficient ;

[0023] Step S2: PM2.5 capture and light signal acquisition

[0024] The air to be tested is blown into the PTFE hydrophobic dustproof membrane on the free end surface of the microcantilever beam substrate through the airflow inlet. PM2.5 particles form a uniform adhesion layer on the surface of the PTFE hydrophobic dustproof membrane, generating a mass load m. Under the action of the mass load, the free end of the microcantilever beam substrate bends downward. The optical signal output by the broadband light source is split into two paths by a 2×2 fiber coupler, and is reflected at the sensing grating and the reference grating, respectively. The reflected light is sent to the photodetector through the 2×2 fiber coupler for optical signal acquisition and conversion into a voltage signal.

[0025] Step S3: Signal Processing and Interference Separation

[0026] The voltage signal from the photodetector in step S2 undergoes two-stage filtering. The data processor, based on the voltage-wavelength calibration curve of the photodetector, calculates the real-time wavelength from the filtered voltage signal; this is combined with the temperature compensation coefficient from step S1. Perform precise separation calculations for temperature interference to obtain the effective wavelength offset that eliminates the influence of temperature.

[0027] Step S4: Concentration Conversion and Data Output

[0028] The mass-wavelength sensitivity coefficient in step S1 Wavelength-concentration conversion factor The effective wavelength offset obtained in step S3 is used to calculate the concentration. The results are verified and anomalies are handled by the built-in rationality judgment logic of the preset data processor. The current concentration value, detection time and temperature are displayed in real time on the display.

[0029] Preferably, the specific steps for starting and initializing the monitoring device in step S1 are as follows:

[0030] Step S11: Ensure the casing is parallel to the horizontal plane, clean the airflow inlet and outlet areas, and connect the power supply;

[0031] Step S12: The broadband light source is started by triggering the start command through the data processor, and continuous light is output. The 2×2 fiber coupler, sensing grating and reference grating enter the working state.

[0032] Step S13: The photodetector is preheated, and filtered clean air is introduced into the airflow inlet. After the output signal of the photodetector stabilizes, the data processor records and stores three sets of core baseline parameters.

[0033] Preferably, the deformation of the free end of the microcantilever beam base bending downwards under mass load in step S2 is... With quality The relationship is linear, as shown in the following formula:

[0034]

[0035] in, The elastic modulus of monocrystalline silicon is 135 GPa. Let L be the moment of inertia of the cross section, and L be the length of the free end of the microcantilever beam base. The bending deformation causes the surface fiber grating to stretch synchronously, increasing the grating pitch and causing the central reflection wavelength to shift towards the longer wavelength direction.

[0036] Preferably, the optical signal output by the broadband light source in step S2 is split into two paths by a 2×2 fiber coupler, namely a sensing optical path and a reference optical path.

[0037] The sensing optical path: The optical signal is emitted from a broadband light source and transmitted to the sensing grating via a 2×2 fiber coupler. The reflected wavelength signal carries both PM2.5 load and temperature information. The signal is transmitted back via optical fiber to a 2×2 fiber coupler, and then transmitted through the 2×2 fiber coupler to the input end of the photodetector.

[0038] Reference optical path: The optical signal is emitted from a broadband light source and transmitted to the reference grating via a 2×2 fiber coupler, reflecting only the wavelength signal carrying temperature information. The reflected light signal is transmitted to the photodetector via a 2×2 fiber optic coupler and converted into a voltage signal. and .

[0039] Preferably, the two-stage filtering in step S3 includes: hardware filtering and software filtering;

[0040] The hardware filtering uses an RC low-pass filter circuit to filter out high-frequency electromagnetic interference.

[0041] The software filtering uses the Kalman filter algorithm to process five consecutive sampling points to eliminate wavelength fluctuations caused by instantaneous airflow impact;

[0042] The wavelength value calculation method is as follows: the data processor calculates the filtered wavelength value based on the voltage-wavelength calibration curve of the photodetector. , Solving for real-time wavelength , The solution accuracy is ±0.01 pm;

[0043] The accurate calculation method for temperature interference separation is as follows: reference grating wavelength offset Combined with temperature compensation coefficient Obtain changes in ambient temperature Based on the temperature response consistency of fiber Bragg gratings, the temperature interference component of the sensing grating. Finally, the effective wavelength shift caused solely by PM2.5 quality was extracted: This completely eliminates the influence of temperature on wavelength detection.

[0044] Preferably, the specific steps for concentration conversion in step S4 are as follows:

[0045] Step S41: Calculate the adhesion quality from the effective wavelength offset ;

[0046] Step S42: Calculate the PM2.5 mass per unit volume, i.e., concentration, based on airflow parameters. ;

[0047] Step S43: Using moving average optimization, the average value of the C value calculated in step S42 for 5 consecutive times is taken to eliminate the instantaneous error caused by accidental particle detachment;

[0048] The data processor has built-in rationality judgment logic, as follows:

[0049] If C < 0 μg / m³: it is determined to be zero-point drift, and recalibration is automatically triggered.

[0050] If C > 1000 μg / m³: it is determined to be out of range, an out-of-range prompt is output and the original wavelength data is recorded;

[0051] like Fluctuation > 5pm / s: This is considered an abnormal airflow, triggering fan speed calibration.

[0052] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0053] This invention transmits signals via optical fiber, is unaffected by electromagnetic interference, and has good stability; furthermore, the light source design of this invention is more adapted to the needs of PM2.5 monitoring, with lower hardware costs and higher stability; it is also easy to install and portable.

[0054] The signal detection logic of this invention is more direct, avoiding interference from multiple factors such as gas composition and solid particle scattering, resulting in higher monitoring accuracy. This invention does not require a radiation source, avoiding the safety hazards of the β-ray method, and meets civilian environmental safety standards, thus ensuring high safety.

[0055] The microcantilever beam structure of this invention directly responds to PM2.5 quality, eliminates gas interference, improves anti-interference ability, has better long-term stability, and stronger monitoring specificity.

[0056] The present invention coats a microcantilever beam structure with a PTFE film, which has hydrophobic and dust-resistant properties that can reduce water vapor adsorption and non-target dust accumulation, and the interference offset is much lower than that of traditional fiber optic sensing methods.

[0057] This invention has high sensitivity; the microcantilever beam structure is highly responsive to minute changes in mass, which is superior to traditional light scattering methods. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of the structure of a PM2.5 monitoring device based on fiber optic sensing technology according to the present invention.

[0059] Figure 2 This is a schematic diagram of the fiber optic grating microcantilever beam module of the present invention.

[0060] Figure 3This is a schematic diagram of the sensing module and signal acquisition and processing output module architecture of the present invention.

[0061] Figure 4 This is the optical path diagram of the sensing grating.

[0062] Figure 5 For reference, see the grating optical path diagram.

[0063] In the figure, the reference numerals are as follows: 1 is the outer shell, 2 is the airflow inlet, 3 is the airflow outlet, 4 is the fiber optic grating microcantilever beam module, 4-1 is the microcantilever beam substrate, 4-2 is the sensing grating, 4-3 is the mounting bracket, 4-4 is the base, 5 is the broadband light source, 6 is the 2×2 fiber optic coupler, 7 is the photodetector, 8 is the data processor, 9 is the display, and 10 is the reference grating. Detailed Implementation

[0064] The present invention will be further described in detail below with reference to the accompanying drawings: This embodiment is implemented under the premise of the technical solution of the present invention, and detailed implementation methods are given, but the protection scope of the present invention is not limited to the following embodiments.

[0065] Fiber Bragg grating sensing principle: External strain and temperature will cause a shift in the Bragg reflection wavelength of the fiber Bragg grating. The reflection wavelength of the fiber Bragg grating can be expressed as:

[0066] (1)

[0067] in, The reflected wavelength of the Bragg fiber grating. The effective refractive index of the optical fiber core. The grating period.

[0068] The reflected wavelength of the fiber Bragg grating changes with temperature and strain. It can be represented as:

[0069] (2)

[0070] in, For the elasto-optic tensor components of the optical fiber material. In response, The coefficient of thermal expansion of the optical fiber material. The thermo-optic coefficient of the optical fiber material. This refers to temperature changes.

[0071] By selecting core materials with matching coefficients of thermal expansion (CTE), the additional stress on the microcantilever beams and fiber gratings caused by temperature changes is reduced from the source, thus shielding the effects of temperature. The value is zero; only stress affects the change in Bragg wavelength.

[0072] Based on the drift value of the Bragg reflection wavelength of the grating The strain value can be obtained accordingly. A miniature fan drives the air to be monitored to enter through airflow inlet 2. After being filtered by the filter screen set at airflow inlet 2, the air flows smoothly over the surface of the micro cantilever beam substrate 4-1. The adhesion of PM2.5 particles increases the mass of the free end of the micro cantilever beam substrate 4-1. According to the mechanical principle of cantilever beam, the free end will produce a downward bending deformation (the degree of deformation is proportional to the total mass of the attached particles). This deformation causes the sensing grating 4-2 attached to the surface of the micro cantilever beam substrate 4-1 to undergo a synchronous tensile deformation, resulting in an increase in the grating pitch of the sensing grating 4-2 and a shift of its central reflection wavelength towards the longer wavelength direction.

[0073] Broadband light source 5 continuously outputs light in the 1520-1580nm range, which is transmitted to sensing grating 4-2 via single-mode fiber. Sensing grating 4-2 reflects only the light signal near the center wavelength, and the reflected light returns to photodetector 7 via the same path. Photodetector 7 collects the center wavelength of the reflected light in real time and compares it with the initial wavelength recorded during device initialization. By comparing (1550.000nm), the wavelength shift was calculated. After filtering out noise interference using the Kalman filter algorithm, the data processor 8 inputs the data into the preset calibration formula:

[0074] (3)

[0075] Where C represents the PM2.5 concentration, and k is obtained through calibration experiments using a standard PM2.5 generator. The calibration experiment involves introducing gases of different concentrations and taking readings after the data stabilizes, thus obtaining the correspondence between different PM2.5 concentrations and wavelength shift values ​​as a reference. It is directly converted into real-time PM2.5 concentration values, and the final concentration data is output to the display 9 (such as an LCD screen) through the interface to achieve real-time monitoring.

[0076] like Figure 1 As shown, the PM2.5 monitoring device based on fiber optic sensing technology involved in this embodiment includes: a fiber optic grating micro cantilever beam module 4, a PTFE hydrophobic and dustproof film layer, a sensing module, a signal acquisition and processing output module, and a housing 1; the fiber optic grating micro cantilever beam module 4, the sensing module, and the signal acquisition and processing output module are all fixedly installed inside the housing 1, and the PTFE hydrophobic and dustproof film layer is disposed on the fiber optic grating micro cantilever beam module 4;

[0077] like Figure 2As shown, the fiber optic grating microcantilever beam module 4, serving as the sensing core, includes: a microcantilever beam base 4-1, a sensing grating 4-2, a fixing frame 4-3, and a base 4-4. The microcantilever beam base 4-1 has a fixed end at one end and a free end at the other along its length; the free end is suspended to ensure unconstrained deformation. The lower surface of the fixed end of the microcantilever beam base 4-1 is fixedly connected to the top of the fixing frame 4-3; the free end of the microcantilever beam base 4-1 is suspended, and the sensing grating 4-2 is provided on its upper surface; the bottom end of the fixing frame 4-3 is rigidly connected to the upper surface of the base 4-4, and the base 4-4 is rigidly connected to the device housing.

[0078] PTFE hydrophobic and dustproof membrane: The membrane is applied to the upper and lower surfaces of the free end of the micro cantilever beam substrate 4-1 through a low-temperature spraying process. The membrane uniformly covers the sensing grating 4-2 area and has a bonding strength of ≥5MPa with the micro cantilever beam substrate 4-1 to prevent it from falling off.

[0079] The sensing module includes: a broadband light source 5, a 2×2 fiber optic coupler 6, and a reference grating 10; the signal input end of the broadband light source 5 and the 2×2 fiber optic coupler 6 are connected by optical fiber, and the signal input and output ends of the 2×2 fiber optic coupler 6 are connected by optical fiber to the reference grating 10 and the sensing grating 4-2, respectively.

[0080] The signal acquisition and processing output module includes: a photodetector 7, a data processor 8, and a display 9; the signal input terminal of the photodetector 7 is connected to the signal output terminal of the 2×2 fiber optic coupler 6 via optical fiber, the signal output terminal of the photodetector 7 is connected to the signal input terminal of the data processor 8, and the signal output terminal of the data processor 8 is connected to the signal input terminal of the display 9; the photodetector 7 and the data processor 8, as well as the data processor 8 and the display 9, are fixed together by a waterproof connector.

[0081] The outer shell 1 is made of ABS engineering plastic. One side of the outer shell 1 is provided with an airflow inlet 2 (with a built-in 5μm filter to filter PM10 and larger particles), and the other side is provided with an airflow outlet 3 (with a built-in micro fan). The airflow channel is directly opposite the free end of the micro cantilever beam base 4-1 to ensure that PM2.5 particles are efficiently attached to the membrane surface. The base 4-4 is rigidly connected to the outer shell 1.

[0082] like Figure 3 The optical path diagram shown is as follows: The broadband light source 5 outputs an optical signal that is transmitted to a 2×2 fiber optic coupler 6. The 2×2 fiber optic coupler 6 splits the light into two paths: one path is output to the sensing grating 4-2, and the other path is output to the reference grating 10. After passing through the sensing grating 4-2 and the reference grating 10, the light is reflected and transmitted through the 2×2 fiber optic coupler 6 to the signal input terminal of the photodetector 7. The photodetector 7 collects the wavelength signals emitted by the reference grating 4-2 and the reference grating 10. The signals are processed by the data processor 8 and then output to the display 9 through the interface.

[0083] The core principle of the PM2.5 monitoring device based on fiber optic sensing technology is as follows: This monitoring method takes the physical transmission chain of "PM2.5 mass load → micro-cantilever beam mechanical deformation → fiber optic grating strain → wavelength shift" as its core. It eliminates environmental interference through dual-grating temperature compensation and achieves accurate monitoring by combining a linear concentration conversion model. It is different from traditional indirect monitoring methods such as "spectral absorption" and "charge induction" and has the technical characteristics of "direct response, strong anti-interference and controllable accuracy".

[0084] Step S1: Device Deployment and System Initialization

[0085] The PM2.5 monitoring device based on fiber optic sensing technology is horizontally fixed in the test environment (indoor / outdoor, industrial area / traffic intersection, etc.), ensuring that the outer shell 1 is parallel to the horizontal plane (to avoid additional stress on the micro-cantilever beam caused by gravity); the airflow inlet 2 (with a 5μm pre-filter) and airflow outlet 3 (built-in micro fan) areas are cleaned to ensure that the airflow channel from "airflow inlet → sensing cavity → airflow outlet" is unobstructed. A 5VDC regulated power supply is connected, and the start command is triggered by the data processor 8: the broadband light source 5 (SLED) starts, outputting continuous light in the 1520-1580nm range, with the power stabilizing at 10mW±0.1mW; the 2×2 fiber optic coupler 6, sensing grating 4-2, and reference grating 10 enter the working state; the photodetector 7 (wavelength resolution 0.01pm, response speed 1kHz) is preheated for 30 minutes to eliminate the influence of device temperature drift. Filtered clean air (PM2.5 concentration ≤ 0.1 μg / m³) is introduced into airflow inlet 2 and maintained for 10 minutes until the output signal of photodetector 7 stabilizes. Then, data processor 8 records and stores three sets of core baseline parameters: initial wavelength of sensing grating. (Target value 1550.000nm ± 0.01nm, corresponding to the strain baseline of the microcantilever beam under no load); initial wavelength of the reference grating (Reflects only the ambient temperature baseline, without the influence of mechanical deformation); Baseline voltage of photodetector 7 (Verifying the stability of the light source by establishing a baseline for optical signal electro-electric conversion under clean air conditions). The core parameter calibrated by standard traceability equipment before shipment is applied: quality-wavelength sensitivity coefficient. (12 pm / μg, i.e., the wavelength shift caused by each 1 μg of PM2.5 adsorbed, determined by the size of the microcantilever beam and the stress sensitivity of the fiber grating); wavelength-concentration conversion factor (0.8 μg / (m³・pm), calibrated by airflow velocity, sensor cavity volume, and capture efficiency); temperature compensation coefficient (0.01 pm / ℃, reference grating temperature response coefficient, used for subsequent interference separation).

[0086] Step S2: PM2.5 capture and light signal acquisition

[0087] The airflow system precision speed control data processor 8 starts the micro fan in the airflow outlet 3 and adjusts the speed through PWM signal to stabilize the airflow speed at 0.5m / s±0.05m / s; the air to be tested is filtered through the inlet 5μm filter and blown along the outer shell 1 to the PTFE hydrophobic dustproof membrane on the free end surface of the micro cantilever beam base 4-1.

[0088] Particle Adhesion and Mechanical Deformation Conduction: Due to inertial collisions, PM2.5 particles in the air form a uniform adhesion layer on the surface of the PTFE hydrophobic dustproof film, generating a mass load m (range 0.01μg-10μg). The free end of the micro-cantilever beam base 4-1 bends downwards under this load. According to the formulas of mechanics of materials, the deformation... With quality The relationship is linear, as shown in the following formula:

[0089] (4)

[0090] in, The elastic modulus of monocrystalline silicon is 135 GPa. The moment of inertia of the cross section; the bending deformation causes the surface sensing grating 4-2 to stretch synchronously, the grating pitch increases, and the central reflection wavelength shifts to the longer wavelength direction.

[0091] The optical signal output from the broadband light source 5, which is used for synchronous acquisition of dual grating signals, is split into two paths by a 2×2 fiber coupler 6, including a sensing optical path and a reference optical path.

[0092] like Figure 4 As shown, the sensing optical path is as follows: the optical signal is emitted from the broadband light source 5 and transmitted to the sensing grating 4-2 via the 2×2 fiber coupler 6, reflecting a wavelength signal carrying both PM2.5 load and temperature information. The signal is transmitted back to the 2×2 fiber coupler 6 via optical fiber, and then transmitted to the input end of the photodetector 7 via the 2×2 fiber coupler 6.

[0093] like Figure 5 As shown, the reference optical path is as follows: the optical signal is emitted from the broadband light source 5 and transmitted to the reference grating 10 via the 2×2 fiber coupler 6, reflecting only the wavelength signal carrying temperature information. The reflected light signal is transmitted to the photodetector 7 via a 2×2 fiber coupler 6 and converted into a voltage signal. and .

[0094] Step S3: Signal Processing and Interference Separation

[0095] Original signal noise reduction for the acquired , Two-stage filtering is performed, including hardware filtering and software filtering;

[0096] Hardware filtering: High-frequency electromagnetic interference is filtered out through an RC low-pass filter circuit (cutoff frequency 10Hz);

[0097] Software filtering: The Kalman filter algorithm (Q=1e-6, R=0.01, where Q and R are the parameters selected when performing Kalman filtering) is used to process 5 consecutive sampling points to eliminate wavelength fluctuations caused by instantaneous airflow impact.

[0098] The wavelength value calculation data processor 8 calculates the wavelength value based on the voltage-wavelength calibration curve of the photodetector 7, and then processes the filtered wavelength value. , Solving for real-time wavelength , The solution accuracy is ±0.01pm.

[0099] Accurate separation and calculation of reference grating wavelength offset due to temperature interference Combined with temperature compensation coefficient Obtain changes in ambient temperature Based on the temperature response consistency of fiber Bragg gratings, the temperature interference component of the sensing grating. Finally, the effective wavelength shift caused solely by PM2.5 quality was extracted: This completely eliminates the influence of temperature on wavelength detection.

[0100] Step S4: Concentration Conversion and Data Output

[0101] Step S41: Calculate the adhesion quality from the effective wavelength offset ;

[0102] Step S42: Calculate the PM2.5 mass (concentration) per unit volume based on airflow parameters. ;

[0103] Step S43: Moving average optimization, taking the average value of the C value calculated in step S42 for 5 consecutive times to eliminate the instantaneous error caused by accidental particle detachment.

[0104] The result verification and anomaly handling data processor has built-in logic for determining reasonableness:

[0105] If C < 0 μg / m³: it is determined to be zero-point drift, and recalibration is automatically triggered.

[0106] If C > 1000 μg / m³: it is determined to be out of range, an "out of range" prompt is output and the original wavelength data is recorded;

[0107] like Fluctuation > 5pm / s: This is considered an abnormal airflow, triggering fan speed calibration.

[0108] Real-time display: The current concentration value (unit μg / m³), detection time, and temperature are output via an LCD screen, with an update frequency of 1Hz.

[0109] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A PM2.5 monitoring device based on optical fiber sensing technology, characterized in that, It comprises a fiber grating micro-cantilever beam module (4), a PTFE hydrophobic dustproof film layer, a sensing module, a signal acquisition and processing output module, and a shell (1); the fiber grating micro-cantilever beam module (4), the sensing module, and the signal acquisition and processing output module are fixedly arranged in the shell (1), and the PTFE hydrophobic dustproof film layer is arranged on the fiber grating micro-cantilever beam module (4); The fiber grating micro-cantilever beam module (4) comprises a micro-cantilever beam base (4-1), a sensing grating (4-2), a fixing frame (4-3), and a base (4-4); one end of the micro-cantilever beam base (4-1) along the length direction is a fixed end, and the other end is a free end; the lower surface of the fixed end of the micro-cantilever beam base (4-1) is fixedly connected with the top end of the fixing frame (4-3); the free end of the micro-cantilever beam base (4-1) is suspended, and the upper surface is provided with the sensing grating (4-2); the bottom end of the fixing frame (4-3) is rigidly connected with the upper surface of the base (4-4), and the base (4-4) is rigidly connected with the shell (1); The PTFE hydrophobic dustproof film layer is arranged on the upper and lower surfaces of the free end of the micro-cantilever beam base (4-1); The sensing module comprises a broadband light source (5), a 2×2 optical fiber coupler (6), and a reference grating (10); the broadband light source (5) is connected with the signal input end of the 2×2 optical fiber coupler (6), the signal input and output ends of the 2×2 optical fiber coupler (6) are respectively connected with the reference grating (10) and the sensing grating (4-2); The signal acquisition and processing output module comprises a photodetector (7), a data processor (8), and a display (9); the signal input end of the photodetector (7) is connected with the signal output end of the 2×2 optical fiber coupler (6), the signal output end of the photodetector (7) is connected with the signal input end of the data processor (8), and the signal output end of the data processor (8) is connected with the signal input end of the display (9); One side of the shell (1) is provided with an air inlet (2), and the other side is provided with an air outlet (3), thereby forming an air flow guiding structure; the free end of the micro-cantilever beam base (4-1) is arranged towards the air inlet (2). The PTFE hydrophobic dustproof film layer is coated on the upper and lower surfaces of the free end of the micro-cantilever beam base (4-1) through a low-temperature spraying process, the PTFE hydrophobic dustproof film layer uniformly covers the sensing grating (4-2) region, and the bonding strength of the PTFE hydrophobic dustproof film layer with the micro-cantilever beam base (4-1) is greater than or equal to 5 MPa. 2.The PM2.5 monitoring device based on fiber sensing technology according to claim 1, wherein, The shell (1) is made of ABS engineering plastic. 3.The PM2.5 monitoring device based on optical fiber sensing technology according to claim 1, wherein, A 5 μm filter screen is arranged in the air inlet (2) for filtering PM10 and above particles; a micro fan is arranged in the air outlet (3). 4.The PM2.5 monitoring device based on optical fiber sensing technology according to claim 1, wherein, The following steps are included:

5. A monitoring method based on the PM2.5 monitoring device based on the optical fiber sensing technology according to any one of claims 1-4, characterized in that, Step S1: device deployment and system initialization Step S2: PM2.5 capture and light signal acquisition The PM2.5 monitoring device based on optical fiber sensing technology is horizontally fixed to the scene to be measured, the monitoring device is started and initialized, the data processor (8) records the initial wavelength of the sensing grating , the initial wavelength of the reference grating , and the baseline voltage of the photodetector , three groups of core baseline parameters are stored; the data processor (8) loads the core parameters calibrated by a standard traceable device before factory: mass-wavelength sensitivity coefficient , wavelength-concentration conversion coefficient , and temperature compensation coefficient ; The air to be measured is blown to the PTFE hydrophobic dustproof film on the free end surface of the micro-cantilever beam base (4-1) through the air inlet (2), PM2.5 particles form a uniform adhesion layer on the surface of the PTFE hydrophobic dustproof film layer, and a mass load m is generated; ​ The free end of the micro-cantilever beam substrate (4-1) is bent downward under the action of a mass load, and the light signal output by the broadband light source (5) is split into two paths by the 2*2 optical fiber coupler (6), and reflected at the sensing grating (4-2) and the reference grating (10) respectively, and the reflected light is transmitted to the photoelectric detector (7) through the 2*2 optical fiber coupler (6) for light signal collection and conversion into a voltage signal; Step S3: signal processing and interference separation The voltage signal of the photoelectric detector (7) in step S2 is filtered in two stages, and the data processor (8) calculates the filtered voltage signal into real-time wavelength according to the voltage-wavelength calibration curve of the photoelectric detector (7); and the temperature compensation coefficient in step S1 is combined The temperature interference is accurately separated and calculated to obtain an effective wavelength shift amount eliminating the temperature influence. Step S4: concentration conversion and data output The concentration conversion is performed by the mass-wavelength sensitivity coefficient in step S1 and the wavelength-concentration conversion coefficient and the effective wavelength offset obtained in step S3, the result verification and abnormal processing are performed by the preset data processor (8) with reasonable judgment logic, and the current concentration value, detection time and temperature are displayed in real time through the display (9).

6. The monitoring method according to claim 5, characterized in that, The specific steps for starting and initializing the monitoring device in step S1 are as follows: Step S11: Ensure that the shell (1) is parallel to the horizontal plane, clean the air inlet (2) and air outlet (3) area, and connect the power supply; Step S12: Trigger the start command through the data processor (8), start the broadband light source (5), output continuous light, and put the 2*2 optical fiber coupler (6), sensing grating (4-2) and reference grating (10) into working state; Step S13: Preheat the photoelectric detector (7), and pass filtered clean air into the air inlet (2), and after the output signal of the photoelectric detector (7) is stable, record three groups of core baseline parameters and store them by the data processor (8).

7. The monitoring method of claim 5, wherein, The deformation amount of the free end of the micro-cantilever beam substrate (4-1) in step S2 bending downward under the mass load is linearly related to the mass , and the formula is as follows: wherein, is the elastic modulus of single crystal silicon 135 GPa, is the cross-sectional moment of inertia, L is the length of the free end of the micro-cantilever beam base; the bending deformation drives the surface fiber Bragg grating (4-2) to stretch synchronously, the grating pitch increases, and the center reflection wavelength shifts to the long wave direction.

8. The monitoring method according to claim 7, characterized in that, In step S2, the light signal output by the broadband light source (5) is split into two paths by the 2*2 optical fiber coupler (6), which are the sensing light path and the reference light path respectively; Sensing light path: the light signal is emitted by a wide spectrum light source (5), transmitted to a sensing grating (4-2) through a 2*2 optical fiber coupler (6), reflected wavelength signals carrying PM2.5 load and temperature double information are transmitted back to the 2*2 optical fiber coupler (6) through an optical fiber, and then transmitted to the input end of a photoelectric detector (7) through the 2*2 optical fiber coupler (6); ​ Reference light path: the optical signal is emitted by a wide spectrum light source (5) and transmitted to a reference grating (10) through a 2x2 fiber coupler (6), only the wavelength signal carrying temperature information is reflected The reflected optical signal is transmitted to a photodetector (7) through a 2x2 fiber coupler (6), and is converted into a voltage signal and .

9. The monitoring method according to claim 8, characterized in that, The two-stage filtering in step S3 includes hardware filtering and software filtering; The hardware filtering filters out high-frequency electromagnetic interference through an RC low-pass filter circuit; The software filtering uses Kalman filtering algorithm to process 5 consecutive sampling points to eliminate wavelength fluctuations caused by instantaneous air flow impact; The wavelength value solving method is that the data processor (8) solves the real-time wavelength according to the voltage-wavelength calibration curve of the photoelectric detector (7) based on the filtered voltage signal of the photoelectric detector (7). 、 The solving precision is ±0.01pm. 、 ​ The temperature interference precise separation calculation method is: reference grating wavelength offset , combined with temperature compensation coefficient , get the environmental temperature change ; based on the consistency of fiber grating temperature response, the temperature interference component of sensing grating ; finally extract the effective wavelength offset caused only by PM2.5 mass: , completely eliminate the influence of temperature on wavelength detection.

10. The monitoring method according to claim 9, characterized in that, The specific steps for concentration conversion in step S4 are as follows: Step S41: Calculate the attachment quality from the effective wavelength offset ; Step S42: Calculate the mass of PM2.5 per unit volume, i.e. concentration, in combination with the air flow parameter ; Step S43: Use sliding average optimization to take the average value of the C values calculated by step S42 for 5 times in a row to eliminate instantaneous errors caused by accidental particle shedding; The data processor (8) has built-in reasonableness judgment logic as follows: If C < 0 μg / m³: Determine zero drift, and automatically trigger recalibration; If C > 1000 μg / m³: Determine as out of range, output out of range prompt and record original wavelength data; If Fluctuation > 5 pm / s: Determine air flow abnormal, trigger fan speed calibration.

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