Abstract:
Methods and systems for sorting particles entrained in a gaseous stream are disclosed. A representative system, among others, includes a particle scanner, a sorter, which is in pneumatic communication with the particle scanner, and a controller, which is in electrical communication with the particle scanner and sorter. The particle scanner is adapted to receive a gaseous stream and measure a characteristic of a particle entrained in the gaseous stream. The controller is adapted to classify the scanned particle according to the measured characteristic of the particle. The sorter includes an electrically controlled valve. Responsive to the particle being classified as belonging to a first category, the controller signals the valve to deflect the trajectory of the particle. 
     A representative method, among others, for sorting particles entrained in a gaseous stream can be broadly summarized by the following steps: receiving particles in a gaseous stream; classifying a particle from the received stream of particles according to a property of the particle, wherein the particle is classified as belong to one category of a plurality of categories, and wherein the received particle has an initial trajectory; and responsive to the particle being classified as belonging to a first category of the plurality of categories, altering the trajectory of the particle.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a Continuation-In-Part of U.S. utility patent application entitled “Method and Instrumentation for Measuring Fluorescence Spectra of Individual Airborne Particles Sampled From Ambient Air” filed on Jun. 19, 2002, and accorded Ser. No. 10/360,767, now U.S. Pat. No. 6,947,134 which is a Continuation-In-Part of U.S. utility application accorded Ser. No. 09/579,707 filed May 25, 2000, which issued as U.S. Pat. No. 6,532,067 on Mar. 11, 2003, which in turn claims priority to U.S. provisional application accorded Ser. No. 60/147,794 filed Aug. 9, 1999, all of which are entirely incorporated herein by reference. 

   GOVERNMENT INTEREST 
   The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without the payment of any royalties thereon. 

   BACKGROUND 
   1. Technical Field 
   The present invention is generally related to the sorting of particles. 
   2. Description of the Related Art 
   The collection and monitoring of particles separated from a gas is needed in many diverse situations. Some of these situations include defense against biological warfare agents in battlefield and other military applications; and protecting the general public against: airborne pathogenic agents released by terrorist groups; genetically modified material used in biotechnology applications; infectious organisms contaminating air in hospitals, research labs, public buildings, and confined spaces such as subway systems; and pollutant aerosols that damage the respiratory system. The collection and measurement of infectious organisms are of interest to a wide community of public health officials because they can cause infectious diseases or chemical damage to the respiratory system. These particles are also of concern to the Department of Defense (DOD) because of their possible use in biological warfare and terrorism. 
   Air quality monitoring is also an important public health need. As the world&#39;s population rises and world travel becomes increasingly easy, the degree and pace at which communicable diseases can spread has resulted in significant concerns regarding potential epidemics from airborne disease transmission. Recirculation of air in buildings and other enclosed spaces such as subways and airplanes has lead to a potentially significant public health issues. Identification and control of infectious disease organisms in hospitals represents another major need. The Environmental Protection Agency cites indoor air pollution causing “sick building syndrome” as a major environmental problem in the United States. 
   Threats from microorganisms in the air as a result of natural phenomena or human-induced activities such as the examples discussed above cannot be adequately monitored and evaluated with current technology. Early warning, hazard recognition, personal protective equipment, exposure evaluation, and environmental monitoring are needed to prevent and reduce impacts from airborne infectious or genetically modified material. Near real-time monitoring is necessary to avoid exposure and to initiate early treatment to arrest disease progression. 
   SUMMARY 
   Systems and methods for sorting particles in a gaseous stream are provided. Briefly described, one embodiment of an apparatus includes a scanner, a sorter, which is in pneumatic communication with the scanner, and a controller, which is in electrical communication with the scanner and sorter. The scanner is adapted to receive a gaseous stream and measure a characteristic of a particle entrained in the gaseous stream. The controller is adapted to classify the scanned particle according to the measured characteristic of the particle. The sorter includes an electrically controlled valve. Responsive to the particle being classified as belonging to a first category, the controller signals the valve to deflect the trajectory of the particle. 
   An embodiment of a method can be broadly summarized by the following steps: receiving particles in a gaseous stream; classifying a particle from the received stream of particles according to a property of the particle, wherein the particle is classified as belong to one category of a plurality of categories, and wherein the received particle has an initial trajectory; and responsive to the particle being classified as belonging to a first category of the plurality of categories, altering the trajectory of the particle. 
   Other systems, methods, features, and/or advantages will be or may become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and/or advantages be included within the description and be protected by the accompanying claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The components in the drawings are not necessarily to scale. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
       FIG. 1  is a block diagram of an embodiment of an aerosol particle sorter system (APSS). 
       FIG. 2  is a block diagram of an embodiment of a particle scanner. 
       FIG. 3  is a block diagram of an embodiment of a particle sorter. 
       FIG. 4  is a block of a second embodiment of a particle sorter. 
       FIG. 5  is a block diagram of an embodiment of an aerosol particle sorter system (APSS) including a particle diluter assembly. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , an embodiment of a aerosol particle sorter system (APSS)  10  includes components such as a particle scanner  12 , a controller  14 , a particle sorter  16  and a pump  18 , which are approximately longitudinally aligned and which approximately define a longitudinal axis  20 . The APSS  10  is immersed in a gas  22 , such as the atmosphere, having particles  24  therein. The pump  18  draws gas and particles into the APSS  10  through an induction port  26  and exhausts at least the gas out of an eduction port  28 . Generally, the particles  24  include many types of particles, which may be classified into predetermined categories. For example, all of the particles of type  24 (A) can belong to category  1 ; all of the particles of type  24 (B) belong to category  2  and so on. 
   Gas  22  and particles  24  are drawn from the induction port  26  into the particle scanner  12 . The particle scanner  12  scans the particles  24  as the particles flow through the particle scanner  12 . From the particle scanner  12 , the gas  22  and particles  24  flow into the particle sorter. The pump  18  draws the gas through the particle sorter  16  and exhausts at least the gas  22  through the eduction port  28 . 
   As particles  24  are drawn through the particle scanner  12 , the particles pass through region  31 , which is known as the scan zone. When a particle in the scan zone  31 , the particle scanner  12  measures physical and/or optical properties or characteristics of the scanned particles  24  while the particles are in a scan zone  31 . The measured quantities are provided to the controller  14  via an electrical connection  32 . 
   The controller  14  includes a processor  34  and a particle characteristic database  36 . The particle characteristic database  36  includes known physical and/or optical properties of various particles. The processor  34  uses the measured quantities reported by the particle scanner  12  to determine whether a scanned particle belongs to a category of particles and whether the category of particles is one of interest. Generally, particles of interest are sorter from uninteresting particles, and the other particles exit the APSS  10  via the eduction portion  28 . 
   Whether or not a particle is of interest or not depends upon the category of the particle, and categories are established by the operator of the APSS  10 . Having identified a particle of interest, the controller  14  sends a trigger signal to the particle sorter  16 , via an electrical connection  38 , which prompts the particle sorter  16  to sort particles of interest from other particles when the particles of interest are in a target zone  39 . 
   Generally, the APSS  10  is used to sort airborne particles and, in that case, the mean velocity (v) of the particles through the APSS  10  is governed by the pump  18 . The distance (D) between the scan zone  31  and the target zone  39  is fixed and known. Consequently, the time (t) for a particle of interest to traverse the distance D is simply D divided by v(t=D/v). The controller  14  triggers the particle sorter  16  at the appropriate time such that the particle of interest is in the target zone. In some embodiments, the controller  14  calculates the delay time between when a particle is in the scan zone  31  and when it is in the target zone  39 . In some alternative embodiments, the operator of the APSS  10  provides the delay time to the APSS  10 . 
   In some embodiments, the APSS  10  is used to sort particles when there is no gas flow through the instrument, i.e., particles that are not carried by an airflow through the instrument, but instead fall through the instrument because of gravitational acceleration. In this embodiment, the APSS  10  is aligned generally vertically and the particle scanner  12  detects a particle at two or more different vertical locations. The controller  14  then determines the velocity of the particle. In some embodiments, the controller  14  can also determine the acceleration of the particle. Generally, the acceleration is not necessary because the particles are normally falling at their terminal velocity. The controller  14  is adapted to determine the delay time between when a particle is scanned and when it is in the target zone  39  so that particles of interest can be sorted. 
   Generally, the APSS  10  is used to sort airborne particles whose drift rate through the APSS  10  is approximately that of the gas. In some embodiments, the pump  18  induces a drift rate of approximately 10 meters per second through the APSS  10 . The controller  14  knows the drift rate (10 m/sec.) and the longitudinal position of where particles are scanned and the longitudinal position of where particles are sorted. Thus, for the case of particles having constant velocity, the trigger signal for sorting a given particle is a known constant delay from the time at which the particle is scanned. 
   Referring to  FIG. 2 , which illustrates components of the particle scanner  12  as seen from above, particles entrained within a stream of air are drawn into the particle scanner  12  and are directed downward toward the scan zone  31 . The scan zone  31  is defined by two nearly orthogonal, different-wavelength laser trigger beams (Lasers  110 (A) and  110 (B)), which are aimed and focused precisely to define an approximate 15-μm diameter focal volume position just upstream (about 50 micron) of a first focal plane of reflecting objective  130 . In some embodiments, the lasers  110 (A) and  110 (B) are diode lasers  1  and  2 , respectively, which respectively emit light at 670 and 635 nm. 
   As a particle  24  passes through the intersection of trigger beams from lasers  110 (A) and  110 (B) (defined as the trigger volume), light is scattered from the particle  24  and is detected by photomultipliers (PMTs)  140  and  150 . PMT  140  is equipped with a narrowband interference filter such that it only detects light scattered from the trigger beam from laser  110 (A). 
   Likewise, PMT  150  is equipped with a narrowband interference filter so that it may only detect scattered light from the trigger beam from diode laser  110 (B). The intensity of the scattered light may be approximately proportional to the size of the particle. To avoid detection of particles outside the size range of interest, the output signals from PMTs  140  and  150  are processed by a pair of single channel analyzers (SCA)  160  and  170  which operate as discriminators in a window mode. 
   The PMT output pulses must exceed a preset lower voltage level and be less than a preset higher voltage level (as set in the window mode) before the SCA may provide an output pulse. Thus, fluorescence spectra are measured only for particles falling within a preset size interval. 
   The two SCA outputs are fed into a logic AND gate  180 , which produces an output pulse only when the SCA output signals overlap. The output of AND gate  180  triggers a probe laser  190  to fire and also turns on a camera controller  195 , which activates the a camera  197  to record only when the probe laser  190  fires. Thus, particles not flowing through trigger volume  131 , which would not be illuminated by the central portion of the beam from the probe laser  190 , and which are not in the focal region of reflecting objective  130 , are ignored. In some embodiments, the probe laser  190  is a Q-switched UV laser. 
   The system is completed by spectrograph  196  with long pass filter  198 , which disperses the fluorescence to camera  197  and camera controller  195 . The output of camera controller  195  is fed to the controller  14  where data may be displayed, stored and analyzed. In particular, pattern recognition algorithms are employed by the controller  14  to detect and classify the particles  24 . 
   Various modifications and alternatives are possible. For example, in an alternative embodiment, leakage of scattering from trigger beams from lasers  110 (A) and  110 (B) may be eliminated by signaling the lasers to turn off using the same signal from the logic circuit as is used to trigger the probe laser  190 . Probe laser  190  is preferably a tightly focused pulsed UV laser triggerable on demand and of sufficiently high intensity or fluency to excite fluorescence in microparticles. 
   In a preferred embodiment, probe laser  190  is a Q-switched UV laser, either 266 nm, 4th harmonic of a Nd:YAG laser, 30- or 70-ns pulse duration, 0.1 to 0.2 mJ per pulse (Spectra Physics models X-30 or Y-70), or 351 nm, 3rd harmonic of a Nd:YLF laser, 120 ns pulse duration, 1.65 mJ per pulse (Quantronix). The Q-switched laser was set to fire within approximately 3 microseconds of the trigger pulse (from the AND circuit), during which time the particle traveled (at a speed of about 10 m/s) about 30 micrometers. Various other probe lasers may be employed, depending on the type of particle and fluorescence to be detected. 
   The vertical displacement between the location where the particle is detected (trigger volume) and the location where the particle is probed (detection volume) can be compensated for by a small vertical displacement of the focal volume of trigger beams from lasers  110 (A) and  110 (B) and the beam from probe laser  190 , which is focused at a focal plane of the reflecting objective. 
   Alternatively, the displacement of these two volumes may be compensated for by a variable electronic delay, with the delay based on the speed at which particles are introduced into the focal volume. 
   In some embodiments, multiple-wavelength excitation (e.g., one wavelength within the absorption band for tryptophan, and a longer wavelength for other biological molecules) may be used to better identify biological particles. 
   Reflecting objective  130  preferably has a large numerical aperture that can collect fluorescence from the emitting particle over a large solid angle, and focus it onto the slit of a spectrograph without chromatic aberration. In a preferred embodiment, reflective objective  130  (a so-called Schwartzchild reflecting objective) is manufactured by the Ealing Company and has numerical aperture 0.5. 
   Alternatively, the sensitivity of the particle scanner  12  may be increased by adding a spherical reflector on the side opposite the Schwartzchild objective, or by replacing the Schwartzchild reflective objective  130  with a parabolic or ellipsoidal reflector. With this modification, particles would be excited to fluoresce when they traverse the focal point of the reflector. The parabolic reflector would collect the fluorescence, which would be focused onto the slit of spectrograph  196  as with the Schwartzchild reflecting objective. The ellipsoidal reflector may collect the fluorescence and focus it onto the slit of the spectrograph  196  positioned at the second focal point of the mirror. 
   In another embodiment, the camera  197  is manufactured by Princeton Instruments. Camera  197  is placed at the exit port of the spectrograph  196  (an Acton model SP-150 with 300 groove/mm grating blazed at 500 nm, numerical aperture 0.125, input slit width 1 mm). The image intensifier of camera  197  acts as a fast shutter, opening when the targeted particle is illuminated by the UV laser. A long pass filter  198  is placed in front of spectrograph  196  to block elastically-scattered light and to pass the fluorescence. 
   In another embodiment, the camera  197  is a multiple-channel photomultiplier tube (PMT), and the camera controller  195  is manufactured by Vtech. However, in alternative embodiments, a multiplexer can also be used. A multiple-channel PMT provides the advantages of comparable sensitivity, compactness, lighter weight, and lower cost, as compared to other controllers such as an intensified charge coupled device controller. A 32 channel system provides sufficient spectral resolution to classify bioaerosol particles and provides for rapid sampling of aerosol particles and portability. 
   Further details of a particle scanner  12  can be found in U.S. patent application Ser. No. 10/360,767, which is hereby incorporated by reference. In addition further details regarding fluorescence of ambient aerosols including biological particles can be found in the following publications, which are hereby incorporated by reference: “Fluorescence Spectra of Atmospheric Aerosol at Adelphi, Md., USA: Measurement and Classification of Single Particles Containing Organic Carbon,” Atmospheric Environment, 38, 1657-1672 (2004), Pinnick, Ronald G.; Hill, Steven C.; Pan, Young-le; Chang, Richard K.; and “Single-Particle Fluorescence Spectrometer for Ambient Aerosols,” Aerosol Science and Technology 37:627-638 (2003), Pan, Yong-le; Hartings, Justin; Pinnick, Ronald G.; Hill, Steven, C.; Halverson, Justin; Chang, Richard K. 
     FIG. 3  illustrates a first embodiment of the particle sorter  16 . In this embodiment, the particle sorter  16 (A) includes particle receptors  40 (A) and  40 (B), and a particle deflector  42 . The particle receptors  40  are in pneumatic communication with the pump  18 . The dashed lines  44  and  46  represent two different trajectories, trajectory I and trajectory II, respectively, for particles  24 . Particles classified as belonging to category  1  travel generally along trajectory I and particles classified as belonging to category  2  travel generally along the trajectory II. 
   In the embodiment illustrated in  FIG. 3 , particles  24 (A) are in category  1  and are the type that are of interest. It is desired that these particles be separated from other particles in the gas  22 . The particle receptor  40 (A) includes a valve  48 (A) and a filter  50 . The valve  48 (A) generally remains closed until it is triggered by the controller  14  to open. The filter  50  is adapted to filter particles  24 (A) out of the gas. 
   The particle receptor  40 (B) also includes a valve  48 (B). The valve  48 (B) remains generally open unless it is triggered by the controller  14  to close. Generally, one of the valves  48 (A) or  48 (B) is open while the other valve is closed, and the controller  14  causes the valves  48 (A) and  48 (B) to reciprocate back and forth between open and closed depending upon which category of particle is currently being sorted. 
   The particle deflector  42  includes a pump  52 , pressurized gas canister  54 , a valve  56  and a nozzle  58 . The pump  52  pumps gas into the gas canister  54  so that the gas canister  54  remains pressurized. 
   The valve  56  is in pneumatic communication with the gas canister  54  and in electrical communication with the controller  14 . Upon receiving a triggering signal from the controller  14 , the valve  56  opens and releases pressurized gas from the gas canister  54 . In another embodiment, the valve  56  is a current-loop actuated (CLA) pulse wave valve such as a Pulsed Supersonic Valve C-211 by RM Jordan, Inc, Grass Valley, Calif. In yet another embodiment, the valve  56  is a piezo-electric valve or a solenoidal valve, which are known to those skilled in the art. Generally, the valve  56  is adapted to operate, open and close, up to approximately 500 times a second or more. Currently, the Pulsed Supersonic Valve C-211 can be operated to be open for pulse lengths as short as 20 microseconds. The scope of the present invention is intended to include any valve adapted to be electrically controlled. 
   The nozzle  58  is affixed to the valve  56  and gas released from the gas canister  54  flows through the nozzle  58  into the particle sorter  16 (A). The nozzle  58  is aligned such that the released gas is directed towards the target zone  39  and such that the initial trajectory of the released gas is approximately perpendicular to the longitudinal axis  20  of the APSS  10 . 
   At the appropriate time, the controller  14  sends a trigger signal to the valve  56  and the valves  48 (A) and  48 (B). Responsive to the trigger signal, the valve  48 (A) opens and the valve  48 (B) closes, thereby causing gas to flow through the particle receptor  40 (A) and preventing gas from flowing through the particle receptor  40 (B). The valve  56  opens responsive to receiving the trigger signal, thereby causing a burst of gas  62  to be released from the gas canister  54 . The gas  62  deflects the trajectory of a target particle  60 (A). The valves  48 (A) and  48 (B) remain in their current state until the particle  60 (A) has entered the particle receptor  40 (A), and then they reciprocate. In other words, if particle receptor  40 (A) is a first particle receptor and particle receptor  40 (B) is a second particle receptor, when target particle  60 (A) is deflected toward first particle receptor  40 (A), it is simultaneously deflected away from particle receptor  40 (B). The controller  14  controls how long the valves  48  remain in a given state and how long the valve  56  remains open. 
   In some embodiments, particles are sorted by deflecting the trajectory of the particles using merely the valves  48 (A) and  48 (B). In this embodiment, when a particle of interest is in the target zone  39 , the valve  48 (A) is opened and the valve  48 (B) is closed. The valves remain in that configuration until the particle of interest has been drawn into the particle receptor  40 (A), and then, the valves reciprocate. 
   In some embodiments, the particles are sorted by the particle deflector  42  merely deflecting the trajectory of selected particles. In this embodiment, the particle sorter  16 (A) does not include valves  48 , or if the valves  48  are present, they remain open, and in either case, the pump  18  draws gas through the particle receptors  40 (A) and  40 (B) simultaneously. When a particle of interest is in the target zone  39 , the controller  14  triggers the particle deflector  42 , which then emits the burst of gas  62 , thereby deflecting the particles of interest such that the particles of interest flow into the particle receptor  40 (A). 
     FIG. 4  depicts a top view of another embodiment of the particle sorter  16 . The trajectory of a target particle  60 (B) is into the page. The particle sorter  16 (B) includes a plurality of particle deflectors  64  and multiple particle receptors  66 . In this embodiment, the particle receptors  66 (A),  66 (C) and  66 (D) are all for receiving particles whose trajectories have been deflected by at least one of the particle deflectors  64 , and the particle receptor  66 (B) is for receiving particles whose trajectories have not been deflected. The particle deflectors  64 (A) and  64 (B) are used to deflect particles towards the particle receptor  66 (C). The particle deflector  64 (A) is used singularly to deflect particles towards the particle receptor  66 (A) and the particle receptor  64 (B) is used to deflect particles towards the particle receptor  66  (D). As those skilled in the art will recognize, the particle sorter  16 (B) can include more particle receptors  66  and more particle deflectors  64 . In another embodiment, the particle deflectors are positioned in the particle sorter  16 (B) at different longitudinal locations. In that case, the particle deflectors  64  that are longitudinally farthest from the particle receptors  66  deflect the particles that require the most amount of deflection, and the particle deflectors  64  that are longitudinally closest to the particle receptors  66  deflect the particles that require the least amount of deflection. 
   In some embodiments, the controller  14  controls not only how long the valve  56  of the particle deflector remains open, but also the escape velocity of the emitted gas  62 . Such control of escape velocity is normally accomplished by controlling the pressure in the pressurized gas canister  54 . Controlling the escape velocity provides a means for determining the amount of deflection that a given particle should receive. In this embodiment, the pump  52  is in electrical communication with the controller  14  such that the controller  14  can control the amount of pressure in the gas canister  54 . 
   Referring to  FIG. 5 , in some embodiments, the APSS  10  includes a particle diluter assembly  68 . The particle diluter assembly  68  attaches to the induction port  26  and is in electrical communication with the controller  14  via electrical connectors  70  and  72 . 
   The particle diluter  68  includes a counter assembly  74  and a dilution chamber  76 , which are in pneumatic communication via a connecting pipe  78 . Particles  24  and gas  22  are drawn into the counter assembly via an induction port  80 . The counter assembly  74  counts the particles  24  as they are drawn into the counter assembly  74  and communicates the particle count to the particle controller  14  via the electrical connection  70 . From the counter assembly  74  the particles flow into the dilution chamber  76  via the connecting pipe  78  and through the induction port  26 . 
   The dilution chamber  76  includes a dilution port  82  having a valve  84  and a filter  86  therein. If the particle current density in the particle sorter  16  is too great, then the particle sorter  16  can not effectively sort particles. To prevent this from happening, the controller  14  monitors the particle flux in the particle counter assembly  74 , and when the particle flux reaches a predetermined level, the controller  14  opens the valve  84 , thereby allowing gas to enter into the dilution chamber  76 . The filter  86  is adapted to filter particles out of the gas flowing through the dilution port  82  such that clean gas dilutes the particle current density in the dilution chamber  76 . 
   In some embodiments, the induction port  80  also includes a valve (not shown) which is in electrical communication with the controller  14 . The controller  14  controls the particle current density in the APSS  10  by appropriately controlling the amount of gas and particles flowing through the induction port  80  and the amount of gas flowing through the dilution port  82 . 
   In some embodiments, the pump  18  is a variable pump that is adapted to pump gasses at various rates, and the pump  18  is controllable by and in communication with the controller  14 . The controller  14  uses the variable pump  18  to control the rate at which airborne particles flow through the APSS  10 . By controlling the rate (velocity) at which gas and particles  24  are drawn into and through the APSS  10 , the controller  14  controls the rate at which particles enter the target zone  39 . Thus, the controller  14  can use the pump  18  to control the rate at which particles enter the target zone  39  of the particle sorter  16  such that the particle sorter  16  does not become swamped with more particles than it can handle. A variable pump can be used in conjunction with the particle diluter assembly  68  or independently thereof. 
   It should be emphasized that the above-described embodiments are merely possible examples of implementation. Many variations and modifications may be made to the above-described embodiments. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.