Real-time particulate matter detection method and device based on light interference principle

Abstract

The invention provides a real-time particulate matter detection method and device based on a light interference principle, the device comprises a shell, a particulate matter sensor module is arranged in the shell, the particulate matter sensor module comprises a light splitting and focusing module, the light splitting and focusing module is used for splitting a light source into incident light and reference light, and focusing the incident light to an area where particulate matter to be detected is located; the scattered light collection and interference module is used for collecting scattered light generated by the particulate matters and performing interference on the scattered light and the reference light; a light source driving module and a signal preprocessing module are further arranged, the light source driving module is connected with the light source and used for driving the light source, and the signal preprocessing module is connected with the scattered light collection and interference module and used for preprocessing interference signals; and the control and analysis module is used for providing a control signal for the light source driving module and carrying out particulate matter related detection according to the preprocessed interference signal. The problems of low signal-to-noise ratio, low coupling efficiency and poor anti-shielding capability are solved.

Description

Technical Field

[0001] This invention relates to the technical field of particulate matter detection, and more particularly to a method and apparatus for particulate matter detection. Background Technology

[0002] Traditional particulate matter sensor solutions involve light emitted from a light source striking the particles. Since the particle size is comparable to the wavelength of the light source, the Mie scattering model applies. According to this model, the particles scatter light in all directions, which is received by a detector. This photodetector can be placed at a fixed scattering angle, and the output particle concentration is calculated based on the intensity of the scattered light signal and the amount of signal per unit time. These devices typically have an air duct that carries the particles into the optical detection area. Therefore, traditional particulate matter sensors contain fans or air pumps; their size is an order of magnitude larger than the solution in this patent, and they also generate some noise. Because the scattered light signal is very weak, the entire detection area of ​​the sensor must be in a sealed, dark environment to prevent interference from ambient light.

[0003] Currently, the miniaturized sensor for detecting particulate matter in open environments is the BMV080 product, a collaboration between FKORESH and Bosch. Its principle is that light emitted from the light source passes through a lens and is incident on airborne particles. According to the Mie scattering model, the backscattered light from the particles returns along the original path and undergoes self-mixing interference (SMI) with the original laser cavity of the light source. By detecting the optical interference signal, the first and second velocities of the particles are calculated to obtain the output particle concentration information. The product is named VCSEL with integrated Photodiode (ViP), and the light source uses a vertical-cavity surface-emitting laser (VCSEL) with an integrated photodetector (PD) developed and manufactured by FKORESH. Its key feature is that the photodetector chip and the light source chip are integrated onto a single chip. This solution requires the use of ViP products manufactured by Fasten. It detects the SMI signal of the backscattered light from particles. According to the Mie scattering model, the intensity of the backscattered light is very low, resulting in a low signal-to-noise ratio. Moreover, there cannot be any obstructions within a certain distance in front of the detection area, otherwise the particle detection sensor will malfunction. Since the detector 301PD is integrated into the laser cavity of the light source, the particle scattered light signal must enter the laser cavity to interfere, resulting in very low coupling efficiency. Summary of the Invention

[0004] To address the technical problems of low signal-to-noise ratio, low coupling efficiency, and poor anti-obstruction capability in existing particulate matter detection technologies, this invention proposes a real-time particulate matter detection method and device based on the principle of optical interference.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0006] A real-time particulate matter detection device based on the principle of optical interference includes a housing. A particulate matter sensor module is disposed inside the housing. The particulate matter sensor module includes a beam splitting and focusing module and a scattered light collection and interference module. The beam splitting and focusing module includes a light source. The beam splitting and focusing module is used to split the light source into incident light and reference light, and to focus the incident light on the region where the particulate matter to be measured is located. The scattered light collection and interference module is used to collect the scattered light generated by the particulate matter and to interfere with the scattered light with the reference light.

[0007] The housing also includes a light source driving module and a signal preprocessing module. The light source driving module is connected to the light source generator and is used to drive the light source generator. The signal preprocessing module is connected to the scattered light collection and interference module and is used to preprocess the interference signal.

[0008] The housing also houses a control and analysis module, which provides control signals to the light source driving module and performs particulate matter related detection based on the preprocessed interference signal.

[0009] Preferably, the housing is made of a non-transparent material, while the optical path outlet is made of a transparent material;

[0010] The optical components of the beam splitting and focusing module and the scattered light collection and interference module adopt symmetrical or asymmetrical structures.

[0011] Preferably, the beam splitting and focusing module includes, in sequence, a light source generator, a collimating lens, a first beam splitter, and a first focusing lens; the scattered light collection and interference module includes, in sequence, a collecting lens, a second beam splitter, a second focusing lens, and a detector.

[0012] Preferably, the light source generator includes a VCSEL, a distributed feedback laser, and a laser LED, and the selected wavelength is in the infrared band invisible to the human eye;

[0013] The collecting lens includes an aspherical lens, a compound lens group, a Fresnel zone plate, or an immersion objective with an aperture value of 0.2-0.5;

[0014] The detector includes a PIN photodiode, an avalanche photodiode, a multiplier photodiode, and a phototransistor.

[0015] Preferably, the first beam splitter is a beam splitter in which the intensity of the incident light is greater than the intensity of the reference light, and the second beam splitter is a beam splitter in which the intensity of the scattered light is greater than the intensity of the reference light.

[0016] Preferably, the signal preprocessing module includes at least a signal amplification module, a low-pass filter module, and a digital-to-analog converter module connected in a secondary manner, and the signal amplification module is connected to the detector.

[0017] Preferably, the control and analysis module includes a microcontroller and a data analysis module connected together. The microcontroller is connected to the digital-to-analog conversion module. The data analysis module includes an FFT analysis module, a particulate matter concentration calculation module, and a particulate matter diameter classification module. The FFT analysis module is connected to the microcontroller and is used to obtain the number of frequency domain signal pulses, pulse width, and pulse peak information based on the preprocessed interference signal through frequency domain analysis. The particulate matter concentration calculation module obtains the average velocity of the particulate matter through angle integration and calculates the particulate matter concentration in combination with the number of frequency domain signal pulses. The particulate matter diameter classification module calculates the particulate matter diameter based on the pulse width or pulse peak and classifies the particulate matter according to the diameter.

[0018] A real-time particulate matter detection method based on the principle of optical interference includes the following steps:

[0019] S1: The control and analysis module sends a control signal to the light source driver module to modulate the light emission frequency of the light source generator;

[0020] S2: The beam splitting and focusing module splits the light source into incident light and reference light, and focuses the incident light on the region where the particulate matter to be measured is located, while the particulate matter to be measured undergoes Miller scattering;

[0021] S3: The scattered light collection and interference module collects the scattered light generated by the particulate matter and interferes the scattered light with the reference light;

[0022] S4: The signal preprocessing module receives the interference light and preprocesses the interference signal;

[0023] S5: The control and analysis module performs particulate matter correlation detection based on the preprocessed interference signal and feeds back the detection results to the host computer. The correlation detection includes particulate matter concentration detection and particulate matter diameter classification.

[0024] Furthermore, particulate matter concentration detection includes:

[0025] S51: Perform a Fast Fourier Transform (FFT) on the time-domain interferometric electrical signal after converting the analog signal to a digital signal to convert it to a frequency-domain signal, and obtain a list of frequencies of all peaks. Each peak corresponds to one particulate matter, and N is the number of particulate matter.

[0026] S52: Calculate the velocity components of a single particle along the main ray of scattered light based on the Doppler frequency shift principle, and obtain a list of velocity components. ;

[0027] S53: Calculate the average velocity of all particles by integrating over a 360° angle. ;

[0028] S54: Calculate particulate matter concentration based on the average velocity and number of all particulate matter:

[0029] ;

[0030] Where C is the particulate matter mass concentration, S is the correlation coefficient with sensor sensitivity, and T is the detection unit time.

[0031] Furthermore, the particle diameter classification includes: establishing relationship curves between particle diameter and pulse peak value and pulse width through calibration tests; and in the actual measurement stage, inferring the particle diameter from the particle diameter-pulse peak value curve or the particle diameter-pulse width curve, thereby achieving particle diameter classification.

[0032] The beneficial effects of this invention are as follows:

[0033] This invention uses separate light source and detector products, which are highly mature and low-cost. In contrast, the ViP process, which uses integrated detectors, is less mature, has a lower yield, and results in higher costs. This invention avoids complex air ducts or redundant structures, thus preventing noise from fan vibrations affecting signal acquisition. It also compresses all components into a small volume, facilitating miniaturization and integration.

[0034] In this invention, by controlling the angle between the incident light and the main ray of the scattered light, the scattered light is collected in a non-backscattering direction. According to the Mie scattering model, backscattered light has low intensity. This scheme uses scattered light at other angles, increasing the signal strength and thus significantly improving the signal-to-noise ratio. A beam splitter allows the reference light and scattered light to directly coincide in space, and then be received together by the detector, instead of being coupled into the laser cavity. Almost all scattered light can participate in interference, greatly improving coupling efficiency.

[0035] In this invention, the direction of collecting scattered light is not in the direction of incident light; that is, the principal ray of the incident light and the principal ray of the scattered light are off-axis. This angle can be controlled. The collecting lens only receives scattered light at a specific angle. When there is an obstruction in front, the path of the light reflected by the obstruction usually returns along the reverse path of the incident light. It is difficult for the reflected light from the obstruction to enter the scattered light collecting part of the particulate sensor module, thus avoiding the influence of obstructions on the sensor performance. Only the light emitting / receiving part of the housing is made of transparent materials such as quartz glass and resin, while other parts are blocked. Physical isolation suppresses ambient light to a certain extent. The detector does not receive simple scattered light, but an interference signal superimposed by the reference light and the scattered light. Ambient light is chaotic and cannot form a stable interference with the reference light, so it will not be misidentified as a valid signal, further improving the anti-interference capability.

[0036] Detecting particulate matter using ViP products manufactured by FastPass requires calculating the first and second velocities to obtain the three-dimensional magnitude of the spatial velocity vector, resulting in numerous hardware components, complex structures, and high computational requirements. This invention provides a method for calculating particulate matter concentration output. Based on FFT frequency domain analysis and angle integration, it obtains the quantity and velocity information of particulate matter from the frequency domain signal. A single detector can calculate the equivalent velocity, and then, based on the effective area coefficient of the detection area, the mass concentration of particulate matter is obtained. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the structure of the real-time particulate matter detection device based on the principle of optical interference of the present invention.

[0039] Figure 2 This is a flowchart of the real-time particulate matter detection method of the present invention.

[0040] Figure 3 This is a schematic diagram of the detection area and optical path direction of the particulate matter to be tested according to the present invention.

[0041] Figure 4 The diagram shows the interference signals. (a) is the interference signal of a single particle, (b) is the interference signal of multiple particles containing noise, and (c) is the FFT frequency domain signal.

[0042] Figure 1 In the diagram, 100 is the housing, 101 is the control and analysis module, 102 is the light source driving module (top) and the signal preprocessing module (bottom), which are not drawn separately, 201 is the light source generator, 202 is the collimating lens, 203 is the first beam splitter, 204 is the first focusing lens, 4 is the particulate matter to be measured, 301 is the detector, 302 is the second focusing lens, 303 is the second beam splitter, and 304 is the collecting lens. Figure 3 In the diagram, 1 represents the particulate matter detection area, 2 represents the optical path length variation, and 3 represents the angle between the principal ray of the incident light and the principal ray of the scattered light. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Example 1

[0045] A real-time particulate matter detection device based on the principle of optical interference, such as Figure 1 As shown, the particulate matter to be detected is located outside the entire device. The device includes: a housing 100, which is made of a non-transparent material, such as black resin or other plastics, or stainless steel. The housing 100 has a certain dustproof and waterproof function to protect the main key components and circuits from damage. The light path outlet is made of a transparent material, that is, the light output and light receiving parts of the light path are made of transparent materials, such as quartz glass or resin plastic. A particulate matter sensor module is installed inside the housing 100. The particulate matter sensor module includes a beam splitting and focusing module and a scattered light collection and interference module. The beam splitting and focusing module includes a light source generator 201. The beam splitting and focusing module is used to split the light source into incident light and reference light, and focus the incident light on the area where the particulate matter to be detected is located. The scattered light collection and interference module is used to collect the scattered light generated by the particulate matter and interfere with the scattered light with the reference light.

[0046] Specifically, the beam splitting and focusing module includes, in sequence, a light source generator 201, a collimating lens 202, a first beam splitter 203, and a first focusing lens 204.

[0047] The light source generator 201 is used to emit infrared light to provide initial detection light for the collimating lens 202 and is the optical signal source of the entire optical link.

[0048] In this embodiment of the application, the light source generator 201 includes, but is not limited to, a vertical cavity surface-emitting laser (VCSEL), a distributed feedback laser (DFB), and a laser LED. The selected laser wavelength is in the infrared band invisible to the human eye, that is, the wavelength is greater than 780nm.

[0049] The collimating lens 202 is used to convert the light emitted by the light source generator 201 into parallel light, providing uniform parallel incident light for the first beam splitter 203 and ensuring the stability of subsequent beam splitting. The collimating lens 202 can be an aspherical lens, a Fresnel lens, a plano-convex lens, or a biconvex lens.

[0050] The first beam splitter 203 is used to split parallel light into reference light and incident light, providing incident light for the first focusing lens 204 and reference light for the second beam splitter 203, which is the basis for the beam splitting of interference signal generation.

[0051] In this embodiment, the first beam splitter 203 is preferably a beam splitter with an incident light intensity ratio greater than the reference light intensity ratio, such as the common 9:1 or 7:3 beam splitters. Depending on the application scenario, a 5 / 5 beam splitter can also be selected.

[0052] The first focusing lens 204 is used to focus the incident light onto the detection area, enhancing the incident light intensity to increase the intensity of the scattered light from the particles, providing high-energy irradiation light to the external particles, and causing effective scattering of the particles. Since the intensity of the scattered light from Mie scattering is positively correlated with the intensity of the incident light, the focused light intensity is strong, and the intensity of the scattered light from the particles is increased, further improving the signal-to-noise ratio. The first focusing lens 204 can be an aspherical lens, a Fresnel lens, a plano-convex lens, or a biconvex lens.

[0053] Specifically, the scattered light collection and interference module includes, in sequence, a collection lens 304, a second beam splitter 203, a second focusing lens 302, and a detector 301.

[0054] The collecting lens 304 is used to collect the scattered light from the particles, convert the scattered light into parallel light, provide interferometric scattered light for the second beam splitter 203, and improve the scattered light collection efficiency to enhance the interference signal.

[0055] In this embodiment, the collecting lens 304 is preferably a high numerical aperture (NA) device. The larger the NA, the more scattered light is collected, the stronger the signal, and the better the signal-to-noise ratio. Aspherical lenses, compound lens groups, Fresnel zone plates, and immersion objectives can be used, and the numerical aperture (NA) is preferably 0.2-0.5.

[0056] The second beam splitter 203 is used to make the reference light and the scattered light from the collecting lens 304 coincide in space, satisfying the interference condition and providing a convergent interference light signal for the second focusing lens 302. The second beam splitter 203 preferably has a beam splitting ratio that makes up a high proportion of the scattered light signal, such as a 9:1 or 7:3 beam splitter.

[0057] The second focusing lens 302 is used to converge the interference light output from the second beam splitter 203 and precisely focus it onto the photosensitive surface of the detector 301, thereby improving the light energy utilization rate and signal strength, providing the detector 301 with a high signal-to-noise ratio interference light signal, and ensuring the accuracy of electrical signal conversion. The second focusing lens 302 can be an aspherical lens, Fresnel lens, plano-convex lens, biconvex lens, etc.

[0058] The detector 301 is used to convert the interference light signal converged by the second focusing lens 302 into a weak current signal, thereby realizing the conversion of optical signal to electrical signal and providing electrical signal input for the signal preprocessing module.

[0059] In this embodiment, the detector 301 includes, but is not limited to, PIN photodiode, avalanche photodiode, multiplier photodiode, and phototransistor; the detector 301 should be selected with low dark current and low noise to avoid interference with weak interference signals, ensure the purity of the original signal, and improve the signal-to-noise ratio.

[0060] The overall working process of the particulate matter sensor module is as follows:

[0061] The light beam emitted by the light source generator 201 is converted into parallel light by the collimating lens 202. The first beam splitter 203 splits the parallel light into a reference beam and an incident beam. The first focusing lens 204 focuses the incident light onto the detection area, causing effective scattering of the particles. The collecting lens 304 collects the scattered light from the particles and converts it into parallel light. The second beam splitter 203 makes the reference beam and the scattered light from the collecting lens 304 coincide spatially. The second focusing lens 302 converges the interference light output from the second beam splitter 203, which is received by the detector 301 and converted into a weak current signal. The optical path difference between the reference beam and the scattered light must be within the coherence length of the selected light source. If the optical path difference between the reference beam and the scattered light is an even multiple of half the wavelength of the light source, the amplitude of the interference light signal is the strongest; if it is an odd multiple, the interference light signal is the weakest; other cases are in between. Figure 1 As shown, the solid lines with arrows represent the reference light and the incident light, while the dashed lines with arrows represent the path of the scattered light. The spatial overlap of the reference light and the scattered light is one of the prerequisites for light interference; after the reference light and the scattered light spatially overlap, they are received by detector 301.

[0062] The optical paths of the beam splitting and focusing module and the scattered light collection and interference module can adopt symmetrical or asymmetrical structures, as long as the interference requirements are met. The angle between the incident principal ray and the scattered principal ray is adjusted according to the application scenario, preferably 30°, 45°, or 60°.

[0063] The housing 100 also includes a light source driving module and a signal preprocessing module. The light source driving module is connected to the light source generator 201 and is used to drive the light source generator 201. The signal preprocessing module is connected to the scattered light collection and interference module and is used to preprocess the interference signal.

[0064] Specifically, the light source driving module is used to drive the light source generator 201, which is the power source for the optical detection link. The light source 201 driving module preferably has a circuit for driving the light source generator 201 to work normally, such as common constant current source, constant voltage source driving method, DC-DC power supply module, LDO linear regulator, or other driving methods and modulation schemes that can meet the driving requirements of the light source generator 201.

[0065] Specifically, the signal preprocessing module includes at least a signal amplification module, a low-pass filter module, and a digital-to-analog converter module connected in sequence, with the signal amplification module connected to the detector 301.

[0066] The signal amplification module amplifies the weak current signal output by detector 301, providing a processable voltage signal for the low-pass filter module. This is the first step in signal preprocessing, increasing signal strength to suit subsequent modules. Specifically, the signal amplification module can be a cross-group amplifier, an integrated TIA chip, or an adjustable gain TIA.

[0067] The low-pass filter module is used to filter high-frequency noise in the output voltage of the signal amplification module, retaining the effective interference modulation signal, providing a clean analog signal for the digital-to-analog conversion module, and ensuring signal quality. The low-pass filter module can employ active / active low-pass filters, switched-capacitor filters, integrated filter chips, etc.

[0068] The analog-to-digital converter (ADC) module converts the analog signal output from the low-pass filter module into a digital signal, providing an analyzable digital input to the microcontroller of the control and analysis module 101, thus achieving the crucial analog-to-digital signal conversion. The ADC module can employ a pipelined ADC, embedded ADC, independent ADC chip, integrated ADC, etc.

[0069] The housing 100 also contains a control and analysis module 101, which is used to provide control signals to the light source driving module and to perform particulate matter related detection based on the preprocessed interference signal.

[0070] Specifically, the control and analysis module 101 includes a microcontroller and a data analysis module connected together. The microcontroller is connected to the digital-to-analog conversion module, and the data analysis module communicates with the host computer through a communication interface.

[0071] The microcontroller (MCU) is used to provide control signals to the light source 201 driving module to modulate the light emission frequency of the light source generator 201, such as by using PWM modulation signals. At the same time, it receives digital signals from the digital-to-analog converter module and transmits them to the data analysis module. It is the control core of the system and coordinates the workflow of each module.

[0072] The data analysis module is used to perform particulate matter-related detection on the digital signals transmitted from the microcontroller, and uploads the detection results to the host computer via the communication interface through the microcontroller, realizing the analysis and output of particulate matter data. The data analysis module includes an FFT analysis module, a particulate matter concentration calculation module, and a particulate matter diameter classification module. The FFT analysis module is used to obtain information such as the number of frequency domain signal pulses, pulse width, and pulse peak value through frequency domain analysis. The particulate matter concentration calculation module obtains the average velocity of particulate matter through angle integration, and calculates the particulate matter concentration by combining it with the number of frequency domain signal pulses (representing the number of particulate matter). The particulate matter diameter classification module calculates the particulate matter diameter based on the pulse width or pulse peak value, and classifies the particulate matter according to the diameter.

[0073] Example 2

[0074] In one specific embodiment, a real-time particulate matter detection device based on the principle of optical interference includes a housing 100 made of resin or other plastics. The beam splitting and focusing module sequentially includes a light source generator 201, a collimating lens 202, a first beam splitter 203, and a first focusing lens 204. The light source generator 201 uses a VCSEL, the collimating lens 202 is a plano-convex lens with a focal length of 4mm, the first beam splitter 203 is a thin rectangular beam splitter used in normal scenarios, therefore the ratio of the intensity or power of the reference light to the incident light is 5 / 5, and the first focusing lens 204 has a focal length of 6mm. The scattered light collection and interference module includes a plano-convex lens; the scattered light collection and interference module sequentially comprises a collection lens 304, a second beam splitter 203, a second focusing lens 302, and a detector 301. The collection lens 304 is an aspherical lens with NA=0.23, the second beam splitter 203 is a thin rectangular beam splitter with a 5 / 5 beam splitting ratio between the intensity or power of the reference light and the scattered light, the second focusing lens 302 is a biconvex lens with a focal length of 5mm, and the detector 301 is a silicon photodiode. The optical components of the beam splitting and focusing module and the scattered light collection and interference module are arranged in a symmetrical structure, as shown in the figure. The signal preprocessing module includes at least a signal amplification module, a low-pass filter module, and a digital-to-analog converter module connected in sequence. The signal amplification module is a cross-group amplifier, the low-pass filter module is a passive low-pass filter, and the digital-to-analog converter module is an integrated ADC chip.

[0075] The other structures are the same as in Example 1.

[0076] Example 3

[0077] In one specific embodiment, a real-time particulate matter detection device based on the principle of optical interference includes a housing 100 made of resin or other plastics. The beam splitting and focusing module sequentially includes a light source generator 201, a collimating lens 202, a first beam splitter 203, and a first focusing lens 204. The light source generator 201 uses a VCSEL, the collimating lens 202 is a plano-convex lens with a focal length of 4mm, and the first beam splitter 203 is a thin rectangular beam splitter used in scenarios where the scattered light from the particulate matter is weak. To increase the intensity of the incident light from the particulate matter, the ratio of the intensity or power of the reference light to the incident light is 1 / 9. The first focusing lens... 204 uses a plano-convex lens with a focal length of 6mm; the scattered light collection and interference module sequentially includes a collecting lens 304, a second beam splitter 203, a second focusing lens 302, and a detector 301. The collecting lens 304 is an aspherical lens with NA=0.23, the second beam splitter 203 is a thin rectangular beam splitter with a beam splitting ratio of 1 / 9 between the intensity or power of the reference light and the scattered light, the second focusing lens 302 is a biconvex lens with a focal length of 5mm, and the detector 301 is a silicon photodiode. The optical components of the beam splitting and focusing module and the scattered light collection and interference module adopt a symmetrical structural layout, as shown in the figure. The signal preprocessing module includes at least a signal amplification module, a low-pass filter module, and a digital-to-analog converter module connected in sequence. The signal amplification module uses a cross-group amplifier, the low-pass filter module uses a passive low-pass filter, and the digital-to-analog converter module uses an integrated ADC chip.

[0078] The other structures are the same as in Example 1.

[0079] Example 4

[0080] A real-time particulate matter detection method based on the principle of optical interference, such as Figure 1 As shown, the steps include:

[0081] S1: The control and analysis module 101 sends a control signal to the light source driving module to modulate the light emission frequency of the light source generator 201;

[0082] S2: The beam splitting and focusing module splits the light source into incident light and reference light, and focuses the incident light on the region where the particulate matter to be measured is located, while the particulate matter to be measured undergoes Miller scattering;

[0083] S3: The scattered light collection and interference module collects the scattered light generated by the particulate matter and interferes the scattered light with the reference light;

[0084] S4: The signal preprocessing module receives the interference light and preprocesses the interference signal;

[0085] S5: The control and analysis module 101 performs particulate matter correlation detection based on the preprocessed interference signal and feeds the detection results back to the host computer.

[0086] After the incident light passes through the first focusing lens 204, it forms an elliptical region with a small spot and high light intensity near the focal point. According to the Mie scattering model, the intensity of the scattered light is directly related to the intensity of the incident light. The intensity of the scattered light generated by the particles when passing through this region will also be greatly increased. The length of the minor semi-axis of the elliptical region is the waist radius of the Gaussian beam of the light source. This is related to the focal length and diameter of the focusing lens, as well as the wavelength of the light source. Similarly, the length of the major semi-axis of the ellipse is related to the focal length and diameter of the focusing lens and the wavelength of the light source.

[0087] When the particulate matter to be measured enters the detection area, its scattered light signal is strong, and the collecting lens 304 can collect the scattered light signal. When the particulate matter is stationary in the detection area, it can be known that the optical path difference between the reference light and the scattered light is a constant value. The optical path of the reference light is the distance traveled by the light emanating from the light source generator 201, through the collimating lens 202, the first beam splitter 203, the second beam splitter 203, the second focusing lens 302, and finally to the detector 301. The optical path of the scattered light is the distance traveled by the light emanating from the light source generator 201, through the collimating lens 202, the first beam splitter 203, the first focusing lens 204, the particulate matter to be measured, the collecting lens 304, the second beam splitter 203, the second focusing lens 302, and finally to the detector 301.

[0088] If the optical path difference between the reference light and the scattered light is an even multiple of half the wavelength of the light source, the amplitude of the interference signal is strongest; if it is an odd multiple, the interference signal is weakest; other cases fall between the two. Because the particles being measured are disturbed by airflow or pass through the detection area at a certain speed due to methods such as air pumps, the optical path difference between the reference light and the scattered light is constantly changing. The intensity of the interference signal detected by detector 301 will continuously change between its maximum and minimum values, forming modulation. This modulated signal is the desired target signal. The amplification module of detector 301 will amplify this signal step by step and also has the function of removing DC signals and low-frequency signals, such as the low-frequency jitter noise signal of ambient light and the strong DC signal of the reference light.

[0089] like Figure 3 As shown, the elliptical region is the detection area 1 for the particles being measured. The horizontal dashed line represents the direction of the incident principal ray, and the dashed line with an arrow represents the direction of the scattered principal ray. If the angle 3 between the two dashed lines (principal rays) is 0°, it results in the collection of backscattered light. However, this patent, by controlling the size of the angle, can collect scattered light from any direction. The projected distance of the particle's path through the detection area along the direction of the scattered principal ray (the dashed line with an arrow in the figure) is the change in optical path, i.e., the distance between the particle's path through the detection area and the direction of the scattered principal ray (the dashed line with an arrow in the figure). Figure 3 The change in optical path length is 2, and this change in optical path length will cause modulation of the interference signal.

[0090] Let the expression for the incident light be:

[0091]

[0092] The expression for scattered light is:

[0093]

[0094] In the formula Let be the expression for the change of the electric field intensity of the incident light with time, describing the time-varying electric field characteristics of the incident light. The amplitude of the incident light is denoted by , which represents the intensity of the incident light and is a constant value. j is an imaginary value. The laser angular frequency, Let be the expression for the change of the electric field intensity of the scattered light over time. The amplitude of the scattered light varies with time. This is because the scattering efficiency changes with factors such as the particle's position and size as it moves from the detection area to its exit, causing the amplitude to change. This is the change in phase of the scattered light over time as it passes through the detection area, i.e., the phase difference between the scattered light and the reference light, caused by the change in optical path due to the particles passing through the detection area.

[0095] The amplitude of the incident light is related to the power of the laser incident on the particle and the size of the spot focused by the lens. The amplitude of the scattered light is calculated according to the Mie scattering model, which is related to a variety of factors, such as the intensity of the incident light, the size of the particle, and the scattering angle.

[0096] The intensity of the interference light after the reference light and scattered light are coherently received by detector 301 is:

[0097] ;

[0098] After unfolding, we get:

[0099] ;

[0100] After substituting and simplifying, we get:

[0101] ;

[0102] in, To perform the operation of taking the real part, for .

[0103] In an ideal situation, the interference signal of a single particle is as follows: Figure 4As shown in (a), when a particle enters the detection area and leaves the detection area, the intensity of the interference signal changes continuously between the maximum and minimum values. It is important to note that the maximum (minimum) value of the signal is related to the diameter of the particle. When other conditions remain unchanged, such as the power of the light source generator 201, the optical path structure, and the angle of scattered light collection, the size of different particles can be distinguished by the different maximum (minimum) values, and particles can be classified according to their diameter. For example, PM2.5 is a particle with a diameter less than or equal to 2.5 micrometers, and PM10 is a particle with a diameter less than or equal to 10 micrometers. The width of a single pulse from the maximum to the minimum and back to the maximum can also be used to evaluate the diameter of the particle.

[0104] However, the actual situation is not that only one particle passes through the detection area during this short period of time, but rather that multiple particles pass through the detection area at different speeds; in addition, there are many other sources of noise, such as dark current in detector 301, shot noise, unstable noise from the light source generator 201 signal, and noise from stray light signals entering detector 301, etc. Figure 4 (b) shows a scenario where multiple particles enter the detection area simultaneously, and it can be seen that the number of particles entering the detection area is no longer distinguishable in the time domain signal.

[0105] Therefore, the invention employs the following method in step S5: the control and analysis module 101 in step S5 performs particulate matter correlation detection based on the preprocessed interference signal, including particulate matter concentration detection and particulate matter diameter classification.

[0106] The method for detecting particulate matter concentration is as follows:

[0107] S51: The time-domain interferometric electrical signal, after being converted from an analog signal to a digital signal, is converted into a frequency-domain signal by performing a Fast Fourier Transform (FFT), such as... Figure 4 As shown in (c), obtain a list of frequencies for all peak values. Each peak corresponds to one particulate matter, and N is the number of particulate matter.

[0108] S52: Calculate the velocity components of a single particle along the main ray of scattered light based on the Doppler frequency shift principle, and obtain a list of velocity components. :

[0109] The velocity component is derived from the Doppler frequency shift principle as follows:

[0110] ;

[0111] in, The wavelength of the light source is denoted as .

[0112] S53: Since the velocity direction of particles in an open environment is arbitrary and isotropic (without a fixed direction of motion, and turbulence and random motion exist), it is necessary to statistically average all velocity components and calculate the average velocity of all particles through angular integration.

[0113] ;

[0114] S54: Calculate particulate matter concentration based on the average velocity and number of all particulate matter:

[0115] ;

[0116] Where C is the particulate matter mass concentration in μg / m3, S is the correlation coefficient with sensor sensitivity, which is directly related to the effective cross-sectional area of ​​the detection area, and T is a user-defined detection unit time.

[0117] The method for classifying particle diameter is as follows: According to the Mie scattering model, the intensity of scattered light from a particle is positively correlated with its diameter (the larger the diameter, the stronger the scattered light); the peak-to-peak value of the interference signal directly reflects the intensity of the scattered light. Under fixed optical path / circuit parameters, the peak-to-peak value of the pulse is monotonically increasing with the particle diameter (the larger the diameter, the larger the peak-to-peak value). The larger the particle diameter, the longer it takes to pass through the detection area, and the wider the pulse width. Therefore, the relationship curves between particle diameter and peak-to-peak value and pulse width can be established through calibration tests. In the actual measurement stage, the particle diameter can be inferred from the particle diameter-peak-to-peak value curve or the particle diameter-pulse width curve, thereby achieving particle diameter classification.

[0118] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A real-time particulate matter detection device based on the principle of light interference, characterized in that, The application relates to a real-time particulate matter detection device based on a light interference principle, which comprises a shell (100) provided with a particulate matter sensor module, a light source driving module and a signal preprocessing module. The shell (100) is further provided with a control and analysis module (101) for providing a control signal for the light source driving module and performing particulate matter related detection according to the preprocessed interference signal.

2. The real-time particulate matter detection device based on the light interference principle according to claim 1, characterized in that: the shell (100) is made of non-transparent material as a whole, and the light path outlet is made of transparent material; the optical elements of the light splitting and focusing module and the scattered light collecting and interference module adopt a symmetrical or asymmetrical structure. The light splitting and focusing module comprises a light source generator (201), a collimating lens (202), a first beam splitter (203) and a first focusing lens (204) in sequence; and the scattered light collecting and interference module comprises a collecting lens (304), a second beam splitter (203), a second focusing lens (302) and a detector (301) in sequence.

4. The real-time particulate matter detection device based on the light interference principle according to claim 3, characterized in that: the light source generator (201) comprises a VCSEL, a distributed feedback laser and a laser LED, and the selected wavelength is in the infrared invisible waveband for human eyes; the collecting lens (304) comprises an aspheric lens, a composite lens group, a Fresnel zone plate or an immersion objective lens with an aperture value of 0.2-0.5; the detector (301) comprises a PIN photodiode, an avalanche photodiode, a multiplication photodiode and a phototriode; the first beam splitter (203) is a beam splitter with a larger proportion of incident light intensity than that of reference light; and the second beam splitter (203) is a beam splitter with a larger proportion of scattered light intensity than that of reference light. The signal preprocessing module at least comprises a signal amplification module, a low-pass filtering module and a digital-analog conversion module connected in sequence, and the signal amplification module is connected with the detector (301).

3. The real-time particulate matter detection device based on the principle of optical interference according to claim 1, characterized in that, ​ ​ ​ ​ ​ 5. The real-time particulate matter detection device based on the principle of light interference according to claim 3, characterized in that, ​ 6. The real-time particulate matter detection device based on the principle of optical interference according to any one of claims 1-5, characterized in that, ​ 7. The real-time particulate matter detection device based on the principle of optical interference according to any one of claims 3-5, characterized in that, The control and analysis module (101) comprises a microcontroller and a data analysis module connected thereto, the microcontroller is connected with a digital-analog conversion module, the data analysis module comprises an FFT analysis module, a particulate matter concentration calculation module and a particulate matter diameter classification module, the FFT analysis module is connected with the microcontroller and is used to acquire the number of frequency domain signal pulses, the pulse width and the pulse peak value information through frequency domain analysis based on the preprocessed interference signal; the particulate matter concentration calculation module acquires the average velocity of particulate matter through angular integration and calculates the particulate matter concentration in combination with the number of frequency domain signal pulses; the particulate matter diameter classification module calculates the diameter of particulate matter according to the pulse width or the pulse peak value and classifies the particulate matter according to the diameter.

8. A real-time particulate matter detection method based on the principle of light interference, using the real-time particulate matter detection device based on the principle of light interference according to any one of claims 1-7, characterized in that, The method comprises the steps of: S1: the control and analysis module (101) sends a control signal to the light source driving module to modulate the light source generator (201) to emit light at a frequency; S2: the light splitting and focusing module splits the light source into incident light and reference light and focuses the incident light on the region where the particulate matter to be measured is located, and the particulate matter to be measured generates Mie scattering; S3: the scattered light collection and interference module collects the scattered light generated by the particulate matter and interferes the scattered light with the reference light; S4: the signal preprocessing module receives the interference light and pre-processes the interference signal; S5: the control and analysis module (101) performs particulate matter related detection based on the preprocessed interference signal and feeds back the detection result to the upper computer, and the related detection comprises particulate matter concentration detection and particulate matter diameter classification.

9. The method for detecting particulate matter in real time based on the principle of optical interference according to claim 8, characterized in that, The particulate matter concentration detection comprises: S51: The time domain interference electric signal converted into a digital signal is converted into a frequency domain signal by fast Fourier transform to obtain a frequency list of all peak values Each peak value corresponds to a particulate matter, and N is the number of particulate matters. S52: Calculate the velocity component of the single particle in the direction of the main light ray of the scattered light based on the Doppler shift principle to obtain a list of velocity components ; S53: Average velocity of all particulate matter by 360° angular integration ; S54: calculating the particulate matter concentration based on the average velocity and the number of all particulate matters: ； Wherein, C is the particulate matter mass concentration, S is a coefficient related to the sensitivity of the sensor, and T is the unit time of detection.

10. The method of claim 8, wherein the method is a real-time particulate matter detection method based on optical interference principle. The particulate matter diameter classification comprises: establishing the relationship curves of the diameters of particulate matters with the pulse peak value and the pulse width through calibration tests, and inversely deducing the diameters of particulate matters through the particulate matter diameter-pulse peak value curve or the particulate matter diameter-pulse width curve in the actual measurement stage, so as to realize the classification of the diameters of particulate matters.

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