Abstract:
The present invention relates to an explosive device comprising an explosive material, and at least one igniting stimulus configured to ignite the explosive material when activated. The explosive device further comprises a sheet of material provided with at least one hole at least partially filled with the explosive material, each hole forms an opening in a first side of said sheet material and said at least one igniting stimuli is arranged on said first side. The invention also relates to a method for manufacturing an explosive device.

Description:
TECHNICAL FIELD 
     The present invention relates to an explosive device, especially suitable to be implemented in a planar design, such as a sheet of material. The invention also relates to a method for manufacturing the explosive device. 
     BACKGROUND 
     Explosive devices used for penetrating pressurized gas containers, today in combination with inflatable rescue equipment, such as disclosed in the published WO 2008/013489, are rather bulky and have a complex design with many different components. 
     Other penetrating devices are based on one or more moving components that mechanically penetrate the pressurized gas containers. This requires a complex design in order to ensure proper functionality and as a result of the complex design, the weight is normally rather high. 
     For instance, U.S. Pat. No. 5,413,247 by Glasa, describes a system wherein a sharp object is mechanically moved using a spring loaded force. Alternatively, the force needed to advance the sharp object could be provided by a pyrotechnical charge. In both cases the dimension of the sharp object will determine the size of the hole. 
     In addition, a German utility model DE 296 06 782 U1 describes an automatic rescue device for sea and air transport including a water sensor. A puncture device is briefly discussed, which is used to open a pressurized gas cylinder. The puncture device could be implemented as a chemical reaction unit, and more specifically be constructed as a pyrotechnical detonator situated outside a gas management device through which the gas flow when the gas cylinder is opened. A hollow needle could also be used for manually puncturing the closure of the gas cylinder if needed. 
     The major disadvantage with prior art devices is that they are bulky and have a complex design, with or without moving parts. When implementing an explosive device in a system, e.g. for penetrating a gas cylinder or for igniting a charge in military applications, space is a crucial limitation, and there still exists a need to reduce the size of present explosive devises. 
     SUMMARY OF THE INVENTION 
     An object with the present invention is to provide an explosive device which is smaller and easier to manufacture compared to prior art devices. 
     A solution to the object is achieved by providing a sheet of material with one or more holes having an opening to a first side of the sheet material. The holes are at least partially filled with an explosive material and one or more igniting stimuli configured to ignite the explosive material when activated are arranged on the first side. 
     An advantage with the present invention is that a very small and compact explosive device may be manufactured compared to prior art devices. 
     Another advantage with the present invention is that a simple construction with few non-moving components is achieved compared to prior art devices. 
     Yet another advantage with the present invention is that it has a low weight and is inexpensive to manufacture. 
     Still another advantage with the present invention is that the explosive device is very stable compared to prior art devices and may be handled easier. 
     Further advantages and objects will be apparent to a skilled person from the detailed description below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective view of a first embodiment of an explosive device. 
         FIG. 2  shows a cross-sectional view of the explosive device in  FIG. 1  along A-A. 
         FIG. 3  shows a top view of a circuit board provided with electronics coupled to a second embodiment of an explosive device. 
         FIGS. 4   a - 4   d  illustrate a method for manufacturing the explosive device in  FIG. 1 . 
         FIGS. 5   a  and  5   b  illustrate the function of the explosive device in  FIG. 1  when mounted to a pressurized container of air. 
         FIGS. 6   a - 6   d  show alternative embodiments of an explosive device according to the invention. 
         FIG. 7  shows an explosive device in a multilayered structure 
         FIG. 8  shows an explosive device provided with two independent igniting stimuli. 
         FIGS. 9   a - 9   d  illustrate a method for manufacturing the explosive device in  FIG. 6   a.    
     
    
    
     It should be noted that the figures in the drawings are not scale, and primarily serves the purpose of enhancing certain details of the invention. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows a perspective view of a first embodiment of an explosive device  10  comprising a sheet of material  11  having a through hole  12  filled with an explosive material  13 , such as AgN 3  or PETN. Two surfaces  14  and  15  made from a conductive material, e.g. copper, are arranged on the sheet of material  11 . A conductor  16 , such as an exploding bridge wire (EBW) or an resistive thermal igniter, is electrically connected between the two surfaces  14  and  15 , e.g. by soldering, clamping or conductive glue. An ignition transfer material  17  is arranged between the conductor  16  and the explosive material  13  in the hole  12 . 
     It should be noted that it is essential that the two conductive surfaces  14  and  15  are insulated from each other, which in this embodiment is achieved by selecting the sheet of material  11  to have insulating properties, such as a printed circuit board. The explosive device  10  is activated by applying suitable pulse of energy between the conductive surfaces  14  and  15  as illustrated in  FIG. 3 . The pulse of energy may be an electrical pulse, mechanical pulse or a laser pulse (laser ignition) depending on what type of conductor is used. 
       FIG. 2  shows a cross-sectional view of the explosive  10  device in  FIG. 1  along A-A. The explosive material  13  completely fills the through hole, and there is even some material that extends beyond the through hole as indicated by the bowed shape  18  of the upper part of the explosive material  13 . A film  19  is also provided at the lower part of the through hole to provide a seal which prevents the explosive material  13  to migrate from its position within the hole  12 . 
       FIG. 3  shows a top view of a circuit board  20  provided with electronics  21  coupled to a second embodiment of an explosive device  22 . The only difference between the embodiment described in connection with  FIGS. 1 and 2  is that an exploding foil  23  acts as a conductor between the conductive surfaces  14  and  15 . The explosive device in  FIG. 3  also comprises a hole  12  completely filled with an explosive material  13 , and an ignition transfer material  17  is provided between the conductor and the explosive material  13 . 
     Each conductive surface  14 ,  15  of the explosive device  22  is connected to the electronics using electrical connection  24  and  25 , respectively, which preferably are etched on the circuit board  20 . The electronics  21  are preferably surface mounted control electronics that provides suitable energy to activate the explosive device. The electronics may also comprise communication means to receive instructions to activate the explosive device from an external transmitter and/or sensor device. 
       FIGS. 4   a - 4   d  illustrate a method for manufacturing the explosive device in  FIG. 1 . In  FIG. 4   a , the non-conductive sheet of material  11  with the through hole  12  and conductive surfaces  14  and  15  is placed on a support  41  in such a way that the upper surface of the support  41  covers the complete opening of the through hole  12  on a second side of the sheet of material  11 . A funnel  40  is arranged on a first side, opposite to the second side of the sheet of material  11  and a first end  42   a  of a guiding pin  42  is introduced into the funnel and the through hole, as indicated by arrow  43 , to align the small funnel opening with the hole  12 . 
     The guiding pin  42  preferably has a snug fit when introduced into the funnel and have the first end  42   a  has a tapered shape to automatically align the hole and the funnel to each other. The guiding pin  42  is thereafter retracted, leaving the small funnel opening aligned with the hole  12  on a first side of the sheet of material  11 , and the support  41  covering the opening of the hole on the second side of the sheet of material  11 . 
       FIG. 4   b  shows the compressing stage of the manufacturing procedure, in which explosive material  44  is provided into the funnel in a loose powdered form. The amount of powder is predetermined and is positioned in the narrow part of the funnel  40 . A tool  45  preferably having a concave tip  46  is introduced into the funnel  40 , as indicated by arrow  47 , in order to compress the powder of loose explosive material  44 . The explosive material could be any type of primary explosives, but is preferably AgN 3  and PbN 6 . 
       FIG. 4   c  shows the result of the compressing stage when the tool  45  is retracted from the funnel  40 , as indicated by the arrow  48 . The funnel  40  is thereafter removed and the sheet of material  11  is moved from the support  41 . In  FIG. 4   d , a film  19  is mounted to the second side of the sheet of material  11  and a conductor is attached between the conductive surfaces  14  and  15  before the ignition transfer material  17  is arranged over the conductor and the compressed explosive material  13 , which completes the process. 
     However, it should be mentioned that the film  19  on the second side of the sheet material  11  may be attached before the sheet of material is placed on the support  41  as illustrated in  FIG. 4   a . The essential function of the film is to provide a defined interface surface to which additional equipment may be attached, as shown in connection with  FIGS. 5   a  and  5   b.    
       FIGS. 5   a  and  5   b  illustrate the function of the explosive device in  FIG. 1  when attached to additional equipment, such as a pressurized gas container  50 . Other types of additional equipment, e.g. a fuze, may be attached to the explosive device for military applications. 
     The film  19  is arranged adjacent to an opening  51  of the pressurized gas container  50 , which is covered with a membrane  52 . The explosive device is activated by applying a potential between the conductive surfaces  14  and  15 , whereby an igniting stimuli, such as a conductor applied between the conductive surfaces  14  and  15 , and an ignition transfer material  17  embedding the conductor. The conductor, e.g. a bridge wire, exploding bridge wire or an exploding foil, and the ignition transfer material  17  ignites the explosive material  13  when activated, and the result of the explosion is illustrated in  FIG. 5   b.    
     The ignition stimuli, i.e. conductor and ignition transfer material  17 , and the explosive material  13  are disintegrated after the explosion and an opening  53  is created in the film  19  and the membrane  52  allowing pressurized gas, e.g. CO 2 , to escape from the pressurized gas container  50  through the explosive device as indicated by the arrow. 
     Furthermore, it should be noted that some of the energy from the explosion is preferably absorbed in the substrate  11 , provided an energy absorbent material is used. The energy absorbent material preferably includes a laminated structure, composite structure, random fibres or ceramics. The energy absorbent material will then expand, e.g. by delaminating the structure as indicated in  FIG. 5   b , see reference numeral  54 . 
     The purpose with the energy absorbing material is mainly to limit the destructive forces on adjacently arranged devices on the substrate and/or the fixture to with the explosive device is mounted. The energy released from the explosion into the substrate is used to delaminate the substrate. 
       FIGS. 6   a - 6   d  show alternative embodiments of an explosive device according to the invention. 
       FIG. 6   a  illustrates a third embodiment of an explosive device  60  comprising a main substrate  61  having an opening  62 , preferably having a circular cross-section, completely filled with an explosive material  63 . Conductive surfaces  64  and  65  are arranged on an upper surface of the main substrate  61  and a conductor  66  is arranged between the conductive surfaces  64  and  65  directly on top of the explosive material  63 . The conductor  66  is preferably implemented as a bridge wire, exploding bridge wire (EBW) or an exploding foil, and may be integrated with an plastic material. 
     The explosive device  60  may be manufactured using a similar process as described in connection with  FIG. 4   a - 4   d  with a few exceptions, as illustrated in connection with  FIGS. 9   a - 9   d.    
     An additional substrate  67  having an additional opening  68  is arranged to the lower surface of the main substrate  61 , opposite to the upper surface, and a booster explosive  69 , such as PETN, is arranged in the additional opening  68  adjacent to the explosive material  63 . The additional opening  68  is preferably circular and wider than the opening  62  in the main substrate  61 , to create an explosive device that is self-focusing to a focal point FP, as illustrated in  FIG. 6   a.    
       FIG. 6   b  illustrates a fourth embodiment of an explosive device  70  comprising a main substrate  71  having an opening  72 , preferably having a circular cross-section, partly filled with an explosive material  73 . The thickness of explosive material  73  preferably corresponds to 10-20% of the thickness of the main substrate  71 , i.e. if the substrate is 10 mm then the thickness of the explosive material  73  within the opening  72  is 1-2 mm. Thus, it may be necessary to provide a printed circuit board having an increased thickness compared to normal circuit boards, when used as a substrate as illustrated in  FIG. 6   b.    
     The main substrate  71  has an upper surface and an opposing lower surface, and the explosive material  73  is arranged within the opening  72  at the lower surface of the main substrate  71 . An ignition bead  74  is placed within the opening  72  on top of the explosive material  73 , and ignition wires  75  connected to the ignition bead  74  extend from the opening  72  and are available at the upper surface of the main substrate  71 . An additional substrate  67  similar to the substrate described in connection with  FIG. 6   a  may also be provided. 
     The use of an ignition bead  74  may lead to a delay, which may be disadvantageous, in contrary to the use of EBW, exploding foil and bridge wire which act instantly when initiated. 
       FIG. 6   c  illustrates a fifth embodiment of an explosive device  80  comprising a multilayered structure. A first layer comprises a main substrate  81  having a recess  82  completely filed with an explosive material  83 . The recess has an opening in an upper surface of the main substrate  81  and a thin wall  84  separates the explosive material  83  from a lower surface of the main substrate  81 . A second layer is arranged to the lower surface of the main substrate  81 , which second layer corresponds to the additional substrate  67  having an opening  68  filled with a booster explosive  69  as described above. 
     A third layer comprises an ignition substrate  85  arranged to the upper surface of the main substrate  81 . A through hole  86  is provided through the ignition substrate  85  and aligned with the opening of the recess  82 . Conductive surfaces  76  and  77  are provided on the upper surface of the ignition substrate  85 , which is made from a non-conductive material. A fuse composition (or ignition material)  87  is provided in the through hole  86  and a conductor  88  is arranged between the conductive surfaces and through the fuse composition  87 . The conductor  88  may be implemented as an ignition wire. 
       FIG. 6   d  illustrates a sixth embodiment of an explosive device  90  comprising a conductive substrate  91 , preferably made from aluminum, having a through-hole  92 . An explosive material  93  is provided in the through-hole  92 . An electrically insulating material  94  is provided completely around the through-hole  92  on the upper surface to insulate conductive surfaces  95  and  96 . A conductor  98  is connected between the conductive surfaces, and a fuse composition (or ignition material)  97  is arranged on top of the conductor and the explosive material  93 . An additional layer with a booster explosive may naturally be attached on the lower surface of the substrate  91 . 
     The hole, or recess, in the above described embodiments preferably has a circular opening with a diameter ranging between 0.5-5 mm. less than 150 mg of explosives is preferably used and the thickness of each substrate is preferably less than 10 mm if a printed circuit board is used. The printed circuit board preferably has a laminated structure to absorb energy when the explosive material is activated, and preferably comprises an anisotropic material such as glass fibers and epoxy. 
     The thickness of the substrate  91  in  FIG. 6   d  is preferably less than 2 mm when aluminum is used. 
       FIG. 7  shows an explosive device  100  in a multilayered structure comprising four printed circuit boards  101 ,  102 ,  103 ,  104 . Electrical connections  105  are created on the circuit boards and via holes  106  interconnect the electrical connections on different layers. Conductive surfaces  107  and  108  are provided on the upper surface of the circuit board  104  arranged at the top of the multilayered structure, and a film  109  is provided on the lower surface of the circuit board  101  arranged at the bottom of the multilayered structure. 
     A through hole  110  is arranged through all circuit boards  101 - 104  and is in this embodiment completely filled with an explosive material  111 . A conductor  112  is provided between the conductive surfaces  107  and  108  and an ignition transfer material  113  is arranged over the explosive material  111  and the conductor  112 , as described in connection with  FIG. 1 . 
     An isolator  114 , preferably silicone rubber or Latex®, is provided in the upper surface covering the conductive surfaces  107  and  108  as well as the ignition transfer material  113 , the explosive material  111  and the conductor  112 . The purpose with the isolator is to confine the moisture sensitive components of the explosive device  100 . Furthermore, a conformal coating  115 , preferably Parylene®, is provided around the complete explosive device  100  to improve ignition reliability. The purpose of the conformal coating is to isolate the explosive device from a hostile environment and maintain a suitable interior operating environment to ensure proper operation. 
       FIG. 8  shows a top view of an explosive device  120  provided with two independent igniting stimuli  118  and  119 . The explosive device  120  comprises a substrate  121  having four separate conductive surfaces  122 ,  123 ,  124  and  125  arranged in relation to a hole  116  being filled with an explosive material  117 . A first conductor  126  is connected between conductive surfaces  122  and  123 , and a second conductor  127  is connected between conductive surfaces  124  and  125 . The conductors are, in this embodiment, exemplified as bridge wires but other types of conductors may naturally be used. A first ignition transfer material  128  is provided between the first conductor  126  and the explosive material  117 , and a second ignition transfer material  129  is provided between the second conductor  127  and the explosive material  117 . 
     In this embodiment, the first igniting stimulus comprises the first conductor  126  and the first ignition transfer material  128 , and the second igniting stimulus comprises the second conductor  127  and the second ignition transfer material  129 . However, it is possible to implement each ignition stimulus without having an ignition transfer material as described in connection with  FIGS. 6   a - 6   d.    
     The two igniting stimuli  118  and  119  of the explosive device  120  is configured to be connected through wires to an external control unit  130 , which may be implemented on the same substrate as the explosive device. The wires connect each conductive surface to the control circuit  130 , whereby the control circuitry may independently control the activation of each igniting stimulus  118  and  119 . 
     For instance, the control circuit may initiate the first igniting stimulus  118  and monitor the result of the activation. If the explosive device is not activated due to a malfunction in the first igniting stimulus, the control circuit may initiate the second igniting stimulus to activate the explosive device. 
       FIGS. 9   a - 9   d  illustrate an alternative process for manufacturing an explosive device, as described in connection with  FIG. 6   a . The process is similar to the process described in connection with  FIGS. 4   a - 4   d , with a few basic differences. 
     The explosive device is manufactured up-side-down as illustrated in  FIG. 9   a . The conductive surfaces  64  and  65  on the substrate  61  are placed downwards, and a plastic film having an integrated conductor  66 , such as a bridge wire, is arranged in such a way that a connection is made between the conductive surfaces via the conductor  66  in the film. A support  55  is used together with a funnel  40  and a guiding pin  42  to align the hole  62  with the funnel opening, as described above. 
       FIG. 9   b  illustrates the compressing stage of the manufacture process, in which a tool  56 , preferably having a flat surface, is used to compress the explosive material and bring it into contact with the conductor  66  in the film. 
       FIG. 9   c  shows the result of the compressing stage when the tool  56  is retracted from the funnel  40 , as indicated by the arrow  48 . The funnel  40  is thereafter removed and the sheet of material  11  is moved from the support  55  and is flipped over. In  FIG. 9   d , an additional substrate  67  with a booster explosive  69  is attached to the substrate  61  as described in connection with  FIG. 6   a.    
     Although all previously described embodiments of the explosive device have been exemplified using a flat substrate, the invention should not be limited to this, since it is highly possible that a curved substrate may be used. The explosive device is still based on a sheet of material with a planar surface. 
     The fuse composition used in combination with a thin wire, e.g. having a diameter of about 0.03 mm, may comprise lead tricinat or lead styphnate. 
     Another suitable fuse composition preferably comprises:
         20 percent DDNP (DiazoDiNitroPhenol) or KDNBF (Potassium dinitrobenzo-furoxan),   20 percent Zirconium powder (micro sized—2 μm)   60 percent Potassium chlorate (KClO 3 )       

     A binder of nitrocellulose resin (4%) is added to the mixture. 
     It should be noted that an essential advantage with the present invention is that a very small amount of explosive material is needed for proper operation compared to prior art devices. As an example, 15 mg of explosive material will have the same effect as 200-400 mg of explosive material in prior art penetrating devices.