CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from provisional U.S. patent application No. 60/905,957 filed Mar. 9, 2007, entitled â€œSystem to defeat improvised explosive devices based on passive IR sensors.â€

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'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. 1a is a graphical representation of prior art infrared motion detection;

FIG. 1b 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 Î¼m, 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'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'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. 1a 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. 1b. 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's sensor that also is incident to the sensor at an energy level sufficient to create surface charge in the sensor's elements. A carbon dioxide laser, which transmits at principal wavelength bands centered between about 9.4 to 10.6 Î¼m, 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 Î¼m, 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 1Radiation power versus required exposuretime to activate a single detector elementRadiation powerRequired Exposure time(microwatts)(sec)0.1010.001.001.0010.000.10100.000.01

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 183Ã—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 1.25Ã—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 138Ã—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.