Abstract:
Apparatus and methodology utilizing nearfield microwave technology to detect contraband/forbidden substances concealed within metallic containers. Apparatus and methodologic microwave operating frequency determines the metallic thickness through which detection is possible, and also the expectable “depths” for detection within a metallic container. Special and important attention is paid to the appropriate positional and distance locating of the invention apparatus relative to a suspected “substance-containing” metallic container for detection to be most effective. Preferably, this distance is substantially equal to the closest distance from the central radiating plane of a lens/antenna (which is employed, according to a preferred practice of the invention) at which a conductive, metallic surface will regeneratively parasitize the lens/antenna.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to the filing date of co-pending U.S. Provisional Application, Ser. No. 60/367/954, filed Mar. 25, 2002 for “Dielectric Detection Through Conductive Metal”. The entire contents of that provisional patent application are hereby incorporated herein by reference. 
    
    
     INTRODUCTION 
     This invention relates to substance detection based upon substance dielectric characteristics, and more specifically to apparatus and a method utilizing near-field microwave technology for detecting and identifying the presence (dielectric “signatures”) of selected kinds of substances which are hidden behind an electrically conductive metal expanse. 
     While there are many fields of application for this invention, a preferred and best mode embodiment of, and manner of practicing, the invention are described and illustrated herein in the context of detecting contraband and/or dangerous substances, such as certain drugs and explosives, which may be carried clandestinely concealed in otherwise innocuous, sealed metal containers, such as in cans of olive oil. 
     Near-field microwave technology has established itself as a powerful and versatile tool for detecting, via observing dielectric characteristics of, various substances that prove to be illusive, even invisible, to other detection modes. This technology and its detection capability are timely, and are of great interest today especially in the heightened sense of concern that people feel and express for personal security in places such as airports and aircraft. 
     A number of now-issued U.S. patents describe and attest to the power and versatility of microwave detection practices, and these patents include: 
     U.S. Pat. No. 4,234,844, Electromagnetic Noncontacting Measuring Apparatus 
     U.S. Pat. No. 4,318,108, Bidirectionally Focussing Antenna 
     U.S. Pat. No. 4,532,939, Noncontacting, Hyperthermia method and Apparatus of Destroying Living Tissue in Vivo 
     U.S. Pat. No. 4,878,059, Farfield/Nearfield Transmission/Reception Antenna 
     U.S. Pat. No. 4,912,982, Non-Perturbing Cavity Method and Apparatus for Measuring Certain Parameters of Fluid Within a Conduit 
     U.S. Pat. No. 4,947,848, Dielectric-Constant Change Monitoring 
     U.S. Pat. No. 4,949,094, Nearfield/Farfield Antenna with Parasitic Array 
     U.S. Pat. No. 4,975,968, Timed Dielectrometry Surveillance Method and Apparatus 
     U.S. Pat. No. 5,083,089, Fluid Moisture Ratio Monitoring Method and Apparatus 
     U.S. Pat. No. 6,057,761, Security System and Method 
     The contents of each of these just-mentioned patents are hereby incorporated herein by reference. 
     The present invention, while based in part upon certain structures and methodologies expressed in these patents, makes a significant departure in the form of my recent discovery that, under special structural and methodologic circumstances, it is possible to employ nearfield microwave technology effectively to “see through” an otherwise, and normally thought of, occluding barrier expanse of conductive metal, thus to detect various metal-hidden substances of societal concern, such as illegal drugs, and explosives. Prior detection approaches utilizing the specific technology described in the patents listed above have, by contrast, involve substance detection through shrouding or intervening media which is not formed of metal. By including the new capabilities offered by the present invention, the “escape hatch” of metallic hiding or shrouding employed by those engaged in such practices is easily and significantly checked. 
     The manners of implementing and practicing this invention, and their respective advantages and contributions to the art, will become quite fully apparent from the following detailed descriptions of the preferred and best mode embodiment, and manner of practicing, the invention, especially as read in light of the accompanying illustrative drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified, schematic, partly fragmentary side view of apparatus constructed in accordance with a preferred embodiment of the present invention. 
     FIG. 2 is an enlarged, fragmentary detail generally drawn from a portion of FIG.  1 . 
     FIG. 3 illustrates, in a isolated fashion, an attachable/detachable component which is employed in the invention embodiment illustrated in FIGS. 1 and 2 to define what is referred to herein as an interrogation face. 
     FIGS. 4 and 5 illustrate two different modifications of the invention. All of these figures can be viewed also as illustrating the practice and methodology of the invention. Structures shown in these drawing figures are not drawn to scale with one another. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings, and referring initially to FIGS. 1-3, inclusive, indicated generally at  10  is a system including apparatus, or structure,  12  which is constructed in accordance with a preferred and best mode embodiment of the present invention. These three drawing figures also collaboratively join with text below in describing and illustrating the preferred methodology involving practice of the invention to detect a selected substance  14 , such as a contraband drug, like cocaine, which is packaged and “hidden” inside a sealed container (generally shown fragmentarily at  16 ), which container otherwise contains an innocuous substance, such as olive oil shown fragmentarily at  18 , all shrouded, or jacketed, by a can (not fully shown) formed by sheet metal  20 . Sheet metal  20 , also referred to herein as a conductive expanse (an electrically conducted expanse), has an outside exposed surface  20   a , and is formed herein of a typical metallic “canning” material, such as steel or aluminum. Expanse  20  herein has a typical can-wall thickness of about 0.09-inches. Substance  14  has been clandestinely concealed behind metallic expanse  20  (in the “can”) with the likely confident view that it is probably undetectable by most, if not all, conventional contraband scanning technologies, principally because of the presence of metallic jacketing. 
     The structure and methodology of the present invention function in the nearfield of microwave electromagnetic radiation, and may be constructed to function essentially anywhere within the recognized microwave spectrum, ranging in frequency from about 300-MHz to about 30-GHz. Apparatus  12  as illustrated and now described herein is specifically designed to operate within this spectrum at the frequency of about 627-MHz—a frequency which has been found to work extremely effectively for the through-metal detection of substances, such a illegal drugs, like cocaine, as well as other illegal and/or dangerous contraband substances, such as various explosives. The wavelength λ in air of this operating frequency is about 18.83-inches. In general terms, whatever the operating wavelength is, the thickness of metal through which detection is most effective in accordance with this invention is about 0.005-λ. Given this chosen, and herein illustrative and representative, operating frequency, various dimensions expressed below, and illustrated in the drawings, are specific to this choice. How they would understandably need to be varied to accommodate other operating frequencies is a matter well known to those generally skilled in the relevant art. Such “relevant-art” knowledge will be aided by making reference to the above-identified, previously-issued U.S. patents. 
     Continuing with the description of what is shown in FIGS. 1-3, inclusive, generally included in system  10  for energizing apparatus  12 , in accordance with practice of the invention, is an appropriate and conventional microwave power source  22 , which is drivingly connected to apparatus  12 , and also appropriate performance-monitoring apparatus  24  which monitors the functioning of apparatus  12 , during use, to produce interpretable output information regarding through-metal detected substances. Further included in apparatus  12  is a torroidal receiver ring  25  which is appropriately positioned in the apparatus as will shortly be more fully explained. 
     Apparatus  24  may conveniently be otherwise conventional structure that typically observes certain electrical voltage, current and/or phase conditions extant in the operation of apparatus  12  during its “detecting and investigative use, to produce the mentioned interpretable output information which is preferably based upon pre-use, systemic “calibration”. 
     It may be useful at this point in this text to point out that a reading of U.S. Pat. No. 4,234,844, referred to above, provides a very full description of apparatus quite like apparatus  12  herein, but there illustrated structured to perform a quite different kind of investigative operation. 
     Additionally included within apparatus  12 , and also quite well discussed in the &#39;844 patent just mentioned above, are a nearfield, bi-directionally radiating torroidally configured, body-of-revolution lens/antenna  26 , having a body  26   a  formed of polystyrene, and a central, circular, driven radiating element  26   b . Element  26   b  occupies a plane  28  which is disposed normal to the respective planes of FIGS. 1 and 2 in the drawings, with plane  28  also being disposed normal to the bi-directional radiation axis  30  (see the dash-double-dot lines in FIGS. 1 and 2) that lies within the planes of these two drawing figures. Plane  28  is referred to herein as the central radiating plane of lens/antenna  26 . Axis  30  coincides with the axis of revolutional symmetry of lens/antenna body  26   a . Power source  22  directly drives element  26   b  via an appropriate electrical driving connection established therewith (not specifically shown in detail). 
     In the embodiment of the invention now being described, the right side of lens/antenna body  26   a  terminates at an aperture which is shown at  26   c , which aperture lies in a plane that substantially parallels plane  28  at a distance pictured in FIG. 2 as D 1 . This distance preferably is substantially 0.15-λ, where λ is the wavelength of the operating frequency of apparatus  12  in air. 
     Formed as an annular projecting rim  26   d  which circumsurrounds aperture  26   b  is structure which is designed slideably to receive and support a spacer element which is constructed as illustrated in FIG.  3  and given reference numeral  32 . As can be seen, spacer  32  has a somewhat U-shaped configuration as it is seen in FIG. 3, including an open side  32   a  which permits it to be slid onto rim  26   d  preferably in a very modest clearance-fit manner. This spacer is designed so that when it is fully seated in place, lens axis  30  resides in relation to the spacer at the location shown for this axis in FIG.  3 . Spacer  32  is designed to define what is called herein an interrogation face  32   b  which lies at the distance designated D 2  in FIG. 2 from the nominal plane of driven element  26   b . Distance D 2  herein preferably is about 0.25-λ This dimension, notably, defines the closest distance from the plane of driven element  26   b  at which a metal surface, such as surface  20   a  will regeneratively parasitize lens/antenna  26 . Lens/antenna structure  26  and spacer  32  herein are collectively referred to as lens/antenna interrogation structure. 
     With respect to the capability of the structure and methodology of this invention to perform in relation to detecting substances through metallic expanses, and was mentioned earlier, it is preferably designed to work in conjunction with such metallic expanses that have thicknesses preferably about equal to or less than what is referred to herein as a defined fraction of λ, which fraction is preferably about 0.005 of λ This metal thickness consideration is illustrated as D 3  in FIG.  2 . 
     During use, and following a calibration procedure which will be described, apparatus  12  is positioned relative to a metallic expanse, such as sheet metal  20 , in a manner whereby the exposed outwardly facing face  32   b  of spacer  32  contacts the outer surface  20   a  of metal expanse  20 , with lens/antenna axis  30  positioned to intersect the expected location of substance  14 , as illustrated in FIGS. 1 and 2. Under these circumstances, the preferred range within which substance  14  lies to be easily detectably is indicated generally at D 4  in FIG. 2, and this range extends up to about 0.375-λ. A preferable maximum range within which substance detection is accomplishable is indicated at D 5  in FIG. 2, and this range extends to a distance of about 2.5-λ. 
     In preparation for utilizing apparatus  12  to detect a substance, such as substance  14 , the apparatus is positioned with face  32   b  of spacer  32  in contact with surface  20   a  of the suspect metallic container, and with the driven element powered, the apparatus is slid in a surface manner over surface  20   a  to detect an voltage amplitude peak so-to-speak, as monitored by apparatus  24 . This sliding-contact procedure is implemented in a manner whereby the radiation axis of the apparatus will, at some point, pass through any hidden contraband substance. With the apparatus positioned at a location where that peak is observed, a slight back and forth adjustment is made in the operating frequency of the system (a very modest adjustment) to fine-tune a maximum peak condition, and the apparatus is then in a condition actually detecting substance  14 . The voltage-peak condition now in existence gives an indication regarding the dielectric characteristics of substance  14 , and by correlating this observed peak with certain pre-calibration data, the nature of substance  14  can be interpreted for identification. 
     Pre-calibration is accomplished by performing the same “interrogation” process which has just been described for a selected variety of substances possessing essentially the sane expectable dielectric constants known to characterize “forbidden” substances. Voltage peaks associated with these known, pre-calibration materials are noted, and then later employed in a correlation process to identify hidden, unknown substances. 
     Turning finally now to the modifications shown in FIGS. 4 and 5, in FIG. 4 there is a fragmentary cross-sectional showing of a modified lens/antenna body structure  40 . This modified body structure is made with aperture structure  40   a  that includes an “interrogation face”  40   b.    
     FIG. 5 illustrates fragmentarily yet another modified lens/antenna body structure  42  which is built with an aperture structure  42   a  having a two-dimensionally, concavely shaped interrogation face  42   b . This face is shaped to fit conformably with the outside surface  44   a  of a cylindrical metallic container  44 . Another approach toward accommodating such curved container surfaces could include providing a collection of different spacers, like spacer  32 , having differently curved interrogation surface selected to “fit” to the respective outside curved surfaces of various different cylindrical containers. Absolute complementary curvature matching, while preferred, is not required. Matching, and closely matching, curved interfaces of this nature are referred to herein as possessing “local coplanarity”. 
     Accordingly, a preferred and best mode embodiment of, and manner of practicing the present invention, and certain variations thereof, have been illustrated and described. Other variations and modifications coming within the scope of the present invention are, of course, possible, and will be understood by those skilled in the art.