BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is the simplified geometry of the reader, shield and card.
FIG. 2 illustrates the physics of eddy current shielding.
The FIG. 3, FIG. 4, FIG. 5, and FIG. 6 are design drawings that represent examples of specific embodiments of the invention.
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
The use of a shield to modify the mutual inductance of the reader and the card and/or self-inductance of the card antenna allows for a shield design that can be tailored closely to requirements of multiple applications. This invention can be used to design a physical shield for “smart” contactless ID badges that are meant to both be read by a remote transceiver as well as be displayed visibly while inside the holder. Several different embodiments of a badge holder have been implemented and tested with cards that adhered to ISO/IEC7810 standard.
Although other materials can be used, aluminum is an inexpensive effective shielding material that can completely block a standard smartcard reader (for example Model SDO10, 13.56 MHz card readers sold by SCM Microsystems) when covering one side of a typical contactless smartcard. Even when a 2.5 cm strip along the side of the smartcard is exposed, a shield covering the remaining portion has been shown to reduce the distance at which a standard card reader can read the smartcard to 18% of the distance at which the card reader can read the unshielded card. To prevent even this slight decrease in shielding efficiency, the card holder can have a mechanism to position the card and shield to prevent the card from sliding away from the shield.
One embodiment, shown in FIG. 3, involves sandwiching the shielding aluminum means or its alloy piece (FIG. 3, part 6) between two pieces of plastics (FIG. 3, parts 7 and 8) at the back of the cardholding means. The advantages of this cardholder design is good shielding, good protection to the ID card, good protection to the shielding material since it is in between two plastic pieces and low cost. The front piece of the cardholder that secures the card in place is shown in FIG. 3, part 9. One drawback to this particular embodiment is that the holder is slightly bulky compared to non-shielding holders due to the extra plastic layer in the middle. Another embodiment, shown in FIG. 4, involves using an aluminum plate or its alloy (FIG. 4, part 6) directly as the back piece of the cardholder. The front of the holder can be a polymeric material as shown in FIG. 4, part 9) that allows visual inspection of the inserted card. A side view of the assembly is also shown in FIG. 4.
A schematic for one potential preferred embodiment is shown in FIG. 5. In this drawing, light (10) is received by an optical detector (11) which controls the current through the shield (2) to modify how much current is induced in the card coil (3) which in turn affects its ability to power RFID circuitry and electronics (12). As shown in the schematic, this embodiment allows the shield to be controlled so that the smartcard user does not have to remove the smartcard from the shield in order to have the smartcard be readable by the remote transceiver. This adds a level of convenience and security to the design since the card is less likely to be inadvertently left in an unshielded position. Since the surface of the card can be accessed in this embodiment, the control of the shielding switch can, among other things, be optical, mechanical or electrical. One example of an electrical actuation technique would be to use electromagnetic waves. The optical receiver/switch can be easily replaced by many other electrical and mechanical switches; how to implement such a control would be obvious to a person with ordinary skill in this area. For example, a simple push-button switch, or a microprocessor-controlled transistor can be used, as well as any other circuit that momentarily interrupts the current path through the shield. Alternatively, one can use an embodiment such as the ones shown in FIG. 3 or FIG. 4 and exert mechanical force by pushing through the opening in the shield to deflect the card away from the shield a sufficient distance to allow the card to be read. Obvious alternative methods exist such as using hinges to manipulate the distance of the shield from the card; in this configuration, rotating or moving the shield away from the card will allow the card to receive and transmit signals.
Another embodiment is to implement an optical sensing means such that it becomes part of the RFID circuitry or antenna means to allow control of the smartcard directly without the need for a shield. This concept is shown in FIG. 6. Here, the optical detector (11) is embedded in the RFID electronics (12) and the reception of light controls whether the RFID chip responds to the interrogating signal from the reader coil. An easy alternative is to move the optical detector such that it controls the current through the antenna circuit (3) rather than the RFID chip. Again, optical receiver/switch can be easily replaced by many other electrical or mechanical switches.
An optical switch or other device can be effectively used to interrupt or control the current or smartcard operation regardless of the operating frequency of the device. Such switches can also be configured for response to nearly all RF or UV frequencies
Testing was done to verify the effectiveness of the shielding device. The shield completely blocked the reader from accessing the card even when the card was in direct contact with the reader. Tests with electrical interruption of the current flow have indicated that designs such as that shown in FIG. 5 (with the push-button switch) effectively allow users to control whether or not the card or RFID device is shielded.
Patent Application
20080055093
