Abstract:
A system for detecting electromagnetic surface waves scattered from a guiding medium, the system comprising: a guiding medium for guiding electromagnetic surface waves; a transmitter arranged to cause electromagnetic surface waves to be transmitted along the guiding medium; at least one transducer arranged to receive electromagnetic waves scattered from said guiding medium as a result of disruption to a surface wave passing over the guiding medium; and a sensor coupled to the transducer and arranged to detect said received electromagnetic waves.

Description:
[0001]    Aspects relate to a system and method for detecting scattered signals. In particular, the disclosure relates to a system and method for detecting electromagnetic surface waves scattered from a guiding medium suitable for carrying electromagnetic surface waves. 
       BACKGROUND 
       [0002]    The applicant&#39;s prior published patent application GB2494435 discloses a communication system which utilises a guiding medium which is suitable for sustaining electromagnetic surface waves. The contents of GB2494435 are hereby incorporated by reference. The present application presents various applications and improvements to the system disclosed in GB2494435. 
       SUMMARY 
       [0003]    A first aspect provides a system for detecting electromagnetic surface waves scattered from a guiding medium, the system comprising: a guiding medium for guiding electromagnetic surface waves; a transmitter arranged to cause electromagnetic surface waves to be transmitted along the guiding medium; at least one transducer arranged to receive electromagnetic waves scattered from said guiding medium as a result of disruption to a surface wave passing over the guiding medium; and a sensor coupled to the transducer and arranged to detect said received electromagnetic waves. 
         [0004]    A second aspect provides a method of detecting electromagnetic surface waves scattered from a guiding medium in a system, the system comprising: a guiding medium for guiding electromagnetic surface waves; a transmitter arranged to cause electromagnetic surface waves to be transmitted along the guiding medium; at least one transducer arranged to receive electromagnetic waves scattered from said guiding medium as a result of disruption to a surface wave passing over the guiding medium; and a sensor coupled to the transducer and arranged to detect said received electromagnetic waves; the method comprising: transmitting electromagnetic surface waves along the guiding medium; receiving scattered electromagnetic surface waves at said at least one transducer in the presence of a disruption to the surface waves passing over the guiding medium; and detecting said received electromagnetic waves. 
         [0005]    Further examples of features of embodiments are recited in the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0006]    Embodiments will now be described, by way of example only, and with reference to the accompanying drawings, in which: 
           [0007]      FIG. 1  shows a system in accordance with a first embodiment; 
           [0008]      FIG. 2  shows a system in accordance with a second embodiment; and 
           [0009]      FIG. 3  is a flow chart showing a method in accordance with an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    A first embodiment will be described in connection with  FIG. 1 .  FIG. 1  shows a system  100  which may be used to detect surface waves scattered as space waves due to objects near or on the guiding medium, or breaks in the guiding medium. The system  100  includes a guiding medium  101 . The guiding medium  101  is a high impedance channel in which the reactive impedance is higher than the resistive impedance. Such a channel is suitable for the propagation of electromagnetic surface waves. In this example, the guiding medium includes a dielectric layer  102  and a conductive layer  103 . This guiding medium is similar to the one described in the applicant&#39;s co-pending patent application published under number GB2494435. As will be appreciated, the high impedance channel may take other forms, as described in GB2494435. 
         [0011]    The dielectric layer  102  is a sheet of material having a uniform thickness. The width and length of the dielectric layer  102  will vary depending on the specific application. In this example, an upper surface  104  of the dielectric layer  102  is the surface over which surface waves are transmitted. The conductive layer  103  is also a sheet of material having a uniform thickness. The width and length of the conductive layer  103  are generally the same as those equivalent dimensions of the dielectric layer  102 , but they are not necessarily the same. The conductive layer  103  is positioned against the dielectric layer  102 . The dielectric layer  102  and the conductive layer  103  accordingly form a dielectric coated conductor. 
         [0012]    The upper surface  104  of the dielectric layer  102 , and hence the guiding medium  101 , has a reactive impedance which is greater than its resistive impedance. Such a surface is suitable for guiding surface waves. In particular, the reactance and resistance is such that the surface is suitable for guiding Zenneck surface waves. The layer of air formed above the guiding medium acts as the transmission medium for the surface wave. 
         [0013]    The system  100  includes a transmit launcher  105  and a receive collector  106 . The system  100  also includes a transmitter  107  and a receiver  108 . The transmitter  107  is arranged to transmit a signal to transmit launcher  105 . The transmit launcher  105  modulates a carrier signal which is then launched onto the guiding medium  101 . The receive collector  106  receives the surface waves which have propagated over the guiding medium  101 . The receive collector  106  has the same construction as the transmit launcher  105 . However, it operates in reverse, collecting surface waves from the guiding medium  101 , rather than launching them. The receive collector  106  demodulates the carrier signal and passes the received signal to the receiver  108 . 
         [0014]    The system  100  effectively forms a communications channel in which signals may be sent from one point to another, via the guiding medium  101 . Accordingly, the guiding medium  101  acts as a transmission line. As such, anything which interferes with the transmission of signals along the transmission line may cause the signal to be scattered as a space wave. Such a wave may then be detected. 
         [0015]    The system  100  also includes a transducer array  109 , which is coupled to a receiver  110 . The transducer array  109  is arranged to detect surface wave signals scattered from the surface of the guiding medium  101 . Scattering may occur due to obstacles near or on the guiding medium  101 , or breaks in the guiding medium. The receiver  110  is coupled to a detector unit  111 , which is arranged to detect scattered surface waves. The transducer array  109  is mounted in close proximity to the guiding medium  101 . The detector unit  111  is calibrated to determine when scattered surface waves represent an object nearer to the guiding medium  101 , or a break or disruption to the surface on which the guiding medium is attached. 
         [0016]    It has been appreciated by the applicant that when items move close to the guiding medium  101 , or when an item is positioned on the guiding medium or the guiding medium breaks, the surface wave is scattered as a space wave. Such a space wave may be detected by the transducer array  109 , receiver  110  and detector unit  111 . 
         [0017]    There are various applications for this system. For example, the system  100  may be used to detect damage to a surface, including the appearance of gaps or movement in a surface. For example, a guiding medium  101  may be placed on a structurally important surface of a vehicle, such as an aircraft wing. Any movement, cracks or gaps that appear in the surface will stretch, move or break the guiding medium. Such movement will result in scattering of the surface wave, which may be detected by detector unit  111 . 
         [0018]    A second embodiment will now be described in connection with  FIG. 2 .  FIG. 2  shows a system  200  which may be used to detect surface waves scattered as space waves due to objects near or on the guiding medium, or breaks in the guiding medium. The system  200  includes a guiding medium  201 . The guiding medium  201  is a high impedance surface in which the reactive impedance is higher than the resistive impedance. In this embodiment, the guiding medium  201  is a surface over which surface waves may propagate in several directions. This is in contrast to the previous embodiment in which surface waves generally propagate in a single direction along a channel. As with the previous embodiment, the guiding medium includes a dielectric layer  202  and a conductive layer (not shown). The guiding medium is similar to the one described in the applicant&#39;s co-pending patent application published under number GB2494435. As will be appreciated, the high impedance channel may take other forms, as described in GB2494435. 
         [0019]    The dielectric layer  202  is a sheet of material having a uniform thickness. The width and length of the dielectric layer  202  will vary depending on the specific application. In this example, an upper surface of the dielectric layer  202  is the surface over which surface waves are transmitted. The conductive layer is also a sheet of material having a uniform thickness. The width and length of the conductive layer are generally the same as those equivalent dimensions of the dielectric layer  202 , but they are not necessarily the same. The conductive layer is positioned against the dielectric layer  202 . The dielectric layer  202  and the conductive layer accordingly form a dielectric coated conductor. 
         [0020]    The upper surface of the dielectric layer  202 , and hence the guiding medium  201 , has a reactive impedance which is greater than its resistive impedance. Such a surface is suitable for guiding surface waves. In particular, the reactance and resistance is such that the surface is suitable for guiding Zenneck surface waves. The layer of air formed above the guiding medium acts as the transmission medium for the surface wave. 
         [0021]    The system  200  includes a surface wave launcher  203 . The system  200  also includes a transmitter  204 . The transmitter  201  is arranged to transmit a signal to surface wave launcher  203 . The surface wave launcher  203  modulates a carrier signal which is then launched onto the guiding medium  201 . In this embodiment, the surface waves propagate in a fan-like pattern, as shown in  FIG. 2 . When an obstacle is placed in the path of the surface waves, some of the surface wave is scattered as a space wave. This is also true when objects are moved within close proximity of the guiding medium  201 , or if the guiding medium is broken, thereby causing disruption in the propagation path. 
         [0022]    The system  200  also includes a transducer antennas  205 A,  205 B, which are coupled to a mulitchannel RF receiver  206 . The antennas  205 A,  205 B are equivalent to the transducer array  109  shown in  FIG. 1 , and are arranged to detect surface wave signals scattered from the surface of the guiding medium  201 . Scattering may occur due to obstacles near or on the guiding medium  201 , or breaks in the guiding medium. The receiver  206  is coupled to a detector unit  207 , which is arranged to detect scattered surface waves. The antennas  205 A,  205 B are mounted in close proximity to the guiding medium  201 . The detector unit  207  is calibrated to determine when scattered surface waves represent an object nearer to the guiding medium  201 , or a break or disruption to the surface on which the guiding medium is attached. 
         [0023]      FIG. 3  is a flow-chart showing a method in accordance with an embodiment. The process begins by transmitting an electromagnetic surface wave along the guiding medium (S 300 ). Following this, any scattered surface waves are received by the one or more transducers (S 301 ). Finally, the received waves are detected by the detector (S 302 ). 
         [0024]    Further modifications and variations of the aforementioned systems and methods may be implemented within the scope of the appended claims.