Optically based particulate matter sensing

Abstract

A device for sensing particulate matter in a fluid includes a fluid flow conduit fluidically connected to an interaction chamber, a light source positioned to illuminate the interaction chamber, and a light detector assembly positioned to receive light scattered by particulate matter present in the interaction chamber. The light detector assembly includes a light detector and an optical element configured to provide light to the light detector based on an angle of incidence of the scattered light.

Description

Background Technology

[0001] Various types of particulate matter sensors exist, including optical scattering-based sensors, filter-based light absorption sensors, diffusion-charge-based sensors, weight-filtering analysis-based sensors, beta-attenuation sensors, conical element oscillating microbalance sensors, and photoacoustic sensors. Summary of the Invention

[0002] This document describes a method for optical-based particulate sensing, for example, for determining the concentration of particulate matter in a fluid or the size distribution of particulate matter (such as micrometer-sized particles). The systems described herein utilize the principle of light scattering, such as systems incorporating optical particle counters (OPCs).

[0003] In one aspect, an apparatus for sensing particulate matter in a fluid includes a fluid flow conduit fluidly connected to an interaction chamber; a light source positioned to illuminate the interaction chamber; and a photodetector assembly positioned to receive light scattered by particulate matter present in the interaction chamber. The photodetector assembly includes a photodetector; and an optical element configured to provide light to the photodetector based on the incident angle of the scattered light.

[0004] An embodiment may include any combination of one or more of the following features.

[0005] The optical elements are directly mounted on the photodetector.

[0006] Optical elements are configured to allow light to pass through to a photodetector. The optical elements include optical fibers, the ends of which are aligned with the photodetector. The optical fibers include multimode fibers with cladding. The optical elements include interference filters. The optical elements include bandpass or shortpass filters. The optical elements include bandpass filters configured to allow light transmission within a transmission band, wherein for normal incidence, the wavelength of the scattered light is within approximately 10% of the lower limit of the transmission band. The bandpass filters are configured to allow light transmission within a transmission band, wherein for incident angles above normal incidence, the transmission band is not centered on the wavelength of the scattered light.

[0007] The optical elements are configured to allow light to be reflected to the photodetector.

[0008] One or more of the photodetector and optical elements are segmented. The photodetector is segmented into multiple sub-sensors, each of which measures a corresponding angular portion of the scattered light.

[0009] In one aspect, a mobile communication device includes the means of the preceding aspect, which includes any combination of one or more of the foregoing features.

[0010] In an aspect that can be combined with the preceding aspects, a method for sensing particulate matter in a fluid includes: illuminating an interaction chamber with an illumination beam, the fluid containing particulate matter being present in the interaction chamber; and detecting light scattered by particulate matter present in the interaction chamber via a photodetector assembly including a photodetector, including: filtering the scattered light with an optical element, the filtering allowing the light to reach the photodetector based on the incident angle of the scattered light; and detecting the light via the photodetector.

[0011] An embodiment may include any combination of one or more of the following features.

[0012] Filtering scattered light includes allowing light to transmit to a photodetector. Filtering scattered light includes receiving the scattered light into an optical fiber, the end of which is aligned with the photodetector. Filtering scattered light includes filtering the scattered light through an interference filter. Filtering scattered light includes allowing light transmission within a transmission band, wherein for incident angles above normal incidence, the transmission band is not centered on the wavelength of the scattered light. Allowing light transmission includes allowing light to propagate through an interference filter.

[0013] Filtering scattered light involves reflecting the light back to a photodetector.

[0014] This method involves determining the properties of particles in a fluid based on light scattered by the particles. Determining the properties of the particles includes determining the concentration of the particles in the fluid. Determining the properties of the particles also includes determining the size distribution of the particles.

[0015] In one aspect that can be combined with one or more of the preceding aspects, an apparatus for sensing particulate matter in a fluid includes a fluid flow conduit fluidly connected to an interaction chamber; an illumination assembly positioned to illuminate the interaction chamber using a shaped illumination beam having an intensity that increases along the diameter of the illumination beam from a first side of the illumination beam to a second side of the illumination beam opposite to the first side; and a photodetector disposed on the first side of the illumination beam and positioned to receive light scattered by particulate matter present in the interaction chamber.

[0016] An embodiment may include any combination of one or more of the following features.

[0017] The second side of the illumination beam corresponds to the particle furthest from the light detector.

[0018] The device includes: a light source configured to output an initial illumination beam; and an optical element positioned between the light source and an interaction chamber and configured to shape the initial illumination beam into a shaped illumination beam.

[0019] The device includes multiple light sources arranged to form a shaped illumination beam.

[0020] In one aspect, a mobile communication device includes the means of the preceding aspect, which includes any combination of one or more of the foregoing features.

[0021] In an aspect that can be combined with one or more of the preceding aspects, a method for sensing particulate matter in a fluid includes: illuminating an interaction chamber with a shaped illumination beam having an intensity that increases along the diameter of the illumination beam from a first side of the illumination beam to a second side of the illumination beam opposite to the first side, wherein the fluid containing particulate matter is present in the interaction chamber; and detecting light scattered by particulate matter present in the interaction chamber by a photodetector disposed on the first side of the illumination beam.

[0022] An embodiment may include any combination of one or more of the following features.

[0023] Illuminating the interaction chamber using a shaped illumination beam includes outputting an initial illumination beam from a light source; and shaping the initial illumination beam by means of optical elements positioned between the light source and the interaction chamber.

[0024] Illuminating an interaction chamber using a shaped illumination beam involves operating multiple light sources, with the light emitted by each of the multiple light sources together forming a shaped illumination beam.

[0025] This method involves determining the properties of particles in a fluid based on light scattered by the particles. Determining the properties of the particles includes determining the concentration of the particles in the fluid. Determining the properties of the particles also includes determining the size distribution of the particles.

[0026] The methods described herein can offer one or more of the following advantages: Optical particulate sensors can operate with high sensitivity and high energy efficiency, and can accurately detect and measure particulate matter over a wide range of sizes and concentrations. Optical particulate sensors are robust to changes in the position of particles within the sensor and can produce particle size measurements independent of particle position. Optical particulate sensors are compact and can be manufactured using mass production techniques such as semiconductor processing, resulting in low cost. The sensors can be integrated into various types of devices, such as handheld devices, automotive equipment, or industrial equipment, and are therefore suitable for a wide range of applications. Attached Figure Description

[0027] Figure 1A and Figure 1B This is a diagram of an optical particulate sensor.

[0028] Figure 2 This is a diagram of light scattering.

[0029] Figure 3This is a graph showing the relationship between scattered light intensity and particle size.

[0030] Figure 4 This is a diagram of an optical particulate sensor.

[0031] Figures 5A-5C It is a diagram of the light source.

[0032] Figure 6 It's a flowchart.

[0033] Figure 7 This is a diagram of the photodetector assembly.

[0034] Figure 8A and 8B It is a graph of light transmission.

[0035] Figure 9A and 9B This is a diagram of the photodetector assembly.

[0036] Figures 10A-10E It is a graph of light transmission.

[0037] Figure 10F It's a diagram of solid angles.

[0038] Figure 11 It's a flowchart.

[0039] Figure 12 It is a diagram of a mobile computing device. Detailed Implementation

[0040] This document describes a method for optical-based particulate sensing, for example, for determining the concentration of particulate matter in a fluid or the size distribution of particulate matter (such as micrometer-sized particles). The systems described herein utilize the principle of light scattering, such as systems incorporating optical particle counters (OPCs).

[0041] The optical-based particulate sensor described herein incorporates features that can reduce the dependence of the measured intensity of scattered light on the location of the particles from which the light is scattered, thereby improving the accuracy of the sensor. In some examples, the optical-based particulate sensor described herein can measure only certain angular portions of the scattered intensity distribution, for example, which helps to suppress stray light based on the incident angle, wavelength, or both.

[0042] In some examples, the sensor may be incorporated into a specific arrangement of optical elements or system components to shape the illumination beam to mitigate the position-dependent intensity of the scattered light. In some examples, the sensor may implement angular filtering to selectively filter the scattered light by the angle of incidence before detection. For example, angular filtering can be achieved by utilizing the angular selectivity of an interferometric filter or by total internal reflection.

[0043] Figure 1A and Figure 1B Top and side views of an optical particulate sensor 100 are shown, which is configured to detect particulate matter in a fluid, such as an aerosol. The particulate sensor 100 detects the intensity of light scattered by individual particles. The signal based on the detected intensity can be used to characterize the particulate matter in the fluid, for example, to determine the concentration of particulate matter in the fluid, the size distribution of particulate matter in the fluid, or both. In some examples, the particulate sensor 100 may be part of a particulate sensor system, such as an integrated microfluidic system (e.g., a system based on complementary metal-oxide-semiconductor (CMOS) technology).

[0044] The particulate sensor 100 includes a light source 102 (e.g., a vertical-cavity surface-emitting laser (VCSEL), a light-emitting diode (LED), a laser diode, or another type of light source) operable to emit a light beam 106 into a particle-light interaction chamber 110 (also simply referred to as interaction chamber 110). Fluid flows through a fluid flow conduit 112, which may be substantially perpendicular to the direction of the light beam 106 (as shown), or may be oriented in another direction relative to the light beam 106. Figure 1A and 1B In one example, the path of beam 106 is in the y-direction, and the fluid flow conduit 112 is in the x-direction. In some examples, particulate sensor 100 may include one or more optical elements, such as reflective surfaces, apertures, or other optical elements, to guide light from light source 102 into interaction chamber 110.

[0045] As fluid flows through conduit 112, beam 106 interacts with particles in the fluid within particle-light interaction chamber 110. This interaction causes light scattering, resulting in an intensity distribution 115 that differs from one or more characteristics of the particles, such as particle shape, material composition, and particle size. A portion of the scattered light is directed toward a photodetector 114 (e.g., a photodiode) operable to detect the scattered light. Light that does not interact with the particles continues its journey into light-trapping chamber 118 to prevent reflection back toward detector 114.

[0046] Detector 114 can be implemented as, for example, an optical photoelectric sensor operable to measure the signal of a single particle. In this case, the pulse height (e.g., the intensity of the optical signal corresponding to the light scattered by a single particle) is proportional to the particle size, and the pulse count rate corresponds to the number of particles detected. If the quantity of the volume being analyzed is known (e.g., airflow rate, measurement time), the concentration of particulate matter in the fluid can be derived, for example, from the number of particles detected. Detector 114 can be integrated into, for example, a semiconductor chip, which may also include electronics for reading, amplifying, and processing the signal. In some cases, the processing circuitry may reside on a separate chip. In some examples, the photodetector can be divided or segmented into multiple sub-sensors, each measuring a different portion of the scattered intensity distribution, thereby helping to reduce ambiguity in particle sizing.

[0047] Also refer to Figure 2 The position of the particle relative to the photodetector 114, as well as the size and shape of the photodetector, define the angular portion of the scattering distribution received by the photodetector 114, hereinafter referred to as the "solid angle". For example, for scattering by particle P1 located at the far side 200 of the interaction chamber 110 relative to the photodetector 114, scattered light within the solid angle α is received by the photodetector 114. However, for scattering by particle P2 located at the near side 202 of the interaction chamber 110 relative to the photodetector 114, scattered light within the larger solid angle β is received by the photodetector 114. This difference in solid angle for particles P1 and P2 of the same size leads to a difference in the signal intensity detected by the photodetector 114, which in turn may introduce the possibility of error in particle size determination, for example, leading to underestimation or overestimation of the particle size.

[0048] Figure 3 This is an example graph showing the relationship between the intensity of scattered light from a particle and its diameter at three different locations in the interaction chamber: at the center of the interaction chamber (curve 300), 250 μm further away from the detector (curve 302), and 250 μm closer to the detector. For a particle with a diameter of 1.5 μm, changing the particle's position results in a significant change in intensity (as can be seen from the cross-sectional point along the vertical line at 1.5 μm). Projecting these intensities back to the reference curve at the center position reveals the particle size determination error (shown in gray here), also known as the particle size determination estimation uncertainty, with a lower bound at dmin and an upper bound at dmax. In this particular example, the particle size determination error extends over most of the measurement range of interest, thus limiting the performance of this sensor to particle counting only.

[0049] In some examples, the intensity distribution of the illumination beam can be shaped to at least partially compensate for the location-dependent signal intensity. For example, the illumination beam can be shaped to have an asymmetric intensity distribution relative to the illumination chamber, such that the beam intensity is greater at the far side 200 of the interaction chamber than at the near side 202 (e.g., in contrast to a shape that is substantially symmetrical relative to the interaction chamber, such as having a Gaussian intensity distribution centered on the center of the interaction chamber). The asymmetric intensity distribution can at least partially offset the intensity difference of the scattered light as a function of particle position, helping to mitigate potential particle size determination errors.

[0050] Reference Figure 4 The optical-based particulate sensor 400 includes an illumination assembly 430 configured to illuminate an interaction chamber 110 using a shaped illumination beam 432. The shaped illumination beam refers to an illumination beam having an intensity distribution asymmetrical relative to the interaction chamber. For example, the shaped illumination beam 432 may have an increasing intensity along its diameter from a first side 442 closest to the photodetector 114 to a second side 440 furthest from the photodetector 114, as shown in the cross-sectional intensity distribution 450 of the shaped illumination beam 432. This shaping results in a weighting of the scattered signal from particles in the interaction chamber 110, which is inversely proportional to the solid angle of the particles, for example, causing the scattered signal from particles furthest from the photodetector 114 to increase relative to the scattered signal from particles closer to the photodetector 114. This weighting of the scattered signal can then help reduce signal variation and improve accuracy in particle size determination. For example, in some examples, the signal variation caused by the position of particles in the particulate sensor 400 can be reduced to about 10% of the amplitude of the sensed signal, while the uncompensated error can reach, for example, 80% and more of the signal amplitude.

[0051] exist Figure 4 In one example, the illumination assembly 430 includes a light source 102 that emits a beam 434, and an optical element 436 positioned between the light source 102 and the interaction chamber 110 and configured to shape the beam 434 into a shaped illumination beam 432. For example, the optical element 436 may include one or more refractive elements (such as lenses), or one or more diffractive elements, or a combination of refractive and diffractive elements. In some examples, the illumination assembly 430 may include elements arranged or configured to generate the shaped illumination beam 432 (relative to...). Figure 6 (Discussion) Multiple transmitters.

[0052] In some examples, the shaped illumination beam 432 can be formed by one-dimensional shaping of the beam 434, which can be, for example, a collimated beam. In some examples, the shaped illumination beam 432 can be formed by volumetric shaping of the beam 434. For example, volumetric shaping can be used to account for signal variations caused by changes in particle position along the optical path 106 or along the direction of fluid flow through the interaction chamber 110.

[0053] As described above, in some examples, the lighting components may include multiple light sources arranged or configured to generate the shaped lighting beam 432. Figures 5A-5C Examples of multiple light sources are shown in the image.

[0054] refer to Figure 5A In some examples, the lighting assembly may include an array of multiple light sources 602 (such as multiple VCSELs). The power of each light source 602 (depicted by gray shading in the figure) can be controlled to achieve a target intensity distribution as the output from the multiple light sources 602. Reference Figure 5B In some examples, the lighting assembly may include light sources 612 arranged in an irregular pattern to achieve a target intensity distribution. For example, the spacing between adjacent light sources 612 may vary in the lighting assembly. (See reference) Figure 5C In some examples, the lighting components may include multiple light sources 612 of different sizes arranged to achieve a target intensity distribution. Other methods may also be used, such as... Figures 5A-5C A combination of one or more methods.

[0055] Reference Figure 6 In an example of an optical-based particulate sensing method, a fluid containing particulate matter flows through the interaction chamber (700) of the particulate sensor.

[0056] The interaction chamber is illuminated using a shaped illumination beam (702) having an intensity distribution asymmetrical relative to the interaction chamber. For example, the shaped illumination beam may have an increasing intensity along its diameter from a first side of the illumination beam to a second side opposite the first side. In some examples, the shaped illumination beam can be generated by shaping the beam from the light source using one or more optical elements positioned between the light source and the interaction chamber. In some examples, the shaped illumination beam can be generated by operating multiple light sources arranged or configured to generate the shaped illumination beam.

[0057] Light scattered by particles present in the interaction chamber is detected by a photodetector (704). The shaped illumination beam can at least partially cancel out variations in the scattered signal, which may be caused by differences in the solid angles between particles located at different positions around the interaction chamber, thus helping to improve accuracy.

[0058] The signal of light detected by the photodetector is used to characterize particulate matter in the fluid (706), such as determining the concentration or size distribution of particulate matter in the fluid.

[0059] In some examples, optical-based particle sensors can implement angle filtering to at least partially compensate for the dependence of the intensity of the scattered light signal on the position of the particles in the interaction chamber. For example, an optical-based particle sensor may include optical elements, such as interferometric filters or optical fibers, that allow only scattered light satisfying a threshold solid angle (e.g., light within the threshold solid angle) to reach the photodetector. This angle filtering can at least partially harmonize the solid angle at which light scattered by particles at various locations in the interaction chamber is received by the photodetector, thereby helping to mitigate potential particle size determination errors.

[0060] Reference Figure 7 An optically based particulate sensor that achieves angle filtering may include a photodetector assembly 800 positioned to receive light scattered by particles in the interaction chamber 110 of the particulate sensor. The photodetector assembly 800 includes a photodetector 814 (e.g., a photodiode) and optical elements including a thin-film interference filter 816. For example, the interference filter 816 may be disposed on the surface of the photodetector 814, for example, using thin-film fabrication techniques.

[0061] In some examples, the interference filter 816 may be a short-pass or band-pass filter that transmits only light within a desired angular range (e.g., light that satisfies a threshold solid angle). Light with an incident angle outside the threshold solid angle is not transmitted by the interference filter 816 and therefore does not reach the photodetector 814.

[0062] As mentioned above Figure 2 In the absence of angular filtering, the solid angle at which a photodetector receives light is larger for particles closer to the photodetector than for particles farther away. For example, light scattered by a particle P1 farther from the photodetector is received by the photodetector within a solid angle α, while light scattered by a particle P2 closer to the photodetector is received within a larger solid angle β. For particles P1 and P2 of the same size, this difference in solid angle results in a difference in the signal intensity detected by the photodetector.

[0063] The angle filtering achieved by the interference filter 816 can at least partially coordinate the solid angle of light received by the photodetector 814 at all positions within the interaction chamber, thereby reducing signal intensity differences caused by position-based differences in the solid angle of the light received by the photodetector 814. The interference filter 816 can prevent light exceeding a threshold angle of incidence from reaching the photodetector. Figure 7In the example, the interference filter 816 can be designed such that the threshold angle β′ is less than β, and is typically equal to or less than α. Reducing the threshold angle to a value substantially below the angle (α) of the farthest possible particle can lead to a decrease in signal strength, thus affecting the sensor's detection capability. Figure 7 In this example, the threshold angle is set to α, meaning that the solid angle at which the photodetector 814 receives light scattered by the particle is the same, regardless of the particle's position in the interaction chamber 110. Therefore, in this example, for particles of the same size, the amount of scattered light reaching the photodetector 814 will be substantially the same regardless of the particle's position in the interaction chamber 110, thus producing substantially the same signal intensity regardless of the particle's position in the interaction chamber 110. This at least partial coordination of the solid angle at the position in the interaction chamber 110 can help mitigate potential particle size determination errors.

[0064] refer to Figure 8A and 8B In some examples, interference filters can be implemented as short-pass or band-pass filters. Such filters have one or more transmission bands, which are the wavelength ranges through which light is substantially transmitted through the filter and otherwise blocked (reflected or absorbed). The transmission bands of an interference filter are defined by an angular range and wavelength. Typically, the transmission bands of an interference filter depend on the angle of incidence of light on the filter and generally shift towards shorter wavelengths as the angle of incidence increases.

[0065] In some examples, when the desired angular transmission range covers normal incidence, a transmission band can be designed (in the case of a bandpass filter) such that the lower edge of the transmission band lies at the selected wavelength. The upper edge of the transmission band is defined by the highest incident angle of the desired angular transmission range. For monochromatic applications, a short-pass filter with a cutoff centered at the desired threshold incident angle at the target wavelength can be used.

[0066] In some examples, if the desired angular transmission range covers an angular range with a lower limit greater than 0° relative to normal incidence, the filter can be designed as a bandpass filter, where the lower transmission limit is centered on a wavelength higher than the target wavelength. The lower transmission limit is defined as the minimum permissible angle of incidence at which the desired wavelength is transmitted, and the upper transmission limit is defined as the maximum permissible angle of incidence at which light is transmitted for the target wavelength. In this way, such a filter only transmits the desired angular portion of the selected wavelength of light. This can be applied to reduce stray light.

[0067] Refer again Figure 7 In some examples, the presence of the interference filter 816 can introduce the additional benefit of reducing the amount of stray light reaching the photodetector 814, thereby helping to improve the signal-to-noise ratio.

[0068] In some examples, the photodetector 814, the interference filter 816, or both can be segmented to allow the capture of additional information about the distribution of scattered light, which can be used, for example, to more accurately estimate the particle size or other properties of the particulate matter, such as optical properties (e.g., the refractive index of the particles).

[0069] Angular filtering of transmitted light can also be achieved in reflection mode. Here, scattered light bounces off the thin-film filter before reaching the detector. In this configuration, the bandpass filter can be replaced by a notch filter, where the upper and lower limits of the reflection band are defined by the angular portion to be received by the photodetector.

[0070] Angular filtering is typically designed for monochromatic applications and a single angular region. However, the basic principle can be extended to multi-color or multi-angle band operation, or any combination of both. Therefore, filters are characterized by one or more transmission / reflection bands, where each transmission band can be optimized for filtering multiple different wavelengths and multiple different angular bands. Although the definition of transmission / reflection bands is more complex in these cases, the basic concept of angular filtering remains the same as described.

[0071] Reference Figure 9A and Figure 9B Optical-based particulate sensors that achieve angle filtering (e.g., Figure 1A and Figure 1B The sensor 100 may include a photodetector assembly 150 positioned to receive light scattered by particles in the interaction chamber of the particulate sensor. The photodetector assembly 150 includes a photodetector 164 (e.g., a photodiode) and optical elements including an optical fiber 166, such as a multimode fiber, wherein the end of the optical fiber 166 is positioned such that light propagating through the optical fiber 166 is incident on the photodetector 164.

[0072] Angular filtering of incident light by optical fiber 166 can be achieved by utilizing the effect of total internal reflection, for example, as occurs in multimode optical fibers or similar optical guiding optics. Specifically, the optical fiber or optical guiding structure 166 includes a core 168 and a cladding 170. The refractive index of the core 168 and the cladding 170 can affect the acceptance angle of optical fiber 166, which is a threshold angle. Below this threshold angle, light is accepted by optical fiber 166 (and therefore can reach photodetector 164), and above this threshold angle, light cannot propagate in optical fiber 166 (and therefore will not reach photodetector 164). Light that cannot propagate in the optical fiber is coupled in the waveguide and is scattered and refracted out of the optical guiding fiber.

[0073] Angle filtering, implemented by multimode fiber 166 or an optical guide structure, can at least partially coordinate the solid angle of light received by photodetector 164 at all positions within the interaction chamber, thereby reducing signal intensity differences caused by position-based variations in the solid angle of light received by photodetector 164. Fiber 166 can prevent light exceeding a threshold angle of incidence from reaching the photodetector. The threshold angle can be, for example, an angle below which total internal reflection occurs in fiber 166.

[0074] By designing the optical fiber 166 such that its threshold angle is smaller than the solid angle at which light scattered by particles near the optical fiber 166 is received by the photodetector 164, the positional dependence of the signal strength can be reduced. For example, the optical fiber 166 may have a threshold angle between the solid angle at which the photodetector 164 receives light scattered by particles near the optical fiber 166 and the solid angle at which it receives light scattered by particles far from the optical fiber 166.

[0075] Figure 9A The image shows optical fiber 166 receiving light scattered by a particle at point A, which is far from optical fiber 166. Figure 9B The diagram illustrates how fiber 166 receives light scattered by a particle at point D closer to fiber 166. The threshold angle of fiber 166 coordinates the solid angle at which it receives scattered light, thereby reducing the positional dependence of the solid angle and, consequently, reducing the positional dependence of the intensity of the scattered light received by photodetector 164 for a given particle size. For example, in Figure 9A and 9B In the example, the threshold angle is chosen to match the solid angle of the farthest particle (the particle at point E). This ensures that the solid angle of the light scattered by the particle received by the photodetector 164 is the same regardless of the particle's position within the interaction chamber. Therefore, for particles of the same size, the amount of scattered light reaching the photodetector 164 will be substantially the same regardless of the particle's position within the interaction chamber, which in turn means that the intensity signal of a particle of a given size will be substantially the same regardless of its position within the interaction chamber. This at least partial coordination of the solid angle across positions within the interaction chamber can help mitigate potential errors in particle size determination.

[0076] Also refer to Figures 10A-10E This illustrates the effect of particle position on the light received by the photodetector with and without angular filtering provided by multimode fiber or other optical guiding devices 166. Figures 10A-10E Each of them corresponds to Figures 9A-9BThe angular transmission of light at the corresponding point in the graph. Unfiltered curves 180a-180e correspond to the angular dependence of light reaching the photodetector without angular filtering through fiber 166. Here, the photodetector has the same dimensions as the fiber inlet and is positioned at the same location as the fiber end face. As can be seen from the unfiltered curves 180a-180e, particles located closer to photodetector 164 have a wider angular transmission range than particles located farther from photodetector 164 (e.g., the solid angle of light scattered by these particles is larger). For example, for the particle at point D closer to photodetector 164 ( Figure 10D The scattered light arrives at the photodetector at a solid angle of ±45°. In contrast, for particles at point E, which is far from the photodetector, the scattered light arrives at the photodetector at a much smaller solid angle of ±32°. This difference in solid angle leads to the position-dependent intensity discussed above, which can cause errors in particle size estimation.

[0077] Figure 10F The difference in solid angle between two different examples is shown. In one example, an optical fiber is used to collect light, and in another example, a photodiode with the same core diameter is used. The dashed area represents the solid angle of collection with the photodiode relative to the particle distance. The shaded area corresponds to the solid angle of collection with the optical fiber relative to the particle distance, where the angle filtering principle described above is applied. In this example, an optical fiber with a core diameter of 1000 μm and refractive indices of 1.5 and 1.43 for the core and cladding materials is used. In this particular example, the particle is positioned at the center of the optical axis of the fiber / detector, while the distance from the fiber / photodiode varies between 0 and 1.5 mm. Figure 10F As can be seen, angle filtering using total internal reflection provides a constant solid angle regardless of the particle position from the fiber endface up to the critical distance, where the geometric solid angle is smaller than the fiber's acceptance angle. Therefore, the useful measurement area is limited to this critical distance to ensure a constant solid angle.

[0078] By incorporating fiber 166 that enables angle filtering, the position dependence of angular transmission is reduced, as shown in filtering curves 182a-182e. For example, by utilizing fiber 166 with a threshold acceptance angle equal to the minimum solid angle in the position dependence (here, ±27°), the position dependence of signal strength can be essentially eliminated.

[0079] Reference Figure 11 In an example of an optical-based particulate sensing method, a fluid containing particulate matter flows through an interaction chamber (250) of a particulate sensor. The interaction chamber (252) is illuminated using an illumination beam.

[0080] Light scattered by particles present in the interaction chamber is filtered (254) by an optical element of the photodetector assembly. In some examples, the optical element is an optical fiber filtered by total internal reflection based on the angle of incidence of the light. In some examples, the optical element is an interference filter, such as a thin-film interference filter, which allows light to be transmitted over a range of incident angles. Angular filtering of the scattered light can at least partially coordinate the solid angle at which the photodetector receives light scattered by particles at various locations in the interaction chamber, helping to mitigate potential particle size determination errors.

[0081] Light transmitted through the optical element is detected by a photodetector (256). The signal of the light detected by the photodetector is used to characterize particulate matter in the fluid (258), such as determining the concentration or size distribution of particulate matter in the fluid.

[0082] Reference Figure 12 The particulate matter sensor system 350 described above can be integrated into a mobile computing device 352, such as a mobile phone (as shown), tablet computer, or wearable computing device. The particulate matter sensor system 350 can be operated by a user, for example, through an application running on the mobile computing device 352, to perform air quality tests. The test results can be displayed on the screen 354 of the mobile computing device 352, for example, to provide the user with substantially real-time feedback on the air quality in the user's environment.

[0083] The particulate sensor system described herein can also be incorporated into other devices, such as air purifiers or air conditioning units; or used in other applications, such as automotive or industrial applications.

[0084] Many embodiments have been described. However, it should be understood that various modifications can be made without departing from the spirit and scope of the invention. For example, some of the steps described above may be independent of the order and can therefore be performed in a different order than that described.

[0085] Other embodiments are also within the scope of the appended claims.

Claims

1. A device for sensing particulate matter in a fluid, the device comprising: A fluid flow conduit, which is fluidly connected to the interaction chamber; An illumination assembly positioned to illuminate the interaction chamber using a shaped illumination beam having an intensity that increases along the diameter of the illumination beam from a first side of the illumination beam to a second side of the illumination beam opposite to the first side; as well as A photodetector is disposed on the first side of the illumination beam and positioned to receive light scattered by particles present in the interaction chamber.

2. The apparatus of claim 1, wherein the second side of the illumination beam corresponds to the particle furthest from the photodetector.

3. The apparatus according to claim 1 or 2, comprising: A light source configured to output an initial illumination beam; as well as An optical element is positioned between the light source and the interaction chamber and is configured to shape the initial illumination beam into the shaped illumination beam.

4. The apparatus according to claim 1 or 2, comprising a plurality of light sources arranged to form the shaped illumination beam.

5. A method for sensing particulate matter in a fluid, the method comprising: An interaction chamber is illuminated using a shaped illumination beam having an intensity that increases along the diameter of the illumination beam from a first side of the illumination beam to a second side of the illumination beam opposite to the first side, in which a fluid containing particulate matter is present; as well as The light scattered by the particles present in the interaction chamber is detected by a photodetector disposed on the first side of the illumination beam.

6. The method of claim 5, wherein illuminating the interaction chamber with a shaped illumination beam comprises: The initial illumination beam is output from the light source; as well as The initial illumination beam is shaped by optical elements positioned between the light source and the interaction chamber.

7. The method of claim 5 or 6, wherein illuminating the interaction chamber with the shaped illumination beam comprises operating a plurality of light sources, wherein light emitted by each of the plurality of light sources together forms the shaped illumination beam.

8. The method of claim 5 or 6, further comprising determining the properties of the particles in the fluid based on light scattered by the particles.

9. The method according to claim 8, wherein, Determining the characteristics of the particulate matter includes determining the concentration of the particulate matter in the fluid.

10. The method of claim 8, wherein determining the characteristics of the particulate matter includes determining the size distribution of the particulate matter.

11. A mobile communication device comprising the apparatus according to claim 1.

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