Abstract:
A vapor detector is disclosed, that includes a chemically sensitive waveguide and a light detector coupled to the waveguide. The light detector is adapted to respond to light transmitted through the waveguide. Vapors reacting with the waveguide reflect light transmitted through the waveguide. The light detector recognizes changes in the transmitted light to identify the vapor that reacted with the waveguide.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The following applications contain subject matter related to the present application and are assigned to the assignee of the present application: co-filed applications with Ser. Nos. ______ and ______. 
     
    
     GOVERNMENT CONTRACT  
       [0002] This invention was made with Government support under Defense Applied Research Projects Agency contract number DABT63-97-C-0018. The Government has certain rights in this invention. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0003]    Without limiting the scope of the invention, its background is described in connection with land mine detection, as an example.  
           [0004]    Anti-personnel mines, commonly called land mines, cause severe injuries and casualties to thousands of civilians and military troops around the world each year. There are over 120 million land mines currently deployed in over 60 countries around the world. Each year, over 2 million new land mines are laid, while only about 100,000 mines are cleared.  
           [0005]    These mines are typically deployed randomly within a strategic area and may be buried or camouflaged so they are invisible to a casual observer. Mines may instantly and indiscriminately claim unsuspecting victims who step or drive on the mine&#39;s triggering mechanism. The clandestine and indiscriminate nature of land mines make them a particularly dangerous weapon for anyone in close proximity to the mine.  
           [0006]    Mines contain an explosive, which rapidly accelerates shrapnel or other projectiles when activated. Many mines contain trinitrotolulene (TNT), which is a common explosive compound. TNT and other explosives are polynitroaromatic compounds that emit a vapor. This emitted vapor may be useful to detect mines and other explosives.  
           [0007]    Current detection methods range from high-tech electronic (ground penetrating radar, infra-red, magnetic resonance imaging) to biological detection schemes (dog sniffers and insects or bacteria) to simple brute force detonation methods (flails, rollers and plows) and the use of hand-held mechanical prodders. Most of these methods are very slow and/or expensive and suffer from a high false alarm rate. Mines usually do not possess self-destroying mechanisms and due to their long active time jeopardize the lives of millions of people. Furthermore, mines are difficult to find with commercial metal detectors, because their metal content is very low and in some cases even zero.  
         SUMMARY OF THE INVENTION  
         [0008]    Therefore, a system that detects mines having little or no metallic content is now needed; providing enhanced design performance and accuracy while overcoming the aforementioned limitations of conventional methods.  
           [0009]    Generally, and in one form of the invention, a vapor detector includes a chemically sensitive waveguide and a light detector coupled to the waveguide. The light detector is adapted to respond to light transmitted through the waveguide. Vapors react with the waveguide alter the transmission of light through the waveguide. The light detector recognizes changes in the transmitted light to identify the vapor that reacted with the waveguide.  
           [0010]    In one embodiment of the present invention, the vapor detector has a waveguide that is self-supporting.  
           [0011]    In another embodiment of the present invention, the waveguide has a reflective region to improve light transmission.  
           [0012]    In yet another embodiment of the present invention, the vapor detector has a light source to direct light through the waveguide.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the s accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which:  
         [0014]    [0014]FIG. 1 is a schematic of a vapor detector;  
         [0015]    [0015]FIG. 2 is a schematic of a vapor detector having a focused light source;  
         [0016]    [0016]FIG. 3 is a schematic of a multiple vapor detector;  
         [0017]    [0017]FIG. 3 a  is a schematic of a multiple vapor detector;  
         [0018]    [0018]FIG. 4 is a schematic of a radiation detector; and  
         [0019]    [0019]FIG. 5 is an illustrative embodiment of a vapor detector being used in a mine field.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that may be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.  
         [0021]    For purposes of illustration, a vapor detector that uses a polymer waveguide sensitive to polynitroaromatic compounds is provided. The principles and applications of the present invention are not limited only to detecting explosives; being applicable to detection of radiation, a variety of vapors from many different substances or both, or contaminants in liquids or solutions.  
         [0022]    Referring now to FIG. 1, a schematic representative of a vapor detector  5  is shown. A waveguide  10  may be formed from a variety of polymer compounds, such as polyvinylchloride (PVC), for example, that are suitable for producing an optically clear structure. The waveguide  10  is impregnated or infused with a chemical, Jeffamine T-403 (developed by TEXACO) for example, that reacts with vapor from the compound to be detected.  
         [0023]    In this specific example, Jeffamine also acts as a plasticizer for the PVC compound. Inherent rigidity in the PVC compound allows the waveguide  10  to be self-supporting. A self-supporting waveguide  10  simplifies production and reduces associated costs of the device. The waveguide  10 , alternatively, may be deposited on a substrate (shown in FIG. 2).  
         [0024]    For example, in operation, the vapor detector  5  may be used as follows. Many land mines contain TNT, which is a polynitroaromatic compound. Jeffamine T- 403  reacts with TNT vapor thereby altering the light absorbent properties of the waveguide  10 . Other chemicals may be mixed with the polymer of the waveguide  10  to allow the vapor detector  5  to detect other compounds. The vapor detector  5  may also incorporate several waveguides  10  to detect multiple compounds at a single location.  
         [0025]    A light source  12  may be used to emit light  14  into waveguide  10 . The light source  12  may be an incandescent lamp, an LED, a laser or any other light producing device known in the art. Vapor  16  that has reacted with chemicals within waveguide  10  absorbs some of the light  14 . The remainder of light  14  passes through waveguide  10  into a light detector  18 .  
         [0026]    Light detector  18  analyzes the characteristics of the light  14  that is transmitted through the waveguide  10 , which has been exposed to vapor  16 , to identify the compound that emitted vapor  16 . Light detector  18  may be a semi-conductor photo-detector, a photo-multiplier tube, a bolometer or other heat or light-sensitive detector known in the art.  
         [0027]    Now referring to FIG. 2, an alternative embodiment of the invention is illustrated. Light  14  from light source  12  may be focused with one or more lenses  20  to obtain a more accurate transmission of light  14  through waveguide  10 . A light block  22  may be used to direct light  14  into waveguide  10  and eliminate any stray light from sources other than the intended light source  12 . A reflective region  23  may be included on the waveguide  10  to further enhance the intensity of transmitted light  14 . The reflective region  23  may be made from polished metal or any other suitable reflective material.  
         [0028]    Another embodiment of the invention is illustrated in FIG. 3. A beam splitter  24  may be used to create multiple beams of light  14  from a single light source  12 . These multiple beams of light  14  may be directed into multiple different waveguides  10  by lenses  20  and light blocks  22 . The light  14  is transmitted through the waveguides  10  into multiple light detectors  18 . Each waveguide  10  may be compounded with a different chemical to detect a unique compound. A vapor detector  5  with multiple, individually configured waveguides  10  could detect the presence of several different compounds located in a single area.  
         [0029]    Another embodiment of the invention is illustrated in FIG. 3 a . Multiple beams of light  14  may be directed into multiple different waveguides  10  by multiple light sources  12 . Multiple beams of light  14  are transmitted through the waveguides  10  into multiple light detectors  18 . Each waveguide  10  may be compounded with a different chemical to detect a unique compound. Each light source  12  may emit a different wavelength of light, which is also designed to detect a unique compound. Alternatively, as indicated by the dotted lines, one embodiment of the invention may have a single waveguide  10 .  
         [0030]    Now referring to FIG. 4, a radiation detector  6  may contain waveguide  10 , which may contain a chemical that emits light when exposed to radiation. Radioactive particle  26  impinges waveguide  10  and causes a reaction with a chemical in the waveguide  10  that produces light  14 . The light  14  is transmitted through waveguide  10  and into light detector  18 . Light detector  18  analyzes the characteristics of the light  14  that is transmitted through the waveguide  10 , and signals the presence of radiation within the area.  
         [0031]    The source radiation must be converted into visible light prior to its detection by light detector  18 . This is accomplished by a scintillation chemical compounded in the waveguide  10 . A scintillation chemical is a material that emits optical photons in response to ionizing radiation. Optical photons are photons with energies corresponding to wavelengths between 3,000 and 8,000 angstroms. Thus, the scintillation compound converts source radiation energy from radioactive particle  26  into visible light energy, which may then be detected by the light detector  18 .  
         [0032]    Examples of scintillation layer material for this application may include: GdO 2 S 2 , Csl, Csl:TI, BaSO 4 , MgSO 4 , SrSO 4 , Na 2 SO 4 , CaSO 4 , BeO, LiF, CaF 2 , etc. A more inclusive list of such materials is presented in U.S. Pat. No. 5,418,377, which is incorporated herein by reference. Commercial scintillation layers may contain one or more of these materials.  
         [0033]    Referring now to FIG. 5, the vapor detector  5  is shown in use in an area that contains one or more land mines  28 . The vapor detector  5  is enclosed in a robust housing  30 , which protects the vapor detector  5  from hostile environmental conditions such as rain, snow, sunlight and even wild animals. The housing  30  may be designed to shockproof the vapor detector  5  for deployment by airplane or parachute. The housing  30  may also use a self-righting design that ensures proper vapor detector  5  orientation if the vapor detector  5  is deployed by aircraft.  
         [0034]    Land mine  28  contains an explosive that emits vapor  16 , which emanates into vents  32  in the housing  30  and exposes vapor detector  5 . Vapor  16  reacts with chemicals within waveguide  10 . Light  14  transmitted through waveguide  10  is partially absorbed by the reactants and is detected by light detector  18 . Light detector  18  signals the presence of land mine  28  in the area.  
         [0035]    The housing  30  may also be fitted with a fan  34 . The fan  34  operates to increase air flow from the surrounding area across the waveguide  10 . The fan  34  decreases the time necessary for the vapor detector  5  to detect vapor  16  in an area. The fan  34  also increases the sensitivity and range of the vapor detector  5  by exposing the waveguide  10  to a larger volume of air and vapor  16  within the area.  
         [0036]    The housing  30  also contains a power supply for the circuitry of the vapor detector  5  and the fan  34 . The power supply may be a battery, solar power or a combination of battery and solar power.  
         [0037]    While this invention has been described in reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.