Patent Publication Number: US-7581501-B1

Title: Dipole antenna projectile with sensor

Description:
STATEMENT OF GOVERNMENT INTEREST 
   The inventions described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalties thereof. 

   BACKGROUND OF THE INVENTION 
   The invention relates in general to projectiles and in particular to projectiles equipped with sensors for transmitting data from the projectile to a base station. 
   There are situations when it is desired to sense, remotely, an area. The phenomenon that is being sensed may be acoustic waves (i.e., to overhear human speech), heat, chemical presence, environmental conditions, or other measurable items. The placement of the sensor may be difficult in situations such as urban military combat, civilian law enforcement (i.e., covert surveillance or hostage rescue operations) and civilian firefighter rescue operations. These and other situations require placement of the sensor from a distance. In the past, such sensors were manually placed by a human who was subjected to great risk of harm. 
   The present invention overcomes the risks associated with manual placement of sensors by providing a remote sensing device that may be launched from a tube, such as, for example, a shotgun. 
   SUMMARY OF THE INVENTION 
   An aspect of the invention is a projectile including a hollow conductive casing including a forward section and a rear section, and an insulating ring disposed between the forward section and the rear section to isolate, electrically, the forward section from the rear section whereby the forward and rear sections comprise a dipole antenna. In an embodiment, the forward and rear sections are made from a metal material. The projectile may further include a tail fin disposed aft of the rear section. For sensing purposes, at least one sensor is disposed in the conductive casing. 
   Another aspect of the invention is a projectile including a hollow casing, a tail fin disposed on an aft end of the hollow casing, and an axial rod disposed on a longitudinal axis of the projectile where one end of the axial rod protrudes outward from a forward section of the hollow casing and another end of the axial rod connects to the tail fin. The projectile may further include a relatively soft, ductile material that fills a volume in a forward end of the forward section and a relatively hard, dense material that fills a volume adjacent to and aft of the relatively soft material. At least one sensor may be disposed in the casing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The  FIG. 1  which is not necessarily to scale, is a schematic view, partially in section, of an embodiment of a projectile in accordance with the invention. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION 
   The present invention is a fin-stabilized projectile suitable for launching from, for example, a 12-gauge shotgun, 37 mm or 40 mm gun or a similar weapon. The projectile is designed to penetrate some easily breakable materials, such as, a double-pane window, but to not penetrate tougher materials, such as, walls. In this example, the projectile may be shot through a window to gain entry to a target location, but further penetration is inhibited. The projectile is designed to be launched from a distance of about 100 feet and have a radio frequency transmitting range of about 300 feet. The ability of remote emplacement reduces the risk to operating personnel. 
   Referring now to the  FIG. 1 , an embodiment of a projectile  10  in accordance with the invention includes a hollow conductive casing including a forward section  12  and a rear section  14 . An insulating ring  16  is disposed at approximately the midpoint between the forward section  12  and the rear section  14  to insulate, electrically, the forward section  12  from the rear section  14  so that the forward and rear sections  12 ,  14  comprise, that is, form a dipole antenna. Forward and rear sections  12 ,  14  must be electrically conductive and therefore may be made of a metal material. An exemplary overall length for the projectile  10  is about one and a half inches. 
   The projectile  10  further includes a tail fin  18  disposed aft of the rear section  14 . An axial rod  20  (such as a threaded screw or bolt) is disposed on the longitudinal axis X-X of the projectile  10 . One end  22  of the axial rod  20  protrudes slightly outwards from the forward section  12 . This end  22  may have, for example, a shape of a rounded end. The other end  24  of the axial rod  20  connects to the tail fin  18 , using, for example, threads. 
   It is important that the forward and rear sections  12 ,  14  be electrically insulated from each other. This electrical isolation may be accomplished in different ways, although the insulating ring  16  is present in each embodiment. In an embodiment, the tail fin  18  is made of an electrically insulating material so that the axial rod  20  may be made of a conductive material, such as a metal, and may contact forward section  12  where rod  20  protrudes outward from forward section  12 . An optional insulating bushing or washer  40  (shown in dashed lines in the  FIG. 1 ) may surround rod  20  so that tail fin  18  may be made of a conductive material. In another embodiment, the axial rod  20  may be made of an insulating material. In yet another embodiment, an optional insulating bushing or washer  42  (shown in dashed lines in the FIGURE) may be used to prevent rod  20  from contacting forward section  12 . 
   At least one sensor  26  is disposed in the conductive casing, for example, in the rear section  14 . The sensor may be, for example, an acoustic sensor (microphone), a heat sensor, a chemical sensor, or other sensor. Known radio frequency electronics  28  are connected to the sensors  26  and the dipole antenna  12 ,  14  (connection not shown) for transmitting information received from the sensors  26 . The electronics  28  include a power supply (not shown), such as a lithium battery that is activated by an inertial switch. The projectile  10  is internally potted with, for example, epoxy  36  to provide inertial damping for the internal components. The projectile  10  may be color-coded to associate it with a fixed frequency for the radio transmitter. In an embodiment, the projectile  10  is coated with an insulating material  30 , such as, TEFLON, to maintain insulation between the front and rear sections  12 ,  14  in wet, electrically-conductive environments. 
   The radio frequency electronics  28  include a transmitter circuit that matches the dipole. The transmitter circuit has two feed wires (not shown) that connect to dipole antenna sections  12 ,  14 , respectively, 180 degrees out of phase. In an exemplary embodiment, a location of the feed wires is on either side of the insulating ring  16  and close to the insulating ring  16 . Further, the matching transmitter circuit may be placed at the ring  16 . However, due to the small size of the device, placement of the RF components may not be critical. 
   A relatively soft, ductile material  32  fills the volume in the forward end of the forward section  12  and a relatively hard, dense material  34  fills the volume adjacent to and aft of the relatively soft, ductile material  32 . An example of material  34  is a dense, hard metal alloy such as, a copper alloy or steel, generally with a yield stress of several million psi. A relatively high density is needed to ensure projectile flight stability. 
   An exemplary material  32  is one with a relatively low yield stress and a relatively high ductility so that it deforms upon first impact and the deformation is permanent. High ductility is indicated by relatively high values of elongation at fracture and reduction in area observed during standard tensile tests. It is intended that material  32  may permanently deform and increase its diameter upon penetration of a barrier, such as, a window, thereby reducing the likelihood that the projectile  10  may penetrate a second barrier, such as, an internal wall. 
   In use, the projectile  10  is generally launched from a gun, such as, a 12 gauge shotgun, into an area that one wishes to monitor with the sensors  26 . The projectile  10  will penetrate, for example, a glass window, but will not penetrate a wall or floor because of the structural nose features. An inertial sensor may activate the power supply for the electronics  28 . The sensors  26  begin sensing and the electronics  28  transmit the sensors&#39; signals via the dipole antenna sections  12 ,  14  to a remote listening location. 
   While the invention has been described with reference to certain preferred embodiments, numerous changes, alterations and modifications to the described embodiments are possible without departing from the spirit and scope of the invention as defined in the appended claims, and equivalents thereof. 
   Finally, any numerical parameters set forth in the specification and attached claims are approximations (for example, by using the term “about”) that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of significant digits and by applying ordinary rounding.