CN117723472A - Low background noise particulate matter detector - Google Patents

Low background noise particulate matter detector Download PDF

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CN117723472A
CN117723472A CN202311821060.5A CN202311821060A CN117723472A CN 117723472 A CN117723472 A CN 117723472A CN 202311821060 A CN202311821060 A CN 202311821060A CN 117723472 A CN117723472 A CN 117723472A
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particles
particulate matter
light
sample cell
signal light
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黄辉
蔡伟成
李兆林
马松
孙希明
黄火林
陈景
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Dalian University of Technology
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Dalian University of Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/02—Investigating particle size or size distribution
    • G01N15/0205—Investigating particle size or size distribution by optical means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/02—Investigating particle size or size distribution
    • G01N15/0205—Investigating particle size or size distribution by optical means
    • G01N15/0227—Investigating particle size or size distribution by optical means using imaging; using holography
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/03—Cuvette constructions
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/27—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands using photo-electric detection ; circuits for computing concentration
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/64—Fluorescence; Phosphorescence
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/64—Fluorescence; Phosphorescence
    • G01N21/645—Specially adapted constructive features of fluorimeters
    • G01N21/6456—Spatial resolved fluorescence measurements; Imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/64—Fluorescence; Phosphorescence
    • G01N21/645—Specially adapted constructive features of fluorimeters
    • G01N2021/6482—Sample cells, cuvettes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/64—Fluorescence; Phosphorescence
    • G01N2021/6495—Miscellaneous methods

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Abstract

A low background noise particulate matter detector comprises a light source, a photoelectric detector, an optical lens, an external magnetic field and a black sample cell. The inner surface of the black sample cell is black and is used for absorbing excitation light, and the material of the black sample cell is opaque and does not generate fluorescence; the side wall of the black sample cell is provided with a plurality of mutually perpendicular small-hole channels which are respectively connected with the light source and the photoelectric detector; the excitation light emitted by the light source enters the black sample cell through one of the small hole channels, and irradiates the sample to be measured; the particle in the sample to be measured emits signal light under the irradiation of the excitation light, and the signal light enters the photoelectric detector through the other small hole channels; the particles realize on-line imaging and identification of bubble particles, ferromagnetic particles and nonferromagnetic particles by utilizing gravity and an externally applied magnetic field; the optical lens is positioned in the small hole channel and is used for focusing excitation light or signal light; the size, the components and the content of the particles in the sample to be detected can be obtained through the information such as the intensity distribution, the spectrum and the like of the test signal light.

Description

Low background noise particulate matter detector
Technical Field
The invention relates to the technical field of stray light detection, in particular to fluorescence and scattered light detection of particulate matters, which can be used for detecting the particulate matters in liquid and gas.
Background
When the light beam encounters an object to be detected, effects such as absorption, scattering, fluorescence and the like can occur, so that light rays with disordered propagation directions (namely stray light) are generated, and information such as components and sizes of the object to be detected can be obtained through analyzing the stray light.
Detection principle of fluorometer: the object to be measured is irradiated with "excitation light" having a short wavelength to generate fluorescence having a long wavelength (the propagation direction of fluorescence is disordered, which can be regarded as stray light). Detection principle of turbidity meter: the excitation light irradiates and is scattered by the particles (e.g., mie scattering and Rayleigh scattering), and the direction of the scattered light is also cluttered (also known as stray light). Therefore, the fluorescence and scattered light are collectively referred to as stray light (i.e., light having a disordered propagation direction), and the stray light is used as signal light, so that information such as the component of the object to be measured can be obtained by analyzing the stray light.
For turbidimeters and fluorometers, the intensity of excitation light (mW magnitude) is approximately 10% higher than that of stray light (fW-nW magnitude) 6 ～10 12 Multiple, even small leakage of excitation light can overwhelm stray light (the leaked excitation light is called background)Light), the interference of the excitation light with the signal light is serious, which becomes a main factor restricting the improvement of the detection accuracy. Currently, turbidity meters and fluorometers typically employ a transparent cuvette as the sample cell. However, the sidewall of the cuvette is transparent, and part of the excitation light can enter the transparent sidewall and propagate and diverge in the transparent sidewall, so that the excitation light is very easy to mix into stray light, and the stray light is submerged by the excitation light (i.e., the signal light is submerged by the background light), thereby reducing the detection sensitivity. In addition, the existing turbidimeter and fluorometer have separate structures of an excitation light path, a detection light path and a sample cell (cuvette), so that the turbidimeter and the fluorometer are large in size and not vibration-resistant, and are difficult to be used for portable online detection.
In addition, for an engine, particulates in the engine oil (such as metal chips generated by engine wear) may damage the engine, and it is highly desirable to detect the size, content and material of the particulates in the engine oil. However, the components of the engine oil are complex, and the engine oil has strong fluorescence and stray light, which can cover scattered light generated by particulate matters, so that the conventional fluorescent instrument and turbidity instrument are difficult to detect the particulate matters in the engine oil. Currently, the engine oil particulate matter detectors (such as an oil metal particle sensor GTI-PQM-06A and a metal abrasive dust sensor SLFM 01-S2) are based on the electromagnetic induction principle, and only large-size particles (ferromagnetic particles >40 μm and nonferromagnetic particles >135 μm) can be detected, and the sensitivity is low (the detection cannot be carried out when the number of the particles is small).
Annotation: stray light (such as scattered light and fluorescence) generated by particulate matter is hereinafter referred to as "signal light"; stray light generated by non-particulate matter (for example, excitation light mixed with signal light through the side wall of a cuvette, stray light of engine oil itself) is called "background light", "background interference" or "background noise" (the three are synonymous).
Therefore, exploring a new optical detector with an integrated structure to reduce the interference of background light, reduce the volume of the detector and realize the high-sensitivity detection of the particulate matters in the engine oil is a current urgent problem to be solved.
Disclosure of Invention
The invention provides a low background noise particulate matter detector, which adopts a black sample cell to reduce background light interference, thereby improving detection sensitivity and reducing the volume of the detector.
A low background noise particulate matter detector comprises a light source, a photoelectric detector, an optical lens and a black sample cell.
The inner surface of the black sample cell is black and is used for absorbing excitation light, and the material of the black sample cell is opaque and does not generate fluorescence; an inlet and an outlet of a sample to be detected are formed in the black sample pool; the side wall of the black sample cell is provided with a plurality of mutually perpendicular small-hole channels which are respectively connected with the light source and the photoelectric detector and respectively used as an excitation light channel and a signal light channel; the excitation light emitted by the light source enters the black sample cell through one of the small hole channels, and irradiates the sample to be measured; the particle in the sample to be measured emits signal light under the irradiation of the excitation light, and the signal light enters the photoelectric detector through the other small hole channels; the motion trail of the ferromagnetic particles or the charged particles is deflected by utilizing an external magnetic field or an external electric field, so that the online imaging and identification of the ferromagnetic particles or the charged particles are realized; the inside of the sample cell is provided with a plurality of layers of channels, and particles with different sizes or densities respectively enter the different channels under the action of gravity or inertia force, so that the sizes and the densities of the particles are optically imaged and distinguished; the optical lens is positioned in the small hole channel and is used for focusing excitation light or signal light; and the size, the components and the content of the particulate matters in the sample to be detected are known through the intensity distribution and the spectrum of the test signal light.
When the direction of the signal light channel is consistent with the flowing direction of the particles, the fluid section coincides with the focal plane of the photoelectric detector, so that all the particles can be detected.
The low background noise particulate matter detector also comprises an external magnetic field and a transparent window, wherein the transparent window is positioned at a port of the signal light channel, which is close to one side of the black sample cell; the external magnetic field source is positioned outside the black sample cell; when the direction of the signal light channel is perpendicular to the flowing direction of the particles, the flowing direction of the ferromagnetic particles is deflected by using an external magnetic field, the ferromagnetic particles are adsorbed on a transparent window, and the surface of the transparent window coincides with the focal plane of the photoelectric detector, so that the particles on the surface of the window can be clearly imaged.
The low background noise particulate matter detector also comprises an external electric field and a transparent window, wherein the transparent window is positioned at a port of the signal light channel, which is close to one side of the black sample cell; the external electric field source is positioned outside the black sample cell; when the direction of the signal light channel is perpendicular to the flowing direction of the particles, the flowing direction of the charged particles is deflected by an external electric field, the charged particles are adsorbed onto the transparent window, and the surface of the quartz window coincides with the focal plane of the photoelectric detector, so that the particles on the surface of the window can be clearly imaged.
The photoelectric detector is a photoelectric detector array, an image sensor or a camera.
The excitation light emitted by the light source propagates along the focal plane (i.e., the propagation path of the excitation light is parallel to and coincident with the focal plane) and selectively irradiates the particulate matter in the focal plane region.
The propagation direction of the excitation light emitted by the light source forms a certain included angle with the surface of the transparent window of the signal light channel, and the included angle is smaller than the complementary angle of the total reflection angle, so that particles can be irradiated from the back of the transparent window, and back scattered light is collected, so that the signal intensity is enhanced.
The wavelength of the light source is in the range of 600 nm-1600 nm.
The surface of the optical lens is plated with an antireflection film, and the side surface and the hole wall of the optical lens are sealed by glue with matched refractive indexes, so that the reflection and the divergence of excitation light on the surface and the side surface of the optical lens are reduced.
The black sample cell is preferably made of black anodic aluminum oxide material. The black surface is used for absorbing the excitation light so as to reduce the reflection and scattering of the excitation light on the inner wall of the sample cell, thereby reducing the background noise. In addition, the side wall of the black sample cell is made of opaque materials, so that excitation light cannot enter the side wall for transmission (the problem of light guiding of the side wall of the transparent cuvette is solved), and the background noise can be further reduced. Annotation: the black refers to a color capable of efficiently absorbing excitation light (the black is related to the wavelength of excitation light), and is not limited to the black seen by naked eyes.
The black sample cell is internally provided with a polygonal, spherical or ellipsoidal closed space (the internal size is between 1mm and 1 m). The inside multilayer passageway that is provided with of sample cell, after the sample that awaits measuring gets into the sample cell from the entry, under gravity or inertial force's effect, the flow path of particulate matter in the sample can take place the deflection, and the particulate matter of different sizes or density then gets into different passageways respectively to the realization filters the size and the density of particulate matter. It is also possible to increase the inertial force of the particles by arranging a swirl of the fluid (similar to the principle of a centrifuge) so that the particles are more easily separated. Annotation: the movement track of the particulate matter is determined by external resultant force, and the external resultant force comprises fluid driving force (such as driving force on the particulate matter when engine oil flows), gravity and inertia force of the particulate matter and the like; the particles may deviate from the flow trajectory of the sample (i.e., deviate from the flow trajectory) under the force of gravity or inertia, wherein the larger the size and density of the particles, the more the trajectory deviates.
The small hole channel penetrates through the side wall of the black sample tank; the mutually perpendicular small hole channels can reduce the interference of background light (when the optical paths of the excitation light and the signal light are mutually perpendicular, the cross overlap of the two is minimum, and the mixing of the excitation light into the signal light can be reduced to the greatest extent).
The black sample cell can realize different functions by designing a signal light channel. For example, (1) the direction of the signal light path coincides with the sample flow direction (as in fig. 5, the signal light collection direction is "parallel" to the sample flow direction): at this time, the fluid cross section (the cross section perpendicular to the flow direction) coincides with the focal plane of the detector (the two are parallel to each other), so that all particles flowing through the fluid cross section can be detected by the photodetector (i.e., zero leak detection). For example, (2) the direction of the signal light path is perpendicular to the sample flow direction (as in fig. 6, the signal light collection direction is "perpendicular" to the sample flow direction): for ferromagnetic particles (or charged particles), because the particles can be adsorbed to a transparent window (the surface of the window is parallel to and coincides with the focal plane of the detector) at one end of the signal light channel close to the sample cell by an external magnetic field (or electric field), the particles can be clearly imaged, so that the size of the particles can be distinguished; for nonferromagnetic particles (or uncharged particles), the particles are not adsorbed on the transparent window (i.e. are not in the focal plane) along with the sample to be measured, so that the particles are not imaged on the transparent window; further, with respect to the non-ferromagnetic particles (or uncharged particles), since the flow trajectory of the particles is parallel to the focal plane, the flow trajectory of the particles can be photographed, thereby distinguishing the size and density thereof according to the degree of deviation of the trajectory under the action of gravity or inertial force (fig. 3 and 4).
Therefore, if the above two signal light channels (perpendicular or parallel to the sample flow direction) are provided in one black sample cell, imaging of the total particulate matter and the ferromagnetic particulate matter can be achieved, and the content of the non-ferromagnetic particulate matter (non-ferromagnetic particulate matter=total particulate matter-ferromagnetic particulate matter) can be obtained by statistical analysis. Annotation: the flowing direction is parallel or vertical to the direction of the signal light channel, and the included angle between the flowing direction and the direction is not required to be strictly equal to 0 degree or 90 degrees, so that the deviation of 0-60 degrees is allowed; the magnetic field can be applied by an electromagnet (a switchable magnetic field is switched on and off), and the attracted ferromagnetic particles flow away along with the sample to be tested when the magnetic field is switched off, so that the next test is started.
The black sample cell can realize the identification of ferromagnetic particles and nonferromagnetic particles through an externally applied magnetic field. Wherein the direction of the externally applied magnetic field (namely, the direction of the magnetic induction intensity) is consistent with the direction of the signal light channel. Under the action of a magnetic field, the flowing direction of ferromagnetic particles deflects and is adsorbed to a quartz window at one end of a signal light channel close to a sample cell, and the quartz window is positioned on a focal plane of a photoelectric detector, so that ferromagnetic particles attached to the surface of the quartz window can be clearly shot by a camera, and the identification and detection of the ferromagnetic particles are realized. Annotation: the detection method is similar to that of charged particles (the charged particles are adsorbed on the surface of a quartz window under the action of an external electric field, and the charged particles can be identified by adopting focal plane imaging).
The black sample cell (shown in fig. 3 and 4) is internally provided with a plurality of layers of channels (the width of each channel is larger than the size of the particles), so that the size and the density of the particles can be identified. In the absence of an applied electric field or magnetic field, the particles entering from the inlet above the sample cell will gradually sink in the flow under the action of gravity. The larger the particle size (subject to different gravity forces), the faster the particle will sink. Therefore, after flowing horizontally for a certain distance, the particles with different sizes are dispersed, large particles sink faster and enter the lower channel, and small particles sink slower and enter the upper channel, so that the particles with different sizes enter different channels respectively. In addition, by adjusting the sample flow rate, the degree of dispersion of the particulate matter sink (the slower the flow rate, the higher the degree of dispersion) can also be adjusted. According to the quantity of the particles in different channels shot by the camera, the quantity of the particles with different sizes can be counted. The more the number of channel layers is arranged in the sample cell, the higher the detection resolution of the particle size is.
The photodetector, which may also be a photodetector array (e.g., an image sensor), is capable of imaging the particulate matter (each particulate matter being distinguishable). The detector array has the following advantages over using a single detector (which cannot be spatially imaged): (1) By imaging, the background light can be spatially separated (i.e., the background light at different spatial locations is imaged differently and thus received by the detectors at different locations), so that the background light of the entire space is spread over all the detectors, so that the intensity of the background light received by a single detector is substantially reduced (i.e., the background interference is reduced), and the background interference is reduced as the detector density is increased; (2) The single feature of the background light (no contour details) can be removed by image processing; (3) For the particulate matter, at a specific moment, the position of the particulate matter is fixed (the imaging position of the particulate matter is also fixed), so that the signal light of the particulate matter is only received by the photoelectric detector at the specific position (i.e. the signal is not shared by other detectors), and the signal light intensity is kept unchanged; (4) By increasing the density of the detector (e.g., increasing the pixel density), the signal-to-noise ratio (reducing background light interference) can be increased, as well as the sharpness of the image; (5) Only the signal light propagating in a straight line can be collected and imaged by the lens, and the distorted propagating light (such as the excitation light and the signal light reflected by the side wall) generates a blurred virtual image, which can be removed by image recognition, thereby further improving the signal-to-noise ratio. Therefore, by the optical imaging method, the signal-to-noise ratio can be improved (the background interference is reduced, the signal intensity is kept), the background interference can be further distinguished and eliminated by combining the image recognition technology (for example, a blurred image or an abnormal shape image can be judged to be a virtual image), and the detection sensitivity is improved.
Annotation: the defects of the existing turbidimeter are as follows: (1) Only one photodetector can test the total signal light intensity (spatial imaging cannot be performed), so that background noise cannot be reduced (all background light is received by a single photodetector), and the shape, size and quantity of the particles cannot be distinguished through imaging, so that the method cannot be used for detecting the particles in engine oil (because the background noise of engine oil is too large); (2) Because the particles are mobile and their positions are not fixed (difficult to be in the focal plane), they cannot be imaged clearly and imaging detection methods are difficult to use. Compared with the method, the method and the device have the advantages that the signal light channels (parallel or perpendicular to the flowing direction) are arranged, so that the particles flow through the same focal plane (or are attached to the same focal plane), and the imaging problem of the flowing particles is solved; further, by providing a multi-layered channel structure in the sample cell (fig. 3 and 4), the discrimination of the size and density of the particulate matter is achieved. Therefore, the invention not only can observe the size and the quantity of the particles, but also can distinguish the components (ferromagnetic, nonferromagnetic, charged and uncharged); in addition, the invention realizes high-sensitivity detection of the particulate matters in the engine oil by reducing background noise (combining a black sample cell, space imaging and image recognition); in addition, because the composition of the engine oil is complex (e.g., the refractive index is not uniform), the scattering effect of the particulate matter (secondary scattering of scattered light of the particulate matter) is enhanced, and thus the imaging of the particulate matter (halation effect of the edges of the particulate matter) is enlarged, so that small particulate matter (particulate matter smaller than 15 μm can be distinguished) is easier to observe.
The excitation light enters the black sample cell through the excitation light channel and then is transmitted along the focal plane, so that particles in the focal plane area (figure 1) are selectively irradiated, and the area (non-imaging area) outside the focal plane is not irradiated, thereby avoiding generating background light in the non-imaging area and reducing background interference.
When the focal plane is positioned on the surface of the transparent window of the signal light channel (fig. 2), the incident direction of the excitation light forms a certain included angle with the surface of the window, and as long as the included angle is smaller than the complementary angle of the total reflection angle (the total reflection angle is derived from the interface between engine oil and air), the excitation light cannot pass through the transparent window to enter the signal light channel, so that the background interference is reduced. In addition, after the excitation light is totally reflected, particles can be irradiated from the back surface of the transparent window, so that back scattered light can be collected, and the signal intensity is enhanced.
The light source is preferably a light source with a wavelength in the range of 600nm to 1600 nm. In the wave band, the absorption loss of engine oil is small, and the fluorescence intensity generated by the engine oil can be reduced, so that the background noise is reduced.
And a transparent window is arranged at one end (close to the inner wall of the sample tank) of the small hole channel close to the sample to be detected. The transparent window is used for sealing the small hole channel, so that a sample to be tested cannot flow into the small hole channel; the transparent window is positioned on the focal plane of the detector and can be used for attaching ferromagnetic particles (or charged particles) to realize clear imaging of particles; the transparent window is preferably made of quartz glass (or quartz lens).
The small hole channel is internally embedded with an optical lens, and the side surface of the lens is sealed with the side wall of the channel. The inner wall of the small hole channel is also black (namely, the whole surface of the black sample cell is black).
The optical lens is arranged in the excitation light channel, and is used for converging an excitation light beam (namely, a light source is arranged at the focus of the lens) to change the excitation light beam into a parallel light beam, wherein the excitation light beam is perpendicular to the collecting direction of the signal light, so that the interference on the signal light is reduced.
The surface of the first optical lens is plated with an antireflection film (or called an antireflection film) for reducing the reflectivity of the lens surface, so that the excitation light divergence caused by surface reflection is reduced. Annotation: for excitation light, each time anti-reflectionThe light will change its propagation direction, so that multiple reflections will cause the propagation direction of the excitation light to become cluttered (light diverged) and thus mixed into the signal light (received by the photodetector together with the signal light); since the excitation light intensity (in milliwatt) is 10 of the signal light intensity (in picowatt) 9 The mixing of even a small amount of excitation light can cause the signal light to be submerged.
The side surface of the first optical lens is bonded and sealed with glue with matched refractive indexes (the refractive index of the glue is the same as or close to that of the lens), so that the reflectivity of the side surface of the lens is close to zero, and light can pass through the side surface of the lens and enter the hole wall; since the hole wall is black, light incident to the hole wall can be absorbed. Therefore, the light reflection of both the surface and the side of the first optical lens can be greatly reduced, thereby reducing the excitation light interference (i.e., background interference).
The second optical lens is positioned in the signal light channel and is used for converging the signal light so as to improve the collection efficiency of the signal light and enable more signal light energy to be received by the photoelectric detector.
The optical axes of the first optical lens and the second optical lens are perpendicular to each other.
The optical lens, preferably a plano-convex lens or a prism, has a diameter of 0.1mm to 1m, preferably 5mm to 20mm. Annotation: the flat side of the plano-convex lens can be used as a transparent window at the front end of the pinhole channel.
The invention has the beneficial effects that: (1) Compared with the existing sample cell (transparent cuvette), the side wall of the black sample cell is black and light-tight, so that excitation light can be prevented from entering the side wall to spread, and the black surface can absorb the excitation light, so that the back and forth reflection and divergence of the excitation light in the sample cell can be eliminated, and the interference of the excitation light on signal light is reduced; (2) By arranging the signal light channel, all particles flow through the same focal plane (or are adsorbed on the same focal plane), the imaging problem of flowing particles is solved, the size and the number of the particles can be observed, and the components (ferromagnetic, nonferromagnetic, charged and uncharged) of the particles can be distinguished; (3) The optical imaging method based on the photoelectric detector array can improve the signal-to-noise ratio (average background noise and uneven signal) and can further judge and eliminate the background interference by combining the image recognition technology, thereby improving the detection sensitivity; (4) The first optical lens can eliminate light reflection on the surface and the side surface, thereby further reducing background interference; (5) Compared with the prior fluorescent instrument and turbidity instrument, the sample cell is only used for placing the sample to be measured, and excitation light interference needs to be eliminated outside the sample cell, so that the light path is complex and the instrument is heavy; moreover, since the flowing particulate matter is difficult to focus, has no imaging function, and cannot reduce noise by image recognition, it is difficult to use for detection of a sample having a complex composition (such as engine oil).
Drawings
FIG. 1 is a schematic diagram (top view) of a low background noise particulate matter detector;
FIG. 2 is a schematic diagram (side view) of a low background noise particulate matter detector;
FIG. 3 is a schematic diagram of a second embodiment of a low background noise particulate matter detector (front view);
FIG. 4 is a schematic diagram (side view) of a second embodiment of a low background noise particulate matter detector;
FIG. 5 is a schematic diagram (top view) of a third embodiment of a low background noise particulate matter detector;
FIG. 6 is a schematic diagram (top view) of a fourth embodiment of a low background noise particulate matter detector;
FIG. 7 is a photograph of a low background noise particulate matter detector;
fig. 8 shows the actual imaging effects of particulate matter in engine oil, (a) the first actual imaging effect, (b) the second actual imaging effect, and (c) the third actual imaging effect.
In the figure: 1-a black sample cell; 2-a sample inlet to be measured; 3-a sample outlet to be tested; 4-particulate matter (4.1-large particles, 4.2-medium particles, 4.3-small particles); 5-a light source; 6-excitation light; 7-a first optical lens; 8-signal light; 9-transparent window (e.g., quartz plate); 10-a second optical lens; 11-photodetectors (image sensors); 12-focal plane; 13-ferromagnetic particles (or charged particles); 14-magnets (or electrodes); 15-black anodized aluminum separator.
Detailed Description
The present patent will be described in detail below with reference to the embodiments and the accompanying drawings, and it should be noted that the described embodiments are only intended to facilitate understanding of the present patent, and do not limit it in any way.
Example 1
The invention provides a first structure of a low background noise particulate matter detector, as shown in fig. 1 and 2 (a physical photograph is shown in fig. 7), which comprises a light source 5 (an LED with the wavelength of 638 nm), a first optical lens 7, a second optical lens 10, a black sample cell 1, a photoelectric detector (a photoelectric detector array or an image sensor) 11 and engine oil inlets and outlets 2 and 3. The sample cell 1 is rectangular, and two adjacent side walls (top and front side) are respectively provided with an excitation light channel and a signal light channel which are respectively communicated with the light source 5 and the photoelectric detector 11; excitation light 6 emitted by the excitation light source 5 passes through an excitation light channel, then enters the sample cell 1 through the first optical lens 7, and irradiates engine oil particles 4 in the sample cell to generate scattered light 8; the scattered light 8 enters the signal light path through the second optical lens 10 and is then received by the photodetector 11, thereby imaging the particulate matter 4 to know the position, size and shape of the particulate matter 4.
The inner surface of the sample cell 1 is treated with anodized aluminum to be black (absorbance is greater than 94%), so that the excitation light 6 can be absorbed, so as to avoid multiple back and forth reflections of the excitation light 6 inside the sample cell 1 (i.e., to avoid the excitation light 6 from entering the photodetector 11). Annotation: black anodized aluminum can also be replaced by a carbon nanotube coating to absorb excitation light.
The surface of the first optical lens 7 is plated with an optical antireflection film, and the side surface of the lens is adhered and fixed with the inner wall of the excitation light channel by using refractive index matching glue.
A photograph of the detector is shown in fig. 7. The imaging effect of the particles is shown in fig. 8, wherein the bright spots are particles, the line segments are particle tracks, the upper part is low-density particles, the lower part is high-density particles, and the black background indicates that the background light is effectively inhibited.
Example 2
The second structure (fig. 3 and 4) of the low background noise particulate matter detector provided by the invention is characterized in that a plurality of partition boards 15 (black anodic aluminum oxide partition boards) are arranged in a sample cell 1, so that a multi-layer channel is formed; the top and the front side of the sample cell) are respectively provided with an excitation light channel and a signal light channel which are respectively communicated with the light source 5 and the photoelectric detector 11.
The sample cell inlet 2 is arranged above the sample cell, and the sample flows through the multi-layer channel and then flows out from the outlet 3 below the other side (figure 3). The second optical lens 10 is placed at the front end of the signal light path, and the image sensor 11 is placed behind the lens 10 (fig. 4). The focal plane 12 of the image sensor is perpendicular to the multilayer channel (i.e. the focal plane is parallel to the fluid cross-section of the channel) so that particles flowing through the multilayer channel can be clearly imaged by the image sensor 11.
The particles of different sizes will flow into different multilayer channels, respectively, due to the force of gravity. For example: the particles with the largest diameter (heavier particles) will drop first and flow into the channel near the inlet 2 (i.e. the leftmost channel in the multilayer channel); the smallest diameter particles will fall into the channel away from the inlet 2 (i.e. the rightmost channel in the multilayer channel). Thus, different sized particles will enter the channel differently (as the size decreases, the channel moves from left to right), thereby achieving particle size discrimination. Excitation light 6 is incident into the sample cell through a first optical lens 7, the beam diameter being large enough to ensure that all particles in the channel are illuminated, and the scattered light 8 produced is imaged by a photodetector 11. Annotation: the more the number of channel layers is arranged in the sample cell, the higher the detection resolution of the particle size is; the different density particles may also be distinguished in the same way, e.g. the particles with the greatest density fall first, thus entering the leftmost channel.
Example 3
The third structure of the low background noise particulate matter detector provided by the invention is shown in fig. 5. The sample cell 1 is L-shaped, and two adjacent side walls (front side and right side) are respectively provided with an excitation light channel and a signal light channel which are respectively communicated with the light source 5 and the photoelectric detector 11; excitation light 6 emitted by the excitation light source 5 passes through an excitation light channel, enters the sample cell 1 from the first optical lens 7, irradiates particles 4 in engine oil in the sample cell, and generates scattered light 8; the scattered light 8 enters the signal light path from the second optical lens 10 and is then received by the photodetector 11, and the particles 4 can be imaged by testing the scattered light 8 to know the position, size and shape of the particles 4. It should be noted that in this structure the fluid cross-section (the cross-section perpendicular to the flow direction) coincides with the focal plane of the detector (both parallel to each other), so that all particles flowing through the fluid cross-section can be detected by the photodetector (i.e. zero leak detection).
In order to integrate with the inner wall of the sample cell 1, the lenses 7 and 10 are plano-convex lenses, and the flat surface of each lens is flush with the inner wall of the sample cell, so that dead zones can be avoided when the sample to be tested flows.
The collection direction 8 of the signal light is consistent with the sample flow direction 2 (all left to right); the imaging focal plane 12 is determined by the lens 10, and only the particles located in the focal plane 12 can be clearly imaged on the photodetector 11; the focal plane 12 is perpendicular to the collection direction 8 of the signal light and also perpendicular to the sample flow direction 2. At this time, all the particles 4 flow through the focal plane 12, so that all the particles can be detected, i.e., zero leak detection is achieved.
The excitation beam 7 propagates along the focal plane 12 and irradiates only the area near the focal plane 12 (i.e., irradiates only the imaging area), so that no background light is generated in the area outside the focal plane, thereby reducing background interference.
Example 4
In the fourth structure (fig. 6) of the present invention, an optical glass sheet (quartz sheet) is placed as a transparent window 9 at the front end of the signal light channel of the L-shaped sample cell, and an electromagnet (or electrode) 14 is placed behind the photodetector 11. The electromagnet (or electrode) 14 can attract the ferromagnetic (or charged) particles 13 to the surface of the window 9 (the magnetic field direction is from left to right), which coincides with the imaging focal plane 12, so that the ferromagnetic (or charged) particles 13 attracted to the surface of the window 9 can be clearly imaged by the image sensor 11. For non-ferromagnetic (or charged) particles, they will not be attracted to the surface of the window 9 and will not be imaged. Thus, this structure (FIG. 6) can be used to identify ferromagnetic (or charged) particulate matter. At this time, the excitation light 6 is obliquely incident to the surface of the quartz plate 9 through one prism 7, then is incident to the lower surface of the quartz plate (i.e. the interface between the quartz plate 9 and the air in the signal light channel), and is totally reflected on the lower surface (the total reflection angle is determined by the refractive index of quartz and air), so that the excitation light 6 cannot enter the signal light channel (cannot be received by the photodetector), thereby reducing the background interference; and, the totally reflected light may back-illuminate ferromagnetic (or charged) particles 13 adsorbed on the surface of the quartz plate 9, thereby generating back-scattered light 8 and imaging by the photodetector 11. Annotation: the excitation light 6 may directly irradiate ferromagnetic (or charged) particles 13 on the surface of the window 9 (without total reflection by the lower surface of the quartz plate 9), thereby producing forward scattered light 8; since the sample cell 1 has an L-shaped structure, the sample flow direction on the surface of the window 9 is parallel to the surface of the window (from bottom to top), and the collection direction of the signal light is perpendicular to the sample flow direction. Annotation: under the irradiation of the excitation light 6, if the particulate matter 4 can emit fluorescence 8, the composition of the particulate matter 4 (different substances have different characteristic fluorescence spectra) can be known by analyzing the spectrum of the fluorescence 8. Fluorescence imaging can be achieved by combining spectral analysis with imaging. Similarly, the electromagnet 14 is replaced by an electrode, so that the charged particles 13 in the engine oil can be adsorbed to the surface of the window 9, and the charged particles can be identified and detected.
Finally, it should be noted that the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the scope of the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention.

Claims (10)

1. The low background noise particulate matter detector is characterized by comprising a light source, a photoelectric detector, an optical lens and a black sample cell;
the inner surface of the black sample cell is black and is used for absorbing excitation light, and the material of the black sample cell is opaque and does not generate fluorescence; an inlet and an outlet of a sample to be detected are formed in the black sample pool; the side wall of the black sample cell is provided with a plurality of mutually perpendicular small-hole channels which are respectively connected with the light source and the photoelectric detector and respectively used as an excitation light channel and a signal light channel; the excitation light emitted by the light source enters the black sample cell through one of the small hole channels, and irradiates the sample to be measured; the particle in the sample to be measured emits signal light under the irradiation of the excitation light, and the signal light enters the photoelectric detector through the other small hole channels; the particle material deflects the motion track of the ferromagnetic particle or the charged particle by using an external magnetic field or an external electric field, so as to realize online imaging and identification of the ferromagnetic particle or the charged particle; the optical lens is positioned in the small hole channel and is used for focusing excitation light or signal light; and the size, the components and the content of the particulate matters in the sample to be detected are known through the intensity distribution and the spectrum of the test signal light.
2. The low background noise particulate matter detector of claim 1, wherein the flow cross section coincides with the focal plane of the photodetector when the direction of the signal light path coincides with the flow direction of the particulate matter, such that all particulate matter can be detected.
3. The low background noise particulate matter detector of claim 1, further comprising an externally applied magnetic field and a transparent window, the transparent window being positioned at a port of the signal light channel on a side near the black sample cell; the external magnetic field source is positioned outside the black sample cell; when the direction of the signal light channel is perpendicular to the flowing direction of the particles, the flowing direction of the ferromagnetic particles is deflected by an external magnetic field, the ferromagnetic particles are adsorbed on a transparent window, and the surface of the transparent window coincides with the focal plane of the photoelectric detector.
4. The low background noise particulate matter detector of claim 1, further comprising an external electric field and a transparent window, the transparent window being positioned at a port of the signal light channel on a side near the black sample cell; the external electric field source is positioned outside the black sample cell; when the direction of the signal light channel is perpendicular to the flowing direction of the particles, the flowing direction of the charged particles is deflected by an external electric field, the charged particles are adsorbed onto the transparent window, and the surface of the quartz window coincides with the focal plane of the photoelectric detector.
5. The low background noise particulate matter detector of claim 1, wherein the photodetector is a photodetector array, an image sensor, or a camera.
6. The low background noise particulate matter detector of claim 1, wherein the excitation light emitted by the light source propagates along the focal plane and selectively irradiates particulate matter in the focal plane region.
7. The low background noise particulate matter detector of claim 1, wherein the excitation light emitted by the light source has a propagation direction that forms an angle with the surface of the transparent window of the signal light channel, and the angle is smaller than the complementary angle of the total reflection angle, so as to irradiate the particles from the back surface of the transparent window, and collect the back scattered light to enhance the signal intensity.
8. The low background noise particulate matter detector of claim 1, wherein the light source has a wavelength within a range of 600nm to 1600 nm.
9. The low background noise particulate matter detector of claim 1, wherein the surface of the optical lens is coated with an anti-reflection film, and the side surface and the hole wall are sealed by glue with matched refractive indexes, so as to reduce reflection and divergence of excitation light on the surface and the side surface.
10. The low background noise particulate matter detector of claim 1, wherein a plurality of layers of channels are arranged in the black sample cell, and particulate matters with different sizes or densities respectively enter the different channels under the action of gravity or inertia, so that the size and the density of the particulate matters are optically imaged and distinguished.
CN202311821060.5A 2023-09-26 2023-12-27 Low background noise particulate matter detector Pending CN117723472A (en)

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