Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-03-02
2004-09-07
Lee, Benjamin C. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S005250, C310S31300R, C333S154000, C333S195000
Reexamination Certificate
active
06788204
ABSTRACT:
The invention relates to a surface-wave transducer device—also called TAGs—and to identification systems in which it is used.
DE 42 17 049 discloses a passive surface sensor which can be interrogated in wireless mode. In this context, energy is transmitted by radio to the sensor from an interrogation device, the interrogation being done by means of chirped transmission signals. The sensor has transducers and reflectors. The reflectors reflect the chirp signal in a time-staggered sequence, so that the sensor returns a time-staggered chirp signal to the interrogation device. The reflection principle means that the surface-wave sensor described above (also called SAW—surface acoustic wave—sensor in the following text) has a very high insertion loss of the order of 50 dB, for example. When the chirp signal has been received by an SAW interdigital transducer as the input transducer, this transducer produces a surface wave which propagates on the substrate of the SAW arrangement in the direction of the reflectors. When an SAW is received, each individual reflector element returns a correspondingly reflected SAW to the SAW transducer which, for its part, produces an electromagnetic signal from the SAW. However, since each reflector element returns not just one SAW to the SAW transducer, but rather the reflector elements also reflect signals amongst one another, the reflections are inevitably relatively small, and a large part of the energy coming from the SAW transducer is lost in the reflector arrangement, so that only a low output power can be achieved. The problem of “internal reflection” from the reflectors cannot be avoided, in principle.
U.S. Pat. No. 5,734,326 discloses an SAW arrangement which comprises a synchronisation transducer and a multiplicity of tap transducers. When excited by a radio-frequency pulse signal, this SAW arrangement transmits a specific identification signal, so that the receiver in the interrogation unit can receive and process the transmitted TAG signal. A prerequisite of this processing, however, is that a filter in the interrogation unit is tuned exactly to the TAG from which the TAG signal is received. Accordingly, a prerequisite of the processing of a TAG signal is that the interrogation unit already knows which TAG identifier it has to search for, so that the filter in the interrogation unit can be preset accordingly for utilising the TAG signal. Hence, U.S. Pat. No. 5,734,326 discloses a TAG system which has very restricted options for application. If the interrogation unit does not know the identification of the TAG, it is impossible in practice to tune the filter in the interrogation unit to the TAG, because it would take too long to interrogate every conceivable variant.
A further disadvantage of the TAG disclosed in U.S. Pat. No. 5,734,326 is that the tap transducers are not programmable, which makes them considerably more complicated and expensive to manufacture.
If the TAG were intended to be capable of long interrogation range, the energy of the RF pulse signal would have to be increased considerably. To do this, however, the signal would have to have such a high output level that it would infringe the normal conditions of licensing authorities, which limit the signal forms and power spectra of transmitters to a specific level so that no undesirable interference is produced, such as is known from radar technology, although these are permitted there in a specific frequency range owing to important monitoring functions (air traffic monitoring).
Furthermore, “1996 IEEE International Frequency Control Symposium”, pages 208-215 “Wireless Integrated System for SAW-Identification Marks and SAW-Sensor Components”, and 1993 “Ultrasonic Symposium”, pages 125-130, “Programmable Reflectors for SAW-ID-Tags”, and “IEEE Ultrasonics Symposium”, October 1998, “SAW Delay Lines for Wirelessly Requestable Conventional Sensors”, and 1993 “Ultrasonics Symposium”, pages 1267-1270 “2.5 GHz-Range SAW Propagation and Reflections Characteristics and Application to Passive Electronic Tag and Matched Filter” and, in addition, IEEE “Ultrasonics Symposium 1998” “On-Chip Correlation—A New Approach to Narrowband SAW Identification Tags” disclose further SAW TAG arrangements which likewise have a very high insertion loss (TAG attenuation) and accordingly also permit only a very short distance of 1.3 m that can lie between an interrogation device and the TAG in order that any communication at all is possible between the interrogation unit and the TAG. Furthermore, the known SAW TAG devices are characterised by a low bit capacity of approximately 20 bits.
In addition, various identification systems with coded passive transponders or SAW structures are disclosed in the following publications: DE 44 05 647 A1, DE 42 00 076 A1, DE 34 38 050 A1, U.S. Pat. No. 4,059,831, DE 34 38 053 C2, DE 43 36 504 C1, DE 43 10 610 A1, DE 34 38 052 C2, DE 43 36 897 C1, DE 31 02 334 C2, U.S. Pat. No. 4,096,977, U.S. Pat. No. 5,734,326, U.S. Pat. No. 5,374,863, U.S. Pat. No. 4,604,623, DE 34 38 051 A1 and DE 34 38 051 C2. However, all these publications disclose systems which have certain disadvantages; for example, either the interrogation distances are too short (<1.3 m), the insertion losses are correspondingly too high or the solutions illustrated are virtually infeasible from the point of view of cost or permit only poor flexibility on account of a low bit capacity.
The object of the invention is to provide a surface-wave transducer device which has a low insertion loss, allows a considerably greater interrogation distance than with previously known TAGs, and has an increased bit capacity. The device should enable free programming that is simple to perform. The invention proposes a surface transducer device having the features according to claim
1
. Advantageous developments are described in the subclaims.
The invention is based on the idea of providing a surface-wave transducer device with a combinational arrangement of a dispersive transducer device having a non-dispersive transducer device. A dispersive transducer device is capable of using a chirp signal to produce a surface-wave pulse signal, which is received by the non-dispersive transducer device, comprising n transducers, and is converted by this non-dispersive transducer device into a pulse code signal sequence which identifies the surface-wave transducer device. The pulse signal sequence is then transmitted by the surface-wave transducer device via an antenna and can be received by an interrogation unit within an identification system and evaluated on the basis of the identifier.
An SAW transducer device according to the invention is characterised by interrogation distances which are significantly longer than those known hitherto, has a very high bit capacity available and is very simple to program. The reason for the long interrogation distance and the correspondingly low insertion loss is that, once a signal is received from an interrogation device (interrogator), the SAW transducer device according to the invention converts the interrogation signal in the dispersive SAW transducer device into a time-compressed surface-wave signal which is received by the non-dispersive transducer device.
The non-dispersive transducer device also receives the interrogation signal and produces corresponding SAW signals which are received by the dispersive transducer. After receiving the signals, the said dispersive transducer converts the surface waves into corresponding electromagnetic signals. The identical transit times of the signals from the dispersive transducer device to the non-dispersive transducer device and vice versa mean that two identical signals are superimposed on one another at the output, so that the code signal to be transmitted by the TAG can have a higher signal power. Accordingly, the TAG's response signal to an interrogation signal comprises two components; since both components are transmitted synchronously by the TAG, however, and both signal components can have the identical signal form, the TAG according to th
Ianelli Zbigniew
Koslar Manfred
Christie Parker & Hale LLP
Lee Benjamin C.
Nanotron Gesellschaft fur Mikrotechnik mbH
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