Abstract:
Provided is an apparatus for preventing eavesdropping using a piezoelectric film. The apparatus includes a vibrator including the piezoelectric film, conductive layers connected to top and bottom surfaces of the piezoelectric film, and electrodes connected to the conductive layers, and a noise signal generator electrically connected to the vibrator to generate and transmit an electrical noise signal to the vibrator. The vibrator generates vibration in a solid body in close contact with itself in response to the electrical noise signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 2008-37661, filed on Apr. 23, 2008, the disclosure of which is incorporated herein by reference in its entirety. 
       BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an apparatus for preventing eavesdropping using a piezoelectric film and, more specifically, to an apparatus for preventing eavesdropping using a piezoelectric film that is attached to a window or wall in order to prevent attempts to sense minute vibration of the window or wall due to sound waves from human voices. 
         [0004]    2. Discussion of Related Art 
         [0005]    Modern technology has made it possible to eavesdrop on indoor-conversations by measuring minute vibration of a window, door, or wall due to sound waves from human voices. 
         [0006]    To prevent eavesdropping, jamming techniques have been developed. For example, a vibrator may be attached to a window, door, or wall to generate artificial noise vibration, so that even if vibration of the window, door, or wall is measured using eavesdropping apparatuses, it is difficult to understand conversations. 
         [0007]      FIG. 1  illustrates a first example of a conventional apparatus for preventing eavesdropping. 
         [0008]    Referring to  FIG. 1 , the conventional apparatus for preventing eavesdropping includes two vibrators  101  and  105  and a noise signal generator  103 . The vibrators  101  and  105  closely contact an object  100 , such as a window, door, or wall, which can vibrate due to sound waves. The noise signal generator  103  is connected to the vibrators  101  and  105 . 
         [0009]    In general, the vibrators  101  and  105  are attached at corners of the window where they are less visible. When one vibrator is enough for one window  100 , each of the vibrators  101  and  105  may be attached at one corner of a corresponding window  100 , as shown in  FIG. 1 . In this case, the output impedance of the noise signal generator  103  may be appropriately designed Such that the two vibrators  101  and  105  are connected in parallel to the single output terminal using a pair of electrical wires. In the apparatus shown in  FIG. 1 , the noise signal generator  103  generates an appropriate noise signal, and the vibrator (or an additional vibrator)  101  vibrates the window or wall in response to the noise signal, thereby jamming vibration of the window or wall due to sound waves. Specifically, the noise signal generator  103  generates a white noise or colored noise signal which the vibrator  101  converts into noise vibration to drown out vibration due to sound waves. As a result, even if the vibration of the window or wall is measured, an eavesdropping apparatus cannot discern the vibration due to sound waves from the vibration caused by the vibrator  101 . 
         [0010]      FIG. 2  illustrates a second example of a conventional apparatus for preventing eavesdropping. 
         [0011]    The apparatus shown in  FIG. 2  is based on the same principle as the apparatus shown in  FIG. 1  insofar as vibrators  201 ,  203 ,  205 , and  207  and a noise signal generator  211  are used. However, unlike the apparatus shown in  FIG. 1 , the apparatus shown in  FIG. 2  is adopted when a target object, such as a window or a door, has a large area and requires more than one vibrator. 
         [0012]    Referring to  FIG. 2 , when a window  200  is twice as wide as the window  100  shown in  FIG. 1 , two vibrators  201  and  203  may be used. Thus, vibrators  201 ,  203 ,  205 , and  207  may be attached at diagonally opposite corners of the sliding windows  100 . In this case, two of the vibrators  201 ,  203 ,  205 , and  207  must be connected by electrical wires to a corresponding output terminal of the noise signal generator  211 , making electrical connection of the vibrators  201 ,  203 ,  205 , and  207  much more complicated than in the apparatus of  FIG. 1 . 
         [0013]    In most cases, since a conference room or an office to which the above-described apparatus for preventing eavesdropping is likely to be applied has many very large windows, more vibrators are required. 
         [0014]    Therefore, in the conventional apparatuses for preventing eavesdropping, the number of vibrators depends on the size of the window, and the arrangement of the vibrators and electrical wires connected to the vibrators becomes complicated for larger windows. 
         [0015]    In addition, when a vibrator is brought into close contact with a sliding window, the following problems may occur. 
         [0016]      FIG. 3  is a diagram for explaining problems of a conventional apparatus for preventing eavesdropping. 
         [0017]      FIG. 3  shows a case where the conventional apparatus for preventing eavesdropping is attached to a common sliding window  300 . In this case, since a vibrator  301 , which is an essential part of the conventional apparatus, is quite thick, when the vibrator  301  is attached inside the sliding window  300 , the window  300  may not open. Accordingly, while eavesdropping may be prevented, the window  300  cannot be opened or else the vibrator  301  may detach and fall off. 
       SUMMARY OF THE INVENTION 
       [0018]    The present invention is directed to an apparatus for preventing eavesdropping using a piezoelectric film. 
         [0019]    The present invention is also directed to an apparatus for preventing eavesdropping that generates noise vibration using a piezoelectric film to facilitate electrical wiring and application to ordinary windows. 
         [0020]    One aspect of the present invention provides an apparatus for preventing eavesdropping using a piezoelectric film. The apparatus includes: a vibrator including the piezoelectric film, conductive layers connected to top and bottom surfaces of the piezoelectric film, and electrodes connected to the conductive layers; and a noise signal generator electrically connected to the vibrator to generate and transmit an electrical noise signal to the vibrator wherein the vibrator generates noise vibration in a solid body in close contact with itself in response to the electrical noise signal transmitted from the noise signal generator. 
         [0021]    The solid body may be a material capable of vibrating in response to an external sound signal. Each of the conductive layers may be selected from the group consisting of a conductive metal layer, a conductive polymer layer, and an organic conductive layer. The piezoelectric film may be formed of a material selected from the group consisting of polyvinylidenefluoride (PVDF), hexafluoropropylene (HFP), vinylidenefluroethylene (VDF/TrFE) polymer, and fluorine resin. Each of the electrodes may be formed by adhering a metal tape coated with a conductive adhesive to the conductive layer. Alternatively, each of the electrodes may be formed by printing silver paste or conductive mixture ink on the conductive layer. The apparatus may further include a protective film coated on the entire surface of the vibrator. Alternatively, the protective film may be coated on the entire surface of the vibrator except a portion that is in close contact with the solid body. The noise vibration may have a frequency capable of jamming vibration of the solid body in response to an external sound signal. The vibrator may be cut to a size corresponding to the size of the solid body brought into close contact with the vibrator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The above and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which: 
           [0023]      FIG. 1  is a diagram illustrating a first example of a conventional apparatus for preventing eavesdropping; 
           [0024]      FIG. 2  is a diagram illustrating a second example of a conventional apparatus for preventing eavesdropping; 
           [0025]      FIG. 3  is a diagram for explaining problems of a conventional apparatus for preventing eavesdropping; 
           [0026]      FIG. 4  schematically illustrates a vibrator according to an exemplary embodiment of the present invention; and 
           [0027]      FIG. 5  is a diagram illustrating an apparatus for preventing eavesdropping using a piezoelectric film according to an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0028]    Hereinafter, an apparatus for preventing eavesdropping using a piezoelectric film according to an exemplary embodiment of the present invention ill be described in detail with reference to the accompanying drawings. 
         [0029]      FIG. 4  schematically illustrates a vibrator according to an exemplary embodiment of the present invention. 
         [0030]    Referring to  FIG. 4A , a vibrator  400  according to an exemplary embodiment of the present invention includes a piezoelectric film  401 , conductive layers  403 , electrodes  407  and  409 , and a protective film  405 . The vibrator  400  is brought into close contact with a vibrating medium  420  Such as a window or wall. Reference numerals  430  and  440  are cross-sectional views taken along line  410 . 
         [0031]    The piezoelectric film  401 , which is the most essential part of the vibrator  400 , is formed of a piezoelectric material that converts an electrical signal into physical vibration. 
         [0032]    The piezoelectric film  401  may be formed of a material selected from the group consisting of polyvinylidenefluoride (PVDF), hexafluoropropylene (HFP), vinylidenefluroethylene (VDF/TrFE) polymer, and fluorine resin. 
         [0033]    The conductive layers  403  are used to apply electric signals to the piezoelectric film  401 . The conductive layers  403  may be formed of a highly conductive metal such as copper (Cu), silver (Ag), gold (Au), and aluminum (Al), or a nonmetal such as a conductive polymer or an organic conductive material, for example, polyaniline, polythiophene, poly3,4-ethylene dioxythiophene (PEDOT), polypyrrole, or polyphenylenevinylene (PPV). 
         [0034]    As can be seen from  FIG. 4 , the electrodes  407  and  409  may be an upper electrode  407  and a lower electrode  409 , which function as contact points for transmitting electric signals causing the piezoelectric film  401  to vibrate. The upper and lower electrodes  407  and  409  may be formed by adhering a metal tape coated with a conductive adhesive to the conductive layer  403  or printing silver paste or conductive mixture ink on the conductive layer  403 . 
         [0035]    The protective film  405  is used to protect the piezoelectric film  401 , the conductive layer  403 , and the upper and lower electrodes  407  and  409 . The protective film  405  may be formed of a polymer such as polyethylene, polyvinyl chloride, polyethylene terephthalate, or derivatives thereof. 
         [0036]    The vibrator  400  may be brought into close contact with the vibrating medium  420 , such as a glass panel, door, or wall, and generates noise vibration capable of jamming vibration caused by sound waves. 
         [0037]    When the vibrator  400  in reference numeral  430  is combined with the vibrating medium, such as a window, a contact medium  411 , such as an adhesive, may be used to ensure close adhesion of the vibrator  400  to the vibrating medium. In this case, however, since vibration is indirectly transmitted to the vibrating medium through the protective film  405  and the contact medium  411 , vibration efficiency is not optimal. 
         [0038]    In the vibrator in reference numeral  440 , unlike the vibrator in reference numeral  430 , a protective film  441  is coated on the entire surface of the vibrator  400  except a portion closely contacting the vibrating medium  420 . In this case, the vibrator  400  directly transmits vibration to the vibrating medium  420 , which is a more efficient way to transmit vibration to the vibrating medium  420 . Here, vibration can be directly transmitted to the vibrating medium  420  since the vibrator  400  is closely adhered to the vibrating medium  420  using the contact medium  411 , such as an adhesive. 
         [0039]    As shown in  FIG. 4 , the vibrator  400  according to the present invention may have the form of a long roll with stub-type electrodes attached at regular intervals. Then, no matter how big or small the vibrating medium  420  is, the vibrator  400  can simply be cut to a size corresponding to the size of the vibrating medium  420 . Accordingly, it is very easy to attach the vibrator  400  compared to conventional apparatuses for preventing eavesdropping. 
         [0040]      FIG. 5  is a diagram illustrating an apparatus for preventing eavesdropping using a piezoelectric film according to an exemplary embodiment of the present invention. 
         [0041]    Referring to  FIG. 5 , a vibrator  510  of an apparatus for preventing eavesdropping according to an exemplary embodiment of the present invention may be adhered to a large window  500 , and electrodes of the vibrator  510  may be connected to a noise signal generator  513 . With this configuration, eavesdropping through vibration of the window  500  can be prevented. 
         [0042]    It can be seen that electrical wiring of the apparatus shown in  FIG. 5  is very simple compared to the conventional apparatus shown in  FIG. 2 . Also, even if the window  500  is a sliding window, the thinness of the vibrator  510  according to the present invention makes it easy to open and close the window  500 . 
         [0043]    In particular, since the vibrator  510  according to the present invention closely contacts the entire bottom surface of the window  500 , it is only necessary to cut the vibrator  510  according to the size of the window  500 . Therefore, unlike the conventional art, there is no need to attach several vibrators on larger windows. 
         [0044]    As described above, an apparatus for preventing eavesdropping according to the present invention can generate noise vibration using a piezoelectric film so that wiring can be simplified and the apparatus can be attached to ordinary windows. 
         [0045]    While exemplary embodiments of the invention are illustrated in the drawings and described above in specific terms, neither the drawings nor the above description are not intended to place any limitations whatsoever on the purpose, constitution, or effects of the invention itself. Those of ordinary skill in the art may discover that various changes in form and details can be made to the exemplary embodiments. However, let it be clear that such changes do not constitute changes to the invention itself as long as they do not depart from the scope of the following claims.