Aerosol particle size detection device and method

Abstract

The invention provides an aerosol particle size detection device and method, and relates to the technical field of aerosol optical detection. The laser beam shaping module is used for shaping the laser beam into rectangular uniform light spots, so that the defect of non-uniform light intensity distribution at the edge is overcome, and errors caused by the shape and intensity distribution of the light spots are reduced. And then the air path and detection light chamber module enables the particle flow to vertically pass through the width direction of the rectangular light spot, and the inner diameter of the nozzle is matched with the width of the light spot, so that the geometric path lengths of all particles passing through the detection area are strictly consistent, and high-precision and repeatable flight time measurement is realized. The optical collection module adopts an ellipsoidal reflector, and two focuses are respectively and accurately arranged on a detection point and a light sensing surface of a detector, so that weak scattered light in a large solid angle is efficiently collected and focused, and the signal intensity and the signal-to-noise ratio are improved. And finally, the signal processing and control module realizes direct processing and particle size calculation of the photoelectric signal, so that rapid and accurate aerosol particle size detection is realized.

Description

Technical Field

[0001] This invention relates to the field of aerosol optical detection technology, and in particular to an aerosol particle size detection device and method. Background Technology

[0002] The particle size distribution of aerosol particles is a core parameter characterizing the physical properties of aerosols, and its accurate detection is of great significance for environmental quality assessment, industrial production safety control, public health protection, and aerosol scientific research. Currently, aerosol particle size detection technology based on the principle of optical scattering has become the mainstream application technology due to its advantages of high real-time performance and non-contact detection. Existing single-particle light scattering methods are mainly divided into two categories: one is based on the measurement of the peak intensity of the scattered light pulse, and the other is based on the measurement of particle flight time.

[0003] Peak intensity method: This method inverts the particle size by measuring the peak value of the scattered light pulse generated when a single particle passes through a laser beam. While the principle is simple, for Gaussian light spots with uneven intensity distribution, the peak signals generated when particles pass through the center or edge of the spot can differ significantly, even if the particle size is the same, leading to large measurement errors.

[0004] Time-of-flight (TOF) method: This method inverts particle size by measuring the time required for a particle to pass through a laser beam of a certain width. It has low dependence on the uniformity of the light intensity distribution, but requires the beam to have a well-defined boundary and a uniform width. If the beam boundary is blurred or the width is uneven, the time-of-flight measurement will be inaccurate.

[0005] Furthermore, semiconductor lasers are commonly used as the light source. The original light spot emitted by this source is usually an elliptical Gaussian distribution, with high intensity at the center and low intensity at the edges, and the shape and size of the spot are difficult to control. Directly using this spot for detection, whether using peak spectroscopy or time-of-flight methods, will introduce significant errors.

[0006] Currently, the detection of particle size distribution in aerosol particles suffers from technical problems such as large errors and inaccuracies. Summary of the Invention

[0007] This invention provides an aerosol particle size detection device and method, which solves the technical problem of large and inaccurate particle size distribution detection errors in current aerosol particles.

[0008] In a first aspect, the present invention provides an aerosol particle size detection device, comprising: a laser source module for generating a laser beam; a beam shaping module disposed on the output optical path of the laser source module for shaping the laser beam into a rectangular uniform light spot formed at the detection point; a gas path and detection optical chamber module, including a nozzle for accelerating and guiding the aerosol particle stream, and a detection optical chamber for accommodating the detection point, wherein the outlet inner diameter of the nozzle matches the width of the rectangular light spot, such that the particle stream passes perpendicularly through the width direction of the rectangular light spot; an optical collection and detection module, including an ellipsoidal reflector and a photodetector, wherein a first focal point of the ellipsoidal reflector is disposed at the detection point, and a second focal point coincides with the photosensitive surface of the photodetector, for collecting the scattered light generated when the aerosol particle stream passes through the rectangular uniform light spot and converging it to the photodetector; and a signal processing and control module connected to the photodetector for processing the electrical signal output by the photodetector and calculating the particle size information of the aerosol particles.

[0009] In one possible implementation, the beam shaping module includes a collimating lens, a first cylindrical lens, and a second cylindrical lens arranged sequentially along the optical path; the collimating lens is used to convert the laser beam into parallel light; the first cylindrical lens is used to collimate or compress the beam in the fast axis direction to define the width of the rectangular uniform light spot; and the second cylindrical lens is used to focus or stretch the beam in the slow axis direction to define the height of the rectangular uniform light spot.

[0010] In one possible implementation, the signal processing and control module includes a signal amplification circuit, an analog-to-digital converter (ADC), and an embedded processor. The signal amplification circuit is connected to a photodetector and is used to amplify the scattered light pulse signal. The ADC is used to convert the amplified analog signal into a digital signal. The embedded processor is used to run a particle size detection algorithm and calculate particle size information based on the digital signal.

[0011] In one possible implementation, the width of the rectangular uniform light spot is 1 mm and the height is 2 mm; the nozzle outlet inner diameter is 1 mm.

[0012] In one possible implementation, the ellipsoidal mirror has a reflectivity of no less than 95% for scattered light.

[0013] In a second aspect, the present invention provides an aerosol particle size detection method, applied to the aerosol particle size detection device of the first aspect. The method includes: acquiring scattered light pulse signals of aerosol particles passing through a detection area; extracting independent characteristic parameters characterizing individual particles based on the scattered light pulse signals; the independent characteristic parameters include aerodynamic flight time and optical scattered pulse peak value; calculating aerodynamic particle size estimates and optical particle size estimates based on the independent characteristic parameters and pre-calibrated aerodynamic particle size inversion models and optical particle size inversion models; dynamically determining fusion weight coefficients according to the signal quality of the scattered light pulse signals; and performing fusion calculations using a weighted fusion algorithm based on the fusion weight coefficients, the aerodynamic particle size estimates, and the optical particle size estimates to obtain the aerosol particle size.

[0014] In one possible implementation, based on the scattered light pulse signal, independent characteristic parameters characterizing a single particle are extracted, including: preprocessing the scattered light pulse signal to obtain a preprocessed signal; extracting the pulse width from the waveform of the preprocessed signal as the aerodynamic flight time; and extracting the maximum value of the pulse amplitude from the waveform of the preprocessed signal as the optical scattering pulse peak.

[0015] In one possible implementation, based on independent characteristic parameters and pre-calibrated aerodynamic particle size inversion models and optical particle size inversion models, aerodynamic particle size estimates and optical particle size estimates are calculated, including: inputting the aerodynamic flight time into the aerodynamic particle size inversion model to calculate the aerodynamic particle size estimate; and inputting the optical scattering pulse peak value into the optical particle size inversion model to calculate the optical particle size estimate.

[0016] In one possible implementation, the fusion weighting coefficient is dynamically determined based on the signal quality of the scattered light pulse signal, including: calculating the signal-to-noise ratio (SNR) of the scattered light pulse signal; and dynamically adjusting the fusion weighting coefficient based on the SNR. The fusion weighting coefficient is the weight of the aerodynamic particle size estimate, and the optical particle size estimate is the difference between 1 and the fusion weighting coefficient. A higher SNR results in a smaller fusion weighting coefficient, and a lower SNR results in a larger fusion weighting coefficient.

[0017] In one possible implementation, a weighted fusion algorithm is used to perform fusion calculations based on the fusion weight coefficient, the aerodynamic particle size estimate, and the optical particle size estimate to obtain the aerosol particle size. This includes: multiplying the aerodynamic particle size estimate by the fusion weight coefficient to obtain a first product; multiplying the optical particle size estimate by the difference between 1 and the fusion weight coefficient to obtain a second product; and adding the first product and the second product to obtain the aerosol particle size.

[0018] This invention provides an aerosol particle size detection device and method. The beam shaping module shapes the laser beam into a rectangular uniform spot, overcoming the inherent defect of uneven intensity distribution at the center and edge of traditional Gaussian spots, and reducing systematic errors caused by the shape and intensity distribution of the spot. Subsequently, the gas path and detection optical chamber module ensures the particle flow passes perpendicularly through the width of the rectangular spot, with the nozzle inner diameter matching the spot width, ensuring that the geometric path length of each particle passing through the detection area is strictly consistent, achieving high-precision and repeatable time-of-flight measurement. The optical collection module uses an ellipsoidal reflector with two focal points precisely set at the detection point and the detector's photosensitive surface, efficiently collecting and focusing weak scattered light within a large solid angle, improving signal strength and signal-to-noise ratio. Finally, the signal processing and control module directly processes the photoelectric signal and calculates the particle size, solving the current technical problems of large and inaccurate aerosol particle size distribution detection, and achieving rapid and accurate aerosol particle size detection. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, 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 the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of an aerosol particle size detection device provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of laser component shaping provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of a particle passing through a rectangular light spot to generate a scattered light pulse, provided by an embodiment of the present invention; Figure 4 This is a schematic diagram of a pulse signal generated by the light scattering effect of standard particles of different sizes, provided in an embodiment of the present invention. Figure 5 This is a schematic flowchart of an aerosol particle size detection method provided in an embodiment of the present invention; Figure 6 This is a correction relationship diagram between the measured single-particle flight time and the actual particle size when testing with standard particles of different particle sizes, provided by an embodiment of the present invention. Figure 7 This is a correction relationship diagram between the measured single-particle signal intensity and the actual particle size when testing with standard particles of different particle sizes, provided by an embodiment of the present invention. Figure 8This is a schematic diagram illustrating the variation of weight coefficients with signal-to-noise ratio in a fusion algorithm provided by an embodiment of the present invention.

[0021] Figure label: 1. Laser constant power drive module; 2. Laser assembly; 3. Nozzle; 4. Ellipsoidal reflector; 5. Detected particle; 6. Optical trap; 7. Photodetector; 8. Signal amplification circuit; 9. Analog-to-digital converter; 10. Signal processing module; 11. Sampling air pump; 21. Laser diode; 22. Collimating lens; 23. First cylindrical lens; 24. Second cylindrical lens; 25. Rectangular light spot. Detailed Implementation

[0022] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0023] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of terms such as "exemplary" or "for example" is intended to present the relevant concepts in a specific manner to facilitate understanding.

[0024] Furthermore, the terms "comprising" and "having," and any variations thereof, used in the description of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or modules is not limited to the steps or modules listed, but may optionally include other steps or modules not listed, or may optionally include other steps or modules inherent to such process, method, product, or device.

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the following description will be provided in conjunction with the accompanying drawings and specific embodiments.

[0026] As described in the background section, aerodynamic particle size is a core parameter describing the behavior of particles in airflow, and is typically obtained by measuring the particle velocity in an accelerating airflow. Traditional aerodynamic particle size spectrometers are complex in structure and usually cannot simultaneously provide information on the optical properties of particles. Currently, there is a lack of devices and algorithms that can effectively integrate optical and aerodynamic detection at the single-particle level, making it impossible to simultaneously obtain the optical equivalent particle size and aerodynamic particle size, thus limiting its application in the identification and analysis of complex aerosol components.

[0027] To address the aforementioned technical problems, this invention provides an aerosol particle size detection device and a particle size detection algorithm. This device forms a regular, uniform rectangular detection spot through innovative optical design, achieves aerodynamic particle size measurement through integrated gas path and optical design, and combines a fusion algorithm to comprehensively utilize optical time-of-flight, optical pulse peak value, and aerodynamic time-of-flight information, significantly improving the accuracy and reliability of particle size detection and enabling in-depth analysis of the particle's physicochemical properties.

[0028] like Figure 1 As shown, the present invention provides an aerosol particle size detection device. The device includes: Laser source module, used to generate laser beam.

[0029] The beam shaping module is located in the output optical path of the laser source module and is used to shape the laser beam into a rectangular uniform spot at the detection point.

[0030] The gas path and detection optical chamber module includes a nozzle 3 for accelerating and guiding the aerosol particle stream, and a detection optical chamber for accommodating the detection point. The outlet inner diameter of the nozzle 3 is matched with the width of the rectangular light spot, so that the particle stream passes perpendicularly through the width direction of the rectangular light spot.

[0031] The optical collection and detection module includes an ellipsoidal reflector 4 and a photodetector 7. The first focal point of the ellipsoidal reflector 4 is set at the detection point, and the second focal point coincides with the photosensitive surface of the photodetector 7. It is used to collect the scattered light generated when the aerosol particle stream passes through the rectangular uniform light spot and converge it to the photodetector 7.

[0032] The signal processing and control module, connected to the photodetector 7, is used to process the electrical signals output by the photodetector 7 and calculate the particle size information of the aerosol particles.

[0033] In some embodiments, the beam shaping module includes a collimating lens 22, a first cylindrical lens 23, and a second cylindrical lens 24 arranged sequentially along the optical path; the collimating lens 22 is used to convert the laser beam into parallel light; the first cylindrical lens 23 is used to collimate or compress the beam in the fast axis direction to define the width of the rectangular uniform light spot; and the second cylindrical lens 24 is used to focus or stretch the beam in the slow axis direction to define the height of the rectangular uniform light spot.

[0034] In some embodiments, the signal processing and control module includes a signal amplification circuit 8, an analog-to-digital converter 9, and a signal processing module 10; the signal amplification circuit 8 is connected to the photodetector 7 and is used to amplify the scattered light pulse signal; the analog-to-digital converter 9 is used to convert the amplified analog signal into a digital signal; and the signal processing module 10 is used to run a particle size detection algorithm and calculate particle size information based on the digital signal.

[0035] In some embodiments, the width of the rectangular uniform light spot is 1 mm and the height is 2 mm; the outlet inner diameter of the nozzle is 1 mm.

[0036] In some embodiments, the ellipsoidal reflector 4 has a reflectivity of not less than 95% for scattered light.

[0037] For example, the aerosol particle size detection device includes a light source module, a gas path module, an optical focusing module, a signal acquisition module, and a control processing module. The structure and connection relationship of each module are as follows: Laser source module: Includes laser diode 21 and its driving circuit, used to generate the initial laser beam. Laser diode 21 uses a semiconductor laser source with a wavelength of 650nm-850nm (such as ADL-66801TL), with an output power of 30mW-50mW. The driving circuit adopts a constant power driving method to ensure a constant power output from laser diode 21.

[0038] Beam shaping module: Located behind the optical path of the laser source module, it consists of a collimating lens 22, an aperture, and two orthogonally arranged cylindrical lenses. The collimating lens 22 calibrates the diverging light emitted from the laser diode 21 into parallel light. The first cylindrical lens 23 (focal length 15mm-25mm) compresses the beam in the horizontal direction, and the second cylindrical lens 24 (focal length 30mm-40mm) stretches the beam in the vertical direction, ultimately forming a rectangular spot of 1mm (horizontal width) × 2mm (vertical length) at the detection point, with a spot uniformity ≥92%. The aperture filters stray light to ensure the stability of the spot.

[0039] The gas path and detection chamber module includes nozzle 3, through which particles pass with the airflow, and the detection chamber. Nozzle 3 has an 8mm inner diameter channel at its front end and a 1mm inner diameter outlet, aligned with the 1mm width of the rectangular light spot. This is used to accelerate aerosol particles with the airflow and precisely guide them into the detection chamber, ensuring the particle flow is constrained and passes perpendicularly through the 1mm width area of ​​the rectangular light spot. The detection chamber is a sealed cavity with an internal airflow stabilization section (≥50mm in length) to ensure a stable airflow velocity of 1L / min-2L / min, free from eddies or turbulence. The outlet pipe connects to a filter and a suction pump, forming a stable airflow loop.

[0040] Optical converging module: The core is an ellipsoidal mirror. The first focal point of the ellipsoidal mirror coincides with the detection point (the location of the rectangular light spot) in the detection optical chamber, and the second focal point coincides with the photosensitive surface of the photodetector 7 in the signal acquisition module. The effective converging angle of the ellipsoidal mirror is precisely pointed to the 90° scattering direction (with the laser incident direction as the 0° reference). The ellipsoidal mirror is made of aluminum alloy with a reflectivity of ≥95%, which can efficiently converge the scattered light in the 90° direction to the photodetector 7. The intensity of the scattered light signal is 4-6 times higher than that of traditional plane mirrors.

[0041] Signal acquisition module: includes photodetector 7, signal amplification circuit 8, and analog-to-digital conversion unit 9; photodetector 7 adopts avalanche photodiode (APD), with a response wavelength matching the wavelength of laser diode 21, and the photosensitive surface is aligned with the second focal point of the ellipsoidal mirror; signal amplification circuit 8 has adjustable gain (10). 3 -10 5 The scattered light is converted into a weak electrical signal, which is then amplified; the analog-to-digital conversion unit 9 has a sampling rate of ≥50MHz and converts the analog signal into a digital pulse signal, which is then transmitted to the control processing module.

[0042] Control and processing module: It adopts an embedded microprocessor (such as ARM Cortex-M7 architecture) and is electrically connected to the light source module, gas path module and signal acquisition module respectively; it can adjust the laser power and gas path flow rate, receive and process pulse signals, run a dual-parameter fusion algorithm, and is equipped with a data storage interface (supporting SD card) and a communication interface (supporting USB / Bluetooth) to realize data storage and transmission.

[0043] like Figure 1 As shown, the aerosol particle size detection device of the present invention includes a laser constant power drive module 1, a laser assembly 2, a nozzle 3 with an inner diameter of 1 mm, an ellipsoidal reflector 4, an optical trap 6, a photodetector 7, a signal amplification circuit 8, an analog-to-digital conversion unit 9, a signal processing module 10, and a sampling gas pump 11. 5 is a simulated particle to be detected.

[0044] like Figure 2The diagram shows the laser assembly shaping process. The laser diode 21 emits an elliptical Gaussian beam, which is first shaped into a parallel beam by a collimating lens 22. A first cylindrical lens 23 (e.g., 4mm focal length, used for fast-axis collimation) in the module is responsible for beam expansion and collimation in the X direction (width direction), while a second cylindrical lens 24 (e.g., 10mm focal length, used for slow-axis focusing) is responsible for focusing in the Y direction (height direction). By precisely adjusting the positions and focal lengths of the two lenses, a rectangular beam 25 with a precise size of 1mm (width) × 2mm (length) and uniform intensity distribution is finally formed at the detection point.

[0045] like Figure 3 As shown, the aerosol particles to be tested are drawn by the sampling pump 11 and formed into a collimated, high-speed particle stream through the nozzle 5, which passes perpendicularly through a 1mm wide area of ​​the rectangular light spot 25. Light scattering occurs as the particles pass through.

[0046] The first focal point of the ellipsoidal reflector 4 is precisely located at the center of the detection area, and its second focal point is located on the photosensitive surface of the photodetector 7. This design can efficiently collect and focus scattered light within a large solid angle of 90 degrees onto the photodetector 7.

[0047] The photodetector 7 converts the optical signal into an electrical pulse signal. This signal is amplified by the signal amplification circuit 8, then converted into a digital signal by the analog-to-digital converter 9, and sent to the signal processing module 10 for processing and calculation. For example... Figure 4 The image shows pulse signals generated by the light scattering effect of standard particles of different sizes during actual testing. Power supply noise and interference noise can be eliminated by setting a signal threshold and minimum flight time. The signal processing module 10 obtains the light scattering intensity of the corresponding particle by analyzing the maximum amplitude of the individual particle pulse. The flight time of a particle is obtained by analyzing the time difference between the start time of the rising edge and the end time of the falling edge of a single particle pulse. Measured value.

[0048] This invention provides an aerosol particle size detection device. A beam shaping module shapes the laser beam into a rectangular, uniform spot, overcoming the inherent defect of uneven intensity distribution at the center and edges of traditional Gaussian spots, and reducing systematic errors caused by spot shape and intensity distribution. Subsequently, the gas path and detection optical chamber module ensures the particle stream passes perpendicularly through the width of the rectangular spot, with the nozzle inner diameter matching the spot width, guaranteeing a strictly consistent geometric path length for each particle through the detection area, achieving high-precision, repeatable time-of-flight measurement. The optical collection module uses an ellipsoidal reflector with two focal points precisely positioned at the detection point and the detector's photosensitive surface, efficiently collecting and focusing weak scattered light within a large solid angle, improving signal strength and signal-to-noise ratio. Finally, the signal processing and control module directly processes the photoelectric signal and calculates the particle size, solving the current technical problems of large and inaccurate aerosol particle size distribution detection, and achieving rapid and accurate aerosol particle size detection.

[0049] like Figure 5 As shown, this embodiment of the invention provides a method for detecting the particle size of aerosol particles. It is applied to... Figure 1 The aerosol particle size detection device shown includes steps S101-S105.

[0050] S101. Collect the scattered light pulse signal of aerosol particles passing through the detection area.

[0051] S102. Based on the scattered light pulse signal, extract independent feature parameters characterizing a single particle.

[0052] In some embodiments, independent characteristic parameters include aerodynamic flight time and optical scattering pulse peak.

[0053] As one possible implementation, embodiments of the present invention can preprocess the scattered light pulse signal to obtain a preprocessed signal; extract the pulse width from the waveform of the preprocessed signal as the aerodynamic flight time; and extract the maximum value of the pulse amplitude from the waveform of the preprocessed signal as the optical scattering pulse peak value.

[0054] S103. Based on independent characteristic parameters and pre-calibrated aerodynamic particle size inversion models and optical particle size inversion models, aerodynamic particle size estimates and optical particle size estimates are calculated.

[0055] As one possible implementation, embodiments of the present invention can input the aerodynamic flight time into the aerodynamic particle size inversion model to calculate the aerodynamic particle size estimate; and input the optical scattering pulse peak value into the optical particle size inversion model to calculate the optical particle size estimate.

[0056] S104. Dynamically determine the fusion weighting coefficients based on the signal quality of the scattered light pulse signal.

[0057] As one possible implementation, embodiments of the present invention can calculate the signal-to-noise ratio (SNR) of the scattered light pulse signal; and dynamically adjust the fusion weight coefficient based on the SNR; wherein the fusion weight coefficient is the weight of the aerodynamic particle size estimate, and the optical particle size estimate is the difference between 1 and the fusion weight coefficient; the higher the SNR, the smaller the fusion weight coefficient; the lower the SNR, the larger the fusion weight coefficient.

[0058] S105. Based on the fusion weighting coefficient, as well as the aerodynamic particle size estimate and the optical particle size estimate, a weighted fusion algorithm is used to perform fusion calculation to obtain the aerosol particle size.

[0059] As one possible implementation, embodiments of the present invention can multiply the aerodynamic particle size estimate by the fusion weighting coefficient to obtain a first product; multiply the optical particle size estimate by the difference between 1 and the fusion weighting coefficient to obtain a second product; and add the first product and the second product to obtain the aerosol particle size.

[0060] For example, the aerodynamic flight time is used to derive the particle size. Ideally, the particle is spherical, and its density is the standard density (1 g / cm³) used to define the aerodynamic diameter. The particle has reached a constant velocity when passing through the detection spot area. The relationship between the relaxation time of the particle during the nozzle acceleration process and the particle size is as follows: ; in: It is the particle density (standard density, 1g / cm3). It is the aerodynamic diameter. It is the viscosity of air (which is constant under standard conditions). ). This refers to the relaxation time.

[0061] The larger the particle ( (The larger the relaxation time) The longer the flight time L, the greater its inertia, and the more difficult it is to keep up with the accelerating airflow. The longer it is, the faster the particle travels. for: .

[0062] In the ideal inertial impact model, the particle velocity... With airflow speed It satisfies a simplified velocity relationship.

[0063] ; in, It is a constant related to the instrument structure. (The particle velocity is...) With ease time Substituting, we get: ; Organized ; because , , , , Since they are all constants, we can combine them into a new constant C. This results in an extremely simplified corresponding formula: ; in: It is the aerodynamic diameter. The flight time was obtained through measurement. It is an instrument constant that includes all physical and geometric parameters such as airflow velocity, spot size and spacing, air viscosity, and particle density, and is determined through calibration.

[0064] The actual situation will deviate from the ideal. By using a standard particle to perform linear calibration of the device, the following corresponding formula is obtained: ; It is the first linear constant. It is the second linear constant.

[0065] Derivation of the relationship between the peak value of the light scattering pulse signal and the particle size. Based on Mie scattering theory, the intensity of scattered light from a single particle in a specific direction (90° in this device) is... It can be represented as: ; in, It is the intensity of the incident light. It is the wavelength of the incident light in the medium. It is the distance from the observation point to the particle. It is the Mie scattering intensity function, which is the complex refractive index of the particle. Particle size parameters and scattering angle Complex functions.

[0066] For a fixed incident light wavelength Fixed scattering angle Range (this device focuses on the region around 90°) and ideal state of aerosol particles (its complex refractive index) (which can be considered a constant under certain conditions) Mie scattering intensity function This can be simplified to only relating to particle size. Related functions Therefore, the intensity of scattered light It can be simplified to: ; In the device, the photodetector receives the intensity of the scattered light. Converted to voltage signal This voltage signal and Proportional, that is At the same time, the incident light intensity The voltage is constant within the device. Therefore, the peak voltage output by the detector is... With particle size The relationship can ultimately be represented as: ; Equivalent, ,in, Here are the theoretical coefficients for Mie scattering. Through linear calibration of the apparatus using a standard particle, the following corresponding formula is obtained: ; It is the third linear constant. It is the fourth linear constant.

[0067] Finally, based on the signal-to-noise ratio of the detected signals, different weight values ​​are assigned to the particle size of the two physical quantities, and the results are fused to obtain the final particle size. ; in, To integrate the weighting coefficients, .

[0068] Based on the above theoretical foundation, particle detection algorithms need to first use monodisperse particles of different sizes to compare aerodynamic particle sizes. and optical particle size Each particle is calibrated and then its size is measured and analyzed using a particle size analysis algorithm. The specific process is as follows: S1-S5.

[0069] S1. Signal Acquisition and Processing. Noise suppression and baseline correction are performed on the digital pulse signal; an adaptive threshold filtering algorithm is used to dynamically adjust the filtering threshold (1.2-2 times the background noise amplitude) according to the real-time fluctuation of environmental noise to eliminate noise signals; a baseline correction algorithm is used to eliminate signal drift (baseline fluctuation ≤5mV after correction) to ensure the integrity of the pulse signal waveform.

[0070] For example, monodisperse standard particle solutions of various known particle sizes were prepared (e.g., using 12 groups of monodisperse particles of 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.6 μm, 5.6 μm, 7.8 μm, 10 μm, 12 μm, and 15 μm).

[0071] S2. Aerodynamic flight time extraction: The width of the pulse signal is the flight time of the particle as it passes through the 1mm×2mm rectangular spot detection area. Since the horizontal width of the rectangular light spot is 1mm, the particles pass through the light spot in the horizontal direction with the airflow. The rising edge of the pulse signal corresponds to the particle entering the light spot, and the falling edge corresponds to the particle leaving the light spot. The time difference between the rising edge and the falling edge is accurately measured by the timing unit, which is the flight time T, with a measurement accuracy of 50ns.

[0072] Pulse peak extraction: The maximum amplitude value (Vp) of the pulse signal is identified by the peak detection algorithm. Combined with the light source power, ellipsoidal mirror reflection efficiency and detector response coefficient, Vp is normalized to eliminate the influence of hardware parameter fluctuations.

[0073] For example, multiple monodisperse standard sample solutions are sequentially drawn into the detection device through a sampling pump. After measurement by the signal processing module, the original signals are normalized. Then, the aerodynamic flight time and light scattering intensity peaks corresponding to particles of different sizes are identified and extracted. Finally, the theoretical aerodynamic particle size of different particles is obtained through the theoretical derivation formulas mentioned above. and light scattering intensity particle size .

[0074] S3. Establish a particle size inversion model.

[0075] Based on aerodynamic flight time Optical particle size calculation model: ; in, Aerodynamic particle size, This is the instrument constant. It is related to flight time Spot width and airflow speed Related functions. , These are the coefficients obtained through standard particle calibration. Since the particle passes through a 1mm wide light spot at a constant velocity (determined by the supersonic airflow speed), the flight time... With particle aerodynamic particle size There is a positive correlation. In practical instruments, standard particles of known size are usually used for calibration to establish... and The corresponding curve.

[0076] Based on optical pulse peak Optical particle size calculation model: ; in, This is an optical particle size estimate based on the peak value. , and (Mie scattering theory coefficients) are coefficients obtained through standard particle calibration.

[0077] For example, these 12 sets of data are used to analyze the theoretical particle size obtained based on aerodynamic flight time. The theoretical particle size is obtained by curve fitting with the actual particle size and the peak value of light scattering intensity. Curve fitting was performed with the actual particle size. The time-of-flight-based curve was obtained. Instrument constants of the particle size calculation model ,coefficient Sum of coefficients The calibration value is obtained based on the optical pulse peak value. Mie scattering theoretical coefficients of the particle size calculation model ,coefficient Sum of coefficients The calibration value. For example... Figure 6 The figure shown is a fitting curve based on the relationship between aerodynamic flight time and actual particle size in one embodiment. Figure 7 The figure shown is a fitting curve based on the relationship between the peak light scattering intensity and the actual particle size in one embodiment.

[0078] S4, Fusion Computing.

[0079] Employing a weighted fusion algorithm, comprehensively Model and The model's calculations yielded the final particle size. .

[0080] ; in, To integrate the weighting coefficients, .

[0081] For example, particles of unknown size are introduced into the detection device via a sampling pump, and the signal processing module obtains the particle size using a particle size detection algorithm. This particle size detection algorithm is shown below.

[0082] S4.1 filters the sampled particle pulse signal to improve the signal-to-noise ratio.

[0083] S4.2 Then, the aerodynamic flight time and light scattering intensity peak corresponding to the particles are identified and extracted. S4.3 Next, the pre-calibrated model parameters are called to calculate the corrected particle size based on the time of flight. Corrected particle size with light scattering intensity peak .

[0084] S4.4 Simultaneously, the algorithm analyzes the signal-to-noise ratio of the current optical pulse signal and, according to preset rules (such as...),... Figure 8 As shown, the higher the signal-to-noise ratio, the smaller the value. The optical fusion weight α is dynamically determined.

[0085] S4.5 Finally, the final optical particle size is calculated using a weighted fusion formula. .

[0086] Step S5: Weighting coefficients The dynamic determination of weighting coefficients. Dynamically adjusted based on the signal-to-noise ratio of the main optical pulse signal: Calculate the signal-to-noise ratio of the pulse signal.

[0087] When the signal-to-noise ratio is higher than the first threshold, the peak information is considered reliable, and the peak model is given a higher weight (i.e., Smaller, for example, 0.3).

[0088] When the signal-to-noise ratio is below the second threshold, the peak information is considered susceptible to noise interference, and the time-of-flight model is given a higher weight (i.e., (Larger, for example, 0.7), because the flight time is less dependent on the absolute value of light intensity, and has stronger anti-interference ability.

[0089] The present invention has the following beneficial effects: 1. Excellent spot quality: The Gaussian spot is shaped into a 1mm×2mm rectangular uniform spot by a specific cylindrical lens group, which provides a detection area with clear boundaries and precise size for the time-of-flight method, fundamentally reducing the measurement error caused by spot non-uniformity.

[0090] 2. Precise matching of air path and optical path: Using a 1mm nozzle, the particle stream passes exactly through the 1mm width of the rectangular light spot, ensuring that the path length of each particle through the light spot is consistent, thus guaranteeing the accuracy and consistency of flight time measurement.

[0091] 3. High scattered light collection efficiency and excellent signal-to-noise ratio: The ellipsoidal mirror focuses the scattered light in a 90° direction. Combined with the precise alignment design of the first focal point with the detection point and the second focal point with the detector, the scattered light convergence efficiency reaches more than 90%. The signal intensity is 4-6 times higher than that of traditional plane mirrors. The signal-to-noise ratio of submicron particles is ≥25:1, which solves the problem of weak signal detection.

[0092] 4. Reasonable air path design and accurate flight time detection: The 1mm diameter nozzle restricts the particle trajectory, the steady flow section ensures stable airflow speed, the particle motion state is highly consistent as it passes through the detection area, and the flight time measurement error is ≤50ns, providing accurate data support for particle size inference.

[0093] 5. Dual-physical-quantity optical fusion detection: Innovatively combining aerodynamic time of flight and optical pulse peak By fusing these two independent physical quantities, the advantages of the time-of-flight method (TOF) in terms of strong anti-interference capability and the peak method in terms of high resolution are utilized, thus achieving complementary advantages in optical particle size measurement.

[0094] 6. Adaptive weighting algorithm: Optical fusion weight coefficients The algorithm is dynamically adjusted based on signal quality (such as signal-to-noise ratio) to maintain high accuracy and robustness under different operating conditions.

[0095] Overall Improvement in Accuracy and Value: Compared to single technologies, this invention significantly improves detection accuracy and provides richer data dimensions through hardware spot optimization and algorithm fusion, resulting in higher application value.

[0096] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. An aerosol particle size detection device, characterized by, include: Laser source module, used to generate laser beam; A beam shaping module is disposed in the output optical path of the laser source module and is used to shape the laser beam into a rectangular uniform spot formed at the detection point. The gas path and detection optical chamber module includes a nozzle for accelerating and guiding the aerosol particle stream, and a detection optical chamber for accommodating the detection point, wherein the outlet inner diameter of the nozzle is matched with the width of the rectangular light spot, such that the particle stream passes perpendicularly through the width direction of the rectangular light spot. The optical collection and detection module includes an ellipsoidal reflector and a photodetector. The first focal point of the ellipsoidal reflector is set at the detection point, and the second focal point coincides with the photosensitive surface of the photodetector. It is used to collect the scattered light generated when the aerosol particle stream passes through the rectangular uniform light spot and converge it to the photodetector. The signal processing and control module is connected to the photodetector and is used to process the electrical signal output by the photodetector and calculate the particle size information of the aerosol particles.

2. The aerosol particle size detection device according to claim 1, wherein The beam shaping module includes a collimating lens, a first cylindrical lens, and a second cylindrical lens arranged sequentially along the optical path; the collimating lens is used to convert the laser beam into parallel light; the first cylindrical lens is used to collimate or compress the beam in the fast axis direction to define the width of the rectangular uniform light spot; the second cylindrical lens is used to focus or stretch the beam in the slow axis direction to define the height of the rectangular uniform light spot.

3. The aerosol particle size detection device according to claim 1, characterized in that, The signal processing and control module includes a signal amplification circuit, an analog-to-digital converter, and an embedded processor. The signal amplification circuit is connected to the photodetector and is used to amplify the scattered light pulse signal. The analog-to-digital converter is used to convert the amplified analog signal into a digital signal. The embedded processor is used to run a particle size detection algorithm and calculate particle size information based on the digital signal.

4. The aerosol particle size detection device according to claim 1, characterized in that, The rectangular uniform light spot has a width of 1 mm and a height of 2 mm; the nozzle has an outlet inner diameter of 1 mm.

5. The aerosol particle size detection device according to claim 1, characterized in that, The ellipsoidal reflector has a reflectivity of not less than 95% for scattered light.

6. A method for detecting the particle size of aerosol particles, characterized in that, The method, applied to the aerosol particle size detection device as described in any one of claims 1-5, comprises: Collect the scattered light pulse signal of aerosol particles passing through the detection area; Based on the scattered light pulse signal, independent characteristic parameters characterizing a single particle are extracted; the independent characteristic parameters include aerodynamic flight time and optical scattering pulse peak value; Based on the independent characteristic parameters, and the pre-calibrated aerodynamic particle size inversion model and optical particle size inversion model, the aerodynamic particle size estimate and optical particle size estimate are calculated. The fusion weighting coefficients are dynamically determined based on the signal quality of the scattered light pulse signal. Based on the fusion weighting coefficients, the aerodynamic particle size estimate, and the optical particle size estimate, a weighted fusion algorithm is used to perform fusion calculations to obtain the aerosol particle size.

7. The aerosol particle size detection method according to claim 6, characterized in that, The extraction of independent feature parameters characterizing a single particle based on the scattered light pulse signal includes: The scattered light pulse signal is preprocessed to obtain a preprocessed signal; The pulse width is extracted from the waveform of the preprocessed signal as the aerodynamic flight time; The maximum value of the pulse amplitude is extracted from the waveform of the preprocessed signal as the peak value of the optical scattering pulse.

8. The aerosol particle size detection method according to claim 6, characterized in that, The calculation of aerodynamic and optical particle size estimates based on the independent characteristic parameters and pre-calibrated aerodynamic and optical particle size inversion models includes: The aerodynamic flight time is input into the aerodynamic particle size inversion model to calculate the estimated aerodynamic particle size. The optical scattering pulse peak value is input into the optical particle size inversion model to calculate the estimated optical particle size.

9. The aerosol particle size detection method according to claim 6, characterized in that, The step of dynamically determining the fusion weighting coefficients based on the signal quality of the scattered light pulse signal includes: Calculate the signal-to-noise ratio of the scattered light pulse signal; The fusion weight coefficient is dynamically adjusted based on the signal-to-noise ratio (SNR); wherein the fusion weight coefficient is the weight of the aerodynamic particle size estimate, and the optical particle size estimate is the difference between 1 and the fusion weight coefficient; the higher the SNR, the smaller the fusion weight coefficient; the lower the SNR, the larger the fusion weight coefficient.

10. The aerosol particle size detection method according to claim 6, characterized in that, The aerosol particle size is obtained by performing a weighted fusion calculation based on the fusion weight coefficient, the aerodynamic particle size estimate, and the optical particle size estimate, using a weighted fusion algorithm, including: The aerodynamic particle size estimate is multiplied by the fusion weighting coefficient to obtain the first product; The optical particle size estimate is multiplied by the difference between 1 and the fusion weighting coefficient to obtain the second product; Add the first product to the second product to obtain the particle size of the aerosol particles.

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