Abstract:
Swimmers are detected in a given body of water by dispersing sensors throughout the water column. The sensors adhere to the swimmer and reflect acoustic energy. Acoustic energy is broadcast in the water and the swimmer is detected by the characteristic motion of the sensors clinging to the swimmer as detected by acoustic monitors. The sensors may also fluoresce and be detectible by optical monitors when a portion of the swimmer is above the water.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a divisional of U.S. nonprovisional patent application “Smart Polymeric Multilayer Sensors”, Ser. No. 11/056,023, filed Feb. 11, 2005 now U.S. Pat. No. 7,345,596. 
   Said nonprovisional patent application Ser. No. 11/056,023 in turn claims the benefit of U.S. provisional patent application Ser. No. 60/543,953, filed Feb. 12, 2004, and entitled “Smart Polymeric Multilayer Sensors”. Said provisional application Ser. No. 60/543,953, is incorporated herein by reference. 
   Said nonprovisional patent application Ser. No. 11/056,023 also claims the benefit of U.S. provisional patent application Ser. No. 60/599,141, filed Aug. 5, 2004, and entitled “Surface Swimmer Detection Via Sensors”. Said provisional application Ser. No. 60/599,141, is incorporated herein by reference. 
   This application further incorporates by reference U.S. provisional patent application Ser. No. 60/455,142, filed Mar. 17, 2003, and entitled “Smart Polymeric Multilayer Sensors”. 

   FIELD OF INVENTION 
   This invention is in the field of methods for detecting and tracking a swimmer. 
   BACKGROUND 
   An improved low cost method of detecting underwater and surface swimmers is needed. 
   SUMMARY OF THE INVENTION 
   The Summary of the Invention is provided as a guide to understanding the invention. It does not necessarily describe the most generic embodiment of the invention or all species of the invention disclosed herein. 
   The present invention comprises sensors that are in the form of multilayer polymer micro beads or other shapes and are about nanometers to millimeters in diameter. Said multilayer beads have a change in detectable property, such as color, density, buoyancy, or acoustic reflectivity, which occurs when exposed to a particular triggering stimulus. The change in said property is detectible by an external monitor. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a cross section of a typical three-layer sensor bead. 
       FIG. 2  illustrates the use of a field of sensors in swimmer detection. 
       FIG. 3  illustrates the use of a field of acoustically reflective sensors in swimmer detection. 
   

   DETAILED DESCRIPTION OF INVENTION 
   The following detailed description discloses various embodiments and features of the invention. These embodiments and features are meant to be exemplary and not limiting. 
   The present invention comprises sensors that are in the form of multilayer beads. 
     FIG. 1  illustrates the cross section of a typical sensor structure. Sensor  100  is generally spherical in shape. The sensor comprises a core  102 , intermediate layer  104  and outer layer  106 . 
   Sensors may have an overall diameter in the range of a few nanometers to a few millimeters. 
   Sensors may also have nonspherical shapes, such as fabric swatches. Sensors may also be adhered to base film sheets. 
   Sensors may be distributed in large numbers in a given medium, such as air or water. When an object or chemical or physical effect disturbs said sensors, said sensors react and become detectible by a monitor. Hence the presence of said object, chemical or other physical effect may be detected. 
   Sensors are typically made from polymers. Suitable polymers depend upon the application. Suitable polymers include consumer, specialty, engineering, or high performance resins. Examples of suitable polymers include polyethylene, polypropylene, acrylics, vinyls, polyphenylene ether, and polyphenylene sulfide. 
   Biodegradable polymers such as poly(lactic acid) and aliphatic polyesters may also be used. Biodegradable polymers may be used so that sensors do not foul an ecosystem. Biodegradability can be from days to months depending on the microbe content of the medium that said sensors are distributed in. 
   Sensors may comprise metals. Said metals can be Fe, Cd, Se, Al, or Cu, mixtures thereof or other metals depending on the application. Metals can be employed as alloys, compounds, or in layered combination with polymers. 
   Sensors are typically core/shell in their morphological structure. They can also be other shapes or multilayer films. A shell can be coated onto a core. Alternatively, a core/shell can be polymerized as a core/shell structure. 
   Sensors may be made by known means for producing multilayer coatings. These known methods include the methods described in the Kirk-Othmer Encyclopedia of Chemical Technology, 4 th  Edition, New York: Wiley, 1993, volume 6, pages 606 to 669. Said pages are incorporated herein by reference. 
   The core or intermediate layer of a sensor may exhibit luminescence, color change, change in acoustic reflectivity, electrical properties or other remotely detectible change in response to a specific triggering stimulus. The choice of which layer will be designed and formulated to respond to a given trigger is made depending on the application. 
   Depending on the application the outer layer can be a protective layer, reactive layer or shedding layer. 
   Sensors may be designed to be neutrally buoyant when distributed in a given fluid. 
   Sensors may comprise 1, 2, 3 or more layers wherein the core is considered to be a layer. The number of layers may depend upon the application. For example, Table 1 presents a number of applications of said sensors. Column 1 lists what is detected. Column 2 lists the number of layers in a sensor. Column 3 lists the information provided by the sensors. 
   
     
       
             
           
             
             
             
           
         
             
               TABLE 1 
             
           
           
             
                 
             
             
               Sensor Applications 
             
           
        
         
             
                 
                 
               Information provided 
             
             
               Application 
               Layers in sensors 
               by sensor detection 
             
             
                 
             
             
               Submarine 
               2 or 3 
               Detection of submarine 
             
             
                 
                 
               Tracking of submarine 
             
             
               Swimmer 
               2 or 3 
               Detection of swimmer 
             
             
                 
                 
               Increased acoustic range 
             
             
               Missile 
               1 or 2 
               Detection of missile 
             
             
                 
                 
               Tracking of missile 
             
             
               Wind Shear 
               2 or 3 
               Wind Intensity 
             
             
                 
                 
               Wind direction 
             
             
               Battlefield 
               2 or 3 
               Chemical agent 
             
             
                 
                 
               Biological agent 
             
             
                 
                 
               Dirty bomb 
             
             
               Shipping Container 
               2 or 3 
               Chemical agent 
             
             
                 
                 
               Biological agent 
             
             
                 
                 
               Dirty bomb 
             
             
                 
             
           
        
       
     
   
   The sensors may comprise a core, an intermediate layer and an outer layer. The overall size and density of the sensors is chosen so that the sensors disperse themselves uniformly over a given range of depths in a volume of water. Selected densities in the range of 1.015 to 1.035 g/cc are suitable. 
   The outer layer of said sensors has a density greater than said water. The combined core and intermediate layer have a density less than the water they are distributed in. 
   The intermediate layer further comprises luminescent or dye material. Suitable luminescent materials include inorganic and organic luminescent materials. Suitable inorganic luminescent materials include rare earth metal sulfides, such as AVeda™ pigments provided by United Mineral &amp; Chemical Corp (Lyndhurst, N.J.). Suitable organic luminescent materials include Beaver Luminescent Pigments provided by Beaver Luminescers (Newton, Mass.). 
   IR luminescent dyes may be used when one wishes to detect while maintaining stealth. An IR laser would be used to interrogate sensors at the surface of said volume of water and an IR detector would be used to detect the luminescent emissions of any sensors that had floated to said surface. 
   Suitable thicknesses (diameter) for the core are in the range of 1 nm to 3,000 μm. 
   Suitable materials for the core include polylactic acid, biodegradable polyesters, and polyolefins (e.g., polyethylene, polypropylene). 
   The core may further comprise additives to reduce its density. Suitable additives include glass bubbles or hollow glass spheres. The glass spheres may have a diameter in the range of 1 to 500 microns. The density of the glass spheres may be in the range of 0.1 to 0.5 gm/cc. Suitable glass spheres include Scotchlite™ glass bubbles available from 3M company (St. Paul, Minn.). 
   Glass bubbles may also be added to the intermediate layer or outer layer to modify their respective densities. 
   The lower the density of the core, the faster the sensor will rise when the outer layer spalls off, depending upon the diameter of said sensor. 
   Density reducing agents may also be added to the intermediate layer. 
   The sensor may be designed such that at least a portion of both the intermediate layer and the outer layer spall off of the core when the sensor is subjected to shear forces. The luminant or dye material would then be in the core. 
   The outer layer and the intermediate layer may be a single layer. Similarly, the intermediate layer and the core may be a single layer. In each of these cases, the sensor would be a two-layer sensor. 
   Swimmer Detection 
     FIG. 2  illustrates a method of swimmer detection using the inventive sensors. Similar methods can be used to detect surface water craft. 
   A multiplicity of sensors  200  are seeded in a volume of water  202 . The sensors are deployed just below the surface of the water. The sensors may comprise three layers. 
   Table 2 presents a range of thicknesses of said layers that are suitable for swimmer tracking. Column 1 identifies the layer. Column 2 shows the range of suitable thicknesses. Column 3 shows the activity of the layer. 
   
     
       
             
           
             
             
             
           
         
             
               TABLE 3 
             
           
           
             
                 
             
             
               Sensor Layers for Swimmer Detection and Tracking 
             
           
        
         
             
               Layer 
               Thickness 
               Activity/Function 
             
             
                 
             
             
               Overall sensor 
               10 nm-5,000 μm 
               Detection of swimmer 
             
             
                 
                 
               Increased acoustic range 
             
             
               Outer layer 
                1 nm-3,000 μm 
               Clear adhesive layer 
             
             
               Intermediate layer 
                1 nm-3,000 μm 
               Luminant or acoustic reflective 
             
             
                 
                 
               layer 
             
             
               Core 
                1 nm-3,000 μm 
               Substrate 
             
             
                 
             
           
        
       
     
   
   A sensor may have a spherical shape with a diameter in the range of 100 nm to 10,000 μm. 
   A sensor may be flat shape. Said flat shape may be a square or rectangle with edge lengths in the range of 1 micron to 10 cm. The total thickness may be 15,000 μm or less. 
   A flat sensor may have a woven core structure. 
   A sensor comprises an outer layer. A suitable thickness of said outer layer is in the range of 100 nm to 2,500 μm. 
   Said outer layer may comprise an IR transparent adhesive. Said adhesive may comprise an epoxy, cyanoacrylate, phenolic or other water stable adhesive. 
   A sensor may comprise an intermediate layer. A suitable thickness for said intermediate layer is in the range of 100 nm to 5,000 μm. 
   Said intermediate layer may preferably comprise an IR fluorescent dye. Said intermediate layer may alternatively comprise UV fluorescent dyes. 
   Said outer layer adhesive should be thin enough and transparent enough at suitable frequencies of light so that said sensors will have detectible fluorescence when interrogated by a laser. 
   The sensor further comprises a core. The core is designed such that the sensors are neutrally buoyant with respect to water over a suitable range of depth. 
   A swimmer  204  that comes in contact with said sensors will have said sensors adhere to him/her. 
   The surface  210  of the water  202  may be interrogated by an IR laser  206  from an observation tower  208  or other suitable vantage point. When a sensor adheres to said swimmer, the IR fluorescence from the sensor is visible from said observation tower. 
   Said IR fluorescence may be observed using known means, such as SeaFLIR M® (available from FLIR Systems, Inc., Portland Oreg.), Cohu 2700™ (available from Cohu, Inc., San Diego, Calif.), Sony Block Camera™ (available from Erdman Video Systems, Miami, Fla.) or other suitable IR detection device. 
   Identification can be enhanced by analyzing said fluorescent signal to determine if there is motion characteristic of a swimmer. Said motion can be a periodicity in said signal. Said periodicity may have a characteristic frequency of kicking or arm motion. 
   EXAMPLE 1 
   It is a foggy night. A surface swimmer enters the port area of a submarine base. He comes in contact with neutrally buoyant adhesive coated sensors deployed ½ to 3 feet below the water surface. The sensors adhere to his body, hands, and feet. He does not notice this at first and continues swimming. 
   The sensors are spherical core/shell polymeric material about 4 mm in diameter with a clear transparent phenolic adhesive outer layer. 
   The intermediate layer comprises an IR luminescent spiked polyvinyl alcohol polymer. 
   The core is a biodegradable polymer. 
   The illuminating rays of an IR laser cycle over the port water area. Said rays are incident on the swimmer&#39;s hands and feet which intermittently break though the water&#39;s surface. 
   On illumination, the luminescent sensors sticking to the swimming intruder emit an IR signal which, even though it is a foggy night, are sensed by a Cohu 2700 camera located in a surveillance tower. The tower relays the information to a control area and sets off an alarm for security action. 
   EXAMPLE 2 
   It is a clear night. A surface swimmer in a wet suit enters the water adjacent to a nuclear power plant. He has a propulsion device. 
   His hands, body, and propulsion device come in contact with adhesive, neutrally buoyant sensors deployed from ½ to 3 feet below the surface. Each sensor is a dual coated nylon fabric about ½ inch square. 
   Each sensor comprises an outer layer. Said outer layer comprises a thin (˜500 μm) clear transparent acrylic adhesive material. The adhesive sensors stick to the swimmer and said propulsion device. 
   Each sensor comprises an intermediate layer. Said intermediate layer is an IR activated luminescent spiked polyethylene polymer. 
   Illuminating rays of an IR lamp on a tower which covers the water area near said nuclear power plant are incident on said swimmer. As a result, said sensors emit an IR signal which is sensed by a sensitive IR camera located in a patrolling surface craft. Said patrolling surface craft then signals a security team who interdict said swimmer. 
   EXAMPLE 3 
   There is a morning fog. An underwater swimmer surfaces near a chemical plant. He comes in contact with sensors which are deployed in the water ½ to 4 feet below the surface. The sensors are adhesive and neutrally buoyant. They adhere to said swimmer&#39;s hands and feet which periodically break out from the surface in a swimmer&#39;s motion. 
   Said sensors are ⅝ inch wide by ¼ inch long coated polyester fabric. 
   Said sensors comprise an outer layer. Said outer layer comprises clear transparent cyanoacrylate adhesive. 
   Said sensors further comprise an intermediate layer. Said intermediate layer comprises a biodegradable polymer with dispersed IR pigment. 
   Illuminating rays from an IR lamp periodically flood said port area from a security tower. As a result the sensors adhering to said swimmer are periodically activated and emit an IR signal which is sensed by a Sony Block Camera in said tower. 
   A computerized signal algorithm confirms the presence of said swimmer via the characteristic motions of said IR emissions from his hands and feet as he moves through the water. 
   Security is called to the scene. 
   EXAMPLE 4 
   Referring to  FIG. 3 , an underwater swimmer  302  approaches a protected asset in a port area or in open water and senses an acoustic energy field in his/her area of the water. The swimmer simultaneously passes through a seeded field  304  of first sensors which adhere to him  306 . 
   Said first sensors comprise an outer adhesive layer. 
   Said first sensors further comprise an intermediate layer. Said intermediate layer comprises metal or other acoustically reflective material. 
   An acoustic sensor  308  detects the characteristic swimmer&#39;s motion  310  of said first sensors thus indicating the presence of said swimmer. 
   The acoustic signal is extremely loud such that as said swimmer gets closer to its source, said swimmer experiences discomfort. 
   The swimmer quickly maneuvers to try to avoid both being detected and the acoustic discomfort and quickly comes up to the surface to escape the impinging acoustic energy. 
   However, there are second sensors deployed just below the surface which also adhere to said swimmer&#39;s hands and feet. 
   Said second sensors comprise an outer layer. Said outer layer is adhesive. 
   Said second sensors further comprise an intermediate layer. Said intermediate layer comprises a fluorescent dye. 
   The adhered second sensors emit a characteristic optical signal when interrogated by a laser beam from a surveillance boat. Said optical signal is detected by a sensor on said boat indicating that a swimmer has come to the surface. 
   Security people quickly engage the swimming intruder. 
   While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. Any of the aspects of the present invention found to offer advantages over the state of the art may be used separately or in any suitable combination to achieve some or all of the benefits of the invention disclosed herein.