CN105547944B - A kind of inhalable particles object detecting method based on stacking diffraction - Google Patents

Abstract

The invention discloses a method for detecting inhalable particulate matter based on stacked diffraction, and belongs to the field of inhalable particulate matter detection. The method is to use a laser and an optical lens to generate a laser beam with a diameter of 1-10mm and a wavelength of 200-1000nm and shine it on the air to be measured; when the laser passes through inhalable particles in the air, it will diffract and form an interference pattern on the opposite side of the laser ;Due to the sedimentation rate of inhalable particles under the action of gravity, a series of interference patterns related to these particles can be received by using a high-speed electronic photosensitive element with a frame rate of not less than 600fps; for general inhalable particles such as PM2.5 and PM10, These interference patterns are superimposed on each other, so the holographic shape of these particles can be calculated by using the stacked diffraction algorithm; using the real-time stacked diffraction algorithm, the image of the inhalable particles can be displayed on the display device in time, and the difference can be obtained through the statistics of the processor. Concentration values corresponding to large and small particles. This method does not require cutters such as PM2.5 and PM10, and can perform quasi-real-time three-dimensional imaging of inhalable particulate matter, which is helpful for online research on the behavior of inhalable particulate matter.

Description

A detection method for inhalable particulate matter based on stacked diffraction

technical field

The invention belongs to the field of inhalable particulate matter detection, and specifically relates to reproducing light intensity and phase information of inhalable particulate matter in the air by using stacked diffraction imaging technology, realizing online holographic imaging, and calculating the concentration of inhalable particulate matter with different particle diameters.

Background technique

Smog has become a weather phenomenon that seriously affects people's production and life. Inhalable particulate matter is the core pollution source of smog, which can cause serious harm to human health, especially particles with a diameter of less than 2.5 μm (PM2.5). Directly entering the lungs of the human body is even more harmful. In order to ensure the normal life of the people, it is very urgent to develop real-time and accurate monitoring equipment for inhalable particulate matter, especially PM2.5. The current monitoring methods for inhalable particulate matter mainly include the following.

(1) Filter membrane weighing method, this method allows the air to pass through the pre-placed filter paper after passing through the particle cutters of different particle sizes, and the inhalable particles of different particle sizes such as PM2.5 and PM10 will be collected on the corresponding filter paper; After a certain period of time, the filter paper was taken out, and the concentration of inhalable particulate matter was estimated by comparing the mass change of the filter paper before and after adsorption.

(2) Ray absorption method, which adopts the same technology as the filter membrane weighing method to obtain filter paper with deposited particles, and irradiates it with β-rays; The mass of particulate matter is calculated from the ray absorption and its concentration is calculated (Nong Yongguang et al., Value Engineering, 2013 (35), pp.304-305).

(3) The micro-oscillating balance method, which uses a tapered hollow glass tube, the thick end is fixed, and the thin end is equipped with a filter element. The air enters from the thick head and passes through the cutter of the corresponding particle size, and the inhalable particles of this particle size are trapped on the filter element. Under the action of the electric field, the fine head oscillates at a certain frequency, and the oscillation frequency is inversely proportional to the square root of the fine head weight. According to the change of the oscillation frequency, the mass of the collected particles can be calculated and its concentration can be calculated according to the intake air volume (Nong Yongguang et al., Value Engineering, 2013(35), pp.304-305).

(4) Laser scattering method, which is based on Mie scattering theory, uses laser light as the light source, uses photoelectric devices to receive light intensity, and determines the particle density in the air according to the relationship between scattered light flux and particle size, and calculates the particle concentration (Ge Baozhen et al., Journal of Tianjin University (Natural Science and Engineering Technology Edition), 2013 (1), pp.22-28).

There are certain deficiencies in the above methods:

The filter weighing method and the ray absorption method have a long sampling time, which is not suitable for real-time measurement requirements; the microbalance method is greatly disturbed by humidity and temperature; although the laser scattering method can achieve real-time measurement of inhalable particles, However, due to the relationship between laser light scattering and the refractive index of particles, the accuracy of the results obtained by this method is not good.

None of the above methods can perform online imaging of inhalable particles, and the measurement of inhalable particles of different particle sizes such as PM2.5 and PM10 must also rely on a cutter; this aspect makes it difficult to intuitively see the movement behavior of inhalable particles. On the other hand, it also increases the complexity of device design.

In addition to the above methods, people are now also exploring the use of digital holography to measure PM2.5 and other inhalable particulate matter; this method is based on holographic technology, CCD, CMOS and other photoelectric devices and computer technology, making real-time imaging of inhalable particulate matter possible. The digital holography currently used to observe respirable particles is coaxial digital holography, which uses the scattered light at the edge of the particles as a reference light to record the phase information of respirable particles (Wang Ping, Optical Instrument, 2015 (4), pp .287-292). Although this method can perform holographic imaging of particles, because the object light and the reference light have the same direction, the spectral information of the hologram overlaps seriously, and the resolution of the obtained image is low.

Ptychography-based microscopic techniques emerging in recent years can also be used to record and display holographic images of objects. This method first records a series of diffraction patterns of the object, and each diffraction pattern has at least an overlapping area with another diffraction pattern; then, the object information is obtained through iterative calculations, and the information meets the requirements of all diffraction patterns, thereby recreating the holographic image of the object. This method can obtain images with higher resolution than traditional digital holography, even exceeding the optical limit determined by the Rayleigh criterion (Marrison et al, Sci. Rep, 2013(3), No. 2369). The general stacked diffraction microscopy obtains a series of diffraction patterns that meet the requirements by moving the mutual position of the light source and the sample, usually by means of a micromechanical device. For inhalable particles such as PM2.5 and PM10 in the air, they are not motionless in the air, and they have a certain settling rate. Magnitude (Leng Yin et al., Visualization Study on the Movement of Inhalable Particles in the Standing Wave Sound Field, Journal of Engineering Thermophysics, 2007 (Supplement 1), pp.209-212); according to the Stokes settlement formula , the settling velocity v is proportional to the square of the particle radius r , then the settling velocity of a particle with a particle size of 10 μm is on the order of 5 mm/s. Diffraction these particles and use a high-speed photoelectric sensing device with a shooting rate of not less than 600fps to record their diffraction patterns, then two adjacent frames of diffraction patterns generally have overlapping areas, and the higher the shooting rate, the more overlapping areas Therefore, this method satisfies the conditions required by the stacked diffraction algorithm, so the stacked diffraction algorithm can be used to reproduce the imaging of inhalable particles. This process does not need to remove the particles, so this imaging is online imaging; combined with the positioning technology in the light field, real-time online monitoring of particles can also be realized. Through computer processing, the particles can display their shape and behavior in real time.

Contents of the invention

The purpose of the present invention is to propose a detection method for inhalable particulate matter based on stacked diffraction, which can be used for holographic imaging, real-time three-dimensional reproduction of inhalable particulate matter, and calculation of the concentration of inhalable particulate matter with different particle sizes. This method does not require PM2.5, PM10 and other cutters, and the instrument structure is simple; and it can perform quasi-real-time three-dimensional dynamic display of inhalable particulate matter, which not only has high precision, but also can study the behavior of inhalable particulate matter online.

The technical solution of the present invention is as follows.

A method for detecting inhalable particulate matter based on stacked diffraction microscopy, comprising the following steps: (1) As shown in Figure 1, a laser 1 and an optical lens 2 are used to generate a spherically diverging laser beam and irradiate it to the air to be tested, The laser beam is generally a divergent spot, the cross-sectional area of the spot is in the range of 1 mm ² to 100 mm ² when irradiating air, and the laser wavelength is 200-1000 nm; In chamber 3, the air chamber is input by the input device; the pumping device can be used to discharge the original air in the air chamber to prevent the residual air from causing measurement errors; the input and output devices are kept closed during measurement, so that the air in the air chamber is still; the air chamber is The two surfaces of the laser beam irradiated area are parallel and perpendicular to the central axis of the laser beam. The thickness of the space in the air chamber along this direction is between 0.5mm and 1mm; the distance between the air chamber and the photosensitive element probe is not less than 2cm, and the distance between the air chamber and the The ratio of the distance between the centers of the laser beams is not less than 10.

(2) Use high-speed CCD and other electronic photosensitive elements to receive the laser beam spot passing through the air to be measured, and transmit it to the processor containing the laminated diffraction reproduction system. The transmission device adopts wired transmission or wireless transmission technology such as Bluetooth and Wifi.

(3) After deducting the background information of the inhalable particulate matter information contained in the laser beam spot, perform lamination diffraction reproduction processing; the main calculation process is:

The first step is to determine the relative position of the diffraction spot of the detected particle in the entire spot according to the diffraction pattern of the particle in the light spot, and separate the diffraction spots of different particles, and determine the change of its position according to a series of diffraction patterns;

In the second step, for the first particle, determine the incident light wave function required for the stacked diffraction calculation according to the position of its diffraction pattern The initial value of , where R _j represents the offset of the particle in the j- th diffraction pattern relative to its position in the first diffraction pattern; since the incident wave is a diverging spherical laser beam, the wavelength and distance from the gas cell are known, so the The incident wave function is known, and the incident wave function here can be obtained only by knowing the position of the particle in the spot. Due to the influence of the gas chamber glass, the real wave function is slightly different from this wave function, which can be calculated iteratively later make corrections in

The third step is to calculate the phase distribution of the required particle shape (i.e., the matter function ) is initially set to a circle, the light transmittance is generally set to 1, and the phase is set to 0;

The fourth step is to obtain the initial value of the particle incident function according to the initial value of the incident wave function and the particle function , where the subscript 0 represents the initial value;

The fifth step is to obtain the updated particle incident function value; since the particle size is small enough relative to the distance from the photosensitive element, the diffraction pattern can satisfy the Fraunhofer diffraction condition, and the intensity of the diffraction pattern at this time , F {} represents Fourier transform, fast Fourier transform is used in the operation process;, according to the Fraunhofer diffraction formula, the wave function at the receiving end of the photosensitive element at this time can be calculated as ;Retain the phase part of U ₀ , replace the intensity part with the square root of I , and generate a new wave function at the receiving end ,Right now ;right Perform inverse Fourier transform to obtain a new initial value of the particle incident function ;

The sixth step is to update the object function O and the incident wave function P , and the formulas required for the update are:

The seventh step is to compare whether the accuracy requirements are met, and set the parameter RMS as follows

If RMS is less than the set error value Err , then and P _new are the object function and incident light function respectively, otherwise, replace O ₀ and P ₀ with O _new and P _new , and repeat steps 4 to 7 until the qualified object function and incident light function are obtained; Err is generally The value is 10 ^-3 to 10 ^-5 , the smaller the value, the higher the accuracy and the longer the iteration time;

In the eighth step, for other interested particles, repeat the second to seventh steps until all the shape images of the interested particles are obtained; the parallel calculation method can be used for each interested particle to calculate for each particle at the same time.

(4) Display the shape and phase distribution (i.e., the physical function) of the obtained particles to obtain its three-dimensional image; according to the three-dimensional image, count the concentration of inhalable particles with different particle sizes, and transmit the reproduced image and particle concentration to the display device , the transmission device adopts wired transmission or wireless transmission technology such as Bluetooth and Wifi. Combined with the volume of the air area irradiated by the light spot, the concentration of particles with different particle sizes can be calculated, and then converted into the corresponding mass concentration according to the national standard WS/T206-2001.

(5) The display device will display information such as the reproduced holographic image and the concentration of inhalable particles with different particle sizes on the screen.

The technical effects of the present invention are as follows: (1) ^The present invention can realize online three-dimensional imaging of inhalable particulate matter with high resolution; using a laser with a wavelength of 525nm, the resolution can reach Up to 200nm; fast processing (that is, the value of Err is 10 ^-3 ) and a resolution of 1μm.

(2) The processing time of the present invention for reappearing the appearance of inhalable particulate matter is no more than 5 minutes, and 60 to 100 particles can be processed at the same time by using parallel computing. Quasi-real-time monitoring of particles; combined with the positioning of the particle diffraction pattern by the light field, the particle trajectory can be displayed, which can help to study its behavior.

(3) The present invention can simultaneously perform statistical calculations on the concentration of inhalable particulate matter with different particle sizes without using a cutter.

Description of drawings

Figure 1. Schematic diagram of the device used in a detection method for inhalable particulate matter based on stacked diffraction imaging technology, 1 is a laser, 2 is a lens group, 22 is a small filter hole, 3 is an air chamber (including the valve of the absorption and pumping device), 31 is a barometer, 4 is a high-speed CCD, and 5 is a portable electronic computer (including a processor and a display device).

Figure 2 Diffraction patterns of inhalable particulate matter monitoring in artificially simulated environments. The four pictures are the pictures of four adjacent time points in the order of 1-4, and the scale bar in the figure represents 20 μm.

Figure 3 Reproduction of inhalable particles in the artificial simulated environment, the sub-figure is an enlarged view of the reproduction of the leftmost particle (the particle directly below the sub-figure), the scale of the main graph represents 20 μm, and the scale of the sub-graph represents 1 μm.

Detailed ways

The present invention will be further described below by example. It should be noted that the purpose of the published embodiments is to help further understand the present invention, but those skilled in the art can understand that various replacements and modifications are possible without departing from the spirit and scope of the present invention and the appended claims . Therefore, the present invention should not be limited to the content disclosed in the embodiments, and the protection scope of the present invention is subject to the scope defined in the claims.

Example: Real-time detection of inhalable particulate matter in a simulated environment based on the stacked diffraction algorithm

Build the optical path diagram and connect and debug the corresponding equipment

According to the optical path diagram shown in Figure 1, the optical path for detecting inhalable particulate matter was built and connected to the corresponding equipment. The thickness of the gas chamber used in the laser irradiation area was 1mm, and the receiving device 4 was a high-speed CCD with a shooting rate of 1000fps. The laser light passes through the lens group 2 to form a spherical wave, and the center of the sphere is at the optical small hole 22 .

Get background information

Pump out the air in the air chamber 3; when the air pressure indicator is stable at -0.1Mpa, it indicates that the air in the air chamber has been extracted; the laser with a wavelength of 645nm is irradiated to the air chamber along the thickness direction of the air chamber after beam expansion, and the front surface of the air chamber ( That is, the diameter of the spot near the laser is about 1cm, and the spot is received by the CCD, which is stored as background information.

environmental balance

Open the input device and output device of the air chamber 3, and when the indication of the barometer 31 remains unchanged, it means that the air in the air chamber is the gas in the environment, close the input and output devices, and let it stand for 30 seconds; Lighting a cigarette in a closed environment produces particles.

Obtaining the Diffraction Pattern of the Detected Air

The laser is vertically injected into the air chamber from the irradiation position where the background information is obtained, and the diffraction spot is received by a high-speed CCD. The receiving time of each two adjacent spots does not exceed 1/240s. The typical diffraction pattern of the obtained air is shown in Figure 2. Represents the diffraction patterns at four adjacent moments.

Obtain a reconstructed image of the detected air

Stacked diffraction calculations are performed from the diffraction pattern of air. It can be seen from the typical diffraction pattern 2 that the dust diffraction spots at four moments overlap, so it can be calculated by the stacked diffraction algorithm. The calculation method is carried out according to the method in step (3) of the technical solution, and the values of α and β in the sixth step are 1. The inhalable particle image corresponding to Figure 2 obtained after iteration is shown in Figure 3, and the sub-image of Figure 3 is the enlarged image of the leftmost particle, which shows that this method can perform three-dimensional imaging of PM2.5 and other particles.

Obtaining the concentration of respirable particulate matter

The processor automatically classifies and counts the reproduced image of the sample according to its size. After deducting the background information, counts its number and calculates its volume, and then compares it with the irradiated air volume, and converts it to the air volume under standard conditions, and calculates body concentration; according to the national standard WS/T206-2001, the corresponding mass concentration and pollution index are converted.

the message states

The reappearance image of the particles, the concentration of the particles, the pollution index and other information are displayed on the screen of the portable computer 5; the screen is constantly refreshed, and the dynamic movement process of the particles can be seen.

Claims (8)

1. A method for detecting inhalable particulate matter based on stacked diffraction technology, comprising the following steps: (1) Use a laser and an optical lens to generate a laser beam and shine it on the air to be measured; (2) Use the electronic photosensitive element to receive the laser beam spot passing through the air to be measured, and transmit it to the processor with the laminated diffraction reproduction system; (3) The processor with the stacked diffraction system performs calculation and display of the phase and shape information of the spot. The process includes preliminary positioning of the particles, setting the initial value of the incident light according to the positioning result, and real-time stacked diffraction reconstruction calculation; (4) Count the concentration of inhalable particles with different particle sizes, and transmit the reproduced image and particle concentration information to the display device; (5) The display device will display the reproduced image and the concentration of inhalable particulate matter with different particle sizes. 2. The detection method according to claim 1, wherein the laser beam in step (1) is a spherically diverging laser beam, the cross-sectional area of the spot is in the range of 1 mm ² to 100 mm ² when the air is irradiated, and the wavelength of the laser beam is 200~1000nm. 3. The detection method according to claim 1, characterized in that the air to be measured in step (1) is in a transparent air chamber, the air chamber contains input and pumping devices and a barometer, and the air is measured at both ends of the air chamber Closed, the barometer remains stable. 4. The detection method according to claim 1, wherein the photosensitive element in step (2) is a high-speed CCD camera with a frame rate not lower than 600fps. 5. The detection method according to claim 1, characterized in that the laser beam spot in step (2) is transmitted to the processor through wireless transmission technology. 6. The detection method according to claim 1, characterized in that the reproduced image and particle concentration information in step (4) are transmitted to the display device through wireless transmission technology. 7. The detection method according to claim 1, characterized in that the air to be measured in step (1) is in a transparent air chamber, and the two surfaces of the air chamber irradiated by the laser beam are parallel to the center of the laser beam. The axis is vertical. 8. The detection method according to claim 1, wherein the laser beam in step (1) is a spherical diverging laser beam, the air to be measured is in a transparent air chamber, and the distance between the transparent air chamber and the electronic photosensitive element is not less than 2cm , the ratio of this distance to the distance between the transparent air chamber and the center of the laser beam is not less than 10.