Abstract:
Emitter controller including a controller, and a power amplifier, the controller being connected to a power source, the power amplifier being connected to the controller, the power source and to an emitter, the controller providing a pulse sequence to the power amplifier for operating the emitter, the controller determining the pulse sequence according to an available power voltage level.

Description:
FIELD OF THE INVENTION 
     The present invention relates to methods and systems for producing thermal beacons in general, and to methods and systems for producing thermal marking signals, in particular. 
     BACKGROUND OF THE INVENTION 
     Methods and devices for indicating the presence of an object in darkness (e.g., where darkness is defined as being outside the range of wavelengths invisible to the human eye) are known in the art. Infrared Radiation (IR) and Near Infrared Radiation (NIR) sources (beacons), mainly in the range of 0.7-1 micron are used in various applications as identification devices, for persons and vehicles. Near infrared light can be detected by special equipment which can translate the detected infra red image to a visible one. Different types of infrared beacons are known for use in covert security operations at night, where there is a need to be able to identify friend from foe or criminals from the police, animal watching, and the like. 
     These infrared beacons generally operate in the near IR range, and can be detected by image intensifiers, night vision goggles, black and white cameras, and the like. Black body Infrared beacons operating in the thermal region, such as mid-IR (3-5 micron) and long-IR (8-12 micron) are less prevalent. These infrared beacons generally employ a black body element, which is heated to a high temperature, and emits IR radiation in the thermal region. The blinking feature of the beacon is achieved by constantly rotating the black body element, or mechanically chopping the emitted radiation. Black body Infrared beacons can be detected by thermal cameras. 
     U.S. Pat. No. 4,912,224 to Andersen, entitled “Infrared aircraft beacon light”, is directed to a near infrared aircraft lighting system for use on the exterior of aircraft in combination with an existing visible light beacon. The device includes a ring structure containing infrared source that is installed between a visible light beacon and the aircraft outer surface. The device enables pilots with night vision goggles to fly in formation, and see other aircrafts, which fly in their vicinity. 
     U.S. Pat. No. 5,804,829 to Palmer et al., entitled “Programmable infrared signal beacon”, is directed to a near infrared signal beacon, which provides a visual location signal during poor light conditions. The device can be programmed to signal at least one of a plurality of coded messages, either in the visible light range of spectrum, or in the infrared range of the spectrum. The user of the beacon can select which of the plurality of flashing sequences will be transmitted by the light sources. 
     U.S. Pat. No. 5,225,828 to Walleston et al., entitled “Infrared identification beacon”, is directed to a device for alerting friendly personnel on land, sea or air. The beacon includes at least one near infrared light emitting diode and a visible light emitting diode, providing overlap conductive pole emanation of the NIR and visible light beams. The device can be steady or pulsed. 
     U.S. Pat. No. 5,414,405 to Hogg et al., entitled “Personnel identification device”, is directed to a device including a NIR LED contained within a housing. The device is adapted to be carried externally by a person or an object, such as vehicles, and enables, for example, to distinguish friend from foe in dark conditions. The housing possesses a “stick-on” capability, for example a Velcro or flexible magnetic strip on a base portion. The device is preferably adapted to flash, which enables the use of coded sequences of flashes. 
     U.S. Pat. No. 5,939,726 to Wood et al., entitled “Infrared radiation source”, is directed to a pulsable IR radiation source, which is intended for use in non-dispersive infrared gas analyzers. The device includes an emitting element, which is made of a narrow strip of foil. The emitting element is located in the hermetically sealed metal package with inert gas, such as nitrogen, helium or a combination thereof. The foil is heated by applying electrical power. The IR source provides high efficiency radiation at infrared wavelengths, and operates in the range of 1-3 Watts of power. The IR source cannot operate at high levels of power such as 10 Watts or more. 
     SUMMARY OF THE PRESENT INVENTION 
     It is an object of the present invention to provide a method and a system for emitting pulsed infra red radiation, which overcomes the disadvantages of the prior art. 
     In accordance with the present invention, there is thus provided an emitter controller including a controller, and a power amplifier. The controller is connected to a power source. The power amplifier is connected to the controller, the power source and to an emitter. The controller provides a pulse sequence to the power amplifier for operating the emitter, and the controller determines the pulse sequence according to an available power voltage level. 
     In accordance with another aspect of the present invention, there is thus provided a method for operating an emitter controller. The method includes the steps of detecting a voltage level of a power signal, determining a heating time period, and producing a pulse signal. The power signal is provided to the emitter. The heating time period is determined according to the detected voltage level, and a target heating temperature. The pulse signal is produced according to the heating time period, for operating the power amplifier at the detected voltage level. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: 
     FIG. 1 is a schematic illustration of an apparatus, constructed and operative in accordance with a preferred embodiment of the present invention; 
     FIG. 2 is a schematic illustration of an apparatus, constructed and operative in accordance with another preferred embodiment of the present invention; 
     FIG. 3 is a schematic illustration of a method for operating the system of FIG. 2, operative in accordance with a further preferred embodiment of the present invention; 
     FIG. 4 is schematic illustration of a system, constructed and operative in accordance with another preferred embodiment of the present invention; 
     FIG. 5 is a schematic illustration of an infrared radiation emitter, constructed and operative in accordance with a further preferred embodiment of the present invention; 
     FIG. 6 is a schematic illustration of a high power infrared radiation emitter, constructed and operative in accordance with another preferred embodiment of the present invention; 
     FIG. 7A is a schematic illustration of a long-range multi-directional case, constructed and operative in accordance with a further preferred embodiment of the present invention; 
     FIG. 7B is a schematic illustration of a long-range omni-directional case, constructed and operative in accordance with another preferred embodiment of the present invention; and 
     FIG. 7C is a schematic illustration of a medium-range omni-directional case, constructed and operative in accordance with a further preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention overcomes the disadvantages of the prior art by providing a clear beacon blinking mechanism (black/white i.e., hot/cold) which blinks at a frequency of from a few part of Hz to several Hz. A blinking frequency in the range of 1-2 Hz was found by the inventor to be optimal, from an ergonomic (human factor engineering) point of view. 
     Reference is now made to FIG. 1, which is a schematic illustration of an apparatus, generally referenced  100 , constructed and operative in accordance with a preferred embodiment of the present invention. Apparatus  100  includes a power source  102 , a pulse driver  104  and a pulsable infrared emitter  106 . Pulse driver  104  is connected to power source  102  and to pulsable infrared emitter  106 . 
     Power source  102  can either produce alternating or direct electrical power. Power source  102  provides the electrical power to pulse driver  104 . Pulse driver  104  produces a predetermined periodic electrical pulse, and provides the periodic electrical pulse to pulsable infrared emitter  106 . The periodic electrical pulses periodically heat pulsable infrared emitter  106 , thereby producing periodic thermal radiation. Hence, apparatus  100  blinks at thermal IR wavelengths (which are mid-IR and long-IR, at ranges of 3-5 and 8-12 microns, respectively). Reference is now made to FIG. 2, which is a schematic illustration of an apparatus, generally referenced  110 , constructed and operative in accordance with another preferred embodiment of the present invention. Apparatus  110  includes a voltage multiplier  112 , a voltage regulator  114 , a micro-controller  116 , a power amplifier  118 , an infra red emitter  120  and an indicator  122 . Voltage regulator  114  is connected to voltage multiplier  112  and micro-controller  116 . Voltage multiplier  112  is further connected to a power cell (not shown). Micro-controller  116  is further connected to power amplifier  118 , to the power cell, and to indicator  122 . Power amplifier  118  is further connected to the power cell, and to infra red emitter  120 . Infra red emitter  120 , and indicator  122  are further connected to the power cell. 
     The power cell provides voltage V S  to voltage multiplier  112 . Voltage multiplier  112  multiplies the voltage V S  by a factor of more than one, and provides voltage V M  to voltage regulator  114 . Voltage regulator  114  produces a constant, regulated voltage level V R  and provides it to micro controller  116 . 
     A conventional power cell is characterized by a diminishing voltage curve as it is drained further and further. Therefore, it is likely that the voltage will drop below a predetermined minimal level V min , while the power cell still has enough power to drive the apparatus for an additional period of time. The combination of voltage multiplier  112  and voltage regulator  114  provides a constant regulated operating voltage to micro-controller  116 , even after V S  has dropped below V min . 
     Micro-controller  116  measures V S  and dynamically determines the characteristics of the next pulse. It is noted that micro-controller  116  can use V R  as a reference in the measurement of V S . 
     The infra red emitter  120  has to be heated to a predetermined temperature in order to be detected by a thermal camera. In general, the power amplifier  118  has to provide a certain amount of energy E to infra red emitter  120  for this purpose. Higher amounts of energy might damage the infra red emitter  120 , or prevent rapid cooling thereof. Lower amounts of energy might not heat infrared emitter  120  to temperatures high enough for the thermal camera to detect infrared emitter  120 . 
     It is noted that the energy supplied by the power cell, is proportional to the heating time period T H  and the applied voltage V S −V PA , where V PA  denotes the voltage across the power amplifier  118 . Since V PA  is substantially constant, E is substantially and directly proportional to V S . Hence, for providing a certain amount of energy, one would require a longer heating time at low V S  levels, and a shorter heating time at high V S  levels. 
     The amount of energy required for heating infra red emitter  120  to this temperature may depend on the heat dissipation characteristics of infra red emitter  120 . The micro-controller  116  adds respective considerations when heat dissipation is significant. 
     Micro-controller  116  determines a pulse, operates power amplifier  118  to produce such a pulse, and provides the pulse to infra red emitter  120 . Indicator  122  can be operated to provide an indication signal, respective of the operation of the emitter, an indication of the mode which the apparatus currently operates, and the like. The indication signal can be visual, audible, and the like. 
     Apparatus  110  further includes power management means, which maintain a stable mode of operation as well as providing protection against undesired discharge of the power cell, where one is used. 
     When micro-controller  116  detects that V S  has dropped below a predetermined threshold V THRESHOLD , it can execute a cut-off procedure. The cut-off procedure shuts down apparatus  110 , thereby reducing potential damage thereto. Such a damage can be caused by a complete discharge of the power cell, which is exceptionally significant for Lithium-ion power cells. 
     Reference is further made to FIG. 3, which is a schematic illustration of a method for operating the system  110  of FIG. 2, operative in accordance with a further preferred embodiment of the present invention. 
     In step  130 , a heating temperature to which the emitting element of the emitter has to be heated, is determined. The heating temperature is determined according to the required wavelengths. Accordingly, the determination procedure can also take into account particular characteristics of the emitter. With reference to FIG. 2, micro-controller  116  determines the heating temperature. It is noted that this temperature can further be predetermined and stored in a memory section within micro-controller  116 , or set manually. 
     In step  132 , the voltage level of the power signal, which will be used for heating, is detected. With reference to FIG. 2, micro-controller  116  detects the voltage level V S  of the power cell, and reduces environmental effects such as the voltage gap across power amplifier  118 , and the like, thereby fixing the voltage level V S −V PA  of the power signal. 
     In step  134 , a heating time period T H  is determined. This time period is determined according to the detected power signal voltage level V 5 −V PA , the target heating temperature, and the characteristics of the infra red emitter  120 , such as power efficiency, heat capacitance, power yield, and the like. It is noted that the target temperature can be maintained for a predetermined period of time, by applying a respective voltage level lower than the power signal voltage level V S −V PA . 
     In step  136 , a cooling time period T C  is determined according to the target heating temperature, the characteristics of the emitter and other requirements. The cooling time period determines the next point in time, where a new heating-cooling cycle can commence. With reference to FIG. 2, both steps  134  and  136  are performed by micro-controller  116 . 
     In step  138 , a pulse is produced from the power signal according to the heating time period and the cooling time period. With reference to FIG. 2, power amplifier  118  produces a power signal pulse of V S  for T H , and V C  for T C , where V C  can be zero. 
     In step  140 , a periodic infra red light is emitted. With reference to FIG. 2, infra red emitter  120 , heated to the target heating temperature, emits a short pulse of light and cools down. It is noted that this method can be generalized for complex sequences, produced by a plurality of emitters in many modes, as will be described herein below. 
     Reference is now made to FIG. 4, which is schematic illustration of a system, generally referenced  150 , constructed and operative in accordance with another preferred embodiment of the present invention. System  150  includes a power source  152 , a pulse driver  154  and a pulsable emitter array  156 . Pulse driver  154  is coupled to power source  152  and to pulsable emitter array  156 . 
     Pulsable emitter array  156  includes a plurality of pulsable emitters  161 ,  162 ,  163 ,  164 ,  165 ,  171 ,  172 ,  173 ,  174 ,  175 ,  181 ,  182 ,  183 ,  184  and  185 . Pulsable emitters  161 ,  162 ,  163 ,  164  and  165  are coupled parallel to each other and form a group  160 . Pulsable emitters  171 ,  172 ,  173 ,  174  and  175  are coupled parallel to each other and form a group  170 . Pulsable emitters  181 ,  182 ,  183 ,  184  and  185  are coupled parallel to each other and form a group  180 . Groups  160 ,  170  and  180  are coupled to pulse driver  154 . It is noted that pulsable emitter array  156  can include any number of groups, and each group can include any number of pulsable emitters. 
     Power source  152  provides electrical power to pulse driver  154 . Pulse driver  154  produces a predetermined set of repetitive electrical pulses and provides them to pulsable emitter array  156 . Pulse driver  154  can operate pulsable emitter array  156  in three different modes: a simultaneous mode, a synchronous mode and a combination of simultaneous and synchronous modes. 
     In the simultaneous mode, the system provides the same pulse to each of groups  160 ,  170  and  180 , which in turn produce periodic infrared radiation at the same time. In the synchronous mode, the system provides a different pulse to each of groups  160 ,  170  and  180 , which in turn produce periodic infrared radiation one after the other. 
     Reference is now made to FIG. 5, which is a schematic illustration of an infrared radiation emitter, generally referenced  200 , constructed and operative in accordance with a further preferred embodiment of the present invention. Infrared radiation emitter  200  includes a mounting package  202  with two conductive poles  204  and  206 , feed-through seals  208 , a reflector  210  with cutouts  212  and an emitting element  214 . Infrared radiation emitter  200  further includes a sealing case  216 , which incorporates a window  218 . 
     Window  218  can be made of a material, which is transparent to mid Infrared radiation (3-5 micron), and long infrared radiation (8-12 micron). Window  218  can be made of germanium, zinc-selenide, silicon, and the like. Window  218  can be constructed as a lens, for further directing the emitted light in predetermined directions. Hence, the material from which window  218  is made of, filters out light in undesired wavelengths. 
     Reflector  210  reflects the infrared radiation produced by emitting element  214 . Reflector  210  can be parabolic, elliptic or planar. In the example set forth in FIG. 5, reflector  210  has a parabolic shape. Reflector  210  can be made of aluminum, coated with a reflective materials such as gold and silver. Conductive poles  204  and  206  provide electrical connection as well as structural rigidity to emitting element  214 . Emitting element  214  can be welded to conductive poles  204  and  206 . 
     Emitting element  214  is made of a wire with a diameter, approximately in the range of 0.003″ and 0.030″. It is noted that a wire having a diameter close to 0.003″ will be weaker than a wire having a larger diameter. Alternatively, a wire having a diameter close to 0.030″ will have a slow response to heating, and hence exhibit a low modulation is depth. 
     In the example set forth in FIG. 5, emitting element  214  is a coil made of 0.010″ diameter wire having 10-11 rolls (windings). It is noted that the coil can have between 4 and 20 rolls and more. The diameter of each roll can be in the range approximately between 0.040″ and 0.150″. The gap between every two rolls can be in the range of approximately 0.003″ and 0.040″. Accordingly, in the example shown in FIG. 5, each roll has a diameter of 0.085″ and the gap between every two rolls is 0.010″. Hence, emitting element  214  has a high mechanical strength, and a high power electrical pulse can heat emitting element  214  to up to 1500 degrees Celsius. 
     It is noted that emitting element  214  can be a wire devoid of any rolls. In this case, system  200  operates at a lower radiation efficiency, because the effective area of radiation is smaller than that of an emitting element having rolls. 
     Reference is now made to FIG. 6, which is a schematic illustration of a high power infrared radiation emitter, generally referenced  250 , constructed and operative in accordance with another preferred embodiment of the present invention. Infrared radiation emitter  250  includes a mounting platform  252 , with two conductive poles  254  and  256 , insulating seals  258 , a reflector  260  and an emitting element  264 . Reflective  260  can be parabolic, elliptic, plane, and the like. Emitter  250  further includes a sealing case  270 , which incorporates a window  272 . Window  272  is analogous to window  218  as described herein above in connection with FIG.  5 . 
     Emitting element  264  is made of a filament wire in the shape of a narrow strip of foil, having a length of approximately 0.40″. It is noted, that for high power applications, a strip of foil, having a length close to 0.80″ would be structurally too weak and will have a significantly reduced life span. Alternatively, the emitting area of a strip of foil, having a length less than 0.20″ would be too small. 
     Accordingly, the strip of foil has a width, which can be in the range of approximate 0.020″ and 0.060″ and can have a thickness, in the range of approximately 0.00020″ and 0.00060″. It is noted, that a strip of foil having a thickness close to 0.00020″ can not handle power inputs of more than 2 Watts. Alternatively, the strip of foil having a thickness of more than 0.00060″ does not allow pulse operation in a high modulation rate. 
     In the example set forth in FIG. 6, emitting element  264  is a narrow strip of thin metallic nichrome foil having a width of 0.040″ and a thickness of 0.00050″. This design of emitting element  264  can operate at power levels of 10 Watts. It is noted that other alloys with similar characteristics can also be used, depending on the required implementation. 
     Reference is further made to FIGS. 7A,  7 B, and  7 C. FIG. 7A is a schematic illustration of a long-range multi-directional case, generally referenced  300 , constructed and operative in accordance with a further preferred embodiment of the present invention. FIG. 7B is a schematic illustration of a long-range omni-directional case, generally referenced  310 , constructed and operative in accordance with another preferred embodiment of the present invention. FIG. 7C is a schematic illustration of a medium-range omni-directional case, generally referenced  320 , constructed and operative in accordance with a further preferred embodiment of the present invention. 
     Cases  300 ,  310 , and  320  have holes  302 ,  312 , and  322 , respectively, in which Infrared emitters are placed. Each of the cases  300 ,  310  and  320  can include four, fifteen and five infrared emitters, respectively, or any other number of infrared emitters. Cases  300 ,  310 , and  320  can be made of any semi-rigid material, such as metal, ceramic plastic, and the like. 
     In the examples set forth in FIGS. 7A,  7 B, and  7 C, the cases  300 ,  310 , and  320  are made of aluminum. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims, which follow.