WO2007103793A2 - Filtering optimization methods for particle inspection device - Google Patents

Abstract

Filtering optimization methods for enhancing the performance of a trace collection system. Systems and methods for concentrating the fraction of particles in a gas volume facilitates extraction and detection. Electrostatic, acoustophoretic, fluid dynamic and kinetic means are provided for enriching a selected gas volume with particles for selective filtering and analysis. A laser-based particle analysis system is provided.

Description

FILTERING OPTIMIZATION METHODS FOR PARTICLE INSPECTION DEVICE

FIELD OF THE INVENTION

The present invention relates to trace collection systems and, more particularly, to filtering optimization methods for enhancing the performance of a trace collection system.

BACKGROUND OF THE INVENTION

Explosive, toxic, nuclear, and biological threats, as well as some types of contraband, including drugs, typically are associated with trace particulates, as well as persons handling such items, and items later handled by such persons. There are known systems for detecting particulates (and the compositions of which they are formed), which seek to transfer particulates from an article under inspection (AUI) to a particle detector. Such particle detectors are known. One type of particle detector passes a hot gas over explosive particles or a sample on a fiberglass filter, which then increases the vapor pressure of the organic molecules to be detected, which is then subjected to ion mobility spectrometry (IMS).

Explosives detection for aviation security has been an area of federal concern for many years. Much effort has been focused on direct detection of explosive materials in carry-on and checked luggage, but techniques have also been developed to detect and identify residual traces that may indicate a passenger's recent contact with explosive materials. The trace detection techniques use separation and detection technologies, such as mass spectrometry, gas chromatography, chemical luminescence, or ion mobility spectrometry, to measure the chemical properties of vapor or particulate matter collected from passengers or their carry-on luggage. Parallel efforts in explosives vapor detection have employed specially trained animals, usually dogs, as detectors. The effectiveness of chemical trace analysis is highly dependent on three distinct steps: (1) sample collection, (2) sample analysis, and (3) comparison of results with known standards. (National Research Council, Configuration Management and Performance Verification of Explosives- Detection Systems, 1998.)

If any of these steps is suboptimal, the test may fail to detect explosives that are present. When trace analysis is used for passenger screening, additional goals may include non-intrusive or minimally intrusive sample collection, fast sample analysis and identification, and low cost. While no universal solution has yet been achieved, ion mobility spectrometry is most often used in currently deployed equipment. Several technologies have been developed and deployed on a test or prototype basis. See, Dana A. Shea and Daniel Morgan, "Detection of Explosives on Airline Passengers: Recommendation of the 9/11 Commission and Related Issues", Analysts in Science and Technology Policy Resources, Science, and Industry Division, Congressional Research Service, Order Code RS21920 (Updated August 9, 2006).

There are two issues presented for screening passengers and persons in other roles — interdicting contraband itself, and identifying persons and articles which have been in the same environment as contraband. In the former case, detection focuses on bulk materials, such as explosives, which are generally determined by bulk electromagnetic (e.g., NMR), or bulk radiolucent (e.g., X-ray) techniques. Typically, the lower threshold for bulk detection is reasonably set at a level below which significant direct damage to persons or property is likely, especially as compared to lesser threats. Thus, for example, a lower detection limit of 10-20 grams might be reasonable. In the later case, the screening process seeks to identify microscopic traces, with no reasonable lower limit of detection imposed within the constraints of acceptable false positives. One approach is to direct passengers through a portal, similar to a large doorframe, that contains detectors able to collect, analyze, and identify explosive residues on the person's body or clothing. The portal may rely on the passenger's own body heat to volatilize traces of explosive material for detection as a vapor, or it may use puffs of air that can dislodge small particles as an aerosol. Alternatively, a handheld vacuum "wand" may be used to collect a sample. In both cases, the collected samples are analyzed chemically.

A different approach is to test an object handled by the passenger, such as a boarding pass, for residues transferred from the passenger's hands. In this case, the secondary object is used as the carrier between the passenger and the analyzing equipment. The olfactory ability of dogs is sensitive enough to detect trace amounts of many compounds, but several factors have inhibited the regular use of canines as passenger explosives trace detectors. Dogs trained in explosives detection can generally only work for brief periods, have significant upkeep costs, are unable to communicate the identity of the detected explosives residue, and require a human handler when performing their detection role. In addition, direct contact between dogs and airline passengers raises liability concerns.

Prior efforts have also sought to identify explosive residue particulates on passenger luggage and packages, though a persistent issue is the detection of particles which are deep inside the item under inspection, which may remain contained during normal testing cycles. Traditional particular screening technologies have had significant difficulties extracting trace particles from within passenger bag, and have required a manual process of opening the bag and swabbing the contents. Direct detection of explosives concealed on passengers in bulk quantities has been another area of federal interest. Federal and industry efforts in this area include the development of portal systems utilizing techniques such as x-ray backscatter imaging, millimeter wave energy analysis, or terahertz imaging. As such systems detect only bulk quantities of explosives, they would not raise "nuisance alarms" on passengers who have recently handled explosives for innocuous reasons. Some versions could simultaneously detect other threats, such as nonmetallic weapons. On the other hand, trace detection techniques would likely also detect bulk quantities of explosives, and may alert screening personnel to security concerns about a passenger who has had contact with explosives but is not actually carrying an explosive device when screened. A potential complication of explosives trace detection is the accuracy of detector performance. False positives, false negatives, and innocuous true positives (those which have a legitimate explanation) are all challenges. If the detection system often detects the presence of an explosive when there actually is none (a false positive) then there will be a high burden in verifying results through additional procedures. Because of the large volume of passengers, even small false positive rates may be unacceptable.

Since the sensitivity of the particle collection system will often directly relate to the sensitivity of the detection system as a whole, and therefore by increasing the efficiency of particulate presentation to the detection subsystem, the sensitivity and precision of the system as a whole will be enhanced. A "trace", as used herein, means a small amount of solid or liquid particles, e.g., in the range of 0.5 to 100 microns in diameter. Trace can also be in gas form, whose precipitation mass is similar to the mass of the solid or liquid particles. We will use the term "vapor" interchangeably with trace. Of course, the present invention is not limited by the particular ranges of particle size, nor by the limits of sensitivity of an analysis machine to detect what was captured. US patent application number US 10/511 ,869 (Fredy Oranth), expressly incorporated herein by reference, discloses a vapor inspection system that includes an external enclosure and a flexible conforming device serving as an internal enclosure. In operation, inspected items are inserted into an inspection chamber, enclosed by conforming device. A blower optionally sucks the air out of the inspection chamber, through air pipes, such that conforming device closely fits around inspected items. Thereafter, vapor releasing methods are applied to inspected items in order to release vapors from the items, to release vapors and particles, if such vapors are in and/or on inspected items. Intermittently, concurrently and/or subsequently, the vapor releasing methods are applied, a blower optionally sucks air out of the inspection chamber and the sucked air is passed to a collector, which accumulates vapors and/or solids for inspection. A trace analyzer analyzes the collected vapors and/or solids to determine whether they include chemicals that are being searched for. See also, US patent application number 10/542,426 (Fredy Ornath and Robert Roach), expressly incorporated herein by reference. A compressor pumps air into inspection chamber, while a blower sucks out air for vapor inspection, in order to keep the pressure within inspection chamber constant. The compressor may be implemented together with a blower in the same apparatus or it may be implemented in separate apparatus. Optionally, the air pressure within inspection chamber is set such that the mantle does not touch and/or crush the inspected items, while keeping the effective air volume within inspection the chamber (i.e., within the mantle) minimal. In some embodiments of the invention, the volume of the chamber is not more than 20%, 10% or even 5% above the volume of the inspected items. The empty volume of the chamber is not greater than a predetermined air volume. Keeping the air volume at a minimal level prevents dilution of vapors extracted from the inspected items, dilution which may make the identification of materials to be detected more difficult.

The inspected item may be placed on a conveyor belt, or any other base, which may be impermeable to gases, such that a separate conforming device base is not required. Alternatively or additionally, the conforming device and/or a separate conforming device piece may surround the inspected item from below. Optionally, in this alternative, the conveyor belt and/or any other base on which the inspected items are placed is perforated or otherwise allows air passage, so that air jets may be directed at the items and/or samples may be collected from the inspected items from below.

One type of collection apparatus includes hand held machines, such as described in U.S. Pat. No. 4,909,090 to McGown et al, U.S. Pat. No. 5,092,220 to Rounbehler, and U.S. Pat. No. 5,123,274 to Carroll et al., the disclosures of which documents is incorporated herein by reference. These machines are directed by a human holding the machine to suck air from the surface of inspected luggage. The machines may heat the surface of the luggage and/or direct jets of air at the luggage in order to aid in dislodging vapors from the luggage. These hand held collection apparatus suffer from high cost of operators who need to pass the machine over the luggage and from low accuracy due to collection of only a small portion of the air surrounding the luggage. See, U.S. 10/542426, PCT/IL04/00011, and U.S. 60/372,805, each of which is expressly incorporated herein by reference.

Other collection systems include chambers into which the luggage is inserted, such as described in U.S. Pat. Nos. 5,942,699 and 6,324,927 to Ornath et al., U.S. Pat. No. 4,580,440 to Reid et al., U.S. Pat. No. 5,162,652 to Cohen et al., U.S. Pat. No. 3,942,357 to Jenkins et al., U.S. Pat. No. 3,998,101 to Bradshaw et al., the disclosures of which documents is incorporated herein by reference. The luggage is preferably sealed in the chamber and various methods are used to dislodge vapors from the luggage. The air in the chamber is then passed to an inspection system. The volume of air in these chambers is generally too large such that some contaminants having low dilution rates are not detected. Other collection systems are directed to checking humans and therefore are not sealed. The operation of these systems is similar to that described above, except that there is no airtight seal. Such systems are described, for example, in U.S. Pat. No. 4,909,089 to Achter et al., and U.S. Pat. No. 5,345,809 to Corrigan et al. (paper filter and/or scrubber type collector), the disclosures of which documents is incorporated herein by reference. A trace analyzer optionally operates automatically after a inspection session. Optionally, a user interface displays the names of chemicals which were identified.

One of the methods used to dislodge vapors from humans and luggage is air jets directed at the inspected humans or luggage, as described, for example, in U.S. Pat. No. 4,909,089. In some cases it may be desired to avoid directing air jets at humans, especially at their face. U.S. Pat. No. 4,909,089 suggests suppressing air jets directed at the inspected human's face. U.S. Pat. No.

4,987,767 describes a sampling chamber in which air jet streams are injected from a plurality of ducts in different sides of the chamber so as to induce air flow from the floor of the chamber to its ceiling. This air flow sweeps over individuals or objects passing through the chamber. U.S. Pat. No. 6,073,499 to Settles, the disclosure of which is incorporated herein by reference, describes a portal which relies upon the heat of the human body to generate flow of air towards the ceiling of the portal.

See, US 20040169845 (Nguyen, Dao Hinh, et al.), expressly incorporated herein by reference, which discloses a compact infrared laser scanning apparatus for detecting contraband.

See, US 20040135695 and US 6,975,237 (Barton, Steven M., et al.), expressly incorporated herein by reference, which discloses a system, controller and method of detecting a hazardous condition within an enclosure having a ventilation system.

See, US 20040055399 and US 6,848,325, expressly incorporated herein by reference, disclose an explosives screening device on a vehicle surface employing a gas flow.

See, US 20030106362 and US 6,711,939, expressly incorporated herein by reference, disclose a method and system for expelling test-sample volumes from luggage/packages to test for prohibited materials.

See, US Re. 38,797, US 5,854,431, US 6,085,601, US 6,345,545 and US 6,334,365 (Linker, et al.), expressly incorporated herein by reference, disclose particle and vapor preconcentrator systems for an explosive, etc. detection system. See, US 6,895,801 (Fine, et al), expressly incorporated herein by reference, which discloses a pressure activated sampling system for screening of items for the presence of contaminants, such as explosives residue.

See, US 5,942,699 and US 6,324,927 (Ornath, et al.), expressly incorporated herein by reference, which discloses a methods and apparati for sampling contaminants. See also,

WO2003058207, WO2003058208, WO2003076036, US 6,792,795, US 6,823,714, US 6,948,653, US 6,412,358, US 6,517,593, US 6,632,271, US 6,598,461, US 6,852,539, US 7,060,927, US6,895,804, US 7,032,467, US 7,062,982, US6,619,143, US 6,887,710, each of which is expressly incorporated herein by reference. See, US 5,753,832 and US 5,760,314 (Bromberg, et al.), expressly incorporated herein by reference, which discloses a vapor and particle sampling apparatus.

See, US 5,585,575, US 5,465,607 and US 4,987,767 (Corrigan, et al.), expressly incorporated herein by reference, which discloses an explosive detection screening system.

See, US 5,476,794 (O'Brien, et al.), expressly incorporated herein by reference, which discloses a detection method for checking surfaces for nitrogen-containing explosives or drugs.

See, US 5,162,652 (Cohen, et al.), expressly incorporated herein by reference, discloses a method and apparatus for rapid detection of contraband and toxic materials by trace vapor detection using ion mobility spectrometry.

See, US 5,405,781 (Davies, et al.), expressly incorporated herein by reference, which discloses an in mobility spectrometer apparatus and method, incorporating air drying.

See also Andrew McGiIl, R.; Martin, Michael; Mott, David; Nguyen, Viet; Ross, Stuart; Stepnowski, Jennifer; Stepnowski, Stanley; Summers, Heather; Voicolescu, Ioana; Walsh, Kevin; Zaghloul, Mona E., "Micropreconcentrator for enhanced trace detection of explosives and chemical agents", IEEE Sensors J. 6(5):1094-1103 (October 2006). However, prior art methods, devices, and systems do not optimize the filtration and particle extraction from within the luggage.

There is thus a need for, and it would be highly useful, to have an optimized trace collection system filter. SUMMARY OF THE INVENTION

The present invention seeks to optimize a process for separating or concentrating entrained solids or liquids, and in some cases gaseous components, from a flowing dilute stream. In such a process, the goal is to present the largest representative sample of traces to an analyzer or the like, within system feasibility limits and efficiency constraints.

In a typical trace extraction system, solid particles are entrained in a gas stream. A gas flow is typically used to assist in extracting particles, and therefore a larger volume of gas may be expected to carry with it a larger mass of particles from the object under inspection to a collection region. , A large gas flow volume, however, places strains both the source of gas, and also the the particle concentrator, which must operate on the larger gas flow. In many cases, a physical implementation of a particle concentrator cannot collect all particles of a high volume of rapidly flowing gas within a small collection volume or small collection surface (filter). Rather, the filter has a certain bypass, in which some portion of the particles in the gas travels through the particle concentrator without capture. The present invention therefore seeks to optimize filter or concentrator in a trace collection system to balance between cost, timeliness, and efficiency, and in turn, permit other system components to likewise be optimized.

One way to address the efficiency of a bypass is to effect a volumetric concentration of particles, for example based on their density, aerodynamic properties, or other physical effects, to selectively create an enriched gas volume and a depleted gas volume. The depleted gas volume may then be shunted, permitting subsequent stages to operate only on a portion of the flow. Indeed, the shunted gas flow may advantageously be used to assist in the concentration process, for example by generating a pressure differential.

Likewise, a thermophoretic effect may be employed to repel particles from a warm surface, an electrophoretic effect used to move particles in response to electrical charge, an acoustophoretic effect used to transport particles with sound, and momentum and aerodynamic effects used in conjunction with controlled gas flows to separate dense particles from the carrier gas.

With respect to operating the system within an optimum set of operating parameters, the present invention permits some separation of the gas volume and flow rates used in extraction and transport processes from the gas volume and flow rates used in the collection and analysis processes. This technique therefore provides increased degrees of freedom for achieving a desired regime of operation.

It is therefore an object of the invention to provides a system and method for capturing particles in a flowing gas stream, comprising a conduit, receiving a gas flow having entrained particles and having a cross sectional area; a filter, having an area less than or equal to the cross sectional area, disposed within the conduit, for capturing particles within a portion of the cross sectional area; and at least one of an electrostatic, acoustic, and aerodynamic element for concentrating particles within the cross sectional area from which the filter captures particles, for receiving a gas flow having entrained particles through a conduit having a cross sectional area; capturing particles on a filter, having an area less than or equal to the cross sectional area, disposed within the conduit; and concentrating particles within the cross sectional area using at least one of an electrostatic, acoustic, and aerodynamic element.

In accordance with one embodiment of the invention, the filter is disposed within a region having a first state in which the filter receives particles from the conduit, and a second state in which the filter is separated from gas within the conduit. A second state may provide a second flow path, distinct from the conduit, wherein a gas flow through the second flow path removes at least a portion of the material forming the particles captured by the filter.

An embodiment of the invention provides an electrostatic element to charge particles within the conduit. The filter may be charged to a potential opposite that of the particles. The conduit has a wall, and the wall have a charge pattern to concentrate particles within the conduit away from the wall.

Another embodiment of the invention provides an acoustic element to alter a spatial distribution of particles. The acoustic element, may, for example, create a standing wave within the conduit. Such a standing wave may have a nodal surface which has an adjustable position. The standing wave may be generated by one or a plurality of acoustic transducers. The pattern of standing waves may vary axially along the conduit. An axially oriented barrier may be within the conduit, which, for example, interacts with acoustic waves, for example, reflecting, absorbing, phase shifting, generating, transducing, etc., the acoustic waves. The barrier may also interact with the stream within the conduit, for example, partitioning or redirecting gas flows, creating turbulence or other aerodynamic effects. The barrier may further have electrostatic, thermal, or other properties to facilitate the process.

According to a still further embodiment of the invention, the conduit comprises a Venturi section. In one embodiment, the flow is segregated into distinct paths, while in another embodiment an external gas flow is provided. In either case, an intent is to reduce the pressure distal to a filter or particle collection system, to enhance the flow therethrough. Accordingly, in one embodiment, a Venturi is provided in which portions of the flow are segregated into a first portion, e.g., central, passing though the filter, generally having a slow flow rate, and a second portion, e.g., outer, bypassing the filter, generally having a faster flow rate, the second portion inducing a relative vacuum at a position past the filter, to thereby enhance gas flow of the first portion passing through the filter, e.g., as compared to a state in which the second portion is diverted and does not act to produce a reduced pressure. The faster portion can also be central, with the filter on the outer portion of the conduit. In another embodiment, the conduit comprises a Venturi section in which at least a portion of the flow passes though the filter, further comprising an external pressurized gas or fluid supply producing a flow which bypasses the filter, the flow inducing a relative vacuum at a position past the filter, to thereby enhance gas flow of the portion passing through the filter as compared to a state in which the external pressurized gas or fluid is absent. The conduit need not be linear, and may be curved or have other topologies. The flow need not be segregated in a radially symmetric manner, and the slow flow path may be on an outer portion of the conduit. The Venturi section, for example, may comprise a tube within the conduit, located distal to an expansion in an inner diameter of the conduit.

According to another embodiment of the invention, a subsonic transducer is provided for generating subsonic acoustic waves for dislodging particles from an object.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in order to provide what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. Identical structures, elements or parts which appear in more than one figure are preferably labeled with a same or similar number in all the figures in which they appear. In the drawings:

FIG. IA is an illustration of Venturi filter housing, in accordance with the present invention;

FIG. IB is an illustration of an embodiment of Venturi filter housing, in accordance with the present invention;

FIG. 2 A is an illustration of a basic embodiment of an electrostatic filter, in accordance with the present invention;

FIG. 2B is an illustration of an embodiment of a first state of a dual cycle electrostatic filter, in accordance with the present invention; FIG. 2C is an illustration of an embodiment of a second state of a dual cycle electrostatic filter, in accordance with the present invention;

FIG. 3 A is an illustration of a Basic embodiment of a dual cycle electrostatic charged filter, in accordance with the present invention;

FIG. 3B is an illustration of an embodiment of a first state of a dual cycle electrostatic charged filter, in accordance with the present invention;

FIG. 3 C is an illustration of an embodiment of a second state of a dual cycle electrostatic charged filter, in accordance with the present invention;

FIG. 4 is an illustration of an embodiment a dual cycle electrostatic filter cleaning process, in accordance with the present invention; FIG. 5 A is an illustration of a basic embodiment of an acoustophoresis standing wave filter, in accordance with the present invention;

FIG. 5B is an illustration of an embodiment of a first state of an acoustophoresis standing wave filter, in accordance with the present invention; FIG. 5 C is an illustration of an embodiment of a second state of an acoustophoresis standing wave filter, in accordance with the present invention;

FIG. 6 A is an illustration of an embodiment of an acoustophoresis standing wave filter with a mid-section dampening barrier, in accordance with the present invention; FIG. 6B is an illustration of an embodiment of another state of an acoustophoresis standing wave filter with a mid-section dampening barrier, in accordance with the present invention;

FIG. 6C is an illustration of an embodiment of another state of an acoustophoresis standing wave filter with a mid-section dampening barrier, in accordance with the present invention;

FIG. 7 is an illustration of an embodiment of dual acoustophoresis standing wave filter with a mid-section dampening barrier, in accordance with the present invention;

FIG. 8 is an illustration of an embodiment of a low frequency acoustic particle resonator, in accordance with the present invention; and,

FIG. 9 is an illustration of a low frequency standing wave acoustic particle resonator, in accordance with the present invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Small particle and aerosol collection are a necessity in trace detection, due to the non- volatility of various explosive particles that renders gaseous and other collection methods deficient. For example, the plastic explosives PETN and C4 contain particles that can be analyzed only after physical collection. The collection of particle traces from the air surrounding items of interest, for example, baggage, cargo, or passengers, underscores the need for automation of security related trace detection.

In an embodiment option of the present invention, an electrostatic precipitator (ESP) serves as a front-end Trace Collection Device (TCD) to automated trace detection devices such as human screening portals, non-contact trace detection devices, automated carry-on bag and cargo explosive trace detectors, and trace detectors used for screening mass transportation vehicles such as trains, trucks, or buses.

Electrostatic trapping is more effective than existing pre-collectors used in explosive trace detection. The increased effectiveness is due to (a) unimpeded high-volume particle-laden flow, (b) superior efficiency when dealing with particles of the size in question, for example between about 0.1 and 100 microns, and (c) small volume, weight, and power requirements.

Prior art electrostatic precipitators are either wire/cylinder or wire plate types and usually serve as air cleaners or for the removal of particulate air pollutants. Existing electrostatic precipitator designs pose inherent limitations that render the application of these configurations difficult and inconvenient for trace collection and pre-concentration for use with electrostatic trace collection system.

A significant particular aspect of novelty and inventiveness of the present invention, relates to the use of electrostatic precipitation to enhance particle trapping in airflow-based trace collection systems. For example, even though particles of typical interest in explosive trace collection are in the 1 to 50 micron range, the novel present invention can deal with particles ranging between 0.1 and 100 microns.

The present invention successfully overcomes the following challenges faced when designing the dual cycle electrostatic filter, and widens the scope, of presently known configurations of electrostatic filters, by providing a high volume flow rate required in order to quickly assess the presence of explosive materials on a large number of parcels.

Moreover, the present invention successfully widens the scope of presently known configurations of electrostatic filters, by providing a novel solution for the high volume flow rates problem, which results in high velocities requiring smaller spacing or longer collection plates in prior art electrostatic precipitators configurations. In addition, the present invention successfully addresses shortcomings and limitations of prior art trace collection systems which use very small sample sizes and very low flow rates, and therefore deficiently operate with high volume flow rates.

Furthermore, the system of the present invention provides a successful solution for moving the collected particles to the trace detector, while maintaining the cleanliness of the trace collector.

In order to be able to use available trace analyzers, it is preferred to have a screen and not use a plurality of plates. One aspect of the novelty of the present electrostatic particle concentration device is the fact that the particles are concentrated on a screen that can be inserted to the analyzer and not concentrated on parallel plates as known in the art. It is possible to integrate the filter with the analyzer. In that case, the cleaning of the filter is performed with high velocity air stream.

The present invention displays aspects of novelty and inventiveness by concentrating the particles using an electrical field. In contrast to known electrostatic systems, regular filter and/or other collection means which are not plates may be employed. In addition, the system may employ a charged filter, instead of the normal plates, because particle concentration is possible, requiring a smaller filter device and allowing large air flow through the filter.

According to a first set of embodiments, an ionizer, e.g., a cathodic ionizer having an array of needle ionizers 26 having needle points is used to induce electrical charges on entrained particles, which are then accelerated toward an anode screen which is situated in a central portion of a conduit. A repelling shroud surrounds the flow path and screen, causing the particles to concentrate along the centerline. A vacuum system and/or pressure source (not shown in the figure) propels a large volume of air into the capture system. The vacuum system, for example, consisting of a small standard air pump, provides air flow rates as high as 2,000 1/min. The array of needle ionizers provides ionizing points. The use of needle ionizers as ionizing points are known in the art. For example, needle ionizer ionizing points are common in household electrostatic precipitator air cleaners, which are charged due to interaction with the ionized air. Using the surrounding repelling shroud has the added benefit of preventing the inner side tube wall surface 28 from becoming contaminated and allowing easier cleaning. A short distance downstream, a particle filter 10 acts as the opposing electrode and collects the particles. The collection screen's mesh spacing is fine enough to ensure that little trajectory change is required for particle capture. In addition, the mesh screen is coarse enough as not to overly impede the forceful airflow. A portion of the gas effectively bypasses the screen, while the electrostatic forces tend to concentrate the particles within the entire volume on the screen. It is noted that the mesh itself may be electrically heated to volatilize the particles adhered to, or vapors condensed on, the screen, and thus the sampling operation need not employ a heated gas, and the sample volume may therefore be reduced, since the sampling gas flow need not perform the volatilizing function in addition to the carrier function. Of course, the sampling gas may be heated in known manner.

Referring to FIG. 2A, in a first embodiment of the present invention, the trace collector features the following components: array of needle ionizers 26, particle filter 10, and tube wall surface 28. In this basic embodiment, particles entrained in the gas stream are collected on the filter 10, which is then, for example, removed from the filter housing for analysis, cleaning and/or replacement.

Referring to FIGS. 2B and 2C, in a second embodiment of the present invention, the trace collector features the following components: array of needle ionizers 26, particle filter 10, first airflow passage door 30, second airflow passage door 32, and tube wall surface 28. In this embodiment, a passage door 30 is provided for access to the filter 10, which permits, for example, analysis of particles on the filter 10 and cleaning in situ. For example, in a first stage of the cycle, as shown in Fig. 2B, the door is closed to permit flow of gas with entrained particles from a particle extraction system (not shown), with precipitation of the particles on the filter 10. In a second stage of the cycle, as represented in Fig. 2C (after the primary flow bringing the particles to the filter has ceased), the door is opened and a cross flow of heated gas may be used to volatilize the particles on the filter, and the particle vapors then transported to the analyzer (not shown). The cleaning cycle is shown in Fig. 4, in which a cross flow through the second airflow passage doors 32 flushes the area which normally holds the filter.

Thus, after the particles are collected on the filter 10, a passage door 32 closes off the main airflow passage within the wall surface 28, and opens the passage door 30, and an air flow blowing from a side air passage carries the resulting aerosol to the trace detector. The cleaning procedure of the device is performed by blowing high-speed air through the passages. Referring to FIG. 3 A, in a third embodiment option of the present invention, the embodiment of Fig. 2A is enhanced by providing an electrical potential on the filter. The trace collector thus features the following components: array of needle ionizers 26, chargeable particle filter 24, voltage potential source 34, and tube wall surface 28. In this case, Ionizing needles are charged to a high voltage (10-20 kV) to form a corona. Incoming air passes through the high voltage zone, is ionized, and transfers some of its charge to entrained particles. The ionized species, including the particles, are then accelerated towards the metallic mesh anode by the electric field. A metallic sheath surrounding the flow is also charged to the same level and polarity by a voltage potential source 34. Control over the flow pattern is possible by using a series of rings rather than a continuous tube. Various axial voltage levels can tailor the electric field and control the flow pattern. The flow pattern is a parameter which can be optimized so that the majority of the flow of particles channels to the tube's center, diminishing particle loss to the encompassing surface, avoiding contamination, and avoiding signal loss.

Referring to FIGS. 3B and 3C, in a fourth embodiment option of the present invention, the trace collector features the following components: array of needle ionizers 26, chargeable particle filter 24, potential differentiating source 34, cleaning airflow passage door 30, airflow passage door 32, and tube wall surface 28. As in the embodiment of Figs. 2B and 2C, a passage door 30 is provided for access to the chargeable filter 24, which permits, for example, analysis of particles on the filter 24 and cleaning in situ. For example, in a first stage of the cycle, as shown in Fig. 3B, the door is closed to permit flow of gas with entrained particles from a particle extraction system (not shown), with precipitation of the particles on the chargeable filter 24. In a second stage of the cycle, as represented in Fig. 3C (after the primary flow bringing the particles to the filter has ceased), the door is opened and a cross flow of heated gas may be used to volatilize the particles on the chargeable filter 24, and the particle vapors then transported to the analyzer (not shown). Thus, after the particles are collected on the chargeable filter 24, a passage door 32 closes off the main airflow passage within the wall surface 28, and opens the passage door 30, and an air flow blowing from a side air passage carries the resulting aerosol to the trace detector. The cleaning procedure of the device is performed by blowing high-speed air through the passages.

According to another preferred embodiment of the present invention, a Venturi filter housing is disclosed. A Venturi is a relatively short tube with a constricted throat. In operation, a gas flows through the tube, and the pressure drops at the constricted area. The tapered constriction causes an increase in the velocity of flow of a fluid - gas or liquid - through the tube, and a corresponding decrease in fluid pressure.

Prior art Venturi tubes are widely used for speeding the flow of a fluid. They are found in many applications where the speed of the fluid is important. A Venturi can also be used for creating suction in a vacuum pump and for mixing fluid with air, and form the basis of devices like a carburetor. Venturis are also used to determine fluid pressures and velocities by measurement of differential pressures generated at the constricted throat as a fluid traverses the tube.

More to the point of this invention has been the use of Venturis to lower the pressure at the exhaust point of internal combustion engines to increase the efficiency of the exhaust cycle. Such has been used on aircraft engines which employed a venturi at the end of the exhaust stack to lower the pressure. The Venturi was fed by the on-coming airstream. The extra drag created by the Venturi was more than overcome by the increased power from the engine. There is a need to maximize the capture rate of the filter used for particle trace collection. Thus, there is a need to maintain a high flow rate while using a fine filter which can catch tiny particles. When all of the air flow is forced to pass through a fine filter, the flow velocity is low and only a small fraction of the particles of interest arrive at the filter. In an embodiment option of the present invention as shown in Figs. IA and IB, the Venturi filter housing of the present invention allows a large fraction of flow from the particle extraction mechanism to bypass the filter. The bypass is necessary to increase flow rate from the particle extraction mechanism, and thus increase capture rate of the filter used for particle trace collection.

It is also possible to provide an external supply or pressurized gas or fluid, which bypasses the filter, to generate a partial vacuum, and thereby enhance the flow of the stream passing through the filter. Thus, the particle laden gas stream need not be partitioned in order for a Venturi design to operate.

An advantage of the Venturi filter housing of the present invention is that aerodynamic principles are passively used to increase filter particle capture, as opposed to actively investing effort to increase the capture rate.

A significant particular aspect of novelty and inventiveness of the present invention, relates to increasing the particle capture rate of a filter using passive aerodynamic principles, or tube structure.

FIG. IA, illustrates a Venturi filter housing, featuring a filter 10 and a Venturi 12. Particle- laden flow of air (from the conforming mechanism) is propelled into the filter housing by a vacuum system. A portion of the air goes through the filter 10, while the remaining air bypasses the filter. A Venturi 12 in the structure of the filter housing causes a pressure drop at the downstream side of the filter. The pressure difference between the two sides of the filter increases the effective capture area of the filter, thus increasing the mass flow through the filter, which results in a higher particle capture rate of the filter.

Optionally, the filter is held in place with a screen.

After the particles are captured on the filter, the filter may be removed from the filter housing and moved to a trace analyzer.

Optionally, the filter housing is cleaned between cycles of particle trace collection. For example, the filter housing may be cleaned by passing a high velocity air flow through the filter housing.

It is to be understood that more than one tube can carry the particle-laden-air flow from the particle extraction mechanism to the filter housing. FIG. IB, illustrates a Venturi filter housing, featuring a filter 10 and a Venturi 12. Particle laden flow of air from the particle extraction mechanism is propelled into the filter housing through two tubes 14, 16. The particle-laden flows of air are propelled into the filter housing by a vacuum system. Experiments have shown that the best arrangement of multiple tubes is to arrange their exhaust into the tube upstream of the filter symmetrically with respect to the centerline of the filter.

A significant particular aspect of the present invention, relates to improving filter capture by concentrating the particles, e.g., by a process of aerodynamic contraction/squeezing of the particle- rich fraction of the stream.

In an embodiment option of the present invention, external airflow is used for concentrating the gas stream from the particle extraction mechanism. The external clean airflow is combined with the gas stream from the particle extraction mechanism in such a way that the gas stream from the inside of the particle extraction mechanism is concentrated towards the filter.

In this embodiment, the geometry of the structure prevents the mixing of the streams. The gas from inside of the particle extraction mechanism is concentrated in the middle of the tube because it takes time until the two airstreams mix together, and meanwhile the middle stream is concentrated.

Optionally, when an outer chamber is available, e.g., where there is a conforming mechanism having inner and outer chambers, the air surrounding the conforming mechanism is used as the source for external airflow. Another significant particular aspect of novelty and inventiveness of the present invention, relates to using low- frequency waves for moving particles inside the luggage. In an exemplary embodiment option of the present invention, the low- frequency waves are made by a subwoofer, which produces low frequency acoustic waves, e.g., in the 5-90 Hz range.

In an embodiment option of the present invention, a vibrating acoustic membrane, e.g. a subwoofer, which reproduces the lower end of the audio spectrum, is used to create air currents both inside and around the inspected items. Creating air currents increases the probability that particles within the items dislodge and subsequently be more susceptible to motion caused by air movement inside the inspected luggage. This improves the reliability of the particle collection process since the particles are more uniformly distributed across the body of inspected items. Using a vibrating acoustic membrane to create air currents improves on other vibrating mechanisms that instigate the movement of the inspected items. The timing of the generation of low frequency waves can be in accordance with other activities of the trace collection system so as to improve system performance. Subwoofers are non-directional, and thus can be located anywhere around the inspected items.

Referring to FIG. 9, in an embodiment option of the present invention, the trace collection system features the following components: inspected items 80, vibrating acoustic membrane 36, and conforming mechanism 82. At least one vibrating acoustic membrane 36 creates low- frequency sound waves that loosen particles and transport them from inside to the periphery of the inspected items 80. The trace collection system then conveys the particles to the analyzer.

It is to be understood that various combinations of the aforementioned filter embodiments and methods are also possible. For example, a combination of an electrostatic filter housing and a Venturi filter housing that comprises charging particles, exposing them to an electrostatic field and positioning a Venturi structure to increase flow through the filter.

In another embodiment option of the present invention, acoustophoresis influences the trajectory of particles using high intensity sound waves produced by acoustic resonators, i.e. using moving sound pressure levels for moving particles inside an inspected item. This embodiment therefore employs acoustophoresis particle concentration on a luggage in the diaphragm. The generation of standing sound waves causes particles to concentrate in the wave's trough. This is due to a force created by unequal sound pressure levels (SPL) across the standing wave that pushes the particle toward the low pressure point.

The term "moving sound pressure levels" refers to moving standing waves, preferentially by adjusting the phase of one contributor to the standing wave.

In an embodiment option of the present invention, a vibrating acoustic membrane, e.g. a subwoofer, which reproduces the lower end of the audio spectrum, is used to create moving sound pressure levels for moving particles both inside and around the inspected items. Moving sound pressure levels are utilized to dislodge particles, augment particle trajectory, and move particles in a predefined direction, e.g. towards the location of particle inhaling components of the particle extraction mechanism. This improves the reliability of the collection process since more particles are extracted from the inspected items, collected and analyzed.

Using moving sound pressure levels for moving particles inside the luggage can improve on other vibrating mechanisms that instigate the movement of particles in the inspected items. The timing of the generation of moving sound pressure levels can be in accordance with other activities of the trace collection system so as to improve system performance.

The frequency of the sound pressure levels (standing waves) can be tuned to be undetectable by animals in the proximity of the trace collection system, and these sonic waves of the amplitudes contemplated outside of the chamber and conduit(s) are generally safe for humans as well.

In an optional embodiment option of the present invention, the inspected item is pressurized so air gets into it by applying the following two steps: (1) applying long waves that move particles from the middle of the inspected item to the periphery. (2) "breathing" in order to take it out.

"Breathing" refers to the technique of pressurizing the inspection chamber so that a substantial net mass flow of the active gas (preferentially air) is forced to enter into the inspected item through any openings or small holes which might exist on its exterior. The pressurization can be thought of as the inhale part of the breathing. Depressurization of the chamber results in the active gas being expelled from within the inspected item and hence is analogous to the exhale part of breathing.

Referring to FIG. 8, in an embodiment option of the present invention, the trace collection system features the following components: inspected items 80, vibrating acoustic membrane 36, conforming mechanism 82 and particle inhaling component 84. At least one vibrating acoustic membrane 36 creates low- frequency sound waves that form moving sound pressure levels. Moving sound pressure levels loosen particles and transport them from the inside to the periphery of inspected items 80. The moving sound pressure levels propagate the particles inside the conforming mechanism 82 towards at least one particle inhaling component 84. The trace collection system then conveys the extracted particles to an analyzer. Another significant particular aspect of novelty and inventiveness of the present invention, relates to using acoustic waves for concentrating particles in a moving air stream upstream of the filter. Acoustic waves produce a force on particles suspended in air. While the "Sound Pressure Level" (SPL) forces are slight for normal sound, specially designed acoustic sources can effect high decibel impulses. When two acoustic waves of the same frequency are superposed, a standing wave can be made which preferentially moves particles away from nodes of the wave to anti-nodes. Termed acoustophoresis, standing waves can create a concentrating force on particles suspended in an airstream.

The article "Acoustic Resonator Aerosol Particle Separation," by Joe Frankel

Dr. Michael J. Anderson, Dr. Ralph S. Budwig, Kenneth S. Line, Andrew Cluff, and Song Zhang, U. of Idaho, Dept of ME Report, June 2002 and the article "The Physics and Technology of Ultrasonic Particle Separation in Air," by M. Anderson, R. Budwig, A. Cluff, E. Lemmon, and G. Putnam, WCU 2003, Paris, September 7-10, 2003, each of which is expressly incorporated herein by reference, show the basics of the effect of moving particles in air by arranging locations of standing acoustic waves in a particle-laden air stream. United States Patent 5,192,450, "Acoustophoresis separation method", expressly incorporated here by reference, discloses the idea of separating particles with differing properties by using acoustic waves of two differing frequencies, one may be able to separate particles whose acoustic characteristics match those of the two frequencies. Referring to FIGs. 5A, 5B and 5C, these embodiments add the acoustic field generation system to the embodiments of Figs. 2 A, 2B and 2C. The filter housing features the following: particle filter 10, tube wall surface 22, and vibrating acoustic components 36 and 38. The vacuum system (not shown in the figure) propels a large volume of particle-laden air into the capture system. Vibrating acoustic components 36 produce a standing wave, thereby causing the particles to concentrate toward the wave nodes. The flow of particles then continues towards a standing wave having fewer nodes (generally, a lower frequency) which is produced by vibrating acoustic components 38. The standing waves are controlled to gradually cause the particles to concentrate toward the centerline. In alternative embodiment options, only one standing wave is used or more than two standing waves are used. A short distance downstream, particle filter 10 collects the particles.

Optionally, the filter can be placed at a location other than the center of the tube, and the standing waves can be positioned so as to concentrate the particles towards the filter (and not necessarily the centerline). For example, the node may be a concentric ring within the conduit, in which case the filter may be configured as a ring. Concentrating the particles toward the centerline of the tube has the added benefit of preventing the inner side tube wall surface 28 from becoming contaminated and allowing easier cleaning.

Analogous to Figs. 2B and 2C, Figs. 5B and 5C, show a cleaning or sampling airflow passage to an integrated trace detector. Thus in this embodiment, when the particle-laden air is propelled into the filter housing, airflow passage doors 30 are closed in order to block the cleaning passage and prevent air from escaping there. For example, in a first stage of the cycle, as shown in Fig. 5B, the door is closed to permit flow of gas with entrained particles from a particle extraction system (not shown), with precipitation of the particles on the filter 10. In a second stage of the cycle, as represented in Fig. 5C (after the primary flow bringing the particles to the filter has ceased), the door is opened and a cross flow of heated gas may be used to volatilize the particles on the filter 10, and the particle vapors then transported to the analyzer (not shown). Thus, after the particles are collected on the filter 10, a passage door 32 closes off the main airflow passage within the wall surface 28, and opens the passage door 30, and an air flow blowing from a side air passage carries the resulting aerosol to the trace detector. The cleaning procedure of the device is performed by blowing high-speed air through the passages.

Figs. 6A, 6B, 6C and 7 show an acoustophoretic embodiment of the invention, in which a central barrier 40 is provided within the gas flow conduit. This barrier 40 is provided, for example, to define a set of spaces having a single nodal surface for concentrating particles. As shown in Fig. 6A, the filter housing features the following components: particle filter 10, tube wall surface 22, and vibrating acoustic membranes 36 and 38. The vacuum system (not shown in the figure) propels a large volume of particle-laden air into the capture system. Vibrating acoustic membranes 36 produce a standing wave, thereby causing the particles to concentrate toward the wave nodes. The standing waves are controlled to gradually cause the particles to concentrate toward the centerline of each separated flow portion. In alternative embodiment options, various numbers of acoustic wave sources 36 are employed, as shown in Fig. 7. The barrier 40 terminates in the flow path before the filter 10, and particles flowing past the end of the barrier 40 tend to move toward the center of the flow path. Optionally, the filter can be placed at a location other than the center of the tube, and the standing waves can be positioned so as to concentrate the particles towards the filter (and not necessarily the centerline). For example, the node may be a concentric ring within the conduit, in which case the filter may be configured as a ring. Analogous to Figs. 2B and 2C, Figs. 6B and 6C, show a cleaning or sampling airflow passage to an integrated trace detector. Thus in this embodiment, when the particle-laden air is propelled into the filter housing, airflow passage doors 30 are closed in order to block the cleaning passage and prevent air from escaping there. For example, in a first stage of the cycle, as shown in Fig. 6B, the door is closed to permit flow of gas with entrained particles from a particle extraction system (not shown), with precipitation of the particles on the filter 10. In a second stage of the cycle, as represented in Fig. 6C (after the primary flow bringing the particles to the filter has ceased), the door is opened and a cross flow of heated gas may be used to volatilize the particles on the filter 10, and the particle vapors then transported to the analyzer (not shown). Thus, after the particles are collected on the filter 10, a passage door 32 closes off the main airflow passage within the wall surface 28, and opens the passage door 30, and an air flow blowing from a side air passage carries the resulting aerosol to the trace detector. The cleaning procedure of the device is performed by blowing high-speed air through the passages. In another embodiment option of the present invention, Laser induced fluorescence (LIF) induces the emission from molecules excited to higher energy levels by exposing a substance to laser radiation. Particles in a trace collection system can be excited using a laser. The excited particles will, after some time, usually in the order of few nano seconds to microseconds, return to the ground state and emit light at a wavelength uniquely characteristic to the chemical species of the substance. This fluorescence is measured and analyzed to deduce the nature of the excited particles.

LIF is based on electro-optics techniques, which allow the analysis to be remote and fast, and performed without disturbing the sample object. LIF offers the following advantages: (a) Speed: the detection of a substance can be performed in a fraction of a second.

(b) Remote: the system and the target can be some meters apart from one another.

(c) Sensitive: better than parts-per-million.

(d) Specific: substances can be recognized by their spectroscopic fingerprint

(e) User-friendly: the system can be deployed in few minutes and does not require a specifically trained user.

In another embodiment option of the present invention, a laser beam is used to detect particle traces while they are being extracted or transported from one location to another. The laser beam is used to scan the volume containing the particles, while a detector is used to analyze the escaping photons. The laser beam can be focused on a mobile or stationary filter. For example, the particle collector can be embedded with the membrane or the air tubes.

In another embodiment option of the present invention the tubes are made transparent or translucent materials. In this case, particle analysis can be performed while the particles travel through the air tube. Laser detection can be combined with various air tubes that provide specific particle detection capabilities. For example, laser detection can be used with spiral air tubes, or air tubes with varying diameter. In the latter case particles that travel through the air tube will decrease in velocity, where laser detection can employed with greater efficiency. Concentrating the particles during movement and forming a denser particle concentration increases detection probability.

Additionally and alternatively, laser detection can be used with a mesh of fine multiple air tubes that resemble a radiator. The laser beam can have any shape known in the art, such as a beam of varying diameter, or varying curtain, where the width of the beam is larger then its thickness.

In another embodiment option of the present invention, the laser beam is integrated with a mechanism of conveying gaseous substance within air tubes, such as a laminar or turbulent flow pattern implementation. In another embodiment option of the present invention, more then one laser beam is used to increase particle capture probability.

Numerous types of lasers can be used in the particle detection process. Multiple lasers of differing intensity and wavelength can be advantageous when analyzing for specific materials that are sensitive to distinct wavelengths. In another embodiment option of the present invention, the particles are captured on a filter or on a predefined area, and the laser beam is used for analyzing, and then cleaning the filter or the predefined area that captures the particles. The cleaning process is performed by radiating a high power laser beam towards the filter or towards the predefined area that captures the particles. This can be performed between detection cycles in order to clean the particle filter.

In another embodiment option of the present invention, the air tube transporting the particles feature bends of varying degree. Alternatively, the air tube transporting the particles can be designed like a coil with at least one turn. By changing the characteristics of the transporting air tube the system can increase the probability of particle laser detection. In another embodiment option of the present invention, the laser is positioned outside the transporting air tube, at an acute angle with respect to the air tube. In this embodiment the laser beam passes through a wall of the tube, and intersects a larger section of the transporting air tube than an embodiment wherein the laser is perpendicular to the tube wall, thus increasing the probability of reaching a greater number of particles, and subsequently increasing the probability of particle detection. A laser beam that is aligned with the particle flow vector can potentially 'catch' a great number of particles.

In another embodiment option of the present invention, a laser analyzer is used in conjunction with a resonator that employs sound waves to concentrate particles along the centerline of the air tube. In this scenario, heavier particles adopt a different trajectory than lighter particles. By anticipating particle trajectories as a function of weight and size, the laser can be directed to an area of particular interest. It is to be understood that the particle weight ranges from a few atoms to a few milligrams.

In another embodiment option of the present invention, the laser beam scans a predefined area. Using a scanning laser beam reduces the number of lasers required to scan a specific area. This is specifically advantageous in cases where the laser beam scanner has a scan velocity greater velocity than the scanned particles

In another embodiment of the system, the ability to capture gaseous forms of the trace material is enhanced by the addition of filter material to the existing filter made of materials suitable for absorbing gases. Such materials are known in the art and include activated charcoal, Tenax, RDX^®, and Amberlite XAD-2, XAD-4 and XAD-7.

Further, this embodiment includes the use of filters or swab materials which contain or are made of appropriate gas-absorbing fibrous materials.

Another technique which recently has been used for this purpose is called "Solid Phase MicroExtraction" or SPME using a PDMS/DVB filter as is known in the art. It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in various combinations in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub- combination.

All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference to the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.

While the invention has been described in conjunction with specific embodiments and examples thereof, it is to be understood that they have been presented by way of example, and not limitation. Moreover, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims and their equivalents.

The present invention is not limited in its application by the details of the order or sequence of steps of operation or implementation of the method and/or the details of construction, arrangement, and composition of the components of the device set forth in the following description, drawings or examples. While specific steps, configurations and arrangements are discussed, it is to be understood that this is done for illustrative purposes only. A person skilled in the relevant art will recognize that other steps, embodiments, configurations and arrangements can be used without departing from the spirit and scope of the present invention. The present invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology, terminology and notation employed herein are for the purpose of description and should not be regarded as limiting.

What is claimed is:

Claims

CLAIMS:

1. A system for capturing particles in a flowing gas stream, comprising: a conduit, receiving a gas flow having entrained particles and having a cross sectional area; a filter, having an area less than or equal to the cross sectional area, disposed within the conduit, for capturing particles within a portion of the cross sectional area; and at least one of an electrostatic, acoustic, and aerodynamic element for concentrating particles within the cross sectional area from which the filter captures particles.

2. The system according to claim 1, wherein the filter is disposed within a region having a first state in which the filter receives particles from the conduit, and a second state in which the filter is separated from gas within the conduit.

3. The system according to claim 2, wherein the second state provides a second flow path, distinct from the conduit, wherein a gas flow through the second flow path removes at least a portion of the material forming the particles captured by the filter.

4. The system according to claim 1, wherein an electrostatic element is provided to charge particles within the conduit.

5. The system according to claim 4, wherein the filter is charged to a potential opposite that of the particles.

6. The system according to claim 4, wherein the conduit has a wall, wherein the wall has a charge pattern to concentrate particles within the conduit away from the wall.

7. The system according to claim 1, wherein an acoustic element is provided to alter a spatial distribution of particles.

8. The system according to claim 7, wherein the acoustic element creates a standing wave within the conduit.

9. The system according to claim 8, wherein the standing wave has a nodal surface which has an adjustable position.

10. The system according to claim 8, wherein the standing wave is generated by a plurality of acoustic transducers.

11. The system according to claim 7, wherein a pattern of standing waves varies axially along the conduit.

12. The system according to claim 7, further comprising an axially oriented barrier within the conduit.

13. The system according to claim 1, wherein the conduit comprises a Venturi section in which portions of the flow are segregated into a slow central portion passing though the filter, and a fast outer portion bypassing the filter, the fast outer portion inducing a relative vacuum at a position past the filter, to thereby enhance gas flow of the slow central portion through the filter as compared to a state in which the fast outer portion is diverted.

14. The system according to claim 13, wherein the Venturi section comprises a tube within the conduit, located distal to an expansion in an inner diameter of the conduit.

15. The system according to claim 1 , wherein the conduit comprises a Venturi section in which at least a portion of the flow passes though the filter, further comprising an external pressurized gas or fluid flow bypassing the filter and inducing a relative vacuum at a position past the filter.

16. The system according to claim 1, further comprising a subsonic transducer for generating subsonic acoustic waves for dislodging particles from an object.

17. A method for capturing particles in a flowing gas stream, comprising: receiving a gas flow having entrained particles through a conduit having a cross sectional area; capturing particles on a filter, having an area less than or equal to the cross sectional area, disposed within the conduit; and concentrating particles within the cross sectional area using at least one of an electrostatic, acoustic, and aerodynamic element.

18. The method according to claim 17, wherein the filter is disposed within a region having a first state in which the filter receives particles from the conduit, and a second state in which the filter is separated from gas within the conduit.

19. The method according to claim 18, wherein the second state provides a second flow path, distinct from the conduit, wherein a gas flow through the second flow path removes at least a portion of the material forming the particles captured by the filter.

20. The method according to claim 17, further comprising the step of electrically charging particles within the conduit.

21. The method according to claim 20, wherein the filter is charged to a potential opposite that of the particles.

22. The method according to claim 20, further comprising the step of creating an electrical field pattern within the conduit to concentrate particles away from the wall.

23. The method according to claim 17, further comprising the step of altering a spatial distribution of particles acoustically.

24. The method according to claim 23, wherein a standing wave is created within the conduit.

25. The method according to claim 24, wherein the standing wave has a nodal surface which has an adjustable position.

26. The method according to claim 23, wherein the standing wave is generated by at least one acoustic transducer.

27. The method according to claim 23, wherein a pattern of standing waves varies axially along the conduit.

28. The method according to claim 23, wherein an axially oriented barrier is provided within the conduit.

29. The method according to claim 17, further comprising providing a Venturi section, in which portions of the flow are segregated into a slow central portion passing though the filter, and a fast outer portion bypassing the filter, the fast outer portion inducing a relative vacuum at a position past the filter, to thereby enhance gas flow of the slow central portion through the filter as compared to a state in which the fast outer portion is diverted.

30. The method according to claim 29, wherein the Venturi section comprises a tube within the conduit, located distal to an expansion in an inner diameter of the conduit.

31. The method according to claim 17, further comprising providing a Venturi section in which at least a portion of the flow passes though the filter, further comprising supplying a pressurized gas or fluid which bypasses the filter, and inducing a relative vacuum at a position past the filter.

32. The method according to claim 17, further comprising generating subsonic acoustic waves for dislodging particles from an object.