Patent Publication Number: US-2010107859-A1

Title: Remote explosion of improvised explosive devices

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from provisional U.S. patent application No. 60/905,957 filed Mar. 9, 2007, entitled “System to defeat improvised explosive devices based on passive IR sensors.” 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to improvised explosive devices that are triggered by infrared motion detectors. More specifically, this invention relates to methods for remotely triggering the explosion of such devices and to apparatus for practicing such methods. 
     2. Description of the Related Art 
     In the modern battlefield, enemy combatants such as terrorists or guerillas often use improvised explosive devices (IEDs) as instruments of warfare. Such devices are fabricated in an improvised manner and comprise conventional chemical explosives with a trigger mechanism. In use, IEDs are typically hidden in a fixed location and are designed to be triggered, causing an explosion when a moving target (such as personnel or vehicles) moves into the explosive destruction zone in the proximity of the IED. 
     Trigger mechanisms for IEDs have included proximally operated manual electrical switches (in the case of suicide bombers) and remotely operated improvised electronic apparatuses based upon cellular telephone or radio signaling. Due to the limited and unpredictable availability of personnel for suicide bombing, and due to the effectiveness of radio frequency jamming in preventing the operation of cellular telephone and radio signal operated triggers, enemy combatants in recent years have shifted to the use of motion detectors as a preferred trigger mechanism for IEDs. 
     A motion detector trigger mechanism for an IED typically comprises a commercial off-the-shelf infrared motion detection transducer coupled with trigger electronics designed to ignite the IED explosive when the transducer detects motion in proximity to the device, typically on the order of 10 meters in the case of personnel and somewhat farther in the case of vehicles. In its normal operation, such a device detects target motion and explodes when the target is within the destruction zone of the IED. While the improvised nature of IEDs is such that their zone of destruction varies, a typical motion-activated IED is fashioned so that its zone of destruction roughly matches the range of its motion detector, again on the order of 10 meters or so. Because such devices detonate automatically without the need for a human operator, and because they are not susceptible to radio frequency jamming, they have been particularly lethal and effective battlefield weapons. 
     If, however, such devices can be triggered remotely, when personnel and equipment are outside the destructive zone, the effectiveness of these IEDs as weapons is nullified, saving lives and materiel. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a method and apparatus for triggering certain improvised explosive devices (IEDs) from a distance outside the device&#39;s zone of destruction. IEDs having infrared motion detection trigger mechanisms are detonated by passing remotely generated laser beams over the area within which the IED is located. The moving reflected background scattering of light from the passing laser beams as well as possible direct passing laser illumination of the IED infrared motion detector activate the IED trigger mechanism, causing the IED to detonate. Operation of the invention is remote from the destruction zone of the IED, thereby preserving personnel and materiel. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The foregoing objects, as well as further objects, advantages, features and characteristics of the present invention, in addition to methods of operation, function of related elements of structure, and the combination of parts and economies of manufacture, will become apparent upon consideration of the following description and claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures, and wherein: 
         FIG. 1   a  is a graphical representation of prior art infrared motion detection; 
         FIG. 1   b  illustrates voltage output over time from an infrared motion detection sensor; 
         FIG. 2  is a depiction of the invention as deployed on a vehicle; 
         FIG. 3  is a schematic representation of one embodiment of optics for the present invention; 
         FIG. 4  is; a schematic representation of a scanner serving as optics for the present invention; and 
         FIG. 5  is a depiction of the invention deployed on a vehicle wherein a plurality of lasers is employed. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The typical infrared motion detector is comprised of a package with a sensor having two pyroelectric elements. Each pyroelectric element is composed of a crystalline material that generates a surface electric charge when exposed to infrared radiation. Within the operating range of incident energy, the surface charge generated by an element is proportional to the amount of radiation striking the crystalline material. While sensor elements are sensitive to radiation over a wide range of wavelengths, the detector package typically is fitted with an optical filter window to limit detectable radiation to a range of approximately 8 to 14 μm, corresponding to the principal range of wavelengths of infrared radiation emitted by an object at the temperature of the human body. Sensor packages available at present are responsive to radiation energy on the order of 1 microjoule incident upon the package. 
     In practice, the two elements in a detector sensor are typically arranged to provide output of opposing polarity. Accordingly, when both elements are simultaneously exposed to equal levels of radiation, the output voltages from the sensor elements cancel each other and there is no net output voltage from the sensor. It is only when the elements are simultaneously exposed to different levels of radiation that the sensor provides output voltage. Changes in the output voltage, then, correspond to changes in the relative radiation levels to which the two elements are exposed. 
     To eliminate noise and erroneous readings, the motion detector circuitry is typically provided with an electronic filter to attenuate signals of frequencies too high to correspond to movement of humans. Generally, such filters are low-pass filters calibrated to attenuate signals on the order of 10 Hz or higher in frequency. 
     The detector further comprises a means for focusing radiation incident upon the sensor. Without such focusing means, the range of resolution of the sensor is limited. Generally speaking, among common sensors currently available, absent such focusing means, an infrared source that is farther than about 1.5 meters from the sensor cannot be resolved by the elements to provide a significant resulting output voltage, regardless of position of the source. 
     Various focusing means are used to extend the range of resolution of infrared motion detectors. Most common is a form of Fresnel lens or a parabolic mirror placed between the sensor and the target area. Such an arrangement may extend the detection range of the motion detector to greater than 30 meters. 
     In addition to focusing means for extending the range of resolution, motion detector installations may employ various means for narrowing the field of view of the detector. Such means are employed when it is desired to narrow the target area within which motion is to be detected and are common in improvised explosive devices, where detonation is desired only when the target is within a fairly confined zone of destruction. Commonly employed means for narrowing the field of view include a pinhole lens, in which a sheet of IR opaque material is perforated with a small hole and placed in front of the sensor in the manner of a pinhole camera. Such a pinhole lens may serve both to focus infrared radiation incident on the sensor (and may in fact substitute for standard focusing means such as the Fresnel lens discussed above) as well as to narrow the detector&#39;s field of view. Alternatively, field of view is also commonly narrowed in IEDs by simply placing a tube on the order of 50 mm in length over the front of the sensor, thereby narrowing the field of view to objects appearing in the field of the tube aperture. 
     In typical installations, the detector is positioned so that the sensor&#39;s two elements lie in a roughly horizontal plane. An infrared radiation source passing across the field of view of the sensor in a horizontal direction will activate first one and then the second sensor element. The detection of change in sensor voltage corresponding to such sequential activation is processed by detector electronic circuitry to indicate that motion has been detected within the field of view of the motion detector. 
       FIG. 1   a  illustrates the operation of a typical motion detector diagrammatically. Sensor  102  is comprised of two elements, each of which receives incident radiation along lines  104 ,  106  respectively. Focusing means  108  extends the detection range of sensor  102 , resulting in a field of view of width  110  along the range of the sensor. As discussed above, focusing means  108  may be a Fresnel lens serving simply to extend the range of sensor  102 . Alternatively or in addition, again as discussed above, focusing means  108  may provide a means to narrow the field of view of sensor  108  to no more than width  110 . In any case, a source of infrared radiation moving horizontally along line  112  within field of view  110  provides radiation incident first along line  104  to one element of sensor  102  and then along line  106  to the other element of sensor  102 , thereby generating changing voltage from the sensor over time as illustrated in  FIG. 1   b . Such a characteristic voltage pattern from the sensor indicates that motion has been detected. Responsive to receipt of such a voltage pattern from the sensor, motion detector electronic circuitry provides signaling indicating motion has been detected. 
     The present invention activates the motion detector and thereby triggers the IED by transmitting radiation over the area in which the IED trigger is located in such a manner that the motion detector of the IED responds as if a moving target object were within the range and field of view of the motion detector sensor. By transmitting such radiation from a point outside the destructive zone of the IED, the present invention causes the detonation of the IED remotely, avoiding harm to personnel and equipment. 
     In order to activate the motion detector trigger, the sensor must receive radiation from the invention in the detection wavelength range of the trigger&#39;s sensor that also is incident to the sensor at an energy level sufficient to create surface charge in the sensor&#39;s elements. A carbon dioxide laser, which transmits at principal wavelength bands centered between about 9.4 to 10.6 μm, provides radiation in the detection range of infrared motion detectors commercially available today, which are outfitted with optical filters for sensitivity to infrared radiation in the range of approximately 8 to 14 μm, as discussed earlier. For effective activation of a single sensor element, such radiation must be incident upon the element to provide at least the minimum energy exposure (the product of exposure time and power of radiation incident upon the element) to activate the sensor element. Required exposure to activate a sensor element in commonly available detectors today is on the order of 1 microjoule. Accordingly, there is an inverse relationship between the power of a radiation source and the exposure time required to activate a sensor element, as illustrated in table 1 below. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Radiation power versus required exposure 
               
               
                 time to activate a single detector element 
               
            
           
           
               
               
               
            
               
                   
                 Radiation power 
                 Required Exposure time 
               
               
                   
                 (microwatts) 
                 (sec) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 0.10 
                 10.00 
               
               
                   
                 1.00 
                 1.00 
               
               
                   
                 10.00 
                 0.10 
               
               
                   
                 100.00 
                 0.01 
               
               
                   
                   
               
            
           
         
       
     
     Finally, for effective activation of the motion detector sensor, the incident radiation must activate one and then the other element of the sensor in sequence within the period of time for which the motion detector is calibrated for motion detection. Transition of activation from one element to the other in too brief a time will result in a signal from the sensor that will be attenuated by typical motion detector circuitry and therefore would not be treated as indicative of positive motion detection. 
     Positive motion detection is indicated by changes in radiation incident on the detector within the constraints outlined above. The present invention exposes the detector to such changes in radiation by moving a projected laser beam over an area in the vicinity of the detector. As the beam moves over the area, changes in incident radiation cause the motion detector to create a signal indicating motion in the area, in turn triggering the detonation of the IED. 
     Embodiments of the present invention employ various means to move the beam of the present invention over the area in the vicinity of the detector. In some embodiments, a laser projecting apparatus is affixed to a vehicle or other automotive device. In such embodiments, the beam projected by the apparatus moves over a projection area with the motion of the vehicle. Other embodiments may employ movable mirrors, prisms or other reflective or refractive devices to sweep the projected beam over an area in the vicinity of the detector. In yet other embodiments, the laser projecting apparatus itself may be moved in such a fashion that its projected beam moves over an area in the vicinity of the detector. Examples of such latter embodiments include hand-held or swivel-mounted laser projecting apparatus. It is intended that all such means of moving the projected beam over an area in the vicinity of the IED motion detector are within the scope of the present invention. 
     The radiation may be directly incident from a projecting laser device upon the detector. Alternatively, a detector may be triggered by radiation from a projecting laser device that is reflected by the environment to the detector. Because of the relatively low reflectivity of the typical battlefield environment, lasers effective to cause triggering by reflection must be considerably more powerful than lasers effective to cause triggering by direct illumination of the detector. 
     In application, embodiments of the invention intended for battlefield deployment are transportable to areas where motion-triggered improvised explosive devices may be located. Preferred embodiments may be mobile and may be used to sweep an area for such explosives, causing the detonation of IEDs while personnel and materiel remain outside zones of destruction. 
       FIG. 2  illustrates one mobile embodiment of the invention. Laser  202  mounted on vehicle  204  employs optics  206  to project beam  208  which is swept over an area where motion-activated IEDs are believed to be deployed. 
     In some embodiments, optics  206  may be fixed so that beam  208  is projected at a fixed angle from vehicle  204 . For such embodiments, sweeping of beam  208  over a target zone takes place when vehicle  204  is in motion. In such embodiments, it is advantageous for optics  206  to cause beam  208  to be narrow and tall, thereby providing a wide stripe of radiation in the target zone and increasing the probability that a sweep of the beam will result in activating an IED motion detector. One such embodiment of optics  206  is described in greater detail below in reference to  FIG. 3 . 
       FIG. 3  is a diagrammatic representation of one embodiment employing a beam  208  that is fixed in orientation. A beam of radiation  305  from laser  202  is expanded by first beam expanding lens  304  to form expanding cone  307 . Second beam expanding lens  308  recollimates the beam to emit a beam  208  of larger diameter than beam  305 . Cylindrical lens  306  placed between lenses  304  and  308  causes beam  309  to diverge along its vertical dimension, so that when recollimated beam  208  reaches the target area, it will be narrow and tall in the image plane. As will be understood by those of skill in the art, components of optics  206  may be selected and adjusted to produce a beam configuration of a desired height and width as projected in the target area. 
     In one embodiment of the invention projecting a beam  208  of fixed angle from vehicle  204 , laser  202  operates at 200 watts and optics  206  cause beam  208  to form a projection measuring 183×2.5 centimeters at a target zone roughly 23 meters distant from laser  202 . The sweep of the beam across the target zone when vehicle  204  is traveling at speeds ranging from 32 to 80 kilometers per hour causes activation of motion detectors in the target zone at a distance more than twice the diameter of the nominal 10 meter destruction zone of the IED. 
     Other embodiments of the invention may employ optics  206  to vary the angle at which beam  208  is projected from vehicle  204  over time, resulting in scanning by beam  208  over an area in the target zone. As will be appreciated by those of skill in the art, such variation of the angle of beam  208  may be achieved by employment of scanner technology in optics  206 , whereby suitably adapted galvanoelectric scanning mirrors are employed to deflect the path of beam  208  so that it scans an appropriate area over time in the target zone. One such embodiment of optics  206  is described in greater detail below in reference to  FIG. 4 . 
       FIG. 4  is a diagrammatic representation of an embodiment of optics  206  employing a beam  208  that has been deflected by scanning technology to traverse a given area. A beam  404  emitted by laser  202  is deflected two-dimensionally by a galvanometer scanner  408 , the deflection resulting in scanning beam  208  covering area  420 . The galvanometer scanner  408  consists of a pair of beam deflecting galvano-mirrors  413  and  417  for x-axis (horizontal scanning direction) and y-axis (vertical scanning direction) respectively, the two axes of the mirrors perpendicular to each other at the center of oscillation, and of a pair of servo-motors  410  and  414  for angle control of mirrors  413  and  417 . Controller  406 , acting through drivers  412 ,  416 , controls oscillation of mirrors  413 ,  417  by motors  410 ,  414 , thereby deflecting beam  206  to cover scanned area  420  within the target zone. 
     In one embodiment of the invention employing scanning technology to vary the angle at which beam  208  is projected from vehicle  204  over time, laser  202  operates at 60 watts and optics  206  is configured to produce a beam that scans an area roughly 1.25×2.5 centimeters within the target zone over a 2 hertz frequency. This embodiment has been effective in triggering motion detectors at a distance of 18 meters, again outside the destruction zone of a typical motion-activated IED. As will be clear to those of skill in the art, with higher powered lasers, scan deflection and frequency of optics  206  may be adjusted to result in larger scanned areas within the target zone, thereby increasing the effectiveness of such embodiments. 
     Embodiments need not be limited to employment of a single source of laser radiation. Multiple sources of laser radiation may be used simultaneously to cover a wider target area. Turning to  FIG. 5 , vehicle  502  is outfitted with two larger roof-mounted laser units,  504 ,  506 , emitting beams of radiation  508 ,  510  respectively, as described above. Vehicle  502  is further outfitted with two smaller bumper-mounted laser units,  512 ,  514 , emitting beams of radiation  516 ,  518  respectively. Beams  508 ,  510 ,  512  and  514  may each be directed to a different portion of the target area, ensuring more thorough target area coverage than is provided by a solitary beam. Such embodiments may employ more powerful lasers focused to cause triggering principally by radiation reflected by the environment to the IED motion detector, along with less powerful lasers focused to cause triggering principally by direct illumination of the detector. 
     Such an embodiment with multiple sources of laser radiation has effectively employed a roof-mounted 200 watt laser and a bumper-mounted 25 watt laser. The beam from the roof-mounted laser was expanded by optics along the lines of those discussed in reference to  FIG. 3  above to provide a horizontally oriented 138×2.5 centimeter beam approximately 25 meters in front of the vehicle. The beam from the smaller, bumper-mounted laser was similarly expanded to form an elongated beam shape oriented at approximately 45 degrees and optimized for a target approximately one meter to the side and 8 meters in front of the laser source. 
     Embodiments need not be limited to vehicle-mounted devices. Portable lasers along with portable power supplies may be adapted for hand-held triggering of distant IEDs by foot soldiers. Similarly, embodiments need not be limited to land-based deployment. Airborne vehicles such as helicopters and low-flying drone aircraft may also be effectively outfitted with the present invention for the remote detonation of motion detection triggered improvised explosive devices. 
     Although the detailed descriptions above contain many specifics, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Various other embodiments and ramifications are possible within its scope. 
     While the invention has been described with a certain degree of particularity, it should be recognized that elements thereof may be altered by persons skilled in the art without departing from the spirit and scope of the invention. Further, while specific numbers and parameters have been set forth in keeping with the present state of the art, it will be understood that, if specifics of motion detector technology or improvised explosive device change over time, such numbers and parameters may be adjusted appropriately by persons of skill in the art and remain within the scope of the present invention. Accordingly, the present invention is not intended to be limited to the specific forms set forth herein, but on the contrary, it is intended to cover such alternatives, modifications and equivalents as can be reasonably included within the scope of the invention. The invention is limited only by the following claims and their equivalents.