The present disclosure relates to a system for optically detecting particles and to a corresponding detection method .

State of the art optical particle detectors typically rely on detecting light that is scattered from obj ects or particles that are located in a sampling volume . Such particle detectors typically employ a light source , such as a laser, for illuminating the obj ects or particles in the sampling volume and a photodetector arranged at a certain scattering angle with respect to an optical access defined by the path between a light source and the sampling region . From the resulting signal , a particle concentration within the sampling volume as well as a particle si ze can be estimated .

The described detectors have a number of disadvantages . Firstly, most of the scattered light is lost and does not contribute to the signal as the photodetector is only configured to measure scattered light at a single certain scattering angle . Moreover, in typical scattering, the bulk of the light is scattered in a forward direction, i . e . further along the optical axis , and typically cannot be distinguished from the incident light beam . In addition, light that is absorbed by the particles is also lost and does not contribute to the signal . Furthermore , for actual particle detection, the index of refraction has to be known or assumed for every particle in the sampling region . An obj ect to be solved is to provide an improved concept of a system for detecting particles that overcomes the limitations of state of the art particle detectors .

This obj ect is achieved with the subj ect-matter of the independent claims . Embodiments and developments of the improved concept are the subj ect-matter of the dependent claims .

The improved concept is based on the idea of arranging a plurality of light emitters and detectors in a manner that a light curtain is formed in a probing volume . Particles within the probing volume disturb the light curtain via absorption, reflection and/or scattering, which in turn leads to a change in the detected photo signals of the detectors . A close spacing of light barriers of the light curtain enables an estimation of particle si zes as well as a particle concentration .

For example , a system for detecting particles according to the improved concept comprises a probing volume, an emitter arrangement including an array of light emitters configured to emit light into the probing volume , and a detector arrangement including an array of light detectors configured to detect the light that is emitted by the emitter arrangement into the probing volume . The system further comprises an evaluation circuit that is configured to generate an output signal from detector signals received from the detector arrangement based on the detected light . Each light detector of the array of light detectors is configured to receive light from an associated one of the array of light emitters . An amount of light received by the detector arrangement depends on whether a particle is located within the probing volume .

The light emitters of the emitter arrangement are configured to each emit a beam of light , in particular a substantially collimated or focused beam of light , into the probing volume directed towards an associated one of the light detectors . The light emitters are arranged in an array such that the emitted light beams form an array of substantially parallel beams with respect to each other . The array of light emitters can be one-dimensional or multidimensional , e . g . two dimensional .

The array of light detectors is arranged such that each light detector receives light from an associated one of the array of light emitters . For example , the array of light detectors matches the array of light emitters in terms of number o f elements and/or pitch . Therefore , the array of light detectors correspondingly can be one-dimensional or multidimensional .

In other words , the beams emitted by the light emitters form a light curtain that extends into the probing volume , wherein each beam can be understood as a light barrier . For example , each light barrier extends between one of the light emitters and an associated one of the light detectors i f no particle is located within the probing volume on the respective optical path . Alternatively, the light barrier extends from the light emitter towards an obj ect and is deflected towards the associated one of the detectors via reflection .

An amount of light received by the detector arrangement is influenced by obj ects within the probing volume . For example , less or more light is received by the detectors if an object is located within the probing volume, depending on the configuration of the emitter and detector arrays. In particular, the emitters and detectors could be arranged such that a beam path is blocked if a particle is located in the probing volume within said beam path and no light reaches the respective detector. Alternatively, the emitters and detectors could be arranged such that a beam path between emitter and associated detector is established by an object within the probing volume, e.g. via reflection.

An evaluation circuit, e.g. an integrated circuit, analyzes the photo signals generated by the detector array and generates an output signal based on the photo signals. The output signal can contain information on whether a particle is present in the probing volume and optionally about a particle size, for instance.

The particles can be particles in a gas, e.g. air, such as dust, fine dust, pollen or soot particles. Thus, a detector according to the improved concept can be employed to determine a measure for air quality, for instance.

In some embodiments, the emitter arrangement further comprises an array of lenses that is configured to collimate or focus the light emitted by the array of light emitters.

In order to achieve the aforementioned collimation or focusing, each of the light emitters can comprise a lens of an array of lenses, such that the emitted light is collimated or focused. Therein, the array of lenses matches the array of light emitters in terms of dimensionality, number of elements and/or pitch . This is particularly desirable for light emitters having a diverging emittance of light , e . g . LEDs .

In some embodiments , the detector arrangement is arranged substantially parallel to the emitter arrangement .

In order to ensure a uni formly formed light curtain, the array of light emitters in these embodiments is arranged parallel or substantially parallel to the array of light detectors .

In some embodiments , the detector arrangement is arranged on a side of the probing volume opposite the emitter arrangement such that the array of light detectors faces the array of light emitters .

In these embodiments , the probing volume is arranged in between the array of light emitters and the array of light detectors . This way, a light curtain is reali zed between emitters and detectors in a manner in which a particle present in the probing volume prevents one or more light beams from fully reaching the associated detector . Hence , a particle can be locali zed via a reduced or absent signal in the respective detector .

In some embodiments , the emitter arrangement and the detector arrangement are arranged on a common substrate body such that the array of light emitters and the array of light detectors form a greater array having an alternating arrangement of light emitters and light detectors .

Having the light emitters and light detectors arranged in an alternating pattern, e . g . a checkerboard pattern in the two- dimensional case , can lead to reduced cross talk due to larger spacings between two adj acent detectors . For example , two of these greater arrays on a first and a second common substrate are arranged facing each other enclosing a probing volume in between, wherein the two arrays have a lateral of fset , such that a detector of one greater array directly faces a light emitter of the other greater array and vice versa . Alternatively, a boundary element , e . g . a reflector or an absorber, is arranged on one side of a probing volume and a common substrate having the aforementioned arrangement of light emitters and light detectors are arranged on the opposite side of the probing volume .

In some embodiments , the array of light emitters is formed from micro light emitters , in particular micro-LEDs or VCSELs .

Both micro-LEDs and VCSELs are common choices for miniature light emitters . Choosing these micro obj ects as emitters for a particle detector enables a high resolution while maintaining a small footprint of the sensor . In addition, small pixel si zes are tantamount with an increased sensitivity also for small particles in the pm range or even smaller . In case of micro-LEDs , the emitters can additionally comprise a micro lens for focusing or collimating the emitted light . The micro lenses can be reali zed as a micro-lens array that is arranged above and aligned with the array of micro light emitters .

In some embodiments , the array of light emitters is a display, in particular a micro-LED display . The array of light emitters can be reali zed by a micro-LED display that are readily available and constitute a two- dimensional matrix array of pixels . A micro lens array arranged above the micro-LED display allows for the formation of a light curtain as described .

In some embodiments , the array of light detectors is formed from micro photodetectors , in particular from micro photodiodes .

Analogously to forming the array of light emitters with a micro-LED display, the array of light detectors can be formed by an array of micro photodiodes , such that each of the photodiodes is associated to one of the light emitters . Such an arrangement ensures a high sensitivity and resolution of the resulting particle detector .

In some embodiments , the system for detecting particles further comprises a reflector or absorber that is arranged substantially parallel to the emitter arrangement and to the detector arrangement on a side of the probing volume opposite the emitter arrangement and the detector arrangement .

In embodiments , in which light emitters and detectors are formed on a common substrate , e . g . a micro-LED display in which micro photodiodes are arranged in between the microLEDs forming a checkerboard pattern, an absorber or reflector, e . g . a mirror, can be arranged substantially parallel to the common substrate with the probing volume being located in between, such that the detection solely relies on reflected light , either from the reflector or from obj ects or particles within the probing volume . Therein, the reflector is configured to be reflective in a wavelength range that is emitted by the light emitters while the absorber is configured to be absorbent in said wavelength range .

In some embodiments , the system is sensitive to particles smaller than 3 pm, in particular smaller than 500 nm .

Owing to the possibility of employing micro-si zed light emitters and detectors , particle si zes down to the di f fraction limit can be reliably detected with the proposed light curtain method .

In some embodiments , the system is sensitive to a single particle located in the probing volume .

Due to the fact that each detector is associated to one of the light emitters , already a single particle can be reliably detected as this results in a signi ficantly altered signal in at least one of the light detectors . Hence , in contrast to scattering detectors , the sensitivity of a detector according to the improved concept is greatly enhanced .

In some embodiments , the output signal comprises information about a location and/or a velocity of a detected particle .

By evaluating the location of the light detector that shows an altered amount of received light , the location of a particle within the probing volume at least in the dimensions of the detector array can be determined . Moreover, by evaluating the temporal evolution of the photo signals , also a velocity as well as a si ze of the detected particles can be determined . The aforementioned obj ect is further solved by a particle detector arrangement that comprises a plurality of systems for detecting particles according to one of the embodiments described above . Therein, each system in terms of its optical axis is arranged substantially perpendicular to the respective optical axis of the other systems .

For example , two or three emitter-detector array pairs are employed to form a two- or three-dimensional cavity, in which location, si ze and velocity of particles can be exactly determined .

The aforementioned obj ect is further solved by a method for detecting particles . The method comprises providing a probing volume , emitting, by means of an emitter arrangement including an array of light emitters , light into the probing volume and detecting, by means of a detector arrangement including an array of light detectors , the light that is emitted by the emitter arrangement into the probing volume . The method further comprises generating, by means of an evaluation circuit , an output signal from detector signals received from the detector arrangement based on the detected light . Each of the array of light detectors is configured to receive light from an associated one of the array of light emitters . An amount of light received by the detector arrangement depends on whether a particle is located within the probing volume .

Further embodiments of the method become apparent to the skilled reader from the embodiments of the system for detecting particles described above . The following description of figures of exemplary embodiments may further illustrate and explain aspects of the improved concept . Components and parts of the system for detecting particles with the same structure and the same ef fect , respectively, appear with equivalent reference symbols . Insofar as components and parts of the system correspond to one another in terms of their function in di f ferent figures , the description thereof is not repeated for each of the following figures .

In the figures :

Figures 1 to 6 show di f ferent exemplary embodiments of a system for detecting particles according to the improved concept ;

Figure 7 shows an exemplary embodiment of a particle detector arrangement ;

Figure 8 shows a further exemplary embodiment of a system for detecting particles ; and

Figure 9 shows a further exemplary embodiment of a particle detector arrangement configured as an orientation sensor .

Figure 1 shows a schematic side view of an exemplary embodiment of a system for detecting particles 1 according to the improved concept . The system 1 comprises a first substrate body 10 on which the emitter arrangement 20 is arranged . The emitter arrangement 20 comprises an array of light emitters 21 that are equally distributed across the surface of the substrate body 10 . The schematics show a onedimensional array, however, the concept can be easily expanded to two dimensions , for instance . The light emitters 21 are micro light emitters such as VCSELs or micro-LEDs of a micro-LED display, for example . In this embodiment , emitter arrangement 20 additionally comprises a lens array 22 , e . g . comprising a plurality of micro lenses , thus forming a microlens array, such that a micro-lens is associated to each of the light emitters 21 . In the figure , the lens array 22 is illustrated to be separate from the light emitters 21 , however, the lens array 22 can likewise be integrated in the emitter arrangement 20 .

The system 1 further comprises a second substrate body 10 that is arranged parallel or substantially parallel to the first substrate body 10 with respect to the main plane of extension . On the second substrate body 10 , the detector arrangement 30 is arranged . The detector arrangement 30 comprises an array of light detectors 31 that are equally distributed across the surface of the substrate body 10 . Therein, the equal distribution matches that of the emitter arrangement 20 in terms of number of elements and pitch, for instance . The light detectors 31 a micro light detectors such as micro photodiodes , for example . The second substrate body 10 is arranged such that the detector arrangement 30 faces the emitter arrangement 20 wherein a region in between the emitter arrangement 20 and the detector arrangement 30 defines the probing volume 2 .

As illustrated by means of the dashed arrows in the figure , the light emitters 21 and the light detectors 31 form pairs in a manner, in which each of the light detectors 31 is associated to one of the light emitters 21 . This means that each of the light detectors 31 exclusively, or at least predominantly, receives light from the associated one of the light emitters 21 in case no obj ects are located within the probing volume 2 . This is achieved by forming light beams that are parallel or substantially parallel to each other in a manner that a light curtain is formed between the emitter arrangement 20 and the detector arrangement 30 . Therein, each light beam between a light emitter 21 and the associated lights detectors 31 can be understood as a light barrier of the light curtain . To this end, a lens array 22 focuses or collimates the light from the light emitters 21 towards the associated one of the light detectors 31 .

The system 1 further comprises an evaluation circuit 60 , which in this figure is illustrated as an integrated circuit layer . Therein, the evaluation circuit 60 is electrically connected to the light detectors 31 in order to enable the readout of photo signals generated by each of the light detectors 31 based on received light .

Figure 2 shows the exemplary embodiment of a system for detecting particles 1 of figure 1 . For illustration purposes , the evaluation circuit 60 is not shown in this and in the following figures . Compared to the embodiment of figure 1 , in this embodiment particles 3 are located within the probing volume 2 . For example , the probing volume 2 is fi lled with a gas , e . g . air, that contains particles , such as dust , fine dust , bacteria or pollen, for instance . Thus , a system for detecting particles 1 according to the improved concept can be used for determining or monitoring parameters such as air quality, for instance .

As illustrated in the figure , the particles 3 each obstruct a light path formed between a pair of light emitter 21 and associated light detector 31 . Hence , the resulting photo signal of said light detector 31 in this embodiment shows a reduced, or zero , amount of received light , thus generating a smaller, or no , photocurrent compared to the pairs of light emitter 21 and light detector 31 whose light path is not obstructed . This way, positions and number of particles 3 within the probing volume 2 can be determined . Furthermore , by choosing a small pitch within the array of light emitters 21 and the array of lights detectors 31 , also measurements of particle si zes can be performed by evaluating the signal of neighboring light detectors 31 . Likewise , velocity and hence movement of the particles 3 can be measured by evaluating a change in the signal of neighboring light detectors 31 . These parameters in sum are suf ficient to determine the particle type as di f ferent particles are characteri zed by di f ferent si zes and/or velocities within an air volume .

Figure 3 shows a further embodiment of a system 1 according to the improved concept . In contrast to the system shown in figures 1 and 2 , in this embodiment both substrate bodies 10 are common substrate bodies and comprise both light emitters 21 and light detectors 31 . On each substrate body 10 , the array of light emitters 21 and the array of light detectors 31 are interleaved such that a greater array 40 is formed featuring an alternating arrangement of light emitters 21 and detectors 31 . The two greater arrays 40 are arranged with respect to each other such that again each of the light emitters 21 of the first substrate body 10 is associated to one of the light detectors 31 of the second substrate body 10 , and vice versa .

As illustrated by the dashed arrows in this figure , the alternating arrangement reduces cross talk as even in the case of a diverging light beam, only one of the light detectors 31 is arranged to receive light from a speci fic light emitter 21 as its neighboring elements are light emitters 21 . In this embodiment , two lens arrays 22 are arranged as there are light emitters 21 located on both substrate bodies 10 . Moreover, as illustrated also the light detectors 31 each comprise a lens elements , which may serve to focus light onto a light-sensitive region of the respective light detector 31 . Alternatively, the 2 lens arrays 22 can comprise lenses only for the light emitters 21 .

Figure 4 shows the exemplary embodiment of a system for detecting particles 1 of figure 3 . Analogous to the embodiment of figure 2 , in this embodiment likewise a particle 3 is located within the probing volume 2 . In this embodiment , the system 1 is operated one-sided . This means that only the light emitters 21 on one side of the probing volume 2 are activated to emit light . However, it is illustrated in the drawing, all detector elements 31 are activated to generate a photo signal based on received light . This means that a particle 3 located within the probing volume 2 can obstruct light from reaching the associated light detector 31 of a respective light emitter 21 i f a particle 3 is located on the light path between these two elements . Hence , analogous to the embodiment shown in figures 1 and 2 , the presence of a particle 3 can be detected via a reduced, or zero , photocurrent generated by one of the light detectors 31 on the substrate body 10 opposite the activated light emitters 21 .

Likewise , lights detectors 31 arranged on the same substrate body 10 can be read out in order to detect light that is reflected from the particle 3 back towards said substrate body 10 . This is illustrated by means of the dashed arrows pointing down in figure 4 . The proposed operation scheme therefore causes a twofold change in the detector signals i f a particle 3 is present , therefore potentially leading to an even larger sensitivity compared to the embodiment illustrated in figures 1 and 2 . However, this comes at the cost of reducing the resolution of the system 1 by a factor of 2 .

Figure 5 shows the exemplary embodiment of a system for detecting particles 1 of figures 3 and 4 . In this figure , the system 1 is operated double-sided . This means that the light emitters 21 on both substrate bodies 10 are activated to emit light . Likewise , also in this operational mode all detector elements 31 are activated to generate a photo signal based on received light .

As described above , a particle 3 present within the probing volume 2 again obstructs the light path between at least one of the light emitters 21 and the associated light detectors 31 arranged on opposite sides of the probing volume 2 . Like in the previous figure , lights detectors 31 can in addition from the light of the associated light emitter 21 also receive light that is reflected from the particle 3 , thus leading to an increased photocurrent compared to the case , in which no particle 3 is present to reflect light . Hence , also this embodiment enables the aforementioned detection of a particle 3 in a twofold manner, however, without sacri ficing the resolution by a factor of 2 .

Figure 6 shows a further embodiment of a system 1 according to the improved concept . This embodiment features one substrate body 10 as a common substrate body featuring the aforementioned greater array 40 of interleaved arrays of light emitters 21 and light detectors 31 . The probing volume 2 in this embodiment is defined by the space between said substrate body 10 and a boundary element 50 that is arranged parallel or substantially parallel to the substrate body 10 in terms of the main planes of extension . The boundary element 50 can be an absorber or a reflector, such as a mirror .

I f the boundary element 50 is an absorber, as it is illustrated in the drawing, it is configured to absorb substantially all light that is emitted by the light emitters 21 and reaches a surface of the boundary element 50 . Similar to the embodiments of figures 4 and 5 , the presence of the particle 3 can be veri fied by means of a photocurrent induced by those light detectors 31 that receive light that is reflected from said particle 3 .

I f the boundary element 50 is a reflector, on the contrary, it is configured to reflect light that is emitted by the light emitters 21 and reaches a surface of the boundary element 50 . Speci fically, the reflector is arranged such that again each of the light detectors 31 is associated to one of the light emitters 21 . In other words , each of the light detectors 31 exclusively or predominantly receives light from one of the light emitters 21 , e . g . a neighboring light emitter 21 , i f no particle 3 is present within the probing volume 2 and obstructs said light path between said light emitter 21 , the reflector and the associated light detectors 31 . To achieve this , the boundary element 50 can be arranged at a speci fic tilting angle with respect to the substrate body 10 . Alternatively, the lens array 22 can be configured to reali ze the desired light path .

It is apparent to the skilled reader that the determination of location, si ze and movement of one or multiple particles 3 within the probing volume 2 can be performed with all of the embodiments of the system for detecting particles 1 described throughout the figures 1 to 6 .

Figure 7 shows an exemplary embodiment of a particle detector arrangement 100 comprising multiple systems 1 according to the improved concept . In this speci fic embodiment , two systems 1 according to the embodiment of figures 2 to 5 are arranged perpendicular to each other . This way, a multidimensional light curtain is created for determining position and movement of a particle within the probing volume 2 in multiple dimensions , for instance . It is noted, that such a particle detector arrangement 100 can be formed using any of the exemplary embodiments of the system 1 described above . Moreover, a particle detector arrangement 100 can comprise various di f ferent embodiments of the system 1 .

Figure 8 shows a further embodiment of a system 1 according to the improved concept . In this embodiment , both the emitter arrangement 20 and the detector arrangement 30 are formed by a two-dimensional array, e . g . a matrix, of light emitters 21 and light detectors 31 . For example , the emitter arrangement 20 on the bottom substrate body 10 is a display, e . g . a micro-LED display comprising micro-LEDs as light emitters 21 . For example , the display is a commonly available display typically used in mobile devices , for instance . Accordingly, the detector arrangement 30 on the top substrate body 10 is a detector matrix comprising micro photodetectors , such as micro photodiodes as lights detectors 31 . Properties in various embodiments of micro LED displays and micro photodiodes are a well-known concepts and are not further detailed within this disclosure . The embodiment of a system for detecting particles 1 of figure 8 therefore allows for a determination of particles 3 located within the probing volume 2 in a two-dimensional manner . Therein, the concepts explained using the onedimensional arrays of figures 1 to 7 applies without loss of generality to the shown two-dimensional arrays .

Figure 9 shows a further exemplary embodiment of a particle detector arrangement 100 configured as an orientation sensor . In this embodiment , the particle 3 is a round or spherical obj ect , e . g . a disk or a ball , that is free to move within a predefined probing volume 2 , here illustrated as a spherical enclosed space . As the particle 3 is subj ect to gravity, the position detected by the detector arrangement 100 , i . e . by each of the systems 1 , gives information about the orientation of the detector arrangement 100 , and therefore of the device the detector arrangement 100 is employed in . For example , a particle detector arrangement 100 is shown is employed in a mobile device , such as a smartphone , a tablet computer or a laptop, for instance .

The embodiments of the system for detecting particles 1 and the particle detector arrangement 100 shown in the figures represent exemplary embodiments , therefore they do not constitute a complete list of all embodiments according to the improved concept . Actual systems for detecting particles and particle detector arrangements may vary from the embodiments shown in terms of additional components , shape and configuration, for instance . In particular, features shown in the various figures may be combined with each other and hence form additional embodiments according to the improved concept . This patent application claims priority to German patent application 10 2020 127 466.1, the disclosure content of which is hereby incorporated by reference.

Ref e rence symbols

1 system for detecting particles

2 probing volume

3 particle

10 substrate body

20 emitter arrangement

21 light emitter

22 lens array

30 detector arrangement

31 light detector

40 greater array

50 boundary element

60 evaluation circuit

100 particle detector arrangement