This invention relates to a memory tag powered by a signal generated by a reader, and a reader, and methods of operation of the memory tag and reader.
Memory tags in the form of Radio Frequency Identification (RFID) tags are well known in the prior art and the technology is well established (see for example: RFID Handbook, Klaus Finkenzeller, 1999, John Wiley & Sons). RFID tags come in many forms but all comprise an integrated circuit with information stored on it and a coil which enables it to be interrogated by a read/write device generally referred to as a reader. Until recently RFID tags have been quite large, due to the frequency they operate at (13.56 MHz) and the size of coil they thus require, and have had very small storage capacities. Such RFID tags have tended to be used in quite simple applications, such as for file tracking within offices or in place of or in addition to bar codes for product identification and supply chain management.
Much smaller RFID tags have also been developed, operating at various frequencies. For example Hitachi-Maxell have developed “coil-on-chip” technology in which the coil required for the inductive link is on the chip rather than attached to it. This results in a memory tag in the form of a chip of 2.5 mm square, which operates at 13.56 MHz. In addition Hitachi has developed a memory tag referred to as a “mu-chip” which is a chip of 0.4 mm square and operates at 2.45 GHz. These smaller memory tags can be used in a variety of different applications. Some are even available for the tagging of pets by implantation.
Although it is known to provide tags with their own power source, in many applications the tag is also powered by the radio frequency signal generated by the reader. Such a known system is shown in
The tag 12 similarly comprises a resonant circuit part generally illustrated at 16, a rectifying circuit part generally indicated at 17 and a memory 18. The resonant circuit part 16 comprises an inductor 19 which again comprises in this example a loop antenna, and a capacitor 20. The resonant circuit part 16 will thus have a resonant frequency set by the inductor 19 and capacitor 20. The resonant frequency of the resonant circuit part 16 is selected to be the same as that of the reader 10. The rectifying part comprises a forward-biased diode 21 and a capacitor 22 and thus effectively acts as a half-wave rectifier.
When the reader 10 and the tag 12 are sufficiently close, a signal generated by the frequency generator 13 will cause the resonant circuit part 11 to generate a reader signal comprising a high frequency electromagnetic field. When the resonant circuit part 16 is located within this field, a current will be caused to flow in the resonant circuit part 16, drawing power from the time varying magnetic field generated by the reader. The rectifying circuit part 17 will then serve to smooth the voltage across the resonant frequency part and provide a power supply storage. The rectifying circuit part 17 is sufficient to supply a sufficiently stable voltage to the memory 18 for the memory to operate.
To transmit data from the tag to the reader, the resonant circuit part is also provided with a switch 23, here comprising a field effect transistor (FET). The FET is connected to the memory by a control line 24. When the switch 23 is closed, it causes an increased current to flow in the tag resonant circuit part 16. This increase in current flow in the tag results in an increased current flow in the reader's resonant circuit part 11 which can be detected as a change in voltage drop across the reader inductor 14. Thus, by controlling the switch 23, data stored in the memory 18 of the tag 12 can be transmitted to the reader 10.
There are two normal communication schemes for such known memory tags. In the first, for tags without any processing capability, when power is supplied to the tag by a reader, the tag transmits its stored data to that reader. In the second, for tags which include some processing capability, the memory tag can be silent when powered and only transmit its data when asked. However, in the prior art the reader issues a generic “hello” message and each tag within range responds with its identification and some other information about itself, generally about its characteristics, such as whether it is read only and how much memory it has. If two or more tags are within range of the reader the responses will be garbled if they are all transmitted instantly and the reader will not pursue the communication. However some prior art tags are set-up to wait a random but short period of time before responding and thus the messages might not be garbled. The reader might therefore make repeated attempts to communicate before abandoning the attempt, as in the latter case with random delays the responses from different tags will eventually not overlap, and also as there are other reasons that the communication might be incomplete such as the separation between tag and reader.
However, both of the above schemes mean that any reader which can make contact with the memory tag can obtain the information stored within it. Such indiscriminate transmission of data may be inappropriate for a number of reasons. It may be that there are a number of tags within range of the reader and problems will occur if more than one transmits data at the same time. More importantly, it may be that the user of the reader is not a person for whom the data is intended. This latter reason is of greater relevance as the size of memory tags reduces such that they can be readily secreted such that they can only be located when triggered to transmit the data which they contain.
An aim of the present invention is to provide a new or improved tag and reader which reduce or overcome one or more of the above problems.
According to a first aspect of this invention there is provided a memory tag having a resonant circuit part and a memory including a data store, an operating program and a password register in which is stored a current password;
An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings, wherein:
Referring now to
The memory 34 comprises a data store generally illustrated at 45, a password register 46 and an operating program 47 which is run when the tag 30 receives sufficient power via a reader signal from the reader 31.
The reader 31 comprises a resonant circuit part 51 which comprises an inductor L1 shown at 52, in this example an antenna and a capacitor C1 shown at 53 connected in parallel. A signal generator 54 is connected to the resonant circuit part 51 to provide a drive signal.
The reader 31 further comprises a demodulator, generally shown at 55. The demodulator 55 comprises a splitter 56 connected to the frequency generator to split off a part of the drive signal to provide a reference signal. A coupler 57 is provided to split off part of a reflected signal reflected back from the resonant circuit part 51, and pass the reflected signal to a multiplier shown at 58. The multiplier 58 multiplies the reflected signal received from the coupler 57 and the reference signal received from the splitter 56 and passes the output to a low pass filter 59. The low pass filter 59 passes a signal corresponding to the phase difference between the reference signal and the reflected signal to an output 60. An amplitude modulator is shown at 61 operable to control the amplitude of the drive signal supplied from the frequency generator 54 to the resonant circuit part 51, and thus send specific instructions to the tag 30.
A control unit 62 is operable to receive the output 60 from the low pass filter 59 and validate the received data. The control unit 62 is also operable to control the amplitude modulator 61.
In the embodiment shown in
The memory tag 30 operates as follows with reference to
The reader 31 may operate in one of two ways. Either it simply send signals out in a random fashion and monitors for responses, or it can identify that coupling to a memory tag may have taken place, due to the power thus taken, and in response send out a signal to the memory tag it has identified might be in range. The same effect as the coupling of a memory tag might be experienced by the reader 31 if it is adjacent to a small metal object such as a paper clip or a staple.
Whichever manner the reader 31 operates in, the form of the reader signal 64 is illustrated generally in
When such a signal is received by a tag 30 the program 47, as shown at step 70 of
Thus in this method, if the reader signal received by the memory tag 30 does not contain the current token the memory tag 30 does not announce its presence in any way in response to that reader signal. As a result, even if the reader 31 has detected a power drain due to inductive coupling, it cannot determine for certain that a memory tag 30 is within range or where exactly it might be, as other objects can cause the same effects at the reader. The memory tag 30 therefore remains hidden.
In the above method the same password is used for each instance of communication between the reader 31 and the tag 30. In this case the password for the memory tag may conveniently have been stored in the memory tag at the time of manufacture.
However, it may be desirable to change the password after each such communication, and such a method is illustrated in
Referring now to
If it is desired to further improve security in the communication between the tag 30 and the reader 31 the password may be included in the reader signals 64 and 76 in encrypted form. In such embodiments the operating program 47 of the tag 30 would also include the appropriate decryption routine(s) to enable the received password to be decrypted and compared with the current password stored in the password register 46 or stored as appropriate. The decryption used may be any appropriate method.
A further alteration to the communication between the tag 30 and the reader 31, which may be used in either embodiment described above, involves the reader 31 transmitting a derivative of the password rather than the password itself. Thus, the tag 30 and reader 31, in addition to both being aware of the password also know of a function which can be applied to the password to provide the derivative. The function should, if this is to improve security, be one which when the derivative is known cannot be used to calculate the password. In this scheme therefore the reader 31 calculates the derivative and transmits it to the memory tag 30 which compares the received value with the result of the same calculation which it has also made. If the values of the derivative of the password match then the memory tag 30 will respond to the reader 31 and if not the tag 30 will remain silent.
Thus, in more general terms, what the reader 31 must send to the memory tag 30 to obtain a response to its approach is the correct token which is dependent upon the current password. This token may be a password identical to that currently stored in the memory tag 30 or a derivative of that password.
In a preferred embodiment, the resonant frequency of the resonant circuit parts 32, 51 and hence the frequency of the signal generated by the frequency source 45 is about 2.45 GHz, and the resonant frequency of the resonant circuit part 32 is modulated by about 0.05 GHz either side of this reference frequency. At this frequency, component values for the inductors and the capacitors are small, allowing easy integration of the circuit and require relatively small areas of silicon on an integrated circuit. It is particularly desirable that the tag 30 be provided as an integrated circuit, for example as a CMOS integrated circuit. A schematic of such an integrated circuit is shown at 80 in
In memory tags 30 used with the first method of operation described above, with reference to
Readers 31 enabled for communication with password protected memory tags may operate according to a number of different communication schemes. It may be that the user of the reader 31 knows exactly which password protected memory tag 30 is to be communicated with and if that is the case the reader 31 can be instructed to simply send out the appropriate reader signal to communicate with that memory tag 30. However, it is equally likely that the person using the reader 31 will be unaware of the use of passwords to protect memory tags 30 and thus the reader 31 should be set-up to communicate without any specific input from the user. Thus the reader 31 might start by seeking to communicate with all memory tags within range in conventional fashion as described above in the introductory portion of this specification. If that does not provide the desired result the reader might then move on to poll all password protected memory tags 30 known to be within the relevant “system” and would thus make contact with the relevant tag 30. The time taken to undertake this whole process would only be of the order of milliseconds and therefore the user would not be aware that the communication scheme was so complex and would not experience a noticeable delay.
It will be apparent that the present invention may be used with any type of memory tag 30 and reader 31 in addition to those disclosed herein.
Number | Date | Country | Kind |
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0408597.3 | Apr 2004 | GB | national |