Abstract:
An apparatus for effecting propagation of electromagnetic waves, comprising a hull outer surface, a dielectric material disposed over the hull outer surface, and an electrically conductive member embedded within the dielectric material. When a liquid medium contacts the dielectric material, the liquid medium, the hull outer surface, the dielectric material and the electrically conductive member cooperate to provide a waveguide through which electromagnetic waves can propagate wherein the boundaries of the waveguide are defined by the liquid medium and the hull outer surface. A sensor network can be provided within the dielectric material for receiving power and transmitting information.

Description:
STATEMENT OF GOVERNMENT INTEREST 
   The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to an electromagnetic wave propagation scheme for use with sensors on undersea vehicles. 
   2. Description of the Related Art 
   Undersea vehicles, such as submarines, autonomous undersea vehicles, and autonomous undersea platforms, typical use sensors that are external to the pressure hull of the undersea vehicles. Such sensors are used to measure or detect pressure, acceleration, magnetic fields and acoustic energy. One such sensor is known as a MEMS (Micro Electronic Mechanical System) sensor. MEMS sensors are miniaturized sensors that are very adaptable to the undersea environment. 
   The sensors are typically arranged in a sensor grid, plane or array that can include hundreds of sensors. However, future missions and roles for undersea vehicles will certainly require a significant increase in the number of sensors. Furthermore, the requirements to reduce spectral signatures and increase detection capabilities in hostile and/or unforgiving littoral environments will require sensors that can be integrated into the structure of the undersea vehicles. Prior art techniques of extracting data and providing power to sensor grids or planes will not be able to accurately and efficiently extract data from and provide power to such future sensor configurations. 
   Therefore, what is needed is an apparatus that enables efficient, accurate quick interrogation, powering and reading of sensors used on undersea vehicles. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to, in one aspect, an apparatus for effecting propagation of electromagnetic waves, comprising a hull outer surface, a dielectric material disposed over the hull outer surface, and an electrically conductive member embedded within the dielectric material. When a liquid medium contacts the dielectric material, the liquid medium, the hull outer surface, the dielectric material and the electrically conductive member define or form a waveguide through which electromagnetic waves can propagate wherein the boundaries of the waveguide are defined by the liquid medium and the hull outer surface. In one embodiment, the electrically conductive member comprises microstrip. In another embodiment, the electrically conductive member comprises stripline. In a further embodiment, the electrically conductive member comprises metal tape. In one embodiment, the apparatus further comprises a parasitic radiator embedded in the dielectric material and in electrical signal communication with the waveguide. In one embodiment, the dielectric material is formed by a Special Hull Treatment (“SHT”) made from a commonly used material such as dura which is well known in the art. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The figures are for illustration purposes only and are not drawn to scale. The invention itself, however, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which: 
       FIG. 1  is a block diagram of a communication system that incorporates the electromagnetic wave propagation channel of the present invention; 
       FIG. 2  is a partial cross-sectional view of the electromagnetic wave propagation channel of the present invention; and 
       FIG. 3  is a perspective view, in diagrammatic form, of the electromagnetic wave propagation channel of the present invention embodied in the skin of an undersea vehicle. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In describing the preferred embodiments of the present invention, reference will be made herein to  FIGS. 1–3  of the drawings in which like numerals refer to like features of the invention. 
   As used herein, the terms “electromagnetic wave” and “electromagnetic signals” are used interchangeably and are construed to have the same meaning. As used herein, the terms “hull” and “pressure hull” includes the hulls of ocean-going vessels, submarines, undersea or underwater vehicles, motor boats, and pleasure craft. As used herein, the term “liquid medium” includes oceans, lakes, and rivers. Therefore, although the ensuing description is in terms of the present invention being used in conjunction with an undersea vehicle, it is to be understood that the present invention can be used with almost any type of vessel configured for travel though a liquid medium. 
   Referring to  FIG. 1 , there is shown communication system  10  that utilizes the electromagnetic wave propagation channel of the present invention. Communications system  10  generally comprises transceiver  12 , electromagnetic wave propagation channel  14  of the present invention, parasitic radiator  15  and sensor network  16 . 
   Transceiver  12  includes circuitry for generating and transmitting an encoded R.F. (radio frequency) or microwave signal. The encoded signal contains data that defines interrogation and/or read signals that are used to address individual sensors in sensor network  16 . In a preferred embodiment, the encoded signal contains data that defines a code that corresponds to a particular sensor thereby allowing each sensor to be individually addressed. The encoded signal generated  11  by transceiver  12  also includes a signal component that powers the sensors in sensor network  16 . Transceiver  12  also includes processing circuitry for processing sensor data detected by the sensors of sensor network  16 . 
   In one embodiment, transceiver  12  includes circuitry for formatting sensor data signals into a format that is suitable for processing by a central processor (not shown) that is typically located within the undersea vehicle. In one embodiment, transceiver  12  includes circuitry for converting the formatted sensor data signals into optical signals. In such an embodiment, transceiver  12  includes a fiber optic penetrator (not shown) that functions as an interface between transceiver  12  and the central processor (not shown) within the undersea vehicle. 
   Referring to  FIGS. 1 ,  2  and  3 , electromagnetic wave propagation channel  14  is in electrical signal communication with transceiver  12  and parasitic radiator  15 . Wave propagation channel  14  utilizes pressure hull  18  of the undersea vehicle. Specifically, wave propagation channel  14  generally comprises outer surface  18   a  of pressure hull  18 , a coating of dielectric material  22  that is disposed over outer surface  18   a , and electrically conductive member  24  that is embedded within dielectric material  22 . Dielectric material  22  has a predetermined dielectric constant and insulates electrically conductive member  24  from the liquid medium  26 . Dielectric material  22  has an outer surface  27  that is exposed to liquid  11  medium  26 . When hull  18  is disposed in liquid medium  26  and liquid medium  26  contacts outer surface  27  of dielectric material  22 , a waveguide is formed by liquid medium  26 , dielectric material  22 , electrically conductive member  24 , and hull outer surface  18   a . The signals transmitted by transceiver  12  propagate through the waveguide. The boundaries of the aforementioned waveguide are hull outer surface  18   a  and liquid medium  26 . The electromagnetic wave propagation through dielectric material  22  emulates the properties and characteristics of a Goubau wave which is well known in the art. 
   In one embodiment, the coating of dielectric material  22  has a thickness between one (1) and three (3) inches. However, dielectric material  22  can be configured to have a thickness less than one (1) inch or more than three (3) inches. In one embodiment, dielectric material  22  is formed by a process known in the art as Special Hull Treatment (“SHT”). In such a process, conductive member  24  is inserted into dielectric material  22  as the dielectric material is being poured or disposed over outer surface  18   a . However, it is to be understood that other suitable processes and materials may be used to form the coating of dielectric material  22 . 
   In one embodiment, conductive member  24  is configured as microstrip which is well known in the art. In another embodiment, conductive member  24  is configured as stripline which is well known in the art. In a further embodiment, conductive  11  member  24  is configured as metal tape. 
   In a preferred embodiment, the properties, dimensions and characteristics of dielectric material  22  and conductive member  24  are selected to effect efficient propagation of electromagnetic waves or signals at predetermined R.F. or microwave frequencies. 
   Preferably, the environmental conditions (i.e. pressure, temperature, etc.) to which wave propagation channel  14  will be exposed are considered when determining the dimensions and properties of conductive member  24  and when selecting the particular dielectric material so as to avoid significant impedance mismatches. 
   Parasitic radiator  15  is embedded in dielectric material  22  and is in electrical signal communication with wave propagation channel  14 . Parasitic radiator  15  radiates the signals generated by transceiver  12  through dielectric material  22 . Parasitic radiator  15  may be realized by any one of a number of well known suitable techniques or schemes. 
   Sensor network  16  comprises a plurality of sensors that are arranged in an array, grid, plane or any other suitable configuration. Sensor network  16  further comprises a transceiver that is configured to receive and decode the signals radiated from parasitic radiator  15 . Each sensor may be configured as a MEMS sensor described in the foregoing description. However, other suitable sensors may be used as well. The transceiver of sensor network  16  generates and transmits an encoded R.F. or microwave signal that contains data that represents the sensor output data. The encoded signals transmitted by the transceiver of sensor network  16  are received by parasitic radiator  15 . As a result, the encoded signals generated by the transceiver of sensor network  16  propagate through electromagnetic wave propagation channel  14  and are received by transceiver  12 . Transceiver  12  decodes and processes the received signals and routes the processed signal to the central processor (not shown) within the undersea vehicle. 
   In one embodiment of the invention, each sensor has an inactive operational mode and an active operational mode. When the sensors are in the inactive operational mode, each sensor utilizes energy from the signals generated by transceiver  12  to power the sensor electronic circuitry and/or to charge micro-batteries that power the sensors. When the sensors are in the active operational mode, transceiver module  12  receives the encoded signals generated by the transceiver associated with the sensor network, decodes these signals, formats the decoded signals into a format that is suitable for processing by the central processor (not shown), and converts the formatted signals into optical signals. As described in the foregoing description, the optical signals are routed to the central processor (not shown) via the optical penetrator. 
   In one embodiment of the invention, conductive member  24  is configured as a conductive lattice having a plurality of conductive members  24  that are embedded within and extend throughout the dielectric material  22  so as to form a plurality of waveguides that are in electrical signal communication with each other. This configuration is useful when a plurality of sensor networks are utilized. In such a configuration, each waveguide corresponds to a particular sensor network and transceiver  12  generates and outputs encoded radio frequency signals or microwave signals that contain data that defines particular codes wherein a particular code corresponds to a particular sensor grid and a particular sensor within that sensor grid. This embodiment enables transceiver  12  to interrogate, read or power individual sensors within a particular sensor grid. 
   Useful techniques and schemes for interrogating, powering and reading sensor networks are described in commonly owned and co-pending U.S. patent application Ser. No. 10/652,084, filed 25 Aug. 2003, the disclosure of which is incorporated herein by reference. The techniques and schemes described in the aforementioned pending application may be used in conjunction with the present invention. 
   Although the foregoing description is in terms of the sensor network being embedded in dielectric material  22 , it is to be understood that the sensor network can be located on the exterior of the dielectric material  22 . In such an embodiment, the interface for coupling the encoded electromagnetic signals generated by transceiver  12  to the input of the transceiver of the sensor network is embedded within the dielectric material  22 . 
   Electromagnetic wave propagation channel  14 , parasitic radiator  15  and dielectric material  22  cooperate to substantially eliminate the need to use bundles of wires to communicate with the sensors. As a result, the present invention provides a substantial cost savings when a significantly large number of sensors are being used. Furthermore, electromagnetic wave propagation channel  14 , parasitic radiator  15  and dielectric material  22  enable transceiver  12  to detect encoded signals from individual sensors regardless of the direction from which these signals emanate. Thus, the present invention allows the sensors to be efficiently, accurately and quickly interrogated and read thereby providing an active laboratory for hydrophone monitoring, platform self-quieting, cancellation of magnetic signatures, and other monitoring and processing activities. 
   The electromagnetic wave propagation channel of the present invention can be used in conjunction with commercially available integrated circuits dedicated to R.F. or microwave communication as well as commercially available DSP (digital signal processor) circuits. 
   While the present invention has been particularly described, in conjunction with a specific preferred embodiment, it is evident that many alternatives, modifications and variations will  11  be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.