Particle concentration and particle size synchronous detection system based on local hollow beam self-mixing interference effect

Abstract

The invention relates to a particle concentration and particle size synchronous detection system based on a local hollow light beam self-mixing interference effect, and the system is characterized in that a light beam transmitting module is used for generating a hollow light beam and transmitting the hollow light beam to a to-be-detected atmospheric particle region; the signal acquisition module is used for acquiring a self-mixing interference signal generated after the light beam is scattered or reflected by atmospheric particles; the signal processing module is used for extracting a signal characteristic parameter of the self-mixing interference signal; wherein the signal characteristic parameters comprise frequency, amplitude and phase; and the inversion module is used for utilizing a machine learning model algorithm to invert atmospheric particle concentration and particle size distribution based on the signal characteristic parameters. According to the invention, high-precision and real-time synchronous detection of atmospheric particle concentration and particle size distribution can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of particle detection, and in particular to a particle concentration and particle size synchronous detection system based on the local hollow light beam self-mixing interference effect. Background Art

[0002] Atmospheric particulate matter (PM2.5, PM10, etc.) is an important factor affecting air quality and human health, and its concentration and particle size distribution are key indicators for evaluating the degree of air pollution. Traditional particle detection methods such as weight method, mass spectrometry, and light scattering method have disadvantages such as long detection time, complex equipment, and inability to monitor online in real time. In recent years, laser self-mixing interferometry technology has shown great potential in the field of particle detection due to its advantages such as high sensitivity and non-contact measurement. However, traditional Gaussian beams have problems such as low signal-to-noise ratio and insensitivity to particle size distribution, making it difficult to achieve synchronous and high-precision detection of tiny particle concentration and particle size. Summary of the invention

[0003] The present invention aims to overcome the deficiencies of the prior art and provide a particle concentration and particle size synchronous detection system based on the self-mixing interference effect of a local hollow light beam, so as to achieve high-precision, real-time synchronous detection of atmospheric particle concentration and particle size distribution.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] A particle concentration and particle size synchronous detection system based on the local hollow light beam self-mixing interference effect, comprising: a light beam emission module, a signal acquisition module, a signal processing module and an inversion module;

[0006] The light beam emission module is used to generate a hollow light beam and emit it to the atmospheric particle area to be measured;

[0007] The signal acquisition module is used to collect the self-mixing interference signal generated after the light beam is scattered or reflected by atmospheric particles;

[0008] The signal processing module is used to extract the signal characteristic parameters of the self-mixing interference signal; wherein the signal characteristic parameters include: frequency, amplitude, and phase;

[0009] The inversion module is used to invert the atmospheric particle concentration and particle size distribution based on the signal characteristic parameters using a machine learning model algorithm.

[0010] Optionally, the light beam emission module comprises: a photoelectric unit and a local hollow light beam generating unit;

[0011] The photoelectric unit is used to emit a laser beam;

[0012] The hollow beam generating unit is used to convert the laser beam into a hollow beam.

[0013] Optionally, the hollow beam generating unit includes: a polarizer, a wave plate, a first conical lens, and a second conical lens; wherein the two conical lenses are both flat plate structures without three-dimensional cone tips, the two conical lenses are symmetrically placed, and the laser passes through the center position of the two conical lenses.

[0014] Optionally, the hollow beam generating unit converts the laser beam into a hollow beam, comprising:

[0015] The laser beam is converted into circularly polarized light after passing through a polarizer and a wave plate in sequence;

[0016] The circularly polarized light becomes a parallel outgoing hollow light beam after passing through two symmetrically placed aconical lenses.

[0017] Optionally, the circularly polarized light is transformed into a parallel outgoing hollow light beam after passing through two symmetrically placed axicons, comprising:

[0018] The circularly polarized light changes from solid to hollow through the first axicon and is transmitted along the refraction direction to form a hollow divergent light beam;

[0019] The second conical lens performs collimation processing on the hollow divergent light beam, converts the divergent hollow light beam into a collimated parallel hollow light beam, and realizes the Gaussian solid-Bessel hollow conversion of the incident laser beam.

[0020] Optionally, the light beam emission module is further provided with a focusing lens and an atmosphere container;

[0021] The focusing lens is used to focus the hollow light beam; wherein the focal point formed by the hollow light beam through the focusing lens has an ultra-short Rayleigh length and appears as a light spot in a preset area in the axial direction. Compared with a traditional Gaussian beam, the axial resolution is higher in the axial position and the sensitivity to tiny particles is also higher;

[0022] The atmospheric container is used to contain the atmospheric particles to be tested.

[0023] Optionally, the light beam emitting module emits the generated hollow light beam to the atmospheric particle area to be detected, including:

[0024] When the light beam emitting module irradiates the atmospheric particles to be measured with the focused light beam, the focus of the hollow light beam is inside the atmospheric container. When the atmospheric particles pass through the atmospheric container, the hollow light beam is focused on the atmospheric particles to be measured to form a light spot.

[0025] Optionally, the signal acquisition module includes a photoelectric detector and a data acquisition card;

[0026] The self-mixing interference signal generated by the signal acquisition module after the light beam is scattered or reflected by atmospheric particles includes:

[0027] When the hollow tube bundle irradiates the atmospheric particles to be measured, the light scattered or reflected by the atmospheric particles returns along the original optical path, and self-mixes with the original laser of the photoelectric unit, causing a change in the output power of the photoelectric unit itself, so that the photoelectric detector integrated inside the semiconductor converts the optical signal into an electrical signal, and transmits it to the signal processing module through the data acquisition card.

[0028] The beneficial effects of the present invention are:

[0029] The focal point formed by the local hollow light beam of the present invention through the focusing lens has an ultra-short Rayleigh length and appears as a light spot in a particularly small area in the axial direction. Compared with the traditional Gaussian light beam, its axial resolution in the axial position is higher and its sensitivity to tiny particles is also higher.

[0030] The present invention adopts machine learning algorithm to perform concentration and particle size inversion, thereby improving detection accuracy and efficiency.

[0031] The system of the present invention has a simple structure, is easy to implement, has a fast response speed, can monitor the concentration and particle size distribution of atmospheric particulate matter in real time online, and has good practicality and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0033] Figure 1 This is a schematic diagram of the structure of a particle concentration and particle size synchronous detection system based on the local hollow light beam self-mixing interference effect according to an embodiment of the present invention;

[0034] Figure 2 A schematic diagram of generating a local hollow light beam according to an embodiment of the present invention;

[0035] Figure 3 A schematic diagram of a synchronous detection method according to an embodiment of the present invention;

[0036] Figure 4 A schematic diagram of the relationship for calculating the parameters of an axicon lens according to an embodiment of the present invention;

[0037] Among them, 1. Semiconductor laser LD; 2. Photodetector PD; 3. Polarizer; 4. 1 / 4 wave plate; 5, 6 two oppositely placed flat conical lenses; 7. Focusing lens; 8. Cuvette; 9. Atmospheric particles; 10. Data acquisition card; 11. Signal processing and analysis module; 12. Concentration and particle size inversion module; 13. Focusing point. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] This embodiment proposes a particle concentration and particle size synchronous detection system based on the local hollow light beam self-mixing interference effect, including: a light beam emission module, a signal acquisition module, a signal processing module and an inversion module;

[0041] A beam emission module, used for generating a hollow beam and emitting it to an area of ​​atmospheric particles to be measured;

[0042] A signal acquisition module is used to collect the self-mixing interference signal generated after the light beam is scattered or reflected by atmospheric particles;

[0043] A signal processing module, used to extract signal characteristic parameters from the mixed interference signal; wherein the signal characteristic parameters include: frequency, amplitude, and phase;

[0044] The inversion module is used to invert the atmospheric particle concentration and particle size distribution based on signal characteristic parameters using a machine learning model algorithm.

[0045] Specifically, the system of this embodiment includes the following parts; Generation and emission of local hollow light beam: using optical elements such as polarizers, wave plates, axicons, spatial light modulators, etc. to convert the Gaussian light beam emitted by the laser into a hollow light beam, and then using a focusing lens to convert the local hollow light beam into a convergence focus with an ultra-short Rayleigh length, and emit it to the atmospheric particle area to be measured. Self-mixing interference signal acquisition: using the back-facing photodetector integrated inside the laser to collect in real time the self-mixing interference signal of the laser power change caused by the self-mixing interference effect generated by the atmospheric particles scattered or reflected at the focus of the local hollow light beam and returned to the laser cavity. Signal processing and analysis: filtering and noise reduction are performed on the collected self-mixing interference signal in real time, and Fourier transform, wavelet transform and other algorithms are used to extract signal characteristic parameters such as frequency, amplitude, phase, etc. Concentration and particle size inversion: based on the characteristic parameters of the self-mixing interference signal, a theoretical model between the atmospheric particle concentration and particle size is established, and the atmospheric particle concentration and particle size distribution are inverted using machine learning model algorithms such as neural networks and support vector machines. The process of synchronous detection is shown in the figure below. Figure 3 shown.

[0046] In this embodiment, after extracting the signal characteristic parameters, the interference fringes generated in the time domain signal are used to obtain the number of interference fringes N according to the phase reversal point, and the particle diameter is calculated. λ is the laser wavelength, and the atmospheric particle size can be directly obtained. Then, by collecting the duration in the atmospheric particle area, the distribution of atmospheric particle size during that time can be identified, and the particle size distribution can be statistically analyzed to achieve the measurement of atmospheric concentration.

[0047] Further, the beam emission module includes: a photoelectric unit and a local hollow beam generating unit;

[0048] An optoelectronic unit for emitting a laser beam;

[0049] The hollow beam generating unit is used for converting the laser beam into a hollow beam.

[0050] Specifically, in this embodiment, the optoelectronic unit is a semiconductor laser 1 for emitting a laser beam.

[0051] Furthermore, the hollow beam generating unit includes: a polarizer, a wave plate, a first conical lens, and a second conical lens; wherein the two conical lenses are both flat plate structures without three-dimensional cone tips, the two conical lenses are symmetrically placed, and the laser passes through the center positions of the two conical lenses.

[0052] Furthermore, the hollow beam generating unit converts the laser beam into a hollow beam including:

[0053] The laser beam becomes circularly polarized light after passing through the polarizer and wave plate in sequence;

[0054] The circularly polarized light passes through two symmetrically placed conical lenses and becomes a parallel hollow light beam.

[0055] Furthermore, the circularly polarized light becomes a parallel hollow light beam after passing through two symmetrically placed axicons, including:

[0056] The circularly polarized light changes from solid to hollow through the first aconic lens and is transmitted along the refraction direction to form a hollow divergent light beam;

[0057] The second conical lens performs collimation processing on the hollow divergent light beam, converts the divergent hollow light beam into a collimated parallel hollow light beam, and realizes the conversion of the incident laser beam from Gaussian solid to Bessel hollow.

[0058] Furthermore, the light beam emission module is also provided with a focusing lens and an atmosphere container (i.e., a cuvette 8);

[0059] A focusing lens is used to focus the hollow light beam; wherein the focal point formed by the hollow light beam through the focusing lens has an ultra-short Rayleigh length and appears as a light spot in a preset area in the axial direction. Compared with a traditional Gaussian beam, its axial resolution in the axial position is higher and its sensitivity to tiny particles is also higher;

[0060] Atmospheric container, used to contain atmospheric particles to be tested.

[0061] Furthermore, the light beam emission module emits the generated hollow light beam to the atmospheric particle area to be measured, including:

[0062] When the beam emitting module irradiates the atmospheric particles to be measured with the focused beam, the focus of the hollow beam is inside the atmospheric container. When the atmospheric particles pass through the atmospheric container, the hollow beam is focused on the atmospheric particles to be measured as a light spot.

[0063] Further, the signal acquisition module includes a photoelectric detector and a data acquisition card;

[0064] The signal acquisition module collects the self-mixing interference signals generated by the light beam scattered or reflected by atmospheric particles, including:

[0065] When the hollow light beam irradiates the atmospheric particles to be measured, the light scattered or reflected by the atmospheric particles returns along the original optical path and self-mixes with the original laser of the photoelectric unit, causing the output power of the photoelectric unit itself to change. The photoelectric detector integrated inside the semiconductor converts the optical signal into an electrical signal and transmits it to the signal processing module through the data acquisition card.

[0066] The detailed structure of the system in this embodiment is as follows Figure 1As shown, it includes a semiconductor laser LD 1 and an internally integrated photodetector PD 2, a hollow beam generating module (a polarizer 3, a 1 / 4 wave plate 4, two oppositely placed flat conical lenses 5 and 6), a focusing lens 7, a cuvette 8, atmospheric particles 9, a data acquisition card 10, a signal processing and analysis module 11 and a concentration and particle size inversion module 12; and a focal point 13 after focusing by the focusing lens, i.e., a light spot with an ultra-short Rayleigh length.

[0067] Light with a wavelength of 632nm is reflected by the semiconductor laser 1, and becomes circularly polarized light after passing through the polarizer 3 and the 1 / 4 wave plate 4. The circularly polarized light becomes a parallel hollow light beam after passing through two oppositely placed flat cone lenses (PBA) 5 and 6. The local hollow light beam in the latter half is focused by the focusing lens 7 to irradiate the atmospheric particles. After focusing, the focus of the local hollow light beam is inside the cuvette 8. When atmospheric particles pass through, they focus on the tiny particles to form a light spot. At this time, the scattered or reflected light of the tiny particles will return along the original light path, and self-mixing interference will occur with the original laser in the laser cavity, causing the output power of the laser itself to change, so that the photodetector PD2 integrated inside the semiconductor converts the optical signal into an electrical signal, and transmits it to the signal processing and analysis module through the data acquisition card 10 for filtering, noise reduction and other processing and analysis, extracting the signal characteristic parameters, and finally transmitting it to the concentration and particle size inversion module 12 for concentration and particle size inversion.

[0068] Attached Figure 2 As shown, the flat aconic lens proposed in this embodiment has polarization-related optical properties. Depending on the polarization state of the incident light beam, it can be used to achieve annular convergence or divergence of the light beam; when the incident light is left-handed circularly polarized light, it can also be used to generate a Bessel beam with non-diffraction and self-recovery characteristics. Compared with the traditional aconic lens, the LBTEK flat aconic lens used in the present invention is a flat structure without a three-dimensional cone tip, which is easier to integrate; at the same time, the structural molding of the cone tip part depends on the orientation change of the liquid crystal molecules, which can achieve micron-level processing accuracy; in addition, it also has the characteristics of large dispersion. Based on the optical properties of the above-mentioned flat axicon, a symmetrical structure of two relatively placed flat axicon is adopted. The flat axicon 5 changes the circularly polarized light beam formed by the polarizer and the 1 / 4 wave plate from solid to hollow, and transmits it along the refraction direction to form a hollow divergent light beam; the flat axicon 6 collimates the divergent hollow light beam, and changes the divergent hollow light beam into a collimated parallel hollow light beam, realizing the Gaussian solid-Bessel hollow conversion of the incident laser beam, and the local hollow light beam in the latter half is converted into a focusing point through a focusing lens.

[0069] The advantages of the flat axicon lens proposed in this embodiment compared with the traditional axicon lens are described below:

[0070] In order to achieve an axial light spot with an ultra-short Rayleigh length, the traditional conical lens requires the cone angle to be as large as possible, which means that the processing is difficult and relatively expensive. However, the processing difficulty of the flat conical lens is small and the cost is low. Due to the orientation change of the liquid crystal molecules, the optical properties with polarization-related properties do not require the cone angle to be as large as that of the traditional conical lens.

[0071] The flat axicon has low optical path accuracy, and the effect can be achieved without requiring the laser to pass through the center of the two axicon lenses, which reduces the difficulty of building the optical path. The flat axicon lenses themselves are relatively thin, and placing them relatively close will not affect the formation of the axial light spot.

[0072] Parameter calculation relationship between flat axicon and traditional axicon:

[0073] For traditional refractive axicons, the parameters that are often concerned are its vertex angle α and waist angle β. Assuming that the refractive index of the material of the traditional refractive axicon is n, its deflection angle θ (i.e., the cone angle often mentioned for traditional axicons) satisfies:

[0074]

[0075] When the waist angle β is small, under the small angle approximation condition, it satisfies:

[0076] θ=(n-1)β

[0077] It can be seen that the LBTEK flat axicon with a deflection angle θ=2.3 corresponds to a traditional refractive axicon with α=170 and β=5; the LBTEK flat axicon with a deflection angle θ=4.7 corresponds to a traditional refractive axicon with α=160 and β=10.

[0078] Figure 4 Schematic diagram of the calculation relationship of axon lens parameters.

[0079] The flat conic lens proposed in this embodiment can be made based on an N-BK7 glass substrate and a liquid crystal polymer (LCP) material, and presents a sandwich structure of "front and back glass substrates and an LCP functional film layer in the middle".

[0080] In the LCP layer, the fast axis orientation of the liquid crystal molecules is distributed in an equiperiodic gradient along the radial direction of the substrate, and has the same λ / 2 delay on the entire device plane, which is a single-wavelength device. The flat cone lens has polarization-related optical properties. Depending on the polarization state of the incident light beam, it can be used to achieve annular convergence or divergence of the light beam; when the incident light is left-handed circularly polarized light, it can also be used to generate Bessel beams with non-diffraction and self-recovery characteristics.

[0081] Compared with the traditional conical lens, the flat conical lens has a flat structure and no three-dimensional cone tip, which makes it easier to integrate. At the same time, the structural forming of the cone tip part depends on the orientation change of the liquid crystal molecules, which can achieve micron-level processing accuracy. It also has the characteristics of large dispersion.

[0082] In this embodiment, the focal point formed by the local hollow light beam through the focusing lens has an ultra-short Rayleigh length and appears as a light spot in a particularly small area in the axial direction. Compared with the traditional Gaussian light beam, its axial resolution in the axial position is higher and its sensitivity to tiny particles is also higher.

[0083] This embodiment uses a machine learning algorithm to perform concentration and particle size inversion, thereby improving detection accuracy and efficiency.

[0084] The system of this embodiment has a simple structure, is easy to implement, has a fast response speed, can monitor the concentration and particle size distribution of atmospheric particulate matter in real time online, and has good practicality and promotion value.

[0085] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A particle concentration and particle size synchronous detection system based on the local hollow light beam self-mixing interference effect, characterized in that: include: A beam emission module, a signal acquisition module, a signal processing module and an inversion module; The light beam emission module is used to generate a hollow light beam and emit it to the atmospheric particle area to be measured; The signal acquisition module is used to collect the self-mixing interference signal generated after the light beam is scattered or reflected by atmospheric particles; The signal processing module is used to extract the signal characteristic parameters of the self-mixing interference signal; wherein the signal characteristic parameters include: frequency, amplitude, and phase; The inversion module is used to invert the atmospheric particle concentration and particle size distribution based on the signal characteristic parameters using a machine learning model algorithm.

2. The particle concentration and particle size synchronous detection system based on the local hollow light beam self-mixing interference effect according to claim 1 is characterized in that: The light beam emission module comprises: a photoelectric unit and a local hollow light beam generating unit; The photoelectric unit is used to emit a laser beam; The hollow beam generating unit is used to convert the laser beam into a hollow beam.

3. The particle concentration and particle size synchronous detection system based on the local hollow light beam self-mixing interference effect according to claim 2 is characterized in that: The hollow beam generating unit comprises: a polarizer, a wave plate, a first axicon, and a second axicon; Among them, the two conical lenses are both flat-plate structures without three-dimensional cone tips. The two conical lenses are symmetrically placed, and the laser passes through the center positions of the two conical lenses.

4. The particle concentration and particle size synchronous detection system based on the local hollow light beam self-mixing interference effect according to claim 3 is characterized in that: The hollow beam generating unit converts the laser beam into a hollow beam, comprising: The laser beam is converted into circularly polarized light after passing through a polarizer and a wave plate in sequence; The circularly polarized light becomes a parallel outgoing hollow light beam after passing through two symmetrically placed aconical lenses.

5. The particle concentration and particle size synchronous detection system based on the local hollow light beam self-mixing interference effect according to claim 4 is characterized in that: The circularly polarized light becomes a parallel hollow light beam after passing through two symmetrically placed aconic lenses, including: The circularly polarized light changes from solid to hollow through the first axicon and is transmitted along the refraction direction to form a hollow divergent light beam; The second conical lens performs collimation processing on the hollow divergent light beam, converts the divergent hollow light beam into a collimated parallel hollow light beam, and realizes the Gaussian solid-Bessel hollow conversion of the incident laser beam.

6. The particle concentration and particle size synchronous detection system based on the local hollow light beam self-mixing interference effect according to claim 5 is characterized in that: The light beam emission module is also provided with a focusing lens and an atmosphere container; The focusing lens is used to focus the hollow light beam; wherein the focal point formed by the hollow light beam through the focusing lens has an ultra-short Rayleigh length and appears as a light spot in a preset area in the axial direction. Compared with a traditional Gaussian beam, the axial resolution is higher in the axial position and the sensitivity to tiny particles is also higher; The atmospheric container is used to contain the atmospheric particles to be tested.

7. The particle concentration and particle size synchronous detection system based on the local hollow light beam self-mixing interference effect according to claim 6 is characterized in that: The light beam emission module emits the generated hollow light beam to the atmospheric particle area to be measured, including: When the light beam emitting module irradiates the atmospheric particles to be measured with the focused light beam, the focus of the hollow light beam is inside the atmospheric container. When the atmospheric particles pass through the atmospheric container, the hollow light beam is focused on the atmospheric particles to be measured to form a light spot.

8. The particle concentration and particle size synchronous detection system based on the local hollow light beam self-mixing interference effect according to claim 7 is characterized in that: The signal acquisition module includes a photoelectric detector and a data acquisition card; The self-mixing interference signal generated by the signal acquisition module after the light beam is scattered or reflected by atmospheric particles includes: When the hollow tube bundle irradiates the atmospheric particles to be measured, the light scattered or reflected by the atmospheric particles returns along the original optical path, and self-mixes with the original laser of the photoelectric unit, causing a change in the output power of the photoelectric unit itself, so that the photoelectric detector integrated inside the semiconductor converts the optical signal into an electrical signal, and transmits it to the signal processing module through the data acquisition card.

Images