SAW tags: new ideas

Abstract

In this paper some alternative approaches to SAW tag chevron-type electrode reflectors (as in RAC devices) design and coding are discussed. The first idea is to use 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 he 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 a t 2 GHz frequency range and tag prototype characteristics are presented.

Model-Based Identification Method for Pulse Position Coded Surface Acoustic Wave Identification Tags

“…Since the surface wave is only partially reflected by each reflector, multiple reflections between various reflectors occur. For further details, the interested reader is referred to [8], [13], [20], and [21]. These multiple reflections have the tendency to become more powerful toward the end of the impulse response because an increasing number of reflections can superpose and cause strongly biased RTDT estimates.…”

“…The tags used for simulations and measurements presented in this paper were designed using PPC [8]- [10], where the impulse response is subdivided into groups with k defined reflector positions. In each group, only one reflector is set.…”

“…Typically, the tag identification (ID) is implemented using pulse position coding (PPC), also called time position coding, or variations thereof [8]- [10]. Here, the tag's impulse response is divided into time slots for reflector position calculation.…”

Surface Acoustic Wave RFID Tags

“…Currently existing SAW tag products use the so called time position encoding (Plessky et al, 1995;Stierlin & Küng, 2002), which represents the most straightforward way of data encoding in SAW tags. This is the only method currently used in commercial SAW tags (Reindl & Shrena, 2004;Stelzer et al, 2004).…”

“…The main feature of SAW RFID tags (Reindl & Ruile, 1993;Schmidt et al, 1994;Plessky et al 1995;Reindl et al, 1998;Hartmann, 2002) is that they do not use any autonomous power supply such as batteries. Moreover, they do not include any such circuitry that would need to be powered.…”