This application claims priority to Israel Patent Application No. 218582 having the same title and filed Mar. 12, 2012.
Embodiments disclosed herein relate in general to thermal infrared (TIR) signaling devices (also referred to as “beacons” or “markers”) and in particular to TIR personal signaling devices useful for an individual seeking to be visible to observers which use forward looking infrared (FLIR) systems.
In the past, military night vision systems operated in the near IR spectral band (e.g. star light intensifier systems GEN-III, GEN-IV). In recent years, due to technological advancements in the field of uncooled focal plane arrays (FPAs) and in the field of low-power cryogenic-cooled detectors, many of the sighting systems used by military forces operate in the thermal IR bands (defined as mid wave IR (MWIR) 3-5 μm band and long wave IR (LWIR) 8-12 μm band). Systems based on these advanced TIR technologies are already available and being purchased by military forces around the world. The TIR based imagers are now implemented in most weapon sights, even for small caliber firearms, and in most viewing systems on ground and airborne platforms, and used both night and day. This change has, in turn, created a need for a personal signaling device that will enable a soldier to mark his location to friendly forces equipped with TIR night vision equipment. The soldier might want to mark himself (to mount the signaling device on his helmet), or to mark his location by placing the signaling device on a surface nearby to his location. General specifications of such a device include signaling to ranges of 2 Km and above, small weight and small size, low power consumption and 360 degree horizontal and greater than 60 degree vertical marking capability. In order to achieve good visibility marking, it is necessary to illuminate the observing thermal IR sight in pulsed fashion with a strong IR source, much like the signal generated by a lighthouse. This serves two purposes:
In view of the disadvantages of existing products/technologies there is a need for and it would be advantageous to have a small/lightweight/inexpensive yet powerful TIR marker/beacon that is observable to all fielded FLIRs at long ranges, day and night.
A TIR device according to embodiments disclosed herein includes an exothermally reactive material which, when ignited, emits IR radiation in the thermal IR band; an igniter to ignite the exothermally reactive material source; and a modulator for modulating (i.e. creating a defined “blinking” pattern) and for radiating the IR radiation into a defined field of view to a viewer and for creating a defined blinking pattern with high dynamic range. Exemplarily, the exothermally reactive material is charcoal. The modulator is preferably a rotating mirror rotated by a motor and gear assembly. The mirror has a reflective front surface and a reflective back surface, the latter used to reflect the sky to the viewer. The igniter and the mirror are powered by a power source. Exemplarily, the power source may include one or more batteries. Optionally, the TIR device further includes a built-in test (BIT) unit for allowing the operator to know if the device generates the IR signal. The various components are housed in a housing which is compact, light weight and cool enough to be handheld by a user or mounted on a helmet. Exemplarily, the device surface (“skin”) is kept under ca. 60C.
Non-limiting embodiments are herein described, by way of example only, with reference to the accompanying drawings, wherein:
a)-(d) show various views of a TIR signaling device disclosed herein, in which the various components and their arrangements are made clearer;
a) shows a cross section of a TIR signaling device disclosed herein with the top mesh section and mirror removed, and with details of a charcoal source assembly in a disposable usnit (section A-A);
b) shows yet another view of a TIR signaling device disclosed herein, with the top mesh section and mirror removed, showing the ventilation and air flow design;
Surface cooling element 108 cools the external surface (“skin”) of the device and specific mechanical parts in it. The skin is cooled to a temperature low enough (e.g. 60C) so it can be touched and held by a human hand. An appropriate thermal design assures that the temperature of various components within device 100 does not exceed permitted values. Detector 110 causes the TIR device to start blinking for a preset number of times when a laser range finder is “shot” at the TIR device. The indication provided by BIT unit 112 is useful because the lifetime of the TIR emitting source is limited, typically from 30 minutes to a number of hours, and the user can benefit from the knowledge that the source is still emitting.
In general, any material or compound which can be ignited and caused to burn such that it emits radiation in the required thermal IR wavelength range can be used as source 102. Typically, the exothermic reaction involved will bring a surface of the material to a temperature of a few hundred degrees Celsius. This can be achieved for example by igniting carbon-rich mixtures (such as fuels), by the Thermite reaction (the outcome of mixing metal powder and a metal oxide) or by Lime and Aluminum reactions, to name a few. Exemplarily, the TIR source is charcoal. Preferably, as shown in
One way of implementing such a BIT unit is by using a temperature sensor (not shown), such as a thermocouple, to sense the temperature of an inner surface of the beacon and a LED 224 to provide the indication. The indication is triggered (LED lights up) by a logic circuit which determines if the operation switch is in the “ON” position and if the temperature sensor senses a temperature which is bellow a preset value. The LED may be normally hidden from view (e.g. by a cover), with the cover removed only when the user needs to see the indication. An audio signal or an RF signal may be used instead of a LED for the indication. The implementation of the BIT unit as described would be clear to one of ordinary skill in the art.
a) shows a cross section of device 200 with the top mesh section and mirror removed, and with details of a unit 220 (section A-A).
Charcoal burns from the surface inwards. Hence, the burn time of a charcoal sample depends on the radial dimension of the charcoal tablet. For example; a 1″ diameter cylinder with 1″ height will have a burn time of the order of 45 minutes. This proves too short a time for an infantry soldier who cannot be attentive to the TIR device while focusing on his/her mission. A TIR device disclosed herein achieves more than 1 hour of burn time for a small cylindrical charcoal tablet 2.5 cm in diameter and 2.5 cm long and weighing about 10 gram. The burn time limitation may be overcome by enabling a TIR device to work in sequence with other TIR devices. For example, a plurality of TIR devices can be physically connected together, operating such that a first TIR device will turn on a second TIR device as soon as the operation time of the first TIR device is over. The second TIR device will then turn on a third TIR device and so on, to produce long periods of un-attended signaling.
Minor 210 may be used for removing un-wanted radiation which appears in “Swan bands” (see e.g.
The ignition of the charcoal requires careful attention. Although considered a flammable substance, charcoal in tablet form (charcoal that is ground, mixed with binders and pressed into a tablet, usually using a circular press) requires a few seconds of direct contact with a flame to ignite in a reproducible fashion. Thus, it is not highly ignitable. An oxidizing agent (e.g. NaClO3 or KClO3) is usually added to the charcoal prior to the “tableting” process to speed up the ignition. However, the amount of oxidizing agent that can be added is limited to about 12%-16% (in weight). A higher amount renders the mixture unstable, therefore the need for an ignition train. An ignition train is typically made out of an electronic igniter in contact with another flammable medium which, in turn, ignites the charcoal. To drive the electrical ignition of the system, it is usually required that a capacitor (not shown) on electronic board 212 be charged by the power source and then used to supply sufficient current to the igniter. A typical current value required for an igniter is on the order of a 1.2 Amp current for a few milliseconds. A large enough capacitor is required to supply this current. The major consumption of power is, however, by the motor rotating the mirror (which creates the blinking). To increase the time that the motor can be driven by the power source (batteries), the TIR device may be designed such that it does not “blink” constantly, but rather produces a number of sequential blinks (e.g. 3) and then stops for a few seconds (e.g. 6 seconds) before blinking again. This represents a type of “intermittent” blinking. Such intermittent blinking is tactically acceptable, serves to increase the operation time while keeping the weight of the TIR device to a minimum.
In conclusion, embodiments disclosed herein provide low cost TIR signaling devices that produce a strong blink signal which can be seen by thermal imaging systems from ranges exceeding 2 Km. The signal is due to heat released in a chemical reaction involving charcoal. The heat, coupled with a high emissivity surface, creates the required IR output. The charcoal source (tablet) is disposable, lasts for a while, and can be replaced after it burns out. This provides a far more effective approach in terms of energy/weight and energy/size than current approaches. A small 10 gram piece of charcoal (for example) can burn at 400-500C for >1 hour. The $/BTU of this kind of heat/radiation generation is lower by a large factor than that of any known electrical/electronic TIR signaling device or method. To achieve identical radiation using competing electrical/electronic-based technologies would require a very large electrical power source.
For strong signaling in the long wave IR band (LWIR, 8-12 μm) it is physically advantageous to emit from a larger surface at lower temperatures than to emit high temperatures from a smaller surface. This can be explained by the fact that an increase in emitter temperature does not create a very large change in the LWIR (the change in the MWIR is much stronger). The technology disclosed herein allows heating of large emitting surfaces, while known electrical/electronic-based technologies inherently produce small emitters which need to be amplified by optics, usually at the cost of reducing the field of view of the TIR device.
While this disclosure describes a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of such embodiments may be made. The disclosure is to be understood as not limited by the specific embodiments described herein, but only by the scope of the appended claims.
Number | Date | Country | Kind |
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218582 | Mar 2012 | IL | national |