SAW tags: new ideas

In this paper some alternative approaches to SAW tag design and coding are discussed. The first idea is to use chevron-type electrode reflectors (as in RAC devices) for reflecting “taps”. One of the advantages of the use of oblique reflectors is that there is no multiple reflection in such a system even if many reflectors are placed in the same acoustic channel. It is also important for the 2.5 GHz frequency range that the minimal size of electrode in oblique reflectors is roughly 1.4 larger than for normal reflectors. The small size of the device is another attractive feature. A further idea to be discussed is the possibility to code a tag device simply by the time positioning of the reflectors, which allows calibration problems to be avoided and simplifies the reading system since the phase of the pulses does not need to be measured. Measurements of propagation and reflection of SAW in the 2 GHz frequency range and tag prototype characteristics are presented