Patent Publication Number: US-2020292420-A1

Title: Particle concentrator

Description:
RELATED APPLICATIONS 
     This application is a continuation of application U.S. Ser. No. 15/785,094 filed Oct. 16, 2017, which itself is a continuation of application U.S. Ser. No. 12/231,207 filed Aug. 29, 2008, now U.S. Pat. No. 9,791,353 B2 issued Oct. 17, 2017, which are incorporated by reference as if fully set forth herein. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  is an assembled perspective view of the concentrator  10 , taken from an upper aspect, shown mounted on tripod legs  13 ; 
       FIG. 2  is cross-sectional, perspective view of the concentrator  10 , taken along line  2 - 2  of  FIG. 1 , and taken from an upper aspect; 
       FIG. 3  is an exploded perspective view of the concentrator  10 &#39;s fan assembly  11 , taken from an upper aspect; 
       FIG. 4  is an exploded perspective view of the concentrator  10 &#39;s air processor  12 , taken from an upper aspect; 
       FIG. 5  is a cross-sectional view of the concentrator  10 &#39;s air processor  12 , taken along line  5 - 5  of  FIG. 1 ; 
       FIG. 5A  is an enlarged view of the circled portion  5 A in  FIG. 5 ; 
       FIG. 5B  is an enlarged view of the circled portion  5 B in  FIG. 5 ; 
       FIG. 6  is an enlarged view similar to that of  FIG. 5A , but with airflow lines added to show sampled airflows  102 , primary airflows  103  and secondary airflows  104 ; 
       FIG. 7  is a bottom plan view of the air processor  12 &#39;s top plate  42 ; 
       FIG. 8  is a top plan view of the air processor  12 &#39;s outer hub  80 ; 
       FIG. 8A  is a perspective view of the air processor  12 &#39;s outer hub  80 , taken from an upper aspect; 
       FIG. 9  is a top plan view of the air processor  12 &#39;s inner hub  81 ; 
       FIG. 9A  is a perspective view of the air processor  12 &#39;s inner hub  81 , taken from an upper aspect; 
       FIG. 10  is a perspective view of one of the air processor  12 &#39;s blades  47 ; 
       FIG. 11  is an exploded perspective view of one of the air processor  12 &#39;s blades  47 ; 
       FIG. 12  is a side elevational view of one of the air processor  12 &#39;s blades  47 ; 
       FIG. 12 a    is a top plan view of one of the air processor  12 &#39;s blades  47 ; 
       FIG. 12 b    is a bottom plan view of one of the air processor  12 &#39;s blades  47 ; 
       FIG. 13  is an end elevational view of one of the air processor  12 &#39;s blades  47 ; 
       FIG. 14  is a cross-sectional view of one of the air processor  12 &#39;s blades  47 , taken along line  14 - 14  of  FIG. 12 ; 
       FIG. 15  is an enlarged view of the circled portion  15  in  FIG. 14 ; 
       FIG. 16  is an enlarged view of the circled portion  16  in  FIG. 14 ; 
       FIG. 17  is an exploded perspective view of the lower portion of a concentrator  10   a , taken from an upper aspect; 
       FIG. 18  is an assembled perspective view, partly in cross-section, of the lower portion of a concentrator  10   a , taken from an upper aspect; 
       FIG. 19  is a bottom plan view of the concentrator  10   a;    
       FIGS. 20-21  are graphs showing certain performance characteristics of the concentrator  10 ; 
       FIG. 22  is a perspective view of a concentrator  10   b , taken from an upper aspect; 
       FIG. 23  is a perspective view, partly in cross section of a concentrator  10   b  being used to interrogate a shipping container  137 ; 
       FIG. 24  is a perspective view of a mechanical vibrator  150 , taken from an upper aspect; and 
       FIG. 25  is a cross-sectional view of an electromagnetic vibrator. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Definition 
     When the terms “top” and “bottom” are used in this application, they are not used in any absolute sense, but in a relative sense given one orientation of the particle concentrator being described. This is done for clarity of presentation because it is easier to understand the terms “top” and “bottom” then “first end” and “second end”. The device can be laid on its side, making the “top” a “first end”. 
     BACKGROUND 
     Many human activities are influenced by the presence of a variety of airborne particles. For example, a great number of natural pests and pathogens comprise airborne microscopic biological particles such as molds, fungi, bacteria, viruses, and multi-celled microorganisms. The collection and removal of such particles from the air, such as for observation, identification, examination, testing or analysis, is often made difficult by their small size, fragility, low density, and low volumetric concentration in the air. Unfortunately, it may take only one such particle to create infection or illness, or to contaminate a hospital area. 
     In addition, clean rooms require extremely low concentrations of both organic and inorganic airborne particles to minimize wafer defects and to maintain high device yields. Further, counter-terrorism efforts often hinge on the collection and removal from the air of small numbers of airborne particles such as pathogenic bacteria, their spores, or weaponized viruses or toxins, so that the particles are available for observation, identification, examination, testing or analysis. In addition, the monitoring of luggage for explosives is often now based on the collection and removal from the air of microscopic particles of explosives that may be as small as 1 micron in diameter. 
     The airborne particles of interest may be called particles containing target material, which may be particles containing any material of interest, such as any liquid, solid, organic, inorganic, biological or non-biological material, or mixtures thereof. In the description which follows, the movement of particles containing target material will be described strictly by way of non-limiting example, it being understood that the same or similar description may apply equally well to the movement of any other kind of particle. 
     The term “air” is used broadly, so that it may be any gas or mixture of gasses other than air. 
     Several difficulties are often encountered in removing airborne particles containing target material from large volumes of sampled air. First, a sampled air collection device that produces a sampled airflow  102  having a high flow rate may be heavy and bulky. Second, a high flow rate sampled air collection device may be difficult to use with many types of conventional air samplers, particle analyzers, and analytical devices which are designed to be used with a sampled airflow  102  having a low flow rate, such as a flow rate of 500 liters per minute (LPM), or less. 
     An air sampler may be any device that removes particles containing target material from an airflow, such as from the sampled airflow  102 , so that the particles containing target material may be observed, identified, examined, tested or analyzed. A particle analyzer may be any device that determines the size, concentration, nature, and/or approximate composition (such as biological versus non-biological) of the particles of target material. An analytical device may be any device that detects and/or identifies targeted constituent materials in the particles, including explosives, drugs, bacteria, spores, viruses, toxins, animal and plant pathogens, and industrial chemicals, as nonlimiting examples. 
     Third, a sampled airflow  102  having a high flow rate often results in high air velocities of the sampled air that can be injurious to certain kinds of particles containing target material that are delicate, such as organisms, due to the physical shear forces or desiccation caused by the high air velocities. 
     Fourth, commercially available concentrators (devices for concentrating particles containing target materials from a sampled airflow  102 ), typically require high overall pressure differences for correct operation. Air handlers such as fans, blowers and air turbines that can support those types of pressure differences are often heavy, large in size and inefficient, consuming large amounts of power for a comparatively small sampled airflow  102 . This may not be an issue if the sampled airflow  102  is small, since the total electrical power consumption of the concentrator and its air handler may still be acceptable. However, for applications where the sampled airflow  102  is greater than about 1000 liters/minute, the efficiency of both the concentrator and air handler become very important. For this reason, commercially available concentrator systems are typically not appropriate or available for portable applications where it is desirable to process large quantities of sample air, such as the sampling of shipping containers and ship&#39;s holds, train cars, agricultural settings, open air markets, food processing facilities and large public venues such as auditoriums and arenas, office buildings, and shopping centers. 
     The Concentrator  10   
     Accordingly, in order to address one or more of the difficulties mentioned above, the concentrator  10  may be a relatively small, lightweight, low power consuming, and portable device that can produce and process a sampled airflow  102  having a high flow rate, and concentrate the particles containing target material therein into a secondary airflow  104  having a much lower flow rate that may match the input requirements of any conventional air sampler, particle analyzer, or analytical device. 
     In view of all of the disclosures herein, it is understood that the concentrator  10  may be designed to produce a secondary airflow  104  having any desired flow rate that matches the input requirements of any particular air sampler, particle analyzer, or analytical device, regardless of whether or not the particular air sampler, particle analyzer, or analytical device is a commercial, off-the-shelf device. 
     By way of example, the example concentrator  10  that is described below may be small, lightweight, low power consuming, and portable. It may produce and process a sampled airflow  102  having a relatively high flow rate of about 3,000 to 3,600 LPM, dividing airflow  102  into a primary airflow  103  and a secondary airflow  104 . The sum of the flow rates of the primary and secondary airflows  103 ,  104  will be equal to the flow rate of the sampled airflow  102 . 
     The example concentrator  10  may concentrate into the secondary airflow  104  on the order of about 60% to about 80% of the particles of target material that were present in the sampled airflow  102 . The secondary airflow  104  may have a flow rate that is nominally 1% to 10% of the flow rate of the primary airflow  103 . The secondary airflow  104 , and the concentrated particles containing target material that it carries, may then be conveyed in any suitable way to any suitable air sampler, particle analyzer, or analytical device. This entire process may be accomplished using only 50 to 100 watts of electric power. 
     As best seen in  FIGS. 1-2 , concentrator  10  may comprise two main components, i.e., a fan assembly  11  and an air processor  12 . Regarding the orientation of the concentrator  10 , by way of example it is illustrated as having its central longitudinal axis A oriented vertically, so that its fan assembly  11  is located directly above its air processor  12 . Accordingly, by way of example and for simplicity and ease of understanding, the various parts of the concentrator  10  and their relationships with respect to each other will be described herein with respect to the vertically oriented concentrator  10  that is illustrated. 
     However, it is understood that the concentrator  10 &#39;s axis A may be tipped at any angle up to 180 degrees from the vertical. For example, if its axis A were tipped 90 degrees from the vertical, then its fan assembly  11  and its air processor  12  would be located side by side; and if its axis A were tipped 180 degrees from the vertical, then its air processor  12  would be located directly above its fan assembly  11 . 
     The concentrator  10  may be mounted in any suitable way, at any desired height above the surface which supports it, with any desired orientation of its axis A, such as by the use of length-adjustable tripod legs  13 , or by being mounted in any suitable way to one or more pieces of other equipment. 
     As an alternative, the fan assembly  11  and the air processor  12  may not be connected directly together, but may be remotely connected together in any suitable way by any suitable device such as by any suitable air conduit that extends between the air outlets  55  in the assembly  12 &#39;s top plate  42  and the air inlet  22  of the fan plenum  15  or the air inlet  31  of the fan  16 . 
     The concentrator  10 , its fan assembly  11 , and its air processor  12  may all be called “negative pressure” devices because its fan assembly  11  is operable to create a negative air pressure in the primary airflow outlets  55  in the air processor  12 &#39;s top plate  42 , so that the flow of the sampled air through the assembly  12  is at least partially driven by the ambient, higher pressure sample air that surrounds the air processor  12 . 
     As an alternative, any other suitable fan assembly  11  of any suitable construction that is operable to apply a negative air pressure to the air outlets  55  in the air processor  12 &#39;s top plate  42  may be used in lieu of the fan assembly  11  that is illustrated and described herein. 
     As a further alternative, the fan assembly  11  may be eliminated, so that the concentrator  10  may comprise just a negative pressure air processor  12 . Such a concentrator  10  may then be used by connecting it in any suitable way to any suitable source of negative air pressure. 
     As seen in  FIG. 1 , the concentrator  10  may be utilized by being located directly within the air to be sampled, such as if it were placed in a room full of the air to be sampled. Alternatively, the concentrator  10  may be utilized by being located remotely from the air that is to be sampled, such as is illustrated in  FIG. 23 , in which case the sampled airflow  102  is delivered to the concentrator  10  in any suitable way, such as through an input duct  141 . 
     In view of the disclosures herein, it will be appreciated that the concentrator  10  may be designed to produce and process a sampled airflow  102  having any desired flow rate. This may be done in any suitable way, such as by scaling the concentrator  10  up or down with respect to its size and its number of parts, by increasing the negative air pressure that is applied to its air processor  12 , or by modifying the concentrator  10  in any other suitable way. 
     Concentrator  10 B 
     Turning now to  FIGS. 22 and 23 , an alternative, “shrouded” concentrator  10   b  is illustrated. The concentrator  10   b  of  FIG. 22  may be the same as, or at least, similar to the concentrator  10  of  FIGS. 1-16  and the concentrator  10   a  of  FIGS. 17-19  in all respects, except for those differences which will be made apparent by all of the disclosures herein 
     The concentrator  10   b  may further comprise a hollow annular shroud  147  having an inlet  149  of any suitable size, shape, and construction. There may be more than one inlet  149 . The shroud  147  may enclose the outer surface of the outer hub  80  and be sized to provide an annular air chamber around the outer surface of the outer hub  80 . The shroud  147  may be of any suitable size, shape and construction, and may be assembled to the air processor  12  in any suitable way, such as by being assembled to the top and bottom plates  42 ,  43  of the air processor  12 . 
     The fan assembly  11  may be operable to apply a negative air pressure to the air chamber within the shroud  147  and may at the same time be operable to apply a positive air pressure within the fan plenum  15 . The negative air pressure may cause the sampled airflow  102  to flow into the shroud  147  through its inlet  149 , and to then pass through the concentrator  10   b &#39;s air processor  12 . The positive air pressure may then cause the primary airflow  103  to flow out of the concentrator  10   b  through its fan plenum  15 . 
     The concentrator  10   b  may further comprise any suitable optional input and output ducts  141 ,  142  of any suitable size, shape and construction which may be connected in any suitable way to the concentrator  10   b &#39;s inlet  149  and fan plenum  15 , respectively. 
     The concentrator  10   b  may be used in any suitable way. For example, as seen in  FIG. 23  an input duct  141  may be connected between a shipping container  137 &#39;s outlet port  139  and the concentrator  10   b &#39;s inlet  149 ; while an output duct  142  may be connected between the concentrator  10   b &#39;s fan plenum  15  and the shipping container  137 &#39;s inlet port  138 . 
     The negative air pressure created by the concentrator  10   b  may then cause a sampled airflow  102  to flow from the sample air within the airspace  143  within the shipping container  137 , through the input duct  141 , into the shroud  147 &#39;s inlet  149 , and through the concentrator  10   b &#39;s air processor  12 . The positive air pressure created by the concentrator  10   b  within its fan plenum  15  may then cause the primary airflow  103  to flow from the fan plenum  15 , through the output duct  142  and back into the shipping container  137  through its inlet port  138 . 
     Thus, it has been discovered that the concentrator  10   b  may be operable to create a closed circuit airflow so that the flow of the sampled airflow  102  through the air processor  12  is driven by a combination of positive and negative air pressure created by concentrator  10   b &#39;s fan assembly  11 . 
     As alternatives, the output duct  142  may be eliminated, so that the primary airflow  103  from the fan plenum  15  may be discharged into the air surrounding the concentrator  10   b . As a further alternative, the shroud&#39;s  147  inlet  149  may be located on any suitable surface of the shroud  147  other than on its cylindrical surface  146  as is illustrated in  FIGS. 22-23 . For example, one or more inlets  149  of any suitable size shape and construction may be located on the top or bottom end surfaces  148 ,  165  of the shroud  147 . 
     Concentrator  10   b  may be particularly desirable for vehicle- or aircraft-mounted applications. For example, if its inlet  149  is located in either the top or bottom end surfaces  148 ,  165  of its shroud  147  (see  FIG. 22 ), and if such an inlet  149  is oriented in the direction of travel, then the kinetic pressure created by vehicle or aircraft forward motion can be used to at least assist in driving a sampled airflow  102  through its air processor  12 . By sizing the diameter of shroud  147  so there is no substantive internal pressure difference between its top and bottom end surfaces  148 ,  165  during operation, then the entire outer surface  82  of its outer hub  80  will be uniformly pressurized by the sampled airflow  102 , assuring uniform inward radial flow of the sampled airflow  102  at each sampled airflow inlet pocket  84  in the outer surface of its outer hub  80 , independent of vehicle or aircraft forward velocity. The kinetic pressure in some cases may be adequate to totally drive the sampled airflow  102 , eliminating the need for fan assembly  11 . In such a case the primary airflow  103  may exit the air processor  12  through any suitable respective primary airflow outlet  55  in the air processor  12 &#39;s end plate  42 ,  43  that is located at the opposite end of shroud  147  from where inlet  149  is located. The primary airflow  103  may exit through either end plate  42 ,  43 . 
     As alternatives, the concentrators  10 ,  10   a  may also comprise a shroud  147 , inlet  149 , and optional input and output ducts  141 ,  142 ; and may be used in ways that are the same as, or at least similar to the ways in which the concentrator  10   b  may be used. 
     Fan Assembly  11   
     Returning now to the concentrator  10  of  FIGS. 1-16 , as best seen in  FIGS. 2-3 , the fan assembly  11  may comprise a fan plenum  15 ; a fan  16  having a fan motor  29 ; a fan plate  18 ; and airflow-straightening vanes  19 . A power cable assembly  21  for providing power to the fan motor  29  may, or may not, be part of the fan assembly  11 . 
     As best seen in  FIGS. 1 and 3 , the power cable assembly  21  may comprise a conduit  35 , a pair of through mounting clips  38  for mounting the conduit  35  to the air processor  12 , a right angle mounting clip  39  for mounting the conduit  35  to the plenum  15 , a through connector  37  that may be assembled to the fan plate  18 , and an electrical wire  36  for supplying power to the fan motor  29 . The electrical wire  36  may be routed sequentially through the conduit  35 , through the right-angle mounting clip  39  into the plenum&#39;s air chamber  28 , and through the connector  37  in the fan plate  18  to the fan motor  29 . 
     The fan  16  may also have an impeller  30 , an air inlet  31  in the impeller  30 , impeller vanes  34 , and air outlets  32  between the impeller vanes  34 . Although a high speed electric centrifugal fan  16  is illustrated in the Figures, any suitable fan  16 , having any suitable size, shape, power, construction and air moving capacity may be used, whether electric or not, depending on such factors as, for example, the desired flow rate of the sampled airflow  102  through the concentrator  10  and the space available in or on fan assembly  11  for mounting the fan  16 . A large variety of air movers are available that may be suitable for use as fan  16 . These air movers, such as fans and blowers, are frequently optimized for a specific quality, such as high flow volume, low or high-pressure delivery, and/or positive or negative pressure operation. Centrifugal fans with backward-curved blade designs provide a particularly satisfactory combination of electric-to-pneumatic efficiency and operating flexibility and are a preferred air mover for integration with concentrator  10 . 
     The fan motor  29  and impeller  30  are shown diagrammatically in the Figures, it being understood that any suitable part of the fan motor  29  may be assembled to the fan plate  18  in any suitable way, so that the impeller  30  may rotate with respect to the part of the fan motor  29  that is assembled to the fan plate  18 . 
     The fan plenum  15  may have an air inlet  22 ; an air outlet  23 ; a sidewall  24 ; a mounting flange  25 ; a spacing flange; an annular air discharge chamber  27  between the impeller  30  and the plenum  15 &#39;s sidewall  24 ; and a cylindrical discharge air cavity between the fan plate  18  the plenum  15 &#39;s outlet  23 . Although the plenum  15  is illustrated as being symmetrical about the axis A, it may not be symmetrical about the axis A. Although the plenum  15 &#39;s sidewall  24  is illustrated as having a circular cross-sectional profile of constant size and shape along its length, it may have any other suitable geometric or non-geometric cross-sectional profile, and its cross-sectional area and shape may not be constant along its length. 
     Although eight airflow-straightening vanes  19  are illustrated, there may be fewer, more, or no vanes  19 . If the concentrator  10  comprises one or more vanes  19 , each vane  19  may have any suitable size, shape and construction other than that illustrated, and all of the vanes  19  may or may not have the same size, shape and construction. 
     To assemble the fan assembly  11 , the fan plate  18  may be assembled to fan motor  29 ; and the lower ends of the vanes  19  may be assembled to the top of the fan plate  18 . To assemble the fan  16  within the plenum  15 , the fan  16  (and its assembled fan plate  18  and vanes  19 ), may be inserted through the plenum  15 &#39;s air outlet  23 , and then the outer edges of the vanes  19  may be assembled to the plenum  15 &#39;s sidewall  24 . When the fan  16  has been assembled within the plenum  15  there may be a small clearance between the air inlet  31  of its impeller  30  and the air inlet  22  and mounting flange  25  of the fan plenum  15 . 
     Although the air inlets  22 ,  31  are illustrated as being concentrically arranged, with the inlet  31  being sized larger than the inlet  22 , the inlets  22 ,  31  may have any suitable sizes and any suitable arrangement with respect to each other. For example, they may be concentrically arranged with the inlet  22  being sized larger than the inlet  31 , or the inlets  22 ,  31  may have the same size and be arranged end to end. 
     The various parts of the fan assembly  11  may be assembled together in any suitable way such as by using fasteners; interference fits; friction fits; barbed, threaded, bonded, glued or welded connections; splines; keys; or mechanical couplers. 
     During operation of the concentrator  10  the primary airflow  103  from its air processor  12  may be urged by the fan  16  to flow into the air inlet  22  of the plenum  15  from the primary airflow outlets  55  in the air processor  12 . The primary airflow  103  may then be urged by the fan  16  to flow through the air inlet  31  of the fan  16 &#39;s impeller  30 , and out through the air outlets  32  of the impeller  30 . The sidewall  24  of the plenum  15  may then route the air discharged by the fan  16  upwardly through the plenum&#39;s  15  air chambers  27 ,  28 , between the airflow straightening vanes  19 , and out through the plenum  15 &#39;s air outlet  23 . Due to the plenum  15  and the vanes  19 , the primary airflow  103  may be discharged from the air outlet  23  parallel to the concentrator  10 &#39;s axis A in the form of a primary airflow discharge jet whose cross-section may broaden relatively slowly as it flows away from the concentrator  10 . 
     It has been discovered that by discharging the primary airflow  103  in the form of a jet, by orienting the primary airflow discharge jet so that it flows away from the fan assembly  11  along the concentrator  10 &#39;s axis A, and by constructing the concentrator  10  so that the sampled airflow  102  flows radially inwardly towards its axis A as the sampled airflow  102  enters the air processor  12 , any mixing of the primary airflow discharge jet with the incoming sampled airflow  102  will tend to be desirably minimized. Minimizing such mixing may be desirable because many of the particles containing target material will have been removed from the sampled airflow  102  as it flows through the assembly  12 . Thus, the depleted primary airflow  103  discharged from the fan assembly  11  will contain relatively few remaining particles containing target material. As a result, if the depleted primary airflow  103  is mixed with the incoming sampled airflow  102 , the depleted primary airflow  103  will tend to undesirably reduce, or dilute, the concentration of the particles containing target material in the incoming sampled airflow  102 . 
     In addition, it has been further discovered that the primary airflow discharge jet from the plenum  15  may desirably generate an induced draft effect around the concentrator  10 . An induced draft effect is where the primary airflow discharge jet will entrain some of the air surrounding the concentrator  10 , thereby causing a desirable radially inward flow towards the air processor  12 . It has been further discovered that in a situation where the sampled air around the concentrator  10  is stagnant, this induced draft effect may desirably cause the circular sensing radius of the concentrator  10  to more than double. 
     The concentrator  10 &#39;s circular sensing radius may be defined as the maximum radius around the concentrator  10  from which it will take a predetermined amount of time for sampled air to be drawn into the air processor  12 . For example, if the predetermined amount of time is five minutes, then the circular sensing radius will be eight feet if it took five minutes for air that was formerly eight feet away from the air processor  12  to be drawn into the air processor  12 . It is apparent that doubling the concentrator  10 &#39;s circular sensing radius may be highly desirable, such as in a circumstance where the particles containing target material are not uniformly distributed through the air surrounding the concentrator  10 . 
     However, as an alternative, the fan assembly  11  may be modified in any suitable way so that the discharged primary airflow  103  is discharged from the plenum  15  in any desired direction, either in the form of a jet, or not in the form of a jet. 
     The Air Processor  12   
     As best seen in  FIGS. 1-2 and 4 , the air processor  12  may comprise top and bottom end plates  42 ,  43 , a hollow outer hub  80 , a hollow inner hub  81 , and blades  47 . 
     Although the hubs  80 ,  81  are illustrated as having generally circular cross-sectional profiles of constant size and shape along their respective lengths, either or both may have any other suitable geometric or non-geometric cross-sectional profiles, and their respective cross-sectional areas and shapes may not be constant along their respective lengths. 
     O-rings  68  may be provided for the blades  47 , and an O-ring  101  may be provided for the neck  99  of the inner hub  81 . The O-rings  68 ,  101  may, or may not, comprise part of the air processor  12 . 
     An annular filter  44  may be provided to prevent anything that is significantly larger than a predetermined size from entering the outer hub  80 , to help prevent foreign matter and debris from entering the outer hub  80 . For example, the filter  44  may be selected to prevent the entry of anything that is significantly larger than the particles containing target material. The filter  44  may, or may not, comprise part of the air processor  12 . 
     As best seen in  FIGS. 2, 4 and 7 , the top plate  42  may have a rim  56 , a center plate  52  connected to the rim  56  by four arms  54 , and four primary airflow outlets  55 . The rim  56  may have an annular groove  50  for receiving the top edge of the filter  44 , and an annular recess  51  for receiving the top end of the outer hub  80 . The center plate  52  may define a circular recess  53  for receiving the top neck  98  of the inner hub  81 . 
     As best seen in  FIGS. 2 and 4 , the bottom plate  43  may have an annular groove  57  for receiving the bottom edge of the filter  44 , an annular recess  58  for receiving the bottom end of the outer hub  80 , and an opening  59  for receiving the bottom neck  99  of the inner hub  81 . 
     The Blades  47   
     Turning now to  FIGS. 2, 4, 5-6 and 10-16 , each blade  47  may be symmetrical about an imaginary plane of symmetry that passes longitudinally through the center of the blade  47 ; and may comprise a pair of identical blade elements  60 . Alternatively, each blade  47  may not be symmetrical about such a plane, and the blade elements  60  may not be identical. 
     Each blade element  60  may comprise a blade body  61 ; a rod  69 ; three secondary airflow channel spacers  62 ; three sampled airflow inlet spacers  63 ; three primary airflow outlet spacers  64 ; a pair of optional blade mounting flanges  65 ; an O-ring mounting flange  66  having a groove  67  for an O-ring  68 ; and a pair of outer edges  72  that extend between respective adjacent pairs of the primary airflow outlet spacers  64 . 
     As best seen in  FIGS. 5-6 and 10-16 , a blade  47  may have a pair of sampled airflow inlet ports  75  that may be formed by its pair of cylindrical rods  69 . Cylindrical rods  69  are a preferred method for creating the sampled airflow inlet ports  75  because they may provide a wide range of useful naturally converging-diverging nozzle profiles for the sampled airflow inlet ports  75 , and because rods  69  are commercially available at low cost in a wide variety of sizes, made from many different materials and available with extremely high quality surface finishes. Smaller diameter rods  69  may also be called ‘wires’ in commerce, but no such distinction is recognized herein. Alternatively, the inlet ports  75  may be formed in any other suitable way by any other suitable structure, such being formed by the outer hub  80  (in which case the rods  69  may be eliminated), or by any suitable combination of partly being formed by the rods  69 , and partly being formed by the outer hub  80 . 
     By way of example, the sampled airflow inlet ports  75  will be described and illustrated as being sampled airflow inlet slots  75 , it being understood that the inlet ports  75  may have any other suitable size, shape and construction; and that the same, or similar, disclosures made herein regarding the inlet slots  75  may apply equally well, wholly or in part, to an inlet port  75  that is not an inlet slot  75 . 
     As best seen in  FIG. 6 , the sides of an inlet slot  75 , from its upstream side  75   a , to its through stream side  75   b , to its downstream side  75   c , may have a circular cross-sectional profile due to the cylindrical nature of the rods  69 . Alternatively, the rods  69  and the sides  75   a - 75   c  of the inlet slots  75  may have any other suitable smoothly varying, arcuate profile other than circular, such as oval, elliptical or parabolic. As a further alternative, rods  69  and the sides  75   a - 75   c  of the inlet slots  75  may have any other suitable geometric, or non-geometric cross-sectional profile. In addition, the arcuate length of the upstream and downstream sides  75   a ,  75   c  may be shorter, or longer, than that which is illustrated. 
     The width of an inlet slot  75  may be equal to the minimum distance between the rods  69  (i.e., may be equal to the combined thicknesses of a facing pair of the sampled airflow inlet spacers  63 ), and the length of an inlet slot  75  may be equal to the distance between its adjacent pairs of spacers  63 . 
     Each blade element  60  may have a pair of primary airflow outlet ports  70  that may be defined between its rods  69  and the blade element  60 &#39;s outer edges  72 . Alternatively, the outlet ports  70  may be formed in any other suitable way by any other suitable structure, such by being formed by the outer hub  80  (in which case the rods  69  may be eliminated), or by any suitable combination of partly being formed by the rods  69 , partly being formed by the outer hub  80 , and partly being formed by the outer edges  72 . 
     By way of example, the primary airflow outlet ports  70  will be described and illustrated as being primary airflow outlet slots  70 , it being understood that the outlet ports  70  may have any other suitable size, shape and construction; and that the same, or similar, disclosures made herein regarding the outlet slots  70  may apply equally well, wholly or in part, to an outlet port  70  that is not an outlet slot  70 . 
     As best seen in  FIG. 6 , the upper side of the outlet slot  70  (the downstream side  75   c  of the rod  69 ) may have a circular cross-sectional profile due to the cylindrical nature of the rod  69 . Alternatively, the upper side of the outlet slot  70  may have any other suitable curved (such as oval, elliptical or parabolic), geometric, or non-geometric cross-sectional profile. In addition, the arcuate length of the upper side of the outlet slot  70  may be shorter, or longer, than that which is illustrated. 
     Although the lower side of the outlet slot  70 , i.e., the outer edge  72  of the blade  47 , is illustrated as having a flat cross-sectional profile, it may have any other suitable curved, geometric or non-geometric cross-sectional profile. 
     In addition, the plane of each edge  72  may lie at an inside angle of about 75 degrees with respect to an imaginary plane of symmetry that passes longitudinally through the center of the blade  47  and that bisects the blade  47  into two identical blade elements  60 . It has been discovered that good flow of the primary airflow  103  through the primary airflow slots  70  may be achieved if the inside angle is in the range of from about 70 degrees to about 80 degrees, although the inside angle may be less than 70 degrees or greater than 80 degrees. A preferred inside angle may be about 75 degrees. 
     The width of a primary airflow outlet slot  70  (i.e., the minimum distance between its rod  69  and its outer edge  72 ) may be about the same as the thickness of its adjacent primary airflow outlet spacers  64  (i.e., the distance the spacers  64  extend outwardly past the outer edge  72 ), and its length may be equal to the distance between its adjacent primary airflow outlet spacers  64 . 
     A blade  47  may also have a pair of secondary airflow inlet ports  76  that may be formed by the inner edges  72  of its blade bodies  61 . Alternatively, the inlet ports  76  may be formed in any other suitable way by any other suitable structure, such being formed by the outer hub  80 , or by any suitable combination of partly being formed by the outer hub  80  and partly being formed by any suitably sized and shaped part of the blade bodies  61 . 
     By way of example, the secondary airflow inlet ports  76  will be described and illustrated as being knife-edged secondary airflow inlet ports  76  that are formed by the inner edges  72  of the blade bodies  61 , it being understood that the inlet ports  76  may have any other suitable size, shape and construction; and that the same, or similar, disclosures made herein regarding the inlet slots  76  may apply equally well, wholly or in part, to an inlet port  76  that is not an inlet slot  76 . 
     Although both sides of the inlet slot  76  are illustrated as being knife-edged, as an alternative only one side of the inlet slot  76  may be knife edged. As further alternatives, the inlet slot  76  may be provided with any other suitable knife-edges of any suitable size, shape and construction other than those illustrated, such knife-edges that extend upwardly towards the sampled airflow inlet slot  75  (i.e., towards the downstream side of the inlet slot  75 ), for any suitable distance into the sampled airflow  102  that exits from the sampled airflow inlet slot  75 . 
     As best seen in  FIG. 6 , the sides of an inlet slot  75 , from its upstream side  75   a , to its through stream side  75   b , to its downstream side  75   c , may have a circular cross-sectional profile due to the cylindrical nature of the rods  69 . Alternatively, the sides  75   a - 75   c  of the inlet slots  75  may have any other suitable curved (such as oval, elliptical or parabolic), geometric, or non-geometric cross-sectional profile. In addition, the arcuate length of the upstream and downstream sides  75   a ,  75   c  may be shorter, or longer, than that which is illustrated. 
     Each of a blade  47 &#39;s secondary airflow inlet slots  76  may comprise a secondary airflow channel  73  that is located between its blade bodies  61 . Two of the sides of each channel  73  may be formed by its adjacent pairs of secondary airflow channel spacers  62 , while its other two sides may be formed by the corresponding facing portions of its blade bodies  61 . 
     The width of a secondary airflow channel  73  may be equal to the distance between the corresponding facing portions of its blade bodies  61 , its height may be equal to the distance between its respective adjacent pairs of the secondary airflow channel spacers  62 ; and its length may be equal to the distance between its secondary airflow inlet slot  76  and its secondary airflow outlet slot. 
     The width of a secondary airflow channel  73  may gradually increase for a short distance downstream from its inlet slot  76 , and then stay at this increased width for the remainder of the length of the channel  73 . This may be done in order to convert some of the kinetic energy of the high velocity secondary airflow  104  that enters through the secondary airflow inlet slot  76  into static pressure, so that the air pressure of the secondary airflow  104  within the channel  73  may be closer to the ambient pressure of the sampled air at the outer hub  80 &#39;s sampled airflow inlet pockets  84 , than would otherwise be the case. This “pressure recovery” effect may be useful because, for example: (a) it may desirably reduce the amount of suction that may be required by a downstream air sampler, particle analyzer, or analytical device that may be connected to the air processor  12 &#39;s outlet fitting  77 ; and (b) it may desirably help permit the concentrator  10   a  that is illustrated in  FIGS. 17-19  to be operated as a stand-alone, high-volume, filter-based air sampler. 
     As an alternative, there may be as few as two, or more than three, of the sampled airflow inlet spacers  63 , primary airflow outlet spacers  64 , and secondary airflow channel spacers  62 , respectively; in which case the number of sampled airflow inlet slots  75 , primary airflow outlet slots  70 , secondary airflow inlet slots  76 , and secondary airflow channels  73  of a blade  47  may decrease or increase accordingly. 
     As best seen in  FIG. 6 , when a blade  47  is installed in the outer hub  80  the primary airflow slot  70  may comprise a downstream, primary airflow channel  71  that may be formed between a portion of each edge  72  of the blade  47  and the inner surface  83  of the outer hub  80 . As is also best seen in  FIG. 6 , the plane of each edge  72  may lie at an inside angle of about 75 degrees with respect to an imaginary plane of symmetry that passes longitudinally through the center of the blade  47  and that bisects the blade  47  into two identical blade elements  60 . It has been discovered that good flow of the primary airflow  103  through the primary airflow channels  71  may be achieved if the inside angle is in the range of from about 70 degrees to about 80 degrees, although the inside angle may be less than 70 degrees or greater than 80 degrees. A preferred inside angle may be about 75 degrees. 
     A blade  47  may be assembled in any suitable way, such as by assembling its rods  69  to its spacers  63 ,  64 , and by then assembling together its two blade elements  60 . Any suitable means may be used to assemble a blade  47 , such as by using fasteners; interference fits; friction fits; barbed, threaded, bonded, glued or welded connections; splines; keys; or mechanical couplers. 
     When a blade  47  has been assembled, there may be a fluid-tight seal between the corresponding contacting surfaces of the secondary airflow channel spacers  62  and sampled airflow inlet spacers  63  of its two blade elements  60 . 
     Each blade  47  may have corresponding respective parts in the outer and inner hubs  80 ,  81 , namely: (a) a mounting slot  85 , a sampled airflow inlet pocket  84 , and a sampled airflow inlet slot  90  in the outer hub  80 ; and (b) a mounting slot  94  and a secondary airflow inlet slot  96  in the inner hub  81 . Although twenty blades  47  (and their corresponding respective parts) are illustrated, there may be as few as one blade  47  (and its corresponding respective parts), or there may be more than twenty blades  47  (and their corresponding respective parts). Each blade  47  (and its corresponding respective parts) may, or may not, be the same as the other blades  47  (and their corresponding respective parts), such as with respect to their size, shape, construction and air handling capacity. 
     Each blade  47  may be flat as illustrated, or it may be curved, bowed or twisted between its air inlet and air outlet sides  45 ,  46  and between its top and bottom sides  40 ,  41 . 
     Although the blade  47 &#39;s sampled airflow inlet slots  75 , primary airflow outlet slots  70 , and secondary airflow inlet slots  76  are illustrated as being straight, and as having a constant size and shape along their respective lengths, they may not be straight, and they may not have a constant size and shape along their lengths. 
     Although the blade  47 &#39;s rods  69  are illustrated as being straight, and as having a circular cross-sectional profile that is constant in size and shape along their lengths, they may not be straight, they may have any other suitable geometric or non-geometric cross-sectional profile, and they may not have a constant size and shape along their lengths. In addition, all of the rods  69  may, or may not, be the same in all respects. 
     The Outer and Inner Hubs  80 ,  81   
     As best seen in  FIGS. 2, 4-6, 8, and 8A , the hollow outer hub  80  may have top and bottom ends  87 ,  88 ; a sidewall  89 ; and a central cavity  97 . The outer hub  80  may also have for each blade  47  a respective hub sampled airflow inlet port of any suitable size, shape and construction. For example a hub sampled airflow inlet port may comprise an elongated sampled airflow inlet pocket  84  in the outer surface  82  of its sidewall  89 , and a respective elongated mounting slot  85  in the inner surface  83  of its sidewall  89  for receiving the mounting flanges  65  of its respective blade  47 . 
     Each mounting slot  85  may extend from the hub  80 &#39;s top end  87  to its bottom end  88 . An elongated central portion of each mounting slot  85  may form a sampled airflow inlet slot  90  that is in fluid communication with a respective sampled airflow inlet pocket  84 . The inlet slot  90  and inlet pocket  84  may have a length sufficient to make them operable to convey a sampled airflow  102  to the sampled airflow inlet slots  75  of their respective blade  47 . 
     A sampled airflow inlet pocket  84  may comprise two concave sampled airflow inlet lobes  86 , one on either side of the sampled airflow inlet slot  90 . Although the lateral sides of the pocket  84  and lobes  86  are illustrated as having an arcuate profile of constant size and shape along their lengths, they may have any other suitable profile, and may not be of constant size and shape along their lengths. As an alternative, the sampled airflow inlet pocket  84 , or one or both of its lobes  86  may be eliminated. 
     As best seen in  FIGS. 2, 4-5, 9, and 9A , the hollow inner hub  81  may have top and bottom ends  91 ,  92 , a sidewall  93  and a central cavity  95 . The inner hub  81  may have for each blade  47  a respective elongated mounting slot  94  in the outer surface of its sidewall  93  for receiving the O-ring mounting flange  66  and O-ring  68  of a respective blade  47 . The mounting slot  94  may extend from the hub  81 &#39;s top end  91  to its bottom end  92 . A portion of the mounting slot  94  may form a secondary airflow inlet port  96  for the inner hub  81  that is in fluid communication with the central cavity  95 . The secondary airflow inlet port  96  may have any suitable size, shape and construction. For example, the secondary airflow inlet port  96  may be a secondary airflow inlet slot  96 . The inlet slot  96  may have a length sufficient to make it operable to receive a secondary airflow  104  from the secondary airflow outlet slots of its respective blade  47 . The width of the inlet slot  96  may be selected to be at least as large as the width of its corresponding outlet slots, although its width may be selected to be greater or lesser. 
     The inner hub  81 &#39;s top end  91  may have a neck  98  that is sized to be received by the recess  53  in the top plate  42  of the air processor  12 . The inner hub  81 &#39;s bottom end  92  may have a hollow neck  99  having a groove  100  for an O-ring  101 . The hollow neck  99  may serve as a secondary airflow outlet  99  for the inner hub  81  and may be sized to be received by the opening  59  in the bottom plate  43  of the assembly  12 . 
     The air processor  12  may further comprise an optional outlet fitting  77  having a neck  78  sized to fit within the bottom end  92  of the hub  81 , and a flange  79  that is larger than the opening  59  in the bottom plate  43  of the assembly  12 . 
     Although the outer and inner hubs  80 ,  81  are illustrated as generally being elongated cylinders that are straight along their lengths, either or both of them may not generally be an elongated cylinder and may not be straight. Although their central cavities  97 ,  95  are illustrated as having circular cross-sectional profiles of constant size and shape along their lengths, their central cavities  97 ,  95  may not have a cross-sectional profile of constant size and shape along their lengths, and may have any other suitable geometric or non-geometric cross-sectional profile. The size, shape and construction of the top and bottom plates  42 ,  43 , may be modified in any suitable way so as to be operable with any outer and inner hubs  80 ,  81  of any given size shape and construction. 
     Although the sampled airflow inlet slots  90 , and the secondary airflow inlet slots  96  are illustrated as being straight and as having a constant size and shape along their lengths, they may not be straight and may not have a constant size and shape along their lengths. 
     Assembly of the Air Processor  12   
     The air processor  12  may be assembled in any suitable way, such as by placing the bottom edge of the annular filter  44  in its mounting groove  57  in the bottom plate  43 , and by placing the bottom end  88  of the outer hub  80  in its recess  58  in the bottom plate  43 . There may be a fluid-tight seal between the bottom plate  43  on the one hand, and the bottom end  88  of the outer hub  80  and the bottom edge of the filter  44  on the other hand. 
     The O-ring  101  may be assembled to the neck  99  of the inner hub  81 , by seating it in its groove  100  on the neck  99 . The neck  99 , with its O-ring  101 , may then be inserted into the opening  59  in the bottom plate  43 . The O-ring  101  may provide a fluid-tight seal between the neck  99  and the opening  59 . 
     Each blade  47  may have its O-ring  68  assembled to its O-ring mounting flanges  66  by seating the O-ring  68  in the grooves  67  in its flanges  66 . Each blade  47  may then be inserted into its respective mounting slots  85 ,  94  in the outer and inner hubs  80 ,  81  until it is in contact with the bottom plate  43 . 
     The O-ring  68  may serve multiple functions. As best seen in  FIGS. 5 and 5B , the O-ring  68  may provide a fluid-tight seal between the blade  47  and its mounting slot  94  in the inner hub  81 . In addition, the O-ring  68  may also serve the function of resiliently urging its blade  47  radially outwardly, to properly seat its blade  47  in its respective mounting slot  85  in the outer hub  80 . This may provide the dual functions of: (a) helping to provide a fluid-tight seal between the mounting flanges  65  of its blade  47  and its respective mounting slot  85 , and (b) helping to properly locate the blade  47 &#39;s sampled airflow inlet slot  75  with respect to its respective sampled airflow inlet slot  90  in the outer hub  80 . 
     The top plate  42  may then be assembled to the filter  44 , outer hub  80 , and inner hub  81  by inserting the top edge of the filter  44  into its annular groove  50  in the top plate  42 , by inserting the top end  87  of the outer hub  80  into its annular recess  51  in the top plate  42 , and by inserting the top neck  98  of the inner hub  81  into its circular recess  53  in the top plate  42 . Fluid-tight seals may be provided between the top plate  42  on one hand, and the top end  87  of the outer hub  80 , the neck  98  of the inner hub  81 , and the top edge of the filter  44  on the other hand. 
     The optional mounting feet  49  for the optional tripod legs  13  may be assembled to the bottom plate  43  in any suitable location on the bottom plate  43 . The legs  13  may then be assembled to their respective mounting feet  49 . The mounting feet  49  and legs  13  may, or may not, comprise part of the air processor  12 . 
     It may be preferable that subsequent access to the interior of air processor  12 , such as for cleaning, be performed by removing bottom plate  43 , rather than top plate  42 . This is because it may be difficult to access the connection between fan assembly  11  and air processor  12 , once the fan  16 , fan plate  18  and vanes  19  have been assembled to the fan plenum  15 . 
     The fan assembly  11  and the air processor  12  may be assembled together by assembling the mounting flange  25  of the fan assembly  11  to the top surface of the top plate  43  of the air processor  12 . A fluid-tight seal may be provided between the mounting flange  25  and the top plate  43 . 
     An optional outlet fitting  77 , which may or may not comprise part of the air processor  12 , may be assembled to the bottom plate  43  by inserting its top neck  78  into the secondary airflow outlet  99  of the inner hub  81  until its flange  79  is in contact with the bottom of the bottom plate  43 . Fluid-tight seals may be provided between its neck  78  and the inner hub  81 , and between its flange  79  and the bottom plate  43 . The air input of any suitable air sampler, particle analyzer, or analytical device which may or may not comprise part of the air processor  12 , may then be connected in any suitable way to the bottom neck  48  of the outlet fitting  77  either directly, or indirectly, so that it can receive the secondary airflow  104  and the particles containing target material that it contains from the inner hub  81 . 
     Alternatively, any other suitable outlet fitting  77  may be provided which is operable to serve the functions of the outlet fitting  77 . As a further alternative, the outlet fitting  77  may be eliminated and the air input of the air sampler, particle analyzer, or analytical device may be connected in any suitable way to the secondary airflow outlet  99  of the inner hub  81 , either directly or indirectly. 
     The various parts of the concentrator  10  may be assembled together in any suitable ways, such by using fasteners; interference fits, friction fits; barbed, threaded, bonded, glued or welded connections; splines; keys; or mechanical couplers. 
     The O-rings  68  and  101  may be made from rubber or any other suitable resilient or elastomeric material. The filter  44  may be made from any suitable screening or from any suitable filter media, depending on the size of the undesired particles that it is designed to prevent from entering the outer hub  80 . 
     The fan assembly  11 &#39;s plenum  15 , fan plate  18 , impeller  30 , and vanes  19 ; the power cable assembly  21 &#39;s conduit  35 , connector  37 , and clips  38 ,  39 ; and the air processor  12 &#39;s top and bottom plates  42 ,  43 , outer and inner hubs  80 ,  81 , and blades  47  may be made in any suitable way from any suitable strong, durable substance, such as from metal, plastic, or composite material. 
     Operation of the Air Processor  12   
     In order to create a sampled airflow  102  that flows into the air processor  12 , the fan  16  in the fan assembly  11  may be turned on, to create a negative air pressure in the air outlets  55  in the top plate  42  and in the cavity  97  of the outer hub  80 . The higher ambient pressure sampled air in the vicinity of the inlet pockets  84  and inlet slots  90  of the outer hub  80  may then create a sampled airflow  102  that flows into the pockets  84 , whose curved, concave lobes  86  may desirably impart some rotational motion to the sampled airflow  102  within the pockets  84  before it reaches the inlet slots  90 . 
     For simplicity, and referring now to  FIG. 6 , the flow of the sampled airflow  102  through one pocket  84  and its respective inlet slot  90  and blade  47  will now be described, it being understood that similar comments may apply to the flow of the sampled airflow  102  into the other pockets  84 , inlet slots  90  and their respective blades  47 . In addition, the flow of the sampled airflow  102  through only one of the blade&#39;s  47  sampled airflow inlet slots  75  will be described, it being understood that similar comments may apply to the other of its inlet slots  75 . 
     The sampled airflow  102  from the inlet slot  90  may enter the blade  47  through the sampled airflow inlet slot  75  that is created by its rods  69 . As best seen in  FIG. 6 , the circular profiles of the blade  47 &#39;s rods  69  may force the incoming sampled airflow  102  into two mirror image semicircular flow patterns around the rods  69  relative to an imaginary plane of symmetry that passes longitudinally through the center of the blade  47  and through the center of its sampled airflow inlet slot  75 . 
     The rotation of the two semicircular flow patterns of the sampled airflow  102  as they flow around their respective rods  69  causes the particles containing target material in the sampled airflow  102  to be subjected to strong centrifugal forces that urge the particles containing target material to move towards the imaginary plane of symmetry, thereby concentrating the particles containing target material in the central portion of the sampled airflow  102  as it passes through the sampled airflow inlet slot  75  that is formed by the rods  69 . 
     The blade  47 &#39;s knife-edged secondary airflow inlet slot  76  may then divide the sampled airflow  102  that it receives from the sampled airflow inlet slot  75  into: (a) left and right primary airflows  103  that flow through the left and right primary airflow slots  70  of the blade  47  and into the left and right primary airflow channels  71  between the outer edges  72  of the blades  47  and the inner surface  83  of the outer hub  80 , and (b) one central secondary airflow  104  that passes into the secondary airflow channel  73  within the blade  47 . 
     The rotation of the sampled airflow  102  around the downstream surfaces of the rods  69  as the sampled airflow  102  is divided into the left and right primary airflows  103  by the inlet slot  76  causes particles containing target material in the sampled airflow  102  to be further subjected to strong centrifugal forces that also urge the particles containing target material to move towards the imaginary plane of symmetry, thereby further concentrating the particles containing target material in the central portion of the sampled airflow  102  downstream from the sampled airflow inlet slot  75  that is formed by the rods  69 . 
     The primary airflows  103  from all of the blades  47  enter the central cavity  97  in the outer hub  80  between the blades  47  and exit the central cavity  97  through the primary airflow outlets  55  in the top plate  42 . 
     The secondary airflow  104  that passes into the secondary airflow channel  73  within the blade  47  carries concentrated particles containing target material because it was created from the central portion of the sampled airflow  102  where the particles containing target material were concentrated, while the left and right primary airflows  103  carry relatively few particles containing target material since they received sampled air from the left and right sides of the sampled airflow  102  which carried relatively few particles containing target material after passing through the inlet slot  75 . 
     Many conventional concentrators rely on virtual impaction principles. Incoming air is prepared for the impaction process by first being formed into a very well-defined collimated beam of air, which is also commonly referred to as a jet of air. Collimation of the primary beam is done by using a very gradually tapered primary slit, or a short straight slit section placed immediately before the point where the beam exits the primary collimating structure. 
     Once the beam of air issues out of the primary slit, it flows across a gap and impinges on a secondary surface containing a second slit. The surface the secondary slit is contained within may range from two angled thin plates, to a flat plane. On the order of 10% of the incoming air jet is taken into the secondary slit, while 45% is exhausted to each side of the slit. The momentum of particulates in the primary beam, assisted by the secondary airflow, causes a fraction of the particulates in the primary beam to penetrate into the secondary slit, instead of continuing on in the sharply deflected and bifurcated primary beam paths. Particulates trapped by the secondary airflow appear as a concentrate of particles therein. This process is very energy inefficient, and frictional losses and geometric expansion losses create a large pressure drop across the primary air circuit. 
     It has been discovered that a significant portion of this undesirable pressure drop can be circumvented by the concentrator  10 &#39;s air processor  12 , because it does not convert the incoming sampled airflow  102  into a collimated beam of sample air. Instead, the sampled airflow  102  flows towards, and through the sampled airflow inlet ports  75  as a non-collimated sampled airflow  102 . 
     The sampled airflow  102  is received by the air processor  12 &#39;s sampled airflow inlet ports  75  which, as best seen in  FIG. 6 , form a two-dimensional contracting/expanding nozzle profile that subjects the sampled airflow  102  to significant centrifugal forces that move particles containing target material towards the central portion of the sampled airflow  102  even before the sampled airflow  102  arrives at the narrowest part of the sampled airflow inlet ports  75 . By placing the secondary airflow inlet ports  76  at a location that is appropriately close to the downstream side of their respective sampled airflow inlet ports  75  and by properly shaping the profiles of the inlet ports  75 , the pressure drop that would otherwise be associated with the sampled airflow  102  entering the inlet ports  75  and trifurcating into left and right primary airflows  103 , and into a central secondary airflow  104 , is minimized, while a high rate of concentration into the secondary airflow  104  of particles containing target material that were initially in the sampled airflow  102  is simultaneously realized. 
     The smoothly varying curvilinear profile of the rods  69  that form the sampled airflow inlet ports  75  contributes to a significant reduction in the pressure drop across the inlet ports  75  by minimizing expansion and contraction pressure drops in the sampled airflow  102 . The distance between the sampled airflow inlet ports  75  and their respective secondary airflow inlet ports  76 , and the shape and size of the curvilinear primary airflow channels  71  between the blades  47  and the inner surface  83  of the outer hub  80 , are chosen so that sudden changes in the cross-section of the primary airflows  104  are minimized. This also means that all these characteristic features are of similar size, and that the entire air processor  12  is relatively shallow up to the secondary airflow inlet ports  76 , reducing the volume and weight of the air processor  12 . 
     It is known that particles containing target material that are about 5 microns or less in diameter tend to be very sticky, in the sense that if they impact on a physical surface they tend to adhere to, i.e., plate out on, that surface and are thus undesirably lost from whatever airflow that carries them. 
     However, it has been discovered that the curved, concave, sampled airflow inlet lobes  86  of each inlet pocket  84  help to minimize such losses of particles containing target material from the sampled airflow  102 . This is because the curved nature of the sampled airflow inlet lobes  86  guide the incoming sampled airflow  102  so that it moves towards the rods  69  in curved flow paths which, as best seen in  FIG. 6 , rarely come into contact with the walls of the lobes  86  or with the outer surfaces of the rods  69 . To ensure that a significant number of particles containing target material are not plated out on the surfaces of the lobes  86 , it is necessary that the centrifugal forces associated with curved path airflow of the sampled airflow  102  adjacent to the surfaces of the lobes  86  be low. This may be done by using lobes  86  that have radii of curvature that are significantly larger than the radii of the rods  69 . Since the velocities of the sampled airflow  102  are lower in the lobes  86 , this also assists in minimizing plate-out of particles containing target material in the lobes  86 . 
     In addition, it has also been discovered that since the rods  69  concentrate particles containing target material into the central portion of the sampled airflow  102  as it passes through the sampled airflow inlet slot  75  between the rods  69 , the loss of particles containing target material from the sampled airflow  102  due to their stickiness is minimized since most of the particles containing target material are kept away from, and do not contact, the outer surfaces of the rods  69  as they flow through the sampled airflow inlet slot  75 . In other words, the circumferential flow of the sampled airflow  102  immediately adjacent to the rods  69  creates a buffer layer of clean sample air (i.e., sample air from which most of the particles containing target material have been removed), between the rods  69  and the central portion of the sampled airflow  102  that passes between them. 
     In addition, most of the particles containing target material that are concentrated in the central portion of the sampled airflow  102  also do not contact the blade  47  as they pass through the blade  47 &#39;s knife-edged secondary airflow inlet slot  76  and into the secondary airflow channel  73  within the blade  47 . 
     Further, it has also been discovered that, due to the smooth, slowly varying symmetrical geometry of the secondary airflow channels  73  about an imaginary plane of symmetry that passes longitudinally through the center of the blade  47 , loss of particles containing target material due to their sticking on the sides of the secondary airflow channels  73  may also be minimized. 
     All of the individual secondary airflows  104  in all of the blades  47 , and all of the concentrated particles containing target material that they carry, flow radially inwardly through their respective secondary airflow channels  73 , exit the blades  47  through their respective secondary airflow outlet slots  75 , and enter the central cavity  95  of the inner hub  81  through their respective secondary airflow inlet slots  96  in the inner hub  81 . 
     It is noted that all of the individual secondary airflows  104  are discharged radially inward into the central cavity  95  of the inner hub  81 , towards the axis A, due to the radial arrangement of the blades  47  with respect to the inner hub  81 . 
     It has been discovered that this radially inward discharge of the secondary airflows  104  desirably causes them to collide with each other in the central portion of the cavity  95 , thereby effectively preventing any of the secondary airflows  104  from directly impacting the inner surface of the inner hub  81 . It may be desirable to avoid a direct impact of any of the secondary airflows  104  on the inner surface of the inner hub  81  because if such a direct impact occurred, many of the particles containing target material in the impacting secondary airflow  104  may be undesirably lost by sticking to the inner surface of the inner hub  81 . 
     The secondary airflow  104 , and the concentrated particles containing target material that it carries, may then exit the inner hub  81  through the outlet fitting  77 . 
     The inlet of any suitable air sampler, particle analyzer, or analytical device may be connected to the outlet fitting  77  in any suitable way. As has been mentioned, due to the “pressure recovery” effect that occurs in the secondary airflow channels  73 , the air pressure of the secondary airflow  104  within the channels  73  may be closer to the ambient pressure of the sample air at the outer hub  80 &#39;s sampled airflow inlet pockets  84  than would otherwise be the case. As a result, the air pressure of the secondary airflow  104  within the inner hub  81 , and at the outlet fitting  77  may also be closer to the ambient pressure of the sample air at the outer hub  80 &#39;s sampled airflow inlet pockets  84  than would otherwise be the case. 
     This “pressure recovery” effect may be useful because, for example, it may desirably reduce the amount of suction or negative pressure that the air sampler, particle analyzer, or analytical device may be required to provide to outlet fitting  77  in order to cause the secondary airflow  104 , and the concentrated particles containing target material that it carries, to flow through the concentrator  10  and out through the outlet fitting  77 , at any particular desired flow rate. 
     Several factors may be important in terms of designing the concentrator  10 , such as the pressure-volume properties of the fan  16  that will be used to drive the concentrator  10 . Other important factors may be certain relative dimensions, or ratios, of specific physical features of the concentrator  10 , since the pressure drop and flow characteristics of the concentrator  10 , as well as its ability to separate particles containing target material from the sampled airflow  102 , may be dependent on these parameters. 
     Referring now to  FIG. 6 , the relative dimensions, or ratios, of importance may include the radius of a sampled airflow inlet lobe  86  relative to the radius of its respective rod  69 ; the radius of a rod  69  relative to the width of its respective sampled airflow inlet slot  75 ; the width of a sampled airflow inlet slot  75  relative to the distance to its respective secondary airflow inlet slot  76 ; and the rate at which the primary airflow channels  71  increase in width versus distance from the plane of symmetry. 
     For design purposes where the sampled airflow  102  is air, and where the particles containing target material have a density of about 1 g/cc and have a diameter in the range of from about 1 micron to about 10 microns, the following design relationships may provide some design guidance. The radius of a sampled airflow inlet lobe  86  may be on the order of about 5× to about 20× the radius of its respective rod  69 ; the radius of a rod  69  relative to its respective sampled airflow inlet slot  75  may be in the range of about 0.5 to about 2.0; the ratio of the width of a sampled airflow inlet slot  75  to the distance to its respective secondary airflow inlet slot  76  may be in the range from about 0.5 to about 2.0; the ratio of the width of the secondary airflow inlet slot  76  to the width of its respective sampled airflow inlet slot  74  may be in the range of from about 0.5 to about 1.5. Other dimensions may also assume importance, but the parameters herein noted may have the greatest effect on the flow rate of the sampled airflow  102  through the air processor  12  and the ability of the air processor  12  to concentrate particles containing target material in the secondary airflow  104 . 
     It has been discovered that because of its novel construction, the concentrator  10  may offer many advantages over other devices. For example, it is unusually compact and light in weight for any given desired flow rate of the sampled airflow  102  through it. This may be due to such factors as: (a) the radial arrangement of its outer hub  80 , blades  47  and inner hub  81  about its axis A; (b) the close spacing between its blades  47 &#39;s sampled airflow inlet slots  75  and secondary airflow inlet slots  76 ; and (c) the relatively small amount of power that it consumes, resulting in a smaller, less powerful fan  16  being needed. 
     The concentrator  10 &#39;s advantage of consuming relatively little power for any given desired flow rate of the sampled airflow  102  through it may be because the concentrator  10  requires a relatively small driving pressure difference between its sampled airflow inlet slots  75  and its primary airflow outlets  55 . This relatively small driving pressure difference may be due to such factors as its curvilinear sampled airflow input structures (its rods  69 ) which transfer particles containing target material very efficiently, with only a small pressure drop, into the central portion of the sampled airflow  102  as it passes through the sampled airflow inlet slots  75 . In addition, as best seen in  FIG. 6 , the primary airflow outlet slots  70  are sized with respect to the curvilinear primary airflow outlet channels  71  so that sudden changes in the flow cross sections of the sampled airflow  102  are minimized as it divides into left and right primary airflows  103 , resulting in a small pressure drop between the slots  70  and the channels  71 . Further, the close spacing between the sampled airflow inlet slots  75  and the secondary airflow inlet slots  76  results in a reduced pressure drop between the slots  75 ,  76 . In addition, the radial arrangement of the concentrator  10 &#39;s outer hub  80 , blades  47  and inner hub  81  about its axis A results in relative short flow paths, and relatively small pressure drops, of the sampled, primary and secondary airflows  102 ,  103 ,  104  as they flow through the concentrator  10 . 
     Example Concentrator  10   
     The various parts of the concentrator  10  are at least approximately shown to scale in the Figures. By way of example, the concentrator  10  may have an overall height of about 35.2 cm. Its fan plenum  15  may have a maximum diameter of about 23.8 cm and an overall height of about 17 cm. 
     The filter  44  for the outer hub  80  may be a coarse screen with openings about 0.6 cm square to prevent large debris from entering the outer hub  80 . The outer hub  80  may have an outside diameter of about 16.7 cm and an inside diameter of about 14.8 cm. Each lobe  86  of a sampled airflow inlet pocket  84   86  in the outer hub  80  may be cylindrical in nature and have a circular cross section with a radius of about 0.65 cm. The sampled airflow inlet slots  90  in the inlet pockets  84  may be about 14 cm long and about 3.8 mm wide. Together, two lobes  86  and their respective inlet slot  90  create an opening in the outer surface  82  of outer hub  80  that is 2.29 cm wide. 
     Each blade  47  may be about 6.1 mm thick, as measured between the outer surfaces of its two blade elements  60 . The outer edges  72  of the blade bodies  61  of each blade  47  may be tapered at an angle of about 75° with respect to an imaginary plane of symmetry that passes longitudinally through the center of the blade  47 . The rods  69  of a blade  47  may be about 1.6 mm in diameter and each sampled airflow inlet slot  75  between the rods  69  may be about 0.61 mm wide and about 6.7 cm long. 
     Each secondary airflow channel  73  in a blade  47  may have a knife-edge secondary airflow inlet slot  76  having a width of about 0.61 mm, which may match the 0.61 mm width of its corresponding sampled airflow inlet slot  75 . The inlet slot  76  may be about 0.5 mm downstream from the lowest point of the rods  69 , as best shown in  FIG. 6 . This distance may usefully fall within the range of about 0.3 mm to about 0.8 mm. 
     Each secondary airflow channel  73  may have a length of about 4.75 cm, as measured between its secondary airflow inlet and outlet slots  75 . 
     The width of each secondary airflow channel  73  may increase from its 0.61 width at its inlet slot  76  to a width of about 0.15 cm over a distance of about 0.25 cm downstream from its inlet slot  76 , as best seen in  FIGS. 5A, 6 and 15 . This increase in the width of the secondary airflow channel  73  may be due to its sidewalls within the blade bodies  61  diverging at about a 10 degree angle with respect to an imaginary plane of symmetry that passes longitudinally through the center of the blade  47 , before its sidewalls become parallel to each other about 0.25 cm downstream from the inlet slot  76 . 
     The inner hub  81  may have an internal diameter of about 4.3 cm, with the internal diameter of the outlet fitting  77  being somewhat less. 
     Test Results for Example Concentrator  10   
     For the tests, the fan assembly  11  for the example concentrator  10  was selected to enable the concentrator  10  to have a flow rate of the sampled airflow  102  through it in the range of about 3,000 to 3,600 LPM. When the example concentrator  10  was operated at these flow rates, its total electric power consumption rate was measured to be only 50 to 90 watts. 
     The curves  108 ,  109  in  FIG. 20  show typical data for the Concentration Factor as a function of the Particle Effective Diameter. The Particle Effective Diameter is the effective diameter of the test particles in the sampled airflow  102 . To generate the curves  108 ,  109 , the flow rate of the sampled airflow  102  was 3,600 LPM and 3,000 LPM, respectively, while the flow rate of the secondary airflow  104  was held constant at 300 LPM. 
     The Concentration Factor was determined by taking the ratio of the number of test particles per unit volume in the secondary airflow  104  and the number of test particles per unit volume in the incoming sampled airflow  102 . For example, if the secondary airflow  104  had ten test particles per unit volume, and the sampled airflow  102  had two test particles per unit volume, then the Concentration Factor would be five (i.e., 10/2=5). 
     The test particles that were used in the tests were made by the Duke Scientific Corporation of Palo Alto, Calif. and were fluorescent polystyrene micro spheres, and fragments thereof, having a density of 1.05 g/cc. The curves  108 ,  109  were determined from multiple test runs using a Met One  200 L laser particle counter, made by Met One Instruments, Inc. of Grants Pass, Oreg., to count the number of test particles per unit volume in the sampled airflow  102  and in the secondary airflow  104 . 
     The curves  108 ,  109  show that the test particles of 1.05 g/cc (which is typical of particles of organic target material), and that had effective optical diameters in the range of 0.5 to 1.0 microns were concentrated by a factor of 3× to 5.6×. Test particles in the range of 1.0 to 2.0 microns were concentrated by a factor of 4× to 5.8×, while 10-micron test particles were concentrated by a factor of about 6.4× to 7.3×. 
     Referring now to  FIG. 21 , its curve  110  shows the Relative Concentration in Secondary Airflow as a function of the Secondary Airflow Flow Rate. The Relative Concentration in Secondary Airflow is the relative concentration of the test particles in the secondary airflow  104 , as compared to the Concentration Factor in  FIG. 20 . The Secondary Airflow Flow Rate is the flow rate of the secondary airflow  104 . The open circle data points  111  on the curve  110  are theoretical data points, while the solid circle data points  112  on the curve  110  are actual data points. 
     As shown by the curve  110 , reducing the flow rate of the secondary airflow  104  can significantly further enhance the concentration of the test particles in the secondary airflow  104 . For example, at a flow rate of the secondary airflow  104  of about 40 LPM, the curve  110  shows that the Concentration Factors shown in  FIG. 20  are increased by about 3×. In other words, for 1.0-micron test particles the Concentration Factors of 4.0× to 5.6× shown in  FIG. 20  are increased to about 12× to 16.8×; for 2.0-micron test particles the Concentration Factors of 4.6× to 5.8× shown in  FIG. 20  are increased to about 13.8× to 17.4×; and for 10.0-micron test particles the Concentration Factors of 6.4× to 7.3× shown in  FIG. 20  are increased to about 19.2× to 21.9×. 
     Curve  113  in  FIG. 21  shows the Total Particles Concentrated (Relative %) as a function of the Secondary Airflow Flow Rate of the secondary airflow  104 . The Total Particles Concentrated (Relative %) is the relative percentage of test particles in the sampled airflow  102  that appeared in the concentrator  10 &#39;s secondary airflow  104 , normalized to collection performance at a flow rate of the secondary airflow  104  of 300 LPM (300 LPM=100%). 
     Curve  113  shows that the percentage of test particles that are concentrated in the secondary airflow  104  begins to fall for flow rates of the secondary airflow  104  that are below about 250 LPM, which is about 8% of the flow rate of a sampled airflow  102  having a flow rate of 3,000 LPM, and which is about 7% of the flow rate of a sampled airflow  102  having a flow rate of 3,600 LPM. It is theorized that the collection efficiency eventually falls as the flow rate of the secondary airflow  104  decreases because a certain flow rate of the secondary airflow  104  is required to fully deplete the central portion of the sampled airflow  102  immediately in front of the secondary airflow inlet slot  76  into which the test particles were concentrated. 
     Concentrator  10   a    
     Turning now to  FIGS. 17-19 , the concentrator  10   a  is the same as, or at least similar to the concentrator  10  of  FIGS. 1-16  in all respects, except for those differences which will be made apparent by all of the disclosures herein. In addition, for clarity and simplicity, certain parts of the concentrator  10   a  of  FIGS. 17-19  have been given the same reference numerals, with an “a” suffix, as the reference numerals used for the corresponding respective parts of the concentrator  10  of  FIGS. 1-16 . 
     In general, the primary conceptual difference between the concentrator  10  and the concentrator  10   a  may be that the concentrator  10   a  has been modified so that it may serve the additional function of being its own air sampler, particle analyzer or analytical device, i.e., so that it may remove the particles containing target material from the secondary airflow  104 , so that the removed particles containing target material may be observed, examined, tested and evaluated. 
     As seen in  FIGS. 17-19 , the lower portion of the concentrator  10   a &#39;s air processor  12  may have a filter assembly comprising a bottom end plate  43   a ; a seal  116 ; a filter  117  that may have a filter element  118 ; a filter holder  119 ; a filter support  120 ; a filter adapter  121 ; and mounting feet  49   a  that may also be used to releasably assemble the filter adapter  121  to the bottom of the bottom plate  43   a.    
     The bottom plate  43   a  may have four secondary airflow outlet ports  122 , a support ring  123  for the inner hub  81 , and four arms  124  for supporting the support ring  123 . The bottom of the support ring  123  may have an annular groove  134  for the seal  116 . The bottom plate  43   a  may also have an annular groove  57   a  for receiving the bottom edge of the filter  44   a , an annular recess  58   a  for receiving the bottom end  88  of the outer hub  80 , and an opening  59   a  in the support ring  123  for receiving the bottom neck  99  and O-ring  101  of the inner hub  81 . 
     The filter element  118  may comprise any suitable filter media and may be selected to be able to remove from the secondary airflow  104  the particular kind of particles containing target material that may be of interest to the user of the concentrator  10   a . The filter holder  119  may be of any suitable construction and may have for example, a filter holder handle  124  and a filter holder ring  125  to which the filter element  118  may be assembled. Alternatively, the filter holder  119  may be eliminated, in which case the filter element  118  may be held in place by the filter support  120 . 
     The filter support  120  may have a support ring  126  and four support legs  127 . The filter adapter  121  may have a rim  128 , three mounting notches  129  and a filter cup  130 . Each mounting foot  49   a  may have a filter adapter notch  131  and a bore  132  into which a spring-loaded pin assembly  133  has been assembled. 
     The forgoing components of the concentrator  10   a  may be assembled in any suitable way, such as by assembling the seal  116  in its groove  133  in the bottom of the inner hub support ring  123 . The filter element  118  may be assembled to the filter holder ring  125  or the filter element  118  may have been pre-assembled to the filter holder ring  125 . 
     The filter support  120  may be assembled to the adapter  121  by assembling its support legs  127  to any suitable locations on the inside of the bottom of the adapter  121 &#39;s filter cup  130 , and the mounting feet  49   a  may be assembled to any suitable locations on the outside of the bottom of the adapter  121 &#39;s filter cup  130 . The filter  117  may be releasably assembled to the filter support  120  by placing the filter holder ring  125  onto the support ring  126 . 
     The adapter  121  may then be releasably assembled to the bottom of the bottom plate  43   a  by locating the mounting feet  49   a  in the notches  129  in its rim  128 , as best seen in  FIG. 19 , and by then moving the adapter  121  towards the bottom plate  43   a  until its rim  128  touches the bottom of the bottom plate  43   a . The adapter  121  may then be rotated until the edges of its rim  128  that are adjacent to its notches  129  enter respective notches  131  in the mounting feet  49   a , and are releasably held in place there by the spring loaded pins  133  in the mounting feet  49   a . When the adapter  121  and the bottom plate  43   a  are assembled together, there may be a fluid-tight seal between: (a) the support ring  126 , the filter holder ring  125 , the seal  116  and the bottom of the bottom plate  43   a ; and (b) between the adapter  121 &#39;s rim  128  and the bottom of the bottom plate  43   a.    
     To remove or replace the filter  117  after it has been used, the adapter  121  may be rotated until the edges of its rim  128  that are adjacent to its notches  129  leave their respective notches  131  in the mounting feet  49   a , and are no longer engaged by the spring loaded pins  133 , at which time the adapter  121  may then be removed from the bottom of the bottom plate  43   a.    
     In the example concentrator  10  which was described above, when the sampled airflow  102  had a flow rate of about 3,600 LPM, and the secondary airflow  104  had a flow rate of about 300 LPM, the static pressure of the primary airflow  103  within the central cavity  97  of the outer hub  80  may be about −4.6 cm of water, relative to the ambient pressure of the sampled airflow  102  that surrounds the outer hub  80 . On the other hand, the static pressure of the secondary airflow  104  within the central cavity  95  of the inner hub  81  may be about −0.25 to about −0.4 cm of water relative to the ambient pressure of the sampled airflow  102  that surrounds the outer hub  80 . Therefore there is a static pressure differential of at least about 4.2 cm of water between the relatively higher pressure secondary airflow  104  in the central cavity  95  of the inner hub  81 , and the relatively lower pressure primary airflow  103  in the central cavity  97  of the outer hub  80 . 
     The concentrator  10   a  uses this static pressure differential so that the relatively higher pressure secondary airflow  104  in the central cavity  95  of the inner hub  81  will sequentially flow: (a) through the filter element  118  (which will remove the particles containing target material from the secondary airflow  104  passing through it), (b) into the cavity  135  in the adapter  121 &#39;s cup  130 , (c) out of the cavity  135  through the secondary airflow outlet ports  122  in the bottom plate  43   a , (d) into the central cavity  97  of the outer hub  81  between the blades  47  (where the secondary airflow  104  will mix with the primary airflow  103 ), (e) out of the cavity  97  through the air outlets  55  in the top plate  42 , and (f) and out through the fan assembly  11  in the manner previously described for the primary airflow  103  of the concentrator  10 . 
     This means that the concentrator  10   a  may serve the dual functions of: (a) concentrating the particles containing target material from a high flow rate sampled airflow  102  into a low flow rate secondary airflow  104 , and (b) serving as an air sampler, particle analyzer or analytical device by removing the particles containing target material from the low flow rate secondary airflow  104  in any suitable way, such as by using the filter  117 . 
     Thus, the concentrator  10   a  offers many advantages. For example, it eliminates the need for a separate air sampler, particle analyzer or analytical device to remove the particles containing target material from the secondary airflow  104 ; and its low flow rate secondary airflow  104  through its filter  117  will help to prevent damage to particles containing target material that are delicate, such as if the particles containing target material were organisms. In addition, because of the low flow rate of the secondary airflow  104 , the surface area of the filter element  118  in its filter  117  may be selected to minimize the volume or area of the filter element  118 , thereby potentially maximizing the efficiency with which the particles containing target material that the filter element  118  removed from the secondary airflow  104  can be extracted from the filter element  118 , as compared to a filter element  118  that was sized in area or volume to remove particles containing target material from a high flow rate sampled airflow  102 . 
     Some alternative constructions of the concentrator  10   a  will now be described. First, the filter support  120  may be eliminated, in which case the filter  117  may be releasably assembled directly to the bottom of the hub support ring  123  over the opening  59   a  in any suitable way. 
     Second, the filter  117  and filter support  120  may both be eliminated, and the circular filter  117  may be replaced by one or more annular filter segments  117  that may be releasably secured in any suitable way to the bottom of the bottom plate  43   a  over the secondary airflow outlet ports  122 . 
     Third, the adapter  121  may be releasably assembled to the bottom of the bottom plate  43   a  in any suitable way other than that which was described above; and the adapter  121  may have any other suitable size, shape and construction as long as it is operable to convey the secondary airflow  104  from the opening  59   a  to the secondary airflow outlet ports  122 . 
     Example Uses of the Concentrators  10 ,  10   a ,  10   b    
     Contraband is a serious problem at ports worldwide, and devices are needed that will efficiently interrogate shipping containers  137  (see  FIG. 23 ) of various sizes, ranging from aircraft shipping containers to 40-foot ocean-going shipping containers. By interrogation, it is meant that particles containing target material in the sample air within the shipping containers  137  are removed from such sample air, such as for observation, identification, examination, testing or analysis. The particles containing target material may be particles of any material of interest, such as particles of drugs, explosives, and biowarfare materials. 
     The concentrators  10 ,  10   a , and  10   b  may be particularly helpful in any situation where large volumes of sampled airflow  102  must be processed during the interrogation of the shipping container  137 , and it is desired that the processing time be minimized, whether the large volumes of sampled airflow  102  are from shipping containers  137 , or from any other wholly or partially enclosed spaces of interest, such as sports auditoriums and conference halls. In general, any such wholly or partially enclosed space of interest may be called a “sample space”. 
     After the concentrators  10 ,  10   b  have processed the sampled airflow  102 , particles containing target material may be removed from their respective secondary airflows  104  by any suitable air sampler, particle analyzer, or analytical device that may be connected to their respective outlet fittings  77 . On the other hand, it may not be advantageous to connect a separate air sampler, particle analyzer, or analytical device to the concentrator  10   a , since its filter element  118  will remove particles containing target material from its secondary airflow  104 . 
     By way of example, the use of the concentrator  10   b  to interrogate an ocean going shipping container  137  will now be described, it being understood that the same or similar comments will apply to using any of the concentrators  10 ,  10   a ,  10   b  to interrogate any other wholly or partially enclosed space. 
     An ocean-going shipping container  137  may have an interior volume of up to 50,000 liters, or more. The concentrator  10   b  may have the same performance characteristics that were described above regarding the example concentrator  10 , i.e. the concentrator  10   b  may produce and process a sampled airflow  102  having a flow rate of about 3,600 LPM. Thus, even if the container  137  were entirely empty of contents  144 , the concentrator  10   b  would be able to process one turn of air from inside such a container  137  in only about fourteen minutes. By comparison, typical portable air samplers, particle analyzers, and analytical devices may process a sampled airflow  102  in the range of about 150 to 500 LPM. Accordingly, such devices would take from about 1.7 to about 5.6 hours to process one turn of air from inside such a container  137 , which may be an unacceptably long period of time in view of the large number of containers  137  that may need to be interrogated, and the speed with which dockside transfer procedures for containers  137  are carried out. 
     From the above it is seen that the concentrator  10   b  may be able to process the air from such a container  137  from 7× to 24× faster than a typical portable air sampler, particle analyzer or analytical device. 
     In addition, like the concentrator  10 , the concentrator  10   b  may be easily designed (e.g., by being scaled up in size), so as to be able to produce and process a sampled airflow  102  having any desired flow rate, thereby reducing even further the amount of time it would take for the concentrator  10   b  to process one turn of air from inside a shipping container  137 . 
     The concentrator  10   b  may be used to interrogate a shipping container  137  in any number of ways. For example, it (and its associated air sampler, particle analyzer, or analytical device that is connected to its outlet fitting  77 ) may be placed within the container  137 . The concentrator  10   b  may have several useful attributes for efficient interrogation when it is placed within the container  137 . First, it is compact. Second, it collects sampled air from within the container  137  over a 360° radial swath, providing effective sampling of the largest lateral area possible. 
     Third, the discharge of the primary airflow  103  from its fan plenum  15  in the form of a jet of air may offer the advantages of: (a) being very effective at sweeping the container  137 &#39;s inner surfaces and the outer surfaces of its contents  144 , to release into the air within the container  137  particles containing target material from the container  137 &#39;s interior surfaces and from the outer surfaces of its contents  144 ; and (b) producing an induced draft effect that may desirably cause the circular sensing radius of the concentrator  10   b  to more than double by causing a desirable inward flow of the air within the container towards the concentrator  10   b &#39;s inlet  149 . In other words, the induced draft effect may create large circulating air patterns within the container  137  that ensure more effective sampling of the entire internal volume of the container  137 , since the circulating patterns may serve to move air from even the most remote portions of the container  137  towards the concentrator  10   b.    
     Alternatively, any other suitable air-moving device other than the concentrator  10   b  may provide the jet of air. 
     As seen in  FIG. 23 , another way to use the concentrator  10   b  to interrogate a shipping container  137  may be to locate the concentrator  10   b  (and its associated air sampler, particle analyzer, or analytical device that is connected to its outlet fitting  77 ), outside of the container  137 . 
     In this event, the container  137  may be provided with any suitable inlet and outlet ports  138 ,  139  having any suitable size, shape and construction. The ports  138 ,  139  may be located in any suitable location in any of the container&#39;s sidewalls  161 , doors, top, or bottom in order to access the airspace  143  within the container  137 . Preferably, the ports  138 ,  139  may be located near the top of the container  137 &#39;s sidewalls  161  in order to access the air space  143  that is typically found within the container  137  over the contents  144 , even when the container  137  is considered to be fully loaded. 
     Placing the ports  138 , 139  in the doors may be more practical than other alternatives because it may be, for example, easier and less expensive to retrofit ports  138 ,  139  into the doors, or to replace doors without ports  138 ,  139  with doors having ports  138 ,  139 , than it would be to create the necessary ports  138 ,  139  in the container  137 &#39;s sidewalls  161 , top or bottom. 
     The inlet  149  of the concentrator  10   b &#39;s shroud  147  may be fluidly connected to the container  137 &#39;s outlet port  139  in any suitable way, such as by using any suitable input duct  141  of any suitable size, shape and construction. The duct  141  may convey the sampled airflow  102  from the interior of the container  137  to the shroud  147  of the concentrator  10   b . An optional output duct  142  may fluidly connect the outlet  23  of the fan plenum  15  to the container  137 &#39;s inlet port  138 . Any suitable duct  142  may be used, which may be of any suitable size, shape and construction. If a duct  142  is used, it may convey the primary airflow  103  from the fan plenum  15  to the container  137 &#39;s inlet port  138 . 
     During operation of the concentrator  10   b  of  FIG. 23 , its fan assembly  11  will create a negative air pressure at the primary airflow outlets  55  of the air processor  12  that will enable the relatively higher pressure sampled air in the container  137  to form a sampled airflow  102  that will flow from the airspace  143  in the container  137 , through the input duct  141  to the annular airspace inside of the shroud  147 , and then through the air processor  12 . The primary airflow  103  from its fan assembly  11  may then flow through the output duct  142  to the container  137 &#39;s inlet port  138 , where it may re-enter the airspace  143  in the container  137 . The secondary airflow  104  (and the particles containing target material that it carries), may exit the concentrator  10   b  through the outlet fitting  77 , to which any suitable low flow rate air sampler, particle analyzer, or analytical device may be connected. 
     It has been discovered that a desirable circulatory airflow pattern  145  within the container  137 &#39;s airspace  143  may be created if the ports  138 ,  139  are, as seen in  FIG. 23 , located in the same sidewall  161  of the container  137 , are located near the top of that sidewall  161 , and are located near the corners formed by their respective adjacent sidewalls  161 . In  FIG. 23 , the sidewall  161  in which the ports  138 ,  139  are located comprises the container  137 &#39;s doors. Alternatively, either or both of the ports  138 ,  139  may be located in the container  137 &#39;s top or bottom. 
     By so locating the ports  138 ,  139  as seen in  FIG. 23 , the returning primary airflow  103  from the concentrator  10   b &#39;s output duct  142  will enter the airspace  143  within the container  137  through its inlet port  138  as a jet of high velocity, axially-directed air, which creates a desirable circulatory airflow pattern  145  in the airspace  143 . Corner injection of the primary airflow  103  through the container  137 &#39;s inlet port  138  into the airspace  143  in the form of a jet of air ensures good penetration of the primary airflow  103  into the container  137  and helps ensure that even sample air in the remotest parts of the container  137  may exit the container  137  through its outlet port  139  and enter the concentrator  10   b  through its input duct  141 . 
     As an added benefit, circulating the primary airflow  103  in this manner back into the container  137  minimizes exposure of dock personnel to any dangerous particles containing target material (or any other dangerous particles) that may be present in the primary airflow  103 . However, as an alternative, the duct  142  may be eliminated so that the primary airflow  103  may be ejected into the air in the vicinity of the concentrator  10   b , rather than back into the container  137 . 
     Vibrating the Container  137  and its Contents  144   
     During use and shipment of the container  137 , it is highly likely that a significant number of particles containing target material may have been released into the air within the container  137  by its contents  144 . Many of such particles containing target material may have then adhered themselves to the internal surfaces of the container  137  and to the external surfaces of the contents  144 . 
     It has been discovered that if the walls of the container  137  are vibrated (which will then also vibrate the contents  144 ), such vibrations of the walls of the container  137  and contents  144  may desirably cause at least some of these adhering particles containing target material to be desirably released into the air within the container  137  from the internal surfaces of the container  137  and from the external surfaces of the contents  144 . This may be done either before, or during, the use of the concentrators  10 ,  10   a ,  10   b  to process the air within the container  137 . 
     In the following discussion, vibrating just the container  137  will be discussed, it being understood that vibrating the container  137  will always cause the contents  144  within the container to also vibrate. 
     Any suitable vibration apparatus may be used to vibrate the container  137 , in any suitable way. One or more of the vibration apparatus may be removably or permanently assembled to the container  137  in any suitable way, such as by using mechanical or magnetic fasteners; interference fits; friction fits; barbed, threaded, bonded, glued or welded connections; splines; keys; or mechanical couplers. 
     For example, the vibration apparatus may be any suitable electric, pneumatic, or hydraulic mechanical vibrator having any suitable size, shape and construction, such as the mechanical vibrator  150  that is illustrated in  FIG. 24 . The vibrator  150  may comprise any suitable motor  151  assembled to a base  153  that may be assembled to the container  137 . The motor  151  may rotate an eccentric weight  152 . As the eccentric weight  152  rotates, it subjects the container  137  to a strong vibration. There is nothing per se novel about the vibrator  150 , except for its size, since this manner of generating vibrations is commonly used (on a much smaller scale) for ringless cell phone annunciators. 
     As a further example, if the container  137  is made from steel, the vibration apparatus may comprise any suitable electromagnetic vibrator of any suitable size, shape and construction that may be used to electromagnetically vibrate the container  137  in any suitable way. This will in essence turn the part of the container  137  that is located beneath the electromagnetic vibrator into a sort of loudspeaker. This is because during operation of the electromagnetic vibrator, the part of the container  137  that is located beneath it will form a magnetically permeable diaphragm, which may be made to move in and out in response to the magnetic forces applied to it by a closely coupled electromagnet that forms part of the electromagnetic vibrator. 
     An example of an electromagnetic vibrator  154  is illustrated in  FIG. 25 , and may comprise a cylindrical magnetically permeable housing  155  having a circular cross-sectional profile, a cylindrical magnetically permeable core piece  156 , a cylindrical optional permanent magnet  157 , and an annular electromagnetic winding  158  that encircles the core piece  156 . Together, the core piece  156  and the winding  158  form a powerful electromagnet. 
     The magnet  157  and winding  158  may be assembled to the interior of the housing  155 , and the core piece  156  may be assembled to the magnet  157 . Alternatively, if there is no magnet  157 , then the core piece  156  may be assembled to the interior of the housing  155 . The housing  155 &#39;s annular rim  159  may be releasably or permanently assembled to the container  137 , with a small air gap  160  being located between the container  137  and the core piece  156 . 
     If the vibrator  154  includes a permanent magnet  157 , the functions of the magnet  157  may include biasing the vibrator  154 &#39;s magnetic operating point in any desirably way or assisting in magnetically assembling the vibrator  154  to the container  137 . 
     During operation of the vibrator  154 , when a sinusoidal drive current is applied to its electromagnetic winding  158 , the magnetic force across the air gap  160  will vary as a function of the applied sinusoidal drive current, causing the part of the magnetically permeable container  137  that is located beneath the vibrator  154  to vibrate in and out, thereby turning that part of the container  137  into a loudspeaker element. 
     As an alternative, the housing  155  may have any suitable geometric or non-geometric cross-sectional profile other than circular. For example, the housing  155  may have a square or rectangular cross-sectional profile and be sized so as to fit between the reinforcing ribs that often form part of the sidewalls of a container  137 . 
     As a further alternative, the vibration apparatus may comprise any suitable magnetostrictive or piezoelectric solenoid, which may replace the electromagnetic vibrator  154 . In such an event the part of the container  137  that is located beneath the solenoid may serve as an acoustic transducer that vibrates in and out as a function of the forces applied to it by the solenoid. 
     As another alternative, the vibration apparatus may comprise any suitable acoustic transducer of any suitable size, shape and construction, which may be assembled to the exterior of the container  137  in any suitable way, or which may be located within the container  137  in any suitable way. In either event, the acoustic transducer may be used to cause the container  137  to vibrate in any suitable way. 
     As a further alternative, the vibration apparatus may comprise acoustic energy itself, in which case the acoustic energy may be introduced into the interior of the container  137  in any suitable way, such as through any suitable opening in the container  137 , such through its inlet or outlet ports  138 ,  139 , in order to vibrate the container  137 . 
     It is known that if acoustic energy is injected into one end of a closed-ended structure, at certain frequencies one or more acoustic resonances, i.e., standing waves, will form within the structure. It has been discovered that such acoustic resonances may be used to more effectively vibrate the container  137  as compared to if no acoustic resonances were formed within the container  137  by the inputted acoustic energy. 
     Although forming a single fundamental acoustic resonance within the container  137  may have some value, it has been further discovered that injecting a range of frequencies of acoustic energy into the container  137  may vibrate the container  137  even more effectively, because the antinodes of the acoustic energy resonances will travel down the length of the container  137  and provide, in effect, desirable acoustic energy resonance peaks at different points along the length of the container  137 . At resonance, the acoustic level in the container  137  may be considerably higher than at the input source since each cycle of the inputted acoustic energy serves to constructively build upon the previous cycle. 
     It is well known that odd-harmonics are resonant, so that the first harmonic for the container  137  would have a wavelength of four times the length of the container  137 , the third harmonic would have a wavelength of four-thirds of the length of the container  137 , and so on. For example, for a typical 40-foot shipping container  137 , the fundamental resonant frequency in air at 25° C. is about 7.1 Hz. Any suitable mechanical vibrator  150 , electromagnetic vibrator  154 , magnetorestrictive solenoid, piezoelectric solenoid, or acoustic transducer, such as a conventional loudspeaker may easily generate this fundamental resonant frequency, and the first few odd harmonics, in any suitable way. 
     It has been discovered that cycling the acoustic energy within the container  137  between odd harmonic resonances will cause the container  137  to strongly vibrate. 
     Either or both of the container  137 &#39;s ports  138 ,  139  may also be used to inject acoustic energy into the container  137  at frequencies that are selected to generate resonant acoustic energy peaks that travel longitudinally back and forth within the container  137 , to vibrate the container  137 . 
     More complex or more robust acoustic energy patterns or resonances may be generated within the container  137  if acoustic energy is introduced into the container  137  through both of its ports  138 ,  139  simultaneously, or by varying the phase and frequency of the longitudinal acoustic energy patterns or resonances that are created within the container  137 . 
     As another alternative, the container  137  may be caused to vibrate by placing it on any suitable shaker device of any suitable size, shape and construction. 
     It is to be understood that, without departing from the scope and spirit of the claimed invention, any particular part of any of the concentrators  10 ,  10   a ,  10   b  may be suitably combined or formed with one or more of the other parts of its respective concentrator  10 ,  10   a ,  10   b  to form one integral or composite part; that any particular part of any of the concentrators  10 ,  10   a ,  10   b  that may be made in one piece may instead be made by assembling together in any suitable way, two or more sub-pieces; and that the various parts of each of the concentrators  10 ,  10   a ,  10   b  may be assembled together in any suitable ways other than those described herein, such by using fasteners; interference fits, friction fits; barbed, threaded, bonded, glued or welded connections; splines; keys; or mechanical couplers. 
     It is also to be understood that the specific embodiments of the claimed invention that are disclosed herein were disclosed strictly by way of non-limiting example. Accordingly, various modifications may be made to those embodiments without deviating from the scope and spirit of the claimed invention. Additionally, certain aspects of the claimed invention that were described in the context of a particular embodiment may be combined or eliminated in other embodiments. Although advantages associated with a certain embodiment of the claimed invention have been described in the context of that embodiment, other of the embodiments may also exhibit such advantages. Further, not all embodiments need necessarily exhibit any or all of such advantages in order to fall within the scope of the claimed invention. 
     When the phrase “at least one of” is used in any of the claims, that phrase is defined to mean that any one, any more than one, or all, of the listed things or steps following that phrase is, or are, part of the claimed invention. For example, if a hypothetical claim recited “at least one of A, B, and C”, then the claim is to be interpreted so that it may comprise (in addition to anything else recited in the claim), an A alone, a B alone, a C alone, both A and B, both A and C, both B and C, and/or all of A, B and C. 
     Before an element in a claim is construed as claiming a means for performing a specified function under 35 USC section 112, last paragraph, the words “means for” must be used in conjunction with that element. 
     As used herein, except in the claims, the words “and” and “or” are each defined to also carry the meaning of “and/or”. 
     In view of all of the disclosures herein, these and further modifications, adaptations and variations of the claimed invention will now be apparent to those of ordinary skill in the art to which it pertains, within the scope of the following claims.