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Abstract

The invention relates to a surface-wave transducer device--also called TAGs--and to identification systems with this device. 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 using 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. 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. Surface-wave transducer device comprising the combination of a first transmitter device of the dispersive type and a second transmitter device of the non-dispersive type, comprising a multiplicity of n non-dispersive transducers which can be coded or are coded with an identification code.

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First Claim