Field of the invention

The invention relates to an optical sensor for detecting particles, to a related method, and to a computer program product comprising code to execute this method Background of the invention

Atmospheric particles are microscopic solid or liquid matter suspended in the Earth ^' s atmosphere. Sources of particles can be man-made or natural. They have impacts on climate and precipitation that adversely affect human health, especially the concentration of fine particles (diameter of 2.5 μιτι or less, so-called PM2.5 particles) is very important parameter to monitor the air pollution. PM2.5 particles tend to penetrate into the gas exchange regions of the lung, leads to plaque deposits in arteries and therefore cause severe health problems. In order to determine the concentration of critical particles in air, particle sensors are used to measure the level of pollution in the air. Low-cost systems are available based on the measurements of light scattered at the particle passing by with the air flowing through a detection volume in the sensor driven by a fan or a heater. These pulses are amplified, filtered and counted in an electronic system. US 9,013,693 B2 discloses such a particle sensor system comprising a light source, a flow cell, an irradiating optical system to irradiate the flow cell with one collimated light beam and a light receiving optical system.

Optical sensors, for example the ones operating as PM2.5 detectors, need to provide response, preferably over the full size range of particles up to 2.5μηη, but practically between 0.2 - 2.5 μιτι range of particle sizes to collect the signals for generating reliable information on the total PM2.5 concentration. This means that the detection volume through which the particle containing air flow is passed should be small enough to be able to count the many smaller particles as individual pulses. At the same time a large detection volume is needed to capture a sufficient number of larger particles to obtain a low shot noise level in a given detector response time. Both are conflicting requirements. There is a demand for a particle sensor being able to provide reliable signals with low shot noise over the full range of particle sizes within the scope of application; e.g. less than 2.5 μιτι in diameter for PM2.5 detection, less than 10 m in diameter for PM10 detection etc.

Summary of the invention

It is an object of the present invention to provide an improved optical sensor for particle density detection that provides reliable signals with low shot noise over the full range of particle sizes being of interest. The invention is defined by the independent claims. The dependent claims define advantageous embodiments.

According to a first embodiment an optical sensor for detecting particles within a predefined particle size range passing a detection volume of the optical sensor along a flow of a carrier medium is presented. Carrier media are e.g. gases or fluids. The optical sensor comprises a light source adapted to create at least two separated illumination beams passing the detection volume to illuminate at least some of the particles within the detection volume, the light source comprises at least one light source unit and a lens arrangement, where at least one of the illumination beams is focused onto a focal point providing a highly illuminated small area within the detection volume around the focal point by the lens arrangement enabling detection of the smaller particles within the particle size range and where at least one of the other illumination beams is an essentially parallel light beam providing larger and less illuminated areas within the detection volume compared to the focused illumination beam enabling detection of the larger particles within the particle size range, where a detection system of the optical sensor is adapted to detect intensity variations of the illumination beams or intensities of scattered, reflected or fluorescence light in parallel when particles being illuminated by the illumination beams as detection signals.

The optical sensor according to the present invention provide options for relieving on conflicting requirements for the detection volume through which the particle containing air flow is passed. On the one hand to decrease the detection volume in size to be able to count the many smaller particles as individual pulses and on the other hand to enlarge the detection volume to capture a sufficient number of larger particles to obtain a low shot noise level in a given detector response time by introducing multiple separated sub-detection volumes in the detection volume passed by the carrier medium and by undertaking parallel processing. The carrier medium might be a suitable gas or fluid to be measured and controlled. The detection volume to be passed by the carrier medium might be provided by open pipe comprising side walls made of a material being transparent for the illumination beams or the detection system and/or the light source are arranged inside the detection volume. At least one of the sub-detection volumes provided by the illumination beams can then be made smaller (the focused illumination beam) than the so-called single-particle medium volume (for smaller particles) to avoid an overlap of the detected light intensity variations causing detection signal overlap. The other larger volumes can be used (for larger particles) so that sufficient counting accuracy can be obtained within the given detection integration time. The focused illumination beam measures smaller particles in a "less than one particle at the time" mode. The detection of smaller particles is limited to the particles fitting into the area of high light intensity present at the focal point and a small area around the focal point of approximately the size of the smaller particles to be measured. The illumination beams as essentially parallel light beams creating larger low-illumination intensity areas for measuring particularly the larger particles captured in large volumes, because the smaller particles will not create sufficiently large intensity variations to overcome a certain threshold level to be recognized as detection signals. The term "separated" denotes two illumination beams having different beam shapes. The term "separated" does not exclude any overlapping of the illumination beams. The term "essentially parallel light beam" denotes a light beam, which propagates through the detection volume without having a focal point inside the detection volume. The term "essentially parallel light beam" does not exclude diverging light beams, as long as the diverging light beam provides a light intensity distribution sufficient to detect larger particles in the area selected for particle detection. As an example the essentially parallel light beam may be a collimated light beam, where all light traces of the particular illumination beam are aligned in merely an approximated parallel direction. The illumination beams may at least partly overlap as long as the detector is able to distinguish from which illumination beam the signal originated. In case of applying suitable filter techniques such as pulse lengths of the detected intensity variations (long pulses may

characterize larger particles detected by the non-focused illumination beam and short pulses may characterize smaller particles detected by the focused illumination beam) or additional distinguishing parameters assigned to the illumination beams such as different polarization or different wavelengths, the illumination beams can overlap without any influence on the detection accuracy. However in a preferred embodiment the illumination beams are separate non-overlapping light beams in order to exclude any influence on the detected data eventually caused by overlapping illumination beams in beforehand.

The detection system may comprise a multitude of photon sensors or a camera to spatially resolve and individually select the detection signals from the various areas illuminated by the illumination beams. Alternatively a single photo detector might be used to capture the whole illuminated area by all illumination beams and then filtering out the illuminated areas for each illumination beam in case of the light of the illumination beams having different properties such as different pulse schemes, different colors (wavelengths) or different polarizations or other differences, e.g. the smaller particles will create short pulses of the light intensity variation, whereas the larger particles will create much longer pulses of the light intensity variation when the particle passing the illumination beams. The terms "short" and "longer" depends on the velocity of the particles, which is mainly determined by the velocity of the carrier medium carrying the particles within its flow, on the size of the particles and on the size of the areas illuminated by the illumination beams.

However, the size of the areas illuminated by the illumination beams is determined by the applied the light source, the velocity of the carrier medium is predetermined by a corresponding flow generating module, e.g. a pump or a fan pumping or blowing the carrier medium through the detection volume of the optical sensor. The detection system may detect the light intensity variations in direct mode or scattered, reflective or fluorescence light in an scattering, reflective or fluorescence mode, where in the direct mode particles in the light path shield light from the detector being arranged in line with the light source resulting in an intensity drop as a light pulse, while in the scattering, reflective or fluorescence mode particles scatter or reflect light from the detection beam towards the detector arranged outside the illumination beams or may emit fluorescence light after being illuminated by the illumination beam resulting in an increase of light as the light pulse. The light pulses are transferred into detection signals by the detection system.

The light source might be any light source suitable for the described purposes of the optical sensor. A light source might be a laser or a LED, preferably the light source is semiconductor light source like an edge emitting light source or a Vertical Cavity Surface Emitting Light source (VCSEL). The light source may emit light of wavelengths between 220 nm and 1300 nm. The light source may preferably be adapted to emit light source light with wavelength above 750 nm in the infrared range of the spectrum, most preferably between 780 nm and 1300 nm of the wavelength spectrum. In an embodiment the light source is a VCSEL emitting at 850nm wavelength.

The present invention provides multiple detection sub volumes in the particle containing flow of the carrier medium within the same detection volume being illuminated in order to create light intensity variation and corresponding detection signals. The sizes of these volumes are different so that smaller particles can be detected in focused highly illuminated areas around the focal point, while larger particles are monitored in significantly larger volumes at lower illumination.

In an embodiment the predefined particle size range ranges from particle diameters of 0.2 μιτι to particle diameters of 2.5 μιτι, which is commonly denotes as PM2.5. Depending on the application the optical sensor according to the present invention might be used also for other predefined particle size range, where the properties of the illumination beams, the detection volume and the light source are adapted accordingly. The term "smaller particles" denote the particles within a particle diameter close to the lower boundary of the particle size range (particles with diameters in the lower half of the particle size range), while the term "larger particles" denote the particles within a particle diameter close to the upper boundary of the particle size range (particles with diameters in the upper half of the particle size range).

The optical sensor may for example be used in order to detect or estimate air pollution. The optical sensor may alternatively be used in industrial applications in which an estimation of particle density may be relevant. The optical sensor may be a separate device or integrated in another device. The optical sensor may be used to indicating the particle concentration level in order to drive the operation of an air purifier device. The optical sensor may be used as part of an air purifier system for indoor, by optical light scattering. Alternatively to measurements of particles in air or other gases, the optical sensor according to the present invention might be applied as particle sensor in fluids, e.g. processing fluids, water, beverages or human or animal body fluids. Therefore the optical sensor according to the present invention provides an improved optical sensor for particle density detection providing reliable signals with low shot noise over the full range of particle sizes being of interest. In an embodiment the illumination beams are arranged in a predefined angle to the flow of the carrier medium within the detection volume at predefined different positions along the flow of the carrier medium, where the carrier medium passes the illumination beams one after the other. In a preferred embodiment each of the illumination beams has a central axis, where the central axes are aligned in a predefined angle to the direction of the flow of the carrier medium within one planar plane aligned parallel to the flow of carrier medium. In an embodiment the predefined angle might be a 90° angle, where the illumination beams are aligned perpendicular to (the direction of) the flow of the carrier medium.

The aligned geometrical position of the illumination beams ensure the measurement of the particle sizes for the same limited volume passing the detection volume in order to be able to correlate size data for larger and smaller particles. It further minimizes the detection effort, because the same detection system can be used for all illumination beams to generate the detection signals. In an embodiment at least two illumination beams having different colors and/or at least one of the illumination beams is a polarized light beam. In a preferred embodiment multiple or all illumination beams are polarized light beams. In another preferred embodiment all polarized light beams being polarized differently or all illumination beams having different colors.

In order to provide polarized light beams, the light source comprises polarization filters arranged within the initial beam generated by the light source or arranged within the illumination beams. The polarization filters might by switchable polarization filters. The different colors of the illumination beams might be achieved by arranging suitable color filters into the illumination beams in case of the light source emitting light spread over of a certain wavelengths interval, e.g. white light.

The polarized light and/or the colored light may provide additional information about the nature of the particles and hence a more accurate PM2.5 determination. In another embodiment the light source provides pulsed illumination beams. The pulsed illumination beams enable to measure time dependent signals. This can be done in one illumination beam only not compromising any of the other features of the optical sensor according to the invention. In another embodiment at least two illumination beams, preferably all illumination beams, are pulsed light source beams. Pulsed light source beams give additional information about the nature of the detected particles, e.g. whether they are of biological nature. Therefore in a preferred embodiment at least one of the focused illumination beams and one of the essentially parallel light beams as the other illumination beams are pulsed in order to detect the biological nature of the particles over the full particle size range of the predetermined particle size range, e.g. via stimulated fluorescence.

In another embodiment the detection system comprises a set of multiple light detectors suitably arranged and adapted to measure the intensity variations or scattered, reflected or fluorescence light caused by the particles individually for each illumination beam. Here the detection system may comprise multiple photo detectors, detector array or a camera with a suitable number of pixels providing a suitable resolution to spatially resolve and individually select the detection signals from the various areas illuminated by the illumination beams. Alternatively a single photo detector might be used to capture the whole illuminated area by all illumination beams and then filtering out the illuminated areas for each illumination beam in case of the light of the illumination beams having different properties such as different pulse schemes, different colors (wavelengths) or different polarizations or other differences. The smaller particles will create short pulses of the intensity variation and larger particles will create much longer pulses of the intensity variation as detection signals. So these size classes can be distinguished in the detector system by binning the intensity variations due to light scattered or reflected by the particles on the length of the intensity variations (pulse length). In another embodiment the light source provides at least three illumination beams where the focused beam of the illumination beams is arranged between two essentially parallel light beams of the illumination beams. This geometry has the additional benefit that while passage of a larger particle both the lower area (first of the two essentially parallel light beams) and the top area (second of the two essentially parallel light beams) provide a detection signal. The time difference can be used for determining the particle speed.

In another embodiment the detection system is adapted to determine a particle velocity within the carrier medium for larger particles within the particle size range from the detection signals caused by one particle passing both parallel light beams recorded with a corresponding time difference. The determined particle velocities within the carrier medium can be used to monitor differences/drifts in the speed of the carrier medium and to adapt the calibration of the detection system for potential differences of the speed of the carrier medium, e.g. drifts in pump, fan or buoyancy speeds.

In another embodiment the light source comprises one diode laser as the light source providing a diverging initial light source beam illuminating the lens arrangement, where the lens arrangement is adapted to separate the initial light source beam into the at least two separate illumination beams. Therefore the lens arrangement may comprises at least one collimating lens providing an essentially parallel initial light source beam and at least one focusing lens arranged within the initial light source beam in order to separate the initial light source beam falling onto the collimating lens into the at least two illumination beams, where the focusing lens focus the part of the initial light source beam passing the focus lens to the focal point, where the remaining light of the initial light source beam forms the other illumination beams. In another embodiment the light source comprises at least one light source per illumination beam, where the lens arrangement comprises at least one individual lens per light source only acting on the illumination beam emitted by the associated light source, where the light sources and individual lenses are adapted to provide the illumination beams. This provides the option to individually adapt and individually control the intensity level of each illumination beam and the corresponding

illuminated area. In order to provide illumination beams having different colors, the light sources may emit light at different wavelengths.

The light source may comprise a light source array to provide multiple light source units for providing individual illumination beams. The light source array may comprise at least the first light source unit and a second light source unit. The optical sensor may further comprise a controller. The light sources may be adapted to enable independent detection of the particle. The controller may be adapted to reduce multiple counts of the particle. The reduction of multiple counts of the particle may be done by means of a theoretical model of particle movement stored, for example, in the controller. The theoretical model may enable to determine

coincidences of detection of one particle by means of a first and a second

illumination beam having a corresponding beam shape.

The lens arrangement may, for example, be a lens array or array of micro- lenses. An array of micro-lenses may, for example, be used if the light source array comprises a single chip of semiconductor light sources. The semiconductor light sources may, for example, be Vertical Cavity Surface Emitting Light sources

(VCSEL). A device like a mobile communication device (laptop, smart phone, PAD and the like) may comprise an optical sensor as described above.

According to a further embodiment a method for detecting particles within a predefined particle size range passing a detection volume of an optical sensor according to the present invention along a flow of a carrier medium is presented. The method comprises the steps of:

creating at least two separate illumination beams for passing the detection volume by a light source of the optical sensor comprising at least one light source and a lens arrangement;

- focusing at least one of the illumination beams onto a focal point within the detection volume and providing at least one of the other illumination beams with essentially parallel light beams by the lens arrangement;

illuminating at least some of the particles within the detection volume by the illumination beams;

- detecting the smaller particles within the particle size range with the illumination beam focused onto the focal point within the detection volume;

detecting the larger particles within the particle size range with the illumination beam providing the essentially parallel light beams; and providing detection signals of the detection of smaller and larger particles by the detection system based on intensity variations of the illumination beams or intensities of scattered, reflected or fluorescence light from the particles when particles being illuminated by the illumination beams.

The steps of the method are not necessarily performed in the order as presented above.

The illumination beams may at least partly overlap as long as the detector is able to distinguish from which illumination beam the signal originated. In case of applying suitable filter techniques such as pulse lengths of the detected intensity variations (long pulses may characterize larger particles detected by the non-focused illumination beam and short pulses may characterize smaller particles detected by the focused illumination beam) or additional distinguishing parameters assigned to the illumination beams such as different polarization or different wavelengths, the illumination beams can overlap without any influence on the detection accuracy. However in a preferred embodiment the illumination beams are separate non- overlapping light beams in order to exclude any influence on the detected data eventually caused by overlapping illumination beams in beforehand.

In an embodiment the method comprises the additional steps of

- creating at least three illumination beams by the light source, where the focused beam of the illumination beams is arranged between two essentially parallel light beams of the illumination beams, and

determining a particle velocity within the carrier medium for larger particles within the particle size range from the detection signals caused by one particle passing both essentially parallel light beams with a corresponding time difference.

In another embodiment the method comprises the additional step of measuring the intensity variations caused by the particles individually for each detected particle by the detection system comprising a set of multiple light detectors being suitably arranged.

In another embodiment the method comprises the additional step of adapting the total number of focused and/or essential parallel illumination beams to more than three detection beams in order to reduce a noise level for a particular particle size below a predefined threshold. In order to obtain a low shot noise level in a given detector, the capture of a sufficient number of particles is necessary. Especially for the larger particles, a larger volume, where particles can be detected is required. Therefore optical sensors providing a higher number of illumination beams, especially a higher number of the illumination beams as essentially parallel light beams sensitive to larger particles will result in a higher number of detected larger particles and therefore in a reduced shot noise level and in a better accuracy of the measurement results. As an example for detecting a concentration of 35 pg/m ³ for larger particles at least 100 of these particles have to be measures in the detector response time to have a shot noise level less than 10% requiring at least three illumination beams.

According to a further aspect a computer program product is presented. The computer program product comprises code which can be saved on at least one memory device comprised by the optical sensor according to any one of claims 1 to 10 or on at least one memory device of a device comprising the optical sensor according to any one of claims 1 to 10, wherein the code being arranged such that the method according to any one of claims 1 1 to 14 can be executed by means of at least one processing device comprised by the optical sensor according to any one of claims 1 to 10 or by means of at least one processing device of the device

comprising the optical sensor. The memory device or the processing device may be comprised by the electrical driver and/or the controller and/or the device comprising the optical sensor. A memory device and/or processing device of the device comprising the optical sensor may interact with a memory device and/or processing device comprised by the optical sensor.

It shall be understood that the optical sensor according to any one of claims 1 to 10 and the method of any of claims 1 1 to 14 have similar and/or identical embodiments, in particular, as defined in the dependent claims. It shall be

understood that a preferred embodiment of the invention can also be any

combination of the dependent claims with the respective independent claim.

Further advantageous embodiments are defined below. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. Brief description of the drawings

The invention will now be described, by way of example, based on

embodiments with reference to the accompanying drawings.

In the drawings:

Fig. 1 shows a principal sketch of an embodiment of the optical sensor according to the present invention.

Fig. 2 shows a principal sketch of an embodiment of the light source of the optical sensor according to the present invention.

Fig. 3 shows a principal sketch of another embodiment of the light source of the optical sensor according to the present invention.

Fig. 4 shows a principal sketch of another embodiment of the light source of the optical sensor according to the present invention.

Fig. 5 shows a principal sketch of an embodiment of the detection system of the optical sensor according to the present invention

Fig. 6 shows a principal sketch of an embodiment of a computer program product comprising code for executing the method according to the present invention.

Fig. 7 shows a principal sketch of another embodiment of a computer program product according to the present invention.

Fig. 8 shows a principal sketch of an embodiment of a method for detecting particles using the optical sensor according to the present invention.

In the Figures, like numbers refer to like objects throughout. Objects in the Figures are not necessarily drawn to scale. Detailed description of embodiments

Fig. 1 shows a principal sketch of an embodiment of the optical sensor 100 according to the present invention. The optical sensor 100 detects particles 10, 1 1 within a predefined particle size range passing the detection volume 20 of the optical sensor 100 along a flow of a carrier medium 30. Therefore the optical sensor 100 comprises a light source 40 creating at three illumination beams 50, 51 , 52 being separate and non-overlapping in this embodiment for ease of understanding. The illumination beams 50, 51 , 52 pass the detection volume 20 and illuminate some of the particles 10, 1 1 (as indicated by black circles) within the detection volume 20. The shown size of the particles 10, 1 1 and the illumination beams 50, 51 , 52 shall demonstrate the effect of the optical sensor 100 in general. To provide the required light source beams the light source 40 may comprises one light source unit 41 or three light source units 41 , 42, 43 and a suitable lens arrangement 44, where one of the illumination beams 51 is focused onto a focal point 53 providing a highly illuminated small area (focal area) within the detection volume 20 around the focal point 53 by the lens arrangement 44 enabling detection of the smaller particles 10 within the particle size range and where the other two illumination beams 50, 52 are essentially parallel light beams providing larger and less illuminated areas within the detection volume 20 compared to the focused illumination beam 51 enabling detection of the larger particles 1 1 within the particle size range. The sizes shown in Fig .1 do not represent the real size ratios. The size of the focal area around the focal point 53 is commonly larger than the size of the smaller particles 10, where the size of the larger particles 1 1 is smaller than the diameter of the essentially parallel illumination beams 50, 52. In an embodiment the light source 40 may provide pulsed illumination beams 50, 51 , 52. Pulsed light source beams 50, 51 , 52 give additional information about the nature of the detected particles 10, 1 1 , e.g. whether they are of biological nature. Therefore the focused illumination beam 51 and one of the essentially parallel light beams 50, 52 as the other illumination beams are pulsed light source beams in order to detect the biological nature of the particles 10, 1 1 over the full particle size range of the predetermined particle size range.

In this embodiment the focused beam 51 of the illumination beams 50, 51 , 52 is arranged between the two essentially parallel light beams 50, 52 of the illumination beams 50, 51 , 52. Furthermore the illumination beams 50, 51 , 52 are arranged perpendicular (the predefined angle) in this embodiment to the flow of the carrier medium 30 within the detection volume 20 at the shown predefined positions along the flow of the carrier medium 30, where the carrier medium 30 passes the collinnated illumination beam 50 first followed by passing the focus illumination beam 51 and subsequently the collinnated illumination beam 52. Each of the illumination beams 50, 51 , 52 have a central axis 54, where the central axis 54 here are aligned

perpendicular (here the predefined angle) to the direction of the flow of the carrier medium 30 (indicated by the arrow 30) within one planar plane (here the paper plane), where also the flow of carrier medium 30 lays in.

The optical sensor 100 further comprises a detection system detecting the intensity variations of the illumination beams 50, 51 , 52 in parallel when particles 10, 1 1 being illuminated by the illumination beams 50, 51 , 52. For ease of understanding the detection system 60 is shown as being arranged in line with the light source 40 and the illumination beams 50, 51 , 52 for detecting in the direct mode. However this is only one embodiment of possible arrangements of the detection system 60. In another embodiment not shown here, the detection system 60 is arranged outside the illumination beams 50, 51 , 52 in order to detect scattered, reflected or

fluorescence light from the particles 10, 1 1 passing the illumination beams 50, 51 , 52. The light intensity variations or scattered, reflected or fluorescence light from the particles 10, 1 1 are transferred into corresponding detection signals 61 , which could be processed by a suitable controller in order to calculate the particle sizes of detected particles as well as a corresponding particle concentration and particle size distribution. The detection system 60 might be further adapted to determine a particle velocity within the carrier medium 30 for larger particles 1 1 within the particle size range from the detection signals 61 caused by one particle 1 1 passing both parallel light beams 50, 52 recorded with a corresponding time difference. The determined particle velocities within the carrier medium 30 can be used to monitor differences/ drifts in the speed of the carrier medium 30 and to adapt the calibration of the detection system 60 for potential differences of the speed of the carrier medium 20, e.g. drifts in pump, fan or buoyancy speeds. The corresponding calculations might be executed by the detection system comprising a suitable controller and/or processor to monitor and/or adapt the optical sensor 100.

Fig. 2 shows a principal sketch of an embodiment of the light source 40 of the optical sensor 100 according to the present invention, where polarizing filters 48 and color filters 49 are arranged within the illumination beams generated by the light source 40. The polarization and color filters might be separated in three

corresponding filters each arranged within the individual illumination beams 50, 51 , 52 separately from the neighbored illumination beams 50, 51 , 52. This enables that at least two illumination beams 50, 51 , 52 having different colors and/or at least one of the illumination beams 50, 51 , 52 is a polarized light beam. In a preferred embodiment all three illumination beams 50, 51 , 52 are polarized light beams. In case of individual and separately arranged and controlled polarization filters 48 all polarized light beams 50, 51 , 52 might be polarized differently. The same holds for individual and separately arranged and controlled color filters 49 enabling all illumination beams 50, 51 , 52 having different colors. The polarized light 50, 51 , 52 and/or the colored light 50, 51 , 52 may provide additional information about the nature of the particles 10, 1 1 and hence a more accurate PM2.5 determination. Fig. 3 shows a principal sketch of another embodiment of the light source 40 of the optical sensor 100 according to the present invention. Here the light source 40 comprises one diode laser as the light source unit 41 providing a diverging initial light source beam 55 illuminating the lens arrangement 44, where the lens arrangement 44 is adapted to separate the initial light source beam 55 into the at least two separate non-overlapping illumination beams 50, 51 , 52. Therefore the lens arrangement 44 comprises one collinnating lens 46 arranged in the initial light source beam 55 providing two essentially parallel illumination beams 50, 52 and one focusing lens 47 arranged on top of the collinnating lens 46 on the side facing towards the detection volume 20 in order to separate the initial light source beam 55 falling onto the collinnating lens 46 into the at least two illumination beams 50, 52, where the focusing lens 47 focus the middle part of the initial light source beam 55 passing the focus lens 47 to the focal point 54, where the remaining light of the initial light source beam 55 forms the other illumination beams 50, 52. However, the lens 46 shown here should not have a fully circular shape, because such a lens would provide an illuminated ring around the focused beam 51 , which would lead to overlapping light effects disturbing the particle detection. Therefore the shape of the lens 46 is adapted to emit illumination beams 50, 52 as separated beams. When using a circular lens 46, the front and back parts of the lens 46 (not visible in the side view of Fig.3) should be blocked or shielded. As an alternative when using a circular lens 46, an elliptical initial beam 55 might be used to illuminate lens 46 avoiding the creation of an illuminated ring around the focused illumination beam 51 . Such an elliptical initial beam 55 might be provided by a edge emitting laser diode as the light source unit 41 . Fig. 4 shows a principal sketch of another embodiment of the light source 40 of the optical sensor 100 according to the present invention. Here the light source 40 comprises three light source units 41 , 42, 43 each generating one illumination beam 50, 51 , 52, where the lens arrangement 44 comprises three individual lenses 45 each only acting on the illumination beam 50, 51 , 52 emitted by the associated light source unit 41 , 42, 43, where the light source units 41 , 42, 43 and individual lenses 45 are suitably adapted to provide the separation and non-overlapping of the illumination beams 50, 51 , 52.

This provides the option to individually adapt and individually control the intensity level of each illumination beam 50, 51 , 52 and the corresponding illuminated area within the detection volume 20. In order to provide illumination beams 50, 51 , 52 having different colors, the light sources may emit light at different wavelengths. The light source 40 may comprise a light source array to provide the multiple light sources (here three light source units 41 , 42, 43) for providing individual illumination beams 50, 51 , 52. The optical sensor 100 may further comprise a controller (not shown here). The light source units 41 , 42, 43 may be adapted to enable independent detection of the particle 10, 1 1 . The controller may be adapted to reduce multiple counts of the particle 10, 1 1 . The reduction of multiple counts of the particle 10, 1 1 may be done by means of a theoretical model of particle movement stored, for example, in the controller. The theoretical model may enable to determine

coincidences of detection of one particle 10, 1 1 by means of the illumination beams 50, 51 , 52 having the beam shape as shown in Fig .1 .

Fig. 5 shows a principal sketch of an embodiment of the detection system 60 of the optical sensor 100 according to the present invention, where the detection system 60 comprises a set of multiple light detectors 62 suitably arranged and adapted to measure the intensity variations caused by the particles 10, 1 1

individually for each detected particle 10, 1 1 . Here the detection system 60 may comprise multiple photo detectors 62, a detector array 62 or a camera with a suitable number of pixels 62 providing a suitable resolution to spatially resolve and

individually select the detection signals 61 from the various areas illuminated separately by the illumination beams 50, 51 , 52. The smaller particles 10 will create short pulses of the intensity variation and larger particles 1 1 will create much longer pulses of the intensity variation as detection signals 61 . In an alternative embodiment the detector system 60 of Fig.5 might also be arranged outside the illumination beams, e.g. in a 90° angle to the propagation direction of the illumination beams, to collect the light that is scattered under an angle from the particles, where the detection system 60 is used in an reflective or scattered mode.

Fig. 6 shows a principal sketch of an embodiment of a computer program product 300 comprising code 310 according to the present invention. The computer program product 300 comprises code 310 which can be saved on at least one memory device comprised by the particle sensor 100 according to the present invention, wherein the code is arranged such that the method according to the present invention can be executed by means of at least one processing device comprised by the particle sensor 100 according to the present invention. Fig. 7 shows a principal sketch of an alternative embodiment to the embodiment shown in Fig. 6, where a computer program product 300 comprising code 310 is intended for saving on a device 400 comprising the optical sensor 100 according to the present invention. The computer program product 300 comprises code 310 which can be saved on at least one memory device 70 comprised by the optical sensor 100 or on at least one memory device 410 of a device 400 comprising the optical sensor 100, wherein the code 310 is arranged such that the method according to the present inventions (see also Fig.8) can be executed by means of at least one processing device 80 comprised by the optical sensor 100 or by means of at least one

processing device 420 of the device 400 comprising the optical sensor 100. The device 400 might be a mobile communication device (laptop, smart phone, PAD and the like) comprising the optical sensor 100 as described above.

Fig. 8 shows a principal sketch of an embodiment of a method for detecting particles using the optical sensor according to the present invention. The comprises the steps of creating 210 at least two illumination beams 50, 51 , 52 for passing the detection volume 20 by a light source 40 of the optical sensor 100 comprising at least one light source unit 41 , 42, 43 and a suitable lens arrangement 44, focusing 220 at least one of the illumination beams 51 onto a focal point 53 within the detection volume 20 and providing at least one of the other illumination beams 50, 52 with essentially parallel light beams by the lens arrangement 44, illuminating 230 at least some of the particles 10, 1 1 within the detection volume 20 by the illumination beams 50, 51 , 52, detecting 240 the smaller particles 10 within the particle size range with the illumination beam 51 focused onto a focal point 53 within the detection volume 20, detecting 250 the larger particles 1 1 within the particle size range with the illumination beam 50, 52 providing an essentially parallel light beams; and providing 260 detection signals 61 of the detection of smaller and larger particles 10, 1 1 by the detection system 60 based on intensity variations of the illumination beams 50, 51 , 52 or the scattered, reflected or fluorescence light of these beams when particles 10, 1 1 being illuminated by the illumination beams 50, 51 , 52.

In an embodiment the method may comprise the additional steps (dashed method steps) of creating 21 1 at least three illumination beams 50, 51 , 52 by the light source 40, where the focused beam 51 of the illumination beams 50, 51 , 52 is arranged between two essentially parallel light beams 50, 52 of the illumination beams.50, 51 , 52, and determining 270 a particle velocity within the carrier medium 30 for larger particles 1 1 within the particle size range from the detection signals 61 caused by one particle 1 1 passing both essentially parallel light beams 50, 51 with a corresponding time difference.

In another embodiment the method comprises the additional step (dashed method step) of measuring 280 the intensity variations caused by the particles 10, 1 1 individually for each detected particle 10, 1 1 by the detection system 60 comprising a set of multiple light detectors 62 being suitably arranged.

In another embodiment the method comprises the additional step of adapting

290 the total number of focused and/or essential parallel illumination beams 50, 51 , 52 to more than three detection beams 50, 51 , 52 in order to reduce a noise level for a particular particle size below a predefined threshold.

The steps of the method are not necessarily performed in the order as presented in Fig.8.

While the invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the art and which may be used instead of or in addition to features already described herein. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality of elements or steps. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope thereof.

List of reference numerals:

10 particles (smaller particles) 1 1 particles (larger particles)

20 detection volume

30 carrier medium, flow of the carrier medium

40 light source

41 - 43 light source units of the light source

44 lens arrangement

45 individual lenses of the lens arrangement

46, 47 separating lenses of the lens arrangement

48 polarizing filter

49 color filter

50 illumination beam (as an essentially parallel light beam)

51 illumination beam (as a light beam being focused onto a focal point)

52 illumination beam (as an essentially parallel light beam)

53 focal point of illumination beam 51

54 central axes of the illumination beams

55 initial light source beam

60 detection system

61 detection signals

62 multiple light detectors of the detection system

70 memory device of the optical sensor

80 processing device of the optical sensor

100 optical sensor

200 method of particle detection

210 creating at least two illumination beams

21 1 creating at least three illumination beams

220 focusing at least one of the illumination beams onto a focal point

230 illuminating at least some of the particles

240 detecting the smaller particles

250 detecting the larger particles

260 providing detection signals of the detection of particles

270 determining the velocity of larger particles within the carrier medium

280 measuring the intensity variations caused by the particles individually

290 adapting the total number illumination beams

300 computer program product 310 code of the computer program product

400 device comprising the optical sensor

410 memory device of the device 400

420 processing device of the device 400