Particle preconcentrator

Abstract

An apparatus and method for preconcentrating particles and vapors. The preconcentrator apparatus permits detection of highly diluted amounts of particles in a main gas stream, such as a stream of ambient air. A main gas stream having airborne particles entrained therein is passed through a pervious screen. The particles accumulate upon the screen, as the screen acts as a sort of selective particle filter. The flow of the main gas stream is then interrupted by diaphragm shutter valves, whereupon a cross-flow of carrier gas stream is blown parallel past the faces of the screen to dislodge the accumulated particles and carry them to a particle or vapor detector, such as an ion mobility spectrometer. The screen may be heated, such as by passing an electrical current there through, to promote desorption of particles therefrom during the flow of the carrier gas. Various types of screens are disclosed. The apparatus and method of the invention may find particular utility in the fields of narcotics, explosives detection and chemical agents.

Description

[0001]This is a division of application No. 08 / 988,542 filed Dec. 10, 1997, now U.S. Pat. No. 5,854,431.GOVERNMENT RIGHTS[0002]This invention was made with United States Government support under Contract No. DE-AC04-94AL85000 awarded by the U.S. Department of Energy. The Government has certain rights to this invention.BACKGROUND OF THE INVENTION[0003]1. Field of the Invention (Technical Field)[0004]The present invention relates generally to the field of particle concentrators, and more particularly to an apparatus for pre-concentrating airborne particles to promote their detection, and specifically to a particle preconcentrator apparatus having improved reliability and durability and especially useful for the detection of compounds such as explosives, illegal drugs, other controlled substances and chemical agents. In this application, as set forth more fully later in this disclosure, the term particle is intended not to exclude vapor.[0005]2. Background Art[0006]The use of explosive...

AI Technical Summary

Benefits of technology

[0021]A primary advantage of the present invention is that it is operable repeatedly with a short cycle time.

[0022]Another advantage of the invention is that it is compact and durable, and suitable for use in conjunction with personnel screening at airports and the like.

Problems solved by technology

Current explosives detection systems are hampered, however, by a need to detect explosives residues at extremely low (in the range of parts-per-trillion, ppt) concentrations, and to do so quickly (on a per person or per item basis) and with minimal invasion of the personal privacy of airline travelers and the like.

When an individual handles or otherwise comes in contact with a modest quantity of, for example, an explosive or narcotic substance, significant numbers of particles of the substance typically cling feebly to the person's skin and / or clothing.

Known devices employing high-volume air flows to blow or suction particles from a person suffer from particle concentration dilution, rendering detection unreliable.

Moreover, known detectors for use in testing for explosives or drugs on humans, luggage, motor vehicles, and other bulky items frequently cannot properly process the large air volumes used to collect the target particles.

Particle desorption for presentation to the detector, however, is difficult and slow in volume collection systems.

A particle preconcentrator based upon volume collection techniques is commercially impracticable for purposes of explosives detection due to the size of the device and the unacceptably large amount of time required to desorb the concentrated particles.

The foils, which may incorporate ultra-thin stainless steel films, are expensive to manufacture.

Obtaining the needed surface area for particle collection in a thin foil preconcentrator can result in a physically large unit with excessive dead space or, conversely, very closely-spaced foils.

The high-volume air flow necessary for rapid adsorption frequently causes tearing, displacement, and destruction of the thin, fragile, foils, a problem aggravated when the foils are closely spaced, thereby impeding the discharge.

Discharges sufficiently lowered to reduce foil damage, and which are desirable in the desorption stage, may not be strong enough to release accumulated particles from the foil faces.

Additionally, because the sample-bearing air stream blows parallel past the foils, a boundary layer forms on the foil surfaces, impeding the impact and adhesion of particles upon the foils.

If a significantly large item, e.g., handkerchief, comb, pencil, or the like, should be ingested by the preconcentrator, the foils are susceptible to severe damage and loss of collection surface area.

The membrane filter, however, lacks the ability to quickly desorb the vapors and particles from the surface as does the volume collection method.

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