Abstract:
A piezoelectric device is assembled from a piezofilm sensor enclosed between two layers of a multilayer board with a printed circuit.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates generally to a piezoelectric device.  
         BACKGROUND OF THE INVENTION  
         [0002]    Piezoelectric polymer sensors or piezofilm sensors are increasingly used as piezoelectric sensors. These sensors preferably consist of fluoropolymers, in particular polyvinylidenfluoride (PVDF) and copolymers of PVDF. The piezofilm sensors consist of a piezofilm piece or small plate, on both sides of which is an electrode coating. The electrode coating could be a suitable metal coating, such as silver.  
           [0003]    The piezofilm sensor is generally connected to a printed circuit. “Multilayer” circuit boards are preferably utilized for this application because of the high circuit density. However, often there is very little space available for the measuring point, or region, out of the film sensor and the board.  
         SUMMARY OF THE INVENTION  
         [0004]    The purpose of the present invention is to miniaturize a piezoelectric measuring region. According to the device disclosed herein, a piezofilm sensor is enclosed by two adjacent layers of a multilayer circuit board. The piezofilm sensor is thus completely integrated into the circuit board. Therefore, the space occupied by the piezofilm sensor at the measuring region, is reduced. The result is a significant miniaturization of the measuring region. In addition, the piezofilm sensor is protected against mechanical damage by the circuit board.  
           [0005]    In order to obtain a large measuring impulse, the piezofilm sensor fills as large a surface as possible between the adjacent layers of the circuit board. The surface of the piezofilm sensor is thus at least one fifth, preferably at least one third, and most preferably more than half the surface of the circuit board. By configuring the piezofilm sensor as a flexible foil, such a large-surface piezofilm sensor easily withstands deformations caused by a mechanical impulse. Preferably, the circuit board and the piezofilm sensor enclosed therein are essentially rectangular in shape. The thickness of the piezofilm sensor is typically less than the thickness of the adjacent layers of the circuit board. Electric connections are provided at the edge of the piezofilm sensor.  
           [0006]    It has been determined that forming recesses in the piezofilm sensor does not noticeably influence the sensitivity of the sensor. Accordingly, the piezofilm sensor of the present invention can include recesses to facilitate through-bonding between the layers of the circuit board without impairing the function of the piezofilm sensor. The recesses can be recesses formed along the edge of the essentially rectangular piezofilm sensor or holes formed within the perimeter thereof. To assure greater sensitivity, the piezofilm sensor is preferably positioned in a recess formed in at least one of the two layers of the circuit board between which it is enclosed.  
           [0007]    The piezoelectric device of the present invention could be used in many applications as a measuring device wherein mechanical impulses result in a deformation of the piezofilm sensor. These mechanical impulses could result from any suitable source, such as a hit, vibrations or accelerations. The piezofilm sensor could also be configured as a data-receiving mechanism. Thus, the piezofilm sensor could detect if, when and how an article is subjected to movements, hits or other disturbances. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    One embodiment of the device of the present invention and its use in conjunction with a shot counter for pistols will be exemplarily discussed in greater detail hereinafter in connection with the drawings, in which:  
         [0009]    [0009]FIG. 1 is an assembly view of a multilayer circuit board including a piezofilm sensor according to the present invention; and  
         [0010]    [0010]FIG. 2 is a partially sectioned side view of a pistol including an incorporated multilayer circuit board according to FIG. 1, wherein the circuit board is configured as a shot counter. 
     
    
     DETAILED DESCRIPTION  
       [0011]    Referring to FIG. 1, a rectangular multilayer circuit board  1  includes four layers  1 . 1 ,  1 . 2 ,  1 . 3  and  1 . 4 . Each layer  1 . 1 ,  1 . 2 ,  1 . 3  and  1 . 4  includes conductor paths  2 . 1 ,  2 . 2 ,  2 . 3  and  2 . 4 , respectively. A piezofilm sensor  3  is enclosed between the inner layers  1 . 2  and  1 . 3 . The piezofilm sensor  3  has an essentially rectangular shape. The surface of the piezofilm sensor  3  is approximately half the surface of the individual layers  1 . 1 ,  1 . 2 ,  1 . 3  and  1 . 4 .  
         [0012]    Electronic building components in the form of a capacitor  4 , a resistor  5  and an IC chip  6  are connected to the conductor paths  2 . 1  and  2 . 4  of the outer layers  1 . 1  and  1 . 4 . The electrode layers of the piezofilm sensor  3  are connected to the conductor paths  2 . 3  of the layer  1 . 3  as illustrated in FIG. 1 by the dashed lines  8  and  9 .  
         [0013]    To facilitate bonding of the conductor paths  2 . 1  of the layer  1 . 1  and the conductor paths  2 . 4  of layer  1 . 4  along the dashed line  10 , a recess  11  is formed in the piezofilm sensor  3 . Additional recesses are also formed along an edge of the piezofilm sensor  3  to allow bonding between the conductor paths  2 . 1  and  2 . 2  of the layers  1 . 1  and  1 . 2  and the conductor paths  2 . 3  and  2 . 4  of the layers  1 . 3  and  1 . 4 , which are positioned on opposite sides of the piezofilm sensor  3 . Furthermore, it is possible to form a recess  12  on the side of the layer  1 . 2  which faces the piezofilm sensor  3 . The recess  12  is sized and configured to receive the piezofilm sensor  3 .  
         [0014]    One use of the present invention is illustrated in FIG. 2. The circuit board  1  is positioned in a recess  18 . The recess  18  is formed in a section  13  of the handle  14  of a pistol  15  between the trigger  16  and the barrel muzzle  17 . During firing of the pistol  15 , the section  13  including the circuit board l, and thus the piezofilm sensor  3 , is deformed by the impulse recoil. This deformation causes the piezofilm sensor  3  to emit a signal to the chip  6  in one of the layers  1 . 1  or  1 . 4 . The signal is stored as a count impulse in the store of the chip  6 . The number of shots fired by the pistol  15  can then be determined with a reading device (not illustrated) configured to read data in the store.  
         [0015]    The circuit board  1  with the piezofilm sensor  3  integrated therein can also be inserted into other weapons for the purpose of counting shots fired. For instance, the circuit board  1  could be positioned within the butt plate of a gun or other suitable weapon and operated in a manner similar to that disclosed above.