Abstract:
An aerodynamic sampler for sampling particles from a surface or a flowing gas stream is provided. The sampler can include an arcuate-shaped shroud having a first opening and a second opening, the first opening being directed in a first direction and the second opening oppositely disposed and spaced apart from the first opening. A gas nozzle having at least one gas outlet directed generally in the first direction can be included and may or may not be located at least partially within the shroud. The gas nozzle is operable to supply a gas jet to a surface that is proximate the first opening of the shroud. In addition, a suction device operable to pull or suck the gas proximate the first opening through the second opening and afford for the gas to enter a detector is provided. The arcuate-shaped shroud can be a bell-shaped shroud with the first opening located at a bottom of the bell-shape.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 60/944,923 filed on Jun. 19, 2007, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to devices for obtaining samples for analysis and more particularly to an aerodynamic sampler for chemical and/or biological trace detection. 
     BACKGROUND OF THE INVENTION 
     Modern chemical detectors, such as artificial (electronic) noses, ion-mobility spectrometers, gas chromatographs and the like, have evolved such that miniaturized and hand-held, briefcase-sized-or-smaller chemical trace detectors are now available. If chemical signals are thoroughly dispersed in the atmosphere (e.g. nitrogen compounds in city smog), the application of a small suction at a device inlet can be sufficient to bring chemical traces to bear upon the sensor, thus affording the possibility of a detection step. However, many other cases exist where aerodynamic sampling is required before detection can occur. Canines, for example, are natural chemical trace detectors with a built-in aerodynamic sampler, the slit canine nostril [1], that is positioned in proximity to a trace chemical source with sampling and subsequent detection occurring, or that samples chemical plumes carried by the natural wind. Similarly, an active, air-moving sampler is required to “reach out” from a manmade hand-held or otherwise mobile detector in order to acquire vapor and/or particulate traces from surfaces being sampled. 
     There has been a variety of attempts to provide aerodynamic samplers. The potential-flow suction inlet is well known in fluid dynamics with the application of that science to heating, ventilation and air conditioning documented in many textbooks, e.g. [2]. The potential-flow suction inlet can take on several forms such as a blank tube, flanged tube, bellmouth inlet, etc. However, the “reach” of the potential-flow suction inlet is severely limited by the nature of potential flow. To overcome this limitation, scenting animals have developed long noses and the mobility to position them in close proximity to a scent source [1]. 
     Another approach to aerodynamic sampling uses an intake vortex. Helmholtz&#39;s vortex laws reveal that a line vortex cannot end in free air, but it can attach to a solid surface. For example, jet engines can “suck up” rubble from runways through vortex impingement [3] and a tornado represents a vortex tube that attaches to the ground and extends powerful suction due to the low pressure in the vortex core. The vortex concept has been disclosed in relation to a sampling device with a small tornado-like swirling flow that may “reach out” to a surface and convey vapor/particulate traces from the surface to a sensor element of a trace detector [4]. The upward axial flow along the vortex core transports a trace sample to the inlet of the device, where suction applied to a small central tube captures some of the trace-bearing airstream. Thereafter, the trace-bearing airstream can be interrogated for chemical content by a suitable trace detector such as an ion mobility spectrometer (IMS). 
     SUMMARY OF THE INVENTION 
     An aerodynamic sampler for sampling particles from a surface or a flowing gas stream is provided. The sampler can include an arcuate-shaped shroud having a first opening and a second opening, the first opening being directed in a first direction and the second opening oppositely disposed and spaced apart from the first opening. A gas nozzle having at least one gas outlet directed generally in the first direction can be included and may or may not be located at least partially within the shroud. The gas nozzle is operable to supply a jet of gas to a surface that is proximate the first opening of the shroud. In addition, a suction device operable to pull or suck or otherwise induce a flow of the gas proximate the first opening through the second opening and afford for the gas to enter a detector is provided. The arcuate-shaped shroud can be a bell-shaped shroud with the first opening located at a bottom of the bell-shape. 
     In some instances, the suction device is provided by a fan or blower, while in other instances the suction device is provided by a second gas nozzle that provides a flow of gas in the second direction. Other gas movers may be used, e.g. a positive-displacement pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a first embodiment of an aerodynamic sampler according to the present invention; 
         FIG. 2  is a side view of a second embodiment of an aerodynamic sampler according to the present invention; 
         FIG. 3  is a side view of a third embodiment of an aerodynamic sampler according to the present invention; 
         FIG. 4  is a side view of a fourth embodiment of an aerodynamic sampler according to the present invention; 
         FIG. 5  is a side view of a fifth embodiment of an aerodynamic sampler according to the present invention; 
         FIG. 6  is a side view of a sixth embodiment of an aerodynamic sampler according to the present invention; 
         FIG. 7  is a side view of a seventh embodiment of an aerodynamic sampler according to the present invention; 
         FIG. 8  is a side view of an eighth embodiment of an aerodynamic sampler according to the present invention; and 
         FIG. 9  is a side view of a ninth embodiment of an aerodynamic sampler according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Research experience at the Penn State University Gas Dynamics Laboratory and elsewhere has demonstrated that trace contaminants are effectively dislodged from a surface (e.g. from people&#39;s clothing) by a brief turbulent jet impact [8, 9]. It is known to those in the art that shear stress generated by the jet impact in a direction parallel to the surface being sampled is active in detaching trace-bearing particles from that surface. It is also known that the jet impact “rolls out” along the impacted surface in a “starting vortex” [10] and forms a “wall jet” that can be made to separate from the impacted surface. Capturing the wall jet by suction through an appropriately designed “shroud” can thus afford for a particulate and/or a vapor signal dislodged from the surface to be examined. Such an airborne sampling process can be quite brief (e.g. milliseconds) such that a volume of air sampled is small and can avoid the need for undue pre-concentration. It is thus possible to interrogate the volume of air sampled directly, e.g. using an ion mobility spectrometer (IMS) detector, with appropriate concern for the desorption of trace chemicals from any particles that are captured. 
     Turning now to  FIG. 1 , a first embodiment of an aerodynamic sampler  10  according to the present invention is shown. This embodiment may be referred to as a jet-puff sniffer, the sniffer  10  including an outer, properly-shaped, duct or shroud  12  and an outlet nozzle  14  disposed inside the shroud. In the alternative, a second embodiment wherein an outlet nozzle  14 ′ is disposed outside the shroud  12  is shown in  FIG. 2 . Furthermore, it is appreciated that the nozzle  14  shown in  FIG. 1  is positioned along a central axis of the shroud  12 , however this is not required. 
     A source of compressed gas  18 , illustratively including compressed air, nitrogen, argon, oxygen and the like, is connected to the outlet nozzle  14  to provide a jet  19 , namely a pulse of gas, to a sampling surface S. In some instances, the jet  19  has a pressure up to 10 atmospheres. In other instances, the jet  19  has a pressure of between 1 and 10 atmospheres, while in still yet other instances the jet  19  has a pressure between 2 and 8 atmospheres. A standoff distance h defined as the distance from the shroud  12  to the sampling surface S is preferably small, typically comparable to or preferably less than the shroud diameter, for successful operation. In the alternative, the sampler  10  can be placed in a moving stream and used to sample a moving airstream and the like. 
     A suction device  16  in the form of a fan, blower or the like draws a sample flow into the shroud  12  through a first opening, also known as a shroud inlet  11 , and through a second opening, also known as a shroud outlet  21 , as indicated by arrows  1 . It is appreciated that the sample flow or a portion thereof can be delivered to a detector for analysis, for example to optional chemical analyzer  100 , or to a pre-concentrator if so required. It is further appreciated that the jet  19  can be provided by a source of compressed gas, modern synthetic jet technology [11] or the like, the jet  19  providing an axisymmetric wall jet  13  that separates from the sample surface S as shown in  FIG. 1  due to the adverse pressure gradient imposed upon sample surface S by the shroud inlet  12  and associated airflow. In the alternative, a non-axisymmetric wall jet  13 ′ that also separates from the sample surface S is shown in  FIG. 2 . It is appreciated that the shroud  12  along with the outlet nozzle  14  and  14 ′ are directed generally in the same direction, which in this case is toward the sampling surface S. 
     The supply of compressed gas to the nozzle  14  and  14 ′ can be controlled by solenoid valves known to those skilled in the art and can range from intermittent duration of a few milliseconds to continuous operation. In order to scour a surface and remove particles and/or vapor, a shear stress in the range of 10-30 Pascals (Pa) (0.0015-0.0045 pounds per square inch (psi)) can be used. For example, and for illustrative purposes only, an outlet nozzle having an exit opening with an inside diameter of 1 millimeter (mm) (0.04 inch (in.)) with a standoff distance of 25 mm (1 in.) and a nozzle-exit stagnation pressure of 14 kPa (2 psi) above atmospheric pressure can provide such a shear stress. Such a pressure would result in a mass flow rate through the nozzle of 0.00015 kilograms per sec (kg/sec), corresponding to a volume flow rate of 1.17×10 −4  cubic meters per second (m 3 /sec) (0.25 standard cubic feet per minute (SCFM)). Taking for example a shroud that can collect 5 to 10 times the volume flow rate of the outlet nozzle, i.e. 5.85×10 −4 -1.17×10 −3  m 3 /sec (1.25-2.5 SCFM), a diameter of such a shroud could be of the order of 12 centimeters (cm) (4.7 in.). Larger diameter outlet nozzles could naturally result in higher mass flow rates out of the nozzle and thus larger shrouds. Smaller devices may likewise be designed. 
     In an alternate embodiment shown in  FIG. 3 , where like numerals represent like elements as referenced in previous figures, a sniffer  20  includes an ejector nozzle  22  directed away from the shroud inlet  11  and towards the shroud outlet  21 . The compressed-air source  18  can simultaneously power the jet  19  and provide a suction using the ejector  22  which induces a low-speed flow by way of a pressure drop created by entrainment into a small high-speed turbulent jet  17 . A dump-tube  24  may be provided proximate the shroud outlet  21  in order to collect jet  17  and discard it, thus increasing the concentration of a trace signal originating from the surface S and presented to a detector (not shown) via the airflow indicated by arrows  1 . In addition, optional valves  6 ,  7  and  8 , can be included and used to direct compressed gas to the outlet nozzle  14  and/or ejector  22 . It is appreciated that the embodiment illustrated in  FIG. 3  can be modified in a similar fashion as the embodiment shown in  FIG. 2  with an outlet nozzle  14 ′ disposed outside the shroud  12 , or in a different non-axially-symmetric form. 
     As noted in earlier discussion, the “reach” of heretofore inlets is quite limited. The flow into a bulbous-shaped shroud (i.e., shaped like an animal nose) could be focused in a forward direction to improve the “reach” of sniffing if inlet walls were able to generate vorticity aimed towards a central suction opening. One method to generate such vorticity aimed towards the central suction opening is with moving walls. However, this method requires great mechanical complexity. In the alternative, the same effect can be accomplished with a Coanda-inlet sampler  30  shown schematically in  FIG. 4 . It is appreciated that Henri Coanda proposed [5] an explanation of why a fluid flow clings to a curved surface. Various inventions have put this principle to use, for example in kitchen ventilation [6], but not thus far to the type of aerodynamic sampling described in the present disclosure. 
     The sampler  30  includes a shroud  32  with an outer portion  34  and an inner portion  36 . An outward “step” nozzle  38  is disposed between the outer portion  34  and the inner portion  36  and can be formed by a gap  39  therebetween. It is appreciated that the shroud  32  and/or step nozzle  38  can be axisymmetric in orientation and/or position, or in the alternative, not be axisymmetric. Attached surface jets  35 , generated by compressed gas  37  flowing through the step nozzle  38  and aimed inward, entrain air in order to “focus” the flow. The sampler  30  functions in some sense similarly to the ejector  22  shown in  FIG. 3  and a capture or sample tube  40  captures only the incoming airstream  42  from the immediate forward direction. The remaining air flux can be discarded, in that it does not arise from the desired forward direction and is thus irrelevant to the desired sampling task. 
     It is appreciated that the location of the step nozzle  38  in  FIG. 4  is for illustrative purposes only and in no way limits the embodiment. An inlet of this type typically requires compressed gas to power the Coanda jets  35 . A suction can be applied to the capture tube  40  in order to extract the sampled air and subsequently present it to a detector. The sampler  30  may be used in conjunction with puffer jets, described earlier, in order to dislodge particles and/or vapor from surfaces before “sniffing” them. It is further appreciated that the sample tube  40  can provide the puffer jet, or in the alternative, an outlet nozzle  14 ′ as shown in  FIG. 5  can be provided to afford for a jet of compressed gas to impact a sample surface. 
     For example, and in no way limiting the scope of the embodiment, the sampler  30  could have an inside diameter of shroud  36  of 51 mm (2 inches (in)) with the sample tube  40  having an inside diameter of 13 mm (0.5 inch). Thus in operation, a centrifugal blower known to those in the art could supply the Coanda jet flow  37  with a volume flow rate of 0.014 m 3 /sec (30 SCFM) that would be drawn into the sampler  30  through the inside diameter of shroud  36 . Such a volume flow rate would produce a velocity of 7 meters per second (m/sec) and the sample tube  40  could draw in a volume flow rate of 9.4×10 −4  m 3 /sec (2 SCFM). It is appreciated that the gas flow could be drawn from a region  42  that can be of similar diameter as the inside diameter of the shroud  36  and located as much as, or more than one diameter away from the sampler  30 . 
     Another embodiment of a sampler or sniffer according to the present invention is shown generally at reference numeral  50  in  FIGS. 6 and 7 . This design may be referred to as a radial-jet reattachment sniffer, and works in a manner logically opposite to that of the jet-puff sniffer taught above in that radial jet  53  is produced from a nozzle  52  combined with a flare  54  or  54 ′. Near a surface S, the radial jet  53  attaches to the surface S and produces an internal toroidal vortex  55  between the nozzle flare  54  and the surface S. The vortex  55  sweeps air across the surface S, inward radially from a jet reattachment line  57 , and upward along a centerline where a sample tube  56  withdraws some of the trace-laden air for the chemical detection step. 
     It is appreciated that if the nozzle shroud  52  and flare  54  are angled sharply downward toward the surface S as shown in  FIG. 6 , then a local surface area of small diameter is sampled. In the alternative, the nozzle flare  54 ′ and corresponding radial slot angle  59  can be parallel to the sampling surface S or even inclined up to 30 degrees away from it, and thereby result in a larger-sized radial jet reattachment circular “footprint” on the surface S, as shown in  FIG. 7 . As such, the embodiment affords for large semi-flat surfaces to be sampled, such as suitcases, the door panels of automobiles, etc. It is further appreciated that the samplers resulting in the flow patterns shown in  FIGS. 6 and 7  can be made to be simply interchangeable on the front-end of a trace chemical detection system and/or that many different designs of the nozzle-flare combination  52 - 54 ,  52 - 54 ′ and the like are possible with approximately the airflow effect shown in these figures afforded. In this manner, the sampling surface area for a trace chemical detection system can be varied and thereby provide a single detection system with multiple interchangeable samplers that afford for different-sized surfaces to be tested. 
     Another embodiment of a sampler or sniffer is shown in  FIG. 8  wherein an aerodynamically-assisted sniffer  70  may be integrated with a parabolic “dish” antenna  60 . Vehicles and robotic devices often incorporate parabolic dish antennas for communications and/or for electromagnetic interrogation of a target. Sophisticated actuators are required to aim the dish antenna for these purposes. The same equipment may serve the dual purpose of directional “sniffing” in close proximity to objects, given the antenna modifications illustrated in  FIG. 8 . The electromagnetically-active components of the antenna  60  are the parabolic reflector dish  61  and a signal “pickup” stalk  62  positioned at a parabola focus of the dish  61 . 
     The sniffer  70  includes a sampling tube  73 , plenum  74  and radial nozzle  75  as shown in  FIG. 8 . In addition, compressed air from plenum  74  can be used to generate a radially-outward-flowing turbulent boundary layer  66  along an inner surface of the parabolic reflector dish  61  and thereby afford by entrainment a bulk airflow motion indicated by streamlines  67 . In the alternative, an optional outlet nozzle  14 ′ can be provided as shown in  FIG. 9 , the outlet nozzle  14 ′ affording for compressed gas to impact a sample surface as taught above. In this manner, a narrow stream-tube  68  may be sampled from a direction in which the dish antenna  60  is aimed, and may thus provide a small directional airflow  69  to a chemical detector mounted aft of the antenna  60  and not shown in  FIGS. 8 and 9 . 
     Thus, with the modifications described above, a parabolic dish antenna can also serve a second purpose of directional sniffing for the aerodynamic interrogation of a suspected explosive device, an automobile, a person, etc. for trace chemical species. In  FIGS. 8 and 9  the electromagnetic pickup on the stalk  62  may produce some interference with the aerodynamic sampling function of stream  68 , but such interference can be negligible. Stated differently, any interference of the antenna&#39;s electromagnetic function by the airflow is likewise appreciated to be negligible. In some instances, compressed air is first ejected through sampling tube  73  in a direction towards the stalk  62  and produces a turbulent jet that can impinge upon a surface to be sampled (to the left in  FIGS. 8 and 9 , not shown) and dislodge particles and/or vapor via induced surface shear stress. After a brief interval, suction through sampling tube  73 , discussed above and shown in  FIGS. 8 and 9 , can “inhale” particles and/or vapor from a sample surface and thence present them to a detection device. 
     Such a parabolic dish antenna  61  for a mobile electromagnetic communication device could have a diameter of 46 cm (18 in.) with a collection tube  73  having an inner diameter of 2.5 cm (1 in.) and a slot nozzle  75  having a width of 5 mm (0.2 in.) and a circumference of 23 cm (9 in.). Such dimensions would allow for a gas flow rate of 0.36 m 3 /sec (77 SCFM) out of the slot nozzle  75  and a suction flow of 0.005 m 3 /sec (11 SCFM) through the capture tube  73 , thereby affording for a “reach” of the captured stream-tube  68  to extend from the end of the capture tube  73  to a distance ahead of the parabolic dish antenna  61  equal to, if not greater than the diameter of the dish antenna  61 . 
     As will be clear to those of skill in the art, the embodiments of the present invention described and illustrated herein may be altered in various ways without departing from the scope or teaching of the present invention. For example, all of the embodiments can be used to sample a moving airstream as well as a surface and heated air can be used in the puffer jets in order to better desorb volatile chemicals from a surface. As such, the invention is not restricted to the illustrative examples and/or embodiments described above and the scope of the invention is defined by the scope of the claims. 
     REFERENCES 
     The following are incorporated herein in their entirety by reference:
     [1] Settles, G. S., “Sniffers—Fluid-dynamic sampling for olfactory trace detection in nature and Homeland Security,”  J. Fluids Engrg . Vol. 127, No. 2, pp. 189-218, March 2005.   [2] Goodfellow H, Tähti E, eds. (2001) Local ventilation. Ch. 10 of  Industrial Ventilation Design Guidebook . Academic Press, NY.   [3] H. W. Shin, W. K. Cheng, E. M. Greitzer, and C. S. Tan. Inlet vortex formation due to ambient vorticity intensification.  AIAA Journal  24 (4):687-689, 1986.   [4] US Patent Application Publication No. 2003/0155506 by V. S. Motchkine, L. Y. Krasnobaev, and S. N. Bunker; U.S. Pat. No. 6,828,795 by L. Y. Krasnobaev, V. S. Persenkov, V. V. Belyakov, V. B. Kekukh, S. N. Bunker; U.S. Pat. No. 6,861,646 by V. S. Motchkine, L. Y. Krasnobaev, and S. N. Bunker.   [5] U.S. Pat. No. 2,052,869 by H. Coanda.   [6] Roehl-Hager, H., Koppenwallner, G., and Koppenwallner, G. E., German Patent DE 196 13 513.3, 1996.   [7] R. H. Page, L. L. Hadden, and C. Ostowari. Theory for radial jet reattachment flow.  AIAA Journal  27 (11):1500-1505, 1989.   [8] Smedley G T, Phares D J, Flagan R C (1999) Entrainment of fine particles from surfaces by gas jets impinging at normal incidence.  Experiments in Fluids  26, 324-334.   [9] Gary S. Settles, Heather C. Ferree, Michael D. Tronosky, and Zachary M. Moyer, and William J. McGann, “Natural Aerodynamic Portal Sampling of Trace Explosives from the Human Body,” FAA 3 rd  International Symposium on Explosive Detection and Aviation Security, Nov. 26-30, 2001, Atlantic City, N.J.   [10] H. Z. Lai, J. W. Naughton, and W. R. Lindberg. An experimental investigation of starting impinging jets.  Journal of Fluids Engineering  125 (2):275-282, 2003.   [11] Smith B L, Glazer A, “Formation and Evolution of Synthetic Jets” Physics of Fluids, vol. 10, pp 2281-2297, 1988.   [12] U.S. Pat. No. 6,171,656 by G. S. Settles.   [13] U.S. Pat. No. 4,043,257 by C. P. N. Aaberg; U.S. Pat. No. 4,909,090 by J. B. McGown, E. E. A. Bromberg and L. W. Noble; U.S. Pat. No. 5,092,157 by E. K. Achter, A. L. Carroll, D. P. Rounbehler, D. H. Fine and F. W. Fraim; U.S. Pat. No. 5,123,274 by R. C. Smith; U.S. Pat. No. 5,376,550 by D. H. Fine, F. W. Fraim, S. J. MacDonald and K. M. Thrash, Jr.; U.S. Pat. No. 6,269,703 by W. D. Bowers.