Abstract:
A plasma antenna generator includes a ceramic portion including an ionizable material, an explosive charge adapted to project at least part of the ceramic portion upon detonation at a velocity sufficient to ionize the ionizable material, and a detonator coupled with the explosive charge. A plasma antenna generator includes a housing defining a plurality of openings therein and a plurality of shaped charge devices or a plurality of explosively formed projectile devices received in the openings. Each of the devices includes an explosive charge, a detonator coupled with the explosive charge, and a ceramic liner, the ceramic liner comprising an ionizing material. A method includes providing an explosive device and a ceramic portion comprising an ionizable material disposed proximate the explosive device, detonating the explosive device to propel the ceramic portion, and ionizing the ionizable material to form at least one plasma trail.

Description:
BACKGROUND 
   1. Field of the Invention 
   This invention relates to a plasma antenna generator and a method of using the plasma antenna generator. In particular, the invention relates to a plasma antenna generator comprising a ceramic material that provides ionizable material for plasma antenna generation. 
   2. Description of Related Art 
   Electromagnetic energy can be used in many ways to sense or affect objects from a distance. Radar, for example, is reflected electromagnetic energy used to determine the velocity and location of a targeted object. It is widely used in such applications as aircraft and ship navigation, military reconnaissance, automobile speed checks, and weather observations. Electromagnetic energy may also be used to jam or otherwise interfere with radio frequency transmissions or to affect the radio transmitting equipment itself. 
   In certain situations, it may be desirable to radiate one or more electromagnetic pulses over an area to sense or affect objects within the area. Generally, as illustrated in  FIG. 1 , a signal generator  102  generates an electromagnetic pulse, which is radiated by an antenna  104  as an electromagnetic wave  106 . Upon encountering a boundary, such as a boundary between an object  108  and the air  110 , a portion of the energy of the wave  106  is reflected as an electromagnetic wave  112 . The reflected wave  112  may then be received by a sensor  114 , which analyzes the reflected wave  112  to determine various characteristics of the object  108 . 
   It is often desirable to deploy such antennas, e.g., the antenna  104 , during flight. For example, a spacecraft approaching a planetary body may deploy an antenna so that electromagnetic energy may be directed toward the surface of the body. Conventional antennas generally include rigid or semi-rigid members that may be compactly folded for storage and transport and then unfolded when needed. Alternatively, conventional antennas may be wires that are explosively deployed or deployed by parachutes. A substantial amount of time is often required to deploy such antennas, which results in additional planning to determine the appropriate time to begin deployment so that the antenna will be available when needed. Further, circumstances may arise in which the immediate transmission of electromagnetic energy is desirable. If the antenna has not been deployed, there may not be sufficient time to deploy the antenna and transmit the electromagnetic energy in the desired time frame. 
   It may also be desirable in certain situations to transmit electromagnetic energy having a broad spectrum of frequencies or to transmit low frequency electromagnetic energy. Generally, longer antennas are capable of transmitting electromagnetic energy more efficiently at lower frequencies than shorter antennas. Such longer antennas may typically be capable of transmitting electromagnetic energy having higher frequencies as well. Longer foldable antennas require more storage space, may be more complex, and generally take longer to unfold. 
   SUMMARY OF THE INVENTION 
   In one aspect, the present invention provides a plasma antenna generator. The plasma antenna generator includes a ceramic portion including an ionizable material, an explosive charge adapted to project at least part of the ceramic portion upon detonation at a velocity sufficient to ionize the ionizable material, and a detonator coupled with the explosive charge. 
   In another aspect, the present invention provides a plasma antenna generator. The plasma antenna generator includes a housing defining a plurality of openings therein and a plurality of shaped charge devices or a plurality of explosively formed projectile devices received in the openings. Each of the devices includes an explosive charge, a detonator coupled with the explosive charge, and a ceramic liner, the ceramic liner comprising an ionizing material. 
   In yet another aspect of the present invention, a method is provided. The method includes providing an explosive device and a ceramic portion comprising an ionizable material disposed proximate the explosive device, detonating the explosive device to propel the ceramic portion, and ionizing the ionizable material to form at least one plasma trail. 
   Additional objectives, features and advantages will be apparent in the written description which follows. 

   
     DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. However, the invention itself, as well as, a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, in which the leftmost significant digit(s) in the reference numerals denote(s) the first figure in which the respective reference numerals appear, wherein: 
       FIG. 1  is a stylized diagram of a conventional sensing system; 
       FIG. 2A  is a stylized block diagram of a first illustrative embodiment of an electromagnetic pulse transmitting system according to the present invention; 
       FIG. 2B  illustrates the electromagnetic pulse transmitting system of  FIG. 2A  in operation; 
       FIG. 2C  is a stylized block diagram of a second illustrative embodiment of an electromagnetic pulse transmitting system alternative to that of  FIGS. 2A and 2B  according to the present invention; 
       FIG. 2D  illustrates the electromagnetic pulse transmitting system of  FIG. 2C  in operation; 
       FIG. 3A  is a stylized, partially cross-sectioned, side view of a first illustrative embodiment of an explosive device that may be employed in the embodiments of  FIGS. 2A-2D ; 
       FIG. 3B  is a cross-sectional view of a portion of the liner of  FIG. 3A  that includes a layer of the ionizable material affixed to the liner thereof; 
       FIG. 3C  is a stylized diagram of the explosive device of  FIG. 3A  in operation; 
       FIG. 4A  is a partial cross-sectional, side view of a second embodiment of the explosive device of  FIGS. 2A-2D  alternative to that in  FIGS. 3A-3B ; 
       FIG. 4B  is a cross-sectional view of a portion of an illustrative embodiment of a liner of  FIG. 4A  having a plurality of liners disposed in openings defined by a housing; 
       FIG. 4C  is a stylized diagram of the explosive device of  FIG. 4A  in operation; 
       FIG. 4D  is a stylized diagram of a generally hollow, conical pattern of plasma trails that may be formed by the explosive device of  FIG. 4A ; 
       FIG. 5A  is a side view of a third illustrative embodiment of the explosive device of  FIGS. 2A-2D  alternative to embodiments of  FIGS. 3A-3B  and  FIGS. 4A-4D ; 
       FIG. 5B  is a bottom, plan view of the explosive device of  FIG. 5A ; 
       FIG. 5C  is a cross-sectional view of the explosive device of  FIGS. 5A and 5B  taken along the line  5 C- 5 C of  FIG. 5B ; 
       FIG. 5D  is a partial cross-sectional, side view of an explosively formed projectile device of  FIG. 5C ; 
       FIG. 6A  is a side view of a fourth illustrative embodiment of the explosive device of  FIGS. 2A-2D  alternative to the embodiments of  FIGS. 3A-3B ,  FIGS. 4A-4D , and  FIGS. 5A-5D ; 
       FIG. 6B  is a cross-sectional view of the explosive device of  FIG. 6A  taken along the line  6 B- 6 B in  FIG. 6A ; and 
       FIG. 6C  is a stylized diagram of the explosive device of  FIG. 6A  in operation. 
   

   While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
   The present invention relates to a plasma antenna generator comprising an explosive device that, upon detonation, propels a ceramic portion comprising an ionizable material at a velocity sufficient to ionize the ionizable material. The ceramic portion may comprise a portion of the explosive device or merely be disposed proximate to the explosive device. Further, the ceramic portion may comprise a component having a use other than to provide ionizable material for the plasma antenna generator. For example, the ceramic portion may comprise a component, device, or apparatus that serves another function in a vehicle comprising the plasma antenna generator. Various illustrative embodiments of the present invention are described in greater detail below. 
   A first illustrative embodiment of a plasma antenna generator  200  according to the present invention is shown in  FIGS. 2A and 2B . Referring to  FIG. 2A , the plasma antenna generator  200  includes an explosive device  204  and a detonator  206  attached thereto for detonating the explosive device  204 . A power source  208  is coupled with the detonator  206  via a switch  210  that, when closed, provides a path for power from the power source  208  to activate the detonator  206  and detonate the explosive device  204 . While the switch  210  is illustrated in  FIGS. 2A and 2B  as a common throw-type switch, the invention is not so limited. The switch  210  may be any switch known to the art that is suitable for switching power from the power source  208  to the detonator  206 . In alternative embodiments, for example, the switch  210  may be an electronic switch. 
   In the illustrated embodiment, the explosive device  204  includes an explosive charge (not shown in  FIGS. 2A and 2B ), made of HMX (cyclotetramethylenetetranitramine), an HMX blend, RDX (cyclotrimethylenetrinitramine), an RDX blend, LX-14 (an HMX/estane blend), or the like. However, other suitable explosive materials may be employed. The explosive device  204  may itself include a ceramic portion comprising an ionizable material arranged in various configurations or a ceramic portion  212  may be disposed proximate the explosive device  204  (as will be more fully described below). 
   Upon detonating the explosive device  204 , as shown in  FIG. 2B  and represented by a graphic  213 , particles  214  of the ionizable material are propelled by the explosive force through the air. In the illustrated embodiment, the particles  214  are propelled in any chosen, random, or chance direction, and are aerodynamically heated. In alternative embodiments, the particles  214  may be propelled in a directed fashion. Only one of the particles  214  is shown in  FIG. 2B  for clarity. The particles  214  may be, for example, atoms, molecules, pieces, and/or slugs of the ionizable material. 
   As the particles  214  are heated by friction with the atmosphere, the ionizable material is ionized, producing plasma trails  216  (only one shown for clarity) of ions and free electrons (not individually shown). The free electrons of the plasma trail  216  act as an antenna that may reflect electromagnetic waves  218  or propagate electromagnetic waves  220 . Generally, electromagnetic waves having frequencies below a plasma cut-off frequency of the plasma trail  216  (e.g., the electromagnetic waves  218 ) are reflected by the plasma trail  216 . Electromagnetic waves having frequencies equal to or greater than the plasma cut-off frequency (e.g., the electromagnetic waves  220 ) generally propagate through the plasma trail  216 . The plasma cut-off frequency of the plasma trail  216  is generally proportional to the square root of its electron density. Further, the plasma trails  216  may generally be longer than conventional antennas, thereby allowing electromagnetic waves having lower frequencies (i.e., longer wavelengths) to be reradiated as compared to conventional antennas. 
   In some embodiments, an electromagnetic pulse generator  222  may be combined with the plasma antenna generator  200  to form an electromagnetic pulse transmitting system  224 . In such embodiments, the electromagnetic pulse generator  222  generates a pulse of electromagnetic waves (e.g., the electromagnetic waves  218 ,  220 ) that may be reflected from or propagated through the plasma trail  216 . Particular embodiments of the electromagnetic pulse generator  222  will be discussed in greater detail below. 
   While the plasma antenna generator  200  illustrated in  FIGS. 2A and 2B  includes only one explosive device  204 , the present invention is not so limited and may include any number of explosive devices  204 . For example, in a second embodiment, a plasma antenna generator  226 , as shown in  FIG. 2C , includes two explosive devices  204 , either comprising the ceramic portion  212  comprising an ionizable material or disposed proximate the ceramic portion  212  comprising an ionizable material. Upon detonating the explosive devices  204 , particles  214  are propelled in different directions, as shown in  FIG. 2D . The resulting plasma trails  216  form a dipole-like antenna  221  that reradiates the electromagnetic waves  218  or propagates the electromagnetic waves  220 . Any of the explosive devices  204 , if more than one is present, may be configured to propel the particles in any chosen, random, or chance direction with respect to any of the other explosive devices  204 . As discussed above concerning  FIGS. 2A and 2B , the electromagnetic pulse generator  222  may be combined with the plasma antenna generator  226  to form an electromagnetic pulse transmitting system  228 . 
   The ionizable material may comprise any material capable of being ionized as a result of aerodynamic heating induced by being propelled by the explosive charge  204 . For example, the ionizable material may comprise an alkali metal, a compound of one or more alkali metals (e.g., alkali salts, alkali carbonates, and the like) or may comprise a constituent of a compound of one or more alkali metals. Further, the ionizable material may comprise a clathrate of an alkali metal, a constituent of the clathrate of the alkali metal, an intercalation compound of an alkali metal, or a constituent of the intercalation compound of the alkali metal. Alkali metals include lithium, sodium, potassium, rubidium, cesium, and francium. In any case, the ionizable material is contained in a ceramic portion and the ceramic portion may be crystalline or amorphous (e.g., glass). For example, soda-lime glasses and borosilicate glasses, as well as Ca—Al 2 O 3 —SiO 2 , Mg—CaO, Na—SiO 3 —SiO 2 , and ZnO—SiO 2  ceramics typically contain up to about 15 percent alkali. Other ceramics, such as potassium niobate, tantalum niobate, and barium titanate contain up to about five percent alkali. 
   As indicated above, the explosive device  204  may take many different forms.  FIG. 3A  illustrates a first embodiment of the explosive device  204  according to the present invention. In the illustrated embodiment, the explosive device  204  comprises a shaped charge device  302 . Conventionally, shaped charge devices employ explosive products to create great pressures that accelerate a metallic liner and form a very high-speed jet. Accordingly, materials chosen for conventional shaped charge liners are capable of forming such a jet. The shaped charge device  302  of the present embodiment, however, uses high-pressure explosive products that are created by detonating the highly explosive material to shatter and expel a ceramic liner, rather than forming a conventional jet. Note that a shaped charge device is not required to practice the present invention. 
   As shown in  FIG. 3A , the shaped charge device  302  of the illustrated embodiment comprises an explosive charge  304  partially encased by a casing  306 . The explosive charge  304  may be made of any explosive material capable of accelerating particles of the device  302 &#39;s liner  310  sufficiently to generate a plasma trail. In various embodiments, the explosive material may comprise an explosive having a high detonation velocity and/or high brisance, e.g., materials containing HMX, an HMX blend, RDX, an RDX blend, LX-14, or the like. Generally, a high detonation velocity explosive is characterized as that having a detonation velocity of at least about 6000 meters per second. 
   Still referring to  FIG. 3A , a forward face  308  of the explosive charge  304 , in the illustrated embodiment, is generally V-shaped in cross-section; however, the invention is not so limited. Rather, the forward face  308 , and the ceramic liner  310  affixed to the forward face  308 , may have any cross-sectional shape known to the art, e.g., hemispherical, trumpet-shaped, or the like. The ceramic liner  310  comprises the ionizable material, as discussed above. Alternatively, as shown in  FIG. 5C , the liner  510  may include a layer  318  of the ionizable material affixed to a ceramic base  320 . In such an embodiment, the layer  318  may comprise, for example, an alkali metal, a compound of the alkali metal, a constituent of the compound of the alkali metal, a clathrate of the alkali metal, a constituent of the clathrate of the alkali metal, an intercalation compound of the alkali metal, or a constituent of the intercalation compound of the alkali metal. 
   Referring now to  FIG. 3C , upon detonation of the explosive charge  304  (represented by a graphic  312 ) by the detonator  208 , the ceramic liner  310  shatters into particles  314  (only one indicated for clarity) comprising the ionizable material and are projected forward (as indicated by arrow  316 ). Plasma trails  322  of ions and free electrons are generated as the ionizable material within the particles  314  are propelled through the air. The plasma trails  322  may be used to reradiate the electromagnetic waves  218  or propagate the electromagnetic waves  220 , as discussed above and shown in  FIGS. 2B and 2D . 
   Referring now to  FIG. 4A , a second embodiment  402  of the explosive device  204  according to the present invention is shown. In the illustrated embodiment, the explosive device  204  comprises an explosively formed projectile device  402 . Conventionally, explosively formed projectile devices employ explosive products, created by detonating a highly explosive material, to create great pressures that accelerate a metallic liner while simultaneously reshaping it into a rod or some other chosen shape. The present explosively formed projectile device  402 , however, comprises a ceramic liner that is shattered into particles and projected forward when the explosive material is detonated. 
   In the illustrated embodiment, the explosively formed projectile device  402  comprises an explosive charge  404  partially encased by a casing  406 . The explosive charge  404  may be made of any explosive material known in the art having a high detonation velocity and/or high brisance, as discussed above. The explosively formed projectile device  402  further includes a ceramic liner  408  affixed to a forward face  410  of the explosive charge  404 . Both the forward face  410  and the liner  408  affixed thereto may have any desired shape suitable for an explosively formed projectile device. In one embodiment, the liner  408  comprises a single ceramic liner that includes the ionizable material. 
   Alternatively, as illustrated in  FIG. 4B , the liner  408  may comprise a plurality of ceramic liners  412  held within openings  414  defined by a housing  416 . The ceramic liners  412  comprise the ionizable material, as defined above. While the ceramic liners  412  shown in  FIG. 4B  are concavely shaped, the invention encompasses ceramic liners  412  having any chosen shape suitable for such liners. 
   When the explosive charge  404  is detonated by the detonator  206 , the ceramic liner  408  (of  FIG. 4A ) or the ceramic liners  412  (of  FIG. 4B ) are propelled by the resulting explosive force, as shown in  FIG. 4C . Each of the ceramic liners  412  produces a plasma trail  418  (only one labeled for clarity) that can be used to reradiate or propagate an electromagnetic wave or pulse, as discussed above. 
   In the embodiment illustrated in  FIG. 4B , the ceramic liners  412  are arranged such that a central portion  420  of the housing  416  contains no slugs  416 . As shown in  FIG. 4D , such a configuration is designed to produce a hollow, conical pattern  422  of plasma trails  418  (only one shown). The present invention, however, encompasses any chosen configuration of ceramic liners  412  to produce a desired pattern of plasma trails  418 . 
     FIGS. 5A-5D  illustrate a third embodiment of the explosive device  204  according to the present invention, comprising a multiple explosively formed projectile device  502 . In the illustrated embodiment, a housing  504  contains a plurality of explosively formed projectile elements  506  held in a chosen configuration. Each of the elements  506  comprises an explosive charge  508  partially encased by a casing  510 , as shown in  FIG. 5D . The explosive charge  508  may be made of any explosive material known in the art having a high detonation velocity and/or high brisance, as discussed above. Each of the elements  506  further includes a ceramic liner  512  affixed to a forward face  514  of the explosive charge  508 . Both the forward face  514  and the ceramic liner  512  affixed thereto may have any desired shape suitable for such a device. The ceramic liner  512  comprises the ionizable material, as discussed above. 
   When each of the explosive charges  508  is detonated by the detonators  516 , the ceramic liners  512  are propelled by the resulting explosive force in the same fashion as the second embodiment, as shown in  FIG. 4C . Each of the ceramic liners  512  produces one of the plasma trails  418  (only one labeled for clarity) that can be used to reradiate or propagate electromagnetic waves or pulses, as discussed above. 
   In the embodiment illustrated in  FIGS. 5A-5C , the elements  506  are arranged to produce a hollow, conical pattern similar to the conical pattern  422  of plasma trails  418  (only one shown) produced by the second embodiment, as shown in  FIG. 4D . The present invention, however, encompasses any desired configuration of liners  512  to produce a chosen pattern of plasma trails  418 . For example, various elements  506  held by the housing  504  may ceramic liners  512  having different configurations. 
     FIGS. 6A and 6B  illustrate a fourth embodiment of the explosive device  204  according to the present invention comprising a radial explosively formed projectile device  602 . The device  602  comprises an explosive charge  604  partially encased by a casing  606 . The explosive charge  604  may be made of any explosive material known in the art having a high detonation velocity and/or high brisance, as discussed above. The casing  606  defines a plurality of openings  608  in which are disposed a corresponding plurality of ceramic liners  610 . The ceramic liners  610  comprise the ionizable material, as defined above. Further, the ceramic liners  610  may have a construction such as that shown in  FIG. 5B  or  5 C. 
   When the explosive charge  604  is detonated (represented by a graphic  611 ) by the detonator  208 ,  404 , the ceramic liners  610  are propelled by the resulting explosive force, as shown in  FIG. 6C . Each of the ceramic liners  610  produces a plasma trail  612  (only one labeled for clarity) that can be used to reradiate the electromagnetic pulse emitted from the electromagnetic pulse generator  204  (as illustrated in  FIG. 2B ) or to reradiate the electromagnetic pulse emitted from the coil  410  (as illustrated in  FIG. 4B ). 
   Note that ceramic liners are not used in conventional shaped charge devices or conventional explosively formed projectile devices. Liners for these devices typically comprise copper, a copper alloy, or other such ductile metal that, upon detonation, will form a high speed jet. 
   The electromagnetic pulse generator  204  may be any type of generator known to the art capable of generating an electromagnetic pulse. Examples of such electromagnetic pulse generators can be found in U.S. Pat. No. 6,843,178, which is hereby incorporated by reference in its entirety for all purposes. 
   As discussed above concerning  FIGS. 2A and 2C , some embodiments of the present invention may include a separate ceramic portion  212  that provides ionizable material for plasma antenna generation. In such embodiments, the explosive device  204  may also comprise a ceramic material, wherein both the explosive device  204  and the ceramic portion  212  provide ionizable material for plasma antenna generation. Alternatively, the explosive device  204  may comprise a conventional explosive device (e.g., a conventional shaped charge, explosively formed projectile, or the like), as the ionizable material is provided by the ceramic portion  212 . 
   Moreover, the ceramic portion  212  may employ any desired component comprising a ceramic material that provides sufficient ionizable material for plasma antenna generation. For example, the ceramic portion  212  may take on the form of an element specifically designed and implemented solely to provide ionizable material for plasma antenna generation. Alternatively, the ceramic portion  212  may comprise an ancillary element, device, or apparatus that also serves another purpose but that is disposed proximate the explosive device  204  such that, upon detonation of the explosive device  204 , ionizable material of the element, device, or apparatus is ionized to form a plasma antenna. Examples of such ancillary elements, devices, or apparatuses include, but are not limited to windows (e.g., seeker windows), electronic components, radomes, and the like. Accordingly, the scope of the present invention encompasses the use of any ionizable material-containing element, device, or apparatus as the ceramic portion  212 , so long as the ceramic portion  212  and the explosive device  204  (if it comprises ionizable material) provide sufficient ionizable material to generate a plasma antenna. Note that, with proper deployment timing, a plasma antenna of the present invention may be used to receive electrical signals. 
   This concludes the detailed description. The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below. It is apparent that an invention with significant advantages has been described and illustrated. Although the present invention is shown in a limited number of forms, it is not limited to just these forms, but is amenable to various changes and modifications without departing from the spirit thereof.