Ultra Wide Band RFID Systems based on SAW-tags – SAWTAG

We have simulated the SAW-tags and sensors including LFM chirp IDTs and studied different ways to compress the signals. The devices were designed

The goal of this project is to develop The Ultra-Wide-Band (UWB) SAW-tags and sensors. In this document we report the progress achieved in Jan.-June 2011. Here we concentrated on simulation and design of low frequency test device. The Report describes principles of the UWB signals applied to SAW chirp transducers.

on the next stage we produce SAW-tag/sensor samples, measure them and study the exoerimenal results

nothing to publish at this stage

In this project three technologies come together: RFID tags, surface acoustic waves (SAW) on piezoelectric materials and UWB communications with the goal to create really passive RFID tag with long reading distance and extremely low EM power radiated by the reader antenna.
Radio Frequency Identification (RFID) tags become more and more widespread. In age of Internet-of-Things the RFID tags and sensors will be omnipresent. However, for the operation of the IC chip which generates response of RFID tag some threshold voltage level is necessary to switch transistors of the IC. In many applications the RFID tag cannot have local source of energy and must receive energy from from the “the reader”. If the reading distance of a few meters is demanded the power radiated by antenna must be in a few Watts level, which is prohibitive for many applications. SAW devices, due to high quality factor (Q-factor) of crystals such as Lithium Niobate, can accumulate energy received from antenna and re-radiate it back to the reader. The code information is hidden in the way how the SAW-tag transforms the interrogating pulse. The device is linear, that is, no minimal energy is required and the response is generated at any level of interrogating pulse. It is important to stress that the RFID tags use about the same GHz frequency range as mobile phones for which SAW devices serve as the main part of phone architecture. The technology of SAW devices is now mature and SAW tags can use it with some minor development. For SAW-tags the width of available frequency band B is of primary importance. The number of different codes that can be obtained is determined by the product B*T, where T is the pulse duration, limited in SAW devices to 2 to 4 µs . Using Ultra Wide Band (UWB) signals allows for much wider passbands and the same informational capacity B*T can be achieved with significantly smaller delays and the chip size can be radically reduced. For example we can use, signals with >20% relative band and with –41.3 dBm power level. Using a band B of 500 MHz from 2.0 GHz to 2.5 GHz would satisfy such criteria. It is important that with these frequencies, we remain in the area of standard SAW technology with optical lithography. The UWB SAW-tag can partly process the interrogation signal in a way that the signal reflected by the tag will become distinguishable from the signal sent by the reader and from all signals reflected by environment objects.
In result, we will get small and cheap SAW-tags with practically unlimited number of codes and with the readers radiating microwatt levels of EM power. The existing readers for SAW-tags will be adopted to UWB signals. That will demand modifications in hard and (mainly) software processing the signals.
The SAW-tags can easily adopt functions of sensors. De-facto, calibration procedure in the reader includes rather accurate (remote) measurement of temperature. The measurement of other physical values, such as pressure or stress is also possible with sensors having the structure close to SAW-tags.
Prof. V.Plessky is world-known specialist in SAW physics and devices. Some of his results are now included in manuals (D. Morgan’s book, K.Hashimoto’s book). Prof. S. Balandras in FEMTO created leading academic group in the area of SAW, micro- nano-acoustics, and signal processing. The Senseor company now established in Besançon develops SAW-sensors. The wafer FAB established now in Besançon is another advantage for this project. All that illustrates that the knowledge, technology, know–how and professionals networking is available for developing significant synergy for successful realization of this project.