Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to identification plates for transmitting and receiving data using electromagnetic waves, and in particular, to an identification plate with a damping element for limiting a reading range of the identification plate. 
     2. Description of the Related Art 
     An identification plate is characterized by a data carrier having an electronic chip which can be read remotely by a reading device, and optionally written as well. The energy required for the operation of the chip is received wirelessly from the reading device. Both data and energy are transmitted via an electromagnetic field. 
     Identification plates for the purpose of identifying a person are commonly the size of a credit card. In the case of identification plates having an operating frequency in the UHF range (865-868 MHz) and the SHF range (2446-2454 MHz), it is possible to implement lambda-half dipole antennas, or at least dipole antennas which are mechanically truncated but electrically extended. This construction enables a range of several meters. This range also makes it possible to identify persons in a motor vehicle, thereby also indirectly enabling access control for the motor vehicle used by the identified person. 
     It has been demonstrated that the range between an identification plate and a reading device can be dependent on the type of motor vehicle. In addition, this occurrence has been traced back to, among other things, a layer of insulation in the windshield which insulates against both temperature and light, and which also simultaneously acts to dampen electromagnetic waves. Although every windshield which includes an insulation layer has a window which is transparent to electromagnetic waves, the fact that the reading range depends on the type of motor vehicle persists. 
     Instead of this state of affairs, it would be desirable for the reading range to be consistent across different vehicles. In order to enable a reliable reading of an identification plate located in the interior of a motor vehicle with a strong damping effect, the sensitivity of the reading device would have to be designed for and adjusted to a strong damping effect. In the case of vehicles with a very low damping effect, however, a very large range would result, and this can lead to interference. For example, where there are multiple road lanes with lifting gates, it may be possible that the reading device assigned to the selected road lane is not the only one activated, but rather additional neighboring reading devices are also activated. This would be undesirable. Accordingly, the reading range would need to be reduced for vehicles with a very low damping effect, by suitable means. 
     SUMMARY OF THE INVENTION 
     The invention addresses the problem by creating an identification plate having a reading range that can be adjusted to the damping effect exerted in the interior of a vehicle, thereby giving a consistent reading range. The identification plate has a chip module made of a chip, a coupling element connected to the chip, and an antenna module made of an antenna lead. The coupling element is coupled to the antenna lead by a coupling field that creates a contactless coupling. An adjustable damping element is arranged in the proximity of the coupling element. The damping element projects into the coupling field and dampens the coupling field. In this manner, a maximum value of a transmitting and receiving range of the identification plate can be reduced. 
     The invention is based on the following realizations. The ability to control the sensitivity of the reading device according to the type of motor vehicle would require clear recognition of the motor vehicle type. However, in practice, this would involve a very complex design. The manufacture of identification plates with varying ranges would increase the complexity of production and therefore raise the cost of the identification plate. In addition, in the event that the motor vehicle is exchanged, the identification plate of the person being identified would potentially need to be replaced with another chip having a different range. For this reason, the most efficient approach would be to have a unified design of identical chips, wherein the range thereof can be modified by means of simple, additional measures. 
     In the case of the present invention, it is assumed that all identification plates are built with a uniform design, and are constructed for maximum range by means of an optimal integration of a chip, a coupling element, and an antenna lead. 
     At the same time, the sensitivity of the reading device is adjusted in such a manner that the range is used which is required for a reliable identification of a person in the event that the identification plate is carried in a motor vehicle of a type which, among other motor vehicles which are common on the market and which have been tested, has the highest damping effect on electromagnetic waves. In order that the range is not increased unintentionally in the case of motor vehicles with lower damping effects, the identification plates are artificially dampened, and the range is thereby reduced to the desired distance. A damping element serves the purpose of damping by being mechanically introduced into the proximity of a coupling element between the chip and the antenna lead. The coupling is realized via a coupling field without contact. The damping element projects into this coupling field and dampens the coupling field without damping the electromagnetic field of the antenna lead. In this case, a different degree of damping can be achieved by means of a variable distance or a variable shielding. 
     The coupling field which produces the contactless coupling is a magnetic, inductively generated, or electrical, capacitively generated, or electromagnetic coupling field. 
     The coupling element and the antenna lead are preferably arranged on one support platform. The damping element is oriented parallel to this support platform as an electrically conductive surface, and at least partially shields the coupling element and/or the antenna lead in damping positions. 
     In this embodiment, the coupling element, the antenna lead, and the damping element are oriented in one plane as a unit. As such, the configuration ensures a reproducible amount of damping according to a certain distance between the damping element and the coupling element and/or the antenna lead, or according to a certain shielding of the coupling element and/or antenna lead by means of the damping element. 
     The damping element can be constructed to be displaceable relative to the support platform and parallel to the same. In this case, a displacement of the damping element occurs in the same dimension in which the profiles of the coupling element and the antenna lead rise. This enables a fine, linear modification of the damping according to the displacement of the damping element. 
     The damping element can be mounted on the support platform. In this way, the configuration necessarily leads to a mechanical coupling between the damping element on the one hand, and the coupling element and antenna lead situated on the support platform on the other hand. This configuration simplifies the adjustment of the degree of damping, as well as the physical manipulation of the identification plate. 
     The damping element can be mounted on a support holder. First, the use of a support holder in a motor vehicle is practical because the correct positioning of the identification plate with respect to the window in the windshield, wherein the window is transparent to electromagnetic waves, is ensured in this way. The arrangement of the damping element on the support holder has the effect that a pre-set damping automatically comes into effect when the identification plate is slid into place on the support platform, without the need to undertake any mechanical modifications to the identification plate itself or to the support platform of the same. 
     The damping element can be arranged on a supplementary card which can be slid into the support holder. This makes a different manner of adjusting the damping possible by selecting different supplementary cards for use in the support holder. 
     Position marks that correspond to the different degrees of damping can be arranged on the support platform, on the support holder, and/or on the supplementary card. These position marks, determined based on prior experiments, enable a targeted adjustment of the required degree of damping for the desired reading range of the identification plate by the user. 
     The damping element and/or the support holder can have at least one spring-loaded latch that snaps into place in one of the locking grooves of the support platform and/or the supplementary card. The locking grooves correspond to damping positions. 
     The configuration ensures, by means of the latch and the locking grooves, that the position of the damping element with respect to the support platform is maintained following manual positioning of the same, and is not altered by dislocation or shaking. 
     The identification plate can be designed as a sticker which only reaches its resonance frequency once it is adhered onto the windshield. In contrast to the variants described above, the identification plate remains in the motor vehicle following installation. Then, on the reverse side of the identification plate, facing the interior of the vehicle, the damping element is likewise attached by means of adhesion on a marking. By means of the adhered damping element, various damping levels can be set as described above by means of the position of the adhered damping element on the marking lines. 
     Numerous other objects and advantages of the present invention will be apparent to those skilled in this art from the following description wherein there is shown and described embodiments of the present invention, simply by way of illustration of some of the modes best suited to carry out the invention. As will be realized, the invention is capable of other different embodiments, and its several details are capable of modification in various obvious aspects without departing from the invention. Accordingly, the drawings and description should be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more clearly appreciated as the disclosure of the invention is made with reference to the accompanying drawings. In the drawings: 
         FIG. 1  shows an identification plate having an antenna and coupling element according to a first variation of the present invention; 
         FIG. 2  shows an identification plate having an antenna and coupling element according to a second variation of the present invention; 
         FIG. 3  shows an identification plate having an antenna and coupling element according to a third variation of the present invention; 
         FIG. 4  shows an identification plate having an antenna and coupling element according to a fourth variation of the present invention; 
         FIGS. 5   a  to  5   c  show identification plates having a damping element in different positions; 
         FIG. 6  shows a support platform of an identification plate having different position marks; 
         FIG. 7  shows a support holder having an adjustable damping element; and 
         FIG. 8  shows a supplementary card having a damping element. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The identification plates illustrated in  FIGS. 1 to 4  have different antenna and coupling variants. The identification plate according to  FIG. 1  shows a chip module  10  and an antenna module  12 . The chip module  10  comprises a chip  14  and a coupling loop  16  connected to the chip  14 . The antenna module  12  comprises an antenna lead  18  inductively coupled to the coupling loop  16 . The chip module  10  made of the chip  14  and the coupling loop  16 , as well as the antenna module  12  with the antenna lead  18 , are situated on a support platform  20 , wherein the latter is a plastic film in this case. The antenna lead  18  is an insulated wire attached mechanically to the support platform  20  by means of a laying technique using heat and pressure. 
     The antenna lead  18  is structured in the form of a loop having the shape of a rectangle. A loop  24  is constructed on an arm  22  of the antenna lead  18 , wherein the arm is adjacent to the chip module  10 , and the loop  24  produces a close coupling of the antenna loop to the coupling loop  16  of the chip module  10 . Two arms  26 ,  28  of the antenna lead  18 , the arms lying opposite each other and completing the arm  22  at right angles thereto, are designed with a curved shape. The curved shape produces an electrical extension of a mechanically truncated antenna. On an arm  30  of the antenna loop which lies opposite the arm  22  and the chip module  10 , end regions  32 ,  34  of the antenna lead  18  are positioned parallel, overlapping, and at a small distance to each other, but are not electrically connected. 
     The identification plate illustrated in  FIG. 2  differs from that shown in  FIG. 1  in the design of its antenna module  36 . The antenna module  36  comprises an antenna lead  38  which is arranged and attached on a support platform  20  by means of a laying technique, wherein the support platform  20  comprises a plastic film. The antenna lead  38  has multiple windings, wherein the ends  42 ,  44  thereof are routed to a chip  46  for the HF range, and the ends  42 ,  44  are welded to the terminals of the chip  46 . 
     The windings of the loop formed by the antenna lead  38  likewise have a rectangular structure. On the side which lies opposite the chip  46 , regions of the windings are routed as a loop  48 . Similarly to  FIG. 1 , the chip module  10  is positioned and attached to the support platform  20  in such a manner that the coupling loop  16  is enclosed by the loop  48 . The multiple windings of the antenna lead  38  behave like a single-winding antenna for the chip module  10  in the UHF range due to the capacitive connection, similarly to the illustration in  FIG. 1   
     In the illustration in  FIG. 3 , an antenna module  50  comprises a circuit path which functions as the antenna lead  52  and which is produced by means of an etching technique. The circuit path is produced on a support platform  54  comprised of a printed circuit board. The antenna lead  52  forms a closed antenna loop. A loop  58  is formed on an arm  56  of the antenna lead  52 , wherein the arm is adjacent to the chip module  10 . This loop  58  provides a close coupling of the antenna loop to the coupling loop  16  of the chip module  10 . The coupling is realized inductively via a magnetic coupling field. 
     The illustration in  FIG. 4  differs from  FIG. 3  in the manner of the coupling. The antenna lead  52  forms an open antenna loop. Instead of an inductive coupling, as in  FIGS. 1 to 3 , a capacitive coupling is included which works via an electrical coupling field. A coupling element  60  comprises two vanes  17  connected to the chip  14 . These vanes  17  are situated opposite interrupted segments of an antenna lead  52  of an antenna module  50 , and run parallel to the same. 
     All of the illustrations in  FIGS. 1 to 4  have in common that a field  62  is present, the same being drawn with a dashed line and bounding the coupling element  60 . This field  62  illustrates a region in which the damping of the coupling loop  16  and/or the coupling element  60  takes effect as a result of the insertion of a damping element. 
       FIGS. 5   a  to  5   c  show an identification plate according to  FIG. 1 , having a damping element  64  in various positions above a field  62 . The damping element  64  comprises an electrically conductive surface which is oriented parallel to the support platform  20 ,  54 . The damping element  64  can be displaced relative to the field  62  and parallel to the support platform  20 ,  54 . The adjustment between the chip  14  and the antenna lead  18 ,  38 ,  52  is altered by means of a different width of shielding of the field  62  with the coupling loop  16  and/or the coupling element  60 , the former and the latter being situated in the field  62 . This adjustment becomes worse as the shielding of the field  62  increases, leading to a damping of the identification plate and a reduction in the reading range. 
     Three different damping positions are illustrated in  FIGS. 5   a  to  5   c .  FIG. 5   a  shows a minimal shielding and therefore a minimal damping.  FIG. 5   b  shows a moderate shielding and therefore a moderate damping.  FIG. 5   c  shows a strong shielding and therefore a strong damping. With no damping element  64 , no damping effect exists. The damping element  64  in this case can be a sticker which can be adhered on the respective marked positions. This configuration is relevant for both an identification plate which can be removed from a guide or from a support holder, and also an identification plate in the form of a sticker which can be fixed to a windshield. 
       FIG. 6  shows a support platform of one of the previous embodiments of an identification plate, having different position marks  66 ,  68 ,  70 . Numbers are displayed at the position marks  66 ,  68   70 , and display the degree of reduction of the maximum reading range when the damping element  64  is positioned accordingly. In practice, the position marks are determined by undertaking reading range measurements at the levels associated with each of the marks, and determining the positions of the damping elements at each mark. 
       FIG. 7  shows a support holder  72  for a support platform  20 ,  54  with an identification plate, as is used in practice in a motor vehicle. A damping element  64  which can be moved is situated on the support holder  72 . A spring-loaded latch  74  is arranged on the damping element  64  and can snap into place in one of the locking grooves  76  in the support holder  72  according to the position thereof relative to the support holder  72 . When a support platform  20 ,  54  with an identification plate is inserted into a support holder  72 , the coupling loop  16  and/or the coupling element  60  is then automatically shielded to the degree necessary, thereby achieving the desired damping. The identification plate has its full range when outside of the support holder  72 . 
       FIG. 8  shows a supplementary card  78  with a damping element  64 . This supplementary card  78  is inserted into a support holder  72  together with a support platform  20 ,  54  having an identification plate. A region of the coupling loop  16  and/or the coupling element  60  is then likewise shielded, and the desired damping thereby realized. Three supplementary cards  78  are available, wherein the damping element  64  is arranged at different positions therein. Corresponding number indications show the degree of reduction in range at a prespecified position of the damping element  64 . 
     While the invention has been specifically described in connection with specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.

Technology Category: h