Device for detecting particles in air

Abstract

The inventive concept relates to a device for detecting particles in air, said device comprising a receiver for receiving a flow of air comprising particles, a sample carrier, and a particle capturing arrangement. The particle capturing arrangement is configured to separate the particles from the flow of air for and to collect a set of particles on a surface of the sample carrier. The device further comprises a light source configured to illuminate the particles on the sample carrier, such that an interference pattern is formed by interference between light being scattered by the particles and non-scattered light from the light source. The device further comprises an image sensor configured to detect the interference pattern. The device further comprises a cleaner configured for cleaning the surface of the sample carrier for enabling re-use of the surface for collection of a subsequent set of particles.

Claims

1. A device for detecting particles in air; said device comprising: a receiver for receiving a flow of air comprising particles; a sample carrier; a particle capturing arrangement configured to exert a force on the particles in the flow of air such that the particles are separated from the flow of air for collection of a set of particles on a surface of the sample carrier; a light source configured to illuminate the particles collected on the surface of the sample carrier, such that an interference pattern is formed by interference between light being scattered by the particles and non-scattered light from the light source; an image sensor comprising a plurality of photo-sensitive elements configured to detect incident light, the image sensor being configured to detect the interference pattern formed by interference between light being scattered by the particles on the surface of the sample carrier and non-scattered light from the light source; and a cleaner configured for cleaning the surface of the sample carrier for enabling re-use of the surface for collection of a subsequent set of particles.

2. The device according to claim 1, wherein the force exerted on the particles is an electrostatic force.

3. The device according to claim 1, wherein the particle capturing arrangement is configured to provide the sample carrier with a first electrical charge.

4. The device according to claim 3, wherein the particle capturing arrangement comprises an ionizer system configured to provide the particles in the flow of air with a second electrical charge, wherein the first and second electrical charge have opposite signs such that the particles are electrostatically attracted to the surface of the sample carrier.

5. The device according to claim 3, wherein the cleaner is configured to change the sign of the first electrical charge of the sample carrier such that particles previously attracted by the sample carrier are instead repelled.

6. The device according to claim 1, wherein the particle capturing arrangement is configured such that, in the particle capturing arrangement, the particles are transferred from the flow of air by a gravitational force.

7. The device according to claim 6, wherein the particle capturing arrangement comprises a cyclone configured to separate the particles from the flow of air, wherein the particle capturing arrangement is further configured to allow the separated particles to be transferred such that particles land on the surface of the sample carrier.

8. The device according to claim 1, wherein the light source is configured to emit at least partially coherent light.

9. The device according to claim 1, wherein: the light source is arranged at a first side of the sample carrier; and the image sensor is arranged at a second side of the sample carrier, wherein the second side of the sample carrier is opposite to the first side of the sample carrier; wherein the light source, the sample carrier and the image sensor are further arranged to provide a light path from the light source to the image sensor through the sample carrier and through the surface of the sample carrier with the collected set of particles.

10. The device according to claim 1, wherein the device is further configured to define a particle concentration relation, defining a relation between the set of particles on the sample carrier and a concentration of particles in the flow of air.

11. The device according to claim 10, further comprising a processor configured to perform digital holographic reconstruction on the interference pattern detected by the image sensor to generate an image of the set of particles, the device being further configured to: compare the image of the set of particles to one or more characteristics of particles to identify particles in the image, wherein the device is further configured to calculate a concentration of particles in the received flow of air based on a counted number of identified particles in the image of the set of particles and the defined particle concentration relation.

12. The device according to claim 1, wherein the cleaner comprises any one in a group of: a blowing device configured to provide a flow of air such that the particles on the surface are blown off of the surface, a vibration device configured to generate ultrasonic vibrations to the sample carrier such that the particles on the surface are shaken off of the surface, a sweeping device configured to mechanically sweep the surface of the sample carrier such that the particles on the surface are swept off of the surface, and a rotation device configured to turn the sample carrier such that the particles on the surface are pulled off of the surface by a gravitational force.

13. The device according to claim 1, further comprising a processor configured to perform digital holographic reconstruction on the interference pattern detected by the image sensor to generate an image of the set of particles.

14. The device according to claim 13, the device being further configured to: compare the image of the set of particles to one or more characteristics of particles to identify particles in the image.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above, as well as additional objects, features and advantages of the present inventive concept, will be better understood through the following illustrative and non-limiting detailed description, with reference to the appended drawings. In the drawings like reference numerals will be used for like elements unless stated otherwise.

(2) FIG. 1 illustrates a device for detecting particles in air, the device comprising a particle capturing arrangement and a cleaner, according to an embodiment of the inventive concept.

(3) FIG. 2 illustrates a particle capturing arrangement in the form of a cyclone.

(4) FIG. 3 illustrates a device for detecting particles in air, the device comprising particle collection and cleaning based on electrostatics, according to an embodiment of the inventive concept.

(5) FIG. 4 illustrates further details of the imaging components of the device, such as a sample carrier, a light source, an image sensor, and a processor, according to an embodiment of the inventive concept.

DETAILED DESCRIPTION

(6) FIG. 1 illustrates a device 1 for detecting particles in air, according to an embodiment of the inventive concept. The device 1 comprises a receiver 10 for receiving a flow of air 12, wherein the flow of air 12 comprises particles 2. The flow of air 12 enters a particle capturing arrangement 20 via an air inlet 21. In the illustrated embodiment the particle capturing arrangement 20 further comprises a sample carrier inlet 22, an air outlet 23 and a sample carrier outlet 24. In addition to receiving air, the illustrated particle capturing arrangement 20 receives a sample carrier 70 via the sample carrier inlet 22. The particle capturing arrangement 20 then separates at least part of the particles 2 from the flow of air 12 and transfers them to the sample carrier 70. The sample carrier 70, with the transferred particles 2, subsequently leaves the particle capturing arrangement 20 via the sample carrier outlet 24. The set of particles 2 may be all the particles 2 from the flow of air 12 or a subset of the particles 2 from the flow of air 12. The air may leave the particle capturing arrangement 20 via the air outlet 23. The air from the air outlet 23 may comprise particles 2 that were not transferred to the sample carrier 70. The light source 40 is configured to illuminate the set of particles 2 collected on the sample carrier 70. As the particles 2 are illuminated an interference pattern is formed on an image sensor 50, wherein the interference pattern is formed by interference between light being scattered by the set of particles 2 and non-scattered light from the light source 40. The image sensor 50 comprises a plurality of photo-sensitive elements 52 configured to detect incident light. The image sensor 50 may herein be a charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) camera. Moreover, the image sensor 50 is connected to a processor 120 configured to perform digital holographic reconstruction on the acquired image data.

(7) Subsequent to completion of an image acquisition, the sample carrier 70 is transferred to a cleaner 130, configured to clean the surfaces of the sample carrier 70 from collected particles 2 and other unwanted accumulated matter. In the illustrated embodiment the cleaner 130 is a complete unit through which the sample carrier 70 is moved, and which comprises a sweeping device, such as stationary brushes that are arranged such that as the sample carrier 70 is moved through the cleaner 130, the particles 2 and other unwanted accumulated matter are mechanically swept off of the surfaces of the sample carrier 70. Alternatively, it may comprise moving brushes that perform an active sweeping motion to clean the sample carrier 70.

(8) It should be understood that the cleaner may comprise alternative means for cleaning the surfaces of the sample carrier 70.

(9) In alternative embodiments, the cleaner 130 may comprise a blowing device configured to provide a flow of air such that the particles on the surface are blown off of the surface. Such embodiments may be realized by the use of one or more fans, or by connecting the cleaner to a grid with pressurized air.

(10) In other alternative embodiments, the cleaner 130 may comprise a vibration device configured to generate ultrasonic vibrations to the sample carrier such that the particles on the surface are shaken off of the surface. In alternative embodiments, the cleaner 130 may comprise a rotation device configured to turn the sample carrier such that the particles on the surface are pulled off of the surface by a gravitational force.

(11) Although illustrated here as a complete enclosed unit, the cleaner 130 may alternatively be merely a set of cleaning means, e.g. brushes, installed openly with the other parts of the device, without being arranged inside an individual housing.

(12) Subsequent to being cleaned by the cleaner 130, the sample carrier 70 is returned to the sample carrier inlet 22 of the particle capturing arrangement 20, such that the sample carrier 70 can be re-used for a subsequent particle collection event.

(13) The device 1 may comprise a sample carrier 70, which may comprise a single, unitary substrate that may extend through the sample carrier inlet 22, the sample carrier outlet 24, an image acquisition position, and the cleaner 130. Particle collection may be performed on a portion of the substrate before the portion is transferred to the image acquisition position, thereby presenting a new portion of the substrate in the particle capturing arrangement for making a subsequent collection of particles.

(14) However, the device 1 may alternatively, as indicated in FIG. 1, comprise a plurality of substrates 61, which are moved between different positions for particle collection, image acquisition and cleaning.

(15) FIG. 2 illustrates a particle capturing arrangement 20 in the form of a cyclone. The illustrated cyclone receives a flow of air 12 comprising particles 2 via the air inlet 21. The air is subsequently led to a spinner 26 in the form of a chamber with a conical shape. The air then enters the chamber along a tangent of the inner side wall. By following the side walls of the conically shaped chamber the flow of air 12 forms a rotating flow of air 27 which in the illustrated cyclone follows the helical path of a descending vortex towards the narrow end of the chamber. Part of the particles 2 are spun out towards the side walls of the chamber through centrifugal action and fall onto a surface of the sample carrier 70. In the illustrated cyclone the flow of air 12 subsequently continues as an exit flow 29 from the narrow end of the chamber towards the air outlet 23. The flow of air 12 now comprises less or no particles 2. When the particle collection event is completed, the sample carrier 70 along with the collected particles 2, may continue to be transferred out from the particle capturing arrangement 20.

(16) In the illustrated cyclone a particle concentration relation between the concentration of particles in the flow of air 12 entering the inlet 21 and the number of particles collected onto the sample carrier 70, may be set by for example the efficiency of the particle transfer and/or the volumetric flow rate of the air 12.

(17) FIG. 3 illustrates a device 1 for detecting particles in air, the device comprising particle collection and cleaning based on electrostatics, according to an embodiment of the inventive concept. The device 1 comprises a receiver 10 for receiving a flow of air 12 with particles 2. The flow of air 12 enters a particle capturing arrangement 20 further comprising an ionizer 140 configured to provide the particles 2 with a negative electrical charge. The particle capturing arrangement 20 further receives a sample carrier 70 which is connected to an electric circuit 150. The electric circuit is configured to provide a surface of the sample carrier 70 on which particles are to be collected with a positive electric charge. The negatively charged particles 2 in the flow of air 12 are consequently attracted to the positively charged surface of the sample carrier 70, and are thus pulled towards the sample carrier 70. In this manner, the particle capturing arrangement 20 separates at least part of the particles 2 from the flow of air 12 and collects them on the sample carrier 70. The sample carrier 70, with the collected particles 2, subsequently leaves the particle capturing arrangement and is positioned between the light source 40 and the image sensor 50. As the particles 2 are illuminated by the light source 40, the resulting interference pattern is acquired by the image sensor 50.

(18) Subsequent to completion of the image acquisition, the sample carrier 70 is transferred to a cleaner 130, configured to clean the surfaces of the sample carrier 70 from collected particles 2. In the illustrated embodiment the cleaner 130 comprises an electric circuit 150 configured to provide the sample carrier 70 with a negative electric charge. The negatively charged particles 2 that were previously attracted to the positively charged sample carrier 70 are now repelled by the negatively charged sample carrier 70, and are thus pushed away from the sample carrier 70. In this manner, the sample carrier 70 is cleaned from the particles 2.

(19) It should be understood that the electric circuit 150 may be either an integrated part of the sample carrier 70, or the electric circuit 150 may be a stand-alone unit that follows the sample carrier 70 when circulating in the device 1. The electric circuit 150 in the cleaner 130 is thus the same electric circuit 150 as in the particle capturing arrangement 20. The circuit may therefore be configured to provide the sample carrier 70 with negative charge in a first mode and positive charge in a second mode, and configured to switch between the first and the second modes, depending on whether particle collection or cleaning is called upon. Alternatively, the electric circuit 150 in the cleaner 130 may be a different electric circuit 150 from the electric circuit in the particle capturing arrangement 20.

(20) FIG. 4 illustrates further details of the imaging components of the device 1, such as the sample carrier 70, the light source 40, the image sensor 50, and a processor 120, according to an embodiment of the inventive concept. The sample carrier 70 is configured to provide a light path from the light source 40 to the image sensor 50 through sample carrier 70. This may be accomplished e.g. using a transparent sample carrier 70. In the illustrated embodiment, the non-scattered light from the light source 40, i.e. the reference light, is passed along a common optical path with the light being scattered by the particles 2, i.e. the object light. Thus, the interference pattern is formed within a wavefront passing the particles 2 and the sample carrier 70 in a so-called in-line holography set-up.

(21) In FIG. 4 the image sensor 50 is connected to a processor 120 configured to perform digital holographic reconstruction on the interference pattern detected by the image sensor 50 to generate an image of the set of particles 2. Any suitable algorithm for performing the digital holographic reconstruction may be used, as known to the person skilled in the art, including a Gerchberg-Saxton algorithm or multi-acquisition (multi-depth and/or multi-wavelength) for phase retrieval, or reconstruction based on angular spectrum diffraction by means of Gabor wavelet transform. The processor 120, or another processor, may then identify particles 2 in the image and subsequently count the identified particles 2.

(22) The processor 120 may be implemented as a processing unit, such as a central processing unit (CPU), which may execute the instructions of one or more computer programs in order to implement functionality of the processor 120.

(23) The processor 120 may alternatively be implemented as firmware arranged e.g. in an embedded system, or as a specifically designed processing unit, such as an Application-Specific Integrated Circuit (ASIC) or a Field-Programmable Gate Array (FPGA), which may be configured to implement functionality of the processor 120.

(24) A surface concentration of particles 2 in the sample carrier 70 may be calculated from the counted number of particles 2 in the image and the surface area of the sample carrier 70 that the illumination from the illumination source 40 and the image sensor 50 jointly cover. However, a surface concentration of particles may be calculated from the counted number of particles 2 in a plurality of images to achieve a statistically accurate result. The surface concentration of particles 2 may subsequently be used to determine a concentration of particles 2 in the flow of air 12, corresponding to the concentration in the air at the receiver 10 of the device 1. The concentration of particles 2 in the flow of air 12 may be calculated based on the surface concentration of particles 2 based on one or more of the sample carriers 70 and the particle concentration relation.

(25) As the SNR of the detected interference pattern may decrease with increasing distance between the image sensor and the scattering particle 2, it may be advantageous if the distance between the set pf particles 2 collected on the sample carrier 70 and the image sensor 50 is below a distance threshold. It should therefore be understood that it may be advantageous with a sample carrier 70 close to the image sensor 50, e.g. in immediate proximity of the image sensor. It should be understood that in this respect FIG. 1, FIG. 3 and FIG. 4 should be interpreted as schematic illustrations, wherein the sample carrier 70 is illustrated some distance away from the image sensor 50 for the sake of clarity.

(26) The embodiments of the inventive concept presented above may be applied for a number of different purposes aiming at monitoring particles in interior and exterior air. The particles may be any type of air-borne particulate matter such as pollen, dust, soot, air-borne bacteria, or fungi. There is provided a device for detecting particles in air and determining if the collected particles are particles of interest. The concept allows a high measurement frequency and has a potential of performing automated measurements.

(27) Further, it may be capable of classifying or determining the type of particle collected.

(28) Outdoor applications may be monitoring of exterior air quality for detection of pollen, dust, soot, or other pollutants.

(29) According to an embodiment, a device for detecting pollen in air is provided. Thanks to the present inventive concept, pollen levels in exterior air may be monitored with a high frequency, and with the potential of performing automated measurements. It may also provide measurement stations at a low cost, which may lead to an increased number of measurement stations. This in turn may have the potential of providing more up-to-date and geographically more precise information on pollen levels in exterior air, which may be valuable to people that are affected by pollen allergies.

(30) Indoor applications may be monitoring interior air quality for detection of molds, fungi, pollen, dust, or bacteria. Such monitoring can be applied in a variety of locations, such as public shopping malls, hospitals or laboratories.

(31) Monitoring of air-borne bacteria may be of particular importance in aseptic environments, such as the manufacturing environment for pharmaceutical production. Monitoring of air-borne bacteria in interior air may be required to ensure a sterile manufacturing environment.

(32) Presence of bacteria in the manufacturing environment of pharmaceutical products may contaminate the products and force the products manufactured in a contaminated environment to be disposed. Thus, early detection of presence of bacteria may be highly advantageous, because if production in a contaminated environment is continued, a large quantity of products may have to go to waste.

(33) According to an embodiment, a device for detecting bacteria in air is provided. Thanks to the present inventive concept, bacterial levels in interior air may be monitored with a high frequency, and with the potential of providing results in real-time. As soon as bacterial levels are detected, the production may be stopped such that no or very little of the pharmaceutical products will go to waste.

(34) Moreover, the real-time aspect of the present inventive concept further allows for monitoring of development of bacterial levels over time, by acquiring time sequences of measurements. In this manner bacterial growth may be studied.

(35) In the above the inventive concept has mainly been described with reference to a limited number of examples. However, as is readily appreciated by a person skilled in the art, other examples than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.